Self-doped Ti³⁺ mediated TiO₂/In₂O₃/SWCNTs heterojunction composite under acidic/basic heat medium for boosting visible light induced H₂ evolution

Well-designed Ti³⁺/In³⁺ mediated TiO₂/SWCNTs heterojunction composite for photocatalytic H₂ evolution under visible light has been investigated. The samples, fabricated through one-step sol-gel approach with controlled acidic/basic heat treatment environment, were characterized by XRD, Raman, FE-SEM, TEM, XPS, UV–Vis and PL techniques. The maximum H₂ of 1244 ppm h⁻¹ was evolved over In/SWCNTs/TiO₂, a 4.69, 1.54 and 1.53 times higher than using TiO₂, In/TiO₂ and SWCNTs/TiO₂ samples, respectively. This enhancement was due to faster charges separation and higher visible light absorption by synergistic effect of In/SWCNTs. Using catalyst prepared under basic (H₂)treatment, Ti³⁺ was successfully embedded into In⁺³@TiO₂@SWCNTs, exhibited H₂ production of 1446 ppm h⁻¹ which was 12.49% and 15.02% higher compared to catalysts prepared under CO₂ and N₂ atmospheres, respectively. Thus, surface defects like Ti³⁺ inhibits charges recombination and enables visible light responsive. The quantum yield over Ti³⁺/In³⁺ mediated TiO₂/SWCNTs composite was 0.251%, a 1.13 and 1.2 folds higher compared to CO₂ and N₂ atmospheres, respectively. Besides, excellent stability for H₂ generation was observed in cyclic runs. A possible mechanism is proposed to understand synergistic effects between Ti⁺³/In⁺³ in TiO₂/SWCNTs composite catalyst and has great potential as a green photocatalyst in environmental and energy applications.