The present invention provides a structure in which the surface of a solid substrate of any shape is covered with metal oxide, in particular, a nanostructure composite in which polyethyleneimine, which is an organic substance, and metal oxide, which is an inorganic substance, are combined in nano-meter scale, spreads at the entire surface of a substrate, and the nanostructure composite forms a nano-boundary of complex shapes so as to thoroughly cover the entire surface of the substrate; a structure in which metal ions, metal nano-particles, organic pigment molecules are contained in the nanostructure composite; a process for producing these structures which can produce these structures with ease and efficiently; and an application method for the structures as an immobilized catalyst type reactor.