Photocatalytic oxidation of ethanol and isopropanol vapors on cadmium sulfide

Abstract

CdS-based catalysts preparation has been investigated, and the obtained photocatalysts were characterized and tested in photocatalytic oxidation of ethanol and isopropanol vapors under visible light irradiation (λ>420nm) with oxygen of air. The catalysts were prepared with a two-step method: (1) reaction between CdCl2 and NaOH and (2) exchange of hydroxide ions of Cd(OH)2 intermediate with S2− to form CdS. Influence of the reagents addition rate, stirring rate, temperature of the reaction mixture and the reagents’ ratio on the oxidation rate of alcohols on solids was investigated. It was found that the rate of photooxidation increases with the increase in the stirring rate and with the decrease in the reagents addition rate during the synthesis. The photocatalytic activity as a function of sulfur content reaches the highest value for the stoichiometric CdS, which is obtained at ≥2:1 S2− to Cd2+ molar ratio in precursors. Kinetic features of the isopropanol photocatalytic oxidation were studied. The Langmuir–Hinshelwood model describes satisfactorily the rate vs. concentration curve. The increase in the air relative humidity results in higher isopropanol oxidation rate. Partial deactivation of CdS catalyst was observed and described with exponential decay. Deactivation was less pronounced at high relative humidity. CdS deactivation took place due to the surface sulfur ions oxidation with formation of SO42- groups. The results show a potential of CdS photocatalysis for solar light–driven green oxidation processes of organic compounds.