Synthesis of Oxides/ Chalcogenides nanocomposites and Their Application Related to Environment and Energy

Abstract

Designing a suitable photocatalyst which solve both the issues (energy and environment) always remains a challenge. Energy savings and greenhouse-effect mitigation are embryonic due to the limited fossil fuel resources and increasingly stringent requirement for the environmental protection from major greenhouse gases, including carbon dioxide (CO2), The development of an “artificial photosynthetic system” (APS) having both the analogous important structural elements and reaction features of photosynthesis to achieve solar-driven water splitting and CO2 reduction is highly challenging. Here, the visible-light (≥ 420 nm) photoconversion of CO2methane (CH4) and methanol (CH3OH) over CeO2 nanoparticles, Bi2S3 and CdV2O6 nanorods, hollow and mesoporous CdS microspheres, and their nanocomposites (Bi2S3/CeO2 nanocomposites, CdS/CeO2 core shell nanocomposites and CdS- CdV2O6 common cation heterostructure) is reported. Methane and Methanol can further be used as the fuel. It has been demonstrated that owing to the sufficiently negative conduction band (CB) potential of Chalcogenides (Bi2S3 ~ −0.58 V and CdS ~ -0.80V against standard hydrogen electrode (SHE)), Bi2S3 and CdS based photocatalysts can be utilized as efficient APS for the photoreduction of CO2 into CH4 and CH3OH under visible-light irradiation. The as-synthesized photocatalysts have further been characterized through different techniques. The phase, crystal structure, morphology, composition, optical/photoluminescence property and alignment of energy levels of the as-synthesized Chalcogenide based photocatalysts have been thoroughly studied by different techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption BET, ultraviolet-visible-near infrared diffuse reflectance spectroscopy (UV-Vis-NIR) and Photoluminescence (PL) spectroscopy. The efficiency of the synthesized photocatalysts has been analysed by their application for the reduction of CO2 under visible light in the presence of H2O. Combination of visible light active Bi2S3 and CdS with different metal oxide semiconductors (i.e., CeO2 and CdV2O6) owing to the formation of interface between p-type Chalcogenides and n-type oxides, visibly increases the production of solar fuelsby efficiently promoting the electron transfer from the CB of Chalcogenides (Bi2S3 and CdS) to that of metal oxides (CeO2 and CdV2O6) under visible-light irradiation. As a class of advanced composite material, core/shell structures exhibit unique chemical composition and electro chemical properties. These properties are quite promising not only fundamental but also from the technological point of view as well and improve the interfacial charge transfer process. The high yield of solar fuel (CH4 and CH3OH) is observed in case of CdS/CeO2 coreshell due to formation of close contact in coreshell like morphology.Such composite have hollow structured microspheres coreof CdS with mesoporouschannels that can facilitate efficient adsorption and activation of CO2 for successive photoconversion into CH4 and CH3OH. In addition, the CdS-CdV2O6 hybrid microstructures synthesised by limited chemical conversion rout, CdS acts more like a sensitizer as in dye-sensitized solar cells, and remarkably improves the rate of CH4 production, which is ascribed to the modification of CdS over the CdV2O6 superstructure. Better photocatalytic activity of flower like CdS-CdV2O6 common cationheterostructure than that of single photocatalyst nanocrystals, and other composites isalso attributed to suitable band alignment and common ion which suppresses the electron-hole recombination Moreover, Stability of photocatalyst is also very important along with the photocatalytic efficiency for practical application. The XRD and SEM are recorded after photoreduction and photocatalyst applied for several runs to check the stability of photocatalyst. As synthesized composites show better stability than that of single Chalcogenides. Based on the evidences from the above experiments, chalcogenide/metal oxide composites seem to be promising for the visible-light induced photocatalytic conversion of CO2 into solar fuels.