Angew：共价芘-(硫代)脲框架--H2O2光合成

本文要点：

1. 将光催化1,2,3,4-四氢异喹啉半脱氢反应(THIQ-SDR)与双电子氧还原反应(2e- ORR)配对，是一种同时利用光激发电子和空穴的绿色太阳能化学策略。但目前还缺少高效的光催化剂来驱动上述两个反应。

2. 本文合成了结晶芘-硫脲/尿素共价有机骨架(COF-Py-S和-O),并展示了其作为高性能无金属光催化剂的性能。特别地，COF-Py-S在可见光下显示出较高的2e- ORR到H2O2产率，约为19 mmol·g-1·h-1，最终在长时间照射后收集到固体H2O2产物(Na2CO3•1.5H2O2)。

3. 在自然阳光条件下，COF-Py-S催化剂上的H2O2产生速率进一步增加到约51 mmol·g-1·h-1，是最好的有机光催化剂之一。COF-Py-S也显示出高的THIQ-SDR转化率(~100%)和~92%的3,4-二氢异喹啉(DHIQ)选择性。

4. 理论计算揭示了COF-Py-S比COF-Py-O更强的电子推挽效应，增强了其光诱导电荷载流子，并证实了以硫脲为活性中心的四步2e- ORR机制以及THIQ-SDR到DHIQ的机制，其特征在于硫脲单元上O2吸附和*HOOH脱附的较低能垒。

5. 本工作提供了H2O2和DHIQ在具有电子推挽效应的高效芘(硫代)脲COF光催化剂上的配对光合作用策略。

Figure 1. (a) The synthesis routes and molecular structure of COF-Py-S and COF-Py-O (Inset shown the push-pull effect on the 2D skeletons). (b) The active sites distribution of 2e- ORR (left, light-blue dashed circles) and THIQ-SDR (right, red dashed circle) on COFPy-S and -O, the middle region presents the local molecular orbitals (MOs) of O2. 

Figure 2. PXRD patterns of (a) COF-Py-S, (b) COF-Py-O, and (c) COF-Py-DBA. Observed patterns are shown in black, Pawley-refined patterns in red, the difference between observed and refined profiles in orange, simulated in blue and Bragg positions in green. The simulated structure model for COF-Py-S (d), COF-Py-O (e), and COF-Py-DBA (f). Atoms are represented as follows: C (gray), N (blue), O (red), and H (cyan). N2 adsorption-desorption isotherm and pore size distribution (inset) of COF-Py-S (g), COF-Py-O (h), and COF-Py-DBA (i). 

Figure 3. (a) FT-IR spectra of COF-Py-S, COF-Py-O and COF-Py-DBA. (b) 13C solid-state NMR spectra of COF-Py-S. (c) N 1s XPS spectra of COFs. (d) S 2p XPS spectra of COF-Py-S. UV-vis DRS spectra (e) and band structures (f) of three COFs.

Figure 4. (a) Time-dependent H2O2 photogeneration under visible light illumination (λ > 420 nm) for COF-Py-S, COF-Py-O, and COF-PyDBA with the H2O2 production rates of 19.15 ± 1.53, 8.22 ± 0.32, and 2.77 ± 0.14 mmol g−1 h−1, respectively (the error bars were obtained based on three independent measurements). (b) Comparison of COF-based photocatalysts for H2O2 production with sacrificial agent. (c) THIQ conversion rate and DHIQ selectivity of COF-Py-S and COF-Py-O. (d) Performance of COF-Py-S for five consecutive cycles of H2O2 production. The performance of H2O2 production (e), THIQ conversion rate and DHIQ selectivity (f) using COF-Py-S under nature sunlight illumination. (The experiment was conducted on a sunny to cloudy day, from 9:00 to 13:00 hours, on 23 July 2024 in Shanghai). (g) FT-IR spectra of COF-Py-S before and after photocatalysis. (h) The PXRD patterns of solid H2O2 (Na2CO3•1.5H2O2, inset is the digital image of prepared solid H2O2 powder; the additional peaks marked with “*” can be ascribed to hydrated Na2CO3 (Na2CO3•H2O or Na2CO3•7H2O)).

Figure 5. Transient photocurrent responses (a), EIS spectrum (b), and PL spectroscopy (c) of COFs. (d) LSV curves for COFs. H2O2 selectivity (e) and calculated average number of transferred electrons (f). 

Figure 6. (a) H2O2 production of COF-Py-S with different scavengers, and the H2O2 yields under different conditions were 95.74 ± 7.65, 98.37 ± 0.21, 19.14 ± 0.31, 29.62 ± 1.13, 50.39 ± 5.07, and 95.45 ± 2.22 μmol from left to right, respectively. (the error bars were obtained based on three independent measurements). (b) EPR spectra of COF-Py-S. (c) O2 adsorption energy of COF-Py-S on different sites. Gibbs free energy diagrams of 2e- ORR (d) and THIQ-SDR (e) for COF-Py-S and -O. (f) In situ DRIFTS spectra of COF-Py-S recorded during photocatalytic H2O2 and DHIQ production. Optimized structure snapshots of key reaction intermediates in 2e- ORR (g) and THIQ-SDR (h) on COF-Py-S. The THIQ or DHIQ moleculars are highlighted in blue. The active sites are highlighted with red dashed circles. (i) The proposed 2e- ORR and THIQ-SDR mechanistic catalytic cycle diagrams over COF-Py-S.

https://doi.org/10.1002/anie.202424110