Isotherm models for adsorption of heavy metals from water - A review

Recent advancements on 2D nanomaterials as emerging paradigm for the adsorptive removal of microcontaminants

Water reservoirs are facing increasing prevalence of microcontaminants originating from agricultural runoff, industrial effluents, and domestic wastewater. The persistence of microcontaminants leads to disruptions in aquatic ecosystems and poses potential long-term health risks to humans, even at minimal concentrations. However, traditional wastewater treatment methods are inefficient to eliminate the microcontaminants because of their intricate chemical structures and low concentration. In this regard, nano-adsorption employing nanomaterials as adsorbents presents a viable alternative, offering enhanced efficiency and specificity towards the removal of microcontaminants. Amongst all, two-dimensional (2D) nanomaterials, including graphene oxide (GO), layered double hydroxides (LDHs), MXenes, and boron nitrides (BNs), exhibit distinctive characteristics such as a high surface area, remarkable chemical stability, and tendency of diverse surface functionalization, rendering them particularly effective in adsorbing pollutants from water. Therefore, the present review provides an exhaustive literature and comparative analysis of the aforementioned 2D nanomaterials-based adsorbents concerning their efficacy in adsorbing microcontaminants of pharmaceuticals and personal care products origin such as antibiotics, steroids, bisphenols, phthalates, parabens, and benzophenones. The different aspects of 2D adsorbents including adsorption capacity, mechanisms involved, kinetic and isotherm models followed for removal of a variety of microcontaminants have been congregated. Also, the information on recyclability, reusability, and stability of the adsorbents has been summarized to highlight their viability. Further, the limitations and future aspects related to the use of 2D nanomaterials-based adsorbents towards pollutant removal have been discussed. Overall, 2D nanomaterials holds great promise as efficient adsorbents for environmental remediation and can also be explored for industrial adsorption applications.

Inverse Vulcanization-Induced Self-assembly of Polysulfide into Responsive Micelles and their Templated Hydrogel Adsorbent for Sr2+ Removal

Albeit sulfur-rich polymers have attracted increasing attention and become easily accessible, especially after the emergence of inverse vulcanization, a myriad of polysulfides suffer from limited water solubility due to the hydrophobic nature of sulfur and comonomers, hindering their use in water-related fields (e.g., metal remediation). Inverse vulcanization of water-soluble monomers still remains limited, let alone the understanding of its reaction mechanism in water and of its solution properties. In this study, sodium acrylate was employed to copolymerize with elemental sulfur in water to synthesize ionic polysulfides (SSAC) using organic bases as catalysts. A mechanism involving nucleophilic attack initiation, carbanion propagation, and water-involved hydrolysis termination is reported for the formation of SSACs with molecular weights of 1.1 to 1.7 kDa. There also exists possible side reactions of sulfur hydrolysis in alkaline water that produced sulfur oxoacid and its salts as byproducts. The ionic SSAC was demonstrated to be superhydrophilic and, more importantly, identified to self-assemble into stable negatively charged colloids with a hydrodynamic size of ∼130 nm and a critical micellar concentration of ∼10 mg/L. Then, the SSAC micelles were templated into a homogeneous sulfur-rich hydrogel (SSAC hydrogel) as physical cross-links via an ion-imprinting technique aided by sodium alginate. The hydrogel exhibits self-healing ability and outstanding adsorption capability to Sr2+ with a qm of 134.4 mg/g and good robustness in a wide range of temperature (25 to 55 °C) and pH (4 to 10). Also, fast adsorption kinetics and good selectivity in the presence of Ca2+, Mg2+, and K+ with high concentrations were demonstrated.

A comprehensive review on the adsorption of dyes onto activated carbons derived from harmful invasive plants

The proliferation of invasive plant species such as Ailanthus altissima, Reynoutria japonica, and Alternanthera philoxeroides pose a significant ecological and economic challenge, including adverse impacts on native biodiversity, agriculture, and infrastructure. The production of activated carbons from these invasive plants offers a sustainable approach to addressing environmental pollution in the context of wastewater treatment. Activated carbons are renowned for high adsorbability and porous structure, hence, they may be highly effective in removing contaminants including dyes. Here, we review the conversion of invasive plant biomass into activated carbons production for dye removal by the adsorption technique. Influential factors, optimization conditions, adsorption models, mechanisms, and regeneration studies were systematically discussed. Remarkably, the efficacy of activated carbons derived from invasive plants such as Leucaena leucocephala pods cactus fruit peels achieved exceptionally high capacities of 584.3-806.4 mg/g for organic dyes. We also analyzed dual benefits of transforming invasive plant biomass into high-value activated carbons for wastewater treatment and managing invasive plants. It is, therefore, suggested that this approach can satisfy the sustainable development goals and solve the current global environmental challenges.

Facile fabrication of chitosan-based molecular imprinted microspheres to adsorb selectively, release and anti-bacteria for berberine

Berberine hydrochloride (Ber), a bioactive compound widely found in the roots, rhizomes, stems and barks of Coptis chinensis, has demonstrated efficacy in treating many diseases, such as cancer, congestive heart failure, Alzheimer's disease, especially inflammatory caused by bacteria. The molecularly imprinted microspheres based on chitosan were fabricated to adsorb selectively, release and anti-bacteria of Ber. The Ber surface molecularly imprinted microspheres (Ber-PSSS@GCS-MIPs) were synthesized using crosslinked chitosan as matrix, Ber as template, and sodium 4-styrene sulfonate (SSS) as functional monomer via a redox surface-initiating system -NH2/-S2O82-. The microspheres were characterized by fourier transform infrared reflection (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Adsorption kinetics, isotherms and imprinting factor were investigated, and the drug release performance and antibacterial activity were evaluated. As a result, via electrostatic interaction and "lock-key" imprinted cavities, the adsorption capacity of Ber-PSSS@GCS-MIPs reaches 185 mg/g at 2 h, significantly higher than 51 mg/g observed for non-imprinted microspheres. The adsorption of Ber-PSSS@GCS-MIPs. follows pseudo-second-order kinetics, with adsorption amount decreasing as temperature increases and salt concentration rises. Ber-PSSS@GCS-MIPs show excellent recognition and selectivity with an imprinting factor of 3.07, a selectivity factor exceeding to 2. The adsorption capacity remains at 82.4 % of three times cycles. The Ber-PSSS@GCS-MIPs loaded drug microspheres attain slow and sustained release for 70 % at 139 h. The relative antibacterial rate of Ber-PSSS@GCS-MIPs loaded Ber is higher than non-imprinted microsphere and control against S. aureus and E. coli.

Efficient removal of cadmium (II) and arsenic (III) from water by nano-zero-valent iron modified biochar-zeolite composite

For the removal of Cd(II) and As(III) from water, this study synthesized a nano-zero-valent iron-loaded biochar-zeolite composite material (nZVI-BCZo) using a liquid-phase reduction method, with biochar, zeolite, and FeSO₄·7H₂O as precursors. The successful incorporation of nZVI onto the BCZo was verified through Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FTIR) analyses, which revealed significant modifications in the surface oxygen-containing functional groups. Batch adsorption experiments were conducted to evaluate the adsorption characteristics and performance of nZVI-BCZo for Cd(II) and As(III). Under optimal conditions (pH 6.0, temperature of 310 K, and an adsorption time of 360 min), the maximum adsorption capacities for Cd(II) and As(III) were found to be 28.09 mg/g and 186.99 mg/g, respectively. The influence of pH on removal efficiency was more pronounced than that of temperature, with nZVI-BCZo exhibiting a higher affinity for As(III) compared to Cd(II). Kinetic analysis showed that the adsorption process is primarily controlled by chemical adsorption and follows a monolayer adsorption mechanism. Regeneration tests demonstrated that nZVI-BCZo retained good adsorption capacity after three cycles, with adsorption efficiencies of 67.78 % for Cd(II) and 53.04 % for As(III), indicating its potential for repeated use in water treatment applications. The economic evaluation revealed that nZVI-BCZo has a lower processing cost. Therefore, this study established nZVI-BCZo as an efficient, reusable, and cost-effective adsorbent for the treatment of heavy metal-laden water.

Cellulose Nanocrystal and Polymer Composite Microspheres for Methylene Blue Adsorption

In the present study, cellulose composite microspheres were synthesized based on the reversed-phase suspension method by introducing cellulose nanocrystals (CNCs) into polyacrylamide (PAM), followed by partial hydrolysis. Their adsorption performance for methylene blue (MB) dye in aqueous solution was investigated by varying the CNC content, pH value, and particle size of the microspheres, showing excellent removal efficiency and a good regeneration performance. In addition, the adsorption kinetics were determined in accordance with the quasi-secondary kinetic model, and the equilibrium isotherm performance followed the Langmuir adsorption model. This work provides a reliable experimental basis and solid theoretical foundation for the potential application of cellulose-based composite microspheres in the field of wastewater treatment. They are expected to represent a highly efficient adsorbent material and promote the development of related fields.

Investigation of cadmium removal using tin oxide nanoflowers through process optimization, isotherms and kinetics

The present study demonstrates a treatment approach that utilizes flower-shaped tin oxide nanoparticles for the removal of cadmium from synthetic wastewater by adsorption. Tin oxide nanoparticles were synthesized using a simple and eco-friendly method and employed for the removal of cadmium ions from wastewater. The nanoflowers were successfully characterized using Fourier Transform Infrared Spectroscopy, X-Ray Diffraction Analysis, Scanning Electron Microscope and Brunauer-Emmett-Teller (BET) surface area analysis. The batch adsorption process was optimized by response surface methods to investigate the influential parameters of the adsorption process. Optimal removal efficacy was achieved at a pH value of 9.0, a mixing time of 20 min, and an adsorbent amount of 15 mg. The results indicated that the adsorbent achieved a maximum removal efficiency of 99.14 ± 0.10% for Cd(II)ions in domestic wastewater. The adsorption equilibrium process was elucidated by Langmuir, Freundlich, Sips and Toth isotherm models using nonlinear regression. In addition, error functions such as Chi-square (X2, Average Relative Error (ARE), Root Mean Squared Error (RMSE) and HYBRID were used to test the validity of the nonlinear models. The results indicated that the Sips model, with an R2 value of 0.9894, accurately matched the experimental data and adsorption capacity of 57.12 mg g- 1 for Cd(II) was calculated respectively. The sorption kinetics were well characterized by a pseudo-second-order kinetic model. The results demonstrated that adsorption of cadmium onto the surface of SnO2 nanoparticles is influenced by both monolayer adsorption and multi-site interactions. These findings indicate that SnO2 nanoparticles are suitable for removing cadmium from aqueous solutions in batch processes.

Multifunction hydrogen-bonded organic framework aerogel platform for detection and removal of heavy metal ions in pear juice

Heavy metal ions (HMIs) in food pose significant health risks due to their bioaccumulation and toxicity, necessitating effective detection and remediation methods. This study explores a multifunctional hydrogen-bonded organic framework (HOF-16) wrapped in sodium alginate (SA) to form a stable HOF-16/SA aerogel for detecting and removing HMIs in pear juice. The HOF-16 fluorescence probe exhibits excellent sensitivity with limits of detection of 0.49, 0.60, and 0.44 μmol/L for Pb(II), Cu(II), and Cd(II), respectively. The maximum adsorption capacities of HOF-16/SA aerogel for Pb(II), Cu(II), and Cd(II) are 284.69, 248.08, and 183.94 mg/g, respectively. The removal efficiency of HOF-16/SA aerogel for HMIs in pear juice exceeds 98 % without negative impacts. Sensitive detection of HMIs is attributed to the fluorescence quenching effect caused by electron transfer, while electrostatic interactions and complexation enhance the effective adsorption performance. This study provides a HOF-aerogel platform with great potential for detecting and removing HMIs from food matrix.

Selective Recovery of Gold from Aqueous Media Using Magnetic PEG-Crosslinked Polystyrene

PEG-cross-linked and triethylenetetramine (TETA)-terminated polystyrene chains were formed on the surface of magnetic nanoparticles through atom transfer radical polymerization (ATRP). The prepared organic-inorganic hybrid material (denoted as MNP-PEGPS-L) was used to adsorb Au(III) ions from aqueous solutions. The MNP-PEGPS-L adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and vibrating-sample magnetometry (VSM). BET measurements showed that the particles have a porous structure, and their specific surface area was found to be 29.13 m2·g-1. Dynamic light scattering (DLS) analysis revealed that the hydrodynamic diameter distribution of the adsorbent particles follows a bimodal pattern, with two peaks appearing at 705 nm and 4087 nm. The particles in an aqueous solution with pH = 3 exhibited the highest zeta potential value (+22 mV) and, therefore, showed greater resistance to agglomeration. In adsorption studies, the equilibrium concentrations of ions (Ce values) were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The equilibrium adsorption capacity (Qe) was optimized in Au(III)-containing solutions at a pH of 3, an adsorbent dose of 0.2 mg·mL-1, a contact time of 60 min, and a temperature of 25 °C. Examination of the adsorption kinetics indicated that the adsorption of Au(III) ions occurs via chemisorption. The maximum adsorption capacity (Qmax) obtained from the Langmuir isotherm model (monolayer adsorption), was measured to be approximately 280 mg·g-1. Additionally, the study of the thermodynamics of adsorption demonstrated that the adsorption phenomenon is endothermic and occurs spontaneously. Overall, the prepared magnetic polymer adsorbent showed promising results in the recovery of gold ions from aqueous solutions due to its high hydrophilicity, high porosity, and excellent recyclability.

Adsorption of Cu(II) and Pb(II) in Aqueous Solution by Biochar Composites

In this study, straw biochar (TB) was prepared by pyrolysis at 500 °C, and biochar composite material (TBS) was prepared by a 1:4 mass ratio with sludge (TS). Scanning electron microscopy and Fourier transform infrared spectroscopy were utilized to characterize the material before and after adsorption. The results demonstrated that TBS possesses significant pore structure characteristics and abundant active functional groups such as hydroxyl, carboxyl, and carbonyl groups, providing a structural basis for its efficient adsorption of heavy metal ions in aqueous solutions. The adsorption performance of the remediation materials for Cu(II) and Pb(II) in aqueous solution was systematically investigated. Experimental data showed that TBS achieved maximum adsorption capacities of 60.86 and 46.98 mg/g for Cu(II) and Pb(II) at equilibrium, respectively, exhibiting superior adsorption efficiency. Through fitting analysis using adsorption kinetic models and isothermal adsorption models, it was found that the pseudo-second-order kinetic model and Freundlich isothermal model could more accurately describe the adsorption process of the two heavy metal ions, indicating that chemical adsorption was the dominant mechanism and characterized by multilayer adsorption. Thermodynamic parameter calculations revealed negative ΔG values and positive ΔH and ΔS values, suggesting that the adsorption process was a spontaneous, entropy-increasing, and endothermic reaction. These research results fully validate the excellent removal capabilities of TBS for Cu(II) and Pb(II). This study has shown that TBS can be considered a promising and cost-effective adsorbent, demonstrating its potential to adsorb heavy metal ions in water.

Unraveling the adsorption potential of Zr dithiol (MOF-DSH) through experimentation and neural network modeling

In this study, an aqueous-stable metal-organic framework with two thiol groups was synthesized using Zr as the metal centre and dimercaptosuccinic acid as the ligand through a conventional heating method for the removal of Cd(ii) from aqueous solution. Different characterization tools, including XRD, FT-IR, BET, SEM, TGA, and XPS, were employed. XRD results showed a characteristic pattern of a hexa-cluster, which was in agreement with the simulated MOF-801, and the corresponding vibrational peaks were observed in the FT-IR spectra. The synthesized MOF was thermally stable up to 300 °C, as demonstrated by TGA, and exhibited a specific surface area of 290 m2 g-1. Cadmium adsorption studies performed at different pH values showed a maximum adsorption capacity of 91.5 mg g-1 at pH 6. The adsorption behavior was well described by the Langmuir model and the pseudo-second order (PSO) kinetics, confirming the involvement of a monolayer with chemisorption as the dominant mode of adsorption. The synthesized MOF could be reused at least 4 times while retaining ∼80% of its initial adsorption capacity. FT-IR, XPS, and pH studies after Cd(ii) adsorption revealed that the predominant mode of interaction of Cd(ii) with the MOF is an ion-exchange mechanism. An artificial neural network-based (ANN) methodology was employed to model the adsorption capacity of Cd(ii) and predict the adsorption capacity as a function of Cd(ii) concentration, time of contact, and pH of the medium. The model demonstrated excellent results, with an average error of 2.3% and precision of 3.0%. The outcomes of these studies were consistent with the experimental results.

Sustainable Adsorbent: Activated Carbon From Waste Styrofoam for Efficient Aluminum Removal

This paper reports on batch investigations utilizing activated carbon (AC) made from waste Styrofoam to adsorb aluminum (Al3+) from aqueous solutions. The AC morphology and structure were examined using Fourier-transform infrared spectroscopy, scanning electron microscopy, and surface area analysis. The factors affecting the performance of adsorption were thoroughly examined. Al3+ removal was found to be maximal, that is, 98.65% using 0.2 g of AC at 90 min in a solution of pH 5 maintained at 60°C. Using a flame-mode atomic absorption spectrophotometer (AAnalyst 700, PerkinElmer, USA), the quantity of Al3+ in the adsorption solution was measured. For the purpose of studying adsorption, the pseudo-first-order, pseudo-second-order, Langmuir, Freundlich, Temkin, Jovanovich, and Harkins-Jura isotherms were analyzed. The kinetic study shows that the adsorption of Al3+ onto Al3+ is controlled by pseudo-second-order kinetics. It was observed that among these models, the Langmuir model showed the most favorable fit for the equilibrium data on the removal of Al3+ onto AC, with a strong fit (R2 = 0.995). The values of thermodynamic parameters such as entropy (ΔS°), Gibbs free energy (ΔG°), and enthalpy (ΔH°) show that the adsorption process is spontaneous and exothermic in nature. In Al3+ solutions with low concentrations, the AC exhibited a high adsorption rate. In addition, a check of the error function was performed. To find out if the AC could be utilized again after the adsorption procedure, desorption investigations were carried out. Due to its high adsorption capacity (> 98%) and porous structure, the prepared AC shows significant promise as an alternative adsorbent for Al3+. These findings demonstrate that the AC is both effective and efficient in removing Al3+ from wastewater.

Biochar doping of synthesized mordenite improves adsorption and oxidation in As(III) removal: Experiments and DFT calculations

In this study, a composite material was synthesized through the co-pyrolysis of biochar doped with synthetic mordenite. The adsorption experiments conducted with BC@ASM on As(III) facilitated the determination of the optimal mass ratio of 20:1 (ASM: Yak dung) and a pyrolysis temperature of 500 °C. The adsorption properties of ASM and BC@ASM were examined through batch adsorption experiments and a range of characterization techniques. And the reaction mechanism was further elucidated by DFT calculations, revealing the essential difference in the adsorption of As(III) by ASM and BC@ASM. The adsorption kinetics of As(III) were found to align with both the pseudo-second-order and Elovich kinetic models, while the isothermal adsorption was consistent with the Freundlich model. The maximum theoretical adsorption capacities were determined to be 371.9 mg/g and 449.6 mg/g, respectively. When the initial concentration of arsenite (As(III)) is 100 mg/L, the optimal dosage of synthetic mordenite is determined to be between 6 and 8 g/L, while the optimal dosage of the composite material ranges from 5 to 6 g/L. The composite material demonstrated significant resistance to fluctuations in pH. Within the pH range of 2-12, the removal efficiency is sustained between 78.3% and 88.7%. Furthermore, the adsorption capacity exhibited minimal sensitivity to the presence of anions such as chloride (Cl⁻), nitrate (NO₃⁻), bicarbonate (HCO₃⁻), and sulfate (SO₄2⁻) in the surrounding environment. In addition, BC@ASM facilitated the formation of arsenite-tannic acid complexes, which markedly improved its adsorption capacity for arsenite. In conclusion, the composite material presents a viable approach for addressing arsenic contamination in aquatic environments, while the foundational data offers a novel perspective for the remediation of metallic pollutants.

Synthesis of honeycomb-like citric acid-crosslinked chitosan hydrogel beads (cCHBs): Insight into structural characteristics of Cu(II)-loaded cCHBs (cCHBs-Cu(II))

To date, it has been regarded as one of the most challenging issues to construct novel adsorbents possessing excellent adsorption performance toward heavy metals including copper ions (Cu(II)). Especially, it is controversy about the structural characteristics of chitosan-based adsorbents adsorbed with Cu(II) ions, which could function as new adsorbents. In this study, we adopt a freeze-drying process to synthesize honeycomb-like chitosan hydrogel beads crosslinked with citric acid (cCHBs), further characterize the microstructures of cCHBs and eventually reveal the thermodynamics equations for the removal of target Cu(II). The results show that (1) the tricarboxylic groups within citric acid could prompt to construct long-range ordered channels of cCHBs under a freeze-drying process; (2) the maximum adsorption capacity of cCHBs for Cu(II) was 195.3 mg g-1 calculated by a Langmuir model; (3) the adsorption process of Cu(II) onto cCHBs was a spontaneous, endothermic, and entropy-increasing process. Moreover, the structural characteristics for honeycomb-like cCHBs adsorbed with Cu(II) (cCHBs-Cu(II)) as new adsorbents have been revealed with the adsorption of phosphate anions, which were further simulated with density functional theory (DFT). Accordingly, the superior adsorption performance of cCHBs and cCHBs-Cu(II) sheds light on a significant candidate for selective separation of a series of oxyanions.

Reducing the migration of cadmium, lead and nickel in soil using rice straw-based humic acid modified bentonite

With the continuous advancement of industrial development, the contamination of soil by potentially toxic element ions has emerged as an escalating issue, posing significant threats to both ecological systems and human health. Clay minerals have long been considered as green and economic remediation agents for polluted soil. However, their current application is hampered by low and inconsistent fixation efficiency. Here, a new clay composite BHA@B was prepared by modifying bentonite with biomass humic acid (BHA) prepared from rice straw. The BHA@B was characterized by FTIR, SEM and XRD and then tested as a remediation agent for potentially toxic element ion-contaminated soil. The effect of BHA@B on the prevalence of different fractions of Cd, Pb and Ni in soil and its ability to stabilize these metals were investigated using the BCR sequential extraction method. Treatment with BHA@B reduced the weak acid-extractable and reducible fractions of cadmium, lead and nickel by 22.5 and 8.1%, 17 and 11.4%, and 19.8 and 14%, respectively, compared with untreated soil. BHA@B transforms potentially toxic elements into oxidizable, residual, and other stable fractions, which greatly reduces the ability of potentially toxic element ions in the soil to migrate into the groundwater. BHA@B is a new, green, low-cost and efficient soil remediation agent.

Adsorption properties of Merrifield-bCCA chelating resins: a new alternative for Pb2+ removal from water

In this work, five new chelating resins (MR n Bz) functionalized with N-benzyl bis(carbamoyl)carboxylic acid molecules (BzbCCA) on their surface were prepared to study the metal ion (M n+) adsorption properties in water. MR n Bz resins were characterized by FTIR, TGA, FESEM and EDS. The surface charge as a function of pH and the chemical adsorption of M n+ on the surface were evaluated through zeta potential (ζ) measurements. The M n+ adsorption capacity of MR n Bz resins was evaluated using Pb2+, Cu2+, Cd2+, and Ni2+ mixture model solutions at low concentrations. MR n Bz resins displayed selective adsorption of Pb2+ even in the presence of a molar excess of other cations, due to the intrinsic affinity and selectivity of BzbCCA molecules for this metal ion. The adsorption isotherms of Pb2+ showed that the adsorption capacity of MR n Bz resins was influenced by the spacer chain length. In addition, the resins were characterized by FTIR, TGA, FESEM and EDS after the M n+ adsorption process, confirming the M n+ loading on the resin surface.

Simultaneous Removal of Heavy Metals and Dyes on Sodium Alginate/Polyvinyl Alcohol/κ-Carrageenan Aerogel Beads

Industrial textile wastewater containing both heavy metals and dyes has been massively produced. In this study, semi-interpenetrating polymer network structures of sodium alginate (SA)/polyvinyl alcohol (PVA)/κ-carrageenan (CG) aerogel beads were synthesized for their simultaneous reduction. The SA/PVA/CG aerogel beads were synthesized through a cost-effective and environmentally friendly method using naturally abundant biopolymers without toxic cross-linkers. The SA/PVA/CG aerogel beads were spheres with a size of 3.8 ± 0.1 mm, exhibiting total pore areas of 15.2 m2/g and porous structures (pore size distribution: 0.04-242.7 μm; porosity: 93.97%) with abundant hydrogen bonding, high water absorption capacity, and chemical resistance. The adsorption capacity and mechanisms of the SA/PVA/CG aerogel beads were investigated through kinetic and isotherm experiments for heavy metals (Cu(II), Pb(II)), cationic dye (methylene blue, MB), and anionic dye (acid blue 25, AB)) in both single and binary systems. The maximum adsorption capacities of the SA/PVA/CG aerogel beads based on the Langmuir model of Cu(II), Pb(II), and MB were 85.17, 265.98, and 1324.30 mg/g, respectively. Pb(II) showed higher adsorption affinity than Cu(II) based on ionic properties, such as electronegativity and hydration radius. The adsorption of Cu(II), Pb(II), and MB on the SA/PVA/CG aerogel beads was spontaneous, with heavy metals and MB exhibiting endothermic and exothermic natures, respectively.

Newly Designed Organic-Inorganic Nanocomposite Membrane for Simultaneous Cr and Mn Speciation in Waters

A sol-gel approach was used to prepare a thin hydrogel membrane based on an organic-inorganic polymer matrix embedded with pre-synthesized gold nanoparticles (AuNPs). The organic polymers utilized were poly(vinyl alcohol) (PVA) and poly(ethylene oxide) 400 (PEO) while tetraethoxysilane (TEOS) served as a precursor for the inorganic silica polymer. AuNPs were synthesized using D-glucose as a reducing agent and starch as a capping agent. A mixture of PVA, PEO, pre-hydrolyzed TEOS, and AuNP dispersions was cast and dried at 50 °C to obtain the hybrid hydrogel membrane. The structure, morphology, and optical properties of the nanocomposite membrane were analyzed using TEM, SEM, XRD, and UV-Vis spectroscopy. The newly designed hybrid hydrogel membrane was utilized as an efficient sorbent for the simultaneous speciation analysis of valence species of chromium and manganese in water samples via solid-phase extraction. This study revealed that Cr(III) and Mn(II) could be simultaneously adsorbed onto the PVA/PEO/SiO2/AuNP membrane at pH 9 while Cr(VI) and Mn(VII) remained in solution due to their inability to bind under these conditions. Under optimized parameters, detection limits and relative standard deviations were determined for chromium and manganese species. The developed analytical method was successfully applied for the simultaneous speciation analysis of chromium and manganese in drinking water and wastewater samples.

Modelling assisted phytoextraction of heavy metals from tannery origin leachate

The toxic tannery solid waste leachate (TSWL) containing heavy metals is generated after the percolation of rainwater in openly dumped tannery solid waste (TSW) which poses a serious threat to the surroundings by leaching down and bioaccumulation. For its management, the phytoextraction potential of Pistia stratiotes L. and Spirodela polyrhiza L. Schleid. was analyzed by growing them individually and combining them in different dilutions of TSWL (0%, 5%, 10%, 15%, and 20%) for 30 days. The removal efficiency of metal content was 79.04% (Cr), 78.49% (Cd), and 88.11% (Cu) in P. stratiotes, 72.55% (Cr), 80.12% (Cd), and 77.70% (Cu) in S. polyrhiza while in the mixture it was 88.39% for Cr, 92.57% for Cd, and 90% for Cu. The translocation factor of all the metals for every plant was greater than 1 indicating that all the plants used in the study proved to be hyperaccumulators. The Langmuir model more efficiently described experimental data for Cd and Cu while the phytoextraction of Cr was explained by the Freundlich model. The RL and 1/n were <1 for the above-mentioned metals indicating the favourable and active absorption of metals in plants. Therefore, based on the modelling-assisted phytoextraction findings it is suggested that the use of hyperaccumulator plants is a cost-effective and sustainable approach for managing the toxic TSWL.

Fabrication of a chitosan-grafted-4‑vinylpyridine/thiol-amine-HZSM-5 nanocomposite via casting method in adsorption of heavy cations from water systems: an evaluation of adsorption mechanism

This study presents the synthesis of low-silica HZSM-5 zeolite through a hydrothermal process. Subsequently, chitosan-grafted-4‑vinylpyridine/thiol-amine-HZSM-5 nanocomposites were fabricated using casting method for the effective removal of copper (Cu2+) and zinc (Zn2+) cations from aqueous systems. The fabricated cast nanocomposites were characterized using XRD, BET, XPS, FESEM, EDX, CHNS, FTIR, and TGA analyses. The simultaneous roles of amine (-NH2) and thiol (-SH) groups in enhancing the adsorption efficiency of Cu2+ and Zn2+ were thoroughly investigated. Additionally, the influence of key factors, including solution pH, contact time, adsorption temperature, and cation concentration, was systematically assessed. Equilibrium data fitting revealed the dominance of monolayer adsorption, as evidenced by the excellent fit of the Redlich-Peterson (R-P) and Langmuir isotherm models for both Cu2+ and Zn2+ cations. Examination of the kinetic experimental data indicated a close correspondence with the double-exponential model. The maximum adsorption capacity of the fabricated cast nanocomposite was determined to be 328.05 mg/g for Cu2+ and 107.96 mg/g for Zn2+ cations. Additionally, the fabricated cast nanocomposite demonstrated satisfactory regeneration capabilities after 9 cycles of desorption. In both synthetic binary and ternary systems, as well as in real wastewater, the adsorption process exhibited antagonistic behavior, indicating that the presence of one type of cation interfered with the adsorption of the other. The nanocomposite displayed a higher affinity for Cu2⁺ compared to Zn2⁺ cations, in both synthetic and real systems, demonstrating its potential for selective heavy metal removal.

Few-layer graphene-hybrid sulfonate hydrogels for high-efficient adsorption of heavy metal (Pb2+, Ni2+, Cd2+) in water treatment

Heavy metal ions pose a significant environmental threat due to their non-degradability and accumulation to toxic levels. In addressing this challenge, we have designed two novel hydrogels through radical polymerization, an efficient and cost-effective method, using sulfonate groups. One hydrogel remained pristine, while the other was hybridized with few-layer graphene (FLG). The incorporation of FLG interacts with the polymeric network without compromising its thermal stability, as confirmed by Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). It also reduces pore size (from 42 to 35 µm), enhances mechanical properties (Young's modulus increased from 32 to 44 kPa), and increases the swelling degree (from 62 to 76), while maintaining a high adsorption capacity. The ability of both hydrogels to adsorb Pb²⁺, Ni²⁺, and Cd²⁺ ions from aqueous solutions was examined. These hydrogels demonstrated high adsorption capacity (qe), with maximum uptake of 631.7 mg/g for Pb²⁺, 633.3 mg/g for Ni²⁺, and 373.1 mg/g for Cd²⁺ in the pristine hydrogels (VBS) and 540.6 mg/g for Pb²⁺, 615.1 mg/g for Ni²⁺, and 304.9 mg/g for Cd²⁺ in the hybrid FLG hydrogels (VBS_G). Adsorption kinetics studies indicated a fit to the pseudo-second-order model for all metal ions. Adsorption isotherms showed that Pb²⁺, Cd²⁺ and Ni²⁺ follow the Freundlich model. To demonstrate reusability and regeneration, hydrogels with adsorbed ions were introduced into acidic media. Evaluating their performance in various water sources, the hydrogels showcased potential as efficient adsorbents for water purification and agricultural applications, offering a promising solution for contaminated water treatment.

Ordered Mesoporous Silica Prepared with Biodegradable Gemini Surfactants as Templates for Environmental Applications

Mesoporous silica sieves have been prepared through sol-gel synthesis using diester gemini surfactants as pore templates, aiming to obtain new materials with potential use for water remediation. A series of mesoporous spherical silica particles of submicron size have been prepared in an alkali-catalyzed reaction, using a tetraethyl orthosilicate precursor and bis-quaternary ammonium gemini surfactants with diester spacers of varied lengths as pore-forming agents. The effect of the spacer length on the particle morphology was studied using nitrogen porosimetry, small-angle X-ray scattering (SAXS), ultra-small-angle neutron scattering, scanning, and transmission electron microscopy (SEM, TEM). The results revealed that for all spacer lengths, a long-range hexagonal pore ordering developed in the materials. The silica particles were nearly spherical, with sizes below 1 micrometer, and a weak dependence of the mean particle size on the spacer length could be observed. The template removal procedure had a strong influence on the porosity: calcination caused a moderate shrinkage of the pores while retaining the hexagonal structure, whereas treatment with acidified ethanol resulted in only partial removal of the surfactants; however, the hexagonal structure was severely destroyed. The applicability of the obtained calcined materials as adsorbents for heavy metal ions from water was studied with the example of Pb(II). A high sorption capacity of 110 mg/g was obtained in batch experiments, at pH 5 and 4 h contact time.

Purification of Biodiesel Polluted by Copper Using an Activated Carbon Prepared from Spent Coffee Grounds: Adsorption Property Tailoring, Batch and Packed-Bed Studies

Biodiesel produced via oil transesterification often contains metallic impurities, such as copper, which affects its quality and engine performance. This study explores the use of activated carbon prepared from spent coffee grounds to remove copper from biodiesel. Activated carbon samples were prepared via biomass pyrolysis and chemical activation with KOH and HNO3. The optimal conditions for copper adsorption were determined using a Taguchi L9 design. Maximum adsorption capacities were 13.4 and 17.3 mg/g at 30 and 40 °C, respectively, in batch adsorbers. In packed-bed columns, the axial dispersion reduced the adsorption efficiency obtaining bed adsorption capacities from 1.9 to 5.1 mg/g under tested experimental conditions. Adsorbent characterization and adsorption modeling indicated that copper removal was driven by multi-cationic interactions, where carboxylic groups from carbon surface acted as key active sites. The new adsorbent outperformed commercial bone char, making it a cost-effective alternative to improve biodiesel production contributing to the energy matrix diversification.

Green synthesis of zinc oxide nanoparticles using Padina pavonica extract for efficient photocatalytic removal of methylene blue

Dye-laden wastewater poses a significant environmental and health threat. This study investigated the potential of green-synthesized zinc oxide nanoparticles (ZnO NPs), derived from Padina pavonica brown algae extract, for the removal of methylene blue (MB) dye. The hypothesis was that utilizing algal extract for ZnO NP synthesis would enhance adsorption capacity and photocatalytic activity for dye removal. The synthesized ZnO NPs, characterized by Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and Zeta Potential, demonstrated high adsorption capacity (Qm = 192.308 mg g-1) and excellent removal efficiency (> 98%) for MB at low dye concentrations. Langmuir isotherm and pseudo-second-order kinetic models best fit the experimental data, suggesting monolayer adsorption and chemisorption as the primary mechanisms. Notably, the green ZnO NPs exhibited greater photocatalytic activity under direct sunlight irradiation compared to other light sources. Additionally, these nanoparticles displayed antimicrobial properties against various bacteria, indicating potential for water disinfection. This research offers a sustainable and environmentally friendly approach for wastewater treatment utilizing green ZnO NPs for efficient dye removal and potential water disinfection applications.

Self-Assembled Bolaamphiphile-Based Organic Nanotubes as Efficient Cu(II) Ion Adsorbents

Self-assembled organic nanotubes (ONTs) have been actively examined for various applications such as chemical separations and catalysis owing to their well-defined tubular nanostructures with distinct chemical environments at the wall and internal/external surfaces. Adsorption of heavy metal ions onto ONTs plays an essential role in many of these applications but has rarely been assessed quantitatively. Herein, we investigated interactions between Cu2+ and single-/quadruple-wall bolaamphiphile-based ONTs having inner carboxyl groups with different inner diameters, COOH-ONT10nm and COOH-ONT20nm. We first examined the effects of Cu2+ on their nanotubular structures using SAXS, STEM, and AFM. COOH-ONT10nm was stable in aqueous Cu2+ solution in contrast to COOH-ONT20nm owing to the presence of polyglycine-II-type hydrogen bonding networks within its wall. Subsequently, we studied the Cu2+ adsorption behavior of COOH-ONT10nm by monitoring the concentration of unbound Cu2+ using linear sweep anodic stripping voltammetry. The Cu2+ adsorption was quick, attributable to efficient Cu2+ partitioning through the open ends of the ONT, followed by fast Cu2+ diffusion in the uniform, relatively large nanochannel. More importantly, the Cu2+ adsorption capacity and affinity of COOH-ONT10nm were measured under different pH conditions using the Langmuir adsorption model. The adsorption capacity was similar at the pH range examined, showing the participation of approximately 25% of the inner carboxyl groups in the adsorption. The adsorption affinity increased with pH, indicating the essential role of the deprotonated carboxyl groups in Cu2+ adsorption. Most interestingly, the Langmuir adsorption constant was significantly higher than those of previously reported synthetic adsorbents and planar monolayer based on carboxyl binding sites. The high Cu2+ affinity of the ONT was attributable to the highly dense binding sites on the well-defined nanoscale concave structure of the inner channel. These results provide a valuable guideline for designing self-assembled nanomaterials for efficient chemical separations, detection, and catalysis.

Current status of microplastic pollution and the latest treatment technologies

With the widespread use of plastics globally, the issue of microplastic (MP) pollution has escalated into a significant social and environmental concern. This paper seeks to comprehensively review the environmental hazards associated with MPs and to present the latest analytical techniques and countermeasures. By analyzing the global distribution of MPs and the hazards they pose to the human body, it is found that MPs come from a variety of sources and are widely distributed, and that their hazards cover the whole body, but there is a lack of specific dose analyses and acute toxicity analyses. To address the challenges of industrial-scale MP treatment, numerous advanced theories and methods have been developed, providing valuable insights for effective remediation. Despite these advancements, notable limitations persist, particularly in the treatment of MPs in residential water supplies. Furthermore, this review identifies promising approaches in the utilization of microorganisms and the synergistic mechanisms of enzymes for MP pollution mitigation. Additionally, the urgent need for the development of standardized methods and a comprehensive legal framework for the isolation and detection of MPs across various environmental media is underscored, providing novel perspectives on the study of MPs.

Modeling of the biomethane production from ultrasonic pretreated fruit and vegetable waste via anaerobic digestion

The global dependency on the depleted fossil fuels has led to the quest for acquiring alternative energy sources. Different types of waste material are generated at a high rate and tapping into their use for greener, alternative energy production is an option. The mesophilic anaerobic co-digestion of fruit and vegetable waste and wastewater treatment plant sewage sludge experiments were conducted using ultrasonic pretreated substrates. Sonication exposure times from 0 to 45 min were selected for the experiments. An automatic methane potential test system (BMP) was used to determine the production rate of biomethane of the fruit and vegetables waste containing 60% fruit and 40% vegetables. The highest cumulative methane production of 238 mL g-1 VS was achieved at sonication time exposure of 45 min. It was observed that an increase in ultrasonic sonication exposure time, improved methane yield. The resulting experimental data was fitted with the modified Gompertz, co-digestion modified Gompertz, original Richards, modified Richards and co-digestion modified Richards models. IBM SPSS Statistics software was used for curve fitting and the estimation of the models' kinetic parameters. The modified Gompertz and Richards models showed higher goodness fit, both with R2 of 0.93 and modified Richards models did not produce a good fit for the data, with R2 of 0.7. The developed co-digestion models considered a combination of substrates that were easily digested as well as complex substrates that required multiple steps of digestion. The results show that the co-digestion modified Gompertz model had a goodness of fit of 0.98. Co-digestion modified Richard's model perfectly fit the experimental data, with R2 of 1. Both the co-digestion modified models are recommended due to their fitting performance. Fruit and vegetable waste comprise multiple substrates including simple sugars that digest readily and much more complex cellulose substrates that require more steps to digest and requiring the second step of digestion after undergoing hydrolysis. Both models took that into account. The aim of this study was to evaluate the suitability of the Gompertz and Richards model in the co-digestion of fruit and vegetables waste with sludge, as well as to develop co-digestion models for the substrates at hand.

Influence of Pseudomonas aeruginosa-based biopolymer on mitigating soil erosion and heavy metal dispersion

Extreme weather phenomena caused by climate change have exacerbated soil erosion and the subsequent dispersion of pollutants. Pseudomonas aeruginosa is known to contribute to the remediation of polluted water and reduce the geochemical mobility of heavy metals in contaminated soil. However, studies on the influence of biopolymers produced by soil microbes and P. aeruginosa on physical soil properties and soil erosion are limited. We aimed to investigate the influence of soil microbes on the mitigation of soil erosion and geochemical dispersion of heavy metals using a naturally occurring microbial substance, P. aeruginosa-based biopolymer (PBB). The PBB comprised carboxyl, hydroxyl, and amine surface functional groups; consequently, the biopolymer effectively sequestered Cd (maximum sorption capacity qm = 45.7 mg/g), Cu (qm = 26.7 mg/g), Pb (qm = 64.9 mg/g), and Zn (qm = 26.1 mg/g) in the solution. The PBB amendment of the soil improved the physical properties associated with soil erosion, increasing soil aggregation stability and shear strength by 41.6% and 36.8%, respectively. The extraction of heavy metals from soil via synthetic precipitate leaching decreased by 54.2% following the PBB amendment, and a negative correlation was observed between soil aggregate stability and heavy metal extraction, indicating that this microbial substance could immobilize pollutants by adsorbing cationic metal ions and inhibiting water-induced disaggregation. In the soil erosion experiments, soil loss and heavy metal extraction decreased by 70.9% and 43.8%, respectively, following the PBB amendment. These aggregation and sorption effects of the PBB underscore the potential of soil microbes to mitigate soil erosion and immobilize the geochemical dispersion of heavy metals, thereby contributing to the conservation of soil and water quality in areas surrounding contaminated slopes and heavy metal-contaminated areas, such as cut slopes, agricultural fields, mine dumps, and dams.

Concentration of Heavy Metals in Traditional and Industrial Fruit Juices from Iran: Probabilistic Risk Assessment Study

Exposure to heavy metals can endanger the health of exposed people in the long term. The consumption of fruit juice is increasing; it is important to estimate the health risk of consumers due to heavy metals. The current study was carried out for the analysis of toxic metals (lead (Pb), arsenic (As), and cadmium (Cd)) and essential elements (copper (Cu) and zinc (Zn)) in 60 samples of traditional and industrial fruit juices (10 samples of different brands of apple, orange, grape, peach, mango, and pineapple) in Hamadan, West Iran, using inductivity coupled plasma optical emission spectrometry (ICP-OES) method. The validation protocol included precision of the analytical method; recovery, the determination of the limit of detection (LOD), the limit of quantification (LOQ), and linearity were measured. Moreover, risk assessment was detected using target hazard quotient (THQ) and cancer risk (CR) by the Monte Carlo simulation (MCS) model. The ranking of metal concentration in traditional and industrial fruit juices was Zn > Cu > As > Pb > Cd. In all samples, concentrations of heavy metals in industrial fruit juices were higher than traditional fruit juices p <  < 0.001. The level of metals in all samples was lower of the US Environmental Protection Agency (USEPA), the World Health Organization (WHO), and the Iran Standard (IS) permissible limit set for drinking water. In terms of non-carcinogenic, values of toxic elements for children and adult in traditional and industrial fruit juices were 1.6E-3 and 1.72E-3 and 2.6E-3 and 1.85E-3, respectively. The 95th percentile of CR in adults and children due to both industrial and traditional fruits juices was higher than 1E-6; hence, reducing the concentration of As in fruit juices should be conducted. Consumption of fruit juice can increase carcinogenic risk of consumers. Therefore, it is recommended to consume it with caution.

Synthesis, characterization, and application of thio-salicylaldehyde schiff base complexes for Cr (VI) adsorption

This study investigates the effectiveness of a Schiff base derived from thio-carbohydrazide and salicylaldehyde as an adsorbent for Cr(VI) removal from wastewater. The Schiff base demonstrated excellent adsorption capacity and reusability, with high removal efficiency and rapid adsorption kinetics. The results were supported by theoretical density functional theory simulations, which revealed the enhanced dynamic nature of the Schiff base system for heavy metal adsorption. These findings highlight the potential of Schiff base complexes as sustainable and efficient adsorbents for industrial wastewater treatment.

Preparation of multi-modified/carbonized/gelatinized starch and its de-risking effect on Cd(II) and hymexazol in wastewater

In this study, starch (S) was gelatinized and carbonized to prepare carbonized/gelatinized S (CGS) as the research material. Then, peat extract (Pe) and surfactants with different ratios were single- and multi-modified on CGS, respectively, to prepare Pe-modified CGS (Pe-CGS) and multi-modified CGS, respectively. The microscopic morphology of multi-modified CGS was studied using various testing methods. The de-risking effect on Cd(II) and hymexazol in wastewater was investigated, and the effects of temperature, pH, and ionic strength were compared. The spheroidal structure of S was destroyed after carbonization, and Pe and surfactants were modified on the surface and changed the surface properties of CGS. The adsorption processes of Cd(II) and hymexazol were suitable to be described by the Langmuir and Freundlich models, respectively. The maximum adsorption capacities (qm) of Cd(II) and adsorption capacity parameter (k) of hymexazol on different modified CGSs presented the peak value at BS/Pe-CGS. With the increase in the modification ratio of Pe, BS, and SDS, qm and k increased, which showed a high value at 100 % modification. Increases in temperature and pH were beneficial to Cd(II) adsorption but were not conducive to hymexazol adsorption. The adsorption amount decreased for Cd(II) and increased first and then reduced for hymexazol with the rise in ionic strength. The adsorption process exhibited spontaneity, endothermic behavior for Cd(II), exothermic behavior for hymexazol, and an entropy-increasing reaction. The adsorption amount of Cd(II) and hymexazol by multi-modified CGS maintained approximately 81 % of the original sample after three rounds of regeneration.

Pyrolytic conversion of cattle manure into value-added products and application of biochar for adsorption of sulfamethoxazole

This study investigated the thermochemical conversion of cattle manure (CM) to propose a sustainable platform for its valorization, and explored the applicability of CM-derived biochar (CMB) as an environmental medium for the adsorptive removal of sulfamethoxazole (SMZ). CM pyrolysis was conducted under two atmospheric conditions (N2 and CO2), and the pyrogenic products were quantified and characterized. Real-time syngas monitoring revealed that CO2 enhanced CO generation from the CM, leading to the formation of a highly porous carbon structure in the produced biochar (CMBCO2). The adsorptive removal of SMZ by CMBCO2 was highly dependent on the pH conditions. The adsorption kinetics of SMZ onto CMBCO2 reached equilibrium within 540 min, following a pseudo-second-order model. The SMZ adsorption isotherms fit the Langmuir-Freundlich model, highlighting the importance of chemisorption in the adsorption process. X-ray photoelectron spectroscopy revealed that SMZ was adsorbed by non-electrostatic mechanisms, including hydrogen bonding, Lewis acid-base interactions, surface complexation, and π-π electron-donor acceptor interactions. This study presents an exemplary strategy for converting livestock waste into valuable resources, enabling the harvesting of energy resources and the production of treatment media for environmental remediation.

A Novel Approach to Waste Recycling and Dye Removal: Lithium-Functionalized Nanoparticle Zeolites

A zeolitic sample, named MT-ZLSH, was synthesized using mining tailings (MT) as the precursor material, resulting in a structure comprising: Linde type A (LTA) and sodalite-hydroxysodalite (ZLSH). This naming convention reflects the material's origin and its structural characteristics. The material was further modified by incorporating lithium, producing MT-ZLSH-Li+. Physicochemical characterizations were performed, and the material was evaluated for its potential to remove methylene blue (MB) from synthetic wastewater through adsorption and photocatalysis. Efficient adsorption was observed under typical wastewater pH conditions, with a maximum adsorption capacity of 23.4 mg·g-1, which fit well with the Langmuir isotherm model. The key mechanisms governing MB adsorption were identified as ion exchange, electrostatic attraction, and hydrogen bonding. The adsorption process was exothermic, with kinetic data fitting both the pseudo-second order and intraparticle diffusion models, achieving 82% removal and a maximum adsorption capacity of 40 mg·g-1 over 12 h. MB adsorption followed a two-step process, initially involving film diffusion, followed by intraparticle diffusion. Additionally, photocatalytic degradation of MB achieved 77% degradation within 180 min. However, a decrease in reusability was observed during a second cycle of MB adsorption and photodegradation, highlighting the need for further optimization to enhance the material's long-term performance.

A comprehensive investigation of the adsorption behaviour and mechanism of industrial waste sintering and bayer red muds for heavy metals

The issue of heavy metal pollution is a critical global concern that requires urgent solution. However, conventional heavy metal adsorbents are too costly to be applied in large-scale engineering. In this study, adsorption behavior and mechanism of sintering red mud (RM-A) and bayer red mud (RM-B) for heavy metals were investigated to address the disposal of red mud as industrial waste and remediation of heavy metal pollution. Batch adsorption experiments were conducted to explore the adsorption performances of RM-A and RM-B under various conditions. Characterization of RM-A and RM-B before and after adsorption by XRD, FTIR and SEM-EDX was applied to investigate the specific adsorption behavior and mechanism. Adsorption experiments of both RM-A and RM-B fitted pseudo-second-order kinetic model and Langmuir isotherm model, with estimated maximum adsorption capacity of 21.96 and 25.19 mg/g for Cd2+, 21.47 and 26.06 mg/g for Cu2+ and 55.47 and 59.65 mg/g for Pb2+, respectively. Precipitation transformation of calcite was the primary adsorption mechanism for RM-A, whereas ion exchange of cancrinite, surface coordination compounds of hematite and minor precipitation transformation of calcite accounted for the adsorption mechanism for RM-B. Overall, RM-A and RM-B exhibited best adsorption performance for Pb2+, with RM-B showing greater adsorption capacity attributed to its higher specific surface area. This study compared the adsorption properties of RM-A and RM-B for the first time and demonstrated that both red muds can be effectively applied to remove heavy metals, thereby contributing to the sustainable industrial waste management and resourceful reuse.

Preparation of Guanidine-Grafted NH2-MIL-101(Fe)/Polyvinylidene Fluoride Mixed Matrix Membranes for Adsorption of Pb2+ for Isopropanol Purification

Electronic-grade isopropyl alcohol is widely utilized in the cleaning of semiconductors and microelectronic components. Removing ions like Pb2+ is crucial since the presence of impurities may cause degradation of electronics, increased failure rates, and short circuits. Membrane materials offer a number of advantages in the field of adsorption separation; however, the lack of adsorption sites results in limited adsorption capacity. In the current work, guanidino-grafted NH2-MIL-101(Fe) was incorporated into polyvinylidene fluoride (PVDF) to prepare MOF/PVDF mixed matrix membranes (NM/PVDF) for the removal of Pb2+ from isopropanol. Benefiting from the larger specific surface area and more lone electron pairs in the guanidine group, the Pb2+ adsorption capacity of the as-prepared NM/PVDF membrane was 29.4458 mg/g, which was higher than that of the NH2-MIL-101(Fe)/PVDF membrane (20.9306 mg/g) and the pure PVDF membrane (6.7324 mg/g). The NM/PVDF membrane was able to reduce the concentration of Pb2+ from 500 to 86.73 ppb. This work highlights the potential of guanidine-grafted Fe-based MOFs/PVDF membranes as adsorbents for acquisition of electronic-grade solvents.

Evaluation of Adsorption Ability of Lewatit® VP OC 1065 and Diaion™ CR20 Ion Exchangers for Heavy Metals with Particular Consideration of Palladium(II) and Copper(II)

The adsorption capacities of ion exchangers with the primary amine (Lewatit® VP OC 1065) and polyamine (Diaion™ CR20) functional groups relative to Pd(II) and Cu(II) ions were tested in a batch system, taking into account the influence of the acid concentration (HCl: 0.1-6 mol/L; HCl-HNO3: 0.9-0.1 mol/L HCl-0.1-0.9 mol/L HNO3), phase contact time (1-240 min), initial concentration (10-1000 mg/L), agitation speed (120-180 rpm), bead size (0.385-1.2 mm), and temperature (293-333 K), as well as in a column system where the variable operating parameters were HCl and HNO3 concentrations. There were used the pseudo-first order, pseudo-second order, and intraparticle diffusion models to describe the kinetic studies and the Langmuir and Freundlich isotherm models to describe the equilibrium data to obtain better knowledge about the adsorption mechanism. The physicochemical properties of the ion exchangers were characterized by the nitrogen adsorption/desorption analyses, CHNS analysis, Fourier transform infrared spectroscopy, the sieve analysis, and points of zero charge measurements. As it was found, Lewatit® VP OC 1065 exhibited a better ability to remove Pd(II) than Diaion™ CR20, and the adsorption ability series for heavy metals was as follows: Pd(II) >> Zn(II) ≈ Ni(II) >> Cu(II). The optimal experimental conditions for Pd(II) sorption were 0.1 mol/L HCl, agitation speed 180 rpm, temperature 293 K, and bead size fraction 0.43 mm ≤ f3 < 0.6 mm for Diaion™ CR20 and 0.315-1.25 mm for Lewatit® VP OC 1065. The maximum adsorption capacities were 289.68 mg/g for Lewatit® VP OC 1065 and 208.20 mg/g for Diaion™ CR20. The greatest adsorption ability of Lewatit® VP OC 1065 for Pd(II) was also demonstrated in the column studies. The working ion exchange in the 0.1 mol/L HCl system was 0.1050 g/mL, much higher compared to Diaion™ CR20 (0.0545 g/mL). The best desorption yields of %D1 = 23.77% for Diaion™ CR20 and 33.57% for Lewatit® VP OC 1065 were obtained using the 2 mol/L NH3·H2O solution.

Effective removal of textile dye via synergy of adsorption and photocatalysis over ZnS nanoparticles: Synthesis, modeling, and mechanism

In this work, we prepared sulfur-zinc nanoparticles (ZnS-TGA) functionalized with thioglycolic acid by a hydrothermal method and tested their photodegradation ability by solar irradiation. ZnS-TGA were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), UV-Vis spectrophotometer and photoluminescence spectroscopy. In the characterization of these nanoparticles, thioglycolic acid proved to be a strong capping ligand, with a specific surface area of 36.82 m2/g and an average size of 7.15 nm. To test the photocatalytic degradability of the product, methylene blue (MB) was used as a model pollutant. Various operational variables were investigated, including pH, amount of nanoparticles, dye concentration, contact time and temperature. The equilibrium adsorption tests, and the statistical physical calculations allowed the analysis of the energetic and steric variables of the adsorption of MB dye molecules on the surface of these nanoparticles. The equilibrium data were well fitted with Langmuir-Freundlich (L-F) and the adsorption kinetics with pseudo-first order. The maximum adsorption capacity of the MB dye removal process was 30.92 mg g-1 at pH 7 and 298 K, and this process was spontaneous and exothermic. The dye molecules and the surface of the nanoparticles exhibited physical interactions with adsorption energies of 23.31-25.92 kJ/mol. The photocatalytic activity of these nanoparticles resulted in a dye degradation efficiency of 91.1 % in 180 min. The photocatalytic efficiency remained almost unchanged after five consecutive degradation cycles, resulting in a methylene blue degradation of 85 %. According to these results, these environmentally friendly nanoparticles have the potential to purify industrial and urban liquids contaminated with harmful organic compounds such as dye molecules.

Eco-friendly engineering of micro composite-based hydroxyapatite bio crystal and polyaniline for high removal of OG dye from wastewater: Adsorption mechanism and RSM@BBD optimization

The presence of harmful substances such as dyes in water systems poses a direct threat to the quality of people's lives and other organisms living in the ecosystem. Orange G (OG) is considered a hazardous dye. The existing paper attempts to evaluate a low-cost adsorbent for the effective removal of OG dye. The developed adsorbent Polyaniline@Hydroxyapatite extracted from Cilus Gilberti fish Scale (PANI@FHAP) was elaborated through the application of the in situ chemical polymerization method to incorporate PANI on the surface of naturally extracted hydroxyapatite FHAP. The good synthesis of PANI@FHAP was evaluated through multiple techniques including X-ray diffraction (XRD), Scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM/EDS), Fourier Transforms Infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) coupled with thermal differential analysis (DTA) analysis. The results reveal a highly ordered disposition of PANI chains on FHAP, resulting in a well-coated FHAP in the PANI matrix. Furthermore, the presence of functional groups on the surface of PANI such as amine (-NH2) and imine (=NH) groups would facilitate the removal of OG dye from contaminated water. The adsorption of OG onto PANI@FHAP was conducted in batch mode and optimized through response surface methodology coupled with box-Behnken design (RSM/BBD) to investigate the effect of time, adsorbent dose, and initial concentration. The outcomes proved that OG adsorption follows a quadratic model (R2 = 0.989). The kinetic study revealed that the adsorption of OG fits the pseudo-second-order model. On the other hand, the isotherm study declared that the Freundlich model is best suited to the description of OG adsorption. For thermodynamic study, the adsorption of OG is spontaneous in nature and exothermic. Furthermore, the regeneration-reusability study indicates that PANI@FHAP could be regenerated and reused up to five successive cycles. Based on the FTIR spectrum of PANI@FHAP after OG adsorption, the mechanism governing OG adsorption is predominantly driven by π-π interaction, electrostatic interaction, and hydrogen bonding interactions. The obtained results suppose that PANI@FHAP adsorbent can be a competitive material in large-scale applications.

Efficient arsenic removal from water using iron-impregnated low-temperature biochar derived from henequen fibers: performance, mechanism, and LCA analysis

The present study aims to investigate the low-energy consumption and high-efficiency removal of arsenic from aqueous solutions. The designed adsorbent Fe/TBC was synthesized by impregnating iron on torrefaction henequen fibers. Isothermal adsorption experiments indicated maximum adsorption capacities of 7.30 mg/g and 8.98 mg/g for arsenic(V) at 25.0 °C and 40.0 °C, respectively. The interference testing showed that elevated levels of pH, HCO3- concentration, and humic acid content in the solution could inhibit the adsorption of arsenic by Fe/TBC. Characterization of the adsorbent before and after adsorption using FTIR and SEM-EDS techniques confirmed arsenic adsorption mechanisms, including pore filling, electrostatic interaction, surface complexation, and H-bond adhesion. Column experiments were conducted to treat arsenic-spiked water and natural groundwater, with effective treatment volumes of 550 mL and 8792 mL, respectively. Lastly, the life cycle assessment (LCA) using OpenLCA 2.0.3 software was performed to treat 1 m3 of natural groundwater as the functional unit. The results indicated relatively significant environmental impacts during the Fe/TBC synthesis stage. The global warming potential resulting from the entire life cycle process was determined to be 0.8 kg CO2-eq. The results from batch and column experiments, regeneration studies, and LCA analysis indicate that Fe/TBC could be a promising adsorbent for arsenic(V).

Biosorption of europium and erbium from aqueous solutions using crosslinked sericin-alginate beads

Critical metals such as rare earths are essential for important industrial applications and for producing high-tech materials. Currently, the development of alternative and non-conventional biomaterials has gained significant interest. This work investigated the use of crosslinked sericin-alginate-based natural polymeric particles for the removal of rare earths from water. Affinity tests showed that sericin-alginate/polyethylene glycol diglycidyl ether had the highest potential for capturing europium (0.258 mmol/g and 94.33%) and erbium (0.259 mmol/g and 94.55%). Next, erbium was selected based on the affinity with sericin-alginate/polyethylene glycol diglycidyl to investigate the effect of dose/pH, biosorption kinetics, isothermal equilibrium, desorption/reuse, and selectivity. The effect of dose and pH showed that 8.0 g/L (95.91%) and pH 5.0 (97.53%) were more efficient in capturing erbium. The biosorption kinetics showed that the equilibration time was reached within 210 min. The PSO and EMTR models effectively represented the kinetics data. The isothermal equilibrium revealed that the maximum uptake capacity for erbium was 0.641 mmol/g. The isothermal curves better fit the Dubinin-Radushkevich (55 °C) and Langmuir (25 and 40 °C) models. Thermodynamic quantitates indicated that erbium uptake was spontaneous, governed by entropic changes, and endothermic. The recovery of Er3+ was greater than 98% and the reuse of the eluent in the cycles enriched the Er3+ load 10-times (1.0 to 9.91 mmol/L). The beads also showed better performance for capturing Er3+ and Eu3+ with other coexisting ions. Characterization analyzes revealed the ion exchange mechanism between Ca2+/Er3+ prevailed in the Er3+ removal. Thus, the results pointed out that crosslinked sericin-alginate can be used as an alternative and promising biosorbent to remove and recover rare earths.

Hybrid method integrating adsorption and chemical precipitation of heavy metal ions on polymeric fiber surfaces for highly efficient water purification

A lot of research has been focused on increasing the specific surface area of adsorbents over a long period of time to remove heavy metal ions from wastewater using the adsorbent. However, porous adsorbents with high specific surface area have demonstrated drawbacks in water purification processes, such as high pressure drop and limitations in the adsorption capacity of heavy metal ions. In recent years, a mechanism-based convergence method involving adsorption/chemical precipitation has emerged as a promising strategy to surmount the constraints associated with porous adsorbents. The mechanism involves amine groups on chelating fibers dissociating OH- ions from water molecules, thereby raising the pH near the fibers. This elevated pH promotes the crystallization of heavy metal ions on the fiber surfaces. The removal of heavy metal ions proceeds through a sequence of adsorption and chemical precipitation processes. An adsorbent based on chelating fibers, integrating adsorption technology with chemical precipitation, demonstrates superior performance in removing significant quantities of heavy metal ions (ca. 1000-2000 mg/g for Cd2+, Cu2+ and Pb2+) when compared to developed porous adsorbents (ca. 50-760 mg/g for same ions). This review paper introduces advanced polymer fibers endowed with the capability to integrate hybrid technology, delves into the mechanism of hybrid technology, and examines its application in process technology for the effective removal of heavy metal ions. The versatility of these advanced fibers extends far beyond the removal of heavy metal ions in water treatment, making them poised to garner significant attention from researchers across diverse fields due to their broad range of potential applications. After further processes involving the removal of templates from chelating polymeric fibers used as supports and the reduction of precipitated heavy metal oxide crystals, the resulting heavy metal crystals can exhibit thin walls and well-interconnected porous structures, suitable for catalytic applications.

Enhanced Cu2+ and Cd2+ removal by a novel co-pyrolysis biochar derived from sewage sludge and phosphorus tailings: adsorption performance and mechanisms

The reutilization of municipal wastes has always been one of the hottest subjects of sustainable development study. In this study, a novel biochar co-pyrolyzed from municipal sewage sludge and phosphorus tailings was produced to enhance the adsorption performance of the composite on Cu2+ and Cd2+. The maximum Cu2+ and Cd2+ adsorption capacity of SSB-PT were 44.34 and 45.91 mg/g, respectively, which were much higher than that of sewage sludge biochar (5.21 and 4.58 mg/g). Chemisorption dominated the whole adsorption process while multilayer adsorption and indirect interaction were also involved. According to the result of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectrum (XPS), the load of CO32-, Mg2+, and Ca2+ on the surface of SSB-PT enhanced the precipitation and ion exchange effect. Posnjakite and CdCO3 were formed after the adsorption of Cu2+ and Cd2+, respectively. Besides, complexation, and metal-π interaction were also involved during the adsorption process. Therefore, this study offered a promising method to reuse sewage sludge and phosphorus tailings as an effective adsorbent.

Silicone-modified black peanut shell (BPS) biochar adsorbents: Preparation and their adsorptions for copper(II) from water

Novel silicone-modified biochar adsorbents (BPS-MBCs) were prepared by utilizing waste black peanut shell (BPS) as a raw biochar and gamma-amino-propyl triethoxysilane (silicone) as an inorganic modifier. The novelty of this work is that the incorporation of silicone into BPS can rise the specific surface area and porosity of BPS-MBCs and elevate their adsorptions for copper (II). Sorption kinetics data for copper (II) were molded using five kinetic equations [i.e. Lagergren 1st-order and 2nd-order, intraparticle diffusion (IN-D), Elovich, and Diffusion-chemisorption]. The equilibrium adsorption data for copper (II) were analyzed using two-parameter isotherm equations [i.e. Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin] and three-parameter Sips, Redlich-Peterson and Toth isotherm models. It was validated that copper (II) sorption on BPS-MBCs matched better with pseudo-2nd-order kinetic, Diffusion-chemisorption and Langmuir isotherm models. The maximal qmLan of BPS-MBC-400 was near 284 mg/g at 45 °C. By multi-phase fitting of IN-D modelling, intra-particle diffusion coefficient (kin-d) and diffusion coefficient of external mass-transfer (DEx-Di) for copper (II) were calculated. The low sorption energy from Temkin and mean free energy from D-R modellings implied that copper (II) sorption was initiated by weak non-covalent bond interactions. Thermodynamic parameters indicated that copper (II) on BPS-MBCs was an endothermic and spontaneous process. Recycling of BPS-MBC-400 for copper (II) suggested it has excellent reusability. The major mechanism of copper (II) on BPS-MBCs is possibly comprised of multiple processes, such as physical adsorption (electrostatic attraction), chemical adsorption (adsorption from functional groups, chelation, and ion exchange) and diffusion-chemisorption. Based on these findings, it is expects that BPS-MBCs are promising sorbents for copper (II) eradication from Cu(II)-including wastewater.

Diclofenac sodium adsorption on activated carbon: experimental, modeling and bayesian statistics

The present study modeled the adsorption process of the drug diclofenac sodium on activated charcoal. For this purpose, a mass balance-based model was used considering a fixed bed column. The mass transfer rate in the solid phase was represented by a driving force model proposed in this study, and a gamma exponent with a range of 0 > γ ≤ 2 was assigned to the model. Different isotherms were adopted to represent the equilibrium at the solid/liquid interface: the Langmuir, Freundlich, Sips and Redlich-Peterson isotherms. The modeling was approached from the perspective of Bayesian statistics, and the Markov chain Monte Carlo method was used for parameter estimation. Model validation was performed with experimental data obtained under different operating conditions of initial concentration ($C_{0.

Water Hyacinth Leaves Are an Efficient, Green, and Cost-Effective Biosorbent for the Removal of Metanil Yellow from Aqueous Solution: Kinetics, Isotherm, and Thermodynamic Studies

Excessive water hyacinth growth in aquatic environments and metanil yellow (MY) dye in industrial wastewater pose severe environmental and public health challenges. Therefore, this study evaluated the effects of various process factors on batch MY biosorption onto water hyacinth leaves (LECs) and MY biosorption kinetics, equilibrium, and thermodynamics. The optimal pH for MY biosorption by LECs was 1.5-2.0. The initial MY concentration affected the equilibrium MY biosorption capacity but not the LEC particle size and solution temperature. However, the LEC particle size and solution temperature affected the MY biosorption rate; the biosorption rate was higher at a lower particle size (0.15-0.3 mm) and a higher temperature (62 °C) than at higher particle sizes and lower temperatures. The pseudo-second-order model adequately described the biosorption kinetics of MY by LECs at the different levels of the process factors, whereas the Sips and Redlich-Peterson models satisfactorily represented the biosorption isotherm of MY. The Sips model predicted a maximum MY biosorption capacity of 170.8 mg g-1. The biosorption of MY by LECs was endothermic and not spontaneous. These findings demonstrate that LECs exhibit great potential for bioremediating MY-contaminated wastewater, thereby providing valuable insights for effective water treatment and pollution control strategies.

Management of ibuprofen in wastewater using electrospun nanofibers developed from PET and PS wastes

Electrospinning is a promising technique for the beneficial use and recycling of plastic waste polymers using simple methodologies. In this study, plastic bottles and Styrofoam wastes have been used to develop polyethylene terephthalate (PET) and polystyrene (PS) nanofibers using electrospinning technique separately without any further purification. The effect of the concentration onto the nanofiber's morphology was studied. The fabricated nanofibers were characterized using Field Emission Scanning Electron Microscope (FE-SEM), Fourier Transformed Infrared Spectroscopy (ATR-FTIR), N2 adsorption/desorption analysis, and water contact angle (WCA). Furthermore, the prepared nanofibers were applied for the adsorption of ibuprofen (IBU) from wastewater. Some parameters that can influence the adsorption efficiency of nanofibers such as solution pH, wt.% of prepared nanofibers, drug initial concentration, and contact time were studied and optimized. The results show that the equilibrium adsorption capacity was achieved after only 10 min for 12 wt% PET nanofibers which is equivalent to 364.83 mg/g. For 12 wt% PS nanofibers, an equilibrium adsorption capacity of 328.42 mg/g was achieved in 30 min. The experimental data was fitted to five isotherm and four kinetics models to understand the complicated interaction between the nanofibers and the drug. Langmuir-Freundlich isotherm model showed the best fit for experimental data for both PET and PS nanofibers. The adsorption process was characterized by predominantly physical reaction rather than chemical adsorption for both materials. The reusability study revealed that the synthesized nanofibers maintain their ability to adsorb/desorb IBU for up to five cycles. The results obtained demonstrated that fabricated nanofibers from plastic wastes could perform promising adsorbents for the management of IBU in wastewater. However, further research is needed for the scaling-up the fabrication which is required for real-world applications.

Moss biomass as effective biosorbents for heavy metals in contaminated water

The study explored batch adsorption of Cd(II) and Pb(II) ions using moss biomass from Barbula consanguinea and Hyophila involuta, assessing removal efficiency concerning various parameters. Both moss species showed high removal rates for Cd(II) (87 % for B. consanguinea and 89 % for H. involuta) and Pb(II) (93 % for B. consanguinea and 94 % for H. involuta) from contaminated water, reaching equilibrium within 30 min. While Cd(II) removal was pH-independent, Pb(II) removal showed pH-dependence, peaking at pH 5.0-5.5. Adsorption isotherm analysis indicated that the Langmuir, Freundlich, Elovich, Sips, and Redlich-Peterson models best described Cd(II) and Pb(II) adsorption onto both moss species (except for Cd(II) adsorption onto H. involuta), with R 2  > 0.98. This confirms a heterogeneous surface with both monolayer and multilayer adsorption sites. The pseudo-second-order kinetic model confirmed chemisorption on moss biomass from both species. FTIR spectra identified major binding sites such as phenols, alkaloids, amines, alkenes, nitro compounds, and low-molecular-weight carbohydrates. EDS analysis validated the bonding of Cd(II) and Pb(II) ions to the biomass surface by displacing Ca(II) ions. According to the Langmuir model, moss biomass exhibited selective adsorption, favoring Pb(II) over Cd(II). B. consanguinea showed a higher adsorption capacity than H. involuta, which is attributed to its higher negative zeta potential. This study underscores the novelty of moss biomass for heavy metal removal in wastewater treatment, highlighting its sustainability, effectiveness, cost-efficiency, versatility, and eco-friendliness.

An Adsorption Based Downstream Processing Approach for Penicillin V from a Penicillium chrysogenum BIONCL I22 Culture Filtrate

Penicillin V (phenoxy methyl penicillin) is highly sought after among natural penicillins because of its exceptional acid stability and effectiveness against common skin and respiratory infections. Given its wide-ranging therapeutic uses, there is a need to establish a greener method for its maximum recovery to reduce the carbon footprint. Here, we have identified and validated optimized operational conditions for resin-based penicillin V recovery. It was observed that Amberlite XAD4 had the highest penicillin V hydrophobic adsorption capacity among the other screened resins. Kinetic and isothermal studies using linear and nonlinear regression analysis showed that the adsorption process well fitted with pseudo-second-order kinetics (R 2 = 0.9816) and the Freundlich adsorption isotherm model (R 2 = 0.9871). Adsorption equilibrium was attained within 4 h, while maximum adsorption was observed at 3 mg/mL penicillin V concentration. Furthermore, the optimized extraction protocol was compared with the conventional butyl acetate-based downstream processing. Under optimum conditions resin-based penicillin V recovery was 2-fold higher as compared to the solvent extraction method and the resin could be reused for over six cycles without compromising the yield. These findings signify substantial progress toward the development of an environmentally sustainable approach for penicillin V recovery and a potentially viable method for extractive fermentation.

Synthesis of zeolite from industrial wastes: a review on characterization and heavy metal and dye removal

Increasing world population, urbanization, and industrialization have led to an increase in demand in production and consumption, resulting in an increase in industrial solid wastes and pollutant levels in water. These two main consequences have become global problems. The high Si and Al content of solid wastes suggests that they can be used as raw materials for the synthesis of zeolites. In this context, when the literature studies conducted to obtain synthetic zeolites are evaluated, it is seen that hydrothermal synthesis method is generally used. In order to improve the performance of the hydrothermal synthesis method in terms of energy cost, synthesis time, and even product quality, additional methods such as alkaline fusion, ultrasonic effect, and microwave support have been developed. The zeolites synthesized by different techniques exhibit superior properties such as high surface area and well-defined pore sizes, thermal stability, high cation exchange capacity, high regeneration ability, and catalytic activity. Due to these specific properties, zeolites are recognized as one of the most effective methods for the removal of pollutants. The toxic properties of heavy metals and dyes in water and their carcinogenic effects in long-term exposure pose a serious risk to living organisms. Therefore, they should be treated at specified levels before discharge to the environment. In this review study, processes including different methods developed for the production of zeolites from industrial solid wastes were evaluated. Studies using synthetic zeolites for the removal of high levels of health and environmental risks such as heavy metals and dyes are reviewed. In addition, EPMA, SEM, EDX, FTIR, BET, AFM, and 29Si and 27Al NMR techniques, which are characterization methods of synthetic zeolites, are presented and the cation exchange capacity, thermodynamics of adsorption, effect of temperature, and pH are investigated. It is expected that energy consumption can be reduced by large-scale applications of alternative techniques developed for zeolite synthesis and their introduction into the industry. It is envisaged that zeolites synthesized by utilizing wastes will be effective in obtaining a green technology. The use of synthesized zeolites in a wide variety of applications, especially in environmental problems, holds great promise.

Amino-modified upcycled biochar achieves selective chromium removal in complex aqueous matrices

Chromium pollution of groundwater sources is a growing global issue, which correlates with various anthropogenic activities. Remediation of both the Cr(VI) and Cr(III), via adsorption technologies, has been championed in recent years due to ease of use, minimal energy requirements, and the potential to serve as a highly sustainable remediation technology. In the present study, a biochar sorbent sourced from pineapple skins, allowed for the upcycling of agricultural waste into water purification technology. The biochar material was chemically modified, through a green amination method, to produce an efficient and selective adsorbent for the removal of both Cr(VI) and Cr(III) from complex aqueous matrices. From FTIR analysis it was evident that the chemical modification introduced new C-N and N-H bonds observed in the modified biochar along with a depletion of N-O and C-H bonds found in the pristine biochar. The amino modified biochar was found to spontaneously adsorb both forms of chromium at room temperature, with binding capacities of 46.5 mg/g of Cr(VI) and 27.1 mg/g of Cr(III). Interference studies, conducted in complex matrices, showed no change in adsorption capacity for Cr(VI) in matrices containing up to 3,000× the concentration of interfering ions. Finally, Cr(III) removal was synergized to 100% adsorption at interfering ions concentrations up to 330× of the analyte, which were suppressed at higher interference concentrations. Considering such performance, the amino modified biochar achieved selective removal for both forms of chromium, showing great potential for utilization in complex chromium pollution sources.