含氟Fe-MCM-48的制备及其在饮用水处理中抑制臭氧氧化生成溴酸盐机制

Preparation of fluorinated Fe-MCM-48 and its mechanism for inhibiting ozone oxidation to bromate in drinking water treatment

  • 摘要: 饮用水厂的臭氧氧化过程中会产生溴酸盐(\mathrmBrO_3^- )等毒性副产物,对人体健康造成较大威胁。非均相催化臭氧氧化技术可以抑制\mathrmBrO_3^- 的生成。Fe-MCM-48介孔分子筛具有独特的三维立方孔道结构,常作为催化剂用于催化臭氧氧化过程。但Fe-MCM-48存在表面酸性位点不足、传质效果差等缺点,这限制了其应用和推广。以FeF3为铁源和氟源,通过一步合成法制备了不同F-Fe-MCM-48并将其用于控制臭氧氧化过程\mathrmBrO_3^- 的产生;利用XRD、TEM和红外光谱等手段研究了F-Fe-MCM-48比表面积和酸性位点等理化性质,考察了F-Fe-MCM-48、溶液pH、叔丁醇(TBA)等因素对\mathrmBrO_3^- 产生情况的影响,同时结合电子顺磁共振等技术揭示催化剂作用机制。结果表明:1)F-Fe-MCM-48具有良好的三维立体介孔结构和较大的比表面积(1 487 m2/g)。在水热反应中,铁原子能够通过替代硅氧四面体中的硅原子,成功地进入分子筛的骨架结构;同时,氟原子也通过取代分子筛表面的Si—OH基团,形成了具疏水性的Si—F基团。2)在臭氧(O3)产量为100 mg/h,Br−投加量为1 000 μg/L条件下,反应60 min后,F-Fe-MCM-48/O3体系中\mathrmBrO_3^- 产生量为70.3 μg/L,抑制率达78.9%,抑制效果是Fe-MCM-48/O3的1.4倍。且在pH为5~9的范围内,F-Fe-MCM-48/O3均保持良好的\mathrmBrO_3^- 抑制效果。3)F-Fe-MCM-48具有丰富的Lewis酸位点,能有效吸附并分解O3,降低溶液中O3浓度,从而抑制了O3对Br−的直接氧化作用。反应过程中产生的\cdot \mathrmO_2^- 和H2O2等活性物种能还原\mathrmBrO_3^- 、\cdot \mathrmBr_2^- 和\cdot \mathrmBr_3^- 等中间产物,进一步抑制F-Fe-MCM-48/O3过程中\mathrmBrO_3^- 的产生。本研究可为臭氧氧化中\mathrmBrO_3^- 的控制提供理论依据。

     

    Abstract: The ozonation process in drinking water plant will generate toxic by-products such as bromate (\mathrmBrO_3^- ), which pose significant threats to human health. Heterogeneous catalytic ozonation process can inhibit the formation of \mathrmBrO_3^- . Fe-MCM-48 mesoporous molecular sieves, with their unique three-dimensional cubic pore structures, are often used as catalyst for catalytic ozonation. However, the insufficient surface acidic sites and poor mass transfer effects of Fe-MCM-48 limit its application and popularization. In this study, F-Fe-MCM-48 was prepared using FeF3 as the iron and fluoride source via a one-step synthesis method. It was applied to inhibit \mathrmBrO_3^- production during the catalytic ozonation process. XRD, TEM and FTIR were used to study the physicochemical properties like specific surface area and acid sites. The influence of F-Fe-MCM-48, solution pH and tert-Butanol (TBA) addition on \mathrmBrO_3^- formation were investigated and the functional mechanism of catalyst was revealed by electron paramagnetic resonance (EPR). Results showed that: 1) F-Fe-MCM-48 possessed a good three-dimensional mesoporous structure and a large specific surface area (1487 m2/g). During hydrothermal reactions, iron atoms replaced silicon atoms in the siloxane tetrahedra to enter the framework of the molecular sieve, and F replaced the Si—OH on the surface to form the hydrophobic Si—F group. 2) With an ozone production of 100 mg/h and a Br− addition of 1000 μg/L, the concentration of \mathrmBrO_3^- in the F-Fe-MCM-48/O3 system after 60 min was 70.3 μg/L, with an inhibition rate of 78.9%, which was 1.4 times of that in Fe-MCM-48/O3. Within a pH range of 5-9, the F-Fe-MCM-48/O3 system maintained good \mathrmBrO_3^- inhibition. 3) F-Fe-MCM-48 was enriched with Lewis acid sites, which could effectively adsorb and decompose O3, thereby reducing its concentration and inhibiting the direct oxidation of Br−. The active species such as \cdot \mathrmO_2^- and H2O2 generated during the reaction process could further reduce intermediates such as \mathrmBrO_3^- , \cdot \mathrmBr_2^- and \cdot \mathrmBr_3^- , thereby further inhibiting the formation of \mathrmBrO_3^- in F-Fe-MCM-48/O3 process. This study can provide theoretical basis for the control of \mathrmBrO_3^- during ozonation.

     

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