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• Zn 2 Ti 3 O 8 /ZnTiO 3 and Zn 2 TiO 4 /R-TiO 2 heterostructures were prepared through a two-step chemical route. • The heterostructure catalysts showed improved photocatalytic activities for CO 2 reduction with H 2 O. • Zn 2 Ti 3 O 8 /ZnTiO 3 and Zn 2 TiO 4 /R-TiO 2 heterojunctions favor the separation and transfer of charge carriers. • The band gap structures and the working mechanisms of Zn 2 Ti 3 O 8 /ZnTiO 3 and Zn 2 TiO 4 /R-TiO 2 heterojuntions were proposed. Photocatalytic reduction of CO 2 with H 2 O on photocatalysts to produce fuels presents great potential to simultaneously address energy and environmental issues. Herein, zinc titanate-based heterostructured nanohybrids including Zn 2 Ti 3 O 8 /ZnTiO 3 and Zn 2 TiO 4 /R-TiO 2 were designed and prepared through a two-step chemical route. When used as photocatalyst for converting CO 2 with H 2 O under UV-light irradiation, the zinc titanate-based heterostructured nanohybrids show high photocatalytic performance, with CH 4 and CO yields significantly higher than those obtained with Zn 2 Ti 3 O 8 , Zn 2 TiO 4 , and rutile TiO 2 as the photocatalysts. The existence of heterojunctions in the nanohybrids was demonstrated by experimental results, and electrochemical impedance spectra also reveal a favorable zinc titanate-based heterostructure. Moreover, based on theoretical calculations, the observed reduced band gap further revealed the effective light-absorption of the heterostructured nanohybrids in CO 2 reduction. It is thus concluded that the synergistic effect of the heterostructure promotes charge separation and fast electron transport, resulting in its enhanced photocatalytic performance in CO 2 reduction. [ABSTRACT FROM AUTHOR]

This approach is developed to achieving smaller bandgap values and a closer bracketing of the CO 2 /reduced-H 2 O/oxidized redox couples to drive the overall conversion reactions of CO 2 and H 2 O, and this is critical for efficient solar energy conversion. Highlights • A new type of spinel germanium and iron double-substituted ZnGa 2 O 4 solid-solution photocatalysts was prepared. • The solid-solution catalysts showed improved photocatalytic activities for CO 2 reduction with H 2 O. • Introducing ZnFe 2 O 4 and Zn 2 GeO 4 into ZnGa 2 O 4 can effectively expand the light-harvesting wavelength range. • A great difference in the mobility between the electrons and holes to lessen the electron–hole recombination rate. • This approach can achieve smaller bandgap values and a closer bracketing of the CO 2 /reduced-H 2 O/oxidized redox couples. The conversion of CO 2 into renewable fuels by artificial photosynthesis is an attractive solution for storing solar energy in the form of chemical fuel. Herein, we presented a general molten-salt route to synthesize spinel germanium and iron double-substituted ZnGa 2 O 4 solid solutions. Introducing ZnFe 2 O 4 and Zn 2 GeO 4 into ZnGa 2 O 4 can effectively expand the light-harvesting wavelength range to improve the ability of photocatalyst in CO 2 reduction and H 2 O oxidation. The solid solutions provide a larger effective mass of holes compared with electrons through the introduction of Fe3d, Ge4s and Ge4p orbitals according to DFT analysis. This leads to a great difference in the mobility between the electrons and holes to lessen the electron–hole recombination rate, and enhance the conversion of CO 2 and H 2 O in kinetics. This approach is developed to achieving smaller bandgap values and a closer bracketing of the CO 2 /reduced-H 2 O/oxidized redox couples to drive the overall conversion of CO 2 and H 2 O. [ABSTRACT FROM AUTHOR]