Effective adsorption of hexavalent chromium through a three center (3c) co-operative interaction with an ionic liquid and biopolymer.

Biopolymers as well as ionic liquids are known for their potential applications. In this work, we report the utility of chitosan as an excellent platform for impregnating the ionic liquid, tetraoctylammonium bromide by ultrasonication and its subsequent adsorption for chromium(VI). The effective mass transfer due to sonication coupled with the hydrogen bonding interaction between chitosan-ionic liquid and the electrostatic interaction involving the amino groups in chitosan and hexavalent chromium governs this three center (3c) co-operative mechanism. The adsorption followed a pseudo second order kinetics with a Langmuir adsorption capacity of 63.69 mg g(-1). Various isotherm models were used to correlate the experimental data and the adsorption process is exothermic with a decreased randomness at the solid-solution interface. The thermodynamics of the spontaneous adsorption process could be explained through a positive co-operative effect between the host (chitosan) and the guest (ionic liquid). The adsorbed chromium(VI) could be converted to ammonium chromate using ammonium hydroxide, thereby regenerating the adsorbent. The method could be translated into action in the form of practical application to a real sample containing chromium.

Microwave assisted solvent free green preparation and physicochemical characterization of surfactant-anchored cellulose and its relevance toward the effective adsorption of chromium.

The molecular interaction between tetrabutylammonium iodide (TBAI) and cellulose and its potential application for the adsorption of chromium is discussed in this paper. The biosorbent was prepared under solvent free conditions using microwave irradiation. A subtle balance between electrostatic and the hydrophobic effects governs the interaction of biopolymer with the surfactant. The interaction between the biosorbent and chromium was comprehensively studied using spectroscopic, thermal and surface analysis techniques. The various analytical parameters that influence the adsorption were optimized, and the maximum adsorption capacity of Cr(VI) obtained from the Langmuir isotherm model was found to be 16.67 mg g(-1). The sorption thermodynamics indicated the spontaneity and exothermic nature of adsorption. The biosorbent could be effectively regenerated using NaOH, which imparts greener aspect to the overall process.

An efficient ultrasound assisted approach for the impregnation of room temperature ionic liquid onto Dowex 1×8 resin matrix and its application toward the enhanced adsorption of chromium (VI).

The work discussed in this paper is based on the utilization of ultrasound in conjunction with an ionic liquid (Aliquat 336) impregnated Dowex 1×8 resin for the effective adsorption of chromium. Ionic liquids are known for their selectivity toward metal extraction and ultrasonic medium offers efficient energy transfer for impregnating the ionic liquid in the resin matrix. The molecular interaction between the ionic liquid impregnated resin and chromium was studied through various physicochemical and spectroscopic techniques. The influence of various analytical parameters on the adsorption of Cr(VI) such as pH, adsorbent dosage, temperature and interference of foreign ions was studied in detail. Chromium (VI) was quantitatively adsorbed in the pH range of 3.5-4, with a high adsorption capacity of 230.9 mg g(-1) in conformity with the Langmuir isotherm model. The study of thermodynamic parameters showed that the adsorption process is exothermic and spontaneous. The adsorbent could be regenerated using 1 mol L(-1) HCl-0.28 mol L(-1) ascorbic acid mixture. Chromium could be effectively detoxified from an industrial effluent and finally the developed method was validated with the analysis of a certified reference material (BCR-715). The obtained results indicated that the ultrasonic assisted impregnation of the room temperature ionic liquid significantly enhances and improves the removal efficiency of Cr(VI).

Ultrasound-assisted preparation and characterization of crystalline cellulose-ionic liquid blend polymeric material: a prelude to the study of its application toward the effective adsorption of chromium.

The molecular interaction of biopolymers with an array of substrates offers interesting insight into the adsorption phenomenon. The present work proposes the preparation and characterization of cellulose-methyltrioctylammonium chloride (MeTOACl)-a room temperature ionic liquid (IL) blend polymeric sorbent and its application for the adsorption of carcinogenic chromium(VI). The blend adsorbent material was synthesized in a relatively green solvent (methylisobutylketone) medium by ultrasonication. The mechanism of interaction of biopolymer with the ionic liquid could be conceptualized as electrostatic attraction, hydrogen bonding, and Van der Waals force of attraction with the hydroxyl groups of cellulose as a bilayer assembly. The composition, crystallinity, and the surface area of the prepared material were comprehensively characterized using FT-IR, solid-state (13)C NMR, TGA, XRD, SEM, EDX, XPS, and BET isotherm study. The adsorption capacity of chromium(VI) calculated from Langmuir isotherm model was found to be 38.94 mg g(-1) with adherence to the second-order kinetics. The study of thermodynamic parameters that affect the sorption process indicated the spontaneity and exothermic nature of adsorption. The green aspect in the methodology is brought out in the regeneration of the adsorbent, where Cr(VI) could be effectively reduced to the less toxic Cr(III) using ascorbic acid.

An enhanced adsorption methodology for the detoxification of chromium using n-octylamine impregnated Amberlite XAD-4 polymeric sorbent.

The remediation of heavy metals requires the development of efficient adsorbents. Macroporous polystyrene divinyl benzene based resins are known for their excellent surface characteristics for the effective adsorption of metals. In this paper, we propose an effective adsorption procedure for chromium (VI) using aliphatic primary amine as a guest in Amberlite XAD-4 polymeric sorbent as the host. The adsorption of chromium was quantitative at pH 2.5. The adsorption process was in accordance with pseudo second order kinetics and the maximum adsorption capacity was found to be 75.93 mg g(-1) with good adherence to Langmuir isotherm model. The free energy change ΔG(0) increased with temperature and the negative ΔH(0) and ΔS(0) values indicate the exothermic nature of adsorption and decreased randomness at the adsorbent-solution interface. In aqueous medium, the water molecules surround the hydrophobic host polymeric matrix and this cage effect is responsible for the reduction in entropy of the system. The regeneration of the adsorbent was effective in alkaline medium and the efficacy of the adsorbent was tested for the removal of chromium from tannery waste water.

A preliminary spectroscopic investigation on the molecular interaction of metal-diphenylthiocarbazone complex with cellulose biopolymer and its application.

Biopolymer adsorbents are versatile in their application for removal of heavy metals. The present work is focused towards the preliminary study of the interaction of diphenylthiocarbazone (DTZ) complex of chromium(VI) in acidic medium with cellulose biopolymer. Chromium-DTZ complex could be quantitatively adsorbed on a cellulose column in the pH range 1.0-2.5 and the effect of various experimental parameters such as stability of the column and the complex, column breakthrough volume, and interfering ions have been studied in detail. The probable mechanism of adsorption of complex on the cellulose biopolymer was corroborated using Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and solid state 13C nuclear magnetic resonance techniques (CP-MAS). The pores formed due to the hydrogen bond between the cellulose layers and then the ensuing occupation of the complex between these layers and on the surface of the biopolymer layer through electrostatic attractive force and Π interaction of aromatic ring with cellulose are expected to play a vital role in the interaction. The cellulose column could be regenerated using environmentally benign polyethylene glycol-400 (PEG-400) in acidic medium. The cellulose biosorbent has been successfully tested to study the removal of chromium as its dithizone complex from synthetic and real waste water samples.

Bio-polymer adsorbent for the removal of malachite green from aqueous solution.

A simple, economical and green methodology has been developed for the adsorption of malachite green using cellulose powder as the adsorbent. Batch experimental procedures were conducted to investigate the adsorption ability of this bio-polymer to remove malachite green from aqueous medium. The adsorbed dye on cellulose was characterized by Fourier transform-infrared spectroscopy (FT-IR). The various analytical parameters such as the effect of contact time, pH, temperature, etc. were optimized. The adsorption was efficient at a neutral pH (7.2) and both Langmuir and Freundlich isotherm models showed good fit into the experimental data. The adsorption kinetics indicated that the adsorption proceeds according to pseudo-second-order model. The adsorption of malachite green was found to be exothermic and it was accompanied by decrease in the entropy. Column studies were performed and the regeneration of the adsorbent was done easily using environmentally benign polyethylene glycol-400.

Simple and selective extraction process for chromium (VI) in industrial wastewater.

A simple and relatively green method has been developed for the determination of chromium based on the extraction of chromium (VI) as its ion-association complex with tetrabutylammoniumiodide (TBAI) in acidic medium. The ion-pair is extracted using isobutylmethylketone (MIBK) as the solvent. The concentration of the extracted chromium (VI) in the organic layer was measured spectrophotometrically at a wavelength maximum of 366 nm and the organic layer was characterized using FT-IR spectroscopy. The influence of various analytical parameters such as pH, aqueous phase volume, equilibration time, interfering ions etc. has been studied in detail. The extracted chromium (VI) was back extracted into the aqueous phase to the non-toxic chromium (III) using ascorbic acid. The calibration graph was linear in the range of 0-2 microg mL(-1) chromium (VI) with a relative standard deviation of 2.4%. A detection limit of 0.25 microg in 25 mL aqueous phase volume could be achieved and the validity of the proposed method has been checked by applying it to synthetic mixtures, spiked water sample, electroplating wastewater and certified reference material BCR-715.

Extractive separation and determination of chromium in tannery effluents and electroplating waste water using tribenzylamine as the extractant.

A simple extractive separation method has been developed for the determination of chromium based on the extraction of Cr (VI) as its ion-pair with tribenzylamine (TBA). The ion-pair is extracted at acidic pH using toluene as the diluent. The concentration of chromium in the organic phase was measured spectrophotometrically at 309 nm. The influence of experimental variables such as pH, sample volume, equilibration time, diverse ions etc. has been studied in detail. The extracted chromium (VI) could be stripped to the aqueous phase using NaOH as the stripping agent. The extracts were characterized using FT-IR spectroscopy. A detection limit of 0.08 microg mL(-1) could be achieved and the validity of the method was checked in real tannery effluent, electroplating waste water and spiked water samples.