Photocatalytic reduction of aqueous carcinogenic pollutants on CdS-polymer nanocomposites

Abstract

Water decontamination from the toxic effluents, for the safe use of human, is the hottest area of research nowadays. 4-nitrophenol and Cr(VI) are the two pollutants of high environmental concern due to their toxic and carcinogenic nature. Furthermore, their remediation is a laborious, time consuming and challenging task. In this context, photocatalysis is believed to be an efficient and safe remediation process, however, photocatalysts suffer from inferior stability and efficiency. Similar problems are also associated with CdS, which is considered a low cost and visible light absorbing material. To improve efficiency and stability of CdS, the CdS-polymer nanocomposites were prepared by the deposition of CdS on the polymeric beads (CS/PVA/TEOS) at ambient conditions. CdS-polymer nanocomposites were observed to be better photocatalysts under solar light than the bare CdS for the reduction of {4-nitrophenol and Cr(VI)} carcinogens. The photoreduction followed pseudo first order kinetics. Notably, the rate of photoreduction was observed to increase with an increase in the percentage of degree of deacetylation (DDA) of the chitosan polymer. Among the four synthesized catalysts, the B4/CdS presented the best catalytic efficiency: Cr(VI) reduced in 4 min with TOF = 6.4 × 10−3 mmol Cr(VI)/(mgcat.⋅min), ΔH# = 5.008 kJ/mol and ΔS# = - 0.856 kJ/mol.K and 4-NP in 8 min with TOF = 4.1 × 10−2 mmol 4-NP/(mgcat.⋅min), ΔS# = - 2.817 kJ/mol.K and enthalpy ΔH# = 14.26 kJ/mol. The effect of various parameters: temperature, pH and catalytic dose was also investigated to assess the optimal conditions for photocatalysis. It is anticipated that a unique combination of chitosan polymer and CdS might offer efficient adsorption and electron transfer, which ultimately triggered the reduction.