Sun Junming, Ma Ding, Zhang He, Liu Xiumei, Han Xiuwen, Bao Xinhe, Weinberg Gisela, Pfänder Norbert, Su Dangsheng
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, People's Republic of China.
J Am Chem Soc. 2006 Dec 13;128(49):15756-64. doi: 10.1021/ja064884j.
A novel in situ autoreduction route has been developed, by which monodispersed silver nanoparticles with tunable sizes could be easily fabricated on silica-based materials, especially inside the channels of mesoporous silica (MPS). 13C CP/MAS NMR spectroscopy was employed to monitor the whole assembly process. It was demonstrated that the amino groups of APTS (aminopropyltriethoxyl silane)-modified MPS can be used to anchor formaldehyde to form novel reducing species (NHCH2OH), on which Ag(NH3)2NO3 could be in situ reduced. Monodispersed silver nanoparticles were thus obtained. In situ XRD and in situ TEM experiments were used to investigate and compare the thermal stabilities of silver nanoparticles on the external surface of silica gels (unconfined) and those located inside the channels of SBA-15 (confined). It was observed that unconfined silver nanoparticles tended to agglomerate at low temperatures (i.e., lower than 773 K). The aggregation of silver nanoparticles became more serious at 773 K. However, for those confined silver nanoparticles, no coarsening process was observed at 773 K, much higher than its Tammann temperature (i.e., 617 K). Only when the treating temperature was higher than 873 K could the agglomeration of those confined silver nanoparticles happen with time-varying via the Ostwald ripening process. The confinement of mesopores played a key role in improving the thermal stabilities of silver nanoparticles (stable up to 773 K without any observable coarsening), which is essential to the further investigations on their chemical (e.g., catalytic) properties.
已开发出一种新型的原位自还原路线，通过该路线可以轻松地在二氧化硅基材料上，特别是在介孔二氧化硅（MPS）的通道内制备尺寸可调的单分散银纳米颗粒。采用13C CP/MAS NMR光谱监测整个组装过程。结果表明，APTS（氨丙基三乙氧基硅烷）修饰的MPS的氨基可用于锚定甲醛以形成新型还原物种（NHCH2OH），Ag(NH3)2NO3可在其上原位还原。由此获得了单分散银纳米颗粒。采用原位XRD和原位TEM实验研究并比较了硅胶外表面（无限制）和SBA-15通道内（受限）银纳米颗粒的热稳定性。观察到无限制的银纳米颗粒在低温下（即低于773 K）倾向于团聚。在773 K时银纳米颗粒的团聚变得更加严重。然而，对于那些受限的银纳米颗粒，在773 K时未观察到粗化过程，该温度远高于其坦曼温度（即617 K）。只有当处理温度高于873 K时，那些受限银纳米颗粒才会通过奥斯特瓦尔德熟化过程随时间发生团聚。介孔的限制作用在提高银纳米颗粒的热稳定性方面起着关键作用（在高达773 K时稳定，无任何可观察到的粗化），这对于进一步研究其化学（如催化）性质至关重要。
