Adsorption Mechanism Of Cr Research Articles

Preparation of chitosan modified fly ash under acid condition and its adsorption mechanism for Cr(VI) in water

Preparation of chitosan modified fly ash under acid condition and its adsorption mechanism for Cr(VI) in water

Adsorption of Cr(VI) onto a low‐cost ceramsite: Preparation, kinetics, and thermodynamics

AbstractA novel composite ceramsite derived from bamboo powders and bentonite was developed as adsorbents for waste water treatment. The microstructure, morphology, and thermal properties of ceramsite were characterized by X‐ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X‐ray fluorescence, and differential thermal analysis. The effect of compositions, sintering temperatures, sintering time, pH, and adsorption time on the adsorption performance of the ceramsites were studied. The results revealed that the maximum Cr(VI) removal rate of 99% can be obtained in the ceramsite with weight ratio bamboo to bentonite of 6:4, the annealing temperature of 1000°C, the solution pH 1 and contact time of 12 h. The adsorption kinetics and adsorption isotherm analysis revealed that the adsorption process best followed pseudo‐second‐order reaction kinetics and the Freundlich adsorption isotherm. The adsorption mechanism was discussed and both chemisorption and physiosorption were proposed as adsorption mechanism of Cr(VI). Moreover, the thermodynamic parameters, including changes in Gibbs free energy, entropy, and enthalpy, were studied in detail. The bamboo powder/bentonite composite ceramsite developed in this work is a promising candidate as an effective and economical adsorbent for Cr(VI) ions removal.

Versatile 3D reduced graphene oxide/poly(amino-phosphonic acid) aerogel derived from waste acrylic fibers as an efficient adsorbent for water purification.

The fabrication of multifunctional materials to remove soluble heavy metal ions and dyes, as well as insoluble oils from waste water is urgently required, yet remains a daunting challenge because of difficulty in controlling their structure and property to satisfy various demands. Herein, for the first time, novel 3D reduced graphene oxide/poly(amino-phosphonic acid) (PAPA) aerogels (rGO/PAPAs) with different PAPA content were developed by solvothermal reduction of the graphene oxide and cross-linking with PAPA chain, and subsequently employed as versatile adsorbent for the removal of complex pollutants such as Cr(III) ion, methylene blue (MB) dye and various kinds of organic solvents from water. Benefiting from the synergistic effect of the reduced graphene oxide (rGO) sheet and PAPA component, as well as its unique 3D structure, the resultant aerogel (rGO/PAPA-2) gained amphiphilic, ultralight, and multifunctional properties. Thus, it showed a fast adsorption rate (within 15min) and high adsorption capacity (up to 327.1mg/g) for Cr(III) ion at an optimal pH of 5.5 due to its unique 3D network structure with abundant amino-phosphonic acid functional groups. The uptake of Cr(III) by rGO/PAPA-2 was fitted well with the Langmuir isotherm and pseudo-second-order kinetic model. The adsorption mechanism of Cr(III) onto rGO/PAPA-2 can be attributed to electrostatic attraction and surface complexation with APA groups. In addition, the rGO/PAPA-2 displayed an excellent adsorption performance for MB (694.5mg/g) and several organic solvents (83.2 to 254.3g/g). Moreover, the rGO/PAPA-2 exhibited a good regeneration (around 99%) and satisfactory recovery abilities for the tested adsorbates. Notably, PAPA chains can be easily prepared from waste acrylic fibers, making it become a cost effective but versatile candidate to prepare new material. Therefore, this work provides a new design strategy to fabricate the rGO/PAPA-2 aerogel with great prospect for sophisticated industrial wastewater cleanup.

Green synthesis of poly(pyrrole methane)-based adsorbent for efficient removal of chromium(VI) from aqueous solution

It has attracted more and more attention to deal with chromium(VI) (Cr(VI)) pollution in wastewater due to its potential harm to human health. In this study, poly(pyrrole methane) (PPm), a potential material for Cr(VI) adsorption, was greenly synthesized for the removal of Cr(VI) from aqueous solution. Further, the Fe3O4 nanoparticles were loaded on the surface of PPm to enhance the separation property. The adsorption of Cr(VI) was favorable at a lower pH value, and it conformed to Langmuir and pseudo-second-order model. When the solution pH was 2, the dosage of PPm was 0.5 g L−1, the reaction temperature was 45 °C, and the reaction time was 24 h, the maximum adsorption capacity of PPm reached 922.49 mg g−1, which was higher than most of the reported adsorbents (40–560 mg g−1). The removal rates reached about 100% even in the presence of competitive ions. The as-prepared adsorbent can be reused for 5 times and the removal rate still exceeded 70%. The adsorption mechanisms of Cr(VI) onto PPm included electrostatic interactions, ion exchange, reduction of Cr(VI) to Cr(III), and immobilization of Cr(III). Although the adsorption capacity of PPm/Fe3O4 was lower than that of the pure PPm (549.75 mg g−1), it can be facilely separated from aqueous solution after adsorption. Notably, this study also provided a facile strategy to prepare adsorbent with active functional groups for efficient removal of Cr(VI) from aqueous solution.

Sustainable Chromium (VI) Removal from Contaminated Groundwater Using Nano-Magnetite-Modified Biochar via Rapid Microwave Synthesis.

This study developed a nano-magnetite-modified biochar material (m-biochar) using a simple and rapid in situ synthesis method via microwave treatment, and systematically investigated the removal capability and mechanism of chromium (VI) by this m-biochar from contaminated groundwater. The m-biochar was fabricated from reed residues and magnetically modified by nano-Fe3O4. The results from scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterisations confirmed the successful doping of nano-Fe3O4 on the biochar with an improved porous structure. The synthesised m-biochar exhibited significantly higher maximum adsorption capacity of 9.92 mg/g compared with that (8.03 mg/g) of the pristine biochar. The adsorption kinetics followed the pseudo-second-order model and the intraparticle diffusion model, which indicated that the overall adsorption rate of Cr(VI) was governed by the processes of chemical adsorption, liquid film diffusion and intramolecular diffusion. The increasing of the pH from 3 to 11 significantly affected the Cr(VI) adsorption, where the capabilities decreased from 9.92 mg/g to 0.435 mg/g and 8.03 mg/g to 0.095 mg/g for the m-biochar and pristine biochar, respectively. Moreover, the adsorption mechanisms of Cr(VI) by m-biochar were evaluated and confirmed to include the pathways of electrostatic adsorption, reduction and complexation. This study highlighted an effective synthesis method to prepare a superior Cr(VI) adsorbent, which could contribute to the effective remediation of heavy metal contaminations in the groundwater.

Characterization of cobalt ferrite-supported activated carbon for removal of chromium and lead ions from tannery wastewater via adsorption equilibrium

In this experiment, cobalt ferrite-supported activated carbon (CF-AC) was developed and characterized via the wet impregnation method for the removal of Cr and Pb(II) ions from tannery wastewater. Batch adsorption was carried out to evaluate the effect of experimental operating conditions (pH of solution, contact time, adsorbent dose, and temperature), and the removal efficiencies of Cr and Pb(II) ions by the developed adsorbents were calculated and recorded for all experimental conditions. These variables were estimated and reported as removal efficiencies of 98.2% for Cr and 96.4% for Pb(II) ions at the optimal conditions of 5, 0.8 g, 80 min, and 333 K for pH, adsorbent dose, contact time, and temperature, respectively. The equilibrium for the sorption of Cr and Pb(II) ions was studied using four widely used isotherm models (the Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherm models). It was found that the Freundlich isotherm model fit better with the coefficient of determination (R2) of 0.948 4 and a small sum of square error of 0.000 6. The maximum adsorption capacities (Qm) of Pb(II) and Cr adsorbed onto CF-AC were determined to be 6.27 and 23.6 mg/g, respectively. The adsorption process conformed well to pseudo-second order kinetics as revealed by the high R2 values obtained for both metals. The thermodynamic parameters showed that adsorption of Cr and Pb(II) ions onto CF-AC was spontaneous, feasible, and endothermic under the studied conditions. The mean adsorption energy (E) values revealed that the adsorption mechanism of Cr and Pb(II) by CF-AC is physical in nature. The results of the study showed that adsorbent developed from CF-AC can be efficiently used as an environmentally friendly alternative adsorbent, for removal of Cr and Pb(II) ions in tannery wastewater.

Low-cost and high-efficiency metallurgical copper slag@polyaniline core–shell composite as an adsorbent for the removal of Cr(VI) from aqueous solution

Industrial heavy-metal waste water causes substantial harm to the environment and human health. Therefore, it is an essential and urgent task to develop an efficient adsorbent with a simple preparation technique, long service life, and easy solid–liquid separation, which can reduce the concentrations of heavy metals in wastewater to an acceptable threshold before discharge. In this study, a core–shell-structured copper slag@polyaniline (CS@PANI) composite was fabricated, which could effectively remove Cr(VI) from wastewater. The effects of the pH value, contact time, Cr(VI) concentration, and temperature on Cr(VI) adsorption were also investigated. The maximum adsorption capacity of CS@PANI for Cr(VI) was up to 452.54 mg/g, under applied experimental conditions. The adsorption kinetics followed the pseudo-second-order model. The Langmuir model was more consistent with the adsorption process between CS@PANI and Cr(VI) than the Freundlich model. After five cycles, the Cr(VI) removal efficiency of CS@PANI remains > 90%, which shows an outstanding stability and regenerability of the prepared composite. Meanwhile, the adsorption mechanism of Cr(VI) on CS@PANI was also investigated. The work suggests an efficient approach for recycling solid wastes in the metallurgical industry.

The adsorption of Cr(VI) from water samples using graphene oxide-magnetic (GO-Fe3O4) synthesized from natural cellulose-based graphite (kusambi wood or Schleichera oleosa): Study of kinetics, isotherms and thermodynamics

Graphene oxide material has been studied widely as a novel adsorbent due to its unique surface structures, excellent physicochemical properties, strong affinity and high efficiency for the metal ions adsorption [Pang H, Wu Y, Wang X, Hu B, Wang X. Recent advances in composites of graphene and layered double hydroxides for water remediation: a review. Chem - Asian J 2019;14:2542–52; Liu X, Ma R, Wang X, Ma Y, Yang Y, Zhuang L, et al. Graphene oxide-based materials for efficient removal of heavy metal ions from aqueous solution: a review. Environ Pollut 2019;252:62–73]. The present report involves Cr(VI) adsorption studies using graphene oxide-magnetic (GO-Fe3O4) based on natural graphite made from kusambi wood from Timor Island, Indonesia. GO with large specific surface area and abundant functional groups was synthesized using Hummers modification method, while GO-Fe3O4 was synthesized using in situ co-precipitation method. Characterization of GO and GO-Fe3O4 material was carried out using FTIR, XRD and SEM-EDX. The maximum adsorption capacity is optimum at the use of 0.1g adsorbent GO-Fe3O4, under conditions: pH 2 with contact time for 80min and temperature of 298K. Nine kinetic models, five ishotherm models and two adsorption thermodynamics were used to study the mechanism of Cr(VI) adsorption on the surface of GO-Fe3O4. The results of kinetics and isotherms modeling show that the adsorption mechanism of Cr(VI) on GO-Fe3O4 follows pseudo-second (PSO) order kinetics with a high regression coefficient (>0.99) and was well described by Langmuir isotherm with adsorption capacity of 3.197mg/g. The thermodynamics data revealed the exothermic nature, a decrease in the randomness or irregularity on the surface of adsorbent during adsorption process and takes place through physisorption. Studies on isosteric enthalpy values show that the adsorption of Cr(VI) on the surface of GO-Fe3O4 is strongly influenced by the amount of adsorbate which tends to decrease in adsorption capacity as the amount of Cr(VI) ions increases.

A review on adsorptive remediation of Cr (VI) by magnetic iron oxides and their modified forms

Cr (VI) is highly toxic, carcinogenic and bio accumulative to living organisms. Its extensive industrial applications contaminate the natural aqueous ecosystems. Different techniques such as photocatalysis, adsorption, reverse osmosis, ion exchange, chemical precipitation, electrochemical reduction, solvent extraction etc. have been investigated to remove hexavalent chromium from contaminated water. Among these, adsorption is deliberated as the most effective and promising process because it is easy to design, simple to operate and suitable to avoid formation of secondary pollutants. Various adsorbents such as clay minerals, biosorbents, industrial wastes and magnetic nanomaterials have been used for the remediation of Cr (VI). The use of magnetic nanomaterials as adsorbents for removal of heavy metals has attracted much attention in recent years because of their large surface area and superparamagnetic characteristics. These materials not only exhibited high adsorption capacity but also could easily be recycled by applying an external magnetic field, making the separation process much easier. In this review, the adsorption behavior of different iron oxides such as maghemites, magnetites, ferrites and their modified forms towards the removal of Cr (VI) was discussed. The present review focuses on adsorption mechanism of Cr (VI) through the evaluation of adsorption capacities. Kinetics, thermodynamics and equilibrium studies for the adsorption process were depicted briefly. Optimum adsorption conditions (initial Cr (VI) concentration, pH, contact time, adsorbent dose and temperature), thermodynamic properties (ΔHo, ΔGo, ΔSo), kinetic model, fitted isotherm, adsorption mechanism and maximum adsorption capacities were listed in the table.

Improved Removal of Cr(VI) using Fe3O4/C Magnetic Nanocomposites Derived from Potassium Fulvic Acid

AbstractThe development of high performance magnetic nanomaterials has a good application prospect in wastewater treatment. Herein, Fe3O4/C nanocomposites was synthesized by eco‐friendly hydrolysis‐calcination method using potassium fulvic acid (FA−K) and FeCl3⋅6H2O as raw materials. The morphology of Fe3O4/C nanocomposites exhibited a loose pore structure with uniform size (a diameter ∼ 27 nm). The prepared Fe3O4/C nanocomposites possessed excellent dispersibility and magnetic properties in aqueous solution. The removal efficiency and maximum adsorption capacity of Fe3O4/C nanocomposites were 98% and 64.0 mg g−1, respectively. Moreover, it was confirmed that the adsorption mechanism of Cr(VI) contains electrostatic attraction and redox reaction. In this work, we provide a convenient means for manufacturing Fe3O4/C nanocomposites, and prove that FA−K is a cheap carbon source for manufacturing Fe3O4/C nanocomposites, which makes Fe3O4/C nanocomposites have potential application value in the effective adsorption of Cr(VI).

Enhanced hexavalent chromium (Cr(VI)) removal from aqueous solution by Fe–Mn oxide-modified cattail biochar: adsorption characteristics and mechanism

ABSTRACTIn the study, a novel Fe–Mn oxide-modified cattail biochar was synthesised and Cr(VI) adsorption on Fe–Mn oxide-modified biochar in water was investigated. XRF, XRD and FTIR results indicated that Fe and Mn were successfully loaded on the surface of Fe–Mn oxide-modified biochar. Batched experiments showed that Cr(VI) adsorption on Fe–Mn oxide-modified biochar fitted well with the pseudo-second-order kinetics model. The Freundlich isotherm adsorption model could better describe the isothermal adsorption process of Cr(VI) onto Fe–Mn oxide-modified biochar. The maximum saturated adsorption capacity data Qm of Fe–Mn oxide-modified biochar at 20°C, 30°C, and 40°C were respectively 46.43, 52.12, and 59.81 mg·g−1. The lower pH contributed to the adsorption of Cr(VI) onto Fe–Mn oxide-modified biochar. The effects of coexisting anions on the Cr(VI) removal efficiency were insignificant. Leaching experiments showed that the leakage risk of Mn2+ during the adsorption process was negligible. The adsorption mechanisms of Cr(VI) onto Fe–Mn oxide-modified biochar mainly involve electrostatic attraction, ligand exchange and complexation. All the results suggested that Fe–Mn oxide-modified biochars could serve as promising adsorbents for Cr(VI) pollution treatment.

Insight into the Adsorption-Interaction Mechanism of Cr(VI) at the Silica Adsorbent Surface by Evanescent Wave Measurement.

The investigation of adsorption performance at the adsorbent surface can help to reveal the treatment mechanism and improve the treatment efficiency of adsorption technology for heavy metal ions (HMIs). This work developed a methodology to investigate the adsorption behavior of HMI Cr(VI) at the silica surface by confined near-field evanescent wave (CNFEW) measurement. A silica optical fiber (SOF) was used as the adsorption substrate and light waveguide element to integrate both Cr(VI) adsorption and CNFEW production on its surface. According to the sensitive CNFEW response, the adsorption behavior of Cr(VI) was in situ monitored and real-time evaluated. The thermodynamic information of adsorption equilibrium constant (Kads) and adsorption free energy (ΔG) and dynamic information of the apparent adsorption rate (vads) and adsorption time (tads) were obtained through Langmuir isotherm and kinetic fitting, respectively. Different reaction performances between Cr(VI) and adsorption sites were successfully differentiated, evaluated, and characterized. A site-decided-mechanism was therefore presented to describe the surface interaction process for Cr(VI), which including fast adsorption on type I Si-O- site through electrostatic attraction with [Formula: see text] and slow adsorption on type II Si-OH site through coordinative interaction with ΔGSiOH-Cr(VI)II = -26.18 kJ mol-1. The adsorption mechanism of Cr(VI) at the SOF silica surface was furthermore verified by zeta potential analysis, Fourier transform infrared investigation, and fluorescence imaging. Unlike conventional ex situ or in bulk detection, the present CNFEW-based approach targets the "localized" adsorption of Cr(VI) adsorbed to the solid adsorbent surface. Consequently, our work favorably constructs a surface platform and provides new insights on understanding the adsorption mechanism for HMIs.

Novel materials for Cr(VI) adsorption by magnetic titanium nanotubes coated phosphorene

The accumulation of Cr(VI) will cause mutagenic and carcinogenic effects on humans. Therefore, the standard regulations have been governed by the EPA to control the chromium content in the effluent and drinking water and have made it mandatory [1]. For the better recovery of the adsorbent; Magnetic nano particle based phosphorene titanium nano tubes were used for the first time in action which has been proven to be superior for the Chormium pollutants. MNP-PN-TNT (Magnetic nanoparticle-Phosphorene-Titanium nano tubes) was synthesized from hydrothermal method in this study. The prepared material is used for effective removal of Cr(VI) from the water by adsorption technique in acidic environment. The adsorption capacity was found to be 35 mg g−1 at the initial concentration of 50 mg L−1maintainingthe temperature under 45 °C. The optimal operation condition is under pH 9, temperature of 25 °C, and dosage of 0.8 g L−1 obtained from RSM (Response Surface Methdology). The adsorption process of MNP-PN-TNT is conformed with a pseudo-second-order kinetic model. Cr(VI) adsorption behavior with MNP-PN-TNT, is spontaneous from the results of thermodynamics analysis. The adsorption mechanism of Cr(VI) with MNP-PN-TNT was evident by O1s, C1s, Cr 2p, Ti 2p, Fe 2p and P 2p of XPS. Cr(VI) is adsorbed with MNP-PN-TNT, in randomness during the adsorption process.

Adsorption mechanism of Cr(VI) onto GO/PAMAMs composites

Graphene oxide/polyamidoamine dendrimers (GO/PAMAMs) composites were used to remove Cr(VI) from simulated effluents, the adsorption kinetics and thermodynamics of Cr(VI) onto GO/PAMAMs were systematically investigated. The results showed that the optimum pH value was 2.5, the removal percentage reached 90.7% for 30 mg/L of Cr(VI) within 120 min. The adsorption process was well described by pseudo-second-order kinetic model. The maximum adsorption capacities of Cr(VI) onto GO/PAMAMs were found to be 131.58, 183.82 and 211.42 mg/g at 293.15, 303.15 and 313.15 K, respectively, which were calculated from the Langmuir model equation. The adsorption thermodynamic parameters indicate that the adsorption of Cr(VI) onto GO/PAMAMs is a spontaneous endothermic process. The XPS analysis reveals the adsorption and removal mechanism of Cr(VI) on GO/PAMAMs that first the Cr(VI) binds to the protonated amine of GO/PAMAMs, then Cr(VI) be reduced to Cr(III) with the assistance of π-electrons on the carbocyclic six-membered ring of GO in GO/PAMAMs, and then Cr(III) was released into solution under the electrostatic repulsion between the Cr(III) and the protonated amine groups.

Chitosan-coated black sesame (Sesamum indicum L.) seed pulp as a novel candidate adsorbent for Cr(VI) elimination.

This study evaluates the application of Cr(VI) adsorption from the prepared synthetic solution by black sesame (Sesamum indicum L.) seed pulp (BSSP) and chitosan (Cts)-coated black sesame seed pulp beads (Cts-BSSP). BSSP and Cts-BSSP were used as an adsorbent without any chemical or physical treatment to remove Cr(VI) from an aqueous medium. The results indicated that the Cr(VI) removal was pH-dependent and reached an optimum at pH 2.0. It has been observed that the percentage of adsorption increased from 62% to 95% when the amount of Cts-BSSP increased from 0.0125 g to 0.0250 g. The required adsorbent amount for the maximum removal was 0.05 g and 0.1 g for Cst-BSSP and BSSP, respectively. The contact time for the adsorption was 120 min and 90 min for BSSP and Cst-BSSP, respectively. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to explore the possible adsorption mechanism for Cr(VI). The equilibrium data for the BSSP and Cts-BSSP were used with the Langmuir and Freundlich adsorption isotherm models to assess the adsorption capacity and relevant mechanism. The adsorption capacity of the Cts-BSSP for Cr(VI) is relatively high compared to BSSP. The monolayer maximum adsorption capacities for Cr(VI) ions were 31.44 and 18.32 mg/g for Cts-BSSP and BSSP, respectively.

Comparison of adsorption affinity of anionic and cationic polyacrylamides for montmorillonite surface in the presence of chromium(VI) ions

Erosion, which is considered to be global problem, is the process of soil environment degradation due to the impact of wind (soil blowing, deflation) and water (soil washing, deep erosion). This leads to destruction of its structure, nutrients removal and finally bedrock exposition and desertification. One of the ways to prevent this phenomenon is the soil conditioners usage. These substances, also called soil flocculants, are macromolecular compounds which contribute to the reinforcement of soil structure as a result of its adsorption on the mineral surface. The soil conditioners commonly used in agriculture is ionic polyacrylamide (PAM)—both anionic and cationic. These macromolecular substances affect soil surface properties and adsorption behaviour of substances present in the environment—nutrients, organic molecules and also hazardous compounds as well as toxic heavy metals (i.e. chromium(VI) ions). The aim of this study was to investigate the impact of solution pH, type of ionic groups in the polyacrylamide macromolecules and chromium(VI) ion concentration on the adsorption mechanism of Cr(VI) and PAM on the montmorillonite surface. The adsorption and electrokinetic properties of the montmorillonite—AN PAM or CT PAM/Cr(VI) systems were examined by means of spectrophotometry, potentiometric titration, SEM, XRD and DRS methods. It was shown that in the adsorbed layer composed of PAM-Cr(VI) complexes reduction of Cr(VI) to Cr(III) takes place.

Synthesis of Novel Magnetic NiFe2O4 Nanocomposite Grafted Chitosan and the Adsorption Mechanism of Cr(VI)

This study prepared chitosan/NiFe2O4 (CNF) nanocomposites for the removal of Cr(VI) ions. The materials were characterized by various analytic methods including scanning electron microscopy, energy dispersive spectrometer, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and zeta potential. The adsorption performance of the nanocomposites was investigated and optimized with Cr(VI) as a target metal ion under various experimental conditions (contact time, adsorbent dosage, pH value, initial metal ion concentration). The results indicate that CNF exhibited better adsorption performance in comparison to original NiFe2O4 nanoparticles. Furthermore, the optimum adsorption capacity of CNF could be obtained within 120 min of contact time under pH 2.0 and 30 °C using 0.1 g CNF. Moreover, the experimental equilibrium data matched the Freundlich isotherm model under the studied concentrations for a specific temperature. The theoretical maximum adsorption capacity calculated with the Langmuir isotherm model reached 31.523 mg/g at 30 °C. Additionally, the adsorption kinetic data was found to be accorded well with the pseudo-second order kinetic model. Intraparticle diffusion was found to be one of the rate-limiting steps. Moreover, the metal-loaded adsorbents with good magnetic performance can easily be reclaimed from aqueous solution by magnetic separation, thus achieving solid–liquid separation, which suggests CNF as a potential recyclable adsorbent for hazardous Cr(VI) ions in waste-water.

One-step synthesis of 1,6-hexanediamine modified magnetic chitosan microspheres for fast and efficient removal of toxic hexavalent chromium

Here, we reported a novel one-step hydrothermal route for the facile synthesis of 1,6-hexanediamine functionalized magnetic chitosan microspheres (AF-MCTS), which were characterized by TEM, FT-IR and XPS to look into its morphology, surface functional groups, and adsorption mechanism of Cr(VI) from the aqueous solution. Cr(VI) adsorption on AF-MCTS as a function of contact time, Cr(VI) concentration, pH, and ionic strength was investigated. The adsorption process follows the Langmuir isotherm model and pseudo-second-order kinetic model. The AF-MCTS exhibited high performance for Cr(VI) removal with very fast adsorption rate (reaching equilibrium within 5 min) and high adsorption capacity (208.33 mg/g), which was 1.1 to 12 times that of other chitosan-based adsorbents. Cr(VI) adsorption onto AF-MCTS was an endothermic and spontaneous process. The recovery and reuse of AF-MCTS was demonstrated 11 times without obvious decrease in adsorption capacity. Mechanism study suggested that –OH rather than –NH2 groups in AF-MCTS were the electron donors for reducing Cr(VI) to Cr3+. Consumption or addition of H+ could trigger the reversible supramolecular coordination between Cr3+ and chitosan. Given the easy preparation, low cost, and remarkable performance, AF-MCTS composite is expected to show promising potential for the practical application in removing toxic Cr(VI) from aqueous media.

Highly Efficient and Reusable Montmorillonite/Fe₃O₄/Humic Acid Nanocomposites for Simultaneous Removal of Cr(VI) and Aniline.

Recyclable nanomaterials are in great need to develop clean technology for applications in the removal of water contaminants. In this work, easily separable montmorillonite/Fe3O4/humic acid (MFH) nanocomposites were fabricated through a facile hydrothermal route. It was found the adsorption ability and stability of MFH was significantly enhanced due to the synergistic effects between montmorillonite, Fe3O4 nanoparticles and humic acid. The MFH nanocomposites are highly efficient and recyclable as they can remove at least 82.3% of Cr(VI) and 95.1% of aniline in six consecutive runs. The adsorption mechanism was investigated by analyzing the kinetic parameters of pseudo first-order, pseudo second-order, and intraparticle diffusion models and describing the equilibrium isotherms of Langmuir and Freundlich models. Results indicated different adsorption mechanisms of Cr(VI) and aniline by MFH. The readily synthesized MFH nanocomposites can act as effective and practical materials for environmental applications.

Effective Removal of Chromium(III) from Low Concentration Aqueous Solution Using a Novel Diazene/Methoxy-Laced Coordination Polymer.

In this study, a novel coordination polymer [CdL2(H2O)0.5]n (1), [HL = 4-(2-(4-((pyridin-3-yl)methoxy)phenyl)diazenyl)benzoic acid] was fabricated via an in situ ligand transformation reaction under solvothermal conditions. The as-prepared polymer exhibited a selectivity and efficiency for Cr(III) removal with a high uptake capacity of 106.13 mg·g−1. Interestingly, even in the low concentration (0.02–0.20 ppm), it still performs a relatively high efficiency (≥ 92.5%) towards the removal of Cr(III) in aqueous solution. Remarkably, it also presents good selectivity and high efficiency (93.3%) for Cr(III) removal in the presences of interfering metal ions. The good removal performance for Cr(III) was demonstrated to be a structure-dependent chemical process between polymer and Cr(III) involving the diazene and methoxy groups in polymer 1, which happened not only on the surfaces of the adsorbent but also in the pores of polymer, giving rise to a strong affinity toward Cr(III) adsorption. The possible adsorption mechanism of Cr(III) was proposed and systematically verified by FT-IR, scanning electron microscope (SEM), atomic force microscope (AFM) and energy dispersive spectrometer (EDS) measurements.