Optical properties of regiorandom polythiophene/Al2O3 nanocomposites and their application to ammonia gas sensing

Polythiophene (PT) and its composite with Al2O3 have been synthesized successfully using chemical oxidation method. The structural, morphological and chemical properties of the nanocomposites (NCs) are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The XRD spectra show the polycrystalline nature and improved crystallinity with Al2O3 doping concentrations. The SEM results reveal that all PT/Al2O3 samples form nano-dimensioned spherical structures spread uniformly throughout the surface. FTIR spectra show the shifting of some bands and appearance of some extra bands in PT/Al2O3 samples as compared to the pure PT indicates a complex formation between the dopant and polythiophene molecules. Optical properties are studied using UV-visible absorption and photoluminescence (PL) spectroscopy. PL spectra of pure PT and PT/Al2O3 samples exhibit mainly three visible emission peaks at around similar to 462, similar to 490 and similar to 522 nm. The two emission peaks centred at similar to 462 and similar to 490 nm in the Soret band region where as single peak at similar to 522 nm in the Q band emission. The NH3 gas sensing properties have been carried out at room temperature by varying the ammonia concentration over a range of 25-650 ppm. The response is found to increase with increasing Al2O3 doping concentration as well as increase of ammonia gas concentrations. The highest Al2O3 doped PT NCs sample shows maximum sensitivity at lower concentration of ammonia gas and rapid response and recovery time.