Photocatalysis of heat treated sodium- and hydrogen-titanate nanoribbons for water splitting, H2/O2 generation and oxalic acid oxidation

Abstract

The photocatalytic activity of sodium titanate (Na1.48H0.52Ti3O7), sodium hexatitanate (Na2Ti6O13), and hydrogen titanate (H2Ti3O7) nanoribbons and anatase TiO2 nanorods were compared for water splitting, oxalic acid photodegradation and H2 and O2 generation using sacrificial agents. The intrinsic properties of the materials were found to affect their performance depending on the particular reaction system. The Na2Ti6O13 nanoribbons, in the presence of RuO2 co-catalyst, outperformed the anatase nanorods, for the water splitting reaction, generating over 10 times more H2/O2. This was thought to derive from their tunnel-like structure which provided better electron/hole separation when compared with TiO2. However, the efficient holes and electrons scavenging in the presence of sacrificial agents, methanol or AgNO3, to generate H2 or O2, respectively, overwhelmed the tunnel-like structure effect. In this case photoactivity was governed by the crystal structure, with observed decreasing activity in the order TiO2>Na2Ti6O13>H2Ti3O7∼Na1.48H0.52Ti3O7, and by the band gap of the semiconductor which determined its capacity to absorb photons in producing electron/hole pairs.