Adsorption Of Hexavalent Chromium Research Articles

Adsorption and Reductive Removal of Hexavalent Chromium from Aqueous Solution by Nanoscale Iron‐modified Dual Surfactants

AbstractIn view of the increasingly prominent environmental pollution caused by heavy metals, nanoscale zero‐valent iron was modified by polyethylene glycol and sodium dodecyl benzene sulfonate (PS‐nZVI) and used to treat Cr(VI). The removal rate of Cr(VI) and equilibrium adsorption capacity of PS‐nZVI can reached 92 % and 122.3 mg ⋅ g−1, respectively, under the conditions of PS‐nZVI 1.0 g ⋅ L−1, initial Cr(VI) concentration 50 mg ⋅ L−1, initial pH 5.5, and reaction temperature 298 K. The adsorption process can be described by quasi‐second‐order kinetics and Langmuir isothermal model, and it is characterized by spontaneous endothermy and monolayer surface chemisorption. The mechanism of Cr (VI) removal by PS‐nZVI can be summarized as follows: First, Cr(VI) is adsorbed on the surface of PS‐nZVI by electrostatic attraction. Then, nZVI and Fe(II) reduce Cr(VI) to Cr(III), and themselves are oxidized to Fe(III). Finally, Cr(III) and Fe(III) form (CrXFe1‐X)(OH)3 or CrXFe1‐XOOH co‐precipitation, which is attached to the PS‐nZVI surface and removed.

Synthesis of a Novel Adsorbing Agent by Coupling Chitosan, β-Cyclodextrin, and Cerium Dioxide: Evaluation of Hexavalent Chromium Removal Efficacy from Aqueous Solutions

The present study aimed at synthesizing a novel adsorbing agent by coupling chitosan, β-cyclodextrin, and cerium dioxide (Chit/β-CyD/Ce). Its efficiency towards the removal of hexavalent chromium from aqueous solutions was studied and compared to an adsorbent comprising of only chitosan and cerium dioxide. Batch water purification experiments in varying experimental conditions (initial adsorbent concentration 5–100 mg/L, adsorbate concentration 0.1–2 g/L, pH 2–11, and temperature 15–50 °C) were carried out to evaluate the effectiveness of both adsorbents. In all the experimental cases, the Chit/β-CyD/Ce adsorbent exhibited the higher efficacy. The optimum operating conditions were found to be at an initial adsorbent concentration of 2 g/L, pH = 3, and temperature of 50 °C, with the Chit/β-CyD/Ce adsorbent being able to fully remove Cr(VI) from solutions with up to 50 mg/L Cr(VI) at these conditions. The adsorption of hexavalent chromium onto both adsorbents occurs in a multilayer pattern of a heterogeneous surface following the Freundlich isotherm model. Furthermore, the adsorption process was exothermic and obeyed the pseudo-second-order kinetic model, thus indicating the occurrence of chemisorption. Finally, FTIR, XRD, and SEM analyses were performed to characterize the synthesized adsorbents and verify the adsorption process.

Adsorption of Hexavalent Chromium Using Activated Carbon Produced from Sargassum ssp.: Comparison between Lab Experiments and Molecular Dynamics Simulations.

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum—an invasive brown macroalga—into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pHPZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m2·g−1). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m2·g−1) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl2 to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO4− and CrO42− anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.

Novel co-polymerization of polypyrrole/polyaniline on ferrate modified biochar composites for the efficient adsorption of hexavalent chromium in water.

It is still a huge challenge to prepare cheap and effective composite materials for removing hexavalent chromium (Cr(VI)) in sewage treatment. In this study, a noval co-polymerization of polypyrrole/polyaniline on ferrate modified biochar (Ppy/PANI/FBC) was fabricated via ferrate-promoted pyrolysis and in-situ oxidative polymerization of pyrrole and aniline molecules to effectively remove Cr(VI) from polluted water. The Ppy/PANI/FBC quickly decreased Cr(VI) concentration from 38.92 to 3.92mg/L within 400min, with an efficient removal efficiency (89.92%), which was significantly higher than that of FBC (4.75%), Ppy/FBC (72.30%), and PANI/FBC (42.43%). These results are mainly caused by its conjugated connection and well-dispersion of Ppy and PANI on the surface of a carbon-based material. Meanwhile, the experimental results were in line with the pseudo-second-order kinetic and Freundlich models. The Ppy/PANI/FBC is featured by a high capacity of Cr(VI) adsorption (up to 203.71mg/g). In addition, it could be adopted for efficiently removing Cr(VI) over a wide pH range (4-9) because of the positively charged nitrogen (-NH.+- and=N+-). The sorption mechanisms of Cr(VI) were identified, including electrostatic interaction with surface protonated nitrogen (N+), ion exchange between the doped Cl- ions and Cr(VI), chemical decrease of the Cr(VI) to Cr(III) by the iron valence cycle and efficient electron transfer of Ppy/PANI/FBC, as well as surface complexation by amine and oxygen-containing groups. More importantly, 97.98% Cr(VI) was efficiently removed in 20min by coupling a photocatalytic reaction, also providing a novel idea for the practical use of adsorbents in wastewater treatment.

Effect of treating a PVC/Aliquat-336 polymer adsorbent with sodium hydroxide on chromium (VI) adsorption

ABSTRACT A PVC adsorbent doped with Aliquat-336 was prepared with the phase inversion method for application to hexavalent chromium adsorption. Scanning electron microscopy (SEM) and BET analysis were used to identify its morphology and texture. SEM images revealed an asymmetrical structure with a macro-porous interior layer and a thin micro-porous top layer. BET analysis showed that the adsorbent had a low specific surface area. The polymer adsorbent was treated with a sodium hydroxide solution. Both treated and untreated adsorbents were utilised to adsorbate hexavalent chromium from an aqueous solution. The adsorption was carried out under different experimental conditions. Adsorption takes 48 h to reach equilibrium. The intraparticle diffusion mechanism controls adsorption kinetics, while the Langmuir model describes the adsorption isotherm. The treatment of the PVC adsorbent with sodium hydroxide enhances its maximum adsorption capacity from 47.3 mg g−1 to 69.05 mg g−1.

Modeling of Hexavalent Chromium Removal with Hydrophobically Modified Cellulose Nanofibers.

Cellulose nanofibers (CNF) are sustainable nanomaterials, obtained by the mechanical disintegration of cellulose, whose properties make them an interesting adsorbent material due to their high specific area and active groups. CNF are easily functionalized to optimize the performance for different uses. The hypothesis of this work is that hydrophobization can be used to improve their ability as adsorbents. Therefore, hydrophobic CNF was applied to adsorb hexavalent chromium from wastewater. CNF was synthetized by TEMPO-mediated oxidation, followed by mechanical disintegration. Hydrophobization was performed using methyl trimetoxysilane (MTMS) as a hydrophobic coating agent. The adsorption treatment of hexavalent chromium with hydrophobic CNF was optimized by studying the influence of contact time, MTMS dosage (0–3 mmol·g−1 CNF), initial pH of the wastewater (3–9), initial chromium concentration (0.10–50 mg·L−1), and adsorbent dosage (250–1000 mg CNF·L−1). Furthermore, the corresponding adsorption mechanism was identified. Complete adsorption of hexavalent chromium was achieved with CNF hydrophobized with 1.5 mmol MTMS·g−1 CNF with the faster adsorption kinetic, which proved the initial hypothesis that hydrophobic CNF improves the adsorption capacity of hydrophilic CNF. The optimal adsorption conditions were pH 3 and the adsorbent dosage was over 500 mg·L−1. The maximum removal was found for the initial concentrations of hexavalent chromium below 1 mg·L−1 and a maximum adsorption capacity of 70.38 mg·g−1 was achieved. The kinetic study revealed that pseudo-second order kinetics was the best fitting model at a low concentration while the intraparticle diffusion model fit better for higher concentrations, describing a multi-step mechanism of hexavalent chromium onto the adsorbent surface. The Freundlich isotherm was the best adjustment model.

Synthesis and characterization of magnetic organic montmorillonite: efficient adsorption of hexavalent chromium.

This research compared two potential adsorbents for the efficient adsorption of toxic hexavalent chromium. The non-magnetic material STAC-Mt and the magnetic material FeSO4-STAC-Mt were synthesized by a simple impregnation method using montmorillonite (Mt), octadearyl dimethyl ammonium chloride (STAC) and ferrous sulfate as raw materials. The structural and morphological characteristics of both adsorbents were investigated by BET, XRD, FTIR, Zeta, VSM, TEM, SEM and XPS techniques. SEM and TEM results clearly revealed that FeSO4-STAC-Mt had a more loosely curled structure than STAC-Mt and the existence of well dispersed diamond-shaped magnetic particles. The saturation magnetization intensity of 17.949 emu/g obtained by VSM further confirmed the presence of magnetite particles in FeSO4-STAC-Mt. Due to the superparamagnetic properties of magnetite, the adsorption performance of FeSO4-STAC-Mt was better than STAC-Mt. FeSO4-STAC-Mt adsorbed up to 43.98 mg/g of Cr(VI), meanwhile it was easily separated from the reaction mixture by an external magnetic field. Intermittent adsorption studies at pH, adsorbent dosage and time revealed a rapid Cr(VI) adsorption process. In combination with response surface optimization analysis, a removal rate of 98.03% of Cr(VI) was obtained at pH 5-6. The adsorption process was properly described by the pseudo-second-order kinetic equation and the Langmuir equation, and the adsorption process was chemisorption and single molecular layer adsorption. In addition, the removal of Cr(VI) reached 72.68% after five cycles, demonstrating the good stability of the FeSO4-STAC-Mt.

Adsorption of hexavalent chromium from aqueous solution by polyamidoamine dendrimer polycondensate

Adsorption of hexavalent chromium from aqueous solution by polyamidoamine dendrimer polycondensate

Hexavalent chromium adsorption by tetrahexylphosphonium modified beidellite clay

The fixation of the hexavalent chromium (CrVI), a toxic component in the wastewater, from the aqueous solutions into the interlayer space of beidellite (Bd) clay was studied, combining theoretical and experimental methods. The structure of intercalated CrVI anionic species to beidellite modified by tetrahexylphosphonium cation (Cr-THP-Bd) was examined using the density functional theory (DFT) calculations on representative structural models. The computed basal spacing (d001) of the Cr-THP-Bd model (15.5 Å) showed a good agreement with the experimental value (15.3 Å) obtained by the XRD method. Calculated intercalation energy of −214.2 kJ/mol demonstrated strong stabilization of chromate anion in the THP-Bd structure. C–H⋅⋅⋅O and O–H⋅⋅⋅O hydrogen bond interactions present in the Cr-THP-Bd model significantly affected the structural stability of the whole studied system. The calculated vibrational spectra from the ab initio molecular dynamics (AIMD) helped identify the Cr–O stretching and O–Cr–O bending vibrational modes of (CrO4)2− anion in the complex FTIR spectra. The amount of (CrO4)2− anion determined by the experiment clearly confirmed that Bd modified by the THP surfactant significantly increased the adsorption of the chromate anion in comparison to pure Na-Bd clay.

Single-step synthesis of activated magnetic biochar derived from rice husk for hexavalent chromium adsorption: Equilibrium mechanism, kinetics, and thermodynamics analysis

This study aims to synthesize activated magnetic biochar using a single-step approach and explore solute-solvent mechanisms for removing hexavalent chromium [Cr(VI)] from the aqueous solution. Agricultural waste rice husk was pre-treated in iron chloride and zinc chloride solution and pyrolyzed at 500°C. Obtained activated magnetic biochar were characterized by SEM, EDS, FTIR, XRD, VSM, and BET to analyze physicochemical features. Adsorption experiments indicated that activated magnetic biochar achieved an adsorption capacity of 9.97 mg/g with removal efficiency of 99.7% for an initial Cr(VI) concentration of 10 mg/L at pH 2 and 351 K. In aqueous solutions, Cr(VI) break down to HCrO4−, CrO42−, and Cr2O72− ions. However, at low pH (∼1–4), HCrO4− ion attributes electrostatic force of attraction, which encourages higher adsorption of Cr(VI) ions. Overall, batch experiments demonstrated that initial pH, Cr(VI) concentration, biochar dose, temperature, and co-existing ions significantly affected the Cr(VI) adsorption using activated magnetic biochar. Therefore, electrostatic interaction and ion exchange dominate Cr(VI) adsorption onto activated magnetic biochar at low pH. Experiments showed heterogeneous non-linear monolayer and spontaneous sorption, which were validated via Temkin isotherm and pseudo-second-order kinetic for Cr(VI) ions. As a result, Cr(VI) adsorption onto activated magnetic biochar occurred due to chemisorption on heterogeneous non-linear monolayers, mainly governed by electrostatic attraction and ion-exchange mechanisms due to enriched oxygen-containing surface groups with activated magnetic biochar. In terms of thermodynamics, the adsorption process for Cr(VI) ions using activated magnetic biochar was endothermic and spontaneous, as a positive ΔS° value indicates randomness during Cr(VI) adsorption at the solution-solute interface. In contrast, the negative value of ΔG° (−15855.3 kJ/mol) at 351 K shows that adsorption was spontaneous. Overall, the activated magnetic biochar synthesized from rice husk was more efficient than raw biochar in removing Cr(VI) ions from the aqueous solution.

Optimized removal of hexavalent chromium from water using spent tea leaves treated with ascorbic acid

Spent tea leaves were functionalized with ascorbic acid to obtain treated tea waste (t-TW) to encourage the adsorption of hexavalent chromium from water. The adsorption removal of Cr(VI) was systematically investigated as a function of four experimental factors: pH (2–12), initial Cr(VI) concentration (1–100 mg L−1), t-TW dosage (0–4 g L−1), and temperature (10–50 °C) by following a statistical experimental design. A central composite rotatable experimental design based on a response surface methodology was used to establish an empirical model that assessed the individual and combined effects of factors on adsorptive removal of Cr(VI). The model was experimentally verified and statistically validated then used to predict optimal adsorption removal of Cr(VI) from water. At optimized conditions, ≥ 99% of 1 mg L−1 Cr(VI) can be removed by 4 g L−1 t-TW at a pH of 9. The adsorptive mechanism was assessed by conducting kinetics and equilibrium studies. The adsorption of Cr(VI) by t-TW followed a pseudo-second-order kinetics model (k2 = 0.001 g mg−1 h−1) and could be described by Langmuir and Temkin isotherms, indicating monolayer adsorption and predominantly adsorbate-adsorbent interactions. The t-TW exhibited a competitive Cr(VI) adsorption capacity of 232.2 mg g−1 compared with the other low-cost adsorbents. These results support the utilization of tea waste for the removal of hazardous metal contaminants from aqueous systems.

Killing Two Birds with One Stone: Biomineralized Bacteria Tolerate Adverse Environments and Absorb Hexavalent Chromium.

Heavy metal ions in contaminated water, such as hexavalent chromium, are harmful to humans. Bacterial biosorption is an ideal method for the treatment of hexavalent chromium. However, hexavalent chromium in solution causes bacteria to produce reactive oxygen species, which leads to bacterial death and affects biosorption. We developed a microfluidics-based biomimetic mineralization method to encapsulate bacteria (e.g., Escherichia coli and Bacillus subtilis) with zeolitic imidazolate framework-8 (ZIF-8), thus allowing the bacteria to form a continuous and homogeneous shell. The artificial shells endowed bacteria with the ability to tolerate harsh environments, which was significant during the treatment of contaminated water. The adsorption of hexavalent chromium was a two-step process: first the fast physical adsorption of ZIF-8 and biosorption by bacteria (up to 30–50% adsorption in 1 day), followed by secondary biosorption after decomposition of the system. The maximum adsorption of hexavalent chromium by the encapsulated bacteria reached 90%. The microfluidic device developed in this study provides a simple method to encapsulate bacteria mildly and enable cell survival in extreme environments, offering the possibility of future microbial applications in environmental and other fields.

Optimizing Cr(VI) adsorption parameters on magnetite (Fe3O4) and manganese doped magnetite (MnxFe(3-x)O4) nanoparticles

Abstract Magnetite as an adsorbent is efficient since iron oxides have high affinities for heavy metal pollutants and are environmentally friendly. Manganese oxides provide catalytic properties which are desirable during the remediation of multi valent pollutants. Magnetite (Fe3O4) and manganese doped magnetite (MnxFe(3-x)O4) nanoparticles were synthesized and characterized to determine the manganese doping effects on magnetite’s crystal and surface properties. Fe3O4 and MnxFe(3-x)O4 showed similarities in crystal morphology indicating that manganese doping did not alter the nature of Fe3O4 nanoparticles. Manganese doping improved magnetite’s thermal properties as well as its surface area providing improved adsorption characteristics. The as-synthesized particles were applied in the optimization of hexavalent chromium adsorption. Adsorption proceeded under similar conditions for both adsorbents indicating their structural similarities. Higher efficiencies were observed on the doped adsorbent due to increased surface area and the presence of additional functional groups. Solution pH significantly affected the adsorption process aiding in the reduction of Cr(VI) ions to the less toxic Cr(III) species. The adsorption distribution coefficient KD indicated that manganese doping significantly improved magnetite’s affinity for hexavalent chromium. Adsorption and reduction were determined to responsible for pollutant reduction in solution at optimal conditions of pH 2, 5 g/L and 100 mg/L for adsorbent mass and solution concentration.

Response surface modeling and optimization of hexavalent chromium adsorption onto eucalyptus tree bark-derived pristine and chemically-modified biochar

Biochar can be used as an adsorbent to remove hexavalent chromium (Cr(VI)) from water containing pollutant due to its low cost of production, non-toxicity, improved textural qualities and high adsorption capacity. This study was aimed to examine and compare the adsorption behaviour of unmodified biochar (BC) and ZnCl2-modified biochar (ZMBC) obtained from eucalyptus tree bark for the removal of Cr(VI) from aqueous solutions. The BC and ZMBC adsorbents were evaluated by various characterization techniques (TGA/DTA, SEM, FTIR, XRD, BET and pHpzc). Optimization by response surface methodology was used in investigating the influence of process factors (Cr(VI) concentration, adsorbent quantity, and pH) on Cr(VI) uptake. Various isotherm (Langmuir, Freundlich, and Temkin) and kinetic (pseudo-first-order (PFO) and pseudo-second-order (PSO)) models were used to test the adsorption experimental data. Under the optimal adsorption conditions (i.e., at 99.9 mg/L Cr(VI) concentration, 1.00 g/L sorbent amount and pH of 9.31), the removal efficiency attained 81.22±0.87% and 97.14±0.32% when BC and ZMBC were used, respectively. A higher surface area, well-developed porous structure, and dominance of active surface functional groups, validated by BET, SEM, and FTIR, contributed to the ZMBC's outstanding performance over BC. Freundlich isotherm and PSO models adequately agreed with the experimental data.

Optimization of Process Parameters for Adsorption of Hexavalent Chromium from Wastewater Using Response Surface Methodology

This study investigated the optimization of process parameters for adsorption of hexavalent chromium with activated carbons extracted from palm tree leaves of Nigerian origin. The effect of process parameters such as adsorbent dosage, initial chromium concentration, temperature, contact time, and adsorbent particle size was studied with the aid of Central Composite Design. The result showed that for the adsorbent dosage, initial concentration, temperature, contact time, and particle size, the optimum conditions were found to be 20 mg, 80 mg/l, 40° C, 40 minutes, and 1400µm, respectively. The actual and predicted values obtained were 72.96 % as well as 70.33 %, respectively, indicating a good correlation with a comparatively small variance of 2.66 %. The Langmuir isotherm showed an R2 of 0.981 and thereby showing better linearity when compared with the Freundlich isotherm. The result of the adsorption kinetics indicated that it was better described by the Pseudo-second order model. The overall adsorption process on the other hand showed an exothermic reaction with an enthalpy value of -18.707. The values of Gibbs free energy (∆G) at various temperatures also revealed a spontaneous reaction and a positive value of entropy. The results obtained showed that the adsorbent was effective in the adsorption of hexavalent chromium.

Removal of Cr(VI) in aqueous solution using cationic gemini surfactant-modified rectorite

The adsorption of hexavalent chromium (Cr(VI)) on rectorite (REC) modified by gemini surfactant (butane-1,4-bis (dodecyl dimethyl ammonium bromide)) (gBDDA) was investigated in this research. The results of a series of characterization methods such as X-ray diffraction (XRD), infrared spectroscopy, and thermogravimetric analysis proved that gBDDA was successfully embedded into the interlayer of REC. The effect of the amount of gBDDA on the adsorption of Cr(VI) by gBDDA-modified REC was studied (gBDDA: cation exchange capacity = 1:2 or 1:4). The adsorption capacity of Cr(VI) by gemini surfactant-modified REC reached 38 mg/g, which was higher than that of tetradecyl trimethyl ammonium bromide-modified REC. In addition, ultrasound-assisted synthesis was found to have an effect on the adsorption capacity of REC modified with a high ratio of gemini surfactant. The structures of gBDDA before and after adsorption were analyzed to clarify the adsorption mechanism. The electrostatic interaction between Cr(VI) and two positively charged groups in the gBDDA was found to be crucial during the adsorption process. The foundings of this study demonstrate that REC modified by gBDDA can be used as an adsorbent for the removal of Cr(VI) in water.

New insights into the cooperative adsorption behavior of Cr(VI) and humic acid in water by powdered activated carbon

Chromium and humic acid often co-exist in wastewater and source waters, and the removal of chromium through sorption by activated carbon may be greatly influenced by humic acid. In this study, we systematically evaluated concurrent adsorption of humic acid (HA) and hexavalent chromium (Cr(VI)) in water by powdered activated carbon (PAC) and further, the effect on conversion to trivalent chromium (Cr(III)). Adsorption of both HA and Cr(VI) was significantly enhanced in the dual adsorbate system as compared to treatments with HA or Cr(VI) alone. The removal of HA increased by 16.0% in the presence of 80 mg/L Cr(VI), while the removal of Cr(VI) similarly increased with increasing levels of HA. However, the promotion effect of HA was found to decrease with increasing pH. With HA at 20 mg/L, removal of Cr(VI) increased from 40.09% to 70.12% at pH 3, which was about twice the increase at pH 10. The cooperative adsorption mechanism was explored using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). Comprehensive analysis of spectra suggested that the mutual promotion between HA and Cr(VI) adsorption was attributable to the formation of Cr(VI)-HA and Cr(III)-HA complexes that were readily adsorbed on the PAC surfaces. The higher HA concentrations increased the reduction of Cr(VI) to Cr(III), which was likely due to the electron transfer provided by the functional groups such as -CO, -OH and -COOH in both PAC and HA. At pH 3, 99.1% of Cr adsorbed on the PAC surface was in the form of Cr(III). These findings imply that the interactions between Cr(VI) and HA in the process of water treatment by PAC provides additional and synergistic benefits, leading to a greater removal of chromium.

The Improvement of Natural Thai Bentonite Modified with Cationic Surfactants on Hexavalent Chromium Adsorption from an Aqueous Solution

This work was performed to evaluate the adsorption properties of modified Thai bentonites (MTBs) on hexavalent chromium (Cr(VI)) by using a popularly capable surfactant (hexadecyltrimethylammonium bromide (HDTMA)) compared to an alternative surfactant (cetylpyridinium chloride (CPC)). The adsorption properties of the surfactant load, adsorbent weight, contact time, initial Cr(VI) concentration, and temperature of the MTBs were evaluated. The results revealed that a higher surfactant load significantly affected the Cr(VI) adsorption, and the equilibrium adsorption was achieved at 60 min. The adsorption capacity improved when the adsorbent weight, contact time, initial concentration, and temperature increased as the highest adsorption capacities of 1CPC and 1HDTMA were 45.55 and 46.03 mg g-1, respectively. The isotherm and kinetic adsorptions were described by the Freundlich model and pseudo-second-order model, respectively, while thermodynamics indicated endothermic adsorption. After adsorption, X-ray absorption near-edge structure and extended X-ray absorption fine structure data showed that Cr ions did not change the valency state between Cr(VI) and Cr(III). Additionally, the adsorption mechanism can be depicted as the ion exchange between the Cr(VI) ion and the surfactant molecule. Structural evaluations by XRD, FTIR, FESEM, EDS, and TEM found that both MTBs (1CPC and 1HDTMA) with the best adsorption performance for Cr(VI) had obvious changes at both the interlayer structure and the external surface. The interlayer spacing was expanded from 14.85 Å to 20.48 Å (1CPC) and 18.79 Å (1HDTMA), and the new functional groups (CH2 scissoring, C–H symmetric stretching, C–H asymmetric stretching, and N–CH3 scissoring) and elemental compositions (Br and Cl) were observed in both MTBs. They demonstrated that the complete intercalation of surfactant molecules on bentonite structures supported Cr(VI) adsorption. Overall, the data indicate that MTBs were perfectly adsorbed on Cr(VI), and CPC was demonstrated to be a cheap alternative agent due to its adsorption capacity compared to the popularly capable HDTMA.

Stability of UV-visible spectrophotometric measurements for investigating the adsorption of hexavalent chromium from wastewater

Stability of UV-visible spectrophotometric measurements for investigating the adsorption of hexavalent chromium from wastewater

High-Efficiency Adsorption of Hexavalent Chromium from Aqueous Solution by Samanea saman Activated Carbon

Heavy metal wastewater pollution has become an environmental and industrial challenge worldwide. Hexavalent chromium (Cr(VI)) is one of the most common forms of chromium metal. Hexavalent chromium pollution is a concern because it was hazardous and can accumulate in the tissues of living organisms and the environment. The adsorption method using activated carbon can be one of the methods to treat hexavalent chromium waste. This study selected Samanea saman as the activated carbon because it contains hemicellulose, lignocellulose, and lignin, which are the requirements for an excellent activated carbon. The study’s objective is to analyze Samanea saman activated carbon (SSAC) to remove hexavalent chromium, measure the adsorption capacity, and determine the appropriate type of adsorption isotherm layer based on the maximum [Formula: see text] and minimum [Formula: see text] values. The process of making activated carbon was activated using K2CO3 through a pyrolysis process and using batch adsorption. The SEM results as characterization of SSAC depicted that the high pore was well developed. The optimal conditions for Samanea saman indicated high efficiency toward hexavalent chromium ions within the following process parameters; pH value 5, adsorbent dosage 5 g, and initial concentration 20 mg/L. The findings demonstrate that SSAC leads to the removal efficiency of hexavalent chromium being 99.90%, with the greatest adsorption capacity of 0.8949 mg/g. Based on the maximum [Formula: see text] and minimum [Formula: see text] values, the most suitable adsorption isotherm model in SSAC was the Freundlich isotherm existing in the monolayer ([Formula: see text]). The experimental results demonstrated that adsorption of Cr(VI) was well performed by SSAC. Thus, the SSAC material is an appropriate adsorbent for the removal of hexavalent chromium in the water and has the potential to be industrial applied.