This work is devoted to the study of structural, morphological, optical and electrical properties of porous PbS-silicon and Al2O3-silicon nanocomposites for their applications in the field of photovoltaic. And also this work presents the decoration effect of titanium dioxide nanotubes by PbS and Ag nanoparticles in the field of photcatalysis (degradation of Escherichia coli bacteria and organic pollutant.