An-Najah Staff

Surfaces of Rutile TiO2 particles have been modified with CdS particles. The TiO2/CdS system has been used as catalyst in water purification by photo-degradation of organic contaminants such as methyl orange (a commonly encountered contaminant dye) and Phenazopyridine (a commonly encountered medically active drug). Both UV and Visible ranges have been investigated. CdS sensitization of TiO2 to visible region has been observed, as the TiO2/CdS system showed higher catalytic efficiency than the naked TiO2 system in the visible region.  While showing relatively higher stability, to photo-degradation conditions, at higher pH values, the TiO2/CdS system was unstable under neutral and acidic conditions. Significant amounts of CdS degraded into hazardous aqueous Cd2+ ions while working at pH 7 or lower. This imposes limitations on future usage of CdS-sensitized TiO2 photo-catalytic systems in water purification processes. In an effort to solve out the leaching difficulties, and to make catalyst recovery easier, the TiO2/CdS system has been supported onto insoluble silica particles giving Silica/TiO2/CdS systems for the first time. The silica/TiO2/CdS system showed lower efficiency than TiO2 and TiO2/CdS systems in both UV and Visible regions. However, silica support has an added application value to the catalytic system, by making its recovery much easier, after reaction completion. Unfortunately the difficulty of the Cd2+ ion leaching out has not been solved out for silica/TiO2/CdS system. Despite the numerous literature reports, on using CdS as sensitizer for TiO2 in degradation studies,  its tendency to leach out puts a limitation on its future usage. Replacement with other more safe dyes should therefore be considered. Effects of catalyst concentration, catalyst recovery, contaminant concentration, temperature and pH, on catalyst efficiency, have also been studied.