Removal of Hexavalent Chromium from Aqueous Solution Using Low-Cost Activated Carbons Derived from Agricultural Waste Materials and Activated Carbon Fabric Cloth

Sorption of Cr(III) and Cr(VI) to K2Mn4O9 nanomaterial a Study of the effect of pH, time, temperature and interferences

A Rancieite type material (K₂Mn₄O₉) nanomaterial was synthesized and tested for the removal of chromium (III) and chromium (VI) from aqueous solutions. The synthesized nanomaterial was characterized using powder XRD and SEM. XRD showed weak diffraction peaks at only at the angles associated with K₂Mn₄O₉. The SEM corroborated that the nanoparticles were present; however, the nanoparticles were clustered into larger aggregates. Batch studies were performed to determine the optimum pH, capacity, time dependency, interferences, and the thermodynamics of the binding. The optimum pH for the binding of Cr(III) and Cr(VI) were determined to be pH 5 and pH 2, respectively. Isotherm studies were performed at temperatures of 4 , 25 , and 45 for Cr(III) and Cr(VI) and showed binding capacities of 21.7 mg/g, 36.5 mg/g, 41.8 mg/g for Cr(III). The Cr(VI) binding capacities were 4.22 mg/g, 4.08 mg/g, and 3.25 mg/g at the respective temperatures. The thermodynamic studies showed that the binding processes for the reactions were spontaneous and endothermic, with a ΔH was 17.54 kJ/mol for Cr(III) and 6.05 kJ/mol for Cr(VI). The of sorption for Cr(III) were determined to be -3.88 kJ/mol, -5.83 kJ/mol and -7.03 kJ/mol at the aforementioned temperatures. The ΔG values for the Cr(VI) sorption were determined to be -4.89 kJ/mol, -5.64 kJ/mol, and -6.05 kJ/mol. In addition, the ΔS values for Cr(III) and Cr(VI) were determined to be 77.92 J/mol and 39.49 J/mol, respectively. The thermodynamics indicate that the binding of Cr(III) and Cr(VI) is spontaneous and endothermic.

A Comparative Study of Raw and Metal Oxide Impregnated Carbon Nanotubes for the Adsorption of Hexavalent Chromium from Aqueous Solution

The present study reports the use of raw, iron oxide, and aluminum oxide impregnated carbon nanotubes (CNTs) for the adsorption of hexavalent chromium (Cr(VI)) ions from aqueous solution. The raw CNTs were impregnated with 1% and 10% loadings (weight %) of iron oxide and aluminum oxide nanoparticles using wet impregnation technique. The synthesized materials were characterized using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Batch adsorption experiments were performed to assess the removal efficiency of Cr(VI) ions from water and the effects of pH, contact time, adsorbent dosage, and initial concentration of the Cr(VI) ions were investigated. Results of the study revealed that impregnated CNTs achieved significant increase in the removal efficiency of Cr(VI) ions compared to raw CNTs. In fact, both CNTs impregnated with 10% loading of iron and aluminum oxides were able to remove up to 100% of Cr(VI) ions from aqueous solution. Isotherm studies were carried out using Langmuir and Freundlich isotherm models. Adsorption kinetics of Cr(VI) ions from water was found to be well described by the pseudo-second-order model. The results suggest that metallic oxide impregnated CNTs have very good potential application in the removal of Cr(VI) ions from water resulting in better environmental protection.

Flexible Electrospun Carbon Nanofiber/Tin(IV) Sulfide Core/Sheath Membranes for Photocatalytically Treating Chromium(VI)-Containing Wastewater

We report an efficient method for fabricating flexible membranes of electrospun carbon nanofiber/tin(IV) sulfide (CNF@SnS₂) core/sheath fibers. CNF@SnS₂ is a new photocatalytic material that can be used to treat wastewater containing high concentrations of hexavalent chromium (Cr(VI)). The hierarchical CNF@SnS₂ core/sheath membranes have a three-dimensional macroporous architecture. This provides continuous channels for the rapid diffusion of photoelectrons generated by SnS₂ nanoparticles under visible light irradiation. The visible light (λ > 400 nm) driven photocatalytic properties of CNF@SnS₂ are evaluated by the reduction of water-soluble Cr(VI). CNF@SnS₂ exhibits high visible light-driven photocatalytic activity because of its low band gap of 2.34 eV. Moreover, CNF@SnS₂ exhibits good photocatalytic stability and excellent cycling stability. Under visible light irradiation, the optimized CNF@SnS₂ membranes exhibit a high rate of degradation of 250 mg/L of aqueous Cr(VI) and can completely degrade the Cr(VI) within 90 min.

Removal of hexavalent chromium ions using CuO nanoparticles for water purification applications

Copper(II) oxide nanoparticles were synthesized at low temperature using cold finger assisted magnetron sputtering technique and were applied as adsorbent for the rapid removal of noxious Cr(VI) ions from the solvent phase. The average size of CuO nanoparticles from TEM analysis was found to be 8nm in addition to this the BET surface area (84.327m(2)/g) was found to be significantly high in comparison to the previously CuO nanoparticles synthesized via green route. The synthesized CuO nanoparticles is crystalline in nature and exhibits monoclinic phase, which was confirmed using various analytical techniques such as SAED, XRD and Raman analysis. The impact of influential parameters including pH, adsorbent dose, contact time, stirring speed, initial Cr(VI) ions concentration, and temperature were optimized using batch adsorption method in order to obtain maximum removal of Cr(VI) ions. From the thermodynamic parameters, the positive value of enthalpy (ΔH) and negative value of Gibbs free energy (ΔG) indicate the endothermic and spontaneous nature of Cr(VI) ions adsorption, respectively. The adsorption kinetics data was well fitted and found to be in good agreement with the pseudo second order kinetic behaviour.

Designing a sulphonic acid functionalized benzimidazolium based poly(ionic liquid) for efficient adsorption of hexavalent chromium

Herein, the facile synthesis of sulphonic acid functioned benzimidazolium based poly(ionic liquid) (SBPIL) is reported for the first time and we investigated its efficacy towards the removal of Cr(vi).

Synthesis and characterization of MCM-49/MCM-41 composite molecular sieve: an effective adsorbent for chromate from water

MCM-49/MCM-41 was synthesized by a fast method via microwave assistance and was characterized for its application in heavy metal adsorption.

Removal of hexavalent chromium by using red mud activated with cetyltrimethylammonium bromide

The removal of hexavalent chromium [Cr(VI)] from aqueous solution by using red mud activated with cetyltrimethylammonium bromide (CTAB) was studied. The optimum operation parameters, such as CTAB concentration, pH values, contact time, and initial Cr(VI) concentration, were investigated. The best concentration of CTAB for modifying red mud was found to be 0.50% (mCTAB/VHCl,0.6 mol/L). The lower pH (<2) was found to be much more favourable for the removal of Cr(VI). Red mud activated with CTAB can greatly improve the removal ratio of Cr(VI) as high as four times than that of original red mud. Adsorption equilibrium was reached within 30 min under the initial Cr(VI) concentration of 100 mg L(-1). The isotherm data were analysed using Langmuir and Freundlich models. The adsorption of Cr(VI) on activated red mud fitted well to the Langmuir isotherm model, and the maximum adsorption capacity was estimated as 22.20 mg g(-1) (Cr/red mud). The adsorption process could be well described using the pseudo-second-order model. The result shows that activated red mud is a promising agent for low-cost water treatment.

A new solid phase microextraction method using organic ligand in micropipette tip syringe system packed with modified carbon cloth for preconcentration of cadmium in drinking water and blood samples of kidney failure patients

A simple and efficient miniaturized solid phase microextraction (M-SPμE) in a syringe system was developed for preconcentration of cadmium (Cd) in environmental and biological samples, followed by flame atomic absorption technique. The syringe system contains the micropipette tip packed with activated carbon cloth, coated with modified magnetic nanoparticles of iron oxide Triton X114 (ACC-NPs). Scanning electron microscopy and energy dispersive spectroscopy used for characterization of the size, morphology and elemental composition of ACC-NPs. The sample solution treated with a complexing reagent 8-hydroxyqunilone (8-HQ), and drawn into the syringe, filled with ACC-MNPs and dispensed manually for 2-10 drawing/discharging cycles. The analyte retained on ACC-NPs in micropipette tip-syringe system were then eluted with different volume of 1.5molL(-1) HCl by 1-5 drawing/discharging cycles. The syringe system directly couple with FAAS for analysis. The influence of different variables on the extraction efficiency of Cd, including adsorbent dosage, pH, sample volume, eluent volume and drawing/discharging cycles of syringe system were optimized. At optimized extraction conditions, the method showed good linearity in the range of 5-250μgL(-1), with a limit of detection 0.15μgL(-1). Repeatability of the extraction (%RSD) was <5%, n=5. The validity and accuracy of the method was checked by the certified reference materials. The proposed method was successfully applied for the determination of Cd in different drinking water and biological samples of kidney failure patients and healthy controls.

Temperature based adsorption studies of Cr(vi) using p-toluidine formaldehyde resin coated silica material

A PTFR coated silica material was developed, characterised and applied for the treatment of hexavalent chromium.

Inorganic nano-adsorbents for the removal of heavy metals and arsenic: a review

Schematic of inorganic adsorbents (INA) for heavy metal removal.

Synthesis of reduced graphene oxide-montmorillonite nanocomposite and its application in hexavalent chromium removal from aqueous solutions

The combination of Mt and rGO protect rGO from aggregation.

Synthesis of porous Fe3O4 hollow microspheres/graphene oxide composite for Cr(vi) removal

A composite of porous Fe3O4 hollow microspheres/graphene oxide (Fe3O4/GO) has been fabricated through a facile self-assembly approach. Driven by the mutual electrostatic interactions, the amine-functionalized Fe3O4 microspheres prepared by a hydrothermal method and then modified by 3-aminopropyltrimethoxysilane were decorated with negatively-charged GO sheets. The Fe3O4 microspheres were hollow with porous surfaces and the surfaces were successfully modified with the amine, which was confirmed by Fourier transform infrared spectroscopy. The specific saturation magnetization of Fe3O4/GO was 37.8 emu g(-1). The sorption performance of Fe3O4/GO for Cr(vi) was evaluated. The maximum sorption capacity for Cr(vi) on Fe3O4/GO was 32.33 mg g(-1), which was much higher than that of Fe3O4 microspheres. The GO sheets could not only prevent agglomeration of the Fe3O4 microspheres and enable a good dispersion of these oxide microspheres, but also substantially enhance the specific surface area of the composite. The Fe3O4/GO composite may be a promising sorption material for the separation and preconcentration of heavy metal ions from aqueous solutions in environmental pollution cleanup.

Mechanisms of chromium and arsenite adsorption by amino-functionalized SBA-15

The adsorption of Cr(VI) and As(III) by amino-functionalized SBA-15 (NH2-SBA-15) from single and binary systems were investigated in this work. The effects of pH and temperature on the adsorption of NH2-SBA-15 were studied. Adsorption kinetics, isotherm model, and thermodynamics were studied to analyze the experimental data. pH 2 was the optimum condition for the adsorption of Cr(VI) and pH 4 for As(III) adsorption. Increasing temperature had a positive effect on the removal of both Cr(VI) and As(III). The Freundlich isotherm model can depict the adsorption process best. The pseudo-second-order kinetic model fitted well with the kinetic data of Cr(VI) and As(III) in the single-component system. In the binary system, the adsorption of As(III) by NH2-SBA-15 was slightly enhanced with the presence of Cr(VI); however, As(III) had no obvious effect on the removal of Cr(VI). Regeneration experiments indicated that 0.1 mol/L NaHCO3 was an efficient desorbent for the recovery of Cr(VI) and As(III) from NH2-SBA-15; the desorption rates for Cr(VI) and As(III) were 91.6 and 33.59 %, respectively. After five recycling cycles, the removal rates were 88 and 7 % for Cr(VI) and As(III) adsorption by NH2-SBA-15, respectively.

Biosorption of Cr(VI) and Zn(II) ions from aqueous solution onto the solid biodiesel waste residue: mechanistic, kinetic and thermodynamic studies

In this present study, the biosorption of Cr(VI) and Zn(II) ions from synthetic aqueous solution on defatted J atropha oil cake (DJOC) was investigated. The effect of various process parameters such as the initial pH, adsorbent dosage, initial metal ion concentration and contact time has been studied in batch-stirred experiments. Maximum removal of Cr(VI) and Zn(II) ions in aqueous solution was observed at pH 2.0 and pH. 5.0, respectively. The removal efficiency of Cr(VI) and Zn(II) ions from the aqueous solution was found to be 72.56 and 79.81%, respectively, for initial metal ion concentration of 500 mg/L at 6 g/L dosage concentration. The biosorbent was characterized by Fourier transform infrared, scanning electron microscopy and zero point charge. Equilibrium data were fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and the best fit is found to be with the Freundlich isotherm for both Cr(VI) and Zn(II) metal ions. The kinetic data obtained at different metal ion concentration have been analysed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion models and were found to follow the pseudo-second-order kinetic model. The values of mass transfer diffusion coefficients (De) were determined by Boyd model and compared with literature values. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were analysed using the equilibrium constant values (Ke) obtained from experimental data at different temperatures. The results showed that biosorption of Cr(VI) and Zn(II) ions onto the DJOC system is more spontaneous and exothermic in nature. The results indicate that DJOC was shown to be a promising adsorbent for the removal of Cr(VI) and Zn(II) ions from aqueous solution.

Selective removal of Cr(VI) from aqueous solution by adsorption on mangosteen peel

Mangosteen peel, rich in polyphenolic compounds, was used to prepare the adsorbent exhibiting highly selective adsorption for Cr(VI) over other metal ions such as Pb(2+), Fe(3+), Zn(2+), Cd(2+), and Cr(3+) at the pH values of 1∼4. The chemical modification method proposed by using calcium hydroxide is quite cost-effective and ecofriendly without using any toxic reagents or causing any secondary pollution. The adsorption isotherm results revealed that the adsorption of Cr(VI) on the gel fit well the Langmuir adsorption model, and the maximum adsorption capacity for Cr(VI) at pH levels 1, 2, 3, and 4 was evaluated to be 2.46, 2.44, 1.99, and 2.14 mol/kg, respectively. The adsorption mechanism for Cr(VI) on the saponified gel was verified to follow an esterifiaction reaction coupled with the reduction of Cr(VI) to Cr(III) in which H(+) plays a role of promoter. Thus, modified mangosteen peel gel has the prominent selectivity and low cost for Cr(VI) removal.

Biosorption of Cr(VI) from aqueous solution by chemically modified potato starch: equilibrium and kinetic studies

The biosorption capacity of chemically modified potato starch (CPS) for Cr(VI) from aqueous solution was investigated. The materials derived from carbohydrates are biodegradable and are generally regarded as safe and environmentally acceptable. The hydroxyl, carboxyl and carbonyl groups are responsible for the biosorption process. In the present study, the influence of various important parameters such as pH, time, biosorbent dose and initial Cr(VI) concentration on the biosorption capacity were investigated. The isotherms such as Langmuir, Freundlich and Tempkin were studied. The Freundlich and the Redlich-Peterson isotherms had been well fitted the biosorption of Cr(VI) with chemically modified potato starch. The kinetics of Cr(VI) removal using chemically modified potato starch was well explained by second-order kinetic model. The thermodynamic parameters were also evaluated from the biosorption measurements. Among the various desorbing agents tested, 98.2 percent chromium recovery was achieved with 0.1molL(-1) NaOH.

Foundry sands as low-cost adsorbent material for Cr (VI) removal

The potential of foundry sands, industrial waste from the iron foundry industry, was evaluated for the removal of Cr (VI) using discontinuous assays. Chemical foundry sands are composed of fine silica sand, furanic resins as binder, chemical catalyst and residual iron particles. The influence ofpH, agitation rate and metal concentration on the removal process was investigated. Kinetic and equilibrium tests were conducted to determine Cr (VI) removal from aqueous solutions at a temperature range of 25-55 degrees C. Cr (VI) removal of 40-100% for a range of pH 6-1.6 was obtained. This removal was attributed to the presence of a large number of protonated silanol and aluminol groups. Cr (VI) adsorption in foundry sands follows a pseudo-second-order kinetic reaction (Ho model, r2 > 0.999) reaching kinetic constants of 0.341, 0.551, 0.775 and 0.920 g/mg h at 25, 35, 45 and 55 degrees C, respectively. The adsorption data were fitted to the Langmuir adsorption isotherm model (r > 0.99) obtaining adsorption capacities (q(max)) of 1.99, 2.40, 2.50, and 3.14 mg Cr (VI)/g sand at 25, 35, 45 and 55 degrees C, respectively. Calculated Gibbs free energy change (deltaG0), adsorption energy (E) and activation energy (E(a)) values indicate that a physisorption mechanism governs Cr (VI) adsorption process in foundry sands.

Biosorption of Ni(II) from aqueous solutions by Litchi chinensis seeds

The potential of Litchi chinensis seeds (LCS) for biosorption of Ni(II) ions from aqueous solutions was investigated in batch systems in terms of kinetics, equilibrium and thermodynamics. Experimental data showed that the biosorption capacity of LCS was dependent on operating variables such as solution pH, initial Ni(II) concentration, contact time, and temperature. The optimum pH value for Ni(II) biosorption was 7.5. Significant enhancement of Ni(II) biosorption was observed by increasing initial metal concentration and temperature. Modeling of sorption kinetics showed good agreement of experimental data with the pseudo-second-order kinetic model. Langmuir model exhibited the best fit to experimental data. According to this isotherm model, the maximum Ni(II) biosorption capacity of LCS is 66.62 mg g(-1). The calculated thermodynamic parameters showed that the biosorption of Ni(II) ions is an endothermic and non-spontaneous process. Results indicate that LCS can be used as an effective and environmentally friendly biosorbent to detoxify Ni(II)-polluted wastewaters.

Development and Environmental Applications of Activated Carbon Cloths

Activated carbon cloths have received growing attention because they offer comparative advantages over the traditional powdered or granular forms of this well-known adsorbent, providing further potential uses for technological innovations in several fields. The present article provides an overview of research studies and advances concerned with the development of activated carbon cloths and their use as adsorbent in environmental applications, mostly reported in the last years. The influence of some fabrics and textile wastes used as precursors, and of main activation process variables on the development and physicochemical, mechanical and/or electrical properties of the resulting activated carbon cloths are first reviewed. Then, investigations dealing with the removal of water and air pollutants by adsorption onto activated carbon cloths, including advances toward optimizing their regeneration after organic vapors saturation, are presented.

Rapid reduction of Cr(VI) coupling with efficient removal of total chromium in the coexistence of Zn(0) and silica gel

The effect of silica gel on the efficiency enhancement of Zn(0) for the reduction of Cr(VI) and removal of total chromium was investigated in this study. The batch experiment was carried at 4 ≤ pH ≤ 10 with 50 μM initial Cr(VI) concentration, and mass loading of 0-40 g/L for silica gel and 0-8 g/L for Zn(0). Results showed limited Cr(VI) reduction in the Zn(0)/H(2)O system, which was attributed to the formation of passivating films on the Zn(0) surface. However, a complete reduction of Cr(VI) by Zn(0) in the presence of silica gel could be achieved at the all tested pHs. The rate of Cr(VI) reduction was markedly enhanced with a pH decrease, an increase of silica gel or Zn(0) loading, and specific surface area of silica gel. Almost complete removal of total chromium was also observed, suggesting that Cr(III) yielded from the reduction of Cr(VI) was adsorbed onto the silica gel and ZnO surface or existed in Zn-Cr mixed oxides or other Zn-Cr co-precipitates. The possible pathways for Cr(VI) reduction and total chromium removal were proposed in this study, revealing the potential mechanism responsible for the rapid reduction of Cr(VI) coupling with the efficient removal of total chromium in the coexistence of Zn(0) and silica gel.

Commercial Coffee Wastes as Materials for Adsorption of Heavy Metals from Aqueous Solutions

This work aims to study the removal of Cu(II) and Cr(VI) from aqueous solutions with commercial coffee wastes. Materials with no further treatment such as coffee residues from café may act as adsorbents for the removal of Cu(II) and Cr(VI). Equilibrium data were successfully fitted to the Langmuir, Freundlich and Langmuir-Freundlich model (L-F). The maximum adsorption capacity of the coffee residues can reach 70 mg/g for the removal of Cu(II) and 45 mg/g for Cr(VI). The kinetic data were fitted to pseudo-first, -second and -third order equations. The equilibrium was achieved in 120 min. Also, the effect of pH on adsorption and desorption was studied, as well as the influence of agitation rate. Ten cycles of adsorption-desorption were carried out revealing the strong reuse potential of these low-cost adsorbents; the latter was confirmed from a brief economic approach.