A nanocomposite of titanium dioxide (TiO2) and polyaniline (PANi) was synthesized by in-situ chemical polymerization using aniline (ANi) monomer and TiCl4 as precursors. SEM pictures show that the nanocomposite was created in the form of long PANi chains decorated with TiO2 nanoparticles. FTIR, Raman and UV-Vis spectra reveal that the PANi component undergoes an electronic structure modification as a result of the TiO2 and PANi interaction. The electrical resistor of the nanocomposite is highly sensitive to oxygen and NH3 gas, accounting for the physical adsorption of these gases. A nanocomposite with around 55% TiO2 shows an oxygen sensitivity of 600–700%, 20–25 times higher than that of neat PANi. The n-p contacts between TiO2 nanoparticles and PANi matrix give rise to variety of shallow donors and acceptor levels in the PANi band gap which enhance the physical adsorption of gas molecules.

Polypyrrole/single wall carbon nanotube composites were synthesized by in-situ chemical polymerization using pyrrole (PPy) as precursor and single wall carbon nanotubes (SWNTs) as additive component. Electron microscope images reveal that SWNTs component acts as nucleation sites for PPy growth in the form of spherical and cylindrical core-shell structures. The SWNTs/PPy core-shell results in thin n-p junctions which modify the PPy bandgap and reduce the work function of electrons. As a result of the strong coupling, Raman and IR spectra show that the PPy undergoes a transition from polaron to bipolaron state, i.e., indicating an increase in the conductivity. In the UV-Vis spectra, the 340 nm adsorption band (π*-π transition) exhibits a red shift, while the 460 nm adsorption band (bipolaron transition) experiences a blue shift indicating a change in electronic structure and a relocation of polaron levels in the band gap of PPy. The modification in PPy electronic structure brings in a synergistic effect in sensing feature. Upon exposure to oxygen (an oxidizing agent) and NH3 gas (a reducing agent), the PPy/SWNTs nanocomposite shows an enhancement in sensitivity exceeding ten folds in comparison with those of PPy or SWNTs.

TiO2 nanocrystals are prepared by pyrolysis of titanium tetrachloride (TiCl4) as precursor in HCl aqueous solution at 80°C. The experimental results show that the HCl concentrations in the synthesizing medium and the following aging are the essential factors affecting the phase formation and phase composition of the resulting TiO2 nanocrystals. The TiO2 suspended in the HCl media is predominant anatase in uniform cluster and the TiO2 deposited in the sedimentation is predominant rutile in the rod-like structure. In the anatase phase, TiO2 crystallites have particle structure of 4–11 nm in mean size depending on the HCl concentration and aging time. In the rutile phase, the mean size of rutile TiO2 is 12-13 nm and there is not much change with HCl environment and aging time. The mean size of TiO2 of around 11-12 nm is considered to be the critical point of phase transition from anatase to rutile in HCl media. Consequence, TiO2 nanocrystallites in pure anatase and rutile phase can be extracted and segregated from the colloidal suspension and the deposited parts in the synthesizing media.

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