Electronic transitions of SWCNTs in comparison to GO on Mn3O4/TiO2 nanocomposites for hydrogen energy generation and solar photocatalysis

Abstract

The conductivity of metal/metal oxide-doped TiO₂ nanomaterials is enhanced by the incorporation of carbonaceous materials, e.g. single-walled carbon nanotubes (SWCNTs) and graphene oxide (GO). Here, a comparative study was conducted on SWCNTs/Mn₃O₄–TiO₂ and GO/Mn₃O₄–TiO₂ composite materials for hydrogen evolution reaction (HER) through water splitting and solar induced photodegradation of methyl orange (MO). The morphology of GO/Mn₃O₄–TiO₂ showed a quasi-spherical network of TiO₂ with patches of Mn₃O₄ nanoparticles dispersed on GO sheets. SWCNTs were adhered on the Mn₃O₄–TiO₂ surface. The novel features of carbonaceous materials (GO/SWCNTs), fast electronic transition properties of SWCNTs and π–π interaction of carbon materials in composites extended the absorption edges in the visible region and thereby led to reduction of band gap energy. Mn–Ti–C linkages in ternary composites were confirmed through FTIR and Raman studies. Quenching of PL intensity indicated suppression of electron–hole recombination on the surface of SWCNTs/Mn₃O₄–TiO₂. XPS demonstrated bonding configuration and oxidation states of components of the SWCNTs/Mn₃O₄–TiO₂ composite. The SWCNTs/Mn₃O₄–TiO₂ nanohybrid structure with tailored properties played a noteworthy role in HER with a low onset potential of ∼320 mV at 10 mA cm⁻², a low R_ct of ∼43.3 Ω, a small Tafel slope of ∼86 mV dec⁻¹ and the highest degradation of MO (∼98%) compared to other catalysts. Our findings suggest that the prepared catalysts are promising candidates for multifunctional purposes.