Biosorption of nickel and copper onto treated alga (Undaria pinnatifida): application of isotherm and kinetic models

Removal of vanadium(V) ions from acidic water using reusable manganese oxide sorbents

Manganese oxide (MnOx) was studied for its ability to adsorb vanadium (V) ions for applications in acidic water treatment. Three MnOx types: naturally-occurring (NatMnO), commercially-derived (ComMnO), and laboratory synthesised (SynMnO) were examined in batch systems under varying pH, adsorbent dosage, ionic strength, and contact time. The greatest V sorption occurred at acidic pH, following the order: NatMnO > SynMnO > ComMnO, with maximum adsorption capacities of 54.0, 26.0, and 10.4 mg/g, respectively (at pH 3.0, mass/volume ratio of 2 g/L, concentration of 100 mg/L, 24 hours). Adsorption equilibrium data best fit the Freundlich isotherm, indicating multilayer adsorption, while kinetic data followed a two-constant rate model, suggesting both physical and chemical sorption. Solution pH was found to have a significant impact, with V removal by MnOx most effective at low pH, likely due to the negative zeta potential of the MnOx under such conditions. MnOx reusability was investigated using repeated sorption and desorption experiments with 0.1 M HCl, 0.1 M NaOH, and deionised water to regenerate the MnOx. The regenerated MnOx exhibited similar or enhanced ability to sorb V ions from solution. Overall, these results confirm the unique ability of MnOx as a reusable sorbent for V removal from acidic water, while also enhancing our mechanistic understanding of the removal process. This finding supports the development of sustainable solutions for acidic water treatment, contributing to efforts to address this critical environmental challenge.

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.

Effect and mechanism of coexistence of microplastics on arsenate adsorption capacity in water

Arsenic pollution control technology in water was important to ensure environmental health and quality safety of agricultural products. Therefore, the adsorption performance of three adsorbents for chitosan, sepiolite, and Zeolitic Imidazolate Framework-8 (ZIF-8) were investigated in arsenate contaminated water. The results revealed that the adsorption capacity of ZIF-8 was higher than that of chitosan and sepiolite. The analysis of adsorption isotherm models showed that the behavior of ZIF-8 was more consistent with the Langmuir model. Furthermore, the adsorption mechanisms of three adsorbents for arsenate were investigated by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The analysis of FTIR showed that ZIF-8 maintained the stability of the interaction with arsenate by forming As-O chemical bonds. However, the effect of chitosan and sepiolite with arsenate was mainly physical adsorption. The analysis of XPS showed that the absorption of ZIF-8 with arsenate involved metal sites and nitrogen through the characteristic peak and the change of the binding energy. Furthermore, the impact of microplastics as a widespread coexistence pollutant in the water on adsorbent performance was investigated. The results indicated that the adsorption capacity of ZIF-8 was almost not affected by microplastics. The maximum adsorption amount of arsenate was changed from 73.45 mg/g to 81.89 mg/g. However, the maximum adsorption amount of chitosan and sepiolite decreased by 31.4 % and 11.6 %, respectively. The analysis of FTIR and XPS revealed that ZIF-8 enhances arsenate adsorption by forming N-O-As bonds in the presence of microplastics. This study provides scientific evidence for the management of arsenate pollution in water bodies, especially in complex water bodies containing microplastics.

Temporal and Within-Sporophyte Variations in Triphenyltin Chloride (TPTCL) and Its Degradation Products in Cultivated Undaria pinnatifida

Undaria pinnatifida can effectively deal with organotin pollution through its excellent accumulation and degradation capabilities found under laboratory conditions. However, nothing is known regarding its accumulation, degradation performance, and related impact factors in the wild farming area. In this study, we monitored triphenyltin chloride (TPTCL) contents and degradation products in different algal parts (blades, stipes, sporophylls, and holdfasts) of cultivated U. pinnatifida from December 2018 to May 2019. Our results showed that sporophytes had an accumulation and degradation capacity for TPTCL. The TPTCL contents and degradation products varied with the algal growth stages and algal parts. TPTCL accumulated in the blades at the growth stage and the blades, stipes, sporophylls, and holdfasts at the mature stage. The TPTCL content among algal parts was blades (74.92 ± 2.52 μg kg-1) > holdfasts (62.59 ± 1.42 μg kg-1) > sporophylls (47.24 ± 1.41 μg kg-1) > stipes (35.53 ± 0.55 μg kg-1). The primary degradation product DPTCL accumulated only in the blades at any stage, with a concentration of 69.30 ± 3.89 μg kg-1. The secondary degradation product MPTCL accumulated in the blades at the growth stage and in the blades, stipe, and sporophyll at the mature stage. The MPTCL content among algal parts was blades (52.80 ± 3.48 μg kg-1) > sporophylls (31.08 ± 1.53 μg kg-1) > stipes (20.44 ± 0.85 μg kg-1). The accumulation pattern of TPTCL and its degradation products seems closely related to nutrient allocation in U. pinnatifida. These results provide the basis for applying cultivated U. pinnatifida in the bioremediation of organotin pollution and the food safety evaluation of edible algae.

Cascading effects of trace metals enrichment on phytoplankton communities of the River Ganga in South Asia

Globally freshwater ecosystems and associated biota including phytoplankton communities are at extreme risk from trace metal pollution originating from geogenic as well as from anthropogenic sources such as release of untreated industrial effluents. In the present study influence of iron- and arsenic-enrichments on structure and metabolism of phytoplankton communities of River Ganga, one of the largest rivers of South Asia, was assessed under laboratory-based microcosm experiments. Surface water samples were collected and subsequently enriched with higher than recommended concentrations of iron (10 mg/L) and arsenic (10 μg/L). The set-up comprised of nine containers of 25 L volume with three containers each for iron- and arsenic-enrichment and was maintained for 30 days. Trace metal enrichment rapidly changed the phytoplankton community structure and chemistry of nutrients uptake. Iron-enrichment prompted diatom blooms comprising of Thalassiosira, succeeded by green algae Coelastrum. Arsenic-enrichment maintained cyanobacteria for longer time-spans compared to the control and iron-enriched containers but significantly lesser abundance of diatoms. Variations in community composition was also reflected in nutrient uptake rates with silicate release in the arsenic-enriched containers at the end of the experiment. Changes in macronutrient dynamics also altered genus growth rates wherein both iron- and arsenic appeared to lower the death rate of Thalassosira but stimulated growth of other genera including Skeletonema and Pandorina. Iron appeared to influence lesser number of genera compared to arsenic which altered growth rates of both diatoms and green algae. This consequently influenced the gross primary productivity values which lowered both in the iron- and arsenic-enriched containers compared to the control owing to decrease in phytoplankton diversity. Iron appeared to drive phytoplankton communities toward a less general and more specialized composition with high abundance of selective species comprising of small diatoms such as Thalassiosira, whereas arsenic appears to select for green algal enrichment in freshwater ecosystems.

Green synthesis and characterization of iron oxide nanoparticles for the removal of heavy metals (Cd2+ and Ni2+) from aqueous solutions with Antimicrobial Investigation

Clove and green Coffee (g-Coffee) extracts were used to synthesize green iron oxide nanoparticles, which were then used to sorb Cd²⁺ and Ni²⁺ ions out of an aqueous solution. Investigations with x-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and desorption (BET), Zeta potential, and scanning electron microscopy were performed to know and understand more about the chemical structure and surface morphology of the produced iron oxide nanoparticles. The characterization revealed that the main component of iron nanoparticles was magnetite when the Clove extract was used as a reducing agent for Fe³⁺, but both magnetite and hematite were included when the g-Coffee extract was used. Sorption capacity for metal ions was studied as a function of sorbent dosage, metal ion concentration, and sorption period. The maximum Cd²⁺ adsorption capacity was 78 and 74 mg/g, while that of Ni²⁺ was 64.8 and 80 mg/g for iron nanoparticles prepared using Clove and g-Coffee, respectively. Different isotherm and kinetic adsorption models were used to fit experimental adsorption data. Adsorption of Cd²⁺ and Ni²⁺ on the iron oxide surface was found to be heterogeneous, and the mechanism of chemisorption is involved in the stage of determining the rate. The correlation coefficient R² and error functions like RMSE, MES and MAE were used to evaluate the best fit models to the experimental adsorption data. The adsorption mechanism was explored using FTIR analysis. Antimicrobial study showed broad spectrum antibacterial activity of the tested nanomaterials against both Gram positive (S. aureus) (25923) and Gram negative (E. coli) (25913) bacteria with increased activity against Gram positive bacteria than Gram negative one and more activity for Green iron oxide nanoparticles prepared from Clove than g-Coffee one.

Effects of Lead and Zinc Exposure on Uptake and Exudation Levels, Chlorophyll-a, and Phycobiliproteins in Sarcodia suiae

The present study aimed to determine the changes in the biosorption, bioaccumulation, chlorophyll-a (chl-a), phycobiliproteins, and exudation in the red seaweed Sarcodia suiae exposed to lead and zinc. The seaweed was exposed to ambient lead and zinc environments for 5 days before being transferred to fresh seawater, and the changes in biodesorption, biodecumulation, chl-a, and phycobiliprotein levels in S. suiae were investigated. Lead and zinc biosorption and bioaccumulation in the seaweed increased with the increase in the lead and zinc concentrations and exposure times. Meanwhile, the biosorption and bioaccumulation of zinc in the seaweed following exposure to zinc were significantly higher (p < 0.05) than the biosorption and bioaccumulation of lead in the seaweed following exposure to lead with the same concentration at each exposure time. The chl-a, phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC) contents in the seaweed significantly decreased with the increase in the lead and zinc concentrations and exposure times. The chl-a, PE, PC, and APC contents in S. suiae, which was exposed to 5 Pb2+ mg/L for 5 days, were significantly higher (p < 0.05) than those in the seaweed exposed to zinc at the same concentration and for the same exposure times. In the lead and zinc exudation tests, the highest biodesorption and biodecumulation were observed on the 1st day of exudation after the seaweed was transferred to fresh seawater. The residual percentages of the lead and zinc in the seaweed cells were 15.86% and 73.08% after 5 days of exudation, respectively. The biodesorption rate and biodecumulation rate of the seaweed exposed to lead were higher than those of the seaweed exposed to zinc. However, the effect of lead on chl-a and phycobiliproteins was greater than that of zinc. This might be the result of lead not being a necessary metal for these algae, whereas zinc is.

Recent advancements in cadmium-microbe interactive relations and their application for environmental remediation: a mechanistic overview

The toxic and persistent nature of cadmium (Cd) in the environment has become a matter of concern with its drastic increase in the concentrations over past few decades. Among the various techniques, the microbial remediation has been accepted as an effective decontamination tool for environmental applications, which is sustainable over a period of time. The Cd decontamination potential of the microbes depends on various internal and external factors that play a crucial role in selection of the microbes for application in a particular environment. Thus, it is important to understand the role of these factors for optimal application of the microbes. This study provides an insight into the mechanisms involved between the microbes and the environmental Cd. The study also briefly reviews the mathematical models that have been used to predict the remediation potential of the microbes and the kinetics involved during the process. A critical analysis of the recent advancements in the techniques for use of bacteria, fungi, and algal cells to remove Cd has been also presented in the manuscript.

Adsorption of heavy metals from the aqueous solution using activated biomass from Ulva flexuosa

The removal of various highly toxic heavy metals from wastewater environment is an important task to improve environment. The biosorption potential of cadmium, cobalt and zinc was evaluated using Ulva flexuosa biomass. The impacts of adsorbent dosage, pH of the medium, contact time, and agitation speed were analyzed. The maximum biosorption potential was reached at pH 4.0, 0.4 g initial biosorbent dosage, contact time 40 min and 30 mg/L initial metal concentration for cadmium, while the other factors were similar to zinc, except 35 min contact time (p < 0.01). The optimum absorption was pH 4, 0.6% adsorbent dosage, after 30 min contact time with the heavy metals and 40 mg/L cobalt concentration. Heavy metal removal efficiency was 94.8 ± 3.3%, 87.5 ± 2.3%, and 90.8 ± 1.4%, for cadmium, cobalt, and zinc, respectively (p < 0.01). The Langmuir constant (R²) was 0.980 for cadmium, 0.838 for cobalt and it was 0.718 for zinc. The present results revealed that the selected acid modified biomass was highly suitable for the adsorption of metal ions such as, Cd²⁺, Co²⁺ and Zn²⁺. The present work revealed the potential application of algal biomass for the removal of various heavy metals from the environment.

Differences in bioaccumulation of Ni and Zn by microalgae in the presence of fulvic acid

In the presence of dissolved organic matter, the mechanism of algal bioaccumulation of different metals is complex, and its significance goes far beyond the alga-metal binary system. In the presence of 10 and 20 mg L^-1 fulvic acid (FA), the maximum tolerance concentrations of Chlorella pyrenoidosa to Ni were 0.25 and 0.26 mmol L^-1, and to Zn were 0.62 and 0.68 mmol L^-1, respectively. Within the maximum tolerance concentration ranges, the bioaccumulation behaviors of Ni and Zn were systematically compared in the presence of FA. The presence of FA shortened the adsorption equilibrium time and decreased the maximum bioaccumulation capacity of Ni and Zn. The bioaccumulation mechanism of Ni by C. pyrenoidosa was more inclined to monolayer adsorption, while the bioaccumulation mechanism of Zn was more inclined to multilayer adsorption. More details were revealed after the bioaccumulated metals were separated into adsorption and internalization states by 0.01 M EDTA elution. The presence of FA decreased more adsorbed Zn than the adsorbed Ni, due to the different competitive roles of FA in the ternary system of Ni and Zn, but the presence of FA increased the internalized Ni might due to the stronger complexation of Ni-FA. This research indicated that algae had unique bioaccumulation mechanisms for different metals in the presence of FA, which is of great significance to accurately evaluate the ecological risk posed by heavy metals.

Carnauba (Copernicia prunifera) palm tree biomass as adsorbent for Pb(II) and Cd(II) from water medium

Plant-based biomass (CFB (carnauba fruit biomass)) obtained from the fruit exocarp of the species Copernicia prunifera (Mill.) H.E. Moore (carnauba) was evaluated for its viability as an adsorbent of potentially toxic metals in aqueous medium. The CFB was characterized by powder X-ray spectroscopy (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and zeta potential to investigate the morphology of the biosorbent and its interaction with water soluble metal ions of Pb and Cd. The biomass presents an amorphous structure, with negative zeta potential (- 2.59 mV), and the presence of functional groups such as O-H, C-O-C, C-H, and C=O. The removal potential of Pb(II) and Cd(II) was performed in a batch system, and monoelement solutions were tested to assess the effects of adsorbent dose and initial metal ion concentration, pH at the point of zero charge (pH_PZC), sorption kinetics, and adsorption capacity. The most appropriate adsorbent concentration was 5 g/L, and sorption studies were carried out at pH 5.0 (pH_PZC = 4.68), in which the surface of the adsorbent shows negative charges and favors the adsorption of metal ions. Kinetic studies showed that the pseudo-second order model best fit the experimental data, and equilibrium was reached at 120 min of contact time. The experimental sorption capacity (SC_exp) for Pb and Cd was around 28 and 34 mg/g, respectively, and six different non-linear isotherm models were used to describe the sorption phenomena, among them, four with 2 parameters, i.e., Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (DR), respectively, and two with 3 parameters, namely, SIPS and Hill. The non-linear Temkin and Freundlich isotherm models best fit the experimental data for Pb(II) and Cd(II), respectively. According to the Langmuir model, Q_max was 26 mg/g and 58 mg/g for Pb(II) and Cd(II), respectively, indicating the efficiency of CFB as a new alternative to conventional methods for the removal of potentially toxic metals from aqueous medium.

Evaluation of CNT-COOH/MnO2/Fe3O4 nanocomposite for ibuprofen and paracetamol removal from aqueous solutions

The nanocomposite CNT-COOH/MnO₂/Fe₃O₄ was synthesized and characterized by different techniques, namely X-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller analysis, magnetic measurement, point of zero charge and hydrophobicity index. Analyzes revealed the groups -COOH, MnO₂ and Fe₃O₄ attached to the carbon nanotubes, the acidic character of the obtained nanocomposite and its stability. The surface area for the obtained nanocomposite was 114.2 m² g^-1. The prepared nanocomposite was used for adsorption of ibuprofen and paracetamol from aqueous solution. Isotherm, kinetic and thermodynamic parameters were determined for predicting the ibuprofen and paracetamol adsorption on synthetized nanocomposite. The equilibrium data obtained from adsorption were well represented by Langmuir model and kinetics data were well fitted by the pseudo-second order model. The maximum adsorption capacity obtained for ibuprofen and paracetamol was 103.093 mg g^-1, 80.645 mg g^-1 respectively. The thermodynamic analysis showed that the adsorption process for both pollutants was spontaneous and endothermic. The synthetized nanocomposite can be a suitable new absorbent for ibuprofen and paracetamol removal from aqueous solutions due to its high adsorbing capacity and it can be separated by an external magnetic field.

Isolation and Characterization of Magnetic Oil Palm Empty Fruits Bunch Cellulose Nanofiber Composite as a Bio-Sorbent for Cu(II) and Cr(VI) Removal

In the present study, magnetic oil palm empty fruits bunch cellulose nanofiber (M-OPEFB-CNF) composite was isolated by sol-gel method using cellulose nanofiber (CNF) obtained from oil palm empty fruits bunch (OPEFB) and Fe₃O₄ as magnetite. Several analytical methods were utilized to characterize the mechanical, chemical, thermal, and morphological properties of the isolated CNF and M-OPEFB-CNF. Subsequently, the isolated M-OPEFB-CNF composite was utilized for the adsorption of Cr(VI) and Cu(II) from aqueous solution with varying parameters, such as pH, adsorbent doses, treatment time, and temperature. Results showed that the M-OPEFB-CNF as an effective bio-sorbent for the removal of Cu(II) and Cr(VI) from aqueous solution. The adsorption isotherm modeling revealed that the Freundlich equation better describes the adsorption of Cu(II) and Cr(VI) on M-OPEFB-CNF composite. The kinetics studies revealed the pseudo-second-order kinetics model was a better-described kinetics model for the removal of Cu(II) and Cr(VI) using M-OPEFB-CNF composite as bio-sorbent. The findings of the present study showed that the M-OPEFB-CNF composite has the potential to be utilized as a bio-sorbent for heavy metals removal.

Two-step adsorption model for Pb ion accumulation at the algae-water interface in the presence of fulvic acid

The effects of fulvic acid (FA) on heavy metal bioaccumulation by algae have been extensively studied, but the quantitative description on its adsorption behavior is not elaborately illustrated. In the study, the two-step adsorption model is firstly proposed to describe the adsorption of Pb by algae in the presence of FA (R² > 0.984), which is characterized with two-plateaus in the biosorption curves. The first plateau in the curve represents a monolayer adsorption process of free Pb²⁺; while the second reveals a multilayer adsorption process of Pb-FA binding to those adsorbed Pb by algae, and the bonding material was called as ternary complex of algae-Pb-(FA-Pb). The formation of the ternary complex caused a sharp increase of the amount of adsorbed Pb by algae which was measured by an atomic absorption spectrophotometry, and a decrease of the toxicity of Pb to algae verified with SEM and TEM images. The ternary phase diagram showed FA could participate in the formation of ternary complexes at very low concentration. The study is important for a comprehensive understanding of the metal-microalgae interaction and its biogeochemical cycle in surface waters.

Removal of tetracycline with aluminum boride carbide and boehmite particles decorated biochar derived from algae

For the first time, using aluminum-boron electrodes in the electrocoagulation cell for harvesting the cultivated Chlorella microalgae and then performing a hydrothermal process of producing biofuel, mesoporous biochar was produced with an average pore diameter of 11.62 nm, a high specific surface area of 126.4 m²/g and a total pore volume of 0.55 cm³/g. Based on the chemical characterization, aluminum boride carbide (Al₃B₄₈C₂) and boehmite [Al₂(OOH)₂] were identified in the biochar composition so that 7.17 wt% Al and 16.67 wt% B were measured on the biochar surface by EDS analysis. As the by-product of hydrothermal converting microalgae Chlorella into biofuel, the residual biochar was innovatively used to separate tetracycline from aqueous solutions. The nonlinear form of the Freundlich model fitted theadsorption equilibrium data well with the least error function value explained by the intraparticle diffusion model. The maximum adsorption capacity of 25.94 mg/g was obtained through endothermic physical adsorption.

Biosorption of Cr(VI) by Halomonas sp. DK4, a halotolerant bacterium isolated from chrome electroplating sludge

This study evaluated Cr(VI) biosorption by a halotolerant gram-negative bacterium Halomonas sp. DK4 isolated from chrome electroplating sludge. The bacterium could withstand high concentrations of Cr(VI) exhibiting a minimal inhibitory concentration (MIC) of 250 mg/L. Plackett-Burman design confirmed glucose, KH₂PO₄, NaCl, inoculum size, and initial Cr(VI) concentration as significant variables influencing the Cr(VI) removal ability of the bacterium. The suspended culture of Halomonas sp. DK4 was able to remove 81% (100 mg/L) of Cr(VI) in optimized MSM medium from aqueous solutions within 48 h. The bacterium also removed 59% Cr(VI) in the presence of 15% NaCl concentration within 72 h. The main mechanism involved in Cr(VI) removal by Halomonas sp. DK4 was determined to be biosorption which was best explained using the Langmuir isotherm model, wherein the maximum adsorption of 150.7 mg/g was observed under equilibrium conditions. Kinetic studies reveal that chemisorption of Cr(VI) by Halomonas sp. DK4 was a rate-limiting process which followed pseudo-second-order kinetics (R² = 0.99). Bacterial biomass exhibited maximum adsorption of 70.3% Cr(VI) at an initial concentration of 100 mg/L under optimal conditions. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the presence of hydroxyl, carboxyl, amide, and phosphate groups on the bacterial surface which may be involved in Cr(VI) adsorption. Scanning electron microscopy coupled energy dispersive X-ray (SEM-EDX) analysis revealed morphological changes in the bacterial cell and accumulation of Cr(VI) on the cell surface. These results suggest the potential application of Halomonas sp. DK4 in the removal of Cr(VI) from saline chromium-containing industrial wastewaters.

Experimental and Modeling Process Optimization of Lead Adsorption on Magnetite Nanoparticles via Isothermal, Kinetics, and Thermodynamic Studies

Lead has been a burgeoning environmental pollutant used in industrial sectors. Therefore, to emphasize the reactivity of lead toward magnetite nanoparticles for their removal, the present study was framed to analyze mechanisms involved in adsorption of lead. Batch adsorption studies have shown remarkable adsorption efficiency with only a 10 mg adsorbent dose used to extract 99% Pb2+ (110 mg L-1) within 40 min at pH 6. Isothermal, kinetic, and thermodynamic studies were conducted, and the equilibrium data was best fit for the Langmuir isotherm model with a maximum of 41.66 mg g-1 adsorption capacity at 328 K. Moreover, a pseudo second order was followed for adsorption kinetics and thermodynamic parameters such as Gibbs energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) that were calculated and revealed the spontaneous, feasible, and exothermic nature of the process.

Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit

Biosorption of Cr(VI) on sulfuric and phosphoric acid-treated Datura stramonium fruit was investigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temperature, and pH value were optimized. Both linear and non-linear regression analysis of isotherm data suggest that Langmuir isotherm model mimics the behavior of Cr(VI) ion biosorption onto Datura stramonium fruit biosorbent. The maximum Cr(VI) ions adsorption capacity of 138.074 mg/g at pH 2 is achieved with phosphoric acid treated Datura stramonium (PDSF). The kinetics of adsorption process is well described by pseudo-second-order model with high R² and low χ² value. The estimated activation energy of < 8 kJ/mol obtained for both raw and chemically modified adsorbents suggests that the adsorption occurs mainly via physisorption. Besides, thermodynamic results reveal that biosorption of Cr(VI) on both treated and untreated Datura stramonium was endothermic, spontaneous, and randomness in nature.

Removal of heavy metals from water sources in the developing world using low-cost materials: A review

Heavy metal contamination is a growing concern in the developing world. Inadequate water and wastewater treatment, coupled with increased industrial activity, have led to increased heavy metal contamination in rivers, lakes, and other water sources in developing countries. However, common methods for removing heavy metals from water sources, including membrane filtration, activated carbon adsorption, and electrocoagulation, are not feasible for developing countries. As a result, a significant amount of research has been conducted on low-cost adsorbents to evaluate their ability to remove heavy metals. In this review article, we summarize the current state of research on the removal of heavy metals with an emphasis on low-cost adsorbents that are feasible in the context of the developing world. This review evaluates the use of adsorbents from four major categories: agricultural waste; naturally-occurring soil and mineral deposits; aquatic and terrestrial biomass; and other locally-available waste materials. Along with a summary of the use of these adsorbents in the removal of heavy metals, this article provides a summary of the influence of various water-quality parameters on heavy metals and these adsorbents. The proposed adsorption mechanisms for heavy metal removal are also discussed.

Biochar synthesized via pyrolysis of Broussonetia papyrifera leaves: mechanisms and potential applications for phosphate removal

In this study, Broussonetia papyrifera leaves collected from land near a restored manganese mine in the Hunan Province of China were converted into biochar under high-temperature anaerobic conditions, regeneration and utilization of agricultural and forest waste, and applied to the prevention of eutrophication. The physicochemical properties of the B. papyrifera biochar were characterized using Micromeritics 3Flex analyzer, scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR), thermogravimetric analyzer (TGA), X-ray photoelectron spectrometer (XPS), zeta potential meter (zeta), and X-ray diffraction (XRD). The effects of pH, ionic strength, coexisting ions, time, initial concentration, and temperature on the decontamination process of phosphate in water were studied. The results indicated that adsorption was enhanced under alkaline conditions. The pseudo-second-order model of adsorption kinetics was applied to illustrate the adsorption processes. The chemical adsorption reaction was the main rate-limiting step in the adsorption process. Isotherm experimental data were best fitted by the Freundlich model at 25 °C and by the Langmuir model at 35 °C. The phosphate combined with B. papyrifera biochar mainly in the forms of exchangeable phosphorus (Ex-P), Al-bound phosphorus (Al-P), and Fe-bound phosphorus (Fe-P). These results indicate that B. papyrifera biochar is a suitable candidate for the treatment of a eutrophic body of water.

Amendment of Caulerpa sertularioides marine alga with sulfur-containing materials to accelerate Cu removal from aqueous media

This study reports a new approach of alga amendment in a live mode. The Caulerpa sertularioides alga was modified with sulfur-containing materials of methionine (C₅H₁₁NO₂S) and sodium sulfate (Na₂SO₄) to more concentrate the sulfur content of the yielded biomass (adsorbent). The simple and amended C. sertularioides alga was fully characterized with FTIR, SEM, EDX, BET, BJH, and pH_zpc techniques. The copper adsorption from aqueous media was done by three adsorbents of C. sertularioides-simple (CSS), C. sertularioides-Na₂SO₄ (CSN), and C. sertularioides-C₅H₁₁NO₂S (CSC). The parameters of pH (2-6), adsorbent dosage (2-10 g/L), and contact time (3-80 min) were optimized at 5, 5 g/L, and 60 min, respectively. According to Langmuir isotherm (the best-fitted model), the maximum adsorption capacity of CSN (98.04 mg/g) was obtained 2.4 times higher than CSC (40.73 mg/g) and 9.5 times higher than CSS (10.29 mg/g). The Cu adsorption process by the adsorbents was best-fitted pseudo-second-order kinetic model. The CSN, CSC, and CSS biomasses were successfully reused 5, 4, and 4 times, respectively. The thermodynamic study revealed that the copper adsorption process by CSN is exothermic and non-spontaneous. Finally, the suitability of adsorbents prepared from algae was tested by cleaning a simulated wastewater.

Graphene oxide nanocomposite hydrogel based on poly(acrylic acid) grafted onto salep: an adsorbent for the removal of noxious dyes from water

In this study, a graphene oxide nanocomposite hydrogel (GONH) based on poly(acrylic acid) grafted onto a natural salep polysaccharide was synthesized and investigated as an adsorbent for the removal of cationic dye from aqueous solution.

Potential of Zeolite and Algae in Biomass Immobilization

The interest in utilizing algae for wastewater treatment has been increased due to many advantages. Algae-wastewater treatment system offers a cost-efficient and environmentally friendly alternative to conventional treatment processes such as electrocoagulation and flocculation. In this biosystem, algae can assimilate nutrients in the wastewater for their growth and simultaneously capture the carbon dioxide from the atmosphere during photosynthesis resulting in a decrease in the greenhouse gaseousness. Furthermore, the algal biomass obtained from the treatment process could be further converted to produce high value-added products. However, the recovery of free suspended algae from the treated effluent is one of the most important challenges during the treatment process as the current methods such as centrifugation and filtration are faced with the high cost. Immobilization of algae is a suitable approach to overcome the harvesting issue. However, there are some drawbacks with the common immobilization carriers such as alginate and polyacrylamide related to low stability and toxicity, respectively. Hence, it is necessary to apply a new carrier without the mentioned problems. One of the carriers that can be a suitable candidate for the immobilization is zeolite. To date, various types of zeolite have been used for the immobilization of cells of bacteria and yeast. If there is any possibility to apply them for the immobilization of algae, it needs to be considered in further studies. This article reviews cell immobilization technique, biomass immobilization onto zeolites, and algal immobilization with their applications. Furthermore, the potential application of zeolite as an ideal carrier for algal immobilization has been discussed.

Effective adsorption of nickel (II) with Ulva lactuca dried biomass: isotherms, kinetics and mechanisms

This study aimed to evaluate the Ni²⁺ ions adsorption capability of Ulva lactuca. The isotherms, kinetics and mechanisms for the adsorption of Ni²⁺ from aqueous solution by Ulva lactuca were also investigated. Influencing factors including initial pH, initial Ni²⁺ concentration, biomass, contact time were examined. The results indicate that the maximum Ni²⁺ adsorption capacity of 38.28 mg/g was obtained at pH 5, initial Ni²⁺ concentration 250 mg/L, biomass dosage 0.5 g/L and contact time 30 min. The adsorption can be well fitted with Langmuir isotherm, and the kinetics were well described by the pseudo-second-order model. The parameters of thermodynamics verified that Ni²⁺ adsorption on Ulva lactuca was a spontaneous and endothermic process. Analyses of FT-IR, SEM-EDS and XPS indicate that carboxyl and hydroxyl groups on the surface of biomass are involved in Ni²⁺ adsorption. The dried biomass of Ulva lactuca can be a cost-effective and eco-friendly adsorbent for the removal of Ni²⁺ from wastewater.

Nickel accumulation by the green algae-like Euglena gracilis

Nickel accumulation and nickel effects on cellular growth, respiration, photosynthesis, ascorbate peroxidase (APX) activity, and levels of thiols, histidine and phosphate-molecules were determined in Euglena gracilis. Cells incubated with 0.5-1mM NiCl₂ showed impairment of O₂ consumption, photosynthesis, Chl a+b content and APX activity whereas cellular integrity and viability were unaltered. Nickel accumulation was depressed by Mg²⁺ and Cu²⁺, while Ca²⁺, Co²⁺, Mn²⁺ and Zn²⁺ were innocuous. The growth half-inhibitory concentrations for Ni²⁺ in the culture medium supplemented with 2 or 0.2mM Mg²⁺ were 0.43 or 0.03mM Ni²⁺, respectively. Maximal nickel accumulation (1362mg nickel/Kg DW) was achieved in cells exposed to 1mM Ni²⁺ for 24h in the absence of Mg²⁺ and Cu²⁺; accumulated nickel was partially released after 72h. GSH polymers content increased or remained unchanged in cells exposed to 0.05-1mM Ni²⁺; however, GSH, cysteine, γ-glutamylcysteine, and phosphate-molecules all decreased after 72h. Histidine content increased in cells stressed with 0.05 and 0.5mM Ni²⁺ for 24h but not at longer times. It was concluded that E. gracilis can accumulate high nickel levels depending on the external Mg²⁺ and Cu²⁺ concentrations, in a process in which thiols, histidine and phosphate-molecules have a moderate contribution.

Ni2+ and Co2+ adsorption using Tectona grandis biochar: kinetics, equilibrium and desorption studies

In this research, the potential of a relatively new adsorbent prepared from Tectona grandis leaves by pyrolysis for heavy metal removal from aqueous solution was studied. Adsorption behavior of the pyrolytic biochar was investigated with respect to Ni²⁺ and Co²⁺ removal with its affinity examined through batch studies and the mechanism elucidated using different empirical isotherm and kinetic models. A significantly higher efficiency of 92.46% and 91.21% was achieved at a weakly acidic pH of 6 and 5, dose of 3 g L^-1 and 2 g L^-1 for Ni²⁺ and Co²⁺ removal, respectively. Pseudo-second-order kinetics and Langmuir isotherm model best represented the adsorption process for both Ni²⁺ and Co²⁺. Thermodynamic analysis proved the endothermic and spontaneous nature of the process. Desorption studies revealed hydrochloric acid to have a high potential toward eluting the adsorbed metal ions. The well-organized microporous structure, the significant surface area value along with the presence of relative functional groups together with its high adsorption capacity for Ni²⁺ and Co²⁺, revealed the significant adsorptive potential of biochar of teak leaves powder for metal ion removal.

Efficient Removal of Tetracycline from Aqueous Media with a Fe₃O₄ Nanoparticles@graphene Oxide Nanosheets Assembly

A readily separated composite was prepared via direct assembly of Fe₃O4 magnetic nanoparticles onto the surface of graphene oxide (GO) (labeled as Fe₃O₄@GO) and used as an adsorbent for the removal of tetracycline (TC) from wastewater. The effects of external environmental conditions, such as pH, ionic strength, humic acid (HA), TC concentration, and temperature, on the adsorption process were studied. The adsorption data were analyzed by kinetics and isothermal models. The results show that the Fe₃O₄@GO composite has excellent sorptive properties and can efficiently remove TC. At low pH, the adsorption capacity of Fe₃O₄@GO toward TC decreases slowly with increasing pH value, while the adsorption capacity decreases rapidly at higher pH values. The ionic strength has insignificant effect on TC adsorption. The presence of HA affects the affinity of Fe₃O₄@GO to TC. The pseudo-second-order kinetics model and Langmuir model fit the adsorption data well. When the initial concentration of TC is 100 mg/L, a slow adsorption process dominates. Film diffusion is the rate limiting step of the adsorption. Importantly, Fe₃O₄@GO has good regeneration performance. The above results are of great significance to promote the application of Fe₃O₄@GO in the treatment of antibiotic wastewater.

Ethylenediamine grafted to graphene oxide@Fe3O4 for chromium(VI) decontamination: Performance, modelling, and fractional factorial design

A method for grafting ethylenediamine to a magnetic graphene oxide composite (EDA-GO@Fe₃O₄) was developed for Cr(VI) decontamination. The physicochemical properties of EDA-GO@Fe₃O₄ were characterized using HRTEM, EDS, FT-IR, TG-DSC, and XPS. The effects of pH, sorbent dose, foreign anions, time, Cr(VI) concentration, and temperature on decontamination process were studied. The solution pH can largely affect the decontamination process. The pseudo-second-order model is suitable for being applied to fit the adsorption processes of Cr(VI) with GO@Fe₃O₄ and EDA-GO@Fe₃O₄. The intra-particle diffusion is not the rate-controlling step. Isotherm experimental data can be described using the Freundlich model. The effects of multiple factors on the Cr(VI) decontamination was investigated by a 2⁵⁻¹ fractional factorial design (FFD). The adsorption process can significantly be affected by the main effects of A (pH), B (Cr(VI) concentration), and E (Adsorbent dose). The combined factors of AB (pH × Cr(VI) concentration), AE (pH × Adsorbent dose), and BC (Cr(VI) concentration × Temperature) had larger effects than other factors on Cr(VI) removal. These results indicated that EDA-GO@Fe₃O₄ is a potential and suitable candidate for treatment of heavy metal wastewater.

Design and function of biomimetic multilayer water purification membranes

Multilayer architectures in water purification membranes enable increased water throughput, high filter efficiency, and high molecular loading capacity. However, the preparation of membranes with well-organized multilayer structures, starting from the nanoscale to maximize filtration efficiency, remains a challenge. We report a complete strategy to fully realize a novel biomaterial-based multilayer nanoporous membrane via the integration of computational simulation and experimental fabrication. Our comparative computational simulations, based on coarse-grained models of protein nanofibrils and mineral plates, reveal that the multilayer structure can only form with weak interactions between nanofibrils and mineral plates. We demonstrate experimentally that silk nanofibril (SNF) and hydroxyapatite (HAP) can be used to fabricate highly ordered multilayer membranes with nanoporous features by combining protein self-assembly and in situ biomineralization. The production is optimized to be a simple and highly repeatable process that does not require sophisticated equipment and is suitable for scaled production of low-cost water purification membranes. These membranes not only show ultrafast water penetration but also exhibit broad utility and high efficiency of removal and even reuse (in some cases) of contaminants, including heavy metal ions, dyes, proteins, and other nanoparticles in water. Our biomimetic design and synthesis of these functional SNF/HAP materials have established a paradigm that could lead to the large-scale, low-cost production of multilayer materials with broad spectrum and efficiency for water purification, with applications in wastewater treatment, biomedicine, food industry, and the life sciences.

Solvent-free synthesis of the cellulose-based hybrid beads for adsorption of lead ions in aqueous solutions

Modified cellulose hybrid beads were synthesised as absorbents for Pb²⁺removal and CaCO₃was utilized to increase pore structure.

Adsorptive removal of nickel(II) ions from aqueous environment: A review

Among various methods adsorption can be efficiently employed for the treatment of heavy metal ions contaminated wastewater. In this context the authors reviewed variety of adsorbents used by various researchers for the removal of nickel(II) ions from aqueous environment. One of the objectives of this review article is to assemble the scattered available enlightenment on a wide range of potentially effective adsorbents for nickel(II) ions removal. This work critically assessed existing knowledge and research on the uptake of nickel by various adsorbents such as activated carbon, non-conventional low-cost materials, nanomaterials, composites and nanocomposites. The system's performance is evaluated with respect to the overall metal removal and the adsorption capacity. In addition, the equilibrium adsorption isotherms, kinetics and thermodynamics data as well as various optimal experimental conditions (solution pH, equilibrium contact time and dosage of adsorbent) of different adsorbents towards Ni(II) ions were also analyzed. It is evident from a literature survey of more than 190 published articles that agricultural solid waste materials, natural materials and biosorbents have demonstrated outstanding adsorption capabilities for Ni(II) ions.

Modeling and optimization of Hg2+ ion biosorption by live yeast Yarrowia lipolytica 70562 from aqueous solutions under artificial neural network-genetic algorithm and response surface methodology: kinetic and equilibrium study

This study was devoted to the investigation of Hg²⁺ ion biosorption by a live yeast organism, namely, Yarrowia lipolytica 70562 (supplied commercially), which was sufficiently identified and studied by SEM-EDS and FT-IR methods.

Kinetics, equilibrium isotherm and neural network modeling studies for the sorption of hexavalent chromium from aqueous solution by quartz/feldspar/wollastonite

A three layer feed forward artificial neural network (ANN) with back propagation training algorithm was developed to model the adsorption process of Cr(vi) in aqueous solution using riverbed sand containing quartz/feldspar/wollastonite (QFW) as adsorbent.