晶种生长法制备银纳米片:老化过程对产物的影响

Seed-mediated Synthesis of Silver Nanoplates: Effects of Aging Process on Production

晶种生长法是获得形貌尺寸可控纳米银材料的常用方法。本文采用晶种生长法制备银纳米片。通过紫外吸收光谱及透射电子显微镜研究了老化过程对产物形貌的影响;同时通过在晶种生长阶段使用不同稀释浓度的晶种溶液,验证了硼氢化钠浓度对产物的影响。结果表明,经充分老化后的晶种溶液,残留的硼氢化钠分解更充分,以此溶液作为晶种进行后续生长时,银离子在琥珀酸作用下缓慢还原并逐渐沉积到晶种上,由于晶种(111)面被柠檬酸根保护,银离子在非(111)面的优先沉积导致片状结构的生成,产物以银纳米片为主。而未经充分老化的晶种溶液中含有未完全反应的硼氢化钠,后续加入的银离子将被残留在晶种溶液中的硼氢化钠迅速还原成银颗粒,而不能缓慢沉积在晶种表面,最终产物以银纳米颗粒为主。

Seed-mediated synthesis is one of the important approaches for preparing silver nanoplates with controllable size and well-defined morphology. In this work, we have investigated the effects of aging process on the synthesis of silver nanoplates by UV-Vis spectroscopy and Transmission Electron Microscopy （TEM）. By diluting the seed solution in the growth stage, we identified the key role of NaBH4 depletion over aging period in the formation of final silver nanoplates. NaBH4 is effectively depleted in the fully-aged seed solution. At the growth stage, usage of this seed solution facilitates slow reduction of silver ions and deposition onto seeds. Preferential lateral growth of facets other than （ 111 ） facet dominates kinetically, producing plate-like morphology, thanks to the protective adsorption of citrate ligands on （111 ） facets. In contrast, in poorly-aged seeds solution, NaBH4 is not fully decomposed and depleted. Silver ions are thus quickly reduced at the growth stage so that non-preferential growth prevails for all facets during deposition, leading to the formation of granule-like nanoparticles.