Barium Zirconate:A New Photocatalyst For Converting CO₂ Into Hydrocarbons Under UV Light

Nowadays with the depletion of the unrenewable fossil fuels and the rising atmospheric levels of carbon dioxide, environmental pollution and the greenhouse effect becomes more obvious, which raises the increasing concerns about the ensuing crisis of the energy supply and the global climate. And CO2 is supposed to be the most important greenhouse gas. An ideal way to cut down the increasing atmospheric levels of CO2 and relieve the crisis of fossil energy simultaneously is to convert CO2 into hydrocarbons under the solar irradiation.BaZrC3 has been extensively studied and used. Due to its small thermal expansion coefficient, poor thermal conductivity, good mechanical properties, thermal stability and low chemical reactivity towards corrosive compounds, it has been investigated in various applications, such as thermal barrier coating material in airspace industry, a good substrate for the manufacturing for high temperature superconductors and material for interface engineering of alumina fiber-alumina matrix composites. The bottom of the CB of BaZrO3 locates at-1.8 eV versus NHE, pH 7.0. The photogenerated electrons in the CB are more negative than the potential of CH4/CO2, HCOOH/CO2, CO/CO2, HCHO/CO2and CH3OH/CO2 redox couples. The corresponded holes in the VB are easy to oxidize H2O. Then the energy of the photogenerated electrons and holes should be sufficient for CO2 photoreduction using water as a reducing agent under UV irradiation,In this report, the photocatalytic activities of BaZrO3 for CO2 reduction were investigated in detail. The BaZrO3 samples were successfully obtained via a Pechini process at different temperature. The prepared samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV-vis reflectance spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the deposition various metal nano particles (NPs) on the surface of BaZrO3 were also discussed. The results proved that the highly dispersed silver NPs play a crucial role on the photocatalytic activities of BaZrO3. The main conclusions are as follows:BaZrO3 is an indirect-gap semiconductor. The calculated band gap (3.2 eV) is smaller than that of experiment value (4.8 eV). The bottom of the CB and the top of the VB of BaZrO3 locates at-1.8 eV and 3.0 eV versus NHE. pH 7.0, the top of the VB is dominated by the contributions of the O2p orbitals, while the CB is predominantly contributed by the Zr4d orbitals in character. The width of its band gap severely restricts the absorption of light. The photocatalytic properties of BaZrO3 have been investigated as a new photocatalyst for CO2 reduction. The BaZrO3 samples obtained at 1273K with 0.3wt% Ag NPs deposited showed the highest photocatalytic activities. Under UV light irradiation, the Ag NPs deposited BaZrO3 showed higher photocatalytic activities than the samples with other metal NPs deposited. The Ag NPs dispersed on BaZrO3 resulting in more efficient separation of the photogenerated electron-hole-pairs, and the electron transmission mechanism should be further investigated in detail to enhance the photocatalytic activities of BaZrO3.