Synthesis of polyaniline nanocomposite and its application for chromium removal from aqueous solution

The aim of this research was to investigate the sorption characteristics of polyaniline coated on sawdust (PAn/SD) for the removal of Cr(VI) ions from aqueous solutions. The sorption of Cr(VI) ions was carried out by the batch method. Characterization of PAn/SD was done by FTIR and SEM. The optimum conditions of sorption were found to be a PAn/SD dose of 0.6 g in 100 mL of Cr(VI) solution (50 mg/L), a contact time of 20 min, pH 2, and a temperature of 20°C, Increased temperature had a negative effect on the removal efficiency. Three equations, that is Morris–Weber, Lagergren, and pseudo‐second‐order, were tested to track the kinetics of the removal process. The kinetic data indicated that the adsorption process was described by the Morris–Weber equation. The Langmuir, Freundlich, and Dubinin–Radushkevick models were used with sorption data to estimate sorption capacity, intensity, and energy. The data were fitted with the Freundlich model. The thermodynamic parameters ΔH, ΔS, and ΔG were evaluated. They showed that the adsorption of Cr(VI) onto PAn/SD was feasible, spontaneous, and exothermic under the studied conditions. For desorption of Cr(VI) adsorbed onto PAn/SD, aqueous NaOH was used; with it, 85% of the adsorbed Cr(VI) could be desorbed. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Application of polypyrrole coated on wood sawdust for removal of Cr(VI) ion from aqueous solutions

In this study polypyrrole (PPy) was synthesised chemically on the surface of sawdust that has already been soaked with monomer solution (pyrrole). FeCl₃ were used as chemical oxidants for oxidation of pyrrole into polymer (PPy/Cl). The sawdust coated by PPy (PPy/SD) was used as an efficient sorbent for removal of Cr(VI) ion from aqueous solutions. It was found that PPy/SD is very easy and simple to prepare and can be used as an effective sorbent for removal of Cr(VI) from water and wastewater solutions. The Cr(VI) removal is assumed to be mainly due to the anion exchange properties of the polymer which is formed as PPy⁺/Cl⁻. The introduced sorbent in this paper shows that PPy/SD can be used to eliminate or separate anionic contaminations from aqueous solutions under open circuit conditions.     

Artificial neural network (ANN) approach for modeling of Cr(VI) adsorption from aqueous solution by zeolite prepared from raw fly ash (ZFA)

In this present work, artificial neural networks (ANN) are applied for prediction of percentage adsorption efficiency for the removal of Cr(VI) ions from aqueous solution by zeolite (ZFA) prepared from raw fly ash (RFA). The off operational parameters such as initial pH, adsorbent dosage, contact time and temperature is studied to optimize the conditions for maximum removal of Cr(VI) ions. Three equations, i.e. Morris–Weber, Lagergren, and pseudo second order have been tested to track the kinetics of removal process. The Langmuir, Freundlich, Redlich–Peterson, Temkin, and D-R are subjected to sorption data to estimate sorption capacity. Thermodynamic parameters showed that the adsorption of Cr(VI) onto ZFA was feasible, spontaneous and endothermic. Artificial neural networks are effective in modeling and simulation of highly non-liner multivariable relationships. The comparison of the removal efficiencies of Cr(VI) using ANN model and experimental results showed that ANN model can estimate the behavior of the Cr(VI) removal process under different conditions.     

Removal of chromium(VI) from aqueous solutions using polypyrrole-based magnetic composites

PPy/Fe₃O₄/AgCl composites were prepared via in situ polymerization for the removal of highly toxic Cr(VI). The structure and morphology of the prepared composites were characterized by the XRD, SEM, TEM, and VSM examinations. Up to 100 % removal was found with 1000 mg/L Cr(VI) aqueous solution at pH 2.0. The process of Cr(VI) ions’ adsorption was easy to reach equilibrium at higher temperatures. Adsorption results showed that Cr(VI) removal efficiency by the composites decreased with an increase in pH. Adsorption kinetics was described by the pseudo-second-order rate model. Isotherm data fitted well to the Langmuir isotherm model. Desorption experiment showed that the regenerated adsorption of PPy/Fe₃O₄/AgCl can be reused successfully for three times successive adsorption–desorption cycles without appreciable loss of its original capacity.     

Remediation of chromium(VI) at polypyrrole-coated titanium

The application of conducting polypyrrole (PPy) and polyaniline (PAni) coated substrates in remediation of chromium, Cr(VI), is an area of considerable interest. Here, we discuss the implementation of PPy-coated titanium as a new material for the reduction of Cr(VI) to the less toxic trivalent state, Cr(III). An alkaline-peroxide based etching process was used to ensure the adhesion of the PPy coatings to the underlying titanium. The PPy films showed excellent resistance to acidic Cr(VI) solutions and remained adherent after continuous exposure to the solutions. In order to optimise the remediation process a number of experimental parameters were investigated, including the thickness of the PPy coating, the reduction potential used in pre-treatment of the PPy and the degree of solution agitation. The durability of the materials on exposure to the Cr(VI) test solutions made them suitable for repeated remediation experiments. Following several test-runs, the cleanup efficiency of the material was found to decrease slightly, however, increasing the exposure/experiment time resulted in significantly improved cleanup ability.     

Application of polypyrrole coated onto wood sawdust for the removal of carmoisine dye from aqueous solutions

In this research, the removal of carmoisine dye from aqueous solutions using polypyrrole coated onto sawdust (PPy/SD) has been investigated. The sorption experiments were performed using both batch and column systems. The effects of some important parameters such as pH, initial concentration, sorbent dosage, exposure time, and temperature on uptake of carmoisine dye were investigated. Based on the data obtained in batch system, it was found that maximum adsorption is occurred under acidic conditions. Complete removal was observed when a dye solution with the initial concentration of 100 mg L^?1 was treated by 1.0 g of the used adsorbent (PPy/SD) at pH value of 4 and room temperature. However, higher sorption was observed at elevated temperature. According to the kinetics study, it was found that the experimental data fitted very well the pseudo‐second‐order kinetic model (k₂ = 0.184 g mg^?1 min^?1). It was found that polypyrrole chemically coated on SD is an efficient system for the removal of carmoisine dye from aqueous solutions. Desorption of the dye‐loaded column was also possible by using dilute NaOH solution with high efficiency (～ 80%). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Removal of Cr(VI) from Aqueous Solutions by a Bacterial Biofilm Supported on Zeolite: Optimisation of the Operational Conditions and Scale‐Up of the Bioreactor

The aim of this study was to investigate the feasibility of a bioreactor system and its scale‐up to remove Cr(VI) from solution. The bioreactor is based on an innovative process that combines bioreduction of Cr(VI) to Cr(III) by the bacterium Arthrobacter viscosus and Cr(III) sorption by a specific zeolite. Batch studies were conducted in a laboratory‐scale bioreactor, taking into account different operating conditions. Several variables, such as biomass concentration, pH and zeolite pre‐treatment, were evaluated to increase removal efficiency. The obtained results suggest that the Cr removal efficiency is improved when the initial biomass concentration is approximately 5 g L^–1 and the pH in the system is maintained at an acidic level. Under the optimised conditions, approximately 100 % of the Cr(VI) was removed. The scale‐up of the developed biofilm process operating under the optimised conditions was satisfactorily tested in a 150‐L bioreactor.     

Selective binding of mercury ions by poly(4‐vinylpyridine) hydrochloride resin

The binding ability of poly(4‐vinylpyridine) hydrochloride resin for Cu(II), Cd(II), Zn(II), Hg(II), Pb(II), Cr(III), and U(VI) was investigated. All these ions, except Hg(II), could be not removed from aqueous solutions under the same conditions. The selective sorption of Hg(II) from mixtures of ions was observed. The elution of Hg(II) bound to the resin was also investigated using various concentrations of nitric acid and perchloric acid. Due to rapid complexation, a high mercury ion‐binding capacity, high selectivity, and ease of regenerability, the resin can be useful for the removal and recovery of mercury ions from aqueous solutions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1557–1562, 1999     

Removal of hexavalent chromium by Kendu fruit gum dust

The ability of a low cost adsorbent material, Kendu fruit gum dust (KGD), for removal of hexavalent chromium, Cr(VI), from aqueous solutions of both a synthetic and industrial (effluent) sample is successfully investigated through batch type experiments. The effects of contact time, Cr(VI) concentration, pH, adsorbent amount, and temperature on the extent of Cr(VI) removal are reported. At a lower initial concentration of Cr(VI) and a lower solution pH, the percent removal is found to be increased. A removal efficiency of 100% has been achieved. In the presence of cyanide ion the adsorption efficiency of KGD decreases. Recycling studies suggest that even after the sixth cycle, only ∼ 20% loss of efficiency of KGD occurs. The adsorption process follows the Freundlich adsorption isotherm model. Another important feature of the investigation includes the studies on the characteristics and analysis of various constituents present in the newly developed absorbent material (KGD). From the thermogravimetric analysis curves of the original KGD and Cr(VI) absorbed KGD, it is observed that the thermal stability of KGD increases due to metal ion adsorption. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1485–1494, 1997     

Poly(glutaraldehyde)‐stabilized fish scale fibrillar collagen–some features of a new material for heavy metal sorption

In this work, fibrillar collagen on scales of Corvina fish (Micropogonias furnieri) was crosslinked and used as a new adsorbent for sorption of Cr(VI) from aqueous solutions. Characterization has suggested that the crosslinked collagen of Corvina scale has higher denaturation temperature in relation to the raw scales. In addition, electrostatic interactions between collagen positive charges and chromate negative charges constitute the majority of the interactions. Solution microcalorimetry experiments have indicated that water swelling of the crosslinked scales is slightly exothermic and increased with increasing temperature. Sorption of Cr(VI) by crosslinked scales increases with increasing initial Cr(VI) concentration in solution and decreases with temperature increasing. The kinetic data of Cr(VI) sorption on crosslinked scales were best fitted to a multilinear exponential model. The values of Cr(VI) diffusion constants increase with both temperature and initial Cr(VI) concentration in solution. The maximum sorption capacity of the new adsorbent for Cr (VI) was found at 39 mg g^?1 and is higher than some commercial adsorbent samples. So, chemically crosslinked Corvina scale is a promising adsorbent for sorption of Cr(VI) from aqueous solutions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Metal ion adsorption behavior of lignocellulosic fiber–ethylene vinyl acetate composites

This study describes the applicability of lignocellulosic fiber dispersed in ethylene vinyl acetate (EVA) to adsorb Pb(II), Cr(III), and Cr(VI) ions in aqueous solutions. Water absorption studies revealed that metal‐ion uptake does not only take place on the surface of the adsorbent but ions can also diffuse into the composite. The adsorption of the metal ions under different experimental conditions was studied. Solute concentration, pH, and contact time were used to assess the adsorption capacity and efficiency. The amount of metal adsorbed increased to 7 mg/g with an increase in solute concentration but compromising the efficiency. Adsorption equilibrium was reached after 3 h, when the maximum lead adsorption was above 80%. The optimum pH for the adsorption of Pb(II) and Cr(III) was 6.5, and pH 2.5 was used for the adsorption of Cr(VI). Competitive adsorption revealed the order of adsorption to be: Pb(II) > Cr(VI) > Cr(III). POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Novel hexamethylene diamine‐functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly[(glycidyl methacrylate)‐co ‐(ethylene glycol dimethacrylate)] (PGME ) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME‐HD ) were tested as potential Cr(VI ) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI ) sorption was investigated in the temperature range 298–343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI ) sorption obeys the pseudo‐second‐order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g^?1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰) and entropy change (ΔS ⁰) and activation energy of sorption (E _a), were calculated. The Cr(VI) adsorption onto PGME‐HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME‐HD sample GMA 60 HD was easily regenerated with 0.1 mol L^?1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed. © 2016 Society of Chemical Industry     

Adsorption of Cr (VI) on synthetic hematite (α-Fe2O3) nanoparticles of different morphologies

The adsorption of Cr (VI) from aqueous solution onto nanoparticles hematite (α-Fe₂O₃) of different morphologies synthesized by acid hydrolysis, transformation of ferrihydrite, sol gel methods has been investigated. The hematite particle sizes were in the range 15.69-85.84 nm and exhibiting different morphologies such as hexagonal, plate-like, nano-cubes, sub-rounded and spherical. The maximum adsorption capacity of Cr (VI) was found to be in the range 6.33–200 mgg^?1 for all hematite samples. The kinetics of sorption was rapid, reaching equilibrium at 45–240 minutes. Sorption kinetics and equilibria followed pseudo-second order and Langmuir adsorption isotherm models. The rate constants were in the range 0.996–2.37×10^?2 g/mg/min for all samples. The maximum adsorption was attained at pH 3.0, while adsorption decreased as the pH increased from pH 3.0 to 10.0. The study revealed that the hematite with plate-like morphology has the highest adsorption capacity. The sorption process has been found to be feasible following a chemisorption process, and adsorption of Cr (VI) onto hematite nanoparticles was by inner sphere surface complexation due to low desorption efficiency in the range 9.54–53.4%. However, the result of ionic strength revealed that the reaction was by outer sphere complexation. This study showed that morphologies play a vital role in the adsorption capacities of samples of hematite in the removal of Cr (VI) from aqueous solution.     

Removal of Cr(VI) from wastewater by adsorption on iron nanoparticles

Due to rapid industrialisation, the presence of heavy metals in water and wastewater is a matter of environmental concern. Though some of the metals are essential for our system but if present beyond their threshold limit value (TLV), they are harmful and their treatment prior to disposal becomes inevitable. The present communication has been addressed to the removal of Cr(VI) from aqueous solutions by nanoparticles of iron. Nanoparticles of iron were prepared by sol–gel method. The characterisation of the nanoparticles was carried out by XRD and TEM analysis. Batch experiments were adopted for the adsorption of Cr(VI) from its solutions. The effect of different important parameters such as contact time and initial concentration, pH, adsorbent dose, and temperature on removal of chromium was studied. The removal of chromium increased from 88. 5% to 99.05% by decreasing its initial concentration from 15 to 5 mg L^?1 at optimum conditions. Removal of Cr(VI) was found to be highly pH dependent and a maximum removal (100%) was obtained at pH 2.0. The process of removal was governed by first and pseudo‐second‐order kinetic equations and their rate constants were determined. The process of removal was also governed by intraparticle diffusion. Values of the thermodynamic parameters viz. ΔG°, ΔH°, and ΔS° at different temperatures were determined. The data generated in this study can be used to design treatment plants for chromium rich industrial effluents. Adsorption results indicate that nanoiron particles can be effective for the removal of chromium from aqueous solutions.     

Removal of hexavalent chromium ion from aqueous solution using nanoscale zero-valent iron particles immobilized on porous silica support prepared by polymer template method

Porous silica supported nanoscale zero-valent iron was prepared by a polymer template method in order to effectively remove a hexavalent chromium ion (Cr(VI)) in an aqueous solution. It did not show a deterioration of Cr(VI) removal efficiency, which could be caused by the surface oxidation and agglomeration of nanoscale zero-valent iron (NZVI) particles. Porous silica by the polymer template method showed quite unique structure, which we named as quasi-inverse opal silica (QIOS), and it showed high surface area (375.4m²/g) and fine pore size (76.5 nm). NZVI immobilized on the surface of QIOS (NZVI@QIOS) was added to an aqueous Cr(VI) solution at 0.025 g/L, and it showed over 96% Cr(VI) removal efficiency. Such a high removal efficiency of Cr(VI) was maintained over two weeks after preparation (92% after 16 days). Morphology of porous silica supported nanoscale zero-valent iron was analyzed by TEM and FE-SEM. Identification of the reaction compounds produced by the reaction of Cr(VI) and zero-valent iron (Fe(0)) was made by the application of XPS.     

Simultaneous adsorption of aniline and Cr(VI) ion by activated carbon/chitosan composite

Activated carbon/chitosan composite has been used as an adsorbent to remove aniline and Cr(VI) ions from aqueous solutions simultaneously. The effects of preparation conditions such as the ratio of activated carbon to chitosan, crosslinking reagents, crosslinking time, and adsorption conditions including adsorbent dosage, pH value of solution, and contact time on simultaneous adsorption of aniline and Cr(VI) ion were investigated. Experimental results showed that epichlorohydrin was the proper crosslinking reagent, and the ratio of activated carbon to chitosan was kept at 1. When the adsorbent dosage was 4.0 g/L, and the concentrations of aniline and Cr(VI) were lower than 50 and 100 mg/L, respectively, both aniline and Cr(VI) were simultaneously removed at natural pH with high removals (>95%). The presence of Cr(VI) enhanced the adsorption of aniline, while the presence of aniline almost had no influence on the adsorption of Cr(VI). The adsorption processes of both aniline and Cr(VI) followed the pseudo‐second‐order kinetics model, but the sorption of Cr(VI) was preferential to that of aniline by this composite. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39903.     

Effective removal of Cr(VI) and methyl orange from the aqueous environment using two-dimensional (2D) Ti3C2Tx MXene nanosheets

Industrial use of heavy metals and dyes critically depends on the effective handling of industrial effluents. Effective remediation of industrial effluents using various adsorbent materials has thus become critical. In this paper, we study two-dimensional MXenes as an adsorbent for removing Cr(VI) and methyl orange (MO) in waters. The physico-chemical performance of MXenes was studied using X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer?Emmett?Teller, scanning electron microscopy, high resolution-transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy techniques. The adsorption system, including influence of contact time, pH of solutions, co-ions, and desorption experiments were performed for effective Cr(VI) and MO removal. The Cr(VI) and MO removal rate of the MXenes was very fast, and the kinetic system was driven by pseudo-second-order kinetics. The sorption isotherm closely well-tailored with the Langmuir isotherm, and the maximum removal efficiencies were 104 and 94.8 mg/g for Cr(VI) and MO, respectively. The MXenes was successfully regenerated by 0.1 M NaOH aqueous solution and can be repeatedly recycled. The uptake of Cr(VI) and MO by the MXenes was mainly due to chemical adsorption, namely electrostatic adsorption, complexation, surface interactions, and ion exchange mechanisms. This investigation demonstrates the selectivity and feasibility of the MXenes as a real adsorbent for eliminating Cr(VI) and MO from the aqueous environment.     

Biosorption of hexavalent chromium from aqueous solutions using raw coconut fiber as a natural adsorbent

Abstract

This work aims to evaluate the Cr(VI) removal efficiency and adsorption capacity of the raw coconut fiber from synthetic aqueous solutions through the operational parameters as well as to represent the mechanisms of removal by kinetic and isotherm models. The experimental study was conducted in batch system and the optimum conditions for the adsorption of this metal by the biomass were according to: pH 2, contact time of 270?min, and 10?g/L of adsorbent dosage concentration. The removal efficiency obtained for Cr(VI) solutions was 99.2% at concentrations of 25–50?mg/L. For the highest concentrations, the removal decreased from 96.3% to 74.4%, when Cr(VI) solutions ranged from 100?mg/L to 250?mg/L, respectively. The adsorption kinetics was applied and showed a good agreement for pseudo-second-order and Elovich models, which point out a chemisorption. For the adsorption capacity at equilibrium conditions, the best fit was for the Redlich–Peterson isotherm indicating favorable adsorption and monolayer coverage.     

Metal sorption properties of sulfur-chlorinated jojoba wax bound to polystyrene beads

A new solid extractant (designated PS-DETA-JS) in which sulfur-chlorinated jojoba wax is bound via an amine spacer group to polystyrene beads was synthesized. The absorption of mercury cations from acidic solutions and of chromate anions from saline solutions onto PS-DETA-JS was investigated. The sorption of mercury ions by the solid extractant was compared with that by liquid-sulfurized jojoba wax impregnated inside macroporous resins. The static and dynamic properties of dichromate sorption from 2–20 g/L NaCl solutions at pH 4.1 were studied. Selective sorption of Cr(VI) was obtained at low chromate concentrations (∼ 6 ppm) in saline aqueous solutions. Complete regeneration of the PS-DETA-JS resin was achieved after the reduction of Cr(VI) to Cr(III) and the elution of the Cr(III) with 1N HCl. © 1997 John Wiley & Sons, Inc.     

Application of kinetic,isotherm and thermodynamic models for the adsorption of Co(II) ions on polyaniline/polypyrrole copolymer nanofibers from aqueous solution

The aim of this research is to investigate sorption characteristics of polyaniline/polypyrrole copolymer nanofibers (PANI/PPy copolymer nanofibers) for the removal of Co(II) ions from aqueous solution. The adsorbent is characterized using FE-SEM, TEM, FTIR, TGA, DSC and BET surface area. The sorption of Co(II) ions by batch method is applied and the optimum conditions are investigated. In optimum condition, removal efficiency was 99.68% for 100 mg L⁻¹ Co(II) solution. It is found that temperature has a positive effect on the removal efficiency. It can be concluded that PANI/PPy copolymer nanofibers are potentially able to removal of Co(II) ions from aqueous solutions.