Development of photocatalyst for effective utilization of solar energy for wastewater treatment

Abstract

Due to rapid industrialisation, large amount of wastewater is generated. The newlinetextile industries which uses dyes and other dyes manufacturing industries, in newlineparticular, discharge highly coloured dyes that can adversely affect plants, marine life newlineand humans. Treatment of this wastewater prior to its discharge into natural water newlinebodies is essential since it could be carcinogenic and toxic. To combat the issue, newlinegovernments have laid down discharge norms that need to be followed while treating newlinethe wastewater. While conventional treatment methods are energy and cost intensive, newlineand generally do not completely degrade the pollutant within optimal operating newlineparameters, advanced oxidation processes (AOP) can mineralise the organic chemicals newlineto harmless water and carbon dioxide. Photocatalysis is one such AOP which thus newlinetreats the effluent with the help of solar energy. In the vicinity of city of Ahmedabad newlineand in the state of Gujarat many dyes and textile industries are present. Current work newlineis an attempt to propose better option to conventional techniques for degradation of newlinesuch dyes from wastewater. newlineMost of the development in this area has been focussed on TiO2 as a newlinephotocatalyst. However, owing to its characteristic bandgap, it is able to utilise only newlinethe ultra-violet region, which is only ~4% of the solar spectrum. Ag2CO3, on the other newlinehand, has a relatively narrow bandgap and can work in visible region (~47% of the newlinesolar spectrum). However, narrow bandgap often results in rapid recombination of the newlinephotogenerated electrons and holes. In order to arrest recombination, Ag2CO3 can be newlinecoupled with other photocatalysts having appropriate band positions and together they newlinecan exhibit better results. newlineThe main objective of this work is to evaluate the treatability of a model dye newlinesample in an efficient and effective manner. In the present study, a series of hybrid newlineAg2CO3/SiC and Ag2CO3/ZnO nanostructures have been successfully synthesised newlinethrough a simple precipitation route. The photocatalytic performance was evaluated newlineby the degradation of MB since it is non-toxic and hence suitable for educational labwork. newlineAll experiments were performed under natural solar irradiation. It was observed newlinethat formation of a heterojunction improves the photoactivity of the hybrid newlinephotocatalysts by inducing a charge transfer between Ag2CO3 and SiC/ZnO. The newlinephotocatalysts were characterized by XRD, SEM, TEM, TGA-DTG, BET and UVVis/ newlineNIR. Among all the hybrid combinations prepared, the best photocatalytic results newlinev newlineand formal quantum efficiency (FQE) under natural sunlight were obtained with newlineAGSC-12 and AGZN-22 composites. It is observed that under experimental newlineconditions, AGSC-12 was able to completely decolourise the dye in 90 min with an newlineFQE of 0.154%. Similarly, AGZN-22, under the experimental conditions could newlinedecolourise MB completely in just 20 min. The FQE of AGZN-22 was found to be newline0.884%. The performance of both these photocatalysts was observed to be much better newlinethan that of the conventionally popular TiO2. newlineFactors viz., photocatalyst dosage, solution pH, solar intensity, substrate and newlineits initial concentration and speed of agitation were found to influence phototreatment. newlineCorresponding optimum parametric values have been found and reported newlinein terms of FQE. The performance of the photocatalysts have also been investigated newlineon real industrial effluent and rate expression developed in terms of TOC. Also, a CPC newlinesolar photoreactor (CPC-P) has been designed and fabricated and investigated for its newlineperformance. Its performance was found to be better than that of the laboratory reactor. newlineWhile the lab reactor could decolourise MB newline