Adsorbent For Removal Of Cr Research Articles

Preparation, characterization and application of polymeric ultra-permeable biodegradable ferromagnetic nanocomposite adsorbent for removal of Cr(VI) from synthetic wastewater: kinetics, isotherms and thermodynamics

Hexavalent chromium (Cr(VI)) contamination in drinking water due to industrial activities is a growing worldwide concern. Cr(VI) concentrations exceeding a few parts per billion (ppb) can cause serious health problems such as asthma, blood cancer, kidney-related diseases, liver and spleen damage, as well as neurological system, immunological deficiencies, and reproductive issues. This study, thus, explored the feasibility of employing a novel polymeric ferromagnetic nanocomposite adsorbent made of low-cost, biodegradable, and ultra-permeable materials from pulp and paper sludge for adsorptive removal of hexavalent chromium (Cr6+) from synthetic wastewater. Vibrating-sample magnetometer (VSM), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmet-Teller surface area (BET), and Fourier transform infrared (FTIR) were used to analyze the produced nanocomposite adsorbent. The Fourier transform infrared results confirmed the presence of adsorptive peaks attributed to −OH, −NH2, and FeO. Scanning electron microscopy micrographs revealed a porous adsorbent surface. XRD revealed the existence of the crystalline spinel-structured magnetite (Fe3O4) phase of iron oxide, while the saturation magnetization was established to be 26.90 emu/g. The Brunauer–Emmett–Teller analysis confirmed a slight decrease in the surface area of the nanocomposite adsorbent to 6.693 m2.g−1, compared to Fe3O4 (7.591 m2.g−1). The optimum conditions for Cr6+ removal were pH 2.0, 1.0 g/L adsorbent dose, room temperature (25°C), 120 min contact time, and 20 mg/L pollutant concentration. During removal, the Cr(VI) was adsorbed by electrostatic attraction and/or reduced to trivalent chromium Cr(III). At low starting Cr(VI) concentrations, chemisorption dominated the removal process, but as concentrations increased, physisorption became more significant. The prepared nanocomposite adsorbent presented exceptional removal efficiency of up to 92.23%, indicating that it may be useful for the adsorption of metal ions from industrial and household wastewater.

Performance and Mechanism of Porous Carbons Derived from Biomass as Adsorbent for Removal of Cr(VI)

To solve the problem of heavy metal hexavalent chromium (Cr(VI)) pollution in water bodies, this study was carried out to prepare nitrogen-doped porous carbon by using bamboo shoots as the raw material and KHCO3 as the activator, which has a good ability to remove Cr(VI) from water bodies. The prepared N-doped carbon materials were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, and scanning electron microscopy (SEM). The results showed that the prepared carbon material had hierarchical pore structures and abundant functional groups, which is conducive to the adsorption of Cr(VI). The effects of various factors on the adsorption performance of Cr(VI), such as the carbon materials prepared under different conditions, the pH of the initial solution, the concentration of the initial solution, and the contact time between the carbon and Cr(VI), were explored. The results showed that the bamboo shoot-based nitrogen-doped carbon materials, especially BSNC-800 (prepared at 800 °C with a mass ratio of KHCO3 to bamboo shoot of 4:1), performed well in removing Cr(VI) from a water solution. The maximum adsorption of Cr(VI) by BSNC-800 under equilibrium conditions was 385.8 mg g−1 (conditions: at the pH of 2 with the initial concentration of 400 mg L−1). The adsorption kinetics and isotherms were analyzed, and the adsorption mechanism was discussed. It can be found that the adsorption of Cr(VI) by BSNC-800 fits better with the Langmuir isotherm model and the pseudo-second-order kinetic model. The adsorption mechanism between the Cr(VI)-containing solution and BSNC-800 was controlled by membrane diffusion and chemisorption. The results broaden the ways of utilizing biomass resources as precursors of carbon materials, which is significant and helpful for applying biomass carbon materials as adsorbents for wastewater treatment.

Designed synthesis of demethylated-hydroxymethylated lignin-based adsorbent for removal of Cr(VI) ions from wastewater

Lignin-based adsorbents for the removal of Cr(VI) ions have attracted intensive attention due to the advantages of renewability, biodegradablity, low cost and environmental friendliness. However, there are still a lot of challenges such as poor adsorption capacity, low lignin content in adsorbents, and harsh preparation conditions. Here, a tandem hydroxymethylation-demethylation method is proposed for preparing an excellent lignin-based Cr(VI) adsorbent (DHKL), which features with high lignin content (>85 wt%) and high hydroxyl content (up to 6.26 mmol/g) under milder conditions. The prepared DHKL exhibits an adsorption capacity reaching up to 1040.9 mg/g and can maintain this capacity even in the presence of other metal ions in the solution. Model analyses indicate that chemisorption occurring in a monolayer is the main process, which is spontaneous and endothermic. Structural changes of DHKL before and after adsorption indicated that Cr(VI) ions are mainly reduced to Cr(III) ions by hydroxyl groups with some of the absorbed Cr ions dispersed into the inner part of DHKL. Based on these results, the detailed possible adsorption mechanism is deduced, providing guidance for designing, producing and utilizing lignin-based adsorbents.

Removal of hexavalent chromium using activated and magnetic Ziziphus Jujube seed biochar — a column study

ABSTRACT In this study, activated and magnetic biochar prepared from Ziziphus Jujube Seeds (ZJS) is used to remove Hexavalent Chromium (Cr(VI)) using Fixed Bed Column Experiment. Physicochemical characteristics of the activated and magnetic biochar such as functional groups, surface area, morphological study, and magnetic properties were analyzed. The column experiment was carried out for varying bed heights (2, 4, 6, 8, 10 cm), flow rates (20, 30 ml/min), and initial chromium concentrations (40, 60, 80 ppm) to determine adsorption performance of the studied biochar. The characteristic study found that magnetic biochar (MB) has good magnetic properties and crystallinity nature with essential functional groups such as C-O, FeO. The study found that Magnetic Biochar (MB) effectively removed 99% of hexavalent chromium through column adsorption under optimal conditions, including bed height of 6 cm, 60ppm Chromium concentration, and flow rate of 20 ml/min. Kinetic model study showed that Magnetic Biochar (MB) showed very good agreement with Adam Bohart Model, with R2 of 0.97, which is best fit model than other model studies whereas the other model showed a lesser R2 value. The study reveals that magnetic biochar from Ziziphus Jujube Seed is optimal adsorbent for removal of Cr(VI) through column adsorption experiment.

Sustainable removal of hexavalent chromium using graphene oxide - Iron oxide reinforced pectin/polyvinyl alcohol magnetic gel beads

The study investigated removal of hexavalent chromium Cr (VI) from aqueous solution using graphene oxide‑iron oxide reinforced pectin/polyvinyl alcohol magnetic gel beads prepared through co-precipitation and freeze-drying technique. Scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer, N2 adsorption-desorption isotherm, and zeta potential are used for characterization. The surface area of magnetic gel beads calculated by BET method was determined to be 100.95 m2/g, significantly higher than that of GO and GO-Fe3O4. The optimum removal efficiency of GO-Fe3O4/Pec/PVA was assessed by batch method at variables such as pH(1–6), adsorption time(0–180 min), and temperature(25–35 °C). Accordingly, 0.2 g GO-Fe3O4/Pec/PVA dose, pH 2, contact time: 120 min at 25 °C were found to be the optimal conditions, and maximum adsorption capacity of GO, GO-Fe3O4 and GO-Fe3O4/Pec/PVA toward Cr(VI) removal was found to be 39.5, 62.5 and 78.55 mg g−1, respectively. Kinetic and isotherm studies indicate adsorption data follow pseudo-second-order kinetic and Langmuir isotherm models. Thermodynamic studies showed adsorption capacities of adsorbents decreased when temperature increased which indicated adsorption for Cr (VI) was an exothermic process. The activation energies were found to be 34.92, 26.57, and 35.23 KJ mol−1 for GO, GO-Fe3O4, and GO-Fe3O4/Pec/PVA, respectively, which illustrated adsorption of Cr(VI) onto the surface of adsorbents was a physical process. The beads exhibit excellent recoverability and reusability over five cycles. Overall, GO-Fe3O4/Pec/PVA demonstrates exceptional adsorption properties and can serve as an efficient, stable, less toxic, and magnetically separable adsorbent for removal of Cr(VI) from aqueous solution.

Preparation and characterization of Allium cepa extract coated biochar and adsorption performance for hexavalent chromium

The elimination of hazardous metal ions from contaminated water has been an important procedure to improve the quality of the water source. Hence, this study presents the fabrication of Allium cepa extract-coated biochar for the elimination of Cr (VI) from wastewater. The synthesized biochar (SBCH) and modified biochar (BMOJ) were characterized by making use of FTIR, BET, XRD, TGA and SEM. Optimum Cr (VI) removal was achieved at solution pH 2, 0.05 g adsorbent dosage and 180 min agitation period. The adsorptive removal of Cr (VI) onto SBCH and BMOJ followed the pseudo-second-order kinetic model with a satisfactory sum of square residuals (SSR) of 3.874 and 5.245 for SBCH and BMOJ, respectively. Meanwhile, Freundlich isotherm was found to best describe the uptake of Cr (VI) SBCH and BMOJ. Experimental data showed an adsorption capacity of 37.38 and 25.77 mg g−1 and a maximum efficiency of 85.42% and 51.63% for BMOJ and SBCH, respectively. BMOJ also showed good antioxidant characteristics. Thermodynamic data revealed that the uptake of Cr (VI) onto the SBCH and BMOJ was an exothermic and endothermic (ΔH: SBCH = − 16.22 kJ mol−1 and BMOJ = 13.74 kJ mol−1), entropy-driven (ΔS: SBCH = 40.96 J K−1 mol−1 and BMOJ = 93.26 J K−1 mol−1) and spontaneous process. Furthermore, BMOJ demonstrated excellent reusability and promising characteristics for industrial applications.

Adsorptive removal of Cr (VI) from wastewater using magnetite–diatomite nanocomposite

Abstract Magnetite-diatomite nanocomposite was synthesized through co-precipitation methods as an effective Cr(VI) removal adsorbent. The properties of diatomite, thermochemically modified diatomite (TMD), and magnetic–diatomite nanocomposite (MDN) were investigated using Fourier-transform infrared spectroscopy, X-ray diffraction analysis, Brunauer–Emmett–Teller, and complete silicate chemical analysis. The MDN shows 98.89% adsorption removal at optimized conditions using the response surface methodology of Box–Behnken Design. The kinetic data for Cr(VI) sorption on MDN were well described by pseudo-second order, which indicates the Cr(VI) adsorption was mainly due to chemisorption. The isotherm data show that the Langmuir and Freundlich models better described Cr(VI) ion sorption data. The thermodynamic parameters ΔG°, ΔH°, and ΔS° were estimated, and the results indicate Cr(VI) sorption on MDN was a spontaneous (ΔG° < 0) and exothermic process (ΔH° < 0). The proper Fe3O4 loading into TMD improves the gram susceptibility (Xg) of MDN for magnet separation. The regeneration of nanocomposite material revealed over 80% Cr(VI) removal efficiency after five consecutive adsorption–desorption cycles. The produced MDN was tested for the removal of Cr(VI) from real tannery wastewater. The obtained results suggest the possibility of using this nanocomposite as an effective, efficient adsorbent to remove Cr(VI) laden wastewater.

Adsorptive removal of Cr(VI) and Cu(II) ions from aqueous solutions by a natural moss

Abstract The aim of the present research is to develop a new, fast, and easily applicable adsorption method for the removal of hazardous Cr(VI) and Cu(II) ions from the polluted industrial wastewater by using Racomitrium ericoides (Brid.) Brid. (REB), a type of moss. Although there are studies in the literature in which different moss species were used for the removal of heavy metals (HMs), REB was used for the first time in this study. Adsorption experiments were carried out through a batch system. The impact of significant experimental parameters showed that the optimum values of initial pH were 2.0 for Cr(VI) retention and 5.0 for Cu(II), and 360 min was selected as the optimum contact time for both HMs. An artificial neural network (ANN) model was applied to create a predictive model for the uptake efficiency of HMs. Adsorption kinetics of Cr(VI) and Cu(II) ions followed the pseudo-second order model. The maximum adsorption capacities of REB identified through the Langmuir model were 41.2 mg g−1 for Cr(VI) and 22.7 mg g−1 for Cu(II) ions. The results of the study demonstrated that REB can be utilized as an abundant, low-cost, and effective adsorbent in removal of HMs from aqueous solutions.

Adsorptive removal of Cr (VI) from aqueous solution using laboratory prepared ZnO nanoparticles

Nano sized zinc oxide (ZnO) been successfully prepared in laboratory by precipitation technique. As prepared ZnO materials were characterized by XRD and SEM analyses. The XRD pattern showed the crystallinity of the material and average crystallite size was found to be 16.61 nm. The SEM images of ZnO nanoparticle revealed that it was flakes like structure having smooth texture. Batch adsorption experiments were performed to investigate the percentage removal of Cr (VI) from aqueous solution. The effects of Cr (VI) concentration, pH of solution, adsorbent dose and contact time variations were studied in order to have adsorptive efficiency of as prepared ZnO nanoparticles. The optimum contact time for maximum adsorption was found to be 90 minutes. The optimum pH was found to be 2.0 at an initial concentration of 20 mg/L. Similarly, the optimum dose of ZnO for the adsorption of Cr (VI) was found to be 0.4 g. The adsorption properties of ZnO were then evaluated by using Langmuir, Freundlich and Temkin isotherm models. The maximum adsorption capacity (Qm) was found to be 3.43 mg/g which is in good agreement with literature value. The correlation value showed that Langmuir isotherm model was found to be more favorable than Freundlich and Temkin adsorption isotherm model, indicating the presence of homogeneous equivalent active sites in ZnO with monolayer adsorption.

Ethylenediamine-functionalized MnFe2O4 @ferrihydrite as a magnetic adsorbent for removal of Cr(VI): Adsorption and mechanism studies

Chromium-contaminated water can seriously harm the health of human being. In this work, a novel magnetic manganese ferrite@ferrihydrite nanocomposites (MnFe2O4 @Fh-EDA) was successfully synthesized utilizing ethylenediamine (EDA) via co-precipitation method and applied in Cr(VI) removal. Batch adsorption tests demonstrated that MnFe2O4 @Fh-EDA (qmax= 51.36 mg/g) could maintain stable removal efficiency (≥ 85.6%) at the pH of 2.0–9.0 and exhibit higher adsorption capacity than that of MnFe2O4 and ferrihydrite. Results revealed that EDA enhanced the adsorption capacity as well as acid resistance of ferrihydrite because the protonation of -NH2 consumed hydrogen ions during adsorption. The magnetic saturation of MnFe2O4 @Fh-EDA (24.82 emu/g) ensured that it could be easily separated and regenerated after reaction. It was also found that electrostatic attraction, ions exchange and redox reactions all contributed to Cr(VI) elimination. In brief, MnFe2O4 @Fh-EDA would be a promising adsorbent as it not only displayed great adsorption capacity but also maintained outstanding magnetic separation capability. Therefore, this work would offer references and inspiration to design the new MnFe2O4-based materials for further applications in heavy metal removal from wastewater.

Adsorptive removal of Cr (VI) using mesoporous iron-aluminum oxyhydroxide-polyvinyl alcohol self-supporting film: Kinetics, optimization studies and mechanism

Adsorptive removal of Cr (VI) using mesoporous iron-aluminum oxyhydroxide-polyvinyl alcohol self-supporting film: Kinetics, optimization studies and mechanism

Adsorptive removal of Cr (vi) onto Xanthated tea waste from aqueous solution

Adsorptive removal of Cr (vi) onto Xanthated tea waste from aqueous solution

Development of nitrogen-doped graphene/MOF nanocomposites towards adsorptive removal of Cr(VI) from the wastewater of the Herbert Bickley treatment works

Industrial effluents laden with Cr(VI) pose considerable health risks to human and animal life if left untreated. Hence, in this work, metal–organic framework-5/nitrogen-doped graphene (MOF-5/NGO) nanocomposites bearing Cr(VI) adsorption properties were fabricated. These unique materials were produced with increasing NGO loadings (0.05, 0.10 and 0.15 wt%) to investigate the role of NGO content on the chemical and physical properties of the composites. The FTIR spectra show the nanocomposites be to be rich in surface –OH and –COOH functional groups. Raman spectroscopy confirmed bond formation between the MOF-5 and NGO through downshift of the G- and 2D-bands. XRD analysis showed MOF-5/NGO nanocomposites, MOF-5 and the NGO to be highly crystalline while thermogravimetric analysis indicated the thermal stabilities of the composites to be enhanced. SEM studies revealed the NGO flakes to be dispersed on the MOF-5 microstructures prior to adsorption and the disappearance of microstructures post adsorption. The as-synthesized nanocomposites exhibited BET surface area in the range 384.55–395.56 m2.g−1 which is a significant increase from that of MOF-5 261.00 m2.g−1. The optimal conditions for maximum Cr(VI) adsorption were determined to be: pH = 2, contact time of 60 min, adsorbent dosage of 6 mg.L−1, initial Cr(VI) concentration of 0.5 mg/L and temperature of 30 °C. A maximum adsorption efficiency of 46.1 % was achieved by the composite MOF-5/NGO (0.05 wt%) and not significantly compromised by competing metal ions. The Cr(VI) removal on MOF-5/NGO nanocomposites is well described by the Langmuir isotherm, confirming a chemisorption process. In addition, the thermodynamic studies confirmed the adsorption process to be favorable, spontaneous and endothermic. The Cr(VI) removal % on MOF-5/NGO from real water was found to be 52.1 %. Therefore, the novel MOF-5/NGO nanocomposite can be applied for efficient Cr(VI) removal from industrial wastewater due to synergistic surface morphologies between NGO and MOF-5 units characterized by better adsorption capacity not met by pristine materials.

Methodical study of chromium (VI) ion adsorption from aqueous solution using low-cost agro-waste material: isotherm, kinetic, and thermodynamic studies.

This study involved preparation and modification of Saccharum officinarium as adsorbent used for the removal of chromium (VI) ions in a batch process. The adsorbent was modified with oxalic acid for improved performance of the adsorbent by increasing the surface area of the adsorbent. Surface morphology of the adsorbents was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), while Fourier transform infrared (FT-IR) analysis was carried out before and after the adsorption of Cr (VI) ions to determine the participating functional group in the processes. The optimum adsorption was attained at pH 2 and contact time of 180min with efficiency of adsorption of 56.7 and 92.6% onto RSO and MSO, respectively. The adsorption capacity increases with increase in initial metal ion concentration of the sorption mixture. The isotherms studies indicate that the experimental data were best fitted to Freundlich, Langmuir, and Sips models with R2 = 0.999 for adsorption of Cr (VI) ions onto raw S. officinarium (RSO) and modified S. officinarium (MSO). The maximum adsorption capacity obtained were 227.27 and 243.90mg*g-1 while the adsorption energy obtained from D-R were found to be 3.460 and 6.325kJ*mol-1 onto RSO and MSO, respectively. This revealed that the physiosorption process was favored in interaction of Cr (VI) ions onto both adsorbents. Separation factors obtained showed that the process is favored with increase in initial concentration of the adsorbate. Thermodynamic parameter values obtained showed that the sorption of Cr (VI) ions onto RSO and MSO is feasible, spontaneous, and endothermic in nature. The positive value of ΔS° indicates increase in disorderliness of the adsorption process. Kinetic data achieved at different initial concentrations of adsorbate have been analyzed, and the mechanism of the reaction was also studied by intra-particle and Bangham kinetic model. Each of the models was tested with R2 ˃ 0.9, where pseudo-second-order is the best-fitted model and Bangham mechanism only fitted with adsorption of Cr (VI) ions onto RSO. The reusability potential of RSO and MSO contributes to the economic values and reliability of the adsorbents for removal of Cr (VI) ions from aqueous solution.

Adsorptive removal of Cr(III)-EDTA chelate from an aqueous solution by magnetic mesoporous silica microspheres.

The 3-aminopropyltrimethoxysilane-modified magnetic mesoporous adsorbent (FNMs/APTES) was synthesized and applied to remove Cr(III)-EDTA chelates from water. The characterization of FNMs/APTES showed that the prepared adsorbent with a magnetic mesoporous structure was successfully grafted by APTES, which has good stability under acid conditions. The maximum capacities of FNMs/APTES for Cr(III)-EDTA adsorption at 15, 25 and 35 °C and pH 4.0 were 12.58, 13.13 and 14.00 mg·g-1, respectively. The adsorption isotherm of FNMs/APTES for Cr(III)-EDTA conforms to the Freundlich model, and the adsorption kinetic model accords with the pseudo-second-order kinetic model. Adsorption of Cr(III)-EDTA on the adsorbent was not affected in the presence of Na+, K+ and Ca2+ even at 100 mmol·L-1. Cr(III)-EDTA was anchored on FNMs/APTES through electrostatic interaction between protonated amino groups of adsorbents and Cr(III)-EDTA anions, and Cr(III)-EDTA chelates were adsorbed as a whole on the adsorbent. The Cr(III)-EDTA-saturated adsorbent can be readily regenerated in HCl solution and 83.03% of the initial Cr(III)-EDTA adsorption capacity remains after four adsorption-regeneration experiment cycles. The results highlighted that the FNMs/APTES as a potential adsorbent can be applied for the minimization of Cr(III)-EDTA chelates from water.

Algal-derived biochar as an efficient adsorbent for removal of Cr (VI) in textile industry wastewater: Non-linear isotherm, kinetics and ANN studies

Textile industries release effluent that contains the vast majority of heavy metals in which Cr (VI) is a toxic carcinogenic element that causes an environmental problem. The aim of the work is to synthesize algae-derived biochar derived from algae using slow pyrolysis at an operating temperature of 500 °C, a heating rate of 10 °C/min and a residence time of 60 min and to use it as an adsorbent to remove Cr (VI). The batch experiment was carried out using different concentrations of Cr (VI) (1, 10, 25, 50, 100, 125, 150 and 200 ppm) at different intervals of time (2.5, 5, 10, 15, 30, 60, 120 and 240 min). The maximum removal percentage of Cr (VI) is 97.88% for the metal concentration of 1 ppm exhibiting non-linear adsorption isotherm (Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin models) and kinetic models (pseudo-first order, pseudo-second order, nth order, and intra-particle diffusion) were analyzed using a solver add-in of Microsoft Excel. According to the results, the Langmuir isotherm model (R2 = 0.999) and pseudo-nth order models are suitable to describe monolayer adsorption and the process kinetics, respectively. The maximum adsorption capacity of algal biochar to adsorb is 186.94 mg/g. For the prediction of the optimal removal efficacy, an artificial neural network of the MLP-2-7-1 model was used. The results obtained are useful for future work using algal biochar as an adsorbent of Cr (VI) from textile wastewater to achieve sustainable development goals.

Full-Lignin-Based adsorbent for removal of Cr(VI) from waste water

The development of full-lignin-based adsorbents with high adsorption capacity for the removal of Cr(VI) ions from wastewater has intensively attracted attention. However, it is still a challenge up to now due to the low reactivity and complexity of lignin structure. Herein, a high hydroxyl content demethylated alkaline lignin (DAL) was prepared using AlCl3 as the modification reagent. With this DAL as the full-lignin-based adsorbent, the adsorption capacity for Cr(VI) was up to 703.6 mg/g at 30 °C. Moreover, when the concentration of Cr(VI) ions was below 100 mg/L, the removal efficiency was high up to 99.9 % by only using 10 mg adsorbent in 50 mL solution. On the basis of the isotherm, kinetic, and thermodynamic model analyses, it could be concluded that the chemisorption occurred in monolayer on the surface of the adsorbent, and the adsorption process was endothermic and spontaneous. The characterizations of the spent adsorbents showed that the adsorption might be driven by the reduction of negatively charged Cr2O72- or HCrO4- ions to positively charged Cr3+, which could generate strong electrostatic interaction with the oxygen containing groups in lignin. Simultaneously, the toxicity of chromium ions was significantly decreased during the reduction. This work provides a new way to realize high adsorption capacity of Cr(VI) ions by a full-lignin-based adsorbent, and accelerates the high-value utilization of lignin.

Inclusion of bimetallic Fe0.75Cu0.25-BDC MOFs into Alginate-MoO3/GO as a novel nanohybrid for adsorptive removal of hexavalent chromium from water

Metal–organic frameworks (MOFs) as porous materials have recently attracted research works in removal of toxic pollutants from water. Cr(VI) is well-known as one of the most toxic forms of chromium and the selection of efficient and effective Cr(VI)-remediation technology must be focused on a number of important parameters. Therefore, the objective of this work is to fabricate a novel nanohybrid adsorbent for removal of Cr(VI) by using assembled bimetallic MOFs (Fe0.75Cu0.25-BDC)-bound- Alginate-MoO3/Graphene oxide (Alg-MoO3/GO) via simple solvothermal process. The aimed Fe0.75Cu0.25-BDC@Alg-MoO3/GO nanohybrid was confirmed by FTIR, SEM, TEM, XRD and TGA. Adsorptive extraction of Cr(VI) from aqueous solution was aimed by various optimized experimental parameters providing optimum pH = 3, dosage = 5–10 mg, starting concentration of Cr(VI) = 5–15 mg L−1, shaking time = 5–10 min. The point of zero charge (pHPzc) was 3.8. For Cr(VI) removal by Fe0.75Cu0.25-BDC@Alg-MoO3/GO, four isotherm models were estimated: Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) with calculated correlation coefficient (R2 = 0.9934) for Langmuir model which was higher than others. The collected results from the kinetic study clarified that pseudo-second order model is the most convenient one for describing the adsorption behavior of Cr(VI) and therefore, the adsorption process was suggested to rely on a chemisorption mechanism. Thermodynamic parameters referred that the adsorption mechanism is based on a spontaneous and exothermic process. Finally, the emerged Fe0.75Cu0.25-BDC@Alg-MoO3/GO nanohybrid was confirmed as an effective adsorbent for extraction of hexavalent chromium from real water specimens (tap, sea water and wastewater) with percentage recovery values > 98%.

Synthesis and Characterization of Fe3O4-Bentonite Nanocomposite Adsorbent for Cr(VI) Removal from Water Solution

Bentonite-magnetite nanocomposite adsorbent (BMNC) was made and investigated for its adsorption removal of Cr(VI) from an aqueous solution. This adsorbent was prepared by the coprecipitation method from sodium bentonite (BNa) with iron chloride solution at controlled pH and under an inert atmosphere. These adsorbents were characterized by atomic absorption spectrophotometer (AAS), Brunauer–Emmett–Teller (BET), dynamic light scattering (DLS), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) analyses. Particle size of BMNC was in the range of 15 to 95 nm as per DLS. The intercalation of magnetite nanoparticles onto the bentonite clay increased its specific surface area from 142 to 177 m2/g as per BET analysis. Experimental design optimization results in 96.5% of Cr(VI) removal from the water solution at optimized adsorption parameters viz., adsorption time of 101 min, pH of 1.95, adsorbent dose of 1.12 g/L, and initial Cr(VI) concentration of 36.2 mg/L. The results of these studies demonstrate that the BMNC performs well. Moreover, the adsorption of Cr(VI) onto the BMNC was found to be the best fit with Langmuir isotherm (R2 = 0.9984) and a maximum adsorption capacity of 98 mg/g. The kinetics of the adsorption process was found to be a pseudo-second-order model (R2 = 0.9912). The BMNC also showed favourable reusability for adsorbate Cr(VI) ions removal from the water solution.

Non linear regression analysis and RSM modeling for removal of Cr (VI) from aqueous solution using PANI@WH composites

An aquatic plant, water hyacinth was used after modification with poly-aniline (PANI@WH) as an adsorbent for removal of Cr (VI) from aqueous solution. The effect of pH, time, dose and concentration on Cr (VI) removal was investigated following batch adsorption process. The adsorption of Cr (VI) on PANI@WH adsorbent followed Freundlich adsorption isotherm as well as pseudo-second-order kinetic model. Maximum adsorption capacity obtained by isotherm has been achieved as 31.45 mgg−1 at 323K. Adsorption of Cr (VI) proceeds through film diffusion rather than intra-particle diffusion. Thermodynamic studies suggested endothermic and spontaneous nature of adsorption due to positive enthalpy and negative Gibbs free energy values. On the basis of the value of mean free energy, Gibb's free energy of adsorption and activation energy obtained in the present investigation suggested that adsorption of Cr (VI) on polyaniline coated water hyacinth occurs through physical adsorption. Surface characterization studies such as Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared, Brunauer, Emmett and Teller surface area, X-ray photoelectron spectroscopy, X-ray diffractometer, atomic force microscopy and high resolution transmission electron microscopy illustrated adsorption mechanism of the adsorbent. The predicted % removal of Cr (VI) was obtain by response surface methodology model are compared with the experimental % removal of Cr (VI) obtained by batch adsorption process. Prepared composite adsorbent can be reused for several cycles and it gives 85% Cr (VI) removal efficiency even after 4th cycle which shows its good regeneration ability.