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In the present work, multi-walled carbon nanotube (MWCNT)-doped TiO₂ nanocomposite films were synthesized by sol–gel method. The influence of nanotube concentration on the structural, electrical and optical properties of the films was investigated. The beneficial effects of the addition of carbon nanotubes into a TiO₂ film and titania-coated MWCNTs have much in common. On the other hand, this work contributes to the previous studies in terms of the optical and electrical properties of MWCNT. For this reason, MWCNT/rare brookite-phased TiO₂ matrix as simple sol–gel deposited composite films were investigated in our study. The XRD studies showed that the composite film has a brookite crystal structure at the annealing temperature of 450^∘C. According to the surface morphology investigations, SEM image of nanocomposite film shows that composite film has a granular and rod-like structure. The absorbance measurements of the films were carried out by the UV–Vis spectrophotometer to investigate transparency and to calculate the bandgap energy of composite films. The surface resistivity of the MWCNT-doped TiO₂ composites decreased from $2.50\times 10^{10}$ to $2.20\times 10^9$ ohm/sq with increase in MWCNT content.

Nanostructured metal oxide-based resistive-type gas sensors are of high research interest. Chemical stability is the most critical issue due to the surface electron species and density. In the present paper, 2D-nanostructured WO₃ was prepared and characterized, and a WO₃-based sensor was fabricated and analyzed. The results showed that the synthesized WO₃ material exhibited nanosheet structure, and during hydrogen sensing testing, the current baseline shifted with various tendencies, even completely opposite directions under different operation temperatures. The chemistry analysis results indicated that water molecule and hydroxyl group were formed under low operation temperature but further oxidation occurred at higher temperatures. The adsorption of H₂ on oxygen terminated WO₃(0 0 1) surfaces by density functional theory (DFT) method indicated that a water molecule formed by adsorption of a hydrogen molecule at the O site with the most thermodynamically stable state, and two surface hydroxyl groups formed by dissociative adsorption with a thermodynamically less stable state. The water molecule and surface hydroxyl groups increased the conductivity of the WO₃ film while that was decreased as the oxidation occurred.

CNT-ZnO nanocomposite powders were synthesized by addition of carbon nanotubes (CNT) during the growth of ZnO nanoparticles using a wet-chemical method. These CNT-ZnO nanocomposites powder were then spin coated on corning glass substrates to obtain thin films which were characterized using X-ray diffraction, scanning electron microscopy and current voltage characteristics. Hydrogen sensing (50- 1000 ppm) carried out on pure and CNT-ZnO nanocomposites at operating temperature of 250 and 300°C in N₂ atmosphere (0.4±0.03 mbar) revealed higher sensitivity in 2 wt.% CNT-ZnO nanocomposite thin film compared to the pure ZnO thin film.