改性光催化剂湿法脱除气态单质汞(4)

图10 消除剂对Hg0脱除效率的影响Fig.10 Effect of scavengers on Hg0removal

基于上述实验和表征,可以推知荧光灯照射下Ag-AgIO3(4%)BiOI光催化剂中Ag、AgIO3和BiOI之间可能的电荷转移方式,如图11所示.由DRS分析得知,AgIO3的带隙能为3.38eV,其EVB和ECB分别为3.83,0.45eV；BiOI的带隙能为 1.71eV,其 EVB和 ECB分别为 2.29,0.58eV.本研究中使用的可见光光源为荧光灯,采用Fluorlog FL3-22荧光光谱仪测试结果显示该荧光灯含有少量波长为 405nm(3.06eV)的紫外光.因此,在荧光灯辐照下,BiOI光催化剂可以被激发产生光生电子-空穴对,而 AgIO3由于其宽带隙(3.38eV)而不能被激发.由于荧光灯的波长具有3.06eV的能量,所以,BiOI的 CB可以跃迁至-1.1eV[34].形成新的能带匹配后,BiOI上CB的电子会转移至AgIO3的CB.另外,由于单质Ag的存在及其等离子体共振效应和良好的导电性,它亦可以产生光生电荷；BiOI光催化剂 CB上电子转移至单质Ag上,而后进一步转移至AgIO3的CB.由于BiOI的CB电位低于氧的还原电位[E0(O2/?O2-) =-0.046eV][18],BiOI上CB的e-将与其表面的O2反应生成?O2-,聚集在Ag颗粒表面上的e-亦能够与吸附在光催化剂上的 O2反应生成?O2-[22].由于 BiOI的VB 高于?OH/OH-的还原电位(1.99eV)[18],所以,BiOI上VB处存在的h+可以将OH-氧化为?OH.由于以上光生电子-空穴对的有效分离,Ag-AgIO3(4%)BiOI的反应体系中会存在大量的活性物质如?O2-、h+和?OH,该分析与 ESR测试结果一致.由消除剂实验可知,Ag-AgIO3(4%)BiOI光催化体系产生的?O2-是主要的活性物种,h+和?OH是次要物种.

图11 Ag-AgIO3(4%)BiOI光催化剂的脱汞机理Fig.11 Mercury removal mechanism of Ag-AgIO3(4%)BiOI photocatalyst

3 结论

3.1 在荧光灯照射下,Ag-AgIO3/BiOI光催化剂呈现出优异的光催化氧化活性,AgIO3负载量为4wt.%时,脱汞活性高达98%.

3.2 反应温度过高时,由于Hg0和O2溶解度的降低,脱汞性能受到限制；与中性溶液相比,酸性条件对Ag-AgIO3(4%)BiOI的脱汞性能几乎没有影响,但较强碱性条件对其活性影响较大；与 NO 相比,SO2对Ag-AgIO3(4%)BiOI光催化剂脱汞活性的影响更大.

3.3 与BiOI相比,Ag-AgIO3(4%)BiOI的等温线和BET比表面积变化均较小,且Ag-AgIO3(4%)BiOI的XRD上未发现Ag和AgIO3的特征衍射峰,说明Ag和AgIO3在BiOI上高度分散.在Ag-AgIO3/BiOI光催化剂体系中,?O2-的作用最大,h+和?OH次之.

[1] Zhao Y, Hao R L, Guo Q.A novel pre-oxidation method for elemental mercury removal utilizing a complex vaporized absorbent [J].Journal of Hazardous Materials, 2014,280:118—126.

[2] Shen B X, Zhu S W, Zhang X, et removal of NO and Hg0using Fe and Co co-doped Mn-Ce/TiO2catalysts [J].Fuel,2018,224:241—249.

[3] Zhang S B, Zhao Y C, Yang J P, et MnOX/TiO2as the SCR catalyst for simultaneous removal of NO and mercury from coal combustion flue gas [J].Chemical Engineering Journal, 2018,348:618—629.

[4] Cho J H, Eom Y, Jeon S H, et al.A pilot-scale TiO2photocatalytic system for removing gas-phase elemental mercury at Hg-emitting facilities [J].Journal of Industrial and Engineering Chemistry,2013,19:144—149.

[5] Li Y, Wu C Y.Role of moisture in adsorption, photocatalytic oxidation,and reemission of elemental mercury on a SiO2-TiO2nanocomposite[J].Environmental Science & Technology, 2006,40:6444—6448.

[6] Wu J, Li C E, Zhao X Y, et oxidation of gas-phase Hg0by CuO/TiO2[J].Applied Catalysis B: Environmental, 2015,176—177:559—569.

[7] Wang L L, Zhao Y C, Zhang J cerium-based TiO2nanofibers for photocatalytic oxidation of elemental mercury in coal combustion flue gas [J].Chemosphere, 2017,185:690—698.

[8] 彭小明,罗文栋,胡玉瑛,等.磷掺杂的介孔石墨相氮化碳光催化降解染料 [J].中国环境科学, 2019,39(8): X M, Luo W D, Hu Y Y, et al.Study on the photocatalytic degradation of dyes by phosphorus doped mesoporous graphite carbon nitride [J].China Environmental Science, 2019,39(8):3277-3285.

[9] 张 喜.新型卤化氧铋BiOX (X=Cl, Br, I)光催化剂的合成、表征及催化性能研究 [D].武汉:华中师范大学, , characterization and photocatalytic activity of BiOX (X = Cl, Br, I) photocatalysts [D].Wuhan:Central China Normal University, 2010.

[10] Hu Y Y, Li Z K, Yang J H, et of methylparaben using BiOI-hydrogel composites activated peroxymonosulfate under visible light irradiation [J].Chemical Engineering Journal, 2019,360:200—211.

[11] Lan H C, Zhang G, Zhang H W, et synthesis of BiOI flower-like microspheres for efficient photocatalytic degradation of BPA under visible light irradiation [J].Catalysis Communications,2017,98:9—12.

[12] Chen J F, Hu C, Deng Z, et into visible light-driven photocatalytic performance of direct Z-scheme Bi2WO6/BiOI composites constructed in-situ [J].Chemical Physics Letters, 2019,716:134—141.

[13] Cai L, Yao J W, Li J B, et synthesis of BiOI-TiO2heterojunction with enhanced visible-light-driven photocatalytic activity [J].Journal of Alloys and Compounds, 2019,783:300—309.

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