August 2001 Ž . Materials Letters 50 2001 53–56 www.elsevier.comrlocatermatlet A sonochemical approach to the confined synthesis of palladium nanoparticles in mesoporous silica Wei Chen a,b, ) , Weiping Cai a , Yong Lei a , Lide Zhang a a Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, People’s Republic of China b Institute of Economy and Technology, UniÕersity of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China Received 25 October 2000; accepted 1 November 2000 Abstract Ž . A sonochemical procedure at room temperature for the preparation of palladium Pd nanoparticles loaded within Ž . mesoporous silica is described. The formation of Pd nanoparticles 5–6 nm in diameter was restricted by the coalescence of the sonochemical reduced Pd atoms inside the confined volumes of the porous solid. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Mesoporous silica; Pd nanoparticles; Sonochemical approach Nano-sized noble metal particles, because of their surface and quantum-size effects, display many novel w x properties 1,2 such as high catalytic activities, in- teresting optical properties and various properties from the fundamental viewpoint. Accordingly, there has been an extensive interest in the development of new methodologies for the fabrications of nanome- ter-sized materials. Among these, some research ef- forts have been directed toward the synthesis of palladium nanocluster, partly because of the impor- w x tant roles played by Pd in catalysis 3–6 . It is well known that the per-atom catalytic efficiency of metal clusters and colloids often increases as the cluster size decreases. However, the probability of cluster aggregation also increases as particle size is reduced wx 7 . To prevent the undesired agglomeration, the ) Corresponding author. Fax: q 86-0551-5591-434. Ž . E-mail address: nanolab@mail.issp.ac.cn W. Chen . processes for producing metal nanoparticles are often performed in the presence of ligands, polymers, or w x various surfactants 8–10 . However, one of the caveats with stabilizers is that strong adsorption to the nanoparticle active sites may diminish catalytic w x activity 11 . Moreover, the stability of metallic col- loids depends on the characteristics of the special protecting agents, which are generally stripped off from the metal surface in vacuum andror with tem- perature, resulting in agglomeration. Thus, for appli- cation, the alternative method for generating stabi- lized metal nanoparticles involves synthesizing them in or on nanoporous supports, which help define particle size and serve to immobilize the resulting particles. Mesoporous solids, due to their large internal surface area and small pore size, have found great w x utility 12–14 . Putting the nano-scaled particles Ž . semiconductors, compounds or metals into the pores of mesoporous solids will form new composite mate- 00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0167-577X 00 00411-0