Cation-exchange mediated synthesis of hydrogen and sodium titanates heterojunction: Theoretical and experimental insights toward photocatalyic mechanism

Abstract Na2Ti3O7/H2Ti3O7 heterojunction nanotubes were obtained through the microwave-assisted hydrothermal method (MAH) with different band gap energy engineering. This study aimed to synthesize sodium titanate nanotubes and evaluate the influence of H+ insertion on their photocatalytic properties. Heterojunctions were identified by X-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy, and their electronic levels and defects were investigated using diffuse reflectance and photoluminescence spectroscopies in the UV-Vis region. The cation exchange process promotes the formation of Na2Ti3O7/H2Ti3O7 heterojunction with coexistence of both phases in the nanotube. Photocatalytic results of Rhodamine-B (Rh-B) dye discoloration show that the prepared materials have activity under visible and UV light irradiation, and are dependent on the proportion of hydrogen and sodium-titanate phases present. The material with highest sodium concentration showed discoloration with a half-life time of 23 minutes under visible light irradiation. Theoretical results reveal the heterojunction band offset as a staggered gap, with the effective bandgap occurring between the O-2p of Na2Ti3O7 and Ti-3d of H2Ti3O7. The charge carrier transfer mechanism in the heterojunctions is well described by Z-scheme, with H2Ti3O7 and Na2Ti3O7 as the main oxidation and reduction phases for dye discoloration.