Promoting Solar‐driven Hydrogen Peroxide Production over Thiazole‐based Conjugated Polymers via Generating and Converting Singlet Oxygen

Abstract

Solar‐driven synthesis of hydrogen peroxide (H2O2) from water and air provides a low‐cost and eco‐friendly alternative route to the traditional anthraquinone method. Herein, four thiazole‐based conjugated polymers (Tz‐CPs: TTz, BTz, TBTz and BBTz) are synthesized via aldimine condensation. BBTz exhibits the highest H2O2 production rate of 7274 μmol g‐1 h‐1 in pure water. Further, the reaction path is analyzed by electron paramagnetic resonance (EPR), in‐situ diffuse reflectance infrared fourier transform (DRIFT) and theoretical calculation, highlighting the prominent role of singlet oxygen (1O2). The generation of 1O2 occurs through the oxidation of superoxide radical (•O2‐) and subsequent conversion into endoperoxides via [4+2] cycloaddition over BBTz, which promotes charge separation and reduces the barrier for H2O2 production. This work provides new insight into the mechanism of photocatalytic O2 reduction and the molecular design of superior single‐polymer photocatalysts.

Regulating Benzene Ring Number as Connector in Covalent Organic Framework for Boosting Photosynthesis of H2O2 from Seawater

“…A comparison in both the H 2 O 2 production rate and raw material cost among reported COF photocatalysts and our cases is shown in Figure b. It is clear that our COF photocatalysts show a comparable H 2 O 2 production rate with most reported COF photocatalysts − but the lowest raw material cost among all reported COF photocatalysts, thereby implying the outstanding advantage of our photocatalysts in industrial application. Catalytic stability represents another factor for industrial application.…”

“…Mott–Schottky (MS) analysis (Figure S5 and S6) was used to estimate the lowest unoccupied molecular orbital (LUMO) level, which gave −0.52 V for ECUT-COF-30 and −0.86 V for ECUT-COF-31. Note that the LUMO levels are more negative than the reduction potential of the oxygen reduction reaction (ORR) in the direct 2e – (+0.68 V) or stepwise 1e – (−0.33 V) fashion (Figure S7), which suggests that our photocatalysts are thermodynamically favorable for photosynthesis of H 2 O 2 through an ORR route. − Moreover, on the basis of the equation E HOMO = E LUMO + E g , we can obtain the highest occupied molecular orbital (HOMO) level of 1.35 V for ECUT-COF-30 and 1.09 V for ECUT-COF-31 (Figure S7), which excludes the possibility of of H 2 O 2 production through water oxidation reaction (WOR, +1.76 V). − …”

Facile synthesis of O-doped carbon nitride nanofibers for two-step single-electron oxygen reduction to H2O2

“…S14, ESI†). 31,54 The significantly decreased H 2 O 2 generation rate in the presence of p -BQ demonstrates that an indirect two-step single-electron process is the dominant pathway for H 2 O 2 generation. Negligible H 2 O 2 was detected by using AgNO 3 as the electron trapping agents, indicating that H 2 O 2 was generated from O 2 reduction rather than water oxidation reaction.…”

“…22–25 Recently, researchers have paid attention to using g-C 3 N 4 and other triazine-based photocatalysts for H 2 O 2 generation. 26–31…”

Crystalline carbon nitrides for photocatalysis

“…H 2 O 2 is a valuable and mild oxidizing chemical extensively used in paper bleaching, environmental remediation, sterilization, energy conversion/storage, and fine chemical synthesis. 255,256 The conventional and prevailing method for industrial production of hydrogen peroxide is the anthraquinone process, which requires intense energy consumption and produces hazardous waste. Therefore, it is highly desirable to develop an eco-friendly and sustainable route for H 2 O 2 synthesis.…”