(222e) Efficient Photoreduction of Bicarbonate to Formate Catalyzed By Gold-TiO 2 composite Nanocatalyst Under Solar Light

TiO₂-catalyzed photoreduction of bicarbonate to value-added formate is studied in the presence of plasmonic gold nanoparticles. The effect of two positive hole scavengers, petroleum derived 2-propanol and green organic solvent glycerol, on the productivity of formate is investigated as well. Under solar light (solar simulator, AM 1.5 filter) the productivity with TiO₂ is 36.7 mM formate/g cat-hr in the presence of glycerol, which is significantly higher than 2-propanol (2.4 mM/hr.gm.catalyst). When illuminated with similar intensity 365 nm light with the photon energy high enough to excite valence band to conduction band electronic transitions in the TiO₂, the productivity of TiO₂ dramatically improves. A remarkably enhanced yield of formate (270 mM formate/g cat-hr) is achieved under solar light using gold-TiO₂ composite in the presence of glycerol as a hole scavenger. In contrast, no effect of gold nanoparticles was observed under 365 light. The improvement in product yield under visible light is attributed to the plasmon resonance induced hot electron transfer from gold nanoparticles to TiO₂. In addition, we studied the Au nanoparticle/TiO₂-catalyzed photoreduction of resazurin and photooxidation of Rhodamine B in parallel. As expected the addition of gold with TiO₂ improves the photoreduction of resazurin to resorufin undersolar light.  Surprisingly, gold nanoparticles adversely affected the photo-degradation rate of rhodamine B under both solar light and 365 nm light. This may be because of hydroxyl radical scavenging by gold nanoparticles.