Efficient photocatalytic decomposition of glucose, starch, and cellulose to C[O.sub.2] using a mesoporous semiconductor thin film

UV light-activated highly efficient photocatalytic decomposition of aqueous glucose and polysaccharides (starch and cellulose) to C[O.sub.2] was successfully achieved by using a mesoporous Ti[O.sub.2] thin film coated on a fluorin[e.sup.-]doped transparent conductive glass (FTO). The external quantum efficiency (η) of 0.08 (=8%) was obtained for glucose photodecomposition at neutral pH based on the total incident UV light, and the internal quantum efficiency (η') was 8 (=800%) based on the photon that was effective for activating the reactant, demonstrating that the major decomposition mechanism is dark auto-oxidation of the activated reactant by [O.sub.2]. Glucose gave η' values of 19 at pH 12 and 25 at pH 2 demonstrating that when a glucose molecule was once activated by one photon, the molecule can undergo auto-oxidative decomposition to C[O.sub.2] at these pH under dark. Water-soluble starch was also photodecomposed completely to C[O.sub.2] with estimated η' value of 8.6. Water-soluble carboxymethyl cellulose (CMC) also underwent decomposition to C[O.sub.2] with similar efficiency of η' = 5. Solid state cellulose powders could be photodecomposed to C[O.sub.2] by sandwiching them between FTO-coated Ti[O.sub.2] thin films.