Synthesis of TiO2 nanoparticles using novel titanium oxalate complex towards visible light-driven photocatalytic reduction of CO2 to CH3OH

TiO2 nanoparticles (NPs) with controlled crystalline structure and morphology were synthesized by a facile hydrothermal method using a novel titanium oxalate complex. The structure, morphology, and spectral properties of the synthesized TiO2 NPs were characterized by X-ray diffraction, Raman spectroscopy, scanning/transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. The titania phases of anatase, rutile, or brookite can be easily tuned by tailoring the solution pH during reaction. Highly ordered flower-like rutile could be obtained with oxalic acid additive. The synthesized TiO2 catalysts showed excellent visible light absorption and remarkable photocatalytic activity for CO2 reduction to CH3OH under both UV–vis and visible light irradiation, mainly due to doped carbon and nitrogen. Bicrystalline anatase–brookite composite afforded maximum CH3OH yield, attributed mainly to the unique electrical band structures and efficient charge transfer between the two crystalline phases.

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► TiO2 NPs with controlled crystalline phase and morphology has been synthesized.
► The synthesized TiO2 is highly active for CO2 reduction under visible light irradiation.
► The junction effect of two crystalline phases is responsible for the high efficiency of brookite–anatase particles.