Harmonizing proton sponge and proton reservoir in conjugated microporous polymers for enhanced photocatalytic hydrogen peroxide production

Photocatalytic technology is highly sought-after for H₂O₂ production; however, the low selectivity between the oxygen reduction reaction (ORR) and water oxidation reaction (WOR) pathways is the primary factor limiting photocatalytic performance. Herein, a strategy that simulates a proton sponge by integrating aliphatic tertiary amines into conjugated microporous polymers (CMPs) to synthesize PPDI-N is reported. This method uses a carboxylic acid contaminant (2,4-dichlorophenoxyacetic acid, 2,4-D) as the proton reservoir to synergistically expedite the photosynthesis of H₂O₂ <i>via</i> a selective one-step 2e^- ORR. Importantly, with the aid of 2,4-D (acting as both a proton supplier and hole scavenger), the H₂O₂ production rate of PPDI-N is 4.4-fold higher than that in pure water, reaching 8.15 mmol g^-1 within 4 h irradiation time, which is 58.2 times greater at the same pH value. By mimicking a photo Fenton-like process with the assistance of Fe²⁺, PPDI-N exhibits an unprecedented removal efficiency (>99%) for 300 ppm of 2,4-D within 60 min. As revealed by Kelvin probe force microscopy and electric surface potential calculations, an enhanced built-in electric field was established in PPDI-N. This work provides valuable guidance for advancing CMP photocatalysts and establishes an ideal scenario for enabling simultaneous photocatalytic mineralization of organic contaminants and H₂O₂ production.