Fluolab【JACS】清华大学朱永法等环保新突破！单光子可见光降解，3天实现100%永久性毒物PFAS全脱氟
文章标题：Photocatalytic Defluorination of Perfluorooctanoic Acid by Twisted Linear Polymer Radicals
通讯作者：Yan Guo, Bin Liu, Yongfa Zhu
文章概要
引言
被誉为“永久性化学物质”的全氟和多氟烷基物质（PFAS）因其卓越的化学稳定性和生物蓄积毒性，已对全球生态环境和人类健康构成了长期的严重威胁。其中作为典型代表的全氟辛酸（PFOA）近期已被国际癌症研究机构列为一类致癌物。这类物质极难降解的根源在于其分子中存在键能极高的碳-氟（C–F）键，常规的物化手段只能对其进行吸附富集，而无法真正破坏其分子结构。现有的破坏性脱氟技术往往高度依赖高温、等离子体或外加牺牲试剂等高能耗、高成本方式，且在面对实际水体中微量级别的污染时效率大打折扣。光催化技术虽然展现出绿色低碳的潜力，但传统催化剂受限于光生载流子极其迅速的复合过程，很难提供足够且持久的还原驱动力。为了攻克这一瓶颈，本研究成功开发出一种新型扭曲线性聚合物光催化剂，利用独特的分子构型在单光子激发下延长还原态寿命，实现了温和条件下PFAS的彻底无害化全脱氟。
Scheme 1. Schematic Illustration Showing the Photoreductive Defluorination of PFOA by Twisted Linear Polymer
主要实验及结论
研究团队通过苏木吉偶联反应精准合成了由双噻吩-芴-吡啶构成的线性共聚物（BT–Fl–Py）。利用固体核磁共振、红外光谱以及X射线光电子能谱等表征手段，证实了该聚合物催化剂独特的供体-π-受体（D–π–A）非对称骨架结构。令人惊群的是，原位光照X射线衍射和红外光谱测试表明，该聚合物在受到光照时，其分子骨架内部的芴单元会发生显著的光诱导构型扭曲弛豫，从而切断了电子的无辐射复合路径。飞秒瞬态吸收光谱和微秒级瞬态荧光光谱进一步证实，这种构型扭曲能有效产生一种长寿命的扭曲内电荷转移态（TICT 1）。该状态不仅将光生还原电子稳定锁定了长达1.04微米，还使其具备了高达负1.6伏的强还原电位，为后续高效的界面电子转移与C–F键活化断裂提供了坚实的能量基础。
Figure 1. Structure of the BT–Fl–Py polymer. (a) Chemical structures of the conjugated polymer photocatalysts. (b) Solid-state 13C NMR spectra of Fl, BT–Fl, and BT–Fl–Py polymers. (c) Pawley refinement with the residual difference plot and the XRD pattern of the BT–Fl–Py polymer before and after irradiation. The schematic diagram shows the formation of light-triggered torsional distortion. (d) Refined crystal lattice structure of the BT–Fl–Py polymer. (e) FTIR spectra of the BT–Fl–Py polymer recorded in the dark and under light irradiation. (f) Calculated infrared vibration of the distorted fluorene.
Figure 2. Formation and characterization of the long-lived TICT1 state. (a) Normalized steady-state absorption spectra of BT–Fl–Py before and after irradiation (upper part). Light-induced normalized absorption difference spectrum (lower part). GSB: ground-state bleaching; ESA: excited-state absorption. (b) TD-DFT simulated spectra of BT–Fl–Py. Blue: ground-state (S0) absorption, dominated by the lowest-energy S0 → S1 transition. Red: calculated light-induced absorption features associated with the optimized net-charged TICT1-related model, used to approximate the oxidized/hole-accumulated photoinduced species. Spectra were convoluted with Gaussian broadening (see Supporting Information for computational details). Inset: schematic of single-photon excitation, followed by torsional relaxation from S0 → S1 to the twisted charge-separated configuration (TICT1). (c) Delay kinetics of TICT1-associated and S1-associated ESA signals of BT–Fl–Py in THF (λex = 420 nm). (d) Transient photoluminescence (TRPL) decay curve of the BT–Fl–Py polymer, focusing on the long-lived component (λex = 405 nm). Measurement conditions: ambient air atmosphere, room temperature, time window = 0–3 μs. Fitting parameters (biexponential): τ1 = 0.22 ± 0.06 μs (normalized relative amplitude A1′ = 0.72), τ2 = 1.04 ± 0.07 μs (normalized relative amplitude A2′ = 0.28). A1′ and A2′ sum to 1, representing the relative contribution of each decay component. (e) Ratio of double-integral area of the in situ EPR signal of BT–Fl–Py powder to the Mn-marker signal in the dark and under light irradiation. (f) Dependence of F– concentration on applied potential (vs Ag/AgCl) during PFOA degradation. Inset: energy band structure of BT–Fl–Py.
Figure 3. Photocatalytic reductive defluorination performance for PFAS. (a) Reaction mode of PFOA in the photocatalytic defluorination process. (b) Comparative wavelength-dependent activity: full-spectrum vs visible-light irradiation (0.05 ppm PFOA). (c) Substrate scope analysis of polyfluoroalkyl substances ([PFAS] = 0.1 ppm, catalyst loading = 0.2 g L–1) (d) Concentration-dependent defluorination efficiency under visible-light irradiation (PFOA: 0.05–2.5 ppm). (e) Long-term operational stability over 3 consecutive cycles (72 h total duration). (f) Custom-designed outdoor photoreactor and experimental setup for photocatalytic PFOA defluorination (reactor scale: 36 × 30 × 5 cm3). (g) Defluorination performance of BT–Fl–Py over 3 days of natural sunlight irradiation (6 h/day).
在实际的催化降解实验中，研究人员将催化剂投入不含任何外加牺牲剂的微量PFOA水溶液中。得益于非极性芳香骨架和芴单元甲基侧链构建的疏水环境，该催化剂展现出惊人的选择性吸附动力学，在短短5分钟内便能将水中的PFOA完全抽提至催化剂表面，从而有效规避了水分子和溶解氧对光生电子的竞争性消耗。固体氟谱测试明显捕捉到了吸附诱导的振动红移以及终端氟原子受到的强电子屏蔽效应，表明C–F键在吸附界面已被显著活化。在波长大于420纳米的可见光连续照射下，界面电子转移顺利启动，系统在30小时内即达到了理论最大氟离子释放量，实现了近乎100%的定量全脱氟降解。随后，研究团队将底物拓展至其他四种结构各异的PFAS及其替代品，均取得了远超传统催化材料的降解表现。更具工业化前景的是，在放大规模的户外中试实验中，利用定制的太阳能反应器，该系统仅凭天然太阳光照射3天即可完成100%的脱氟转化，且催化剂在经历多次循环后仍保持了完美的形貌与催化活性。通过质谱对降解中间体的动态追踪，文章揭示了一条由电子进攻主导脱氟、空穴协助氧化脱羧的双基团协同链剪切降解路径，证实碳骨架最终被安全转化为无害的无机碳和短链非氟羧酸。
Figure 4. Preferential adsorption and activation of PFOA. (a) Water contact angle of BT–Fl–Py. (b) O2-TPD curves of BT–Fl–Py. (c) Independent gradient model based on the Hirshfeld partition (IGMH) analysis of the intermolecular interactions between PFOA– and BT–Fl–Py. (d) Solid-state 19F NMR spectra showing adsorption-induced vibrational shifts. (e) Femtosecond transient absorption spectra of BT–Fl–Py and BT–Fl–Py with PFOA in THF. (λex = 420 nm). (f) Extraction of the kinetics curves of the TICT1 ESA signal.
Figure 5. Possible defluorination and degradation mechanism for PFOA. (a) Defluorination kinetics of 0.25 ppm PFOA with different scavengers using BT–Fl–Py under full-spectrum irradiation during 24 h. (b) Negative-ion TOF-SIMS spectra of BT–Fl–Py before and after 24 h of photocatalytic reaction of 0.05 ppm PFOA under visible-light irradiation. (c) Proposed possible PFOA degradation pathway.
总结及展望
该项工作成功构建了一种极具创新性的扭曲线性聚合物光催化体系，为在全球范围内安全、低碳、彻底清除环境微量PFAS污染开辟了切实可行的新途径。研究巧妙利用分子内的非 adiabatic 扭曲弛豫机制，攻克了单光子催化剂高还原电位与长载流子寿命不可兼得的世纪难题，为低能耗自由基光催化剂的理性设计提供了极具价值的分子构筑范式。鉴于该催化材料完全不含贵金属、生产稳定性高、无需依赖化学添加剂且能直接驱动规模化的太阳光室外作业，该技术有望在不久的将来真正走向工业水处理前线，为绿色可持续的环境生态修复贡献核心材料与技术方案。