Ozone facilitated degradation of caffeine using Ce-TiO₂ catalyst

Abstract

The ozone initiated oxidation of 1,3,7-trimethylxanthine (caffeine), commonly found in wastewaters as model compound is reported using cerium (Ce)/titanium dioxide (TiO₂) as catalyst. The effect of pH and loading of ceria on titania were investigated. Effect of reaction conditions on degradation of caffeine based on their pseudo first-order rate constants were compared. The combination of catalyst Ce-TiO₂ and ozone aeration significantly enhanced the degradation of caffeine compared to uncatalysed ozonation. The oxidation of caffeine ensued via the free radical mechanism, through enhanced ozone decomposition into OH radicals. Ce/TiO₂(0.5 wt%) showed good activity in degradation of caffeine at pH 6, in both natural stream and river water samples showing about 60% total organic carbon removal in 2 h ozonation period. Using liquid chromatography-mass spectroscopy, degradation products were analysed. A reaction intermediate and one final product were positively identified. Nano-catalysts with different loadings of Ce on TiO₂ synthesized by sol-gel route were characterized by scanning electron microscope, transmission electron microscopy, BET and powder X-ray diffraction spectrum techniques. The results showed that the material retained a highly ordered mesoporous structure and possessed large surface area.

Keywords:

• Ce/TiO₂
• heterogeneous catalyst
• ozone
• catalytic ozonation
• caffeine
• degradation

Acknowledgments

The authors are thankful to the National Research Foundation, South Africa and University of KwaZulu-Natal, Durban, for the support.