20:T4e0,Photocatalytic reduction of CO₂ into energy-rich carbon compounds has attracted increasing attention. However, it is still a challenge to selectively and effectively convert CO₂ to a desirable reaction product. Herein, we report a design of a synergistic photocatalyst for selective reduction of CO₂ to CO by using a covalent organic framework bearing single Ni sites (Ni-TpBpy), in which electrons transfer from photosensitizer to Ni sites for CO production by the activated CO₂ reduction under visible-light irradiation. Ni-TpBpy exhibits an excellent activity, giving a 4057 μmol g^-1 of CO in a 5 h reaction with a 96% selectivity over H₂ evolution. More importantly, when the CO₂ partial pressure was reduced to 0.1 atm, 76% selectivity for CO production is still obtained. Theoretical calculations and experimental results suggest that the promising catalytic activity and selectivity are ascribed to synergistic effects of single Ni catalytic sites and TpBpy, in which the TpBpy not only serves as a host for CO₂ molecules and Ni catalytic sites but also facilitates the activation of CO₂ and inhibits the competitive H₂ evolution.21:T510,Synthesizing H₂ O₂ from water and air via a photocatalytic approach is ideal for efficient production of this chemical at small-scale. However, the poor activity and selectivity of the 2 e^- water oxidation reaction (WOR) greatly restricts the efficiency of photocatalytic H₂ O₂ production. Herein we prepare a bipyridine-based covalent organic framework photocatalyst (denoted as COF-TfpBpy) for H₂ O₂ production from water and air. The solar-to-chemical conversion (SCC) efficiency at 298 K and 333 K is 0.57 % and 1.08 %, respectively, which are higher than the current reported highest value. The resulting H₂ O₂ solution is capable of degrading pollutants. A mechanistic study revealed that the excellent photocatalytic activity of COF-TfpBpy is due to the protonation of bipyridine monomer, which promotes the rate-determining reaction (2 e^- WOR) and then enhances Yeager-type oxygen adsorption to accelerate 2 e^- one-step oxygen reduction. This work demonstrates, for the first time, the COF-catalyzed photosynthesis of H₂ O₂ from water and air; and paves the way for wastewater treatment using photocatalytic H₂ O₂ solution.

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