Selvin Rosilda, Chiang Anthony S T
J Nanosci Nanotechnol. 2014 Sep;14(9):7351-9. doi: 10.1166/jnn.2014.9239.
A facile method for the rapid synthesis of fully-dispersible ZSM-5 (Si/Al = 100) of about 30 nm size in high yield (about 91%) is described. The method comprises three steps, viz., concentration of an initial clear solution, low-temperature (80 degrees C) ageing of concentrated sol, and high-temperature (175 degrees C) hydrothermal treatment or microwave heating (175 degrees C) of aged concentrated sol. A simple vacuum-concentration method was used for the extraction of pure NPs of ZSM-5 in solution. XRD, FT-IR, TGA and ASAP characterizations showed that the NPs were partially crystalline. The concentration step accelerated the aggregation of primary units, which helps in the production of a large number of nucleation centers protected by TPA+ ions against aggregation. During low-temperature ageing, the number of critical sized nuclei increases, growing into zeolite. The high-temperature heating results in the complete growth of unreacted silica, giving high yields. A key factor for generating small non-aggregated zeolite crystals is the amount of water in the synthesis sol. The three-step method presented here produces a target material of small and uniform sized, non-aggregated ZSM-5 of about 30 nm in a short reaction time. The results are significant, as the synthesis method adopted here produces much uniform, non-aggregated nanocrystalline ZSM-5 in a shorter time with high yield.
本文描述了一种简便的方法，可高产率（约91%）快速合成尺寸约为30 nm的完全分散的ZSM-5（硅铝比 = 100）。该方法包括三个步骤，即初始澄清溶液的浓缩、浓缩溶胶的低温（80℃）老化以及老化浓缩溶胶的高温（175℃）水热处理或微波加热（175℃）。采用简单的真空浓缩法从溶液中提取纯的ZSM-5纳米颗粒。XRD、FT-IR、TGA和ASAP表征表明这些纳米颗粒是部分结晶的。浓缩步骤加速了初级单元的聚集，这有助于产生大量由TPA⁺离子保护以防聚集的成核中心。在低温老化过程中，临界尺寸的核数量增加并生长成沸石。高温加热使未反应的二氧化硅完全生长，从而实现高产率。合成溶胶中的水量是生成小的、不聚集的沸石晶体的关键因素。这里提出的三步法在短反应时间内可制备出尺寸小且均匀、不聚集的约30 nm的目标材料ZSM-5。这些结果意义重大，因为这里采用的合成方法能在更短时间内以高产率制备出更均匀、不聚集的纳米晶ZSM-5。
