Detailed photocatalytic study of alkaline titanates and its application for the degradation of methylene blue (MB) under solar irradiation

[Display omitted] •A series of alkaline metal titanates were successfully synthesized.•XPS analysis showed oxygen vacancies and Ti3+ ions.•Lithium titanate showed highest photocatalytic activity under sunlight.•The lithium titanate sample was stable upon successive reuse up to four cycles. Alkaline titanate nanomaterials with mixed anatase and titanate phases had been produced via hydrothermal synthesis. The XRD patterns of the samples indicated the presence of the anatase peak at 2θ = ∼25° except for Na-TiO2200°C/12 h. The Dr-UV/Vis analysis indicated that the band gap energy for Li-TiO2200°C/12 h, Na-TiO2200°C/12 h, K-TiO2200°C/12 and Cs-TiO2200°C/12 h to be 3.12, 3.05, 3.07 and 3.17 eV respectively. The alkaline titanate samples were shown to possess lower recombination rate of the photogenerated charge carriers (e−/h+) in comparison to that of pure anatase TiO2, except for K-TiO2200°C/12 h. The surface area of the samples was calculated to be 32.0, 120.0, 155.0 and 24.3 m2 g-1 for Li-TiO2200°C/12 h, Na-TiO2200°C/12 h, K-TiO2200°C/12 h and CsTiO2200°C/12 h respectively. Li-TiO2200°C/12 h exhibited enhanced photocatalytic efficiency in the photodegradation of MB compared to Degussa P25 and anatase TiO2. In addition, NaTiO2200°C/12 h, K-TiO2200°C/12 h and Cs-TiO2200°C/12 h also showed excellent adsorptive properties.