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TiO/g-CN photocatalysts with the ratio of TiO to g-CN ranging from 0.3/1 to 2/1 were prepared by simple mechanical mixing of pure g-CN and commercial TiO Evonik P25. All the nanocomposites were characterized by X-ray powder diffraction, UV-vis diffuse reflectance spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, transmission electron microscopy, photoelectrochemical measurements, and nitrogen physisorption. The prepared mixtures along with pure TiO and g-CN were tested for the photocatalytic reduction of carbon dioxide and photocatalytic decomposition of nitrous oxide. The pure g-CN exhibited the lowest photocatalytic activity in both cases, pointing to a very high recombination rate of charge carriers. On the other hand, the most active photocatalyst toward all the products was (0.3/1)TiO/g-CN. The highest activity is achieved by combination of a number of factors: (i) specific surface area, (ii) adsorption edge energy, (iii) crystallite size, and (iv) efficient separation of the charge carriers, where the efficient charge separation is the most decisive parameter.

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Lanthanum-modified TiO photocatalysts (0.2-1.5 wt% La) were investigated in the methanol decomposition in an aqueous solution. The photocatalysts were prepared by the common sol-gel method followed by calcination. The structural (X-ray diffraction, Raman, X-ray photoelectron spectroscopy), textural (N physisorption), and optical properties (diffuse reflectance spectroscopy, photoelectrochemical measurements) of all synthetized nanomaterials were correlated with photocatalytic activity. Both pure TiO and La-doped TiO photocatalysts proved higher yields of hydrogen in comparison to photolysis. The photocatalyst with optimal amount of lanthanum (0.2 wt% La) showed almost two times higher amount of hydrogen produced at the same time as in the presence of pure TiO. The photocatalytic activity increased with both increasing photocurrent response and decreasing amount of lattice and surface O species. It has been shown that both direct and indirect mechanisms of methanol photocatalytic oxidation participate in the production of hydrogen. Both direct and indirect mechanisms take part in the formation of hydrogen.

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