Computational molecular modeling, i.e., density functional theory-based molecular modelling (DFT B3LYP/6-31-G*) (DFT/MM) verifies equilibrium geometry and surface electron energy structures of van der Waals force (vdW) molecular aggregates. What should be noted for the energy structures is that DFT/MM-predicted UV/Vis spectra are in good agreement with measured spectra of the aggregates.1) With these viewpoints, effective photoelectrochemical water splitting using mesoporous TiO2 anode and platinum cathode2), and effective water photo-splitting to HOOH and H2 on Pt-loaded TiO2 photocatalysts3) are reinvestigated by DFT/MM. DFT/MM-based UV/Vis spectrum analysis verifies that the anatase Yamashita & Jono’s model of HOTi9O18H has no absorption in the UV region, giving visible absorption spectrum with max=536 nm (strength 0.005). Then, DFT/MM was extended to vdW aggregates of smaller-size TiO2 clusters, (TiO2)n (n=1, 2, 4). Interestingly, DFT/MM-derived UV/Vis spectrum of (TiO2)4 shows max at 377 nm (strength 0.003), and the vdW aggregates of (TiO2)4 with H2O and with platinum triangle pole cluster of Pt6 validates that the molecular-structured TiO2 clusters, (TiO2)1~4 work as effective UV-induced photocatalysts2), and work as a UV-sensitizer in photoelectrochemical water splitting on biased TiO2 anode3).
1) Japanese Journal of Applied Physics 57, 121602 (2018).
2) Molecules 2015, 20(6), 9732-9744.
3) ECS Transactions, 80 (10) 1091-1112 (2017).
Dr. Shozo Yanagida is an emeritus professor of Osaka University since 2004 and a research director of “Research Association for Technological Innovation of Organic Photovoltaics” (RATO) of University of Tokyo. A year ago, he started research laboratory, “M3 Laboratory Inc.” in ISRI, Osaka University. When he was staying at SERI (now ENREL) as a visiting professor of Dr. A. Nozik’s group in 1984, he understand that organic and inorganic molecules have a strong tendency to aggregate each other via van der Waals and Coulomb interaction, forming two, three and four molecule aggregates, i.e., molecular structured aggregates. Now, he is focusing DFT/MM on functional materials as molecular vdW aggregates.