本文要点：
开发具有智能自调节功能的多功能光催化剂在光催化过程中具有重要意义。本文构建了一个智能共价有机框架(Por-HQ-COF)用于光氧化、光还原和H2O2生产，该框架具有随pH变化的苯酚-醌转化结构。
作为一种智能光触媒，Por-HQ-COF可以通过包括溶液pH值在内的触发器智能地转换为Por-BQ-COF，反之亦然。苯酚-醌转化的重构不仅显著改变了COF的形貌和比表面积，而且导致能带能量和电荷分布的完全改变，从而影响光电性质。
在酸性条件下，Por-BQ-COF自动转化为Por-HQ-COF，并能高效地将高浓度的Cr(VI)还原为Cr(III)。在中性条件下，超氧阴离子(O2)启动Por-HQ-COF重构为Por-BQ-COF，加速光氧化降解高浓度TC。
在碱性条件下，Por-HQ-COF转化为Por-BQ-COF，可以在没有任何牺牲试剂的情况下有效地光合成H2O2(1525 µmol h−1 g−1，λ > 420 nm ),并揭示了强碱性降低了从H2O提取氢的能垒，并阐明了H2O2产生的活性位点。
这项工作为开发智能光催化剂提供了新的策略，并实现了在全pH环境中的应用。
Scheme 1. Synthetic route (TCPP and TABQ were linked via hydrothermal method to construct Por-HQ-COF, Por-HQ-COF could converted to Por-BQCOF by ·O2− or OH−, Por-BQ-COF could converted to Por-HQ-COF by H+); Photocatalytic process (Por-HQ-COF photoreduced Cr(VI) to Cr(III) at pH < 7, Por-HQ-COF could be convert to Por-BQ-COF accelerate photooxidation TC at pH = 7, Por-BQ-COF had ability of ORR to produce H2O2 at pH > 7).
Figure 1. a) FTIR spectra of Por-HQ-COF and Por-BQ-COF. b) Solid-state 13C NMR spectra of Por-HQ-COF and Por-BQ-COF. c) Powder X-ray diffraction patterns of Por-HQ-COF and Por-BQ-COF. d) Nitrogen adsorption–desorption isotherms of Por-HQ-COF and Por-BQ-COF. e) Corresponding pore size distribution curves of Por-HQ-COF and Por-BQ-COF. f) TGA curves of Por-HQ-COF and Por-BQ-COF under N2 atmosphere. g) SEM image of Por-HQCOF. h) SEM image of Por-HQ-COF converted into Por-BQ-COF. i) SEM image of Por-BQ-COF. j) SEM image of Por-BQ-COF converted into Por-HQ-COF. k, l) TEM image of Por-HQ-COF and Por-BQ-COF and m,n) HRTEM image of Por-HQ-COF and Por-BQ-COF.
Figure 2.a) UV−vis DRS spectra of Por-HQ-COF and Por-BQ-COF. b) The plot of (ahv)2 vs. photon energy of Por-HQ-COF and Por-BQ-COF. c) Cyclic voltammetry profiles of Por-HQ-COF and Por-BQ-COF. d) The optical band structures of Por-HQ-COF and Por-BQ-COF. e) Photocurrent responses of Por-HQ-COF and Por-BQ-COF. f) EIS plots of Por-HQ-COF and Por-BQ-COF. g) PL spectra of Por-HQ-COF and Por-BQ-COF. h) TRPL spectra of Por-HQ-COF and Por-BQ-COF. i)The HOMO and LUMO orbital distributions of the simplified Por-HQ-COF and Por-BQ-COF fragment from DFT simulation. j) Calculated Mulliken atomic charges of the donor and acceptor moieties in Por-HQ-COF and Por-BQ-COF and k) DFT calculation results of the electrostatic potential (ESP) surface.
Figure 3.a) Image of the protonation reaction of Por-BQ-COF in the presence of H+. b) The UV–vis spectra for Cr(VI) photoreduction over Por-HQCOF at pH = 3. c) Effect of different pH on the photocatalytic reduction of Cr(VI) by Por-HQ-COF. d) Effect of different interfering ions on photocatalytic reduction of Cr(VI) by Por-HQ-COF. e) Radical trapping experiments of Cr(VI) reduction by Por-HQ-COF. f) Kinetic rate constants and g) Cyclic reduction of Cr(VI) by Por-HQ-COF (the gray part represented adsorption in the dark).
Figure 4.Time−dependent UV−vis adsorption spectra of high concentration TC (50 mg L−1) solution by a) Por-HQ-COF and b) Por-BQ-COF. c) Photodegraded high concentration TC of Por-HQ-COF and Por-BQ-COF under visible light irradiation, Por-HQ-COF completely converted into Por-BQ-COF after 90 min. d) Color change of TC solution under Por-HQ-COF and Por-BQ-COF. e) FTIR spectra comparison of before and after converted photocatalyst on degradation of TC. f) Radical trapping experiments of TC degradation and g) Cyclic degradation of TC by Por-BQ-COF.
Figure 5.H2O2 photosynthesis. a) Photocatalytic H2O2 production over Por-BQ-COF at different pH conditions. b) The rate constants of H2O2 formation (kf) and decomposition (kd) over Por-BQ-COF at a pH of 13. c) The recycling tests of Por-BQ-COF at a pH of 13. d) Comparison of photocatalytic H2O2 production rates for photocatalysts. e) Comparison of H2O2 production rates over Por-BQ-COF in different atmospheres and scavengers (AgNO3 captures e−, EtOH captures h+), the inserted figure for isotope tracking experiment determined that the O source in H2O2 did not come from H2O. f) Comparison of H2O2 production rates over Por-BQ-COF in different solutions. g) In situ FTIR spectra of Por-BQ-COFrecorded during photocatalytic H2O2 production. h) The O─H bond energy of the adsorbed terminal H2O over the Por-BQ-COF via DFT calculation and i) The Koutecky-Levich plots of Por-BQ-COF obtained by RDE measurements.
Figure 6.a) ESR spectra of Por-BQ-COF and Por-HQ-COF under irradiation (DMPO−·O2−, TEMPO−h+, DMPO−·OH, TEMP−1O2). After irradiation, e− reacted with O2 to generate ·O2−, further converted Por-HQ-COF into Por-BQ-COF, the remaining h+ was left. b) Photocatalysis and conversion mechanism of Por-BQ-COF and Por-HQ-COF and c, I) Optimized structure snapshots of key reaction intermediates in 2e− ORR. c, II) Reaction profiles of 2e− ORR and c, III) The photocatalytic pathway for H2O2 production over Por-BQ-COF in alkaline conditions.
https://doi.org/10.1002/adma.202415126
