通讯作者：曾光明 教授、程敏 副教授

第一作者：刘宏达（2023级博士生）

论文DOI：https://doi.org/10.1002/adfm.76587

全文速览

传统高级氧化过程追求污染物的深度矿化，能耗高、碳排放量大。近年来，将污染物定向转化为可回收聚合物的思路备受关注，但其关键在于如何精准调控活性氧物种的类型和氧化能力，避免过度氧化。单原子催化剂具有结构明确、可设计性强的优势，是建立构效关系和揭示聚合机理的理想平台。然而，目前对单原子位点如何调控活性氧物种生成路径、进而影响聚合选择性的机制尚不清楚，阻碍了高效聚合催化剂的设计。

在此，我们合成了具有Fe-N₁O₃构型的Fe SACs，该材料在活化过一硫酸盐（PMS）去除苯酚方面表现出优异的活性，实现了0.204 min^-1的反应速率常数和82.05%的总有机碳去除率。机理研究表明，苯酚的去除遵循一条由Fe活性位点介导、非自由基单线态氧驱动的聚合途径。生成的单线态氧具有适中的氧化还原电位，它驱动吸附在载体表面的苯酚发生氧化反应，通过亲电攻击形成苯氧基自由基，进而引发高分子量链（≤11个单元）的形成。深入的理论计算揭示，不对称的Fe-N₁O₃位点具有强烈的内部电场和适中的d带中心。这种电子构型不仅增强了PMS的吸附能力以实现持续的单线态氧生成，还基于Sabatier原理赋予了系统抵抗中间体中毒的能力，从而驱动了连续的聚合过程。这一将单原子配位工程与反应选择性控制相结合的根本性机理洞见，为设计以资源回收为核心的低碳、高价值水净化技术提供了变革性的蓝图。

图文导读

Figure 1. (a) Effect of different quenchers on phenol removal by the CB‑Fe‑750‑urea/PMS system and (b) corresponding removal kinetics. HPLC for quantitative detection of (c) the •SO₄^- and (d) •OH. (e) EPR spectra of CB‑Fe‑750‑urea/PMS system with capture agents. (f) PMSO conversion comparison of PMS alone system and CB‑Fe‑750‑urea/PMS system. Influences of (g) AgNO₃ (electron scavenger) and (h) pre-mixed time for the phenol removal in CB‑Fe‑750‑urea/PMS system. (i) Comparison of removal kinetics under different electron quenching conditions. (j) EPR spectra in CB‑Fe‑750‑urea/PMS system with TEMP. Reaction condition: [phenol]₀ = 0.1 mM, [PMS]₀ = 0.32 mM, [catalyst] = 0.1 g L^-1, [MeOH] = [TBA] = 200 mM, [p-BQ] = [CHCl₃] = [TEMP] = [DMSO] = 6 mM, initial pH = 6.74.

Figure 2. (a) Removal of phenol and TOC by CB‑Fe‑750‑urea/PMS system and (b) correlation analysis. (c) Changes in IC during the phenol removal by CB‑Fe‑750‑urea/PMS system. (d) HPLC chromatogram during the phenol removal in PMS, Fe²⁺/PMS or CB‑Fe‑750‑urea/PMS system. (e) MALDI-TOF spectrum of phenol polymerization products eluted using THF. Influences of (f) FA and (g) acetonitrile addition on phenol removal in the CB‑Fe‑750‑urea/PMS system. (h) Optimized adsorption configuration of phenol on Fe-N₁O₃ site. (i) GPC and (j) MALDI-TOF-MS spectra of elution products (dissolved in THF) on the surface of the CB‑Fe‑750‑urea catalysts during 2,6-M-PhOH removal process.

Figure 3. (a) Removal performance and (b) corresponding k_obs of the multiple para-substituted phenolic compounds in CB‑Fe‑750‑urea/PMS system. (c) Linear fitting between -lnk_obs and vertical IP, (d) nucleophilicity and (e) electrophilicity of para-substituted phenolic compounds. Correlation of -lnk_obs with both pKa and (f) vertical IP, (g) nucleophilicity and (h) electrophilicity of para-substituted phenolic compounds. Reaction condition: [pollutant]₀ = 0.1 mM, [PMS]₀ = 0.32 mM, [catalyst] = 0.1 g L^-1.

Figure 4. The (a) removal performance and (b) corresponding k_obs of CB‑Fe‑750‑urea/PMS system under varied pH, inorganic anions and HA. (c) Recycling and regeneration tests of CB‑Fe‑750‑urea catalysts. (d) The phenol performance of CB‑Fe‑750‑urea/PMS system in different water matrices. (e) Schematic of catalyst-filled continuous flow reactor. (f) Removal performance of phenol in CB‑Fe‑750‑urea/PMS system-based continuous flow reactions. (g) The effect of catalyst storage time at room temperature on phenol removal performance. (i) Relative environmental impact of 1 kg phenol removal in life-cycle assessment in CB-Fe-750-urea/PMS, SAFe_0.4-C₃N₄/PMS and Fe-BNC/PMS systems (ReCiPe 2016 v1.1 Midpoint (H)). Reaction condition: [phenol]₀ = 0.1 mM, [PMS]₀ = 0.32 mM, [catalyst] = 0.1 g L^-1, initial pH = 6.74.

全文小结

本研究通过开发一种聚合驱动工艺，致力于将苯酚去除从破坏性矿化转向资源回收。我们设计了一种具有明确结构的Fe 单原子催化剂，其具有不对称的Fe-N₁O₃活性位点。该催化剂以独特的方式将PMS的活化过程专一地引导至生成¹O₂-一种高度选择性的非自由基氧化剂。密度泛函理论计算和实验研究均证实，具有较低d带中心和强内部电场的不对称Fe-N₁O₃活性位点，可通过¹O₂介导的聚合过程去除苯酚。选择性淬灭实验和光谱技术证实，¹O₂可通过亲电攻击酚类氧原子引发聚合反应，从而生成关键的酚氧基自由基，进而持续生成高分子量多酚聚合物。本研究从原子层面阐明了“结构-活性-反应路径”之间的关系，确立了一种通过非自由基聚合途径可控、选择性地去除难降解有机污染物的新策略。尽管前景广阔，但该聚合策略目前仍处于实验室阶段。要将其推进至工程应用，需要针对聚合物选择性、可扩展的产品分离以及全面的环境安全评估开展有针对性的研究。