Mesoporous Aluminosilicates as a Host and Reactor for Preparation of Ordered Metal Nanowires

Abstract

The creation of functional nanomaterials with the controlled properties is emerging as a new area of great technological and scientific interest, in particular, it is a key technology for developing novel high-density data storage devices. Today, no other technology can compete with magnetic carriers in information storage density and access rate. However, usually very small (10–1000 nm3) magnetic nanoparticles shows para- or superparamagnetic properties, with very low blocking temperatures and no coercitivity at normal conditions. One possible solution of this problem is preparation of highly anisotropic nanostructures. From the other hand, the use of purely nanocrystalline systems is limited because of their low stability and tendency to form aggregates. These problems could be solved by encapsulation of nanoparticles to a chemically inert matrix. One of the promising matrices for preparation of highly anisotropic magnetic nanoparticles is mesoporous silica or mesoporous aluminosilicates. Mesoporous silica is an amorphous SiO2 with a highly ordered uniform pore structure (the pore diameter can be controllably varied from 2 to 50 nm). This pore system is a perfect reactor for synthesis of nanocomposites due to the limitation of reaction zone by the pore walls. One could expect that size and shape of nanoparticles incorporated into mesoporous silica to be consistent with the dimensions of the porous framework.Here we suggest a novel synthetic route for the preparation of ordered magnetic nanowires in mesoporous silica matrix. The method is based on intercalation of a hydrophobic metal compound, into the hydrophobic part of silica-surfactant composite. Nanocomposites were characterized by TEM, ED, SAXS, SANS, BET and magnetic measurements. It was shown that shape and size of the particles are in good agreement with the shape and size of the pores. This approach leads to functional materials, which could find an application as high-density data storage devices.However this method has some disadvantages: the quantity of metal intercalates could not be varied or set, and maximal quantity is rather small. Therefore, we suggested another approach based on charging of matrix by replacing part of silicon atoms by aluminum. It gives rise to possibility of controlling loading of metal to pores by varying silicon to aluminum ratio, besides that, the use of mesoporous aluminosilicates as nanoreactors enables one to load cations by simple ion exchange. In the present study mesoporous aluminosilicates prepared by different methods were compared. Incorporation of silver ions into mesoporous silica matrix was studied as a model system. It was shown that shape and size of the particles are in good agreement with that of the pores. Thus, the suggested method leads to one-dimensional anisotropic nanostructures.