Sampa Chakrabarti

Zinc oxide nano-particles - Sonochemical synthesis, characterization and application for photo-remediation of heavy metal

Zinc oxide nanoparticles have been synthesized sonochemically from zinc acetate solution in aqueous methanol, ethanol and iso-propanol containing about 5 volume% of alcohol. Characterization with FESEM, XRD, AFM and BET surface area shows that the synthesized particles differ in shape and size. ZnO synthesized using isopropanol was observed to be the most crystalline one. The synthesized nanoparticles were used for the photocatalytic reduction of hexavalent chromium in aqueous medium under solar radiation. It was observed that the initial reduction rates varied with the difference in morphology of ZnO crystallites.

Photocatalytic degradation of methyl orange dye by pristine titanium dioxide, zinc oxide, and graphene oxide nanostructures and their composites under visible light irradiation

Discharge of azo dyes by textile and allied industries to the environment is a growing problem. Degradation of an azo dye, methyl orange (MO), was tested in simulated wastewater with different oxide nanomaterials acting as photocatalysts under visible light. Titanium dioxide (TiO2), zinc oxide (ZnO), and graphene oxide (GO) were synthesized, characterized, and applied for adsorptive and photocatalytic removal of the dye. Factors such as initial concentration of MO and size of nanoparticle photocatalyst were varied to determine the optimum conditions for dye removal. Finally, nanocomposites of the three materials (GO–TiO2–ZnO) were synthesized and tested for its photocatalytic performance. The composition of the individual oxide in the nanocomposite was then varied to achieve the best photocatalytic performance.

Preparation and characterization of multifunctional cotton fabric by coating with sonochemically synthesized zinc oxide nanoparticle-flakes and a novel approach to monitor its self-cleaning property

Multifunctional cotton fabric has been prepared by pad-dry-coating with sonochemically synthesized zinc oxide nanoparticles. The uniqueness of sonochemical synthesis is that it synthesizes without alkali at near neutral pH and hence the cotton fabric is exposed to less chemical stress. As a result of coating, the fabric shows enhanced mechanical strength, water and stain repellence, antimicrobial properties, UV-blocking capacity and self-cleaning characteristics compared to the uncoated fabric. The self-cleaning property was tested with Trypan Blue dye under sunlight. The attempt of quantifying the self-cleaning process with the rate of decolorization is a novel one. It was observed that about 69% of the colour was removed when the coated fabric was exposed to sunlight for 3 h and 30 min. The fading of colour followed pseudo-first-order kinetics.

Ecotoxicological impact of sunlight assisted photoreduction of hexavalent chromium present in wastewater with zinc oxide nanoparticles on common Anabaena flos-aquae

Hexavalent chromium is more toxic and carcinogenic compared to its trivalent counterpart. Hexavalent chromium can be photocatalytically reduced to trivalent one using zinc oxide semiconductor and solar or UV radiation as light source. But an important ecological aspect is whether the net toxicity decreases after the photocatalytic process. In the present work, we have selected Anabaena flos-aquae as the model organism and examined whether the net toxicity to which it has been exposed in water decreases after photocatalytic reduction of hexavalent chromium using ZnO semiconductor as photocatalyst. We have studied the cumulative toxicities of both chromium (before and after treatment) and ZnO (both nano and micro) separately and as a suspension of ZnO in chromium. Quantitative cell surface roughness analysis was conducted using AFM to confirm the changes in cell surface properties.

Utilization of solar energy for photoreduction of industrial wastewater containing hexavalent chromium with zinc oxide semiconductor catalyst

Abstract Scarcities of water and energy are going to be critical in the near future. A possible remedy is to reuse industrial wastewater after suitable treatment using a renewable energy. In this work, wastewater containing hexavalent chromium is treated with Zinc oxide (ZnO) semiconductor photocatalyst in the presence of sunlight to reduce the more toxic hexavalent metal to its less toxic trivalent counterpart. Thirty five percent reduction was obtained after 2 h with 10 mg/L substrate, 0.4 g/L photocatalyst, and 75kLux solar radiation at 31oC temperature. Process parameters are initial concentration of substrate, loading of photocatalyst, pH and concentration of the electron donor. Initial rate of reduction varied only with ZnO-loading and hence it was zero order with respect to both the substrate and electron donor. An alternative rate equation based on the modified Langmuir Hinshelwood Hougen Watson (LHHW) model compares well with the mechanistic rate equation.

Utilisation of eggshell membrane as an adsorbent for carbon dioxide

Carbon dioxide (CO2) is a major greenhouse gas responsible for global warming. This work aims to explore a cheap and easy way for CO2 adsorption from the atmosphere, by using an eggshell membrane. Eggshell membrane could be used up to four times with intermediate regeneration with acetic acid solution. Atomic absorption spectrophotometer (AAS) analysed the amount of CO2 adsorbed as equivalent calcium (Ca) present in calcium carbonate (CaCO3). An average of 6824 mg COCO2 could be adsorbed per g of eggshell membrane. Scanning electron micrograph (SEM) was used to analyse the surface morphology of the fresh and regenerated eggshell membrane.

Dye-sensitised photocatalytic degradation of PVC-ZnO composite film

The hazard of the disposal of waste plastics, such as Polyvinyl Chloride (PVC), has been considered as world-wide environmental problem. In this work, a composite film comprising PVC and ZnO semiconductor has been prepared and characterised. The efficacy of ZnO to degrade the PVC photocatalytically under UV irradiation with and without Eosin Y dye sensitiser has been explored. The process parameters studied were loading of ZnO and Eosin Y and intensity of UV radiation. The loss of weight of the film was monitored continuously and about 20% of the initial weight of the film was found to be lost within 7200 sec under the experimental conditions. The rate of degradation followed a pseudo first order kinetic model with respect to the net weight. An enhancement of degradation was achieved using dye sensitiser.

Adsorption of model textile dyes from aqueous solutions using agricultural wastes as adsorbents: equilibrium, kinetics and fixed bed column study

Gram husk and groundnut shell are cheap and abundantly available agricultural waste materials in India. A systematic study on the adsorption of some model dyes from aqueous solution on these low-cost adsorbents has been attempted. Model dyes used were Methylene Blue, Rhodamine B, Congo Red, Eosine Y and Metanil Yellow. Equilibrium, kinetics and column experiments were performed. Effects of different process variables have been studied. Equilibrium data fitted well in Langmuir and Freundlich isotherm equations. A model using Freundlich equation has been developed for interpretation of kinetic data. Other models such as Lagergren equation and pseudo second order equation were also used. Of these models, pseudo second order equation was found to be the most satisfactory. Column experiments were carried out with gram-husk and Rhodamine B. The data could be correlated well with BDST model.

Sunlight-Assisted Photo-Fenton Process for Removal of Insecticide from Agricultural Wastewater

Pesticides and insecticides are harmful and toxic organic chemicals that are used for controlling pests and insects in agriculture, thereby considered as necessary evil. Agricultural wastewater, contaminated with such toxic pesticides, pollutes surface and groundwater. Pesticides are able to reach surface waters either directly or indirectly via the discharge of agricultural drainage water from treated land and via runoff after application on hard surfaces (Leu et al. 2004). Organophosphorus pesticides are produced in mass and are widely used in the developing country. 2,2 dichlorovinyl dimethyl phosphate, commonly referred as Dichlorvos (Fig. 2.1) is an organophosphorous insecticide, which is highly toxic, non-biodegradable and difficult to remove by conventional methods. During 2006–2010 period, consumption of Dichlorvos in India was 5833 metric tons. Due to its fairly good solubility [~10 g.L−1 (at 20 °C)] in water (WHO 1978, 1994) it is highly mobile in aquatic environment. Various technologies and processes have been proposed for the treatment of pesticide-contaminated waters. Some conventional techniques including flocculation, filtration and adsorption of activated carbon are only based on a phase transfer of the pollutant. These treatment procedures are either of high cost or a source of secondary pollution due to sludge formation: therefore, there is a need to seek better alternatives (Evgenidou et al. 2005). Advanced oxidation processes (AOPs) are attractive methods for the treatment of wastewaters containing refractory organics due to their efficiency to oxidize a great variety of organic contaminants by the generation of highly reactive hydroxyl radicals (OH•) (Espulgas et al. 2002). Many pollutants, including pesticides, pharmaceuticals and dyes can be completely mineralised by AOP as reported in the works of Chiron et al. (2000), Perez-Estrada et al. (2005) and Lucas and Peres (2006). Heterogeneous photocatalysis using titanium dioxide (TiO2) and solar/UV radiation, combined with hydrogen peroxide (H2O2), and homogeneous processes such as Fenton (Fe2+/H2O2) and photo-Fenton (Fe2+/H2O2/UV/sunlight) reactions are proved to be useful techniques for the treatment of pesticide-contaminated wastewater. There are different ways to produce HO•, among which solar photo-Fenton process is one of the most efficient ones for the treatment of contaminated wastewater (Malato et al. 2002; Oller et al. 2006; Maldonado et al. 2007; Ortega-Liebana et al. 2012; Klamerth et al. 2013).