Rumpa Saha

Sources and toxicity of hexavalent chromium

Chromium exists in oxidation states ranging from −IV to +VI, inclusively. The compounds exhibit a wide range of geometries including square planar, tetrahedral, octahedral, and various distorted geometries. Ore refining, chemical and refractory processing, cement-producing plants, automobile brake lining, catalytic converters for automobiles, leather tanneries, and chrome pigments contribute to the atmospheric burden of chromium. Hexavalent chromium is known to have 100-fold more toxicity than trivalent chromium, for both acute and chronic exposures because of its high water solubility and mobility, as well as easy reduction. The respiratory tract is the major target organ for hexavalent chromium following the inhalation exposure in humans. Chronic inhalation exposure to hexavalent chromium results in effects on the respiratory tract, with perforations and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, and nasal itching and soreness as reported. Chronic human exposure to high levels of hexavalent chromium by inhalation or oral exposure may produce effects on the liver, kidney, gastrointestinal, and immune systems, and possibly the blood. Dermal exposure to hexavalent chromium may cause contact dermatitis, sensitivity, and ulceration of the skin.

A review on natural surfactants

Natural surfactants or biosurfactants are amphiphilic biological compounds, usually extracellular, produced by a variety of microorganisms from various substances including waste materials. There is increasing interest on this topic because of their unique properties such as low toxicity, functionality under extreme conditions, based on renewable substances and biologically degradable nature. The diversity of these molecules supports their potential application in the field of petroleum, medicine, agriculture, food, cosmetics etc. They are also effective in curtailing the green-house effect by reducing the emission of CO2. They can be termed as ‘green’ because of their low toxicity, biodegradability and relative stability under a wide range of physicochemical environments. In spite of possessing diverse structures and better physicochemical properties than chemical surfactants, biosurfactants are not able to compete with their synthetic counterparts because of their high production & downstream costs. The commercial realization of these eco-friendly biomolecules is restricted by low productivity, expensive downstream processing and lack of appropriate understanding of the bioreactor systems for their production. But we expect that in future better reactor design and product recovery technology would be developed and overproducer microbial strain would be screened. Then production cost would be decreased and yield would be increased i.e. the production would be both ecologically & economically favored. The present review deals with an overall view on biosurfactants, their properties, advantages & disadvantages, production, characterization, application along with a recommendation for future research.

Micellar catalysis on 1,10-phenanthroline promoted hexavalent chromium oxidation of ethanol

The kinetics and mechanism of Cr(VI) oxidation of ethanol in the presence and absence of 1,10-phenanthroline in aqueous acid media have been carried out. Monomeric species of Cr(VI) are kinetically active in the absence of phen, while in the phen catalyzed path, the Cr(VI)-phen complex has been suggested as the active oxidant. In the catalyzed path, the Cr(VI)-phen complex participates in the oxidation of ethanol and ultimately is converted into the Cr(III)-phen complex. In the uncatalyzed path, the Cr(VI)-substrate ester experiences an acid catalyzed redox decomposition in the rate-determining step. The uncatalyzed path shows a second-order dependence on [H+], while the phen catalyzed path shows a first-order dependence on [H+]. Both the uncatalyzed and phen-catalyzed paths show first-order dependence on [ethanol]T and [Cr(VI)]T. The phen-catalyzed path is first order in [phen]T. These observations remain unaltered in the presence of externally added surfactants. CPC inhibits the reactions while SDS catalyzes the reactions. The observed miceller effects have been explained by considering partitioning of the reactants between the miceller and aqueous phase.

Chromium removal technologies

Chromium can exist in different oxidation states (e.g. 0, III, VI). Chromium can be both beneficial and toxic to animals and humans depending on its oxidation state and concentration. At low concentration, Cr(III) is essential for animal and human health. Chromium(VI) compounds are highly soluble, mobile and bioavailable compared to trivalent chromium. Chromium(VI) is dangerous for humans due to its toxicity and carcinogenic properties. The presence of hexavalent chromium in waste water is a potential hazard to aquatic animals and humans. Various methods are adopted for the removal of hexavalent chromium from industrial effluents. Among these different techniques, biosorption is the most promising one. In this process, the various components present in biomaterial reduce the toxic hexavalent chromium to non-toxic trivalent chromium. Algae, fungi and bacteria have biosorption properties, and cell walls are responsible for biosorption of dead biomaterial. But this process removes chromium from waste water very slowly. So for chemical modification of biosorbents, optimization of biosorption parameters is required to increase the effectiveness of this process.

Removal of hexavalent chromium from contaminated water by adsorption using mango leaves (Mangifera indica)

AbstractThe objective of this study is to assess the uptake of hexavalent chromium Cr(VI) from aqueous solutions onto mango leave dust. Batch adsorption procedure is utilized to test the ability of leave dust as an adsorbent for Cr(VI) (reduction coupled adsorption). The contribution of various parameters on sorption, such as contact time, sorbate concentration, pH of the medium, and temperature, was estimated, and maximum uptake of Cr(VI) from contaminated water was 250.23 mg g–1 at pH 2.0 and temperature 40°C. Cr(VI) uptake from contaminated water followed the pseudo-first-order rate expression. ΔG0, ΔH0, and ΔS0 have also been evaluated, and it has been concluded that the sorption was feasible, spontaneous, and endothermic in nature. The process follows well Langmuir isotherm. The nature of the possible adsorbent and metal ion interactions was examined by the Fourier transform infra-red (FTIR) technique. FTIR spectroscopy revealed the involvement of –OH, C=O, C–O groups on the cell surfaces in chromium...

Micellar catalysis on picolinic acid promoted hexavalent chromium oxidation of glycerol

Under pseudo-first-order conditions, monomeric Cr(VI) was found to be kinetically active in the absence of picolinic acid (PA), whereas in the PA-promoted path, the Cr(VI)–PA complex undergoes nucleophilic attack by the substrate to form a ternary complex which subsequently experiences redox decomposition, leading to glyceraldehydes and Cr(IV)–PA complex. The uncatalyzed path shows a second-order dependence on [H+], whereas the PA-catalyzed path shows zero-order dependence on [H+]. Both the uncatalyzed and PA-catalyzed path show a first-order dependence on [glycerol]T and [Cr(VI)]T. The PA-catalyzed path is first order in [PA]T. All these observations remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant cetyl pyridinium chloride (CPC) and anionic surfactant sodium dodecyl sulfate (SDS) on the PA-catalyzed path have been studied. CPC inhibits, whereas SDS accelerates the reaction. Here, SDS is a catalyst for glyceraldehydes production and at the same time reduction of carcinogenic hexavalent chromium to nontoxic trivalent chromium. The reaction proceeds simultaneously in both aqueous and micellar phase. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase. The Menger–Portnoy model, Piszkiewicz cooperative model, and pseudo-phase ion exchange model have been tested to explain the observed micellar effect.

Efficient combination of promoter and catalyst for chromic acid oxidation of propan-2-ol to acetone in aqueous acid media at room temperature.

Oxidation of propan-2-ol to acetone was carried out in aqueous media at room temperature. The effect of promoter (PA, bpy, phen), micellar catalyst (SDS, CPC, TX-100) and their combination has been studied. The reactions were performed under the condition [Propan-2-ol]T≫[Cr(VI)]T at 30°C. Then kobs and half life of all the reaction were determined to identify which promoter and which combination are the most effective for this oxidation. Among the promoters phen accelerates the reaction most in aqueous media. In absence of promoters anionic surfactant SDS increases the rate more effectively than neutral surfactant TX-100. CPC retards the rate in comparison to aqueous media. The rate of the oxidation is highest in presence of the combination of bpy and SDS.

Toxicity of inorganic vanadium compounds

Vanadium causes a variety of toxic effects such as hematological and biochemical changes, e.g., hemolysis and decrease in erythrocyte count/hemoglobin level/hematocrit index, neurobehavioral injury, i.e. general activity and learning, and abnormalities in development and reproduction, e.g., ,embryotoxicity, teratogenicity, or morphological and functional lesions in liver, kidneys, bones, spleen and leukocytes. Inhalation of vanadium may cause rhinitis, pharyngitis, chronic productive cough, tracheobronchitis, and bronchopneumonia. Moreover, the most often observed side effects include loss of appetite and significant reduction of body weight, often leading to anorexia, weakness, and nose bleeding, vomiting, diarrhoea, dehydration, pulmonary hemorrhage, or death.

Modernization of surfactant chemistry in the age of gemini and bio-surfactants: a review

Modern surfactant science demands chemistry which is benign by design. Efficient green chemicals like gemini surfactants along with natural resource derived bio-surfactants are thus most dependable in this case. In the search for less pollution and more ecologically beneficial solvents, more and more environmentally accepted trends are emerging every day into the market; species related to properties such as lower toxicity, higher biodegradability, chemical stability, environmental safety, efficient solubilization and of course, ease of recycling, can be vital tools. Bio-surfactants along with geminis are of great interest for their very efficient working ability, lower CMC and other up to date features that modern science desires for the betterment of mother nature. This review contains elaborate discussions on the efficiencies of gemini and bio-surfactants as modern generation green chemicals in various fields viz. in laboratory based kinetic experiments, electron transfer reactions, emulsification, solubilization, and agro-industrial and bio-medicinal fields which provides us with the hope of an amazing future prospect with these types of green chemicals.

Micellar Catalysis on 1,10-Phenanthroline Promoted Chromic Acid Oxidation of Glycerol in Aqueous Media

Abstract On pseudo-first order conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of phenanthroline (phen) whereas in the phen-promoted path, the Cr(VI)-phen complex undergoes a nucleophilic attack by glycerol to form a ternary complex which subsequently experience a redox decomposition leading to glyceraldehydes and Cr(III)-phen complex. The effect of the cationic surfactant, cetyl pyridinium chloride (CPC); anionic surfactant, sodium dodecyl sulphate (SDS) and nonionic surfactant, triton X-100 (TX-100) on the unpromoted and phen-promoted path have been studied. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase.