CdS-sensitized TiO2 in phenazopyridine photo-degradation: catalyst efficiency, stability and feasibility assessment

Mineralization of phenazopyridine, 1, in water, under solar-simulator radiation was efficiently achieved using nanoparticle CdS-sensitized rutile TiO(2), TiO(2)/CdS, 2, as photo-catalysts. Despite that, 2 showed two main drawbacks. Firstly, the system was difficult to recover by simple filtration, and demanded centrifugation. Secondly, the sensitizer CdS showed relatively high tendency to leach out hazardous Cd(2+) ions under photo-degradation reaction conditions. In an attempt to solve out such difficulties, 2 was supported onto sand surface. The sand/TiO(2)/CdS system, 3, was easier to recover but showed slightly lower catalytic activity compared to 2. On the other hand, the support failed to prevent leaching of Cd(2+). This indicates limited future applicability of CdS-sensitized TiO(2) photo-catalyst systems, in solar-based water purification strategies, unless leaching out tendency is completely prevented.