Symmetry-Engineered BINOL-Based Porous Aromatic Frameworks for H<sub>2</sub>O<sub>2</sub> Production via Artificial Photosynthesis and In Situ Degradation of Pharmaceutical Pollutants
Flora Banerjee, Priyojit Das Gupta, Shiladitya Roy, Suman Kalyan Samanta
Abstract
Accomplishing visible light-driven H 2 O 2 production at millimolar concentrations is practically challenging, particularly for organic semiconductors. In this context, achieving a maximum H 2 O 2 production rate of 31.60 mmol·g –1 ·h –1 by using porous aromatic frameworks (PAFs) represents a significant accomplishment. We report the unusual photoactivity of tetraphenylmethane-BINOL-linked PAFs in triplet oxygen activation to facilitate the generation of reactive oxygen species (ROS), as confirmed by their optical and electrochemical responses, despite the absence of a conventional chromophoric moiety. Moreover, an in situ BINOL formation strategy was used to synthesize these PAFs during polymerization in contrast to the reported protocols involving chiral BINOLs as precursors. The as-synthesized polymers had a capsule-like morphology (for TPM-BINOL-6 ), high thermal stability up to 348 °C, and a high Brunauer–Emmett–Teller (BET) surface area of up to 1382 m 2 /g (for TPM-BINOL-4 ). Interestingly, they showed sunlight-driven production of H 2 O 2 via an oxygen reduction reaction of up to 17.05 mmol·g –1 ·h –1 in 1:10 isopropanol in water for TPM-BINOL-6, which was quantified by titration with ceric sulfate. It also exhibited exemplary photocatalytic efficiency with an H 2 O 2 production rate of 6.65 mmol·g –1 ·h –1 in seawater. Interestingly, the H 2 O 2 production rate reached a maximum of 18.03 mmol·g –1 ·h –1 with an SCC efficiency of 4.5% under an AM 1.5G solar simulator and apparent quantum yield (AQY) of 15.8% (at λ = 456 nm) for TPM-BINOL-6 in ethanol:water = 1:10. Moreover, the exceptionally high H 2 O 2 production rate of 31.60 mmol·g –1 ·h –1 was achieved in 1:1 ethanol in water under 50 W blue LED light. Furthermore, these PAFs generated adequate ROS, which were utilized in the photocatalytic degradation of tetracycline via the superoxide intermediate. Additionally, the as-formed H 2 O 2 was further channelized in the pollution abatement catalytic system for the fast degradation of ciprofloxacin (within 4 h) and the reduction of toxic oxometallate Cr(VI) within 10 min, which is one of the earliest reports of utilizing photosynthesized H 2 O 2 for environmental detoxification.