Sorption of chromium(VI) using modified forms of chitosan beads

Bio-based composite from chitosan waste and clay for effective removal of Congo red dye from contaminated water: Experimental studies and theoretical insights

Water pollution due to dyes in the textile industry is a serious environmental problem. During the finishing stage, Congo red (CR) dye, water-soluble, is released into wastewater, polluting the water body. This study explores the effectiveness of utilizing a composite composed of Safi raw clay and chitosan to remove an anionic dye from synthetic wastewater. The chitosan was extracted from crab shells. Its removal performance was compared to that of natural clay. Both the composite and raw clay were used to remove target pollutant. The effects of the chitosan load in the composite, size particles, initial dye concentration, contact time, pH, and temperature on the dye's elimination were tested in batch modes. The composite with 30% (w/w) of chitosan exhibited the highest dye removal. At pH 2, an adsorption capacity of 84.74 mg/g was achieved, indicating that the grafting of the polymer onto clay surface enhances its efficacity and stability in acidic environments. This finding was supported by characterization data obtained from X-ray diffraction (XRD), scanning electron microscopy (SEM), dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FT-IR) analyses. Under optimized conditions of 20 mg dose, pH 2, 30 min of reaction time, and 20 mg/L of dye concentration, about 92% of dye removal was achieved. The Langmuir isotherm model represents dye adsorption by the composite, while dye removal was controlled by pseudo-second-order model. Thermodynamic data of the adsorption (ΔH = +8.82 kJ/mol; ΔG <0) suggested that the dye adsorption was spontaneous and endothermic. The findings provide insights into the dye elimination by the adsorbent, indicating that the removal occurred via attractive colombic forces, as confirmed by density functional theory (DFT) analysis. Overall, the composite of natural clays and chitosan waste is a promising and innovative adsorbent for treating wastewater containing recalcitrant dyes.

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.

Developing nano-micro size chitosan beads using imidazolium-based ionic liquid: A perspective

The aggressive search for unique materials in recent years has put forward chitosan and modified-chitosan as materials with unique structural and morphological characteristics for various important applications. Just as imidazolium-based ionic liquids are the commonly applied ionic liquids (ILs) type for chitosan modifications for various applications, their further modifications into beads for enhancing their properties is now gaining most attention. However, most of the currently prepared imidazolium ILs modified-chitosan beads are not in nano size due to preparation difficulties. In response to this and referencing the research works in the literature, the possible breakthrough directions including synthesis routes, and physical and mechanical transformation processes are proposed. These procedures are expected to provide certain theoretical and empirical basis, as well as technical guide for developing nano-micro size chitosan beads using imidazolium based ILs.

Enhancement effects of dissolved organic matter leached from sewage sludge on microbial reduction and immobilization of Cr(VI) by Geobacter sulfurreducens

Sewage sludge has a high concentration of dissolved organic matter (DOM) which contains compounds that can serve as electron donors or shuttles for metal reduction by dissimilatory metal reducing bacteria (DMRB). In this study, Cr(VI) removal by G. sulfurreducens, a common DMRB present in anaerobic soils, was examined in the presence or absence of sludge DOM. Two different types of sludge DOM were tested; composted sludge DOM (C-DOM) and anaerobically digested sludge DOM (A-DOM). Both sludge DOMs enhanced Cr(VI) reduction by G. sulfurreducens, but C-DOM was more effective likely because it had higher concentrations of humic substances that served as electron shuttles. Transcriptomic studies indicated that G. sulfurreducens utilizes several different mechanisms to tolerate chromium including extracellular Cr(VI) reduction and immobilization by outer membrane c-type cytochromes and electrically conductive pili, intracellular Cr(VI) reduction by triheme cytochromes and NAD(P)H FMN reductase proteins, and chromium efflux by several P-type ATPase and RND transporter proteins. Microscopy experiments also showed that Cr(III) crystals formed on the surface of the cells, indicating that extracellular Cr(VI) reduction and adsorption was involved in the chromium removal process. These results help provide insight into the potential use of sewage sludge as an additive to enhance the bioremediation of chromium contaminated soils.

Electrosprayed Chitosan-Copper Complex Microspheres with Uniform Size

Chitosan-based nano- and microspheres have shown great potential in a broad range of applications, including drug delivery, bone tissue engineering, wastewater treatments, etc. The preparation of uniformly sized spheres with controlled morphology and microstructure is still a challenge. This work investigates the influence of cupric ions (Cu²⁺) on the size, shape, morphology and stability of electrosprayed chitosan–copper (CHT–Cu²⁺) complex microspheres, using chitosans with different degrees of deacetylation. The dynamic viscosity of CHT–Cu²⁺ solutions was measured by Höppler viscometer, while attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used for the identification of dried microspheres. The size, shape and morphology of microspheres were analyzed by light microscope and scanning electron microscopy (SEM), while stability of dried microspheres was evaluated in different buffer solutions. The volume ratio of wet and dry microspheres was assessed based on the estimated diameter of microspheres. The higher concentration of Cu²⁺ ions resulted in a decrease in viscosity of CHT–Cu²⁺ solutions and volume ratio of prepared microspheres. Changes in the intensities and wave numbers of absorption bands of amino and hydroxyl groups, amide I and amide II suggested that the nitrogen and oxygen atoms in chitosan are coordinating the cupric ions. Micrographs obtained by light microscope and SEM showed that all prepared samples are spherical. The increase of cupric ions concentration changed the topography of microspheres and decreased their size. These results indicated the successful electrospraying of CHT–Cu²⁺ microspheres with uniform size and good stability in aqueous medium.

Preparation of Freeze-Dried Porous Chitosan Microspheres for the Removal of Hexavalent Chromium

Novel porous chitosan microspheres were successfully produced by a freezing–lyophilization drying method in this study and were then used as adsorbents to remove a toxic iron metal, hexavalent chromium (Cr(VI)). The effects of the concentration of the chitosan solution, syringe diameter, and freezing time on the morphologies of porous chitosan microspheres were characterized. The metal ion adsorption for Cr(VI) was also studied. Results showed that freezing chitosan hydrogel beads at a temperature of −20 °C and subsequently lyophilizing the frozen structure allowed to easily obtain the porous chitosan microspheres with rough surfaces and large pores, which were more suitable for adsorption materials to remove metal ions. A chitosan solution concentration of 3% (w/v) and a syringe diameter of 500 μm allowed the porous microspheres to have a good sphericity, thinner pore walls, and small pore sizes. The adsorption capacity of porous chitosan microspheres for Cr(VI) increased with the increase in freezing time. The pH of the initial adsorption solution ranged from 3.0 to 5.0 and was beneficial to the maximum adsorption efficiency for Cr(VI). The porous chitosan microspheres prepared with 3% (w/v) chitosan solution at −20 °C for a freezing time of 72 h had a higher adsorption capacity of 945.2 mg/g for Cr(VI) than the those at 24-h and 48-h freezing times. Kinetic study showed that the adsorption process could be described by a pseudo-second order (PSO) kinetic model. The equilibrium adsorption rate constant and the adsorption amount at equilibrium for the porous chitosan microspheres increased with an increase in the freezing time, and those for the porous microspheres prepared with 3% chitosan solution at −20 °C for a 72-h freezing time were 1.83 × 10−5 g mg−1 min−1 and 1070.5 mg g−1, respectively. The porous chitosan microspheres have good potential to facilitate the separation and recycling of expensive and toxic Cr(VI) from wastewater.

Chitosan-Based Nanocomposite Polymeric Membranes for Water Purification-A Review

During the past few years, researchers have focused their attention on developing innovative nanocomposite polymeric membranes with applications in water purification. Natural and synthetic polymers were considered, and it was proven that chitosan-based materials presented important features. This review presents an overview regarding diverse materials used in developing innovative chitosan-based nanocomposite polymeric membranes for water purification. The first part of the review presents a detailed introduction about chitosan, highlighting the fact that is a biocompatible, biodegradable, low-cost, nontoxic biopolymer, having unique structure and interesting properties, and also antibacterial and antioxidant activities, reasons for using it in water treatment applications. To use chitosan-based materials for developing nanocomposite polymeric membranes for wastewater purification applications must enhance their performance by using different materials. In the second part of the review, the performance's features will be presented as a consequence of adding different nanoparticles, also showing the effect that those nanoparticles could bring on other polymeric membranes. Among these features, pollutant's retention and enhancing thermo-mechanical properties will be mentioned. The focus of the third section of the review will illustrate chitosan-based nanocomposite as polymeric membranes for water purification. Over the last few years, researchers have demonstrated that adsorbent nanocomposite polymeric membranes are powerful, important, and potential instruments in separation or removal of pollutants, such as heavy metals, dyes, and other toxic compounds presented in water systems. Lastly, we conclude this review with a summary of the most important applications of chitosan-based nanocomposite polymeric membranes and their perspectives in water purification.

Nature of sorption of trivalent arsenic on novel iron oxyhydroxide stabilized starch/OMMT composite: A mechanistic approach

Materials which are chemically, energetically and operationally acceptable for arsenic water treatment are highly required. In this study a hybrid material (SICC) of aminated starch, oxyhydroxide of iron and OMMT clay has been demonstrated for arsenic treatment. This new material was highly efficient in arsenic water treatment which could reduce arsenic concentration far below detection limits. All binding interactions during material preparation and arsenic sorption were exclusively characterized with FT-IR, XRD and other spectroscopic tools. A molecular modeling on the basis of density functional theory was carried out to verify the above findings. Influence of material dose, treatment time, initial ion concentration, varying temperatures, etc., on extent of sorption was studied in detail. The thermodynamic parameters viz. ΔG (>-11 kJ/mol), ΔH (42.48 kJ/mol), ΔS (177.6 JK^-1 mol^-1) and E a (59.16 kJ/mol) determined the feasibility of the process, its endothermic behavior and most importantly the chemical nature of the sorption accompanied by ion-exchange to some extent. The sorption followed a monolayer chemisorption pattern as determined by the Langmuir model (R² = 0.973, R L = 0.081) with a q_max = 2.04 at 303 K. The binding of As(III) on the material was governed by a pseudo second order kinetic model.

Improved removal capacity of magnetite for Cr(VI) by electrochemical reduction

Aqueous hexavalent chromium (Cr(VI)) poses serious threats to ecological environments. Magnetite is a potential adsorbent for Cr(VI). However, its adsorption capacity is limited due to the formation of Fe(III) oxide coating on magnetite surface. Herein, constant potential reduction was conducted to improve the Cr(VI) removal capacity of magnetite, and the influence of pH, potential, and supporting electrolytes including KNO₃, KCl, and K₂SO₄ on the adsorption capacity was also investigated. The results showed that the highest Cr(VI) reduction percentage reached 93.7% with a total Cr removal capacity of 514.7 mg g^-1 at optimized pH 2 and -0.2 V (vs. SCE) in supporting electrolyte of KNO₃. Cr(VI) was reduced to Cr(III) on the surface of magnetite due to the direct electrochemical reduction at low potentials and reduction by Fe²⁺_aq electrochemically generated from magnetite. The Cr(III) was subsequently removed and easily separated due to the formation of Cr(OH)₃ precipitate on magnetite surface when KNO₃ and KCl were used as supporting electrolyte; however, when K₂SO₄ was used instead, Cr(OH)₃ precipitate was not observed. The decrease in pH and electrical potential was found to facilitate the reduction and removal of Cr(VI). This work proposes a facile method to enhance Cr(VI) removal by iron oxides.

Sustainable treatment of municipal landfill leachate by combined association of air stripping, Fenton oxidation, and enhanced coagulation

The present world has been facing the problem of municipal solid waste disposal with the generation of highly complex and toxic landfill leachate. Thus, in this research work, treatability of landfill leachate had been investigated by the combined approach of air stripping, Fenton oxidation, and enhanced coagulation to comply with discharge standard. At the initial stage of treatment, air stripping of raw leachate was implemented which removes around 51.50% of COD, 74.60% of BOD₅, and 97.60% of NH₃-N within 36 h of optimum retention time. Following air stripping, Fenton oxidation was applied with an optimum molar ratio of 1.9 of H₂O₂/Fe⁺² which register a maximal removal of 67.70% of COD, 92.30% of BOD₅, and 14.90% of Hg. Finally, enhanced coagulation (EC) with in situ formed Mn-Fe hydr(oxides) was employed and optimized by central composite design (CCD) of response surface methodology (RSM). Response surface plots denote an optimum condition of 0.13 M ratio of Mn/Fe, 22.67 mM of coagulant dose, and 7.78 of pH which corresponds to a maximum removal of 55.98% of COD and 77.68% of Hg. FTIR analysis of the precipitates of EC explained that the hydroxyl groups are primarily involved in the process of Hg removal. Moreover, EDAX spectrum also assured the removal of Hg by its existence with Mn-Fe complexes. Thus, the present line of treatment record an overall removal of 90.80% of COD, 98.0% of BOD₅, 97.60% of NH₃-N, and 82.68% of Hg which proves to be effective for the removal of leachate pollutants.

Potential use of green algae as a biosorbent for hexavalent chromium removal from aqueous solutions

The hexavalent chromium Cr(VI) poses a threat as a hazardous metal and its removal from aquatic environments through biosorption has gained attention as a viable technology of bioremediation. We evaluated the potential use of three green algae (Cladophora glomerata, Enteromorpha intestinalis and Microspora amoena) dry biomass as a biosorbent to remove Cr(VI) from aqueous solutions. The adsorption capacity of the biomass was determined using batch experiments. The adsorption capacity appeared to depend on the pH. The optimum pH with the acid-treated biomass for Cr(VI) biosorption was found to be 2.0 at a constant temperature, 45 °C. Among the three genera studied, C. glomerata recorded a maximum of 66.6% removal from the batch process using 1.0 g dried algal cells/100 ml aqueous solution containing an initial concentration of 20 mg/L chromium at 45 °C and pH 2.0 for 60 min of contact time. Langmuir and Freundlich isotherm equations fitted to the equilibrium data, Freundlich was the better model. Our study showed that C. glomerata dry biomass is a suitable candidate to remove Cr(VI) from aqueous solutions.

Equilibrium and kinetics study on removal of arsenate ions from aqueous solution by CTAB/TiO2 and starch/CTAB/TiO2 nanoparticles: a comparative study

We present a comparative study on the efficacy of TiO₂ nanoparticles for arsenate ion removal after modification with CTAB (N-cetyl-N,N,N-trimethyl ammonium bromide) followed by coating with starch biopolymer. The prepared nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), thermogravimetry, scanning electron microscopy (SEM) and electron dispersive X-ray analysis (EDX). The removal efficiency was studied as a function of contact time, material dose and initial As(V) concentration. CTAB-modified TiO₂ showed the highest arsenate ion removal rate (∼99% from 400 μg/L). Starch-coated CTAB-modified TiO₂ was found to be best for regeneration. For a targeted solution of 400 μg/L, a material dose of 2 g/L was found to be sufficient to reduce the As(V) concentration below 10 μg/L. Equilibrium was established within 90 minutes of treatment. The sorption pattern followed a Langmuir monolayer pattern, and the maximum sorption capacity was found to be 1.024 mg/g and 1.423 mg/g after starch coating and after CTAB modification, respectively. The sorption mechanisms were governed by pseudo second order kinetics.

Adsorption of Cr(VI) onto Hybrid Membrane of Carboxymethyl Chitosan and Silicon Dioxide

In this study, a new adsorbent material was synthesized by using carboxymethyl chitosan and silicon dioxide. The hybrid membrane was used as an adsorbent for the removal of Cr(VI) from aqueous solutions. The adsorption potential of Cr(VI) by the hybrid materials was investigated by varying experimental conditions such as pH, contact time, and the dosage of the hybrid membrane. Adsorption isotherms of Cr(VI) onto the hybrid membrane were studied with varying initial concentrations under optimum experiment conditions. The surface property of the hybrid membrane was characterized by SEM (scanning electron microscope) and Fourier transform infrared spectrometer (FTIR). The concentrations of Cr(VI) in solution are determined by ICP-AES (inductively coupled plasma atomic emission spectrometry). The present study investigates the adsorption mechanisms of Cr(VI) onto the hybrid membrane. The results provide new insight, demonstrating that the modified hybrid membrane can be an efficient adsorbent for Cr(VI) from the aqueous solution.

Equilibrium modeling of mono and binary sorption of Cu(II) and Zn(II) onto chitosan gel beads

The objective of the work are in-depth experimental studies of Cu(II) and Zn(II) ion removal on chitosan gel beads from both one- and two-component water solutions at the temperature of 303 K. The optimal process conditions such as: pH value, dose of sorbent and contact time were determined. Based on the optimal process conditions, equilibrium and kinetic studies were carried out. The maximum sorption capacities equaled: 191.25 mg/g and 142.88 mg/g for Cu(II) and Zn(II) ions respectively, when the sorbent dose was 10 g/L and the pH of a solution was 5.0 for both heavy metal ions. One-component sorption equilibrium data were successfully presented for six of the most useful three-parameter equilibrium models: Langmuir-Freundlich, Redlich-Peterson, Sips, Koble-Corrigan, Hill and Toth. Extended forms of Langmuir-Freundlich, Koble-Corrigan and Sips models were also well fitted to the two-component equilibrium data obtained for different ratios of concentrations of Cu(II) and Zn(II) ions (1:1, 1:2, 2:1). Experimental sorption data were described by two kinetic models of the pseudo-first and pseudo-second order. Furthermore, an attempt to explain the mechanisms of the divalent metal ion sorption process on chitosan gel beads was undertaken.

Sorption of copper onto low molecular weight chitosan derivative from aqueous solution

In this study, sorption of copper onto low molecular weight chitosan derivative was studied. Experimental parameters such as pH of the solution (A), temperature (B), dose of the sorbent (C), and concentration of solution (D) were considered. The statistical results indicated that the dose of sorbent (C) and Cu (II) concentration (D) influenced removal efficiency at 5% significance level. Also, some interactions such as ABCD, ACD, ABC and AC affected the removal process. The sorbent was characterized with FTIR, SEM and TG/DSC. Freundlich isotherm model was the best isotherm model. The kinetic study results correlated well with the pseudo-second-order model. The thermodynamic studies revealed that the nature of copper sorption was spontaneous and endothermic. Strong affinity of the sorbent for copper (II) was revealed by the Isothermal Titration Calorimetry (ITC) technique.

Effective removal of Cr(vi) using β-cyclodextrin–chitosan modified biochars with adsorption/reduction bifuctional roles

In this work, beta-cyclodextrin–chitosan modified walnut shell biochars (β-CCWB) were synthesized as a low-cost adsorbent for the removal of heavy metal Cr(vi) from aqueous solutions.

Preparation and Characterization of Chitosan Thin Films on Mixed-Matrix Membranes for Complete Removal of Chromium

Herein we present a new approach for the complete removal of Cr(VI) species, through reduction of Cr(VI) to Cr(III), followed by adsorption of Cr(III). Reduction of chromium from water is an important challenge, as Cr(IV) is one of the most toxic substances emitted from industrial processes. Chitosan (CS) thin films were developed on plain polysulfone (PSf) and PSf/TiO2 membrane substrates by a temperature-induced technique using polyvinyl alcohol as a binder. Structure property elucidation was carried out by X-ray diffraction, microscopy, spectroscopy, contact angle measurement, and water uptake studies. The increase in hydrophilicity followed the order: PSf < PSf/TiO2 < PSf/TiO2/CS membranes. Use of this thin-film composite membrane for chromium removal was investigated with regards to the effects of light and pH. The observations reveal 100 % reduction of Cr(VI) to Cr(III) through electrons and protons donated from OH and NH2 groups of the CS layer; the reduced Cr(III) species are adsorbed onto the CS layer via complexation to give chromium-free water.

Sorption of heavy metal ions onto carboxylate chitosan derivatives--a mini-review

Chitosan is of importance for the elimination of heavy metals due to their outstanding characteristics such as the presence of NH2 and -OH functional groups, non-toxicity, low cost and, large available quantities. Modifying a chitosan structure with -COOH group improves it in terms of solubility at pH ≤7 without affecting the aforementioned characteristics. Chitosan modified with a carboxylic group possess carboxyl, amino and hydroxyl multifunctional groups which are good for elimination of metal ions. The focal point of this mini-review will be on the preparation and characterization of some carboxylate chitosan derivatives as a sorbent for heavy metal sorption.

Adsorption of chromium from aqueous solutions using crosslinked chitosan-diethylenetriaminepentaacetic acid

Chitosan (CH) and its derivatives have been the focus of attention for researchers as potential adsorbents for heavy metal removal. The adsorption potential of chitosan cross-linked with diethylenetriaminepentaacetic acid (CD) for Cr6+ was investigated. CD was characterized by FTIR, XRD, TGA, XPS and ESR techniques. Batch experiments were conducted to optimize the parameters affecting the adsorption of chromium. The optimum pH was found to be 3 and the adsorption process was found to be exothermic. Adsorption isotherms were determined and the maximum adsorption capacity of CD for chromium was found to be 192.3 mg/g which was higher than the adsorption capacity of the adsorbents reported in literature. The thermodynamic parameters, such as Gibbs free energy, changes in enthalpy and changes in entropy change were also evaluated. XPS and ESR studies revealed that Cr6+ adsorbed onto CD was reduced to Cr3+. The efficacy of CD for removal of Cr6+ from chrome plating effluent was demonstrated.

Synthesis, characterization and Cr(VI) uptake study of polyaniline coated chitin

The present work describes the synthesis, characterization of polyaniline coated chitin (PCC) and its application as an adsorbent of the removal of Cr(VI) ions from aqueous solution. The synthesized PCC was characterized using FTIR, XRD, SEM-EDX, BET, TGA, and DSC. The batch adsorption system was used to optimize the various parameters for the removal of Cr(VI) ions from aqueous solution by PCC. The equilibrium data obtained at optimized conditions were well described by Freundlich isotherm model than the Langmuir isotherm model. The values of ΔG(0), ΔH(0) and ΔS(0) indicate the spontaneous and the endothermic nature of the adsorption process. The pseudo-second-order kinetic model fitted well to the kinetic data. The regeneration studies revealed that the Cr(VI) loaded PCC could be reused for three consecutive cycles.

Zr(IV) loaded cross-linked chitosan beads with enhanced surface area for the removal of nitrate and phosphate

In this work, a new method namely silica dissolution method, has been adapted to increase the surface area of the cross-linked chitosan beads. Zr(IV) was loaded in the cross-linked chitosan beads in order to make it selective for the nitrate and phosphate anions from aqueous solutions. Zr(IV) loaded cross-linked chitosan beads prepared by normal method (ZrCB) and silica dissolution method (SD-ZrCB) were characterised using N2 adsorption/desorption studies, SEM, EDAX, XRD, FTIR, TGA, DTA and water regain property. The SD-ZrCB exhibited higher N2 adsorption, water regain property as well as anion adsorption capacity than ZrCB. Batch method was adapted for the adsorption studies. The nitrate and phosphate adsorbed SD-ZrCB was regenerated using 0.025M NaCl solution. There was not much drop in adsorption capacities up to 10th regeneration cycle. Freundlich adsorption isotherm was the best fit adsorption isotherm among Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms which have been used to fit the nitrate and phosphate adsorption data. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of adsorption process.

Biosensing and bioremediation of Cr(VI) by cell free extract of Enterobacter aerogenes T2

Hexavalent chromium or Cr(VI) enters the environment through several anthropogenic activities and it is highly toxic and carcinogenic. Hence it is required to be detected and remediated from the environment. In this study, low-cost and environment-friendly methods of biosensing and bioremediation of Cr(VI) have been proposed. Crude cell free extract (CFE) of previously isolated Enterobacter aerogenes T2 (GU265554; NII 1111) was prepared and exploited to develop a stable biosensor for direct estimation of Cr(VI) in waste water, by using three electrodes via cyclic voltammetry. For bioremediation studies, a homogeneous solution of commercially available sodium alginate and CFE was added dropwise in a continuously stirred calcium chloride solution. Biologically modified calcium alginate beads were produced and these were further utilized for bioremediation studies. The proposed sensor showed linear response in the range of 10-40 μg L(-1) Cr(VI) and the limit of detection was found to be 6.6 μg L(-1) Cr(VI). No interference was observed in presence of metal ions, e.g., lead, cadmium, arsenic, tin etc., except for insignificant interference with molybdenum and manganese. In bioremediation studies, modified calcium alginate beads showed encouraging removal rate 900 mg Cr(VI)/m(3) water per day with a removal efficiency of 90%, much above than reported in literature. The proposed sensing system could be a viable alternative to costly measurement procedures. Calcium alginate beads, modified with CFE of E. aerogenes, could be used in bioremediation of Cr(VI) since it could work in real conditions with extraordinarily high capacity.

Preparation of amino terminated polyamidoamine functionalized chitosan beads and its Cr(VI) uptake studies

Chitosan beads, functionalized by amino terminated hyperbranched dendritic polyamidoamine (up to 3rd generation) were prepared by Michael addition of methyl acrylate to amino groups on the chitosan surface and amidation of terminal ester groups by ethylene diamine. All the three generation chitosan beads were used for chromium removal along with raw chitosan beads. However, the 3rd generation polyamidoamine chitosan beads (3ACB) have been protonated using HCl (3ACBP)/loaded with zirconium using ZrOCl(2)·8H(2)O (3ACBZr) to enhance the sorption capacity towards Cr(VI). The zirconium loaded chitosan beads showed higher Cr(VI) sorption than the other modified chitosan beads. The zirconium loaded chitosan beads were characterized using SEM, EDAX, FT-IR, XRD, DSC and TGA. The system variables studied include agitation time, initial concentration of sorbate, pH, co-ions in the medium and temperature on the sorption of chromium. The chromium uptake onto 3ACBZr obeys the Freundlich isotherm. Thermodynamic studies revealed that the nature of chromium sorption is spontaneous and endothermic. The mechanism of chromium sorption onto the sorbent was established.

Preparation and characterization of La(III) encapsulated silica gel/chitosan composite and its metal uptake studies

Lanthanum loaded silica gel/chitosan composite (LaSiCS) was prepared by mixing silica gel, LaCl(3) · 7H(2)O and chitosan which was then cross-linked with glutaraldhyde. The LaSiCS composite was characterized using FT-IR, SEM-EDAX, XRD and BET. The adsorption of chromium(VI) ions onto LaSiCS composite has been investigated. The LaSiCS composite was found to have excellent chromium adsorption capacity than the silica gel/chitosan composite (SiCS), silica gel (Si) and chitosan (CS). The sorption experiments were carried out in batch mode to optimize various parameters viz., contact time, pH, initial chromium ion concentration, co-ions and temperature that influence the sorption. Langmuir and Freundlich adsorption models were applied to describe isotherm constants. Equilibrium data agreed very well with the Langmuir model. Thermodynamic studies revealed that the nature of chromium sorption was spontaneous and endothermic. The LaSiCS composite removes chromium by electrostatic adsorption coupled reduction/ion-exchange.