Abstract
Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti4+ ions embedded on the inner pore wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. This provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support) of heterogeneous catalytic systems are important in optimization of catalytic efficiency.
Highlights
Economical water splitting technology for the development of low-cost and efficient fuels motivates research in many fields. This particular application of the conversion of solar energy into chemical reaction can be accomplished using a catalytic site mounted on a substrate
The periodic pore system that is characteristic of silica substrates is considered to be one of the best options for use in heterogeneous catalysis research, mostly due to its high surface-to-volume ratio [1]
2, water densities of states and and a cluster of H2O in Figure 2A,B, it is seen that a cluster of H2O molecules provides an occupied absorbance spectra are computed according to Equations (5)–(8), which are simple ways to visualize orbital in the valence band that does not exist in a single water molecule
Summary
Economical water splitting technology for the development of low-cost and efficient fuels motivates research in many fields. The addition of titanium atoms to the inner surface of the silica pore walls provides a photoactive material [5] and introduces numerous charge transfer states, which can be analyzed by atomistic computational modeling [6,7,8]. It has been known since the 1970s that titanium dioxide (TiO2 ) can be used in water-splitting applications [9]. The basic idea is that the existence of trapping states could facilitate charge transfer because it encourages charge separation, which can induce a chemical reaction
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