Amrita Ghosh

Facile electrochemical deposition of Cu7Te4 thin films with visible-light driven photocatalytic activity and thermoelectric performance

We report a facile strategy to fabricate thin films of Cu7Te4 via a two-electrode galvanic method and demonstrate its application as a recyclable photocatalyst with visible-light-driven photocatalytic activity and photostability. The organic dyes Methylene Blue (MB), and Rose Bengal (RB) and Cr(VI) as a toxic metal ion were chosen to explore the photocatalytic performance. MB was completely degraded (97%) under visible light irradiation in 60 min while RB was degraded up to 92% within 90 min irradiation. Furthermore, the Cu7Te4 thin film also showed superior photoactivity to reduce toxic Cr(VI) to Cr(III). The effective removal of Cr(VI) up to 99.8% at pH 2 was observed in 30 min. The related photocatalytic mechanism is discussed based on the active species trapping experiments. In addition, the Cu7Te4 thin film shows improved thermoelectric performance at room temperature, which may be attributed to the lower value of thermal conductivity obtained in the present case.

Electrochemical synthesis of p-CuO thin films and development of a p-CuO/n-ZnO heterojunction and its application as a selective gas sensor

p-CuO thin films have been synthesized on indium tin oxide (ITO)-coated glass substrates and on ZnO/ITO-coated glass substrates using a new, simple, cost-effective electrochemical technique (galvanic deposition) at room temperature. X-ray diffraction (XRD) studies of the films show a monoclinic phase of CuO, and UV-vis spectroscopy of the CuO/ITO film shows an indirect band-gap energy of about 1.85 eV. The surface morphology of CuO thin film consists of a c-axis-grown regular macroporous network structure with deep cavities surrounded by thin solid walls, which are suitable for gas trapping and sensing. Current–voltage characteristics of the formed p-CuO/n-ZnO film show good rectifying behavior. At 1 V reverse bias, the leakage current was as low as 2 × 10−9 A compared to a current of 1.2 × 10−7 A at the same forward bias, resulting in a forward-to-reverse current ratio of about 60. The ideality factor of the diode obtained was quite high, at about 9.5. The frequency dependence of the small signal AC response in both Rp–Cp and Rs–Cs mode of the fabricated heterojunction were measured at a reverse bias of 1.5 V. In the presence of 10 000 ppm gas exposure for gases, including CH4, H2S and CO, frequency-dependent changes in AC responses are different for different gases. The variation of the reactance of the fabricated device shows different behaviour with exposure to different types of gases. The minimum in reactance occurring at different frequencies for different gases indicates the selectivity of the device for gas sensing.

Polyaniline–single walled carbon nanotube composite – a photocatalyst to degrade rose bengal and methyl orange dyes under visible-light illumination

The polyaniline/single walled carbon nanotube (PANI–SWCNT) composites were prepared by the polymerization of an aniline monomer in the presence of sulfosalicylic acid with SWCNT under in situ conditions. PANI and PANI–SWCNT composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultra violet-visible spectroscopy (UV-Vis), Fourier transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and Brunauer–Emmett–Teller (BET) analysis. The application of the composites as a recyclable photocatalysts with visible-light-driven photocatalytic activity and photostability for the degradation of organic dyes – Rose Bengal (RB) and Methyl Orange (MO) – is demonstrated. PANI–SWCNT composite, with 2 weight% SWCNT content, has emerged as the best with degradation efficiencies of 95.91% and 90.34% against the performance of PANI with degradation efficiencies of 85.2% and 75.9% for RB and MO within 10 and 30 minutes, respectively. The synergistic effect between PANI and SWCNT is found to impart improved photogenerated carrier separation in the composite. A possible photocatalytic mechanism on the enhancement of the visible light performance of the composite over pure PANI is discussed based on the results of an active species trapping experiment.

Electrochemical Synthesis of p-CuO Thin Films and Development of a p-CuO/n-ZnO Thin Film Hetero-Contact for Gas Sensing

Thin films of p-CuO has been synthesized using a simple electrochemical technique (Galvanic deposition) on Indium Tin Oxide (ITO) coated glass substrates and on ZnO/ITO coated glass substrates. The films were characterized using X-ray Diffraction Technique (XRD) and UV–VIS spectroscopy. The surface morphology of the films was studied using FESEM. Measurements of electrical properties of the n-ZnO/p-CuO heterojunction were carried out to understand its suitability for gas sensing application.