Effect of TiO2 phase on the photocatalytic degradation of methylene blue dye

Several industrial processes make use of dyes in order to impart colour into their products. These processes release large amounts of dye-containing wastewater which can be hazardous to human health and the environment. This has necessitated the development of cheap, reliable and sustainable technologies that can remediate the effluent, heterogeneous TiO2 photocatalysis is one such technology that has proven successful. Different polymorphs of TiO2 exist and literature suggests that the photocatalytic efficiency of various phases depends on the target pollutant. This study investigated the photocatalytic degradation of methylene blue (MB) dye using of three commercial TiO2 powders with different crystal phases as catalysts. The materials properties for each catalyst were first determined using x-ray diffraction and microscopy. Degradation studies were then conducted on 10 ppm MB solutions using the three powders. Degussa P25 TiO2, a mixture of anatase and rutile was the most efficient compared to the neat anatase and rutile powders, degrading 81.4% of the MB. This catalyst was chosen for optimisation studies, where 95% degradation was achieved at a 0.5 g/L catalyst loading and pH of 10. The degree of mineralisation decreased with increasing MB concentration. The effect of metal doping on the photocatalytic performance of the catalyst was also investigated. Copper doping increased degradation by 2% whilst zinc reduced it to 90%. The complete decolourisation of the MB coupled with the significant decrease in TOC upon completion of the degradation process, indicate that Degussa P25 catalysed photocatalysis is a viable pretreatment technology in dye contaminated wastewater treatment.