Facile preparation of hybrid porous polyanilines for highly efficient Cr(vi) removal

In the present work, leucoemeraldine-based hybrid porous polyanilines (LHPPs) have been synthesized by the Friedel–Crafts reaction of leucoemeraldine and octavinylsilsesquioxane (OVS) for Cr(vi) removal. The resulting LHPPs were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and N₂ adsorption–desorption. The findings indiated that the LHPPs were amorphous, with apparent surface areas (S_BET) in the range of 147 to 388 m² g⁻¹ and total volumes in the range of 0.13 to 0.44 cm³ g⁻¹. Cr(vi) removal experiments displayed that the LHPPs exhibited highly efficient Cr(vi) removal performance. The maximum Cr(vi) removal capacity of LHPP-1 was 990.1 mg g⁻¹ at 308 K and pH 1, which is higher than those of other reported polyaniline-based adsorbents. The adsorption process was a spontaneous, endothermic and chemical adsorption process. The adsorption behavior agreed well with Langmuir models and pseudo second-order equations. X-ray photoelectron spectroscopy and Fourier transformed infrared (FTIR) spectroscopy analysis revealed that the highly efficient Cr(vi) removal performance can be mainly attributed to the existence of numerous amine and imine groups on the surface of the LHPPs; these can function as adsorption active sites for Cr(vi) removal through electrostatic adsorption and reduction to Cr(iii) under acidic conditions. Moreover, the LHPPs exhibited excellent adsorption selectivity for Cr(vi) despite the presence of other metal ions (K⁺, Cu²⁺, Mn²⁺) and anions (NO₃⁻, SO₄²⁻). Therefore, the LHPPs have potential applications for Cr(vi) removal in industrial wastewater.

In the present work, leucoemeraldine-based hybrid porous polyanilines (LHPPs) have been synthesized by the Friedel–Crafts reaction of leucoemeraldine and octavinylsilsesquioxane (OVS) for Cr(vi) removal.     

Mechanism and modeling of hexavalent chromium interaction with a typical black soil: the importance of the relationship between adsorption and reduction

Black soils have a significant retention effect on the migration of Cr(vi) towards groundwater, and Cr(vi) adsorption and reduction are both involved in this process. However, the adsorption and reduction of Cr(vi) were always investigated separately in previous studies resulting in an unclear relationship between them. In this study, the adsorption and reduction kinetic processes of Cr(vi) by a typical black soil were separately investigated under different initial Cr(vi) concentrations (40–400 mg L⁻¹) and pH conditions (3.5–7.0) by the means of desorption treatment, and the equilibrium relationship between aqueous and adsorbed Cr(vi) was innovatively established based on the kinetic data. It was found that under pH 5.7 the adsorbed Cr(vi) content on soil particles was linearly correlated with the remaining Cr(vi) concentration in solution with time (R² = 0.98), and the reduction rate of Cr(vi) in the reaction system was linearly correlated with the adsorbed Cr(vi) content on soil particles with time (R² = 0.99). With pH decreasing from 7.0 to 3.5, the partition of Cr(vi) between solid and aqueous phases turned out to be of a non-linear nature, which can be fitted better by the Freundlich model. The retention of Cr(vi) by black soil was determined to follow the “adsorption–reduction” mechanism, where the Cr(vi) was first rapidly adsorbed onto the soil particles by a reversible adsorption reaction, and then the adsorbed Cr(vi) was gradually reduced into Cr(iii). A two-step kinetic model was developed accordingly, and the experimental data were fitted much better by the two-step adsorption–reduction kinetic model (R² = 0.89 on average) compared with the traditional first-order and second-order kinetic models (R² = 0.66 and 0.76 on average respectively). This paper highlights the novel two step kinetic model developed based on the proposed “adsorption–reduction” mechanism of Cr(vi) retention by a typical black soil.

A novel two-step kinetic model was developed based on the proposed “adsorption–reduction” mechanism of Cr(vi) retention by a typical black soil.     

Efficient removal of chromate ions from aqueous solution using a highly cost-effective ferric coordinated [3-(2-aminoethylamino)propyl]trimethoxysilane–MCM-41 adsorbent

The present investigation involves synthesis and characterization of MCM-41–AEAPTMS–Fe(iii)Cl using coordinated Fe(iii) on MCM-41–AEAPTMS for efficient removal of hazardous Cr(vi) ions from aqueous solution. The adsorbent MCM-41–AEAPTMS–Fe(iii)Cl was characterized using small-angle X-ray diffraction (SAX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier-transform infrared (FT-IR) and Brunauer–Emmett–Teller (BET) surface analyzer techniques. The BET surface area was found to be 87.598 m² g⁻¹. The MCM-41–AEAPTMS–Fe(iii)Cl effectively adsorbs Cr(vi) with an adsorption capacity acquiring the maximum value of 84.9 mg g⁻¹ at pH 3 at 298 K. The data followed pseudo-second-order kinetics and obeyed the Langmuir isotherm model. The thermodynamic data proved the exothermic and spontaneous nature of Cr(vi) ion adsorption on MCM-41–AEAPTMS–Fe(iii). Further, the higher value of ΔH° (−64.339 kJ mol⁻¹) indicated that the adsorption was chemisorption in nature.

The present investigation involves synthesis and characterization of MCM-41–AEAPTMS–Fe(iii)Cl using coordinated Fe(iii) on MCM-41–AEAPTMS for efficient removal of hazardous Cr(vi) ions from aqueous solution.     

Characterization of CMC–LDH beads and their application in the removal of Cr(vi) from aqueous solution

In this study, CMC–LDH beads were prepared and characterized using SEM, FTIR and TG analysis. The beads were applied for the removal of Cr(vi) from aqueous solution. The effects of adsorbent dosage, initial pH and initial concentration of Cr(vi) solution on Cr(vi) uptake were investigated in detail. Moreover, adsorption isotherms and adsorption kinetic models were employed to analyze the adsorption process, and a preliminary study of the reusability of the adsorbent was performed. The experimental results showed that the CMC–LDH beads could remove Cr(vi) from aqueous solution efficiently. When the initial concentration of the Cr(vi) solution was 100 mg L⁻¹ and the adsorbent dosage was 12 g L⁻¹, the removal efficiency of Cr(vi) reached 96.2%. After the CMC–LDH beads were reused 10 times, the removal efficiency of Cr(vi) still remained at 89.6%.

CMC–LDH beads were prepared, characterized and applied for the removal of heavy metal ions in this study.     

Freezing/thawing pretreatment of dormant Aspergillus niger spores to increase the Cr(vi) adsorption capacity: process and mechanism

Hexavalent chromium is a widespread pollutant that threatens ecological and human health. However, its removal from the environment is limited by the high cost and energy consumption rate of current technologies. In this study, the Cr(vi) biosorption mechanism of Aspergillus niger spores pretreated by freezing/thawing was studied by batch experiments and surface chemistry analyses. The results indicated that pretreatment enhanced the spores'' Cr(vi) removal efficiency. The cell surface, internal functional groups, and morphology of the freezing/thawing-pretreated spores (FTPS) before and after Cr(vi) loading were characterized by advanced spectroscopy techniques such as SEM-EDAX, XPS, FTIR, and FETEM analyses. The SEM and BET data showed that the surface of FTPS was rougher than that of untreated spores. The XPS data showed that FTPS bio-transformed Cr(vi) into Cr(iii). The intracellular localization of chromium was visualized by FETEM, and both surface and intracellular structures removed Cr(vi) following pseudo-second-order biosorption kinetics. The biosorption dynamics of Cr(vi) fit the Langmuir isotherm model describing a monolayer. These results suggest that freezing/thawing pretreatment of A. niger spores could lead to the development of a novel, efficient biomaterial for the removal of Cr(vi).

Freezing/thawing pretreatment of A. niger spores could lead to the development of a novel, efficient biomaterial for the removal of Cr(vi).     

High dispersions of nano zero valent iron supported on biochar by one-step carbothermal synthesis and its application in chromate removal

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution. High dispersions of nanoscale zero-valent iron supported on biochar were successfully synthesized by the pyrolysis of an iron-impregnated biomass (corn stover) as the carbon and iron source under nitrogen atmosphere. The effects of the pyrolytic temperature on the Fe mineralogies formed on the biochar are discussed. In general, the effects of the treatment time, initial solution pH, and nZVI/BC dosage on the Cr(vi) removal are presented. The results showed high crystallinity and purity, and nZVI/BC was obtained at a pyrolytic temperature of 800 °C. The batch experimental results determined that the adsorption capacity of Cr(vi) decreases with the increase in the initial pH value from 4.0 to 10.0. The Cr(vi) adsorption kinetics data effectively followed a pseudo-second-order kinetics with a calculated rate constant of 0.0.3396 g mg⁻¹ min⁻¹. The calculated thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were evaluated, and the results indicated that the Cr(vi) reduction on nZVI/BC was a spontaneous and endothermic process. The adsorption mechanism of Cr(vi) was investigated by XRD and XPS analyses and the results demonstrated that Cr(vi) was reduced to Cr(iii) and the oxidation of nZVI occurred during the reaction process. These results prove that nZVI/BC synthesized by a one-step carbothermal method can be considered as a potential candidate for the removal of Cr(vi) from aqueous solutions.

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution.     

Efficient recovery of Cr(vi) from electroplating wastewater by iron-modified sludge-based hollow-structured porous carbon: coexistence effects and competition for adsorption

In the present work, porous carbon was made from sewage sludge and hybrid liriodendron leaves, and modified with iron ions (Fe@LS-BC) carried out on Cr(vi) in aqueous solution from a single-component system and in competitive biosorption with methyl orange (MO) from a binary-component system. The iron ion-modified porous carbon (Fe@LS-BC) showed higher efficiency in the removal of Cr(vi) compared to porous carbon prepared by the co-pyrolysis of sludge and hybrid liriodendron leaves. The incorporation of the Fe element improved the ability of the material to redox Cr(vi), while imparting magnetic characteristics to the porous carbon and improving the reusability of the porous carbon. On the other hand, Fe@LS-BC exhibited a better pore volume, facilitating the contact of the material with Cr(vi) ions. The highest adsorption capacity was 0.33 mmol g⁻¹, and the adsorption experimental results for the single-component and binary-component systems of Cr(vi) matched well with the Langmuir–Freundlich models. When the concentration of MO was 0.2 and 0.8 mmol L⁻¹, respectively, the highest adsorption capacity of Cr(vi) was 0.35 and 0.46 mmol g⁻¹ in the binary system. The positively charged N–CH₃⁺ on the MO molecule promoted the electrostatic adsorption between HCrO₄⁻, CrO₄²⁻, and Fe@LS-BC, and increased the adsorption potential of Cr(vi).

Mechanism for the adsorption of hexavalent chromium and methyl orange in a binary system.     

Removal of Pb(ii) and Cr(vi) from aqueous solutions using the prepared porous adsorbent-supported Fe/Ni nanoparticles

In this study, Fe/Ni nanoparticles supported by a novel fly ash-based porous adsorbent (FBA-Fe/Ni) for Cr(vi) and Pb(ii) removal were investigated. In order to enhance the reactivity of zero-valent iron (ZVI), ZVI particles were deposited on the surface or in the inner pores of FBA as a support material and Ni nanoparticles were introduced. FBA was prepared with the solid waste such as Enteromorpha prolifera, bentonite and fly ash. FBA-Fe/Ni was characterized via Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and the Brunauer–Emmett–Teller model and energy-dispersive spectrometry. The effects of various parameters on Cr(vi) and Pb(ii) removal by FBA-Fe/Ni, such as FBA-Fe/Ni dosage, pH of the solution, reaction temperature, Cr(vi) and Pb(ii) concentrations, co-existing ions and ionic strength were discussed. The possible removal mechanisms were proposed and the results indicated that there was a three-step reaction including the adsorption of Cr(vi) and Pb(ii) on the surface of FBA-Fe/Ni, the subsequent reduction and precipitation. The removal capacity of Cr(vi) and Pb(ii) by FBA-Fe/Ni was 25.07 mg g⁻¹ and 164.19 mg g⁻¹ at 303 K with an initial concentration of 1000 mg L⁻¹ and FBA-Fe/Ni dosage of 0.20 g. In conclusion, this work demonstrated that FBA-Fe/Ni was a promising alternative material for Cr(vi) and Pb(ii) removal.

In this study, Fe/Ni nanoparticles supported by a novel fly ash-based porous adsorbent (FBA-Fe/Ni) for Cr(vi) and Pb(ii) removal were investigated.     

Positive effects of concomitant heavy metals and their reduzates on hexavalent chromium removal in microbial fuel cells

Cr(vi) laden wastewaters generally comprise a range of multiple heavy metals such as Au(iii) and Cu(ii) with great toxicity. In the present study, cooperative cathode modification by biogenic Au nanoparticles (BioAu) reduced from aqueous Au(iii) and in situ Cu(ii) co-reduction were investigated for the first time to enhance Cr(vi) removal in microbial fuel cells (MFCs). With the co-existence of Cu(ii) in the catholyte, the MFC with carbon cloth modified with nanocomposites of multi-walled carbon nanotubes blended with BioAu (BioAu/MWCNT) obtained the highest Cr(vi) removal rate (4.07 ± 0.01 mg L⁻¹ h⁻¹) and power density (309.34 ± 17.65 mW m⁻²), which were 2.73 and 3.30 times as high as those for the control, respectively. The enhancements were caused by BioAu/MWCNT composites and deposited reduzates of Cu(ii) on the cathode surface, which increased the adsorption capacity, electronic conductivity and electrocatalytic activity of the cathode. This study provides an alternative approach for efficiently remediating co-contamination of multiple heavy metals and simultaneous bioenergy recovery.

The cooperative cathode modification by BioAu from Au(iii) and in situ Cu(ii) co-reduction enhanced Cr(vi) removal and bioelectricity generation in MFCs.     

Hexavalent chromium ion and methyl orange dye uptake via a silk protein sericin–chitosan conjugate

Sericin, a protein waste product of the silk industry, was crosslinked with chitosan, and a chitosan–sericin conjugate (CS) was prepared, characterized and used to remove hexavalent chromium (Cr(vi)) ions and methyl orange (MO) dye from aqueous solutions. The CS was shown to effectively remove Cr(vi) ions and MO dye at maximum adsorption capacities (Langmuir) of 139 mg g⁻¹ for Cr(vi) ions and 385 mg g⁻¹ for MO dye. Moreover, the adsorption of both Cr(vi) ions and MO dye was highly pH dependent and varied under different experimental conditions. Cr(vi) ion and MO dye uptake by the CS was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry analysis. Additionally, XPS analysis of the Cr(vi)-loaded CS revealed that Cr(vi) was reduced to the less toxic Cr(iii). The CS was shown not only to be highly amenable to regeneration, but also to be able to effectively remove MO dye and Cr(vi) ions from a binary mixture.

Sericin, a protein waste product of the silk industry, was crosslinked with chitosan, and a chitosan–sericin conjugate (CS) was prepared, characterized and used to remove hexavalent chromium (Cr(vi)) ions and methyl orange dye from aqueous solutions.     

Self-assembly preparation of lignin–graphene oxide composite nanospheres for highly efficient Cr(vi) removal

Recently, research interest in the application of lignin is growing, especially as adsorbent material. However, single lignin shows unsatisfactory adsorption performance, and thus, construction of lignin-based nanocomposites is worth considering. Herein, we introduced graphene oxide (GO) into lignin to form lignin/GO (LGNs) composite nanospheres by a self-assembly method. FTIR and ¹H NMR spectroscopy illustrated that lignin and GO are tightly connected by hydrogen bonds. The LGNs as an environmental friendly material, also exhibit excellent performance for Cr(vi) removal. The maximum sorption capacity of LGNs is 368.78 mg g⁻¹, and the sorption efficiency is 1.5 times than that of lignin nanospheres (LNs). The removal process of Cr(vi) via LGNs mainly relies on electrostatic interaction, and it also involves the reduction of Cr(vi) to Cr(iii). Moreover, LGNs still have high adsorption performance after repeating five times with the sorption capacity of 150.4 mg g⁻¹ in 200 mg g⁻¹ Cr(vi) solution. Therefore, the prepared lignin–GO composite nanospheres have enormous potential as a low-cost, high-absorbent and recyclable adsorbent, and can be used in wastewater treatment.

Lignin/GO (LGNs) composite nanospheres were prepared by self-assembly method, which showed excellent adsorption performance for Cr(vi) removal.     

Synthesis and evaluation of ion-imprinted composite membranes of Cr(vi) based on β-diketone functional monomers

Using Cr(vi) as the imprinted ions and 2-allyl-1,3-diphenyl-1,3-propanedione (ADPD) (a compound synthesized by independent design) as the functional monomer, a series of chromium ion-imprinted composite membranes (Cr(vi)-IICMs) and corresponding non-imprinted composite membranes (NICMs) were synthesized and tested. The results showed that the Cr(vi)-IICM₁₀ membrane prepared under optimal experimental conditions exhibited a high adsorption capacity towards Cr(vi) (Q = 30.35 mg g⁻¹) and a high imprinting factor (α = 2.70). The structural characteristics of Cr(vi)-IICM₁₀ and NICM₁₀ were investigated using FE-SEM, ATR-FTIR, and BET techniques combined with UV-Vis photometry and inductively coupled plasma emission spectrometry (ICP-OES) to evaluate the adsorption performance and permeation selectivity, while the effect on adsorption permeance of varying the experimental conditions including the solvent type, pH, and temperature was also investigated. The results showed that Cr(vi)-IICM₁₀ is a mesoporous material with excellent permeation selectivity, reusability, and favorable pH response, and that its adsorption behavior is in accordance with the Langmuir model and pseudo-first-order kinetics. Thus, Cr(vi)-IICM₁₀ shows great potential towards utilization as a “smart membrane” to control the separation and removal of Cr(vi) in wastewater, and also proved a reasonable design of the new functional monomer ADPD.

Using Cr(vi) as the imprinted ions and 2-allyl-1,3-diphenyl-1,3-propanedione (a compound of independent design) as the functional monomer, a series of chromium ion-imprinted composite membranes and corresponding non-imprinted composite membranes were synthesized and tested.     

Adsorption and reduction of hexavalent chromium on magnetic greigite (Fe3S4)-CTAB: leading role of Fe(ii) and S(−ii)

In this study, a facile one-step route was used to synthesize a novel magnetic mesoporous greigite (Fe₃S₄)-CTAB composite, which was utilized to remove hexavalent chromium (Cr(vi)). The optimized Fe₃S₄-CTAB_0.75 composite with a CTAB dosage of 0.75 g possessed the maximum specific surface, showing the highest Cr(vi) adsorption capacity of 330.03 mg g⁻¹. The mechanism analysis revealed that Fe(ii) and S(−ii) were critical for the reduction of Cr(vi). CTAB can promote the removal of Cr(vi) by Fe₃S₄-CTAB composites, possibly due to increased S(−ii) concentration, better dispersion of nanoparticles, and greater zeta potential. Besides, there is mild effect of Fe⁰ on Cr(vi) removal, which is confirmed by the disappearance of the Fe⁰ peak from the XPS analysis. The pseudo-second-order kinetic model could explain the Cr(vi) removal processes well. The adsorption of Cr(vi) at different initial concentrations was more consistent with a Langmuir isotherm. The existence of H⁺ was beneficial for Cr(vi) removal by Fe₃S₄-CTAB_0.75. Our work confirmed that the obtained Fe₃S₄-CTAB_0.75 composites exhibit considerable potential for Cr(vi) removal from aqueous solution.

The presence of CTAB can promote the removal of hexavalent chromium from the Fe₃S₄-CTAB surface.     

Lead and uranium sorptive removal from aqueous solution using magnetic and nonmagnetic fast pyrolysis rice husk biochars

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars. The porosity, specific surface area, hydrophobility, and reusability of biochar were effectively improved (1–2 times) after magnetic modification. The optimum adsorption conditions were as follows: biochar loading was 0.4 g L⁻¹, pH value was 7.0, and anion strength of NO₃⁻ and PO₄³⁻ were 0.01 mol L⁻¹ for Pb(ii) and 0.04 mol L⁻¹ for U(vi) respectively. Compared with U(vi), Pb(ii) had the faster adsorption rate and higher adsorption capacity on magnetic biochar (MBC). The adsorption experimental data were well fitted by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of Pb(ii) and U(vi) on MBC was 129 and 118 mg g⁻¹ at 328 K respectively, which was significantly higher than that of other sources biochars. Pb(ii) was mainly bonded to biochar by physisorption but the adsorption of U(vi) on biochar was mostly chemisorption. Fe oxides in MBC noticeably improved the ion exchange and complexation action between biochar and metal ion especially for U(vi). The experimental results confirmed MBC material can be used as a cost-effective adsorbent for the removal of Pb(ii) and U(vi) and can be separated easily from aqueous solution when application.

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars.     

Effective removal of Cr(vi) from aqueous solution by biochar supported manganese sulfide

In order to remove hexavalent chromium (Cr(vi)) efficiently and simplify the adsorbent preparation process, we employed a single step method to prepare a new biochar supported manganese sulfide material. The nanoscale MnS particles were highly soldered on the biochar support surface, and this adsorbent displayed the effective removal of Cr(vi) (98.15 mg L⁻¹) via synergistic effect between adsorption and reduction/precipitation under weak acid conditions (pH = 5.0–6.0). The adsorption kinetic data were described well by the pseudo second-order kinetic model, suggesting that the reaction process was a chemisorption process. The adsorption isotherm data were described well by the Redlich–Peterson model, further suggesting that this reaction was a hybrid chemical reaction-sorption process. In addition, the Dubinin–Radushkevich isotherm model with 8.28, 8.57, and 12.91 kJ mol⁻¹ adsorption energy also suggests that it was a chemisorption process. The simple and eco-friendly preparation process, low-cost, and the high removal efficiency could make it a promising material for the purification of Cr(vi)-contaminated wastewater.

In order to remove hexavalent chromium (Cr(vi)) efficiently and simplify the adsorbent preparation process, we employed a single step method to prepare a new biochar supported manganese sulfide material.     

Facile fabrication of a phosphonium-based ionic liquid impregnated chitosan adsorbent for the recovery of hexavalent chromium

Chitosan adsorbents impregnated with a phosphonium-based ionic liquid (Chi_IL), trioctyldodecyl phosphonium chloride, were prepared for the adsorption of hexavalent chromium and compared to the performance of native chitosan. The physical and chemical properties of the adsorbents were characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Effects of various parameters, such as pH, adsorbent dosage, contact time, temperature, and multi-component systems, were systematically examined. Chi_IL showed a high adsorption capacity (282.6 mg g⁻¹) compared to native chitosan (238.1 mg g⁻¹). The adsorption kinetics of the metals followed a pseudo-second-order kinetic model, and the experimental data were a good fit for the Freundlich isotherm model. Following the isotherm and activation energy parameter, adsorption of Cr(vi) onto Chi_IL follows a chemisorption process, possibly through an anionic exchange with the anion of the IL. The thermodynamic parameters suggested that the adsorption of Cr(vi) is a spontaneous and exothermic reaction. In the column adsorption, Chi_IL exhibited a longer column exhaustion time than that of native chitosan owing to the enhanced adsorption capacity caused by the introduction of IL. Moreover, the column with the parameters of 6 cm bed depth, 5 mL min⁻¹ flow rate, and 50 mg L⁻¹ was able to achieve the best performance in Cr(vi) adsorption.

Trioctyldodecyl phosphonium chloride was impregnated onto chitosan and able to efficiently remove Cr(vi) in batch and continuous adsorption. The Cr(vi) was chemically adsorbed onto the adsorbent through anionic exchange with the ionic liquid moieties.     

Ion-imprinted modified molecular sieves show the efficient selective adsorption of chromium(vi) from aqueous solutions

Molecular sieve 5A was modified with (3-aminopropyl) triethoxysilane (APTES) as the support matrix, on which 4-VP was used as the ionic imprinting group. The as-prepared IIZMS-APTES was applied as the adsorbent for the recovery of chromium(vi) from aqueous solutions. The adsorbent was characterized via Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), and X-ray diffraction (XRD). The influences of adsorption time, concentration of the ions, initial pH, and temperature on the adsorption performance to Cr(vi) were investigated. The selectivity and reusability of IIZMS-APTES are also evaluated. The results showed that the maximum adsorption capacity reached 56.46 mg g⁻¹ when the initial concentration of metal ions was at 100 mg L⁻¹ at pH 2 and 30 °C. The adsorption process followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. The IIZMS-APTES exhibits an efficient selective adsorption of Cr(vi) from aqueous solutions.

Molecular sieve 5A was modified with (3-aminopropyl) triethoxysilane (APTES) as the support matrix, on which 4-VP was used as the ionic imprinting group.     

Synthesis and characterization of activated carbon from sugar beet residue for the adsorption of hexavalent chromium in aqueous solutions

A series of micro–mesoporous activated carbons (ACs) were prepared from sugar beet residue by a two-step method including KOH chemical activation and were used for Cr(vi) removal from aqueous solutions. Several characterization techniques, including SEM, TEM, N₂ adsorption, XRD, FTIR, and Raman spectroscopy, were used to determine the chemical and physical characteristics of the ACs, and the adsorption properties of the ACs were tested. The results indicated that the high specific surface area of the ACs reached 2002.9 m² g⁻¹, and the micropore surface area accounts for 85% of the total area. The optimal conditions for achieving the maximum Cr(vi) adsorption capacity of 163.7 mg g⁻¹ by the ACs were activation with a KOH/carbon ratio of 3.0, an initial Cr(vi) concentration of 400 mg L⁻¹, an adsorbent dose of 2.0 g L⁻¹ and pH of 4.5. Therefore, the ACs exhibit excellent adsorption performance for removing Cr(vi) from aqueous solutions. According to an investigation of the adsorption process, the adsorption isotherm is most consistent with the Langmuir isotherm model, and the adsorption kinetics were well described by the pseudo-second-order model.

A series of micro–mesoporous activated carbons (ACs) were prepared from sugar beet residue by a two-step method including KOH chemical activation and were used for Cr(vi) removal from aqueous solutions.     

The development of a ternary nanocomposite for the removal of Cr(vi) ions from aqueous solutions

The aim of this study is to develop a ternary nanocomposite (NC) of polyaniline (PANI)/2-acrylamido-2-methylpropanesulfonic acid (AMPSA)-capped silver nanoparticles (NPs)/graphene oxide quantum dots (PANI/Ag (AMPSA)/GO QDs) as an efficient adsorbent for the removal of the highly toxic hexavalent chromium (Cr(vi)) from polluted water. PANI/Ag (AMPSA)/GO QDs NC was synthesized via in situ oxidative polymerization. The effects of pH, adsorbent dose, initial concentration, temperature, contact time, ionic strength and co-existing ions on the removal of Cr(vi) by PANI/Ag (AMPSA)/GO QDs were investigated. The PANI/Ag (AMPSA)/GO QDs NC (25.0 mg) removed 99.9% of Cr(vi) from an aqueous solution containing 60 mg L⁻¹ Cr(vi) ions at pH 2. Energy dispersive X-ray (EDX) and inductively coupled plasma spectrometry (ICP) studies confirmed the adsorption of Cr(vi) and that some of the adsorbed Cr(vi) was reduced to Cr(iii). Cr(vi) removal by the PANI/Ag (AMPSA)/GO QDs NC followed the pseudo-second order kinetic model, and the removal was highly selective for Cr(vi) in the presence of other co-existing ions. In summary, the PANI/Ag (AMPSA)/GO QDs NC has potential as a novel adsorbent for Cr(vi).

The aim is to develop a ternary nanocomposite of polyaniline/2-acrylamido-2-methylpropanesulfonic acid-capped silver nanoparticles/graphene oxide quantum dots as an efficient adsorbent for the removal of the highly toxic hexavalent chromium (Cr(vi)) from polluted water.