HO Photosynthesis from HO and O under Weak Light by Carbon Nitrides with the Piezoelectric Effect.

Driven by the essential need of a green, safe, and low-cost approach to producing HO, a highly valuable multifunctional chemical, artificial photosynthesis emerges as a promising avenue. However, current catalyst systems remain challenging, due to the need of high-density sunlight, poor selectivity and activity, or/and unfavorable thermodynamics. Here, we reported that an indirect 2e water oxidation reaction (WOR) in photocatalytic HO production was unusually activated by CN with piezoelectric effects. Interestingly, under ultrasonication, CN exhibited an overall HO photosynthesis rate of 918.4 μM/h and an exceptionally high solar-to-chemical conversion efficiency of 2.6% after calibration under weak light (0.1 sun). Mechanism studies showed that the piezoelectric effect of carbon nitride overcame the high uphill thermodynamics of *OH intermediate generation, which enabled a new pathway for 2e WOR, the kinetic limiting step in the overall HO production from HO and O. Benefiting from the outstanding sonication-assisted photocatalytic HO generation under weak light, the concept was further successfully adapted to biomedical applications in efficient sono-photochemodynamic therapy for cancer treatment and water purification.