TiO2 semiconductor photodegradation of substituted resorcinols: |kinetic and mechanistic studies

Abstract

The photocatalytic degradation of 1,3-dihydroxybenzene (1,3-DHB) (resorcinol) and the substituted resorcinols, 3,5-dihydroxytoluene (3,5-DHT), 1,3-dihydroxy-5-methoxybenzene (1,3-DHMB) and 3,5-dihydroxybenzoic acid (3,5-DHBA) in the presence of aqueous suspensions of TiO2 are investigated kinetically and mechanistically. The effects of initial concentrations of the reactants, the pH of the medium, temperature, incident photon flux, and irradiation time are examined in detail. It is found that 1,3-DHB and 3,5-DHT obey pseudo-first order kinetics whereas 1,3-DHMB and 3,5-DHBA obey zero order kinetics. The Langmuir type of plot confirms that reactions take place on the surface of TiO2. 1,3-DHB, 3,5-DHT, and 1,3-DHMB are found to be most efficient at pH 9.0 while 3,5-DHBA had highest efficiency at its natural pH 4.4. The activation energy is found as 11.2 kJ/mol, 17.4 kJ/mol, 17.1 kJ/mol, and 10.3 kJ/mol for 1,3- DHB, 3,5-DHT, 1,3-DHMB, and 3,5-DHBA, respectively. Based on the relative photonic efficiency concept, the quantum yield is found as 0.34, 0.22, 0.35, and 0.38 for 1,3- DHB, 3,5-DHT, 1,3-DHMB, and 3,5-DHBA, respectively. Deposition of Fe3+, Ni2+, Zn2+, Nb5+, Ta5+, Co2+, Mn2+, Al3+, Cr3+ and V4+ on the surface of TiO2 affects the photocatalytic degradation of reactant molecules. Fe3+ showed the highest efficiency.