Alkali metals incorporated ordered mesoporous tantalum oxide with enhanced photocatalytic activity for water splitting

Abstract

Herein, we report a novel synthetic approach for the preparation of alkali (Na, K) metal incorporated ordered mesoporous tantalate composites and their photocatalytic performance for water splitting. With the main focus on sodium based composite materials, a series of samples with ordered mesoporosity and high surface area (108–120 m² g⁻¹) was prepared by a variation of the Ta/Na ratios through a soft templating route. The structural parameters and properties of the samples were analyzed by low angle XRD, N₂-physisorption, TEM and STEM analysis, EDX, XPS, Raman and diffuse reflectance UV-Vis spectroscopy. The incorporation of alkali metals resulted in ordered mesoporous tantalate composites. Furthermore, the addition of alkaline earth (Ca, Ba, Sr) metals to the precursor solution of ordered mesoporous tantalum oxide was attempted. However, alkaline earth metals gave unordered tantalate composites. Photocatalytic investigations for water splitting, by using methanol as a sacrificial agent, indicated that the incorporation of alkali metals enhanced the hydrogen production rate of the photocatalyst whereas addition of alkaline earth metals decreased the hydrogen production. Among the sodium based samples, a Ta/Na ratio of 9 showed the best performance. The efficiency of this sample was further improved through decorated NiO_x as co-catalyst. A 2.5 wt% NiO_x loading was found to be the optimal loading amount, generating 64 μmol h⁻¹ H₂ and 31 μmol h⁻¹ O₂ when tested for overall water splitting.