NiO-SiO2 nanocomposite thin films were prepared by sol-gel technique. The formed films gels were calcined at 200, 400, 600, 800 and 1100. C for 4 h leading to NiO-SiO2 nanocomposites. For these films, the X-ray diffraction, the Fourier transform infrared absorption and the field emission scanning electron microscopy were investigated. Our results show that the NiO(200) diffraction peak dominates in the preset work. NiO phase appeared in the XRD patterns for all samples. The newly prepared photocatalysts films have been evaluated by the determination of their photonic efficiencies for degradation of methylene. The results reveal that the photonic efficiency increases with increasing calcination temperature up to 600 degrees C with the maximum photonic efficiency being 0.62%. In addition, porous structures were observed and improve the sensitivity of these nanocomposites for gas sensing. (C) 2012 Elsevier B.V. All rights reserved.