Easy separable, floatable, and recyclable magnetic-biochar/alginate bead as super-adsorbent for adsorbing copper ions in water media

Sustainable adsorbent design: ZnSA@PEG from agricultural waste for environmental remediation

Antibiotic drugs have the potential to induce persistent impairment to the ecosystem within soil and natural water bodies. To address this issue, this study utilized ofloxacin (OFL) as the research subject; ZnSA@PEG was synthesized employing agricultural waste-derived peanut shell biochar as the primary material, with sodium alginate (SA) serving as the substrate. The biochar was activated using ZnCl2, followed by the incorporation of polyethylene glycol (PEG) into the SA, and subsequently cross-linked with CaCl2. The effect of ZnSA@PEG on OFL removal efficiency was investigated under different influencing conditions. The results showed that ZnSA@PEG had the best removal effect on OFL at pH = 8, with an adsorption amount of 68.57 mg/g (with OFL 50 mg/L, and the ZnSA@PEG was 100 mg), which was 13 times higher than that before unmodified. The adsorption kinetics followed the pseudo-first-order model. The isothermal adsorption data fitted the Langmuir model, with a maximum adsorption capacity of 103.803 mg/g. The adsorption mechanism was primarily attributed to the π-π interactions, hydrogen bonding, and complexation. ZnSA@PEG demonstrated exceptional stability in reusability, which keep the adsorption capacity remained at 39.78 mg/g even after five cycles. In summary, ZnSA@PEG is a highly efficient and reusable adsorbent material with promising applications in antibiotic wastewater.

Bis-Imidazolium-Based Poly(Ionic Liquid)-Functionalized Hydrochar for Efficient Sorption of Methyl Orange and Sodium 2,4-Dichlorophenoxyacetate

Environmentally friendly hydrochar demonstrates excellent performance in the treatment of cationic pollutants, yet its capability to address anions is limited. Cationic imidazolium ionic liquids carry a positive charge, and modification of the surface of hydrochar can increase its positive charge, thereby improving its ability to remove anions. Herein, bis-imidazolium-based poly(ionic liquid)-functionalized hydrochar (BIPIL-HC) was prepared using hydrochar derived from the hydrothermal carbonization of bamboo powder and N,N'-methylene-bis(1-(3-vinylimidazolium)) chloride via free radical polymerization and characterized using different instruments. The behavior of BIPIL-HC in adsorbing methyl orange (MO) and sodium 2,4-dichlorophenoxyacetate (2,4-D Na) was studied by using batch adsorption experiments, including the effects of initial concentration and temperature, solution pH, contact time on adsorption, and regeneration experiments. The adsorption kinetics and isotherms conformed to pseudo-second-order kinetics and Langmuir models. The adsorbing capacity of BIPIL-HC for MO and 2,4-D Na reached 554.91 and 565.50 mg·g-1, respectively. BIPIL-HC is also effective in removing MO and 2,4-D Na under diverse pH values and is highly reusable. Mechanism analysis shows that hydrogen bonding, ion exchange, electrostatic, and π-π interactions promote the adsorption of the two pollutants by BIPIL-HC. Particularly, the imidazolium group of BIPIL-HC is decisive in its capture ability of the two anionic pollutants through anion exchange and electrostatic interaction. These results confirm that the use of ionic liquid functionalization as a method for modifying hydrochar can effectively enhance the treatment capacity of hydrochar for anionic wastewater, and the obtained BIPIL-HC shows promising value in anionic wastewater handling.

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Ultrahigh and rapid removal of Ni2+ using a novel polymer-zeolite-biochar tri-composite through one-pot synthesis route

In this work, a novel adsorbent from alginate, zeolite and biochar has been made through one-pot synthesis route with highly compatible Sodium Dodecyl Sulphate (SDS) modification. This gave ultra-high Ni2+ removal of 1205 mg/g in batch mode while treating almost 200 L of solution in column mode with 1171 mg/g capacity, which are the one of the highest reported values. The Point of Zero Charge (pHzpc) for Ni2+ removal was determined to be 5, with optimal removal efficiency being observed at pH 7, indicating a negative surface charge of the ABPC beads, which aligns with the anionic charge provided by SDS enhancement. Mechanistic studies have been done to show the most prominent mechanisms of metal removal besides demonstrating stability up to 20 cylces with desorption efficiency as high as 97%. The adsorbent is found to be highly cost effective at 1.87USD per kg.

Inkjet-based facile fabrication of a copper ferrocyanide-embedded magnetic alginate microadsorbent for highly enhanced cesium removal

For the first time, simple and facile fabrication of a magnetic alginate microadsorbent via piezoelectric inkjet technology was developed for the selective removal of 137Cs via magnetic separation. Through the ejection of an alginate solution containing potassium ferrocyanide and magnetic nanoparticles (MNPs) into a Cu2+ solution via an inkjet device, the fabrication of a copper ferrocyanide-embedded magnetic alginate microadsorbent (CuFC-MAM) with an average size of 39.38 μm was easily achieved in a one-pot fabrication process; here, the Cu2+ ions acted as both a cross-linker for the gelation of alginate and a Cu source for the in situ synthesis of CuFC with potassium ferrocyanide. The Cs adsorption behavior of CuFC-MAM was effectively fitted by the pseudo-second-order kinetic model and Langmuir isotherm. Owing to the increased specific surface area of CuFC-MAM, its pseudo-second-order rate constant and maximum adsorption capacity were 76.54 and 1.486 times greater than those of CuFC-embedded magnetic alginate macroadsorbents fabricated without inkjet devices. Compared with other Cs adsorbents, CuFC-MAM presented the highest maximum capacity and Kd value; these results were attributed to the high content of CuFC in CuFC-MAM (50.15%). In addition, our CuFC-MAM exhibited an excellent removal efficiency of radioactive Cs, exceeding 99% from seawater.

Magnetic coconut shell biochar/sodium alginate composite aerogel beads for efficient removal of methylene blue from wastewater: Synthesis, characterization, and mechanism

The challenges of recovering powdered biochar and its limited adsorption capacity are major obstacles to the application of agricultural waste in dye adsorption. To address these issues, this work fabricates Fe3O4-modified coconut shells biochar (mCSB)/sodium alginate (SA) aerogel beads using an in-situ crosslinking-gelation method and freeze-drying technology for methylene blue (MB) removal from wastewater. The spherical mCSB/SA aerogel beads with good magnetic properties (12.8 emu·g-1) can be easily separated from aqueous solutions, thereby completely avoiding the hazard of secondary pollution and device obstruction associated with powdered adsorbents. The absorption capability of MB by mCSB/SA aerogel beads was analyzed and optimized at different conditions. Furthermore, the maximum adsorption capacity of mCSB/SA aerogel beads is 625 mg·g-1 for MB, following the Langmuir isotherm model (R2 = 0.9997). Additionally, the adsorption process of MB on mCSB/SA aerogel beads is found to be spontaneous and endothermic, following the pseudo-second-order kinetic (R2 = 0.9991). Encouragingly, the adsorption efficiency of mCSB/SA aerogel beads remains above 95 % even after 5 times of reusability cycles, demonstrating excellent regeneration ability. This work proposes a straightforward and scalable fabrication strategy to convert agricultural waste into efficient adsorbents for wastewater treatment, adhering to the principles of sustainable development.

Eco-Friendly Hydrogel Beads from Seashell Waste for Efficient Removal of Heavy Metals from Water

The objective of this study is to develop a calcium carbonate-based adsorbent derived from Cellana Tramoscrica seashells, incorporated into a sodium alginate matrix (Na-Alg@CTs) to form hydrogel beads, for the efficient removal of Cu (II) and Zn (II) heavy metals from aqueous solutions. XRD, SEM/EDS, and FTIR analysis confirm the successful synthesis and characterization of the fabricated adsorbent. The adsorption study of Cu (II) and Zn (II) onto Na-Alg@CTs hydrogel beads revealed that the Langmuir model was the most suitable for characterizing the adsorption isotherms, suggesting monolayer coverage. Na-Alg@CTs exhibited a maximum Langmuir adsorption capacity of 368.58 mg/g and 1075.67 mg/g for Cu (II) and Zn (II), respectively. Additionally, the kinetics followed the pseudo-second-order model, indicating that the adsorption process is primarily governed by chemisorption. The thermodynamic study suggests that the uptake of metal ions on Na-Alg@CTs hydrogel beads is spontaneous and endothermic. The exceptional adsorption capacity, eco-friendly nature, and low-cost characteristics of Na-Alg@CTs hydrogel beads make them an ideal adsorbent for the removal of Cu (II) and Zn (II) from wastewater.

Construction and characterization of sodium alginate/polyvinyl alcohol double-network hydrogel beads with surfactant-tailored adsorption capabilities for efficient tetracycline hydrochloride removal

The extensive use of tetracycline (TC) for disease control and the residuals in wastewater has resulted in the spread and accumulation of antibiotic resistance genes, posing a severe threat to the human health and environmental safety. To solve this problem, a series of double-network hydrogel beads based on sodium alginate and polyvinyl alcohol were constructed with the introduction of various surfactants to modulate the morphology. The results showed that the introduction of surfactants can modulate the surface morphology and internal structure, which can also regulate the adsorption ability of the hydrogel beads. The SDS-B beads with SDS as surfactant exhibited highest adsorption efficiency for removal of TC with a maximum adsorption capacity up to 121.6 mg/g, which possessed a resistance to various cations and humic acid. The adsorption mechanism revealed that the superior adsorption performance of the hydrogel beads was primarily attributed to hydrogen bonding, electrostatic attraction, and π-π EDA interactions. Adsorption kinetics demonstrated that the pseudo-second-order model fitted the adsorption process well and adsorption isotherm showed the adsorption of TC occurred through both chemical and physical interactions. Moreover, the adsorption efficiency remained approximately 87.5 % after three adsorption-desorption cycles, which may have potential application and practical value in TC adsorption.

Synergy of Magnetic Nanoparticles and Sodium Alginate-Coated Lignin for Effective Pollutant Remediation, Simple Recovery, and Cost-Effective Regeneration

In the pursuit of sustainable materials for environmental remediation, this study presents the development and comprehensive characterization of cobalt ferrite nanoparticles (CFNPs) incorporated in lignocellulosic-derived sodium alginate (CFNPs@LCG-SA) biocomposite beads. These biobased beads exhibit exceptional adsorption capabilities, particularly for methylene blue (MB) dyes, rendering them promising candidates for wastewater treatment. Using a comprehensive range of analytical techniques, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis-derivative thermogravimetry (TGA/DTG), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), etc., we elucidated their structural, physicochemical, and thermal properties. Their multifunctional nature, derived from lignin and sodium alginate components, provides ample active sites for both physical interactions and chemical bonding with contaminants apart from the magnetic character attributed by the CFNPs. With a freeze-drying approach, the optimal adsorption capacity and removal rate of MB reached 97 mg/g and 99%, respectively, and no meaningful decline in their activity was noted even after six cycles. The CFNPs@LCG-SA biocomposite beads emerge as a cost-efficient and sustainable remedy for environmental cleanup, offering valuable perspectives in environmental preservation and advancing green energy technologies.

Valorizing date palm spikelets into activated carbon-derived composite for methyl orange adsorption: advancing circular bioeconomy in wastewater treatment-a comprehensive study on its equilibrium, kinetics, thermodynamics, and mechanisms

Leveraging date palm spikelets (DPS) as a precursor, this study developed a DPS-derived composite (ZnO@DPS-AC) for water treatment, focusing on methyl orange (MO) removal. The composite was synthesized through ZnCl2 activation and pyrolysis at 600 °C. Comprehensive characterization was conducted using TGA, FTIR, XRD, SEM/EDS, and pHPZC. Characterization revealed a highly carbonaceous material (> 74% carbon) with significant porosity and surface functional groups. ZnO@DPS-AC demonstrated rapid MO removal, achieving over 45% reduction within 10 min and up to 99% efficiency under optimized conditions. The Langmuir model-calculated maximum adsorption capacity reached 226.81 mg/g at 20 °C. Adsorption mechanisms involved hydrogen bonding, π-π interactions, and pore filling. The composite showed effectiveness in treating real wastewater and removing other pollutants. This study highlights the potential of agricultural waste valorization in developing efficient, sustainable adsorbents for water remediation, contributing to circular bioeconomy principles.

Preparation of a biochar-lignosulfonate composite material and its adsorption performance for Cu2

Biochar was prepared using peanut shells as raw materials, and then composite amino-functionalized lignosulfonate was used to prepare a biochar/lignosulfonate adsorbent (BC-CLS). The morphology and structure of BC-CLS were characterized using FT-IR, SEM, zeta potential, and XPS. The adsorption performance of BC-CLS was evaluated by batch adsorption experiments and dynamic adsorption experiments (adsorption column flow adsorption). The results showed that BC-CLS adsorbent exhibited significant adsorption performance for Cu2+, including a short equilibrium time (50 min), fast adsorption rate (11 mg g-1 min-1), and high static saturation adsorption capacity (354 mg g-1). Dynamic adsorption experiments indicated that the maximum adsorption capacity of BC-CLS adsorbent was approximately 280 mg g-1, with a removal rate of over 99% after five cycles, meeting the wastewater discharge standard (less than 1 mg L-1). The results demonstrated that the adsorption capacity of BC-CLS adsorbent for Cu2+ was controlled by multiple adsorption mechanisms, including electrostatic attraction, precipitation, and metal ion complexation. Additionally, under pH = 5 conditions, using a 40 mg per L Cu2+ solution, the adsorption performance of BC-CLS adsorbent remained above 60% after five adsorption-desorption experiments, indicating good cycling stability of BC-CLS adsorbent.

A green and economic approach to synthesize magnetic Lagenaria siceraria biochar (γ-Fe2O3-LSB) for methylene blue removal from aqueous solution

In the printing and textile industries, methylene blue (a cationic azo dye) is commonly used. MB is a well-known carcinogen, and another major issue is its high content in industrial discharge. There are numerous removal methodologies that have been employed to remove it from industrial discharge; however, these current modalities have one or more limitations. In this research, a novel magnetized biochar (γ-Fe2O3-LSB) was synthesized using Lagenaria siceraria peels which were further magnetized via the co-precipitation method. The synthesized γ-Fe2O3-LSB was characterized using FTIR, X-ray diffraction, Raman, SEM-EDX, BET, and vibrating sample magnetometry (VSM) for the analysis of magnetic properties. γ-Fe2O3-LSB showed a reversible type IV isotherm, which is a primary characteristic of mesoporous materials. γ-Fe2O3-LSB had a specific surface area (SBET = 135.30 m2/g) which is greater than that of LSB (SBET = 11.54 m2/g). γ-Fe2O3-LSB exhibits a saturation magnetization value (Ms) of 3.72 emu/g which shows its superparamagnetic nature. The batch adsorption process was performed to analyze the adsorptive removal of MB dye using γ-Fe2O3-LSB. The adsorption efficiency of γ-Fe2O3-LSB for MB was analyzed by varying parameters like the initial concentration of adsorbate (MB), γ-Fe2O3-LSB dose, pH effect, contact time, and temperature. Adsorption isotherm, kinetic, and thermodynamics were also studied after optimizing the protocol. The non-linear Langmuir model fitted the best to explain the adsorption isotherm mechanism and resulting adsorption capacity ( q e =54.55 mg/g). The thermodynamics study showed the spontaneous and endothermic nature, and pseudo-second-order rate kinetics was followed during the adsorption process. Regeneration study showed that γ-Fe2O3-LSB can be used up to four cycles. In laboratory setup, the cost of γ-Fe2O3-LSB synthesis comes out to be 162.75 INR/kg which is low as compared to commercially available adsorbents. The results obtained suggest that magnetic Lagenaria siceraria biochar, which is economical and efficient, can be used as a potential biochar material for industrial applications in the treatment of wastewater.

In-situ registration subtraction image segmentation algorithm for spatiotemporal visualization of copper adsorption onto corn stalk-derived pellet biochar by micro-computed tomography

The non-homogeneous structure and high-density ash composition of biochar matrix pose significant challenges in characterizing the dynamic changes of heavy metal adsorption onto biochar with micro-computed tomography (Micro-CT). A novel in-situ registration subtraction image segmentation method (IRS) was developed to enhance micro-CT characterization accuracy. The kinetics of Cu(II) adsorption onto pellet biochar derived from corn stalks were tested. Respectively, the IRS and traditional K-means algorithms were used for image segmentation to the in-situ three-dimensional (3D) visual characterization of the Cu(II) adsorption onto biochar. The results indicated that the IRS algorithm reduced interference from high-density biochar composition, and thus achieved more precise results (R2 = 0.95) than that of K-means (R2 = 0.72). The visualized dynamic migration of Cu(II) from surface adsorption to intraparticle diffusion reflexed the complex mechanism of heavy metal adsorption. The developed Micro-CT method with high generalizability has great potential for studying the process and mechanism of biochar heavy metal adsorption.

Selective removal of thallium from water by MnO2-doped magnetic beads: Performance and mechanism study

Aqueous thallium has posed an increasing threat to environment as human's intensified activities in mining, refining, process and discharge. Remediation on thallium pollution has been of up-most importance to water treatment. In present work, MnO2 and magnetic Fe3O4 have been implanted to sodium alginate (SA) in presence of carboxyl methyl cellulose (CMC), and the resultant beads consisted of SA/CMC/MnO2/Fe3O4 were characterized. The materials were applied to treatment of Tl-contaminated water as adsorbent in lab. The removal results revealed that the adsorption capacity reached 38.8 mg (Tl)·g (beads)-1 and almost 100 % removal efficiency was achieved. The residual Tl was below 0.1 μg·L-1, meeting the discharge standard regulated in China. The kinetic adsorption was better described as a pseudo-second-order and three-step intra-particle diffusion model. Freundlich isotherm was well fitted the experimental data. The absorbent shown an excellent competitive specificity (KTl/M: ∼104!) over common hazardous ions Cu2+, Cd2+, Co2+, Pb2+ and Cr3+, as well as naturally abundant K+ and Na+ (KTl/M: 10-102) in mimic environmental conditions. Regeneration and reusability of the absorbent was also verified by five absorption-desorpotion cycles. XPS results revealed that a redox reaction between Mn4+ with Tl+, and an ion exchange of H+ (-O-Fe) and Tl+ were assumed to be main process for the specific capturing. This study provided an efficient SA/CMC/MnO2/Fe3O4 composite beads that could be a promising adsorbent for Tl-polluted water treatment.

Graphene oxide@Fe3O4-decorated iota-carrageenan composite for ultra-fast and highly efficient adsorption of lead (II) from water

The aggravated problem of lead pollution, especially in aquatic environments, necessitates the development of eminent adsorbents that could radically solve this environmental problem. Hence, a new composite was constructed based on iota carrageenan (i.Carr), graphene oxide (GO) and magnetite (Fe3O4) for removing noxious Pb2+ ions. The GO@Fe3O4-i.Carr composite was characterized by VSM, SEM, XPS, XRD, FTIR and Zeta potential. The removal of Pb2+ ions attained a quick equilibrium of almost 30 min with a removal efficiency reaching 93.68 %. The removal of Pb2+ was boosted significantly, in the order of GO@Fe3O4-i.Carr(1:1) > GO@Fe3O4-i.Carr(1:3) > GO@Fe3O4-i.Carr(3:1). Moreover, acquired experimental data fitted the pseudo 2nd order kinetic model and Freundlich isotherm model with a maximal monolayer adsorption capacity reached 440.05 mg/g. Notably, after five adsorption runs, the composite maintained its removal efficiency exceeding 74 %. The assumed adsorption mechanisms of Pb2+ onto GO@Fe3O4-i.Carr were complexation, precipitation, Lewis acid-base, and electrostatic attraction forces. Overall, the GO@Fe3O4-i.Carr composite elucidated the auspicious adsorbent criteria, comprising fast adsorption with high performance, ease-separation and tolerable recyclability, advising its feasible use to decontaminate water bodies from hazardous heavy metals.

Capturing Cu2+ and recycling spent Cu-adsorbents as catalyst for eliminating Rhodamine B: reactivity and mechanism

The thorny problem of adsorption is the disposing of spent adsorbent. In this manuscript, the exhaust adsorbent of efficient capture Cu(II) over ZSM-5 that supported zero-valent iron (nZVI) was reused as a catalyst for eliminating Rhodamine B (RhB). Batch experiments were used to evaluate the removal performance of Cu2+ and RhB. The results demonstrated that the Cu2+ adsorption process obeyed pseudo-second-order kinetics, and the adsorption performance was dependent on solution pH. The maximum adsorption capacity at the optimal pH 4.0 was 375.9 mg/g; equilibrium was reached rapidly within 35 min. From XPS, the reduction-oxidation between Fe0 and Cu2+ was occurred in the adsorption process, and Fe2+, Fe3+, and Cu0 was formed. In the recycling experiments, RhB was removed by the spent Cu adsorbent, with the removal performance being dependent on the initial Cu concentration, in the order of 5 mg/L > 20 mg/L > 0 mg/L > 100 mg/L > 500 mg/L. RhB removal also improved with increasing H2O2 concentration. More than 99.9% of the RhB was degraded within 8 min using 1.75 mM H2O2, which was a large improvement over the previously used catalyst. The hydroxyl radical was found to be the main free radical responsible for RhB degradation.