Rashmi Sanghi

Biomimetic synthesis and characterisation of protein capped silver nanoparticles

A controlled and up-scalable route for the biosynthesis of silver nanopartilces (NPs) mediated by fungal proteins of Coriolus versicolor has been undertaken for the first time. The fungus when challenged with silver nitrate solution accumulated silver NPs on its surface in 72h which could be reduced to 1h by tailoring the reaction conditions. Under alkaline conditions, the reaction was much faster and could easily proceed at room temperature even without stirring. The resulting Ag NPs displayed controllable structural and optical properties depending on the experimental parameters such as pH and reaction temperatures. The average size, morphology, and structure of particles were determined by AFM, TEM, XRD and UV/Visible absorption spectrophotometry. Fourier transform infrared study disclosed that the amino groups were bound to the particles, which was accountable for the stability of NPs. It further confirmed the presence of protein as the stabilizing and capping agent surrounding the silver NPs. Experiments were conducted both with, media in which fungus was initially harvested and that of pristine fungal mycelium alone. Under normal conditions, in the case of media extracellular synthesis took place whereby other than the fungal proteins, glucose was also responsible for the reduction. In the case of fungal mycelium, the intracellular formation of Ag NPs, could be tailored to give both intracellular and extracellular Ag NPs under alkaline conditions whereby the surface S-H groups of the fungus played a major role.

Poly(methylmethacrylate) grafted chitosan: An efficient adsorbent for anionic azo dyes.

Present study reports on peroxydisulfate/ascorbic acid initiated synthesis of Chitosan-graft-poly(methylmethacrylate) (Ch-g-PMMA) and its characterization by FTIR, XRD and (13)C NMR. The copolymer remained water insoluble even under highly acidic conditions and was evaluated to be an efficient adsorbent for the three anionic azo dyes (Procion Yellow MX, Remazol Brilliant Violet and Reactive Blue H5G) over a wide pH range of 4-10 being most at pH 7. The adsorbent was also found efficient in decolorizing the textile industry wastewater and was much more efficient than the parent chitosan. Equilibrium sorption experiments were carried out at different pH and initial dye concentration values. The experimental equilibrium data for each adsorbent-dye system were successfully fitted to the Langmuir and Freundlich sorption isotherms. Based on Langmuir model Q(max) for yellow, violet and blue dyes was 250, 357 and 178, respectively. Thermodynamic parameters of the adsorption processes such as DeltaG degrees , DeltaH degrees , and DeltaS degrees were calculated. The negative values of free energy reflected the spontaneous nature of adsorption. The adsorption kinetic data of all the three dyes could be well represented by pseudo-second-order model with the correlation coefficients (R(2)) being 0.9922, 0.9997 and 0.9862, for direct yellow, reactive violet and blue dye, respectively with rate constants 0.91 x 10(-4), 1.82 x 10(-4) and 1.05 x 10(-4) g mg(-1)min(-1), respectively. At pH 7, parent chitosan also showed pseudo-second-order kinetics. The temperature dependence of dye uptake and the pseudo-second-order kinetics of the adsorption indicated that chemisorption is the rate-limiting step that controls the process.

Cassia angustifolia seed gum as an effective natural coagulant for decolourisation of dye solutions

Owing to economic advantages in addition to the potential for improved process robustness and to reduce the pollution load on the environment, particularly in water treatment applications in developing countries, an investigation with biodegradable and eco-friendly naturally occurring seed gum as coagulant was undertaken. Naturally occurring Cassia angustifolia (CA) seed gum was evaluated against the chemical coagulant polyaluminium chloride (PAC) for its coagulation ability to remove colour from synthetic dye solutions. Three groups of dyes: Acid Sendula Red, Direct Kahi Green and Reactive Remazol Brilliant Violet were chosen for the case study. For optimum results the variables studied were pH and dosage. CA was found to be a good working substitute alone or in conjunction with a very low dose of PAC for decolourisation of acid and direct, but not for reactive dye solutions. The performance of PAC was better with direct dye and that of CA was better with that of acid dye.

Poly(acrylamide) functionalized chitosan: an efficient adsorbent for azo dyes from aqueous solutions.

In the present communication we report on the optimization of persulfate/ascorbic acid initiated synthesis of chitosan-graft-poly(acrylamide) (Ch-g-PAM) and its application in the removal of azo dyes. The optimum yield of the copolymer was obtained using 16 x 10(-2)M acrylamide, 3.0 x 10(-2)M ascorbic acid, 2.4 x 10(-3)M K(2)S(2)O(8) and 0.1g chitosan in 25 mL of 5% aqueous formic acid at 45+/-0.2 degrees C. Ch-g-PAM remained water insoluble even under highly acidic conditions and could efficiently remove Remazol violet and Procion yellow dyes from the aqueous solutions over a pH range of 3-8 in contrast to chitosan (Ch) which showed pH dependent adsorption. The adsorption data of the Ch-g-PAM and Ch for both the dyes were modeled by Langmuir and Freundlich isotherms where the data fitted better to Langmuir isotherms. To understand the adsorption behavior of Ch-g-PAM, adsorption of Remazol violet on to the copolymer was optimized and the kinetic and thermodynamic studies were carried out taking Ch as reference. Both Ch-g-PAM and Ch followed pseudo-second-order adsorption kinetics. The thermodynamic study revealed a positive heat of adsorption (Delta H degrees), a positive DeltaS degrees and a negative Delta G degrees, indicating spontaneous and endothermic nature of the adsorption of RV dye on to the Ch-g-PAM. The Ch-g-PAM was found to be very efficient in removing color from real industrial wastewater as well, though the interfering ions present in the wastewater slightly hindered its adsorption capacity. The data from regeneration efficiencies for ten cycles evidenced the high reusability of the copolymer in the treatment of waste water laden with even high concentrations of dye.

Chemistry behind the life of a transformer

ConclusionScientific assessment of the insulation conditions rather than years of service determine the remnant life of the transformer. Insulation age of a transformer is exclusively decided by the life of cellulosic materials. Extent of degradation of cellulosic materials can be quantified by measuring dissolved CO2 gas content in oil, degree of polymerization of paper and furan content in oil. Transformer life is shortened by a number of events. Taking action to prevent failure from any of these causes is a method of life extension. Maintaining the insulation system in good order and controlling loads by the use of dynamic loading of the equipment make it possible to improve the utilization of the existing transformer capacity.

Fungal bioremediation of chromates: Conformational changes of biomass during sequestration, binding, and reduction of hexavalent chromium ions

This paper highlights the mechanistic aspects of white rot fungus Coriolus versicolor as a complexing/reducing agent for chromium bioremediation. The chemical reduction of Cr(VI) to Cr(III) via the formation of Cr(VI) thio ester as an intermediate, is pH dependent and controls the overall chromium adsorption kinetics. The strong adsorption affinity of the biomass towards Cr(VI) anions was evaluated by the Freundlich and the Langmuir adsorption isotherms. The FTIR spectroscopic analysis suggested the involvement of amino, carboxylate, and thiol groups from fungal cell wall in chromium binding and reduction. The mechanism of the adsorption was preferential sequestration along with binding of the metal to the ligating groups present in the biomass followed by reduction to trivalent state. The results indicate step-wise progression of overall reaction dictated and modulated by structural and conformation effects in the biomass that lead to saturation, acceleration, and ultimate saturation kinetics effects.

Synthesis and characterization of guar gum templated hybrid nano silica

The objective of the present study was the fabrication of green adsorbent hybrids for which native guar gum was used as template to polymerize tetraethoxysilane. The properties and performances of the hybrids could be tailored by using varying molecular sizes of the partially depolymerized guar gum templates of various molecular sizes as control. Zn(II) uptake from aqueous solution was used as a criterion for evaluating the adsorbent efficiency. The optimum material (H4) in terms of maximum Zn(II) uptake, was obtained when the template size used was 375 kDa at a calcination temperature of 700°C. H4 was also evaluated for Ca(II), Mg(II), Cd(II) and Hg(II) adsorption. To explore the other applicability areas, the hybrids have been extensively characterized using FTIR, XRD, TGA-DTA, PL, SEM, TEM and BET analyses. H4 was found to be as efficient as previously reported vinyl modified-silica nanohybrids. It had a high surface area (264 m(2)/g) with silica nanoparticles in the size range of 90-140 nm. Being thermally very stable and photoluminescent, the material can be potentially used for many biological, medical and environmental applications.

Endothelin receptor antagonists: an overview of their synthesis and structure-activity relationship.

Endothelins (ETs) are potent vasoconstrictor peptides and are associated with several disease states like pulmonary hypertension, systemic hypertension and heart failure. Endothelin-1 (ET-1) is the first member of the family and it has the receptor subtypes known as ETA and ETB. The receptors ETA and ETB are attractive new therapeutic targets for diseases associated with elevated ET-1 levels. Several studies have thus led to the discovery of selective ETA receptor antagonists as well as non-selective ETA/ETB antagonists. The preclinical and clinical studies have clearly established that these antagonists are effective in the treatment of essential hypertension, pulmonary hypertension, heart failure and atherosclerosis. The advances in this area have resulted in the FDA approval of the orally active dual antagonist Bosentan for pulmonary hypertension in 2001. This review highlights the synthesis and structure-activity of the endothelin receptor antagonists and covers the literature in this area up to 2001.

Wastewater Reuse and Management

ion or extraction barriers have been installed and applied in different cases worldwide in order to prevent seawater intrusion at coastal aquifers where extensive pumping of groundwater has resulted in seawater encroachment. Kashef [17] argues that the main disadvantage of this method is the high financial cost which is usually involved. Most of the cases which were proposed for the application of such method were later proved financially unfeasible. Petalas et al. [18] also argue that this method could be proved unfeasible in the case of coastal aquifers which are characterised by a low groundwater resources potential, and therefore, any further extraction of groundwater could have negative impacts (e.g. significant lowering of the piezometric surface of the aquifer system). 17.3.1.2 Injection Barriers Injection barriers are similar in design with the previous ones (extraction wells) by means that they are also related to the installation of a series of groundwater wells along the coastline of the coastal aquifer. However, the principle and therefore the hydrogeological mechanism is quite opposite in comparison with the one above. Freshwater is continuously injected into the aquifer and again in the vicinity of the shoreline; however, in this case, the filter of the injection well should be located exactly at the toe of the interface between the two fluids (fresh and saline groundwater). Todd and Mays [15] refer to the formation of a pressure ridge which is maintained as water is constantly injected into the aquifer, and this can be thought schematically as a hydraulic barrier. This technique requires significant amounts of alternative sources of water of very high quality. The quality of the injected water should be such that it will not create qualitative degradation of the groundwater resources of the aquifer. High quality of water to be injected is mainly suggested for the prevention of well clogging and hence decrease in the productivity of injection. The alternative freshwater resources should be located in the vicinity of the study area in order to also minimise related water transfer costs. Bruington [19] suggests redevelopment of the injection wells when clogging takes place and the effectiveness of the injection barrier is significantly decreased. The quality standards of the injected water should be according to the drinking water standards [20, 21] in order to eliminate contamination or pollution of the aquifer which is under remediation. 17.3.1.3 Underground Barriers Another type of coastal barrier for the prevention of further seawater encroachment in a coastal aquifer is the installation of underground construction works for the immediate prevention of the seawater wedge intrusion. In principle, this technique could be thought as the design of an underground dam which directly stops the intrusion of the seawater immediately at the toe of the interface between freshand seawater. This method simply involves a physical impermeable vertical subsurface 482 A. Kallioras et al.

Microwave irradiation: Way to eco-friendly, green chemistry

This article highlights with examples, the usefulness of microwaves for carrying out a variety of organic transformations