Zeai Huang

Tuning the selectivity toward CO evolution in the photocatalytic conversion of CO2 with H2O through the modification of Ag-loaded Ga2O3 with a ZnGa2O4 layer

Stoichiometric evolutions of CO, H2, and O2 were achieved for the photocatalytic conversion of CO2 with H2O as an electron donor using Ag-loaded Zn-modified Ga2O3. The selectivity toward the evolution of CO over H2 can be controlled by varying the amount of Zn species added in the Ag-loaded Zn-modified Ga2O3 photocatalyst. The production of H2 gradually decreased with increasing amounts of Zn species from 0.1 to 10.0 mol%, whereas the evolution of CO was almost unchanged. The XRD, XAFS, and XPS measurements revealed that a ZnGa2O4 layer was generated on the surface of Ga2O3 by modification with Zn species. The formation of the ZnGa2O4 layer eliminated the proton reduction sites on Ga2O3, although the crystallinity, surface area, and morphology of Ga2O3 as well as the particle size and chemical state of Ag did not change. In conclusion, we designed a highly selective photocatalyst for the conversion of CO2 with H2O as an electron donor using Ag (the cocatalyst for the CO evolution), ZnGa2O4 (the inhibitor of the H2 production), and Ga2O3 (the photocatalyst).

CO2 capture, storage, and conversion using a praseodymium-modified Ga2O3 photocatalyst

Praseodymium-modified gallium oxide (Pr/Ga2O3) was found to show enhanced activity and selectivity toward CO evolution in the photocatalytic conversion of CO2 using H2O as an electron donor in an aqueous solution of NaHCO3 as compared to those of bare Ga2O3. The as-prepared Pr species, including Pr(OH)3 and Pr2O2CO3, on the surface of Ga2O3 were transformed into Pr hydroxycarbonates (Pr2(OH)2(3−x)(CO3)x) and Pr carbonate hydrates (Pr2(CO3)3·8H2O) in an aqueous solution of NaHCO3, and then the Pr2(OH)2(3−x)(CO3)x was further transformed into Pr2(CO3)3·8H2O by CO2 bubbling under photoirradiation. This indicates that CO2 molecules dissolved in water can be captured and stored using Pr species in an aqueous solution of NaHCO3 under CO2 bubbling. More importantly, Pr2(OH)2(3−x)(CO3)x and Pr2(CO3)3·8H2O accumulated on the surface were decomposed to CO over the Ga2O3 photocatalyst with a Ag cocatalyst. Consequently, Ag/Pr/Ga2O3 exhibits much higher activity (249 μmol h−1 of CO) than the pristine Ag-loaded Ga2O3 (136 μmol h−1 of CO).

Enhancement of CO Evolution by Modification of Ga2O3 with Rare-Earth Elements for the Photocatalytic Conversion of CO2 by H2O

Modification of the surface of Ga2O3 with rare-earth elements enhanced the evolution of CO as a reduction product in the photocatalytic conversion of CO2 using H2O as an electron donor under UV irradiation in aqueous NaHCO3 as a pH buffer, with the rare-earth species functioning as a CO2 capture and storage material. Isotope experiments using 13CO2 as a substrate clearly revealed that CO was generated from the introduced gaseous CO2. In the presence of the NaHCO3 additive, the rare-earth (RE) species on the Ga2O3 surface are transformed into carbonate hydrates (RE2(CO3)3·nH2O) and/or hydroxycarbonates (RE2(OH)2(3-x)(CO3)x) which are decomposed upon photoirradiation. Consequently, Ag-loaded Yb-modified Ga2O3 exhibits much higher activity (209 μmol h-1 of CO) than the pristine Ag-loaded Ga2O3. The further modification of the surface of the Yb-modified Ga2O3 with Zn afforded a selectivity toward CO evolution of 80%. Thus, we successfully achieved an efficient Ag-loaded Yb- and Zn-modified Ga2O3 photocatalyst with high activity and controllable selectivity, suitable for use in artificial photosynthesis.

Highly Concentrated CO Evolution for Photocatalytic Conversion of CO2 by H2O as an Electron Donor

Kentaro TERAMURA1,2,*, Kazutaka HORI1, Yosuke TERAO1, Hiroyuki TATSUMI1, Zeai HUANG1, Shoji IGUCHI1, Zheng WANG1, Hiroyuki ASAKURA1,2, Saburo HOSOKAWA1,2, Tsunehiro TANAKA1,2,* 1Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku Katsura, Nishikyoku, Kyoto 615–8510, Japan 2Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, Kyotodaigaku Katsura, Nishikyo-ku, Kyoto 615–8520, Japan *E-mail: teramura@moleng.kyoto-u.ac.jp