Constructing cuprous oxide-modified zinc tetraphenylporphyrin ultrathin nanosheets heterojunction for enhanced photocatalytic carbon dioxide reduction to methane.

The application of supermolecular naonostructures in the photocatalytic carbon dioxide reduction reaction (CORR) has attracted increasing attentions. However, it still faces significant challenges, such as low selectivity for multi-electron products and poor stability. Here, the cuprous oxide (CuO)-modified zinc tetraphenylporphyrin ultrathin nanosheets (ZnTPP NSs) are successfully constructed through the aqueous chemical reaction. Comprehensive characterizations confirm the formation of type-II heterojunction between CuO and ZnTPP in CuO@ZnTPP, and the electron transfer from CuO to ZnTPP through the Zn-O-Cu bond under the static contact. Under the visible-light irradiation (λ > 420 nm), the optimized CuO@ZnTPP sample as catalyst for photocatalytic CORR exhibits the methane (CH) evolution rate of 120.9 μmol/g/h, which is ∼ 4 and ∼ 10 times those of individual ZnTPP NSs (28.0 μmol/g/h) and CuO (12.8 μmol/g/h), respectively. Meanwhile, the CH selectivity of ∼ 98.7 % and excellent stability can be achieved. Further experiments reveal that CuO@ZnTPP has higher photocatalytic conversion efficiency than CuO and ZnTPP NSs, and the photoinduced electron transfer from ZnTPP to CuO can be identified via the path of ZnTPP→ (ZnTPP•ZnTPP)*→ ZnTPP→ Zn-O-Cu → CuO. Consequently, CuO@ZnTPP exhibits a shorter electron-hole separation lifetime (3.3 vs. 9.3 ps) and a longer recombination lifetime (23.1 vs. 13.4 ps) than individual ZnTPP NSs. This work provides a strategy to construct the organic nanostructures for photocatalytic CORR to multi-electron products.