Synthesis of zirconia-based Pyrochlore type photocatalysts

Photocatalyst is an environment purification material that can be removing organic or hazardous substances using solar energy. In recent year, Perovskite photocatalyst has been attracting attention as high performance solar... [ view full abstract ]

Photocatalyst is an environment purification material that can be removing organic or hazardous substances using solar energy. In recent year, Perovskite photocatalyst has been attracting attention as high performance solar cell’s materials. Interference for electron orbital is important for improvement of photoactivity. Metal doping and increment of disorder has been conventional method for the band gap control of photocatalyst.
This study focuses on the Pyrochlore structure of large distortion structure than the Perovskite structure. We expect that the large strain of the structure give effect for the electron orbit, therefore we tried the synthesis of Pyroclore type zirconia-based new photocatalyst. Pyrochlire has A2B2O7 composition consisting of A3+/B4+ or A2+/B5+. It is a big advantage of the combination using the difficult 3-4 valent pair or 2-5 valent pair to develop a new photocatalysts, however applications in zirconia have been not well known. Photoactivity of zirconia is lower than the titania is a common photocatalyst, however it has large band gap. We look forward to make easily insertion levels in its large band gap to develop new photocatalyst material. Therefore we select the zirconium as B site and 3-valent transition metal element (lanthanide element of La, Sm, Nd) as A site, to synthesize zirconia-based pyrochlore type photocatalyst. Identification of XRD was La2Zr2O7, Sm2Zr2O7, and Nd2Zr2O7. In observation crystalline shape, particles of sub-micron particles size has been confirmed in each sample by FE-SEM. La2Zr2O7 was the largest specific surface area, however it was very small value as 5.64m2/g. From UV-vis, respectively absorption edge 461nm (La2Zr2O7), 343nm (Sm2Zr2O7), and a value of each of the bandgap is 2.69eV (La2Zr2O7), 3.61eV (Sm2Zr2O7). Nd2Zr2O7’s adsoeption edge could not identify cause, it has multiplex adsorption bands. We measured the CO2 production rate by acetic acid decomposition experiment as compared to commercial anatase titania (P-25).The photoactivities about 30% (Nd2Zr2O7), 23% (La2Zr2O7), 17% (Sm2Zr2O7) than P-25. From these results, Zirconia-based pyrochlore type photocatalyst addition of lanthanide element is considered to indicate a high photoactivity in this study.