Abstract The present research work explores the room temperature gas sensing ability of hybrid nanocomposites of metal sulphide nanoparticles with polypyrrole (PPy) matrix. Sonochemically synthesized both silver sulphide (Ag2S) and cadmium sulphide (CdS) nanoparticles were mixed in varying ratios with PPy matrix by in-situ oxidative polymerization route. The resulting PPy/(Ag2S:CdS) hybrid nanocomposites were analyzed by characterizing them using FTIR and UV-Visible spectroscopy, XRD, SEM, four-probe conductivity method and gas sensing ability by two-probe gas sensing setup. The current-voltage (I-V) characteristics of the PPy hybrid nanocomposites revealed their semiconducting nature with an electrical conductivity in the range of 10−4 to 10−3 S/cm. As compared to pure PPy, their hybrid PPy/(Ag2S:CdS) nanocomposites showed an enhancement in sensitivity towards ammonia gas detection. The results clearly indicated a synergistic effect between the Ag2S:CdS nanoparticles and the PPy matrix.

A novel process was developed for the synthesis of a mixed phase (constituted of 66% anatase phase) of TiO2 nanoparticles at lower calcination temperature (400 oC) by the sol gel technique using a cost effective and easily available propanol solvent. Stereochemistry of propanol played a crucial role towards crystallographic phase of resultant TiO2nanoparticles where n-propanol gave mixed phase while i-propanol gave pure anatase. A plausible mechanism has been proposed. An effect of crystallographic phase on their photocatalytic activity was studied using degradation of bromophenol blue dye. The rate constants of the dye degradation reaction for anatase phase and mixed phase were found to be 6.86 x 10-3 /s and 1.56 x 10-2 /s respectively. A mixed phase of TiO2 showed faster (120 min for 84%) photodegradation compared to the anatase phase (270 min. for 84%) due to an effect of crystalline and electronic parameters. The cyclic voltammetry results depicted the reducing nature of i- TiO2than n-TiO2, which creates unfavorable situation for the electron transfer from TiO2 to dye.