Photocatalytic reduction of CO 2 toward eight-electron CH 4 product with simultaneously high conversion efficiency and selectivity remains great challenging owing to the sluggish charge separation and transfer kinetics and lack of active sites for the adsorption and activation of reactants. Herein, a defective TiO 2 nanosheet photocatalyst simultaneously equipped with AuCu alloy co-catalyst and oxygen vacancies (AuCu-TiO 2−x NSs) was rationally designed and fabricated for the selective conversion of CO 2 into CH 4 . The experimental results demonstrated that the AuCu alloy co-catalyst not only effectively promotes the separation of photogenerated electron−hole pairs but also acts as synergistic active sites for the reduction of CO 2 . The oxygen vacancies in TiO 2 contribute to the separation of charge carriers and, more importantly, promote the oxidation of H 2 O, thus providing rich protons to promote the deep reduction of CO 2 to CH 4 . Consequently, the optimal AuCu-TiO 2−x nanosheets (NSs) photocatalyst achieves a CO 2 reduction selectivity toward CH 4 up to 90.55%, significantly higher than those of TiO 2−x NSs (31.82%), Au-TiO 2−x NSs (38.74%), and Cu-TiO 2−x NSs (66.11%). Furthermore, the CH 4 evolution rate over the AuCu-TiO 2−x NSs reaches 22.47 μmol•g −1 •h −1 , which is nearly twice that of AuCu-TiO 2 NSs (12.10 μmol•g −1 •h −1 ). This research presents a unique insight into the design and synthesis of photocatalyst with oxygen vacancies and alloy metals as the co-catalyst for the highly selective deep reduction of CO 2 .

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NH 3 is mainly obtained by the Haber−Bosch method in the process of industrial production, which is not only accompanied by huge energy consumption but also environmental pollution. The reduction of N 2 to NH 3 under mild conditions is an important breakthrough to solve the current energy and environmental problems, so the preparation of catalysts that can effectively promote the reduction of N 2 is a crucial step. In this work, BiVO 4 decorated with amorphous MnCO 3 /C double layers has been successfully synthesized by a one-step method for the first time. The C and MnCO 3 have been formed as ultrathin film, which enables the establishment of a uniform and tight interface with BiVO 4 . The temperature-programmed desorption of N 2 (N 2 -TPD) spectra confirmed that the MnCO 3 /C could endow BiVO 4 with a drastic enhancement of the chemical absorption ability of a N 2 molecule compared with the pristine BiVO 4 . Meanwhile, the method of isotope labeling proved that the catalyst exhibited excellent selectivity for the photocatalytic nitrogen reduction reaction (NRR). The production rate of NH 3 up to 2.426 mmol m −2 h −1 has been achieved over the BiVO 4 /MnCO 3 /C, which is almost 8 times that of pristine BiVO 4 . The promoted production rate of NH 3 over BiVO 4 /MnCO 3 /C could be mainly attributed to the cooperative process between MnCO 3 and C amorphous layers. Therefore, this work could provide an alternative insight to understand the NRR process based on the model of a hierarchical amorphous structure.