Silica-Supported Cds-Sensitized Tio2 Particles in Photo-Driven Water Purification: Assessment of Efficiency, Stability and Recovery Future Perspectives
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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). 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. The TiO2/CdS system was unstable under neutral, acidic conditions and basic conditions. Leaching out, of CdS into hazardous aqueous Cd2+ ions, while working at pH 7 or lower occurred. 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 UV regions. In the visible region, the Silica/TiO2/CdS was less efficient than the TiO2/CdS but more efficient than naked TiO2. The silica support has an added application value of making catalyst recovery much easier, after reaction completion. Unfortunately the difficulty of the Cd2+ ion leaching out has been solved out partly only in basic media. Pre-annealing of the catalyst systems did not give significant effect on stability. Despite the numerous literature reports, on using CdS as sensitizer in degradation studies, its tendency to leach out puts a limitation on its future usage. Should this tendency not be solved out completely, replacement with other more safe dyes should be considered. Effects of catalyst concentration, catalyst recovery, contaminant concentration, temperature and pH, on catalyst efficiency, have also been studied.

Nova science Publication ,water purification, Book chapter, 203-226
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