The Molecular Layering Method as a Basis of Chemical Nanotechnology

The molecular layering method (ML) is a technique for the modification of the silica surface by successive, repeated and alternate processing of the solid surface by an excess of appropriate reagents; this is followed by the removal of those reagents, that have not taken part in the reaction, and of any gaseous products formed in the various stages of the treatment. An essential feature of the ML method is the synthesis under conditions far from equilibrium.The present paper presents experimental results of the modification of SiO₂ with volatile chlorides of V, Ti, P, Cr and vapours of H₂O. Industrial silica gel SchSK (with a surface area of 250 m2/g, a mean porous diameter of 14 run, and a particle size of 0.5 mm — 1.0 mm) was used as a solid matrix. Modification of the matrix surface was carried out in a gas flow reactor under an inert dry atmosphere using vapours of VOC1₃, CrO₂Cl₂, POC1₃, TiCl₄ and H₂O.It was possible to form on the surface not only an oxide, but also other structures: a sulphide (using ZnCl₂ and H₂S) and a nitride structure (using vapours of TiCl₄ and NH₃) or their composites were synthesised on the silica surface. The main advantages of the chemical nanotechnology and the ML method over traditional surface processing methods are: strong (chemical) binding of sorbents on the substrate surface, homogenous distribution of heterocomponents over the surface, i.e., high uniformity of covering, and the possibility to control the surface layer composition down to the monomolecular layer, to deposit different atomic layers one by one and to form multicomponent regular structures.