Combustion Synthesis of Nanomaterials for Photocatalytic and Photovoltaic Applications

The major problems the world is facing today are related to energy production and environmental pollution. Increasing oil prices, environmental pollution and energy demand stimulated vigorous research on the development of alternative energy sources. Utilization of solar energy by photocatalytic route may facilitate the removal of pollutants, whereas photocatalytic/(photovoltaic) fuel/(energy) generation may meet the energy demand. The concerns due to the depletion of fossil fuels and environmental problems fostered the research on development of clean energy sources. In this context, hydrogen has the potential to surpass the fossil fuels. From long time, water has been advocated as the choice of compound for hydrogen production. Even though photocatalytic water splitting by either ultraviolet or solar irradiation has been extensively studied, still the efficiency of this process is not satisfactory. Another potential application of photocatalysis is the pollutant degradation, which was carried out both under homogeneous and heterogeneous conditions. Solid semiconductors offer additional advantages like less expensive, robust and can be easily recovered and reused. Even though various attempts have been reported to synthesize a series of semiconductors, there exists a need to revisit the synthetic strategies to design tailor made photocatalysts

Combustion synthesized TiO2 for enhanced photocatalytic activity under the direct sunlight-optimization of titanylnitrate synthesis

Optimized synthesis of Ti-precursor ‘titanylnitrate’ for one step combustion synthesis of N- and C-doped TiO2 catalysts were reported and characterized by using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), diffused reflectance UV–vis spectroscopy, N2 adsorption and X-ray photoelectron spectroscopy (XPS). XRD confirmed the formation of TiO2 anatase and nano-crystallite size which was further confirmed by TEM. UV-DRS confirmed the decrease in the band gap to less than 3.0 eV, which was assigned due to the presence of C and N in the framework of TiO2 as confirmed by X-ray photoelectron spectroscopy. Degradation of methylene blue in aqueous solution under the direct sunlight was carried out and typical results indicated the better performance of the synthesized catalysts than Degussa P-25

Combustion synthesis of cadmium sulphide nanomaterials for efficient visible light driven hydrogen production from water

Anion-doped cadmium sulphide nanomaterials have been synthesized by using combustion method at normal atmospheric conditions. Oxidant/fuel ratios have been optimized in order to obtain CdS with best characteristics. Formation of CdS and size of crystallite were identified by X-ray diffraction and confirmed by transmission electron microscopy. X-ray photoelectron spectroscopy confirmed the presence of C and N in the CdS matrix. The observed enhanced photocatalytic activity of the CdS nanomaterials for the hydrogen production from water (2120 μmol/h) can be attributed to high crystallinity, low band gap and less exciton recombination due to the C and N doping

Novel single pot synthesis of metal (Pb, Cu, Co) sulfide nanomaterials -Towards a quest for paintable electrode materials that supersedes Pt electrode

Novel single pot selective stoichiometric synthesis of cobalt, copper and lead sulfide nanomaterials has been carried out in an energy and time efficient manner by using combustion synthesis for the first time without using surfactants, capping agents and inert atmospheric conditions. X-ray diffraction and transmission electron microscope revealed the formation of respective nanocrystalline metal sulfides with different stoichiometry, whereas, electrochemical impedance analyses confirmed the low charge transfer resistance of all metal sulfide counter electrodes when compared to the Pt counter electrode, indicating their potential to be used as electrode materials. The efficiency of metal sulfide counter electrodes was tested in quantum dot sensitized solar cells (QDSSC) by applying the metal sulfide paint on fluorine doped tin oxide (FTO) plates. Current-voltage characteristics ratified the solar conversion efficiencies of 0.85, 1.3, 0.91 and 0.25, respectively for PbS (2), CuS (3), CoS (2) and Pt counter electrodes with CdS/TiO2 (1:1) working electrode and Na2S electrolyte. Thus the present study furnishes a novel method for the synthesis of metal sulfides as efficient paintable counter electrodes that can overcome Pt as counter electrode in QDSSC

One pot synthesis of CdS/TiO2 hetero-nanostructures for enhanced H2 production from water and removal of pollutants from aqueous streams

To achieve more effective coupling of cadmium sulfide (CdS) to the TiO2, single step synthesis of CdS/TiO2 composites is advantageous. In the present study a novel one pot synthesis of several CdS/TiO2 hetero-nanostructures was explored through combustion technique. As the process involves the simultaneous nucleation of CdS and TiO2 it leads to the proper connectivity between the constituent materials. All the catalysts were characterized by using several techniques and the excellent visible light activity of the composites has been asserted by the H2 production from water containing sacrificial reagents, removal of methylene blue and Cr(VI) from aqueous streams. Therefore the present synthetic strategy which is devoid of using molecular linker at interface is more suitable for solar applications, which require faster rates of electron transfer at the hetero junction

Novel synthesis of C, N doped rice grain shaped ZnS nanomaterials – towards enhanced visible light photocatalytic activity for aqueous pollutant removal and H2 production

Novel single step syntheses of visible active C, N doped zinc sulfide (ZnS) photocatalysts with rice grain morphology have been achieved without using expensive surfactants, capping agents and inert atmospheric conditions by using solution combustion synthesis in an energy and time efficient manner. Several ZnS samples such as ZnS (1 : 2), ZnS (1 : 3), ZnS (1 : 4), ZnS (1 : 5) and ZnS (1 : 6) have been synthesized by varying the metal and sulfur precursor ratio in order to obtain ZnS with desirable characteristics for visible light activity. X-ray diffraction indicated the nanocrystalline size and hexagonal ZnS phase, whereas, transmission electron microscopy confirmed the nanocrystalline size and also revealed the rice grain morphology for ZnS (1 : 5). Diffuse reflectance UV-Vis spectra indicated a red shift in the absorption maxima, possibly due to the decreasing band gap by C, N-doping, which was further confirmed by the elemental analysis and X-ray photoelectron spectroscopy. The visible light photocatalytic activity of the ZnS nanomaterials was assessed by high H2 production (up to 10 000 μmol h−1 g−1 for ZnS (1 : 5)) by water splitting in the presence of Na2S and Na2SO3 sacrificial reagents, whereas, the simultaneous oxidation of MB and reduction of Cr(VI) under natural sunlight complemented the activity of ZnS

Synthesis of CdS/CeO 2 nanomaterials for photocatalytic H 2 production and simultaneous removal of phenol and Cr(VI)

Harvesting visible light of the solar spectrum by coupled semiconductor based systems is advantageous for photocatalytic as well as photovoltaic applications. One pot synthesis of several CdS/CeO2 nanomaterials has been carried out without using expensive surfactants, capping agents and molecular linkers. Various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV–vis spectroscopy, Raman spectroscopy and BET surface area were used to characterize the samples. XRD and Raman spectroscopic data provided the information about the presence of both CdS and CeO2 phases. TEM proves the proper dispersion and well connectivity between the CdS and CeO2 which may be due to the single step synthesis of the composites. UV–vis spectroscopy reveals the absorption in both UV and visible regions due to the presence of both CeO2 and CdS. The visible light activity of the composites have been ascribed by the H2 production from water by using sacrificial reagents, simultaneous removal of phenol and Cr(VI) from aqueous streams. Among the synthesized composites CdS/CeO2 (1:1) has shown superior activity which can be attributed to the optimum sensitization of CeO2 which induces enhanced electron transfer from CdS to CeO2 that decreases the exciton recombination

C And N Doped Nano-Sized Tio2 for Visible Light Photocatalytic Degradation of Aqueous Pollutants

A facile large scale synthesis of high surface area anatase TiO2 nano material has been carried out by using the solution combustion synthesis with very widely available urea as fuel. The as-obtained puffy powder of anatase TiO2 was characterised by X-ray diffraction (XRD), Brunauer–Emmett–Teller surface area analysis, ultraviolet–visible (UV–vis) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques in order to analyse the structural, optical and surface properties of the synthesised material. Diffuse UV–vis spectroscopic data show a red shift in absorption spectra which may be attributed to the possible energy levels added in between the band edges of TiO2 due to the C and N doping as confirmed by XPS. Photocatalytic activity of the catalyst was assessed by the photocatalytic degradation of methyl orange under visible light irradiation. The effect of an electron acceptor in order to maximise the electron trapping for further inhibiting exciton recombination and thereby enhancing the oxidation of dyes has also been studied by using peroxomono sulphate(PMS) as the electron accepto

Novel one pot stoichiometric synthesis of nickel sulfide nanomaterials as counter electrodes for QDSSCs

Solution combustion synthesis has been used for the first time to synthesize metal sulfide nanomaterials. Selective stoichiometric synthesis of nickel sulfide nanomaterials was achieved in a single step by using combustion synthesis under ambient conditions and the samples were tested as counter electrodes in a typical quantum dot sensitized solar cell (QDSSC). By varying the oxidant/fuel ratio, different stoichiometric nickel sulfide nanomaterials were obtained. Interestingly, a maximum of fourfold increase in efficiency (1.1%) was achieved with nickel sulfide counter electrode when compared to the Pt counter electrode (0.25%). This can be attributed to the less charge transfer resistance offered by nickel sulfide samples compared to Pt, which was confirmed by electrochemical impedance spectroscopy. Among different stoichiometric compositions of nickel sulfide, Ni3S2 was found to exhibit the least charge transfer resistance and superior solar cell efficiency. The present study describes a novel selective stoichiometric synthetic approach and facile fabrication procedure for low cost counter electrode materials in QDSSCs