Role of molecular oxygen on the synthesis of Ni(OH)2/TiO2 photocatalysts and its effect on solar hydrogen production activity

Abstract

Molecular oxygen performs a vital role in the photocatalytic activity of anatase TiO2, but there is a little experimental insight into the role of molecular oxygen on the synthesis of TiO2 based photocatalysts. Herein, we have shown that Ni(OH)2/TiO2 prepared in the presence and absence of molecular oxygen results in significantly varied hydrogen production activity. The sample synthesized in the presence of O2 and N2 produced 6624 μmol/h/g and 4468 μmol/h/g of hydrogen under direct solar light exposure. Additionally, the samples prepared in the presence of light irradiation produced 8289 μmol/h/g of hydrogen, a 72 fold jump in hydrogen production compared to TiO2. XPS, FTIR, Raman, and ESR measurements were carried out to investigate the underlined mechanism for such variation in the photocatalytic activity. Our results suggest that the presence of molecular oxygen during Ni(OH)2/TiO2 synthesis causes the formation of terminal OH and reduced the oxygen vacancies on the surface of TiO2, which can significantly alter the H2 production. Also, the reusability of the photocatalysts is greatly affected by the synthesis conditions, namely the presence of light and molecular oxygen.