TiO 2 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 TiO 2 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 TiO 2 catalysts showed excellent visible light absorption and remarkable photocatalytic activity for CO 2 reduction to CH 3OH under both UV-vis and visible light irradiation, mainly due to doped carbon and nitrogen. Bicrystalline anatase-brookite composite afforded maximum CH 3OH yield, attributed mainly to the unique electrical band structures and efficient charge transfer between the two crystalline phases.
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