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Well-designed Ti3+/In3+ mediated TiO 2 /SWCNTs heterojunction composite for photocatalytic H 2 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 H 2 of 1244 ppm h−1 was evolved over In/SWCNTs/TiO 2 , a 4.69, 1.54 and 1.53 times higher than using TiO 2 , In/TiO 2 and SWCNTs/TiO 2 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 (H 2) treatment, Ti3+ was successfully embedded into In+3@TiO 2 @SWCNTs, exhibited H 2 production of 1446 ppm h−1 which was 12.49% and 15.02% higher compared to catalysts prepared under CO 2 and N 2 atmospheres, respectively. Thus, surface defects like Ti3+ inhibits charges recombination and enables visible light responsive. The quantum yield over Ti3+/In3+ mediated TiO 2 /SWCNTs composite was 0.251%, a 1.13 and 1.2 folds higher compared to CO 2 and N 2 atmospheres, respectively. Besides, excellent stability for H 2 generation was observed in cyclic runs. A possible mechanism is proposed to understand synergistic effects between Ti+3/In+3 in TiO 2 /SWCNTs composite catalyst and has great potential as a green photocatalyst in environmental and energy applications. Image 1 • Ti+3/In+3 mediated TiO 2 /SWCNTs composite constructed under H 2 heat treatment. • H 2 production over In/TiO 2 /SWCNTs composite is 4.65 times higher than pure TiO 2. • Using H 2 atmosphere, 1.16 folds higher photoactivity for H 2 achieved than N 2 environment. • Photoactivity enhanced with Ti+3 doping due to synergistic effect with In+3/SWCNTs/TiO 2. • Stability test revealed prolong life of catalyst in cyclic runs using visible light irradiation. [ABSTRACT FROM AUTHOR]