Magnetic kaolinite immobilized chitosan beads for the removal of Pb(II) and Cd(II) ions from an aqueous environment

Adsorption of Chromium (III) and Chromium (VI) Ions from Aqueous Solution Using Chitosan-Clay Composite Materials

In this work, biopolymer chitosan and natural clay were used to obtain composite materials. The overall aim of this study was to improve the properties (porosity, thermal stability and density) of pure chitosan beads by the addition of clay and to obtain a chitosan-based composite material for the adsorption of heavy metals from an aqueous solution, using Mongolian resources, and to study the adsorption mechanism. The natural clay was pre-treated with acid and heat to remove the impurities. The chitosan and pre-treated clay were mixed in different ratios (8:1, 8:2 and 8:3) for chemical processing to obtain a composite bead for the adsorption of chromium ions. The adsorption of Cr(III) and Cr(VI) was studied as a function of the solution pH, time, temperature, initial concentration of the chromium solution and mass of the composite bead. It was found that the composite bead obtained from the mixture of chitosan and treated clay with a mass ratio of 8:1 and 8:2 had the highest adsorption capacity (23.5 and 17.31 mg·g-1) for Cr(III) and Cr(VI), respectively, in the optimum conditions. The properties of the composite materials, prepared by mixing chitosan and clay with a ratio of 8:1 and 8:2, were investigated using XRD, SEM-EDS, BET and TG analysis. The adsorption mechanism was discussed based on the XPS analysis results. It was confirmed that the chromium ions were adsorbed in their original form, such as Cr(III) and Cr(VI), without undergoing oxidation or reduction reactions. Furthermore, Cr(III) and Cr(VI) were associated with the hydroxyl and amino groups of the composite beads during adsorption. The kinetic, thermodynamic and isothermal analysis of the adsorption process revealed that the interaction between the chitosan/clay composite bead and Cr(III) and Cr(VI) ions can be considered as a second-order endothermic reaction, as such the adsorption can be assessed using the Langmuir isotherm model. It was concluded that the composite bead could be used as an adsorbent for the removal of chromium ions.

Properties of biochar colloids and behaviors in the soil environment: Influencing the migration of heavy metals

Biochar pyrolyzed by biomass shows excellent application prospects for heavy metal (HM) remediation, but a part of biochar can be inevitably broken into micro- and nano-sized biochar colloids (BCs) under biological and physicochemical actions in soil. BCs derived in the process of remediation have rough surface, rich elemental species and contents, and multiple functional groups, which are similar to biochar. However, BCs have some unique colloidal properties because of their micro and nano scale size. Due to these properties, BCs exhibit strong mobilities in the soil environment, and the mobilities may be influenced by a combination of colloidal properties of BCs and environmental factors including soil colloids and other soil environmental conditions. In addition, BCs may have affinity effects on HMs through electrostatic adsorption, ion exchange, surface complexation, precipitation/co-precipitation, and redox because of the properties such as large specific surface area, and rich oxygen-containing functional groups and minerals on the surface. This review summarizes the physicochemical and migratory properties of BCs, and the internal and external factors affecting the migration of BCs in the soil environment, and the possible effects of BCs on HMs are high-lighted. This review provides a theoretical basis for the optimization of soil contaminated with HMs after remediation using biochar. Notably, the innovative idea that BCs may influence the presence of HMs in soil needs to be further confirmed by more targeted detection and analysis methods in future studies to prevent the possible environmental toxicities of the lateral and vertical diffusion of HM caused by BCs in soil.

Preparation of magnetic DTPA-modified chitosan composite microspheres for enhanced adsorption of Pb(II) from aqueous solution

In this study, magnetic DTPA-modified chitosan composite microspheres (MDCM) were prepared by reverse emulsion-double crosslinking method (carbodiimide followed by glutaraldehyde) for removal of Pb(II) from aqueous solution. The obtained magnetic adsorbents were characterized by FTIR, SEM, XRD, VSM, BET, and 13C NMR. The effects of the pH, contact time, initial concentration, and competitive metal cations (Na(I), Ca(II), or Mg(II)) on Pb(II) adsorption were investigated. The results revealed that MDCM exhibited high removal performance over a wide pH range and in the presence of competitive metal cations. The maximum adsorption capacity of MDCM for Pb(II) is 214.63 mg g-1 at pH 3, which is higher than most recently reported magnetic adsorbents. Adsorption kinetics and isotherms can be described by the pseudo-second-order model and Langmuir model, respectively. In addition, MDCM is easy to regenerate and can be reused five cycles with high adsorption capacity. Finally, the adsorption mechanism was further revealed by FTIR and XPS analysis. Overall, MDCM has practical application potential in removing Pb(II) from contaminated wastewater due to its high adsorption efficiency, good reusability, and convenient magnetic separation.

Adsorption of Cd(II) ions on magnetic graphene oxide/cellulose modified with β-cyclodextrin: Analytical interpretation via statistical physics modeling and fractal like kinetic approach

In the present study, β-cyclodextrin modified magnetic graphene oxide/cellulose (CN/IGO/Cel) was fabricated for removal of Cd(II) ions. The material was characterized through various analytical techniques like FTIR, XRD, TGA/DTA, SEM, TEM, and XPS. The point of zero charge of the material was obtained as 5.38. The controllable factors were optimized by Taguchi design and optimum values were: adsorbent dose-16 mg, equilibrium time-40 min, and initial concentration of Cd(II) ions-40 mg/L. The material shows high adsorption capacity (303.98 mg/g). The good fitting of Langmuir model to adsorption data (R2 = 0.9918-0.9936) revealed the monolayer coverage on adsorbent surface. Statistical physics model M 2 showed best fitting to adsorption data (R2 > 0.997), suggesting the binding of Cd(II) ions occurred on two different receptor sites (n). Stereographically n > 1 confirming vertical multi-molecular mechanisms of Cd(II) ions adsorption on CN/IGO/Cel surface. The adsorption energies (E1 = 23.71-28.95 kJ/mol; E2 = 22.69-29.38 kJ/mol) concluded the involvement of physical forces for Cd(II) ions adsorption. Kinetic data fitted well to fractal-like pseudo first-order model (R2 > 0.9952), concluding the adsorption of Cd(II) ions occurred on energetically heterogeneous surface. The kinetic analysis shows that both the film-diffusion and pore-diffusion were responsible for Cd(II) ions uptake. XPS analysis was utilized to explain the adsorption mechanism of Cd(II) ions onto CN/IGO/Cel.

Effects of Dietary Supplementation with Chitosan on the Muscle Composition, Digestion, Lipid Metabolism, and Stress Resistance of Juvenile Tilapia (Oreochromis niloticus) Exposed to Cadmium-Induced Stress

The aim of this study was to investigate the effects of dietary chitosan supplementation on the muscle composition, digestion, lipid metabolism, and stress resistance, and their related gene expression, of juvenile tilapia (Oreochromis niloticus) subjected to cadmium (Cd2+) stress. Juvenile tilapia with an initial body weight of 21.21 ± 0.24 g were fed with a formulated feed containing five different levels (0%, 0.5%, 1.0%, 1.5%, and 2.0%) of chitosan for 60 days, while the water in all experimental groups contained a Cd2+ concentration of 0.2 mg/L. The results showed that, compared with the control group (0% chitosan), the contents of crude fat and crude protein in the muscle, the activities of lipase, trypsin, and amylase in the intestine, as well as the relative expression levels of metallothionein (mt), cytochrome P450 1A (cyp1a), carnitine palmitoyltransferase-1 (cpt-1), peroxisome proliferator-activated receptor alpha (pparα), peroxisome proliferator-activated receptor gamma (pparγ), hormone-sensitive lipase (hsl), lipoprotein lipase (lpl), malate dehydrogenase (mdh), leptin (lep), fatty acid synthase (fas), sterol regulatory element-binding protein 1 (srebp1), and stearoyl-CoA desaturase (scd) genes in the liver of juveniles were significantly increased (p < 0.05). In conclusion, dietary chitosan supplementation could alleviate the effects of Cd2+ stress on the muscle composition, digestive enzymes, lipid metabolism, and stress resistance, and their related gene expression, of juvenile tilapia, and to some extent reduce the toxic effect of Cd2+ stress on tilapia.

3D kaolinite/g-C3N4-alginate beads as an affordable and sustainable photocatalyst for wastewater remediation

Graphitic carbon nitride (GCN) is an efficient visible-light-driven metal-free semiconductor with superior photocatalytic activity. However, the main drawbacks of GCN include lower adsorption capacity, poor reusability and recoverability. To address these drawbacks, kaolinite/g-C3N4-alginate beads were fabricated using a cross-linking method to remove brilliant green dye from wastewater via photocatalysis. The characterization studies proved the alginate's potential capability in altering photocatalyst bandgap (2.78 to 2.55 eV) and minimizing recombination of electron-hole pairs. Kaolinite/g-C3N4-alginate photocatalyst removed 97 % of brilliant green (10 mg/L) in 90 min under visible light irradiation. The superior performance of the kaolinite/g-C3N4-alginate beads was ascribed to its improved adsorption and effective utilization of visible light. The key advantages of kaolinite/g-C3N4-alginate beads were their quick recovery and extended reusability upto ten cycles. The sustainability metrics analysis of kaolinite/g-C3N4-alginate beads confirmed the environmental suitability and practicability in wastewater remediation. This study provides new insights into the low-cost and sustainable preparation of highly reusable g-C3N4-based photocatalysts for environmental remediation.

Chitosan/carboxymethylcellulose polyelectrolyte complexes (PECs) are an effective material for dye and heavy metal adsorption from water

Granular macroscopic chitosan/carboxymethylcellulose polyelectrolytic complexes (CHS/CMC macro-PECs) were produced and tested as adsorbents for six pollutants often present in wastewaters: sunset yellow (YS), methylene blue (MB), Congo red (CR) and safranin (S), cadmium (Cd²⁺) and lead (Pb²⁺). The optimum adsorption pH values at 25 °C were 3.0, 11.0, 2.0, 9.0, 10.0, and 9.0 for YS, MB, CR, S, Cd²⁺, and Pb²⁺, respectively. Kinetic studies indicated that the pseudos-econd order model best represented the adsorption kinetics of YS, MB, CR, and Cd²⁺, whereas the pseudo-first order model was the most suitable for S and Pb²⁺ adsorption. The Langmuir, Freundlich, and Redlich-Peterson isotherms were fitted to experimental adsorption data, with the Langmuir model providing the best fit. The maximum adsorption capacity (q_máx) of CHS/CMC macro-PECs for the removal of YS, MB, CR, S, Cd²⁺, and Pb²⁺ was 37.81, 36.44, 70.86, 72.50, 75.43, and 74.42 mg/g, respectively (corresponding to 98.91 %, 94.71 %, 85.73 %, 94.66 %, 98.46 %, and 97.14 %). Desorption assays showed that CHS/CMC macro-PECs can be regenerated after adsorbing any of the six pollutants studied, with possibility of reuse. These results provide an accurate quantitative characterization of the adsorption of organic and inorganic pollutants on CHS/CMC macro-PECs, indicating a novel technological applicability of these two inexpensive, easy-to-obtain polysaccharides for water decontamination.

Carbon nanotube/Chitosan hydrogel for adsorption of acid red 73 in aqueous and soil environments

Acid red 73 is an azo dye, and its residue can pollute the environment and seriously threaten human health and life. In this study, glutaraldehyde was used as the crosslinking agent, chitosan and polyvinyl alcohol were crosslinked under appropriate conditions to obtain a chitosan hydrogel film, and carbon nanotubes were dispersed in the chitosan hydrogel film. The FTIR, XRD, BET, SEM were applied to chatacterize the structure and the morphology of the absorbent and results showed that when the mass fraction of the carbon nanotubes was 1%, the structure was a three-dimensional network with microporous, and the water absorption reached to the maximum value of 266.07% and the elongation at break reached to a maximum of 98.87%. The ability to remove acid red 73 from aqueous and soil environments was evaluated by UV. In the aqueous samples, 70 mg of the adsorbent reached a saturated adsorption capacity of 101.07 mg/g and a removal rate of 92.23% at pH = 5. The thermodynamics conformed with the Langmuir adsorption isotherm and pseudo second-order adsorption kinetic models. In the soil samples, 100 mg of the adsorbent reached an adsorption capacity of 24.73 mg/g and removal rate of 49.45%. When the pH of the soil is between 4 and 7, the removal rate and adsorption capacity do not change much; hence, the pH should be maintained between 5.2 and 6.8, which is extremely suitable for the growth of general plants. Moreover, the experimental results demonstrated that the adsorbent maintained a good removal rate of acid red 73 over six adsorption cycles.

Chitosan Hydrogels for Water Purification Applications

Chitosan-based hydrogels have gained significant attention for their potential applications in water treatment and purification due to their remarkable properties such as bioavailability, biocompatibility, biodegradability, environmental friendliness, high pollutants adsorption capacity, and water adsorption capacity. This article comprehensively reviews recent advances in chitosan-based hydrogel materials for water purification applications. The synthesis methods, structural properties, and water purification performance of chitosan-based hydrogels are critically analyzed. The incorporation of various nanomaterials into chitosan-based hydrogels, such as nanoparticles, graphene, and metal-organic frameworks, has been explored to enhance their performance. The mechanisms of water purification, including adsorption, filtration, and antimicrobial activity, are also discussed in detail. The potential of chitosan-based hydrogels for the removal of pollutants, such as heavy metals, organic contaminants, and microorganisms, from water sources is highlighted. Moreover, the challenges and future perspectives of chitosan-based hydrogels in water treatment and water purification applications are also illustrated. Overall, this article provides valuable insights into the current state of the art regarding chitosan-based hydrogels for water purification applications and highlights their potential for addressing global water pollution challenges.

Adsorption Characterization of Cu(II) and Cd(II) by a Magnetite-Chitosan Composite: Kinetic, Thermodynamic and Equilibrium Studies

Optimizing the use of magnetite-chitosan composites for heavy metal adsorption has been of great interest due to their environmental friendliness. To gain insights into their potential with green synthesis, this study analyzed one of these composites through X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. Adsorption properties were then explored via static experiments to evaluate the pH dependence, isotherms, kinetics, thermodynamics and regeneration adsorption of Cu(II) and Cd(II). Results disclosed that the optimum pH of adsorption was 5.0, the equilibrium time was about 10 min, and the capacity for Cu(II) and Cd(II) reached 26.28 and 18.67 mg/g, respectively. The adsorption amount of cations increased with temperature from 25 °C to 35 °C and decreased with further increase in temperature from 40 °C to 50 °C, which might be related to the unfolding of chitosan; the adsorption capacity was above 80% of the initial value after two regenerations and about 60% after five regenerations. The composite has a relatively rough outer surface, but its inner surface and porosity are not obvious; it has functional groups of magnetite and chitosan, and chitosan might dominate the adsorption. Consequently, this research proposes the value of maintaining green synthesis research to further optimize the composite system of heavy metal adsorption.

Adsorption of Pb(II) from wastewater using a red mud modified rice-straw biochar: Influencing factors and reusability

Efficient environmental remediation of toxic chemicals using effective sorbents has received considerable attention recently. For the present study, the synthesis of a red mud/biochar (RM/BC) composite was performed from rice straw with the aim of achieving Pb(II) removal from wastewater. Characterization was performed by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), Zeta potential analysis, elemental mapping, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results showed that RM/BC had higher specific surface area (S_BET = 75.37 m² g^-1) than raw biochar (S_BET = 35.38 m² g^-1). The Pb(II) removal capacity (q_e) of RM/BC was 426.84 mg g^-1 at pH 5.0, and the adsorption data well fitted pseudo second order kinetics (R² = 0.93 and R² = 0.98), as well as the Langmuir isotherm model (R² = 0.97 and R² = 0.98) for both BC and RM/BC. Pb(II) removal was slightly hindered with the increasing strength of co-existing cations (Na⁺, Cu²⁺, Fe³⁺, Ni²⁺, Cd²⁺). The increase in temperatures (298 K, 308 K, 318 K) favored Pb(II) removal by RM/BC. Thermodynamic study indicated that Pb(II) adsorption onto BC and RM/BC was spontaneous and primarily governed by chemisorption and surface complexation. A regeneration study revealed the high reusability (>90%) and acceptable stability of RM/BC even after five successive cycles. These findings indicate that RM/BC evidenced special combined characteristics of red mud and biochar, hence its use for Pb removal from wastewater offers a green and environmentally sustainable approach fitting the "waste treating waste" concept.

Building of soft-hard compound brush in porous PVA/NH2@TAtZnO plural gel and the high-efficiency anti-interference removal on Pb(II)

In order to promote the heavy metal ions removal of porous gel adsorbent and protect the adsorbent from other pollutants in wastewater, the tetrapod ZnO whiskers (tZnO) modified by amino-chain brush was introduced into the polyvinyl alcohol (PVA) matrix to prepare the PVA/NH₂@TAtZnO composites with brush structure for toxic Pb(II) removal. The adsorption property, adsorption process and adsorption mechanism were studied by adsorption isotherms, adsorption kinetics, adsorption thermodynamics, SEM-EDS analysis and XPS analysis. And the anti-interference ability and anti-interference mechanism were researched by SEM-EDS analysis and XPS analysis. It was found that the PVA/NH₂@TAtZnO composites displayed a soft-hard compound pore-brush structure and showed a good selective adsorption on Pb(II). The research of isotherms and kinetics indicated that the adsorption process was fitted well to Langmuir model and pseudo-second-order model, respectively, and the research of thermodynamics revealed the endothermic nature. The adsorption mechanism was inferred as the combination of predominant chemisorption and subsidiary physisorption. Comparing with the neat PVA matrix, the PVA/NH₂@TAtZnO composites displayed a good anti-interference property on Pb(II) adsorption and showed an alleviative clogging pore-canal structure in the wastewater with SiO₂ NPs or PAC flocculants. The anti-interference intensity ΔQ and anti-interference factor χ were proposed to reflect the anti-interference ability of this adsorbent which was promoted with the increasing amino brush length or density. By the analysis of SEM-EDS and XPS, the anti-interference mechanism was explored as the steric-hinerance effect of tZnO hard brush to suspended SiO₂ NPs pollutant and the coordination effect of functional amino soft brush to soluble PAC pollutant. Besides, the prepared PVA/NH₂@TAtZnO adsorbent possessed a good reusability under multiple adsorption-desorption processes and also presented a well applicability in real water matrix. The research indicated the huge potential of prepared PVA/NH₂@TAtZnO adsorbent in heavy metal ions removal.

“Gamma Irradiation Synthesis of Carboxymethyl Chitosan-Nanoclay Hydrogel for the Removal of Cr(VI) and Pb(II) from Aqueous Media”

Hydrogel composites comprised of N,O carboxymethyl chitosan crosslinked with different weight ratios of acrylic acid and fabricated with nanoclay particle were prepared via gamma irradiation at 25 kGy irradiation dose. The prepared composites were coded as CsAA1Cl, CsAA2Cl and CsAA3Cl based on the weight ratio of acrylic acid to the chitosan derivative. The claimed hydrogels were characterized by FTIR, TGA and XRD. The TGA data implied that the incorporation of clay nanoparticles enhanced the thermal stability of the composites; the decomposition temperature increased up to 500 °C for CsAA3Cl. Three AFM outcomes were used to compare the surface features of the samples; topography, height and surface roughness. The topography data reveals that the nanoclay particles incorporated in CsAA3Cl are intercalated and exfoliated. Then, the optimized sorbent (CsAA3Cl) was investigated as green sorbents for chromium (VI) and lead (II). The data revealed that CsAA3Cl displayed maximum removal performance towards both lead and chromium with removal efficiencies 125 mg/g and 205 mg/g respectively at the optimum application conditions within 90 min only. Also, it was found that the optimum pH value was 9 for chromium and 8 for lead. The data proved that the adsorption of both cations followed pseudo-first order kinetic model. The prepared composites showed acceptable metal uptake capacity at three successive cycles.

Graphical Abstract

A comparative and modeled approach for three biochar materials in simultaneously preventing the migration and reducing the bioaccessibility of heavy metals in soil: Revealing immobilization mechanisms

The effectiveness and feasibility of the three biochar materials for remediation of arsenic (As) and lead (Pb) contaminated soil were explored in this study. Significant reduction of bioaccessibility and migration risks of both heavy metals have been explained mechanistically by incubation, column experiments and numerical simulation. Langmuir equation fitted As and Pb sorption isotherms better in the control and biochar (BC) amended soils, while Freundlich model was more suitable for iron modified biochar (Fe-BC) and sulfur/iron modified biochar (S/Fe-BC) amended soils, indicating that modified biochar promoted chemical adsorption process for As and Pb. For the three biochar materials, S/Fe-BC showed the best effects on reducing the bioavailability of As and Pb, with a decrease of 40.42%-64.21%. The reduction in bioaccessibility by metal portioning into available and non-available fractions was better for illustrating the mechanisms including adsorption, precipitation/coprecipitation and As(III) oxidation behind S/Fe-BC efficacy. Moreover, S/Fe-BC can effectively inhibit the leaching behavior of As and Pb under acid rain, which increased by 99.89% and 90.18%, respectively, compared with the control. The HYDRUS-1D modeling indicated that S/Fe-BC could continuously treat As (100 mg/L) and Pb (1000 mg/L) contaminated water for 16.22 years and 40.86 years, respectively, and ensure the groundwater quality criteria being met. Based on these insights, we believe that our study will provide meaningful information about the potentials of biochar derived materials for soil heavy metals' remediation.

Preparation and Characterization of Low-Cost Ceramic Membrane Coated with Chitosan: Application to the Ultrafine Filtration of Cr(VI)

In this work, low-cost ceramic membranes (CMs) were prepared from ultrafine starting powders such as kaolin, clay, and starch by a dry compaction method. The ceramic membranes were sintered at different temperatures and times and were characterized by XRD, XRF, TG-DTA, SEM-EDS, N₂-BET, water absorption, compressive strength, and pure water flux. The optimal membrane, sintered at 1000 °C for 3 h, possessed water absorption of 27.27%, a compressive strength of 31.05 MPa, and pure water flux of 20.74 L/h m². Furthermore, chitosan crosslinked with glutaraldehyde was coated on the surface of the ceramic membrane by the dip coating method, and the pore size of the chitosan-coated ceramic membrane (CCCM) was 16.24 nm. Eventually, the separation performance of this membrane was assessed for the removal of chromium(VI) from aqueous solution. The ultrafine filtration of Cr(VI) was studied in the pH range of 2-7. The maximum removal of Cr(VI) was observed to be 71.25% with a pH of 3. The prepared CCCM showed good membrane properties such as mechanical stability and ultrafine structure, which have important applications for the treatment of wastewater including such heavy metals.

A newly-constructed bifunctional bacterial consortium for removing butyl xanthate and cadmium simultaneously from mineral processing wastewater: Experimental evaluation, degradation and biomineralization

Due to the technological limitations associated with beneficiation technology, large amounts of flotation reagents and heavy metals remain in mineral processing wastewater. Unfortunately, however, no treatment methods are available to mitigate the resulting pollution by them. In this study, a bacterial consortium SDMC (simultaneously degrade butyl xanthate and biomineralize cadmium) was constructed in an effort to simultaneously degrade butyl xanthate (BX) and biomineralize cadmium (Cd) by screening and domesticating two different bacterial species including Hypomicrobium and Sporosarcina. SDMC is efficient in removing the combined pollution due to BX and Cd with a 100% degradation rate for BX and 99% biomineralization rate for Cd within 4 h. Besides, SDMC can tolerate high concentrations of Fe(III) (0-40 mg/L). It has an excellent ability to utilize Fe(III) for enhanced removal of the combined pollutants. SDMC can effectively remove pollutants with a pH range of 6-9. Further, we discussed pathways for potential degradation and biomineralization: Cd(BX)₂-Cd²⁺, BX^-; BX^--CS₂, butyl perxanthate (BPX); Cd²⁺-(Ca0.67,Cd0.33)CO₃. The removal of the combined pollutants primarily entails decomposition, degradation, and biomineralization, C-O bond cleavage, and microbially induced carbonate precipitation (MICP). SDMC is a simple, efficient, and eco-friendly bifunctional bacterial consortium for effective treatment of BX-Cd combined pollution in mineral processing wastewater.

Preparation of Iron Carbon Composite Material by Extracting Iron from Bauxite Residue and Its Adsorption of Heavy Metal Cd(II)

An effective method of iron extraction from bauxite residue was explored, and iron was used to prepare iron carbon composite material, which have a good adsorption effect on the heavy metal cadmium. After acid washing, acid leaching, Fe(III) reduction and ferrous oxalate decomposition, FeSO₄·H₂O(RM) was successfully extracted from bauxite residue, and the iron loss was only 4.35%. FexOy-BC(RM) nanocomposite materials were prepared by loading FeSO₄·H₂O(RM) onto walnut shell biochar (BC) (a kind of agricultural and forestry waste) by an in situ reduction and oxidation method. The results showed that the adsorption effect of FexOy-BC(RM) on Cd(II) was better than that of commercial FexOy-BC. XPS, TEM, SEM characterization analysis showed that FexOy-BC(RM) immobilized Cd(II) by adsorption, complexation, etc.to achieve a highly efficient adsorption of heavy metal Cd(II) in wastewater.

New insight into the co-adsorption of oxytetracycline and Pb(II) using magnetic metal-organic frameworks composites in aqueous environment: co-adsorption mechanisms and application potentials

The present study aimed to investigate the co-adsorption and application of water stabilized Fe₃O₄@ZIF-8 composite with magnetic cubic crystal structure. This new material was successfully prepared by facile modification strategy and rational design, which was used for simultaneous adsorption of oxytetracycline (OTC) and Pb(II) in aqueous solution. The co-adsorption behavior and mechanism of the composite for OTC and Pb(II) were systematically investigated by characterization techniques and batch experiments, and its application potential was effectively evaluated. The results showed that the synthesized Fe₃O₄@ZIF-8 composite innovatively retained the cubic crystal structure of ZIF-8 and was successfully loaded on the surface of Fe₃O₄ particles with small particle size to form a core-shell structure. The Fe₃O₄@ZIF-8 composite possessed a large specific surface area (1722 m²/g), magnetic separation performance (13.4 emu/g), and rich functional groups. The co-adsorption of OTC and Pb(II) on Fe₃O₄@ZIF-8 had fast reaction kinetics (equilibrium within 90 min) and large adsorption capacity (310.29 mg/g and 276.06 mg/g respectively). The adsorption process for both contaminants followed pseudo-second order kinetics and Langmuir isotherm models and had synergistic and competitive effects at the same time. π-π stacking and electrostatic interaction were the main mechanisms of adsorption. Fe₃O₄@ZIF-8 had good adsorption performance after cyclic adsorption for 4 times and it performed well in the treatment of real waste water. This study provided a new sight for the control of combined pollution of OTC and Pb(II) and proved Fe₃O₄@ZIF-8 composites have great application potentials for complex wastewater treatment.

Removal of phosphorus using biochar derived from Fenton sludge: Mechanism and performance insights

A phosphorus removal biochar adsorbent was prepared from Fenton sludge. The adsorption process was optimized, and its phosphorus adsorption mechanism was discussed. It was found that the phosphorus adsorption performance of biochar prepared from single Fenton sludge (FBC-400) was better than that of co-pyrolysis of Fenton sludge and bamboo powder. The optimum condition was that Fenton sludge pyrolyzed at 400°C (FBC-400). FBC-400 had a larger specific surface area than that prepared by co-pyrolysis with bamboo powder. And the high content of iron element could provide a higher surface charge of the biochar, thereby increasing the electrostatic adsorption of phosphorus onto FBC-400. The phosphorus adsorption was highly pH dependent by FBC-400, which can enhance electrostatic adsorption and increase adsorption capacity in acidic conditions. The effect of coexisting anion on adsorption performance was mainly affected by CO₃ ^2- , reducing the adsorption capacity by at least 49%, whereas other anions had no obvious interference. The adsorption process of FBC-400 accorded with the pseudo-second-order kinetic model and the Langmuir model, which indicated that the adsorption process was monolayer adsorption and mainly chemical adsorption, and the maximum saturated phosphorus adsorption capacity was 8.77 mg g^-1 . The mechanisms for phosphorus adsorption were electrostatic adsorption and inner-sphere complexing. 1 M NaOH was used for desorption, and the adsorption capacity remained at 81% in the fifth cycle. PRACTITIONER POINTS: The Fenton sludge biochar usage as an adsorbent could be a win-win strategy to convert waste biomass to valuable - product. The adsorption process accorded with the Langmuir model, the maximum phosphorus adsorption capacity was 8.77 mg/g at 25°C. The adsorption mechanisms were electrostatic adsorption and inner-sphere complexing. 1M NaOH was used for desorption, and the adsorption capacity remained at 81% in the fifth cycle.

Concurrent elimination and stepwise recovery of Pb(II) and bisphenol A from water using β-cyclodextrin modified magnetic cellulose: adsorption performance and mechanism investigation

Coexistence of heavy metals and endocrine disrupting compounds in polluted water with competitive adsorption behavior necessitates design of tailored adsorbents. In this work, β-cyclodextrin modified magnetic rice husk-derived cellulose (β-CD@MRHC) which can provide independent functional sites for effectively binding the above two types of contaminants was synthesized and used for Pb(II) and BPA elimination in both unit and multivariate systems. Characterizations results confirmed successful β-CD grafting and Fe₃O₄ loading, and the β-CD@MRHC had excellent magnetic property for its effectively recovery from water, which was not affected by the adsorption of pollutants. The β-CD@MRHC possessed superior adsorption performance with maximal Pb(II)/BPA uptake of 266.2 or 412.8 mg/g, severally, and the adsorption equilibrium was fleetly reached in 30 and 7.5 min. Moreover, the β-CD@MRHC could accomplish synergetic Pb(II) and BPA elimination through averting their competitive behaviors owing to diverse capture mechanisms for Pb(II) (ion exchange, complexation and electrostatic attraction) and BPA (hydrogen bonding and host-guest inclusion). Furthermore, after three cycles of step-wise desorption, the binding of Pb(II) as well as BPA byβ-CD@MRHC dropped slightly in dualistic condition. In summary, β-CD@MRHC was a promising tailored adsorbent to practical application for simultaneously removing heavy metals and organic matters from wastewater with high-performance magnetic recovery.

Biochar-supported starch/chitosan-stabilized nano-iron sulfide composites for the removal of lead ions and nitrogen from aqueous solutions

Novel materials that nano-FeS and starch (or chitosan) loaded on peanut shells biochar(Starch-FeS@PSB and Chitosan-FeS@PSB) were prepared and applied for removal of Pb(II) and nitrogen(NO₃-N and NH₄-N) in wastewater. It showed that Starch-FeS@PSB and Chitosan-FeS@PSB had excellent absorptive effects compared with PSB. The maximum adsorption capacity of Pb(II) by Starch-FeS@PSB and Chitosan-FeS@PSB reached 91.74 mg/g, 98.04 mg/g, respectively. Absorption of Pb(II) by Starch-FeS@PSB and Chitosan-FeS@PSB were controlled by monolayer chemisorption. Mechanism studies showed that complexation, electrostatic attraction, REDOX and physical absorption happened on the adsorbent surface. In addition, the maximum adsorption capacity of NO₃-N and NH₄-N by Starch-FeS@PSB and Chitosan-FeS@PSB reached 16.89 mg/g, 15.65 mg/g, and 18.45 mg/g, 18.28 mg/g, respectively. Absorption of N by Starch-FeS@PSB and Chitosan-FeS@PSB were controlled by multilayer chemisorption. Mechanism studies showed that complexation, electrostatic attraction and physical absorption happened on the adsorbent surface. Starch-FeS@PSB and Chitosan-FeS@PSB can be utilized in Pb(II) and N wastewater treatment.

Mechanistic insight and bifunctional study of a sulfide Fe3O4 coated biochar composite for efficient As(III) and Pb(II) immobilization in soils

Trace elements contamination in soil has aroused global concern nowadays, but the efficient, multifunctional, and economically viable method still remains a major challenge. In this research study, a sulfide Fe₃O₄ coated biochar composite (S/Fe-BC) has been synthesized successfully and applied to As(III)/Pb(II) co-contaminated soil. The immobilization efficiency of S/Fe-BC (2%) for the two elements exceeded 90%, and could ensure the synchronous and efficient immobilization in a wide range of pH (4.0-8.0). The TCLP-As and Pb amounts were sharply dropped after 28 days of stabilization; Meanwhile, a majority of exchangeable and carbonate-bound fractions of As and Pb were transferred into the less accessible residuals. Compared with Fe₃O₄ coated BC, the good immobilization performance of S/Fe-BC was mainly related to the enhancement of specific surface area, improvement of ionic exchange process, followed by the increase of Pb(II) precipitation and As(III) oxidation. Furthermore, competitive and synergistic effects were observed. In depth characterization analyses revealed the simultaneous immobilization mechanisms involving the adsorption, precipitation (Pb(OH)₂, PbSO₄, and PbS), co-precipitation (PbFeAsO₄(OH)), and oxidation. Conclusively, outstanding performance of S/Fe-BC composite is considered as a good multifunctional potential candidate for the immobilization of trace elements from a soil system.

Sustainable Development of Magnetic Chitosan Core-Shell Network for the Removal of Organic Dyes from Aqueous Solutions

The wide use of alizarin red S (ARS), a typical anthraquinone dye, has led to its continued accumulation in the aquatic environment, which causes mutagenic and carcinogenic effects on organisms. Therefore, this study focused on the removal of ARS dye by adsorption onto a magnetic chitosan core-shell network (MCN). The successful synthesis of the MCN was confirmed by ATR-FTIR, SEM, and EDX analysis. The influence of several parameters on the removal of ARS dye by the MCN revealed that the adsorption process reached equilibrium after 60 min, pH played a major role, and electrostatic interactions dominated for the ARS dye removal under acidic conditions. The adsorption data were described well by the Langmuir isotherm and a pseudo-second order kinetic model. In addition to the preferable adsorption of hydrophobic dissolved organic matter (DOM) fractions onto the MCN, the electrostatic repulsive forces between the previously adsorbed DOM onto MCN and ARS dye resulted in lower ARS dye removal. Furthermore, the MCN could easily be regenerated and reused for up to at least five cycles with more than 70% of its original efficiency. Most importantly, the spent MCN was pyrolytically converted into N-doped magnetic carbon and used as an adsorbent for various dyes, thus establishing a waste-free adsorption process.

Morphology-controlled fabrication of magnetic phase-change microcapsules for synchronous efficient recovery of wastewater and waste heat

Contamination and waste heat are major issues in water pollution. Aiming at efficient synchronous recovery wastewater and waste heat, we designed a novel CaCO₃-based phase-change microcapsule system with an n-docosane core and a CaCO₃/Fe₃O₄ composite shell. The system was fabricated through an emulsion-templated in situ precipitation approach in a structure-directing mode, resulting in a controllable morphology for the resultant microcapsules, varying from a peanut hull through ellipsoid to dumbbell shapes. The system has a significantly enlarged specific surface area of approximately 55 m²·g^-1 with the CaCO₃ phase transition from vaterite to calcite. As a result, the microcapsule system exhibits improved adsorption capacities of 497.6 and 79.1 mg/g for Pb²⁺ and Rhodamine B removal, respectively, from wastewater. Moreover, increase in the specific surface area of the microcapsule system with a sufficient latent heat capacity of approximately 130 J·g^-1 also resulted in an enhanced heat energy-storage capability and thermal conductance for waste-heat recovery. The microcapsule system also exhibits a good leakage-prevention capability and good multicycle reusability owing to the tight magnetic CaCO₃/Fe₃O₄ composite shell. This study provides a promising approach for developing CaCO₃-based phase-change microcapsules with enhanced thermal energy storage and adsorption capabilities for efficient synchronous recovery of wastewater and waste heat.

Efficient absorptive removal of Cd(Ⅱ) in aqueous solution by biochar derived from sewage sludge and calcium sulfate

Biochar derived from co-pyrolysis of sewage sludge and calcium sulfate was used to remove Cd(II) from aqueous solution. The results showed that the Cd(Ⅱ) adsorption better followed Freundlich model, and the maximum adsorption capacities were 109.0 mg/g (288 K), 127.9 mg/g (298 K) and 145.4 mg/g (308 K). The Cd(Ⅱ) removal was a multi-layer adsorption process dominated by chemisorption, which was also a spontaneous and endothermic process. The contribution of physisorption gradually increased as the Cd(Ⅱ) initial concentration. The Cd(Ⅱ) removal process which better followed pseudo-second-order kinetic model, was divided into three stages. The first (0-0.3 h) and second stages (0.3-2 h) were separately controlled by liquid film diffusion/intraparticle diffusion/chemical reaction and liquid film diffusion/chemical reaction, while the third stage (0.3-24 h) was the dynamic equilibrium process. The speciation distribution of Cd on biochar surface was mainly CdCO₃/CdOOC and CdO/CdSiO₃, indicating coprecipitation, ion exchange and complexation contributed more to the Cd(Ⅱ) removal.