Improvement of eosin visible light degradation using PbS-sensititized TiO2

PbS was prepared by a simple chemical method for use as a photosensitizer with TiO2. Its physico-chemical characterisation reveals a semiconducting behaviour with a band gap energy of 0.41 eV showing efficient visible light absorption. The valence and conduction band energy levels are -0.78 and -1.19 V, respectively. Interparticle electron injection (IPEI) from photoactivated PbS to inactivated TiO2 was demonstrated by the increase of eosin degradation under visible light. Different parameters affecting the photoactivity such as the PbS amount, eosin concentration and initial pH were investigated. Optimal degradation of eosin occurs at a PbS/TiO2 ratio of 10:90, an eosin concentration of 30 mg l(-1), a pH similar to 7, and when using a 2 x 200 W tungsten lamp. These conditions result in a constant decomposition rate of 0.116 min(-1) corresponding to an eosin half-life of 6.4 min. In this case, the rate of degradation of eosin is respectively 20 and 40 times greater than when in contact with pure TiO2 or through direct photolysis. The photoeffeciency of PbS(10%)/TiO2 was compared to that of CdS(10%)/TiO2, Bi2S3(10%)/TiO2, Cu2O(10%)/TiO2 and Bi2O3(10%)/TiO2 using visible and UV-vis light. PbS(10%)/TiO2 has the best efficiency regardless of the wavelength of light used. The contribution of the electromotive force and the band gap of the narrow band gap semiconductor to the photoactivity improvement were discussed. (C) 2007 Elsevier B.V. All rights reserved.