Mechanistic investigation into tribocatalysis: insights from anatase and rutile TiO₂

The study of the mechanism of frictional catalysis has always been a challenging task. There is a controversial topic regarding whether the catalytic essence is electron migration or electron transition. In this study, the exploitation of the distinct photocatalytic performances of anatase and rutile titanium dioxide provided a framework to explore the mechanism of tribocatalysis. In tribocatalytic degradation experiments targeting high-concentration rhodamine B dye solutions (100, 300, and 500 mg L^-1), despite anatase titanium dioxide being an indirect bandgap semiconductor, it exhibited a shorter average carrier lifetime (2.98 ns) compared to the direct bandgap rutile phase (3.04 ns). For rhodamine dyes with a concentration close to the actual industrial dye concentration of 500 mg L^-1, TiO₂ in the anatase structure achieved a degradation rate of 100% after 25 h. However, the degradation rate of rutile structure titanium dioxide after 25 h was only 20%. The presence of vacancies in the anatase structure not only regulates the average lifetime of carriers in indirect bandgap semiconductors, but also provides more active sites for the frictional catalytic reaction. The theory of excitation and recombination of electron-hole pairs provides theoretical and experimental references for understanding and exploring the mechanism of frictional catalysis.