Adsorption Of Cr Research Articles

Cost-effective walnut shell biosorbent for efficient Cr(VI) removal from water: Batch adsorption and optimization using RSM-BBD

The conversion or recycling of waste materials into usable products is a sustainable and ecologically benign strategy, aligning with sustainable development and circular economy principles. This study presents a straightforward and cost-effective method for transforming walnut shells, commonly found in agricultural waste, into a biosorbent material highly effective in eliminating hexavalent chromium (Cr(VI)) from water. The prepared material underwent several analyses to determine its physical characteristics and surface chemistry, revealing an amorphous structure similar to lignocellulosic materials. Using Response Surface Methodology (RSM-BBD), we accurately forecasted and optimized the Cr(VI) adsorption process, evaluating and enhancing factors such as pH, biosorbent dosage, pollutant concentration, and adsorption time. Significant enhancement in the removal percentage (%R) was achieved, reaching 100 % after optimization. The RSM-BBD model provided high-quality prediction for data fitting (R² = 0.999). Various kinetic models, including PFO, PSO, and IPD models, were employed, with the PSO model providing the best depiction of adsorption. Equilibrium data analysis using the Langmuir, Freundlich, Redlich-Peterson and Temkin models revealed that the Freundlich model and R-P better fit the adsorption isotherm of Cr(VI) on treated walnut shell (WST). Furthermore, examination of Gibbs free energy and enthalpy indicated that the adsorption of Cr(VI) onto walnut shells is a spontaneous and exothermic reaction, resulting in the release of thermal energy.

Synthesis, characterization of hydroxyapatite from pomegranate fruit peel for Cr (VI) adsorption: Process modelling, kinetic and isotherm studies

The present work focuses on preparation of hydroxyapatite from pomegranate peels by precipitation method. The hydroxyapatite derived from pomegranate fruit peels (HA-PP) was characterized by XRD, FT-IR, SEM-EDS and BET techniques. The HA-PP has mesoporous in structure and had an area of 99.021 m2/g. Further HA-PP was used as adsorbent for the removal of Cr (VI) ion particles from K2Cr2O7. The adsorption trials were executed and found the optimized solution using response surface methodology (RSM). The experiments included parameters like pH 2, initial chromium concentration 200 mg/L, adsorbent loading 0.8 g, and contact time 60 min, respectively. Cr (VI) removal was 89.4 % at the optimum combination of these process parameters. A mathematical and statistical optimizing technique response surface methodology (RSM) was applied to verify the interactive effects of various parameters on the adsorption capacity. The analysis of variance (ANOVA) was used to predict the adequacy of the model (F 82.16) shows developed model is valid with R2 value 0.987, and p-value (>0.1). In this the Langmuir adsorption isotherm and the pseudo-second-order kinetic model are well explained for Cr (VI) adsorption onto HA-PP. This reaction is spontaneous and endothermic, as indicated by the negative change in the standard free energy (ΔG0 = −0.1732) and ΔH0 (+4.71) value at the selected temperature. The ΔS0 (+15.89) further confirms that the randomness increased at the solid-solution interface during adsorption.

English

English

A Novel Magnetic and Amino Grafted Chitosan-Based Composite for Efficient Adsorption and Reduction of Cr(VI): Performance and Removal Mechanism

A Novel Magnetic and Amino Grafted Chitosan-Based Composite for Efficient Adsorption and Reduction of Cr(VI): Performance and Removal Mechanism

A two-dimensional cobalt-based metal–organic framework efficiently adsorbs Cr(VI) from wastewater

Metal-organic frameworks (MOFs) display multi-level pores and abundant adsorption sites, which can effectively adsorb Cr(VI) from wastewater. In this paper, x-ray single crystal diffraction analysis showed that both the N atom and two carboxyl groups in L2− of [Co(L)(H2O)2]n (1) (H2L = 3, 5-pyridinedicarboxylic acid) underwent coordination reactions with Co(II) in μ3-η1:η1:η1 fashion, giving rise to the formation of a two-dimensional structure. The nano adsorbent of 1 (2D-Co-MOF-N) with a particle diameter about 100 nm was successfully prepared by cell disruption method. The optimal conditions for 2D-Co-MOF-N to adsorb Cr(VI) from wastewater were observed at pH 6.5, T = 30 °C, and a dosage of 0.10 g/L, achieving a maximum adsorption capacity of 207.93 mg/g which was better than most MOFs adsorbents. The present of Cl−, NO3–, SO42−, and PO43− in wastewater inhibited the adsorption of Cr(VI) by 2D-Co-MOF-N due to competitive adsorption. Cycling experiments showed that 2D-Co-MOF-N exhibited admirable structural and performance stability, which could be deemed as a potential candidate for the removal toxic ions from actual wastewater.

Microscopic and macroscopic analysis of hexavalent chromium adsorption on polypyrrole-polyaniline@rice husk ash adsorbent using statistical physics modeling

This paper contributed with new findings to understand and characterize a heavy metal adsorption on a composite adsorbent. The synthesized polypyrrole–polyaniline@rice husk ash (PPY–PANI@RHA) was prepared and used as an adsorbent for the removal of hexavalent chromium Cr(VI). The adsorption isotherms of Cr(VI) ions on PPY–PANI@RHA were experimentally determined at pH 2, and at different adsorption temperatures (293, 303, and 313 K). Multi-layer model developed using statistical physics formalism was applied to theoretically analyze and characterize the different interactions and ion exchanges during the adsorption process for the elimination of this toxic metal from aqueous solutions, and to attribute new physicochemical interpretation of the process of adsorption. The physicochemical structures and properties of the synthesized PPY–PANI@RHA were characterized via Fourier transform infrared spectroscopy (FTIR). Fitting findings showed that the mechanism of adsorption of Cr(VI) on PPY–PANI@RHA was a multi-ionic mechanism, where one binding site may be occupied by one and two ions. It may also be noticed that the temperature augmentation generated the activation of more functional groups of the composite adsorbent, facilitating the interactions of metal ions with the binding sites and the access to smaller pore. The energetic characterization suggested that the mechanism of adsorption of the investigated systems was exothermic and Cr(VI) ions were physisorbed on PPY-PANI@RHA surface via electrostatic interaction, reduction of Cr(VI) to Cr(III), hydrogen bonding, and ion exchange. Overall, the utilization of the theory of statistical physics provided fruitful and profounder analysis of the adsorption mechanism. The estimation of the pore size distribution (PSD) of the polypyrrole-polyaniline@rice husk ash using the statistical physics approach was considered stereographic characterization of the adsorbent (here PPY–PANI@RHA was globally a meso-porous adsorbent). Lastly, the mechanism of Cr(VI) removal from wastewater using PPY-PANI@RHA as adsorbent was macroscopically investigated via the estimation of three thermodynamic functions.

Modeling of hexavalent chromium removal onto natural zeolite from air stream in a fixed bed column

The increasing use of hexavalent chromium (Cr(VI)) has exposed large populations to this environmental and occupational carcinogenic agent. Therefore, researchers have been interested in removing this substance through adsorbents. This study aimed to investigate the efficiency of natural zeolite in the direct adsorption of Cr(VI) from airflow and its adsorption modeling. In this study, a nebulizer device produced the Cr(VI) mist. The efficiency of natural zeolite in Cr(VI) adsorption from airflow, modeling of fixed column adsorption, and the effective parameters on adsorption efficiency including the initial concentration of chromium, airflow rate, and adsorption bed depth were studied. To facilitate the prediction of the performance of natural zeolite’s adsorption column, Yoon–Nelson, Thomas, BDST, and Buhart–Adams models were used. The results showed that the adsorption capacity diminished with increased airflow rate and initial concentration, while it increased with elevated height of the adsorption bed. Yoon–Nelson, Thomas, and BDST models corresponded to experimental data with a correlation coefficient of 0.9933, but the information of the Buhart–Adams model had a lower correlation coefficient (around 0.6677). In conclusion, natural zeolite can be used as an efficient low-cost adsorbent for directly Cr(VI) removing from the airflow in a fixed bed column.

Comparative analysis of Cr(VI) oxyanions adsorption on aged polyamide microplastics: Evaluating UV irradiation versus chemical aging

Microplastics (MPs) commonly undergo aging in various environmental media, affecting both their environmental behavior and Trojan-horse effect for contaminants. However, the mechanisms underlying the different impact of various aging processes on the Trojan-horse effect of polyamide (PA) MPs towards metal oxyanions remain unclear. This study explored how chemical aging and UV irradiation impact the structural characteristics and Cr(VI) adsorption of PA MPs under various influencing factors. Results showed that both aging processes enhanced the negative surface charge, surface oxygen content, and roughness of PA MPs, with FTIR correlation spectroscopy confirming an increase in O-containing functional groups. Cr(VI) adsorption onto aged PA sharply increased by 17.4 % (14 days of UV irradiation), 39.4 % (42 days of UV irradiation), and 21.7 % (chemical aging) compared to original PA. Salinity and natural organic matter had adverse effects on Cr(VI) adsorption. Spectroscopic analyses highlighted the crucial role of hydrophilic amide groups in controlling Cr(VI) adsorption onto aged PA, involving hydrogen bonding, electrostatic interactions, and reduction. Aged PA exhibited higher adsorption capacities but also greater desorption under simulated seawater and intestinal fluid, suggesting increased migration potential for Cr(VI). This study provides helpful insights into assessing the environmental risk of co-existing PA MPs and metal oxyanions, particularly considering the effect of aging processes.

Enhanced adsorption of Cr(VI) pollutants using CaFe2O4@rGO modified-biochar derived from mixture of black soldier flier exuviae and durian peel

To solve the problem of hexavalent chromium (Cr(VI))-polluted water sources, mixed black soldier flier exuviae (BSFE) and durian peel (DP)-derived biochar modified with CaFe2O4@rGO (BC-CFr) was synthesized to remove Cr(VI) from wastewater. Our findings indicated that the adsorption of Cr(VI) on BC-CFr reached a maximum at a pH of 2.0, biochar dosage of 0.3 g/100 mL, and initial Cr(VI) concentration of 50 mg/L, with a Cr(VI) adsorption capacity of 30.8 mg/g, which was approximately two times greater than that on pristine biochar (PBC). The characterization results showed that the as-prepared modified biochar was rich in surface functional groups, including amine groups (−NH2) and active sites. Cr(VI) adsorption followed the Elovich kinetic and Freundlich isotherm models, illustrating the adsorption process involved multilayer on the heterogeneous surface. The thermodynamic study confirmed the adsorption process was endothermic. The proposed adsorption mechanisms included adsorption-coupled reduction, electrostatic attraction, and pore filling. This study provided a simple method to prepare compositing biochar using abundantly available agricultural by-products that dealt with the dual problems of Cr(VI)-contaminated water and agricultural solid waste. Besides, the BC-CFr exhibited high desorption performance and recyclability over five consecutive adsorption-desorption cycles, suggesting the BC-CFr is a feasible nanocomposite biochar for effectively removing Cr(VI) from wastewater in practice.

Tracking the Molecular-Scale Mechanistic Pathway of Trapping-Bonding CTAB/Fe3O4-AS for High-Performance Cr(VI) Adsorption

Cr(VI) contamination threatens the environment and health, necessitating urgent, sustainable removal solutions. Composite biological adsorbents are promising, yet the molecular-level adsorption mechanisms remain unclear. This gap in understanding hinders the development and application of more efficient biological adsorbent materials. Here, we propose a magnetic composite adsorbent based on Aspergillus niger spores (CTAB/Fe3O4-AS) to track the trapping-bonding mechanisms of Cr(VI) on its surface. Characterization analysis showed that Fe3O4 nanoparticles and CTAB form a stable magnetic shell and an outermost quaternary ammonium layer on the spore surface. This synergistic structure enhanced the Cr(VI) adsorption capacity to 186 mg·g−1 at pH 2.0 in solution and achieved a Cr(VI) removal rate exceeding 99 % in electroplating wastewater, with dosage of 1.8 g·L−1 after 180 min. CTAB/Fe3O4-AS selectively removes Cr(VI) from acidic wastewater, with selectivity coefficients of KCr/Zn = 1334 and KCr/Cu = 2661. Cr(VI) removal occurs mainly through chemical adsorption via heterogeneous processes. DFT calculations and MD simulations visualize reaction pathways and interaction strengths at the molecular scale. The quaternary ammonium cation group ((CH3)4-N+) in CTAB traps Cr(VI) ions electrostatically, transferring them to the spore surface. Electron-donating groups (–COO, –NH-) on the spores reduce Cr(VI) to Cr(III). Amide groups in chitin create optimal coordination sites for Cr(III) by twisting, with nitrogen atoms forming stable complexes through coordination bonds with Cr(III)’s vacant orbitals. This study not only developed an efficient microbial-based composite adsorbent but also proposed a novel synergistic adsorption mechanism: electrostatic trapping–reduction–coordination bonding. This provides valuable insights for developing more efficient and applicable heavy metal ion adsorbent materials in the future.

Layer-by-layer adsorption behavior of Cr(VI) on MoS2@Mt induced by sulfamethoxazole

Hexavalent chromium (Cr(VI)) contamination in wastewater is a serious environmental threat. Cr(VI) removal is often interfered by antibiotics in wastewater, however, the underlying mechanism remains unclear. Here, molybdenum disulfide/montmorillonite (MoS2@Mt) composites were prepared and used for Cr(VI) removal to reveal the adsorption behavior of Cr(VI) on MoS2@Mt induced by sulfamethoxazole. The induction effect of the typical antibiotic sulfamethoxazole (SMX) was investigated. The adsorption capacity of MoS2@Mt was maximum at pH 2 and decreased with increasing pH. The performance results showed that SMX promoted Cr(VI) removal, with a maximum increase of 14.80 % in removal efficiency. Cr(VI) adsorption on MoS2@Mt followed the Langmuir model, whereas it was more consistent with the Freundlich model in the presence of SMX. This suggested that SMX induced a monolayer to multilayer shift in Cr(VI) adsorption. XPS results indicated that Cr(VI) removal pathways included Cr(VI) adsorption, chemical reduction of Cr(VI) to trivalent chromium (Cr(III)), and Cr(III) chelation. In particular, electrostatic pulling, coordinated adsorption, and hydrogen bond attraction contributed to Cr(VI) adsorption. Mechanism investigation suggested that Cr(VI) or SMX absorbed on the material surface continued to absorb SMX or Cr(VI) by electrostatic attraction, resulting in layer-by-layer adsorption behavior, which facilitated Cr(VI) removal. In actual wastewater treatment, MoS2@Mt reduced Cr(VI) concentrations (0.15–5 mg/L) to below the World Health Organization standard of 0.05 mg/L in the presence of 0.32 mg/L SMX. Overall, this study revealed the mechanism of SMX-induced Cr(VI) adsorption behavior, which favors the elimination of Cr(VI) from real complex wastewater.

EDAC-modified chitosan/imidazolium-polysulfone composite beads for removal of Cr(VI) from aqueous solution

To enhance the stability and adsorption performance of chitosan in Cr(VI)-contaminated acidic wastewater, a novel EDAC-modified-EDTA-crosslinked chitosan derivative (CSEC) was synthesized via a one-pot method with chitosan, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC), and Na2EDTA as raw materials. To further improve the mechanical strength and separation performance of CSEC, a novel composite bead (CSEP) of CSEC and imidazolium-functionalized polysulfone (IMPSF) was prepared through a phase inversion method. The chemical composition and microstructure of CSEC and CSEP were characterized by FESEM, FTIR, NMR and XPS techniques. The maximum adsorption capacities of CSEC and CSEP for Cr(VI) were 145.96 and 135.82 mg g−1 at pH 3, respectively, and the equilibrium time for Cr(VI) adsorption by CSEC and CSEP was 5 min and 8 h, respectively. The adsorption process of Cr(VI) by both CSEC and CSEP was exothermic and spontaneous. Compared to CSEC, CSEP has significantly enhanced resistance to interference from coexisting anions. The removal mechanism of Cr(VI) by CSEP might involve redox reaction as well as electrostatic attraction between Cr(VI) oxyanions and various nitrogen cations, including protonated amino groups, guanidinium groups, protonated tertiary amine groups, and imidazolium cations. The CSEP beads have potential application value in the treatment of acidic wastewater containing Cr(VI).

Prospective application of eco-friendly banana peel reduced graphene oxide (BRGO) for aqueous Cr (VI) and acid dye adsorption: A waste utilization approach

Banana peels are an environmentally benign alternative to toxic reducing agents. Banana peel-reduced graphene oxide (BRGO) showed high performance in the adsorption of metal and dye ions. Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a Zeta potential analyzer were used to characterize the BRGO. Different influencing factors such as pH, dose, concentration, duration, and temperature, were studied to evaluate the efficiency of the adsorbent. The Langmuir and Freundlich isotherm models were fitted for Cr (VI) and acid dye adsorption. The maximum adsorption capacity (qm) of BRGO for Cr (VI) and AV54 dye were 135.87 and 110.74 mg/g, respectively. The pseudo-second-order kinetic model was better suited for Cr (VI) and AV54 dye adsorption, which indicated chemical adsorption. Thermodynamically, the adsorption exhibited spontaneity and was endothermic. Regeneration and reuse of adsorbents were also studied for potential use in treating tannery effluent.

Efficient selective adsorption of Cr(VI) by S-doped porous carbon prepared from industrial lignin: Waste increment and wastewater treatment

Industrial lignin is a waste product of the paper industry, which contains a large amount of oxygen group structure, and can be used to treat industrial wastewater containing Cr(VI). However, lignin has very low reactivity, so how to enhance its adsorption performance is a major challenge at present. In this study, a two-stage hydrothermal and activation strategy was used to activate the lignin activity and doping S element to prepare high-performance S-doped lignin-based polyporous carbon (S-LPC). The results show that the surface of S-LPC is rich in S and O groups and has a well-developed pore structure, which is very beneficial to Cr(VI) uptake -reduction and mass transfer on the material. In the wastewater, the utmost adsorption potential of Cr(VI) by S-LPC achieved 882.83 mg/g. After 7 cycles of regeneration, the adsorption of S-LPC decreased by only approximately 18 %. Ion competition experiments showed that S-LPC has excellent specificity for Cr(VI) adsorption. In factory wastewater, the adsorption performance of S-LPC for Cr(VI) remained above 95 %, which shows the excellent performance of S-LPC in practical applications. The results are of great significance for green chemical utilization of waste lignin, treatment of industrial wastewater and sustainable development.

Synthesis of Fe3O4@SiO2–branched polyethylenimine nanospheres for removal of Cr(VI) and anionic dyes

There is a need to design and prepare new sorbents for the effective elimination of toxic metal ions and textile dyes from the environment. In the presented study, the preparation of magnetic functionalized silica composite nanospheres for the removal of inorganic and organic pollutants from aqueous solutions is reported. Firstly, the surface of silica coated magnetic nanospheres was functionalized with epoxy groups via a reaction of 3-glycidoxypropyltriethoxysilane. Then, the branched polyethylenimine (BPEI) was attached to generate positive functional charged groups on the on the Fe3O4@SiO2. The performance of the Fe3O4@SiO2-BPEI nanospheres for the removal of Cr(VI) and Congo Red (CR) and Trypan Blue (TB) dyes was studied under various experimental conditions. The optimum pHs values for adsorption of Cr(VI) ions, CR and TB dyes on the Fe3O4@SiO2-BPEI nanospheres were found to be at pH 2.0, and at pH 4.0, respectively. The maximum adsorption capacities of the Fe3O4-@SiO2-BPEI nanospheres for Cr(VI), CR, and TB were obtained as 356.7, 395.3, and 561.8 mg/g within 90 min equilibrium time, an initial concentration of 500 mg/L, and at 25 ºC, respectively. The adsorption of the tested pollutants were well described by the Langmuir isotherm model and second-order kinetic model. After ten reuse cycles, the adsorption capacity of Fe3O4-@SiO2-BPEI nanospheres was not significantly changed for the tested pollutants. The adsorption mechanism of Cr(VI), CR, and TB by the Fe3O4-@SiO2-BPEI nanospheres was evaluated to be related to ion exchange and ion exchange and/or hydrogen bonding interactions, respectively. The results also suggested that the presented adsorbent may serve as a multi-functional adsorbent for the remediation of industrial effluents. In addition, compared to the unmodified Fe3O4@SiO2, the Fe3O4@SiO2-BPEI nanospheres have antibacterial activities against Escherichia coli (American Type Culture Collection (ATCC) 12435), Pseudomonas aeruginosa (ATCC 10145), Listeria monocytogenes (ATCC 7644), and Staphylococcus aureus (ATCC 43300). Based on the obtained results from this work, the branched polyethylene functionalized magnetic silica nanospheres with antibacterial properties can be used as a potential adsorbent for the removal of metal ions and anionic dyes from wastewater.

Integrated experiments and numerical simulations for chromium (VI) surface complexation in natural unconsolidated sediments

This study focuses on the adsorption and transport of Cr (VI) on natural sediments from Qiqihar, China. Through batch and column experiments, we assessed the adsorption capacities influenced by factors such as contact time, initial concentration, pH, ionic strength, solid-to-solution ratio, coexisting ions in groundwater, sediment characteristics and flow rate. The adsorption kinetics of Cr (VI) follow the pseudo-first-order model well, while the isotherms of all three sediments are accurately represented by the Freundlich model. The adsorption edges reveal a strong pH dependence in Cr (VI) adsorption: the stronger the acidity, the more favorable it is for adsorption. The adsorption capacity decreases with an increasing solid-to-solution ratio, stabilizing at higher ratios. Coexisting ions in groundwater reduce Cr (VI) adsorption in loam under neutral pH. Additionally, Fourier transform infrared spectroscopy (FTIR) results indicate that the hydroxyl group is the primary reactive functional group in all three sediments. X-ray photoelectron spectroscopy (XPS) results further show partial adsorbed Cr (VI) was reduced to Cr (III) by organic matters. However, surface complexation reactions dominate the removal of Cr (VI). On the base above, we introduced a surface complexation model, optimizing equilibrium complexation constants by fitting adsorption edges. Subsequently, reactive transport models incorporating both surface complexation and reduction processes for Cr (VI) were established to simulate column experiments. As the flow rate decreases, the adsorption capacity and the amount of reduction reaction for Cr (VI) increase, while the reduction rate decreases. Specifically, the reduction for Cr (VI) was found to be more significant in loam compared to sand, correlating with the organic matter content. The results emphasize the existence of surface complexation reactions and the role of organic matters in electron transfer. Our study provides significant information for understanding Cr (VI) adsorption and transport behavior in natural aquifer sediments.

XG and CS-based self-assembled nanocomposite hydrogel embedding fluorescent NCQDs capable of detection and adsorptive removal of the polar MO and Cr(VI) pollutants

Aiming at dealing with organic and inorganic pollutants dissolved in aquatic environments, we introduce self-assembled fluorescent nanocomposite hydrogel based on a binary polysaccharide network (xanthan gum/chitosan) embedding nitrogen-doped carbon quantum dots not only as a hybrid solid optical sensor for detecting Cr(VI) ions but also to remove anionically charged contaminants Cr(VI) and methyl orange (MO) by acting as an adsorbent. This fluorescent nanocomposite achieved a detection limit of 0.29 μM when used to detect Cr(VI) and demonstrated a fluorescence quantum yield of 59.7 %. Several factors contributed to the effectiveness of the adsorption of Cr(VI) and MO in batch studies, including the solution pH, dosage of the adsorbent, temperature, initial contamination level, and contact time. Experimental results showed 456 mg/g maximum adsorption capacity at pH 4 for MO compared to 291 mg/g at pH 2 for Cr(VI) at 25 °C. In addition to conforming to Langmuir's model, Cr(VI) and MO's adsorption kinetics closely matched pseudo-second-order. Using thermodynamic parameters, the results indicate that Cr(VI) and MO adsorb spontaneously and exothermically. Recycling spent adsorbent for Cr(VI) and MO using NaOH at 0.1 M was possible; the respective adsorption efficiency remained at approximately 82.2 % and 83 % after the fifth regeneration cycle.

Intensified adsorption of chromium (VI) by catalpa-activated carbon from water and real electroplating industry wastewater

ABSTRACT In the present study, a novel adsorbent, activated carbon produced from the catalpa tree fruit was evaluated for adsorption of Cr (VI) from water and real electroplating wastewater. The batch adsorption experiments were conducted to investigate the impact of various operational variables, namely contact time, pH, initial concentration of Cr (VI), and the dose of activated carbon. Experimental data were used to determine the most suitable isotherm and kinetic models. The optimal values of the process were identified at a contact time of 150 min, a pH 2, an initial Cr (VI) concentration of 40 mg/L, and an adsorbent dose of 0.6 g/L that led to mean Cr (VI) removal of 95% with adsorption capacity (q) equal to 75 mg/g. The Langmuir isotherm and pseudo-first-order kinetic models could well explain the adsorption equilibrium. Furthermore, the thermodynamic analysis indicated that the adsorption process was characterised by exothermicity. The efficiency of the adsorbent in removing Cr (VI) from the real electroplating wastewater was obtained about 80%. However, the required adsorbent dose was 1.5 g/L. The fruit of the catalpa tree represents a cost-effective material for producing activated carbon, with a high capacity for adsorbing Cr (VI) from aqueous solution and wastewater.

Influence of the iron-oxide mass fractions of magnetic powdered activated carbon on its hexavalent chromium adsorption performance in water

Magnetic powdered activated carbon (Mag-PAC) is an effective adsorbent to remove hexavalent chromium (Cr(VI)) from water and can be recovered for reuse. However, the tradeoff between the adsorption performance of Cr(VI) and magnetic properties of Mag-PAC remains unclear. Herein, we prepared a series of Mag-PAC adsorbents containing various iron-oxide mass fractions with FeSO4·7H2O as the precursor, using a facile wet-chemical precipitation route and conducted batch experiments to evaluate the Cr(VI) adsorption performance. Results revealed that Mag-PAC was functionalized by magnetic iron oxide comprising crystalline goethite and magnetite structures. Furthermore, its adsorption performance was highly dependent on pH and was most effective at an initial solution pH of 2. Both the sorption rate constant and Cr(VI) adsorption capacity were greatly influenced by magnetization, and they gradually decreased as the iron-oxide mass fraction increased. Among the prepared adsorbents, Mag-PAC-75 (∼32% wt iron) exhibited not only an excellent Cr(VI) adsorption performance (Langmuir adsorption capacity: 75.76 mg/g) but also effective magnetic properties (saturation magnetization: 9.66 emu/g). Coexisting anions had a negligible competitive effect on Cr(VI) removal by Mag-PAC-75 at an initial pH of 2, whereas the presence of tannic acid markedly improved the Cr(VI) elimination. The presence of trivalent chromium on the surface of Mag-PAC-75 confirmed via X-ray photoelectron spectroscopy indicated that some synergistic redox reactions may occur during the sorption process. After five regeneration cycles using NaOH, Mag-PAC-75 continued to exhibit a high Cr(VI) removal efficiency and magnetic stability. These findings indicate that optimizing the adsorption performance and magnetic properties is a key factor for realizing the practical application of Mag-PAC for Cr(VI) removal. Overall, Mag-PAC may have been a promising application prospect for Cr(VI) removal from water due to its high adsorption capacity and magnetic properties, coupled with its good reusability and magnetic stability after regeneration cycles.

Fabrication of Core-Shell Amino-Modified UiO-66@UiO-67 for Catalytic Reduction and Adsorption of Cr (VI)

Fabrication of Core-Shell Amino-Modified UiO-66@UiO-67 for Catalytic Reduction and Adsorption of Cr (VI)