Mousumi Mitra

Reduced graphene oxide-polyaniline composites—synthesis, characterization and optimization for thermoelectric applications

Reduced graphene oxide (rGO) can improve the thermoelectric properties of polyaniline (PANI) by varying its concentration in composites of rGO nanosheets and PANI. The figure of merit (ZT) of rGO–PANI composites is increased with an increasing percentage of rGO (up to 50%), which is 7.5 times higher as compared to pure PANI. High resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analyses show a uniform growth of PANI over the surface of rGO as a template, leading to a more ordered structure with high crystallinity during polymerization. Compared to pure PANI, both the electrical conductivity and thermoelectric power of the rGO–PANI composite is higher due to the increased carrier mobility as confirmed by a Hall effect measurement. Fourier transform infrared spectroscopy (FTIR), ultra-violet visible range spectroscopy (UV-Vis) and Raman spectroscopy analyses reveal that strong π–π interactions assisted the uniform distribution of PANI on the rGO nanosheets. Other strong interactions include electrostatic forces and hydrogen bonding between rGO and PANI, which provide a route for constructing highly ordered chain structures with improved thermoelectric performance of PANI. There is no significant change in the thermal conductivity of the rGO–PANI composite as compared to pure PANI, which improves the thermoelectric performance of composite.

Synthesis, characterization and enhanced thermoelectric performance of structurally ordered cable-like novel polyaniline–bismuth telluride nanocomposite

Bismuth telluride (Bi₂Te₃) nanorods and polyaniline (PANI) nanoparticles have been synthesized by employing solvothermal and chemical oxidative processes, respectively. Nanocomposites, comprising structurally ordered PANI preferentially grown along the surface of a Bi₂Te₃ nanorods template, are synthesized using in situ polymerization. X-ray powder diffraction, UV-vis and Raman spectral analysis confirm the highly ordered chain structure of PANI on Bi₂Te₃ nanorods, leading to a higher extent of doping, higher chain mobility and enhancement of the thermoelectric performance. Above 380 K, the PANI-Bi₂Te₃ nanocomposite with a core-shell/cable-like structure exhibits a higher thermoelectric power factor than either pure PANI or Bi₂Te₃. At room temperature the thermal conductivity of the composite is lower than that of its pure constituents, due to selective phonon scattering by the nanointerfaces designed in the PANI-Bi₂Te₃ nanocable structures. The figure of merit of the nanocomposite at room temperature is comparable to the values reported in the literature for bulk polymer-based composite thermoelectric materials.

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.

Effect of different surfactants and thicknesses on electrodeposited films of bismuth telluride and its thermoelectric performance

Thin films of bismuth telluride using various surfactants such as sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP) have been electrochemically deposited. The influence of different surfactants on crystal orientation and morphology was investigated and correlated with the thermoelectric performance of the electrodeposited films. Since thickness affects the thermoelectric performance compared to the surfactant, thickness- dependent thermoelectric performance has also been investigated. The carrier mobilities of the films obtained are significantly enhanced due to improved surface morphology using different surfactants. Between the two surfactants, films with SDS exhibited the higher value of thermoelectric power, power factor, and figure of merit, which is due to the effect of micelle formation. The XRD pattern of all the films, which are electrodeposited without surfactant or using SDS and PVP, showed preferred crystal orientation along the (018) direction. The roles of organic molecules in the development of nanoparticles with improved thermoelectric properties have been investigated.

Temperature dependent thermoelectric property of reduced graphene oxide-polyaniline composite

A composite material of reduced graphene oxide (rG) nanosheets with polyaniline (PANI) protonated by 5-sulfosalicylic acid has been synthesized via in situ oxidative polymerization method. The morphological and spectral characterizations have been done using FESEM and XRD measurements. The thermoelectric (TE) properties of the reduced graphene oxide-polyaniline composite (rG-P) has been studied in the temperature range from 300-400 K. The electrical conductivity and the Seebeck coefficient of rG-P is higher than the of pure PANI, while the thermal conductivity of the composite still keeps much low value ensuing an increase in the dimensionless figure of merit (ZT) in the whole temperature range.

Improved Photoluminescence Property of CTAB Assisted Polyaniline-AlZnO nanocomposite

Polyaniline-Al doped ZnO ((PANI-AlZnO:: 70:30) nanocomposite was prepared via in situ chemical oxidative polymerization, while the hexagonal powder of AlZnO was synthesized via sol-gel technique, using Hexadecyltrimethylammonium bromide (CTAB) as a capping agent. The prepared nanocomposite was characterized by High resolution transmission electron microscopy (HRTEM), EDAX, X-ray diffraction (XRD) and Fourier transforms infrared (FTIR) spectra. The optical property of the nanomaterials is examined by photoluminescence (PL) spectra analysis. The XRD pattern confirms the formation of Al doped ZnO as well as PANI. The HRTEM images of the composite showed the formation of hexagonal AlZnO embedded in polyaniline matrix. EDAX spectrum shows the compositional analysis of the nanocomposite. FTIR spectra confirm the formation of nanocomposite of PANI and hexagonal AlZnO. The PL intensity of the nanocomposite is improved as compared to pure AlZnO.