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中国物理学会期刊

电子偶素在OMC/SBA-15, OMC@SBA-15及CuO@SBA-15催化剂中的化学猝灭

CSTR: 32037.14.aps.71.20211814

Chemical quenching of positronium in OMC/SBA-15, OMC@SBA-15 and CuO@SBA-15 catalysts

CSTR: 32037.14.aps.71.20211814
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  • 以P123为结构导向剂、TEOS为硅源制备了有序介孔二氧化硅SBA-15, 并以此为模板制备了有序介孔碳(OMC). 小角X射线衍射、高分辨透射电子显微镜和N2吸附/脱附等测试结果均证实SBA-15与OMC具有高度有序的孔结构、相对较高的比表面积, 且孔洞平均尺寸分别约为7.5 nm和3.3 nm. 分别采用固相反应法和浸渍填充法制备了OMC/SBA-15复合材料和OMC@SBA-15及CuO@SBA-15复合材料. 随着OMC和CuO质量分数的增大, 3种复合材料中o-Ps寿命 \tau _4 和其强度 I_4 均减小. o-Ps湮没率 \lambda _4 随OMC和CuO质量分数的变化可用一条或两条直线很好地拟合, OMC/SBA-15, OMC@SBA-15及CuO@SBA-15复合材料中反应速率常数 k 分别为(2.39\pm 0.44)\times 10^7~\mathrms^-1/(6.65\pm 0.94)\times 10^6~\mathrms^-1, (2.28\pm 0.19)\times 10^7~\mathrms^-1(8.76\pm 0.47)\times 10^6~\mathrms^-1. 因此, 3种复合材料中 \tau _4 I_4 降低是由于电子偶素与碳、铜元素在介孔内或孔表面发生了化学猝灭和禁止效应. 同时, 电子偶素也是一种检测多孔材料中孔隙结构的有效探针.

     

    Owing to highly ordered two-dimensional hexagonal structure, large surface area, variable pore size, high thermal stability and especially the electron delocalization energy determined by its frame structure, SBA-15 catalysts have received more and more researchers’ attention. By using the structure-directing agent of P123 and the silicon source of TEOS, we synthesize ordered mesoporous silica SBA-15. At the same time, ordered mesoporous carbon OMC is succefully synthesized with the template of SBA-15. The small angle X-ray diffraction, high resolution transmission electron microscopy and N2 adsorption-desorption measurements are conducted to verify the highly ordered pore structure and relatively high specific surface area of SBA-15 and OMC, and their average pore radius are about 7.5 nm and 3.3 nm, respectively. Positron lifetime spectrum of SBA-15 catalyst is composed of two longer lifetimes and two shorter lifetimes: two longer lifetimes \tau _3 and \tau _4 are the annihilation in micropore and large pore of positronium (Ps), are 7.5 ns and 106 ns. However, there is nearly no longer lifetime component in OMC, which indicates that there might exist the quenching or inhibiting of positronium by carbon material. To verify this guess, we synthesize the catalysts of OMC/SBA-15, OMC@SBA-15 and CuO@SBA-15 by the solid state reaction and the impregnation filling method. With the increasing of OMC and CuO content, both the o-Ps lifetime \tau _4 and its intensity I_4 of these three compounds decrease. The annihilation rate of o-Ps lifetime varying with OMC and CuO content can be better fitted by one or two straight lines, The values of reaction rate constant K in OMC/SBA-15, OMC@SBA-15 and CuO@SBA-15 are (2.39\pm 0.44)\times 10^7~\mathrms^-1/(6.65\pm 0.94)\times 10^6~\mathrms^-1, (2.28\pm 0.19)\times 10^7~\mathrms^-1, and (8.76\pm 0.47)\times 10^6~\mathrms^-1, respectively. Therefore, our results indicate that there are quenching effect and inhibition effect among the carbon, the CuO and the positronium, which lead \tau _4 and I_4 to decrease, and positronium is also a probe for detecting the pore structure of porous material.

     

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