Positron annihilation lifetime spectra for pillared montmorillonite clay (PILC), as encapsulated with chitosan (CS) chains, supported with Pd nanoparticles, fresh and recovered PILC-CS@Pd heterogeneous catalysts, along with the starting montmorillonite clay (MC) were measured. After pillaring modification, as the interlayer nano-space expanded, the sub nanometer level free-volume nanohole size increases obviously from 0.182 nm (MC) to 0.246 nm (PILC). Then, as the CS chains and active Pd species encapsulated within the interlayer nano-space, the -Ps lifetime () and intensity () undergo a continuous decrease, indicating the decrease of the free-volume nanohole size and concentration. Meanwhile, in practical catalytic application scenarios, it is found that the variations of the free-volume parameters show close correlation with the recycling aging behavior and catalytic performance decline of the catalytic nanocomposites. The decrease in density of sub nanometer level molecular stacking due to the leaching of Pd species and degradation of CS chains in the interlayer galleries nano-space of the recovered PILC-CS@Pd hybrid nanocomposite has been sensitively detected by the -Ps probe.

中文翻译：

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柱撑粘土基催化杂化纳米复合材料的正电子湮没光谱研究

测量了用壳聚糖 (CS) 链封装、负载有 Pd 纳米颗粒、新鲜和回收的 PILC-CS@Pd 非均相催化剂以及起始蒙脱石粘土 (MC) 的柱撑蒙脱石粘土 (PILC) 的正电子湮灭寿命光谱。柱化修饰后，随着层间纳米空间的扩大，亚纳米级自由体积纳米孔尺寸明显从0.182 nm（MC）增加到0.246 nm（PILC）。然后，随着 CS 链和活性 Pd 物质封装在层间纳米空间内，-Ps 寿命 () 和强度 () 持续下降，表明自由体积纳米孔尺寸和浓度下降。同时，在实际催化应用场景中，发现自由体积参数的变化与催化纳米复合材料的循环老化行为和催化性能下降密切相关。 -Ps 探针可以灵敏地检测到由于回收的 PILC-CS@Pd 杂化纳米复合材料的层间画廊纳米空间中 Pd 物质的浸出和 CS 链的降解而导致的亚纳米级分子堆积密度的降低。