Quantum yields and relative photonic efficiencies of substituted 1,3-dihydroxybenzenes

Abstract

1,3-dihyroxybenzene (1,3-DHB) is selected as the standard probe and Degussa P25 TiO 2 as the standard photocatalyst for the determination of quantum yields of 3,5-dihydroxytoluene (3,5-DHT), 1,3-dihydroxy-5-methoxybenzene (1,3-DHMB), and 3,5-dihydroxybenzoic acid (3,5-DHBA) based on the relative photonic efficiency concept. A detailed analysis about the incident photon flux and rate of formation of CO 2 for the photocatalytic degradation of 1,3-DHB is done. Fraction of light absorption is measured as a function of incident photon flux and TiO 2 loading. When a TiO 2 concentration of 1 g/l and an incident photon flux of 10.8×10 −6 Einstein/min are used, the quantum yields for the photocatalytic degradation of 1,3-DHB, based on disappearance of 1,3-DHB, and formation of CO 2 are found as 0.06 and 0.34, respectively. The difference between two quantum yields indicate the formation of intermediates during the photodegradation process. The effect of reactant concentration, pH of the medium and temperature of the system are investigated to determine the relative efficiencies of the reactant molecules. Quantum yields of the reactants are found from φ= ζ r φ 1,3-DHB at their natural pH values as 0.22, 0.35, and 0.38 for 3,5-DHT, 1,3-DHMB and 3,5-DHBA, respectively.