Himmat Singh Kushwaha

Efficient Solar Energy Conversion Using CaCu3Ti4O12 Photoanode for Photocatalysis and Photoelectrocatalysis

A highly efficient third generation catalyst, CaCu3Ti4O12 (CCTO) shows excellent photoelectrochemical (PEC) and photocatalytic ability. As only 4% part of the solar spectrum covers UV light, thus it is highly desirable to develop visible light active photocatalyst materials like CCTO for effective solar energy conversion. A direct band transition with a narrow band gap (1.5 eV) was observed. Under light irradiation, high photocurrent density was found to be 0.96 mA/cm2, indicating the visible light induced photocatalytic ability of CCTO. Visible light mediated photocatalytic and photoelectrocatalytic degradation efficiency of CaCu3Ti4O12 pellets (CCTO) was investigated for three classes of pharmaceutical waste: erythrosin (dye), ciprofloxacin (antibiotic) and estriol (steroid). It is found that the degradation process follows first order kinetic reaction in electrocatalysis, photocatalysis and photoelectrocatalysis and high kinetic rate constant was observed in photoelectrocatalysis. This was quite high in comparison to previously reported methods.

Efficient Electron Transfer across ZnO-MoS2-RGO Heterojunction for Remarkably Enhanced Sunlight Driven Photocatalytic Hydrogen Evolution

The development of noble metal-free catalysts for hydrogen evolution is required for energy applications. In this regard, ternary heterojunction nanocomposites consisting of ZnO nanoparticles anchored on MoS2 -RGO (RGO=reduced graphene oxide) nanosheets as heterogeneous catalysts show highly efficient photocatalytic H2 evolution. In the photocatalytic process, the catalyst dispersed in an electrolytic solution (S2- and SO32- ions) exhibits an enhanced rate of H2 evolution, and optimization experiments reveal that ZnO with 4.0 wt % of MoS2 -RGO nanosheets gives the highest photocatalytic H2 production of 28.616 mmol h-1  gcat-1 under sunlight irradiation; approximately 56 times higher than that on bare ZnO and several times higher than those of other ternary photocatalysts. The superior catalytic activity can be attributed to the in situ generation of ZnS, which leads to improved interfacial charge transfer to the MoS2 cocatalyst and RGO, which has plenty of active sites available for photocatalytic reactions. Recycling experiments also proved the stability of the optimized photocatalyst. In addition, the ternary nanocomposite displayed multifunctional properties for hydrogen evolution activity under electrocatalytic and photoelectrocatalytic conditions owing to the high electrode-electrolyte contact area. Thus, the present work provides very useful insights for the development of inexpensive, multifunctional catalysts without noble metal loading to achieve a high rate of H2 generation.

Polyaniline/CaCu3Ti4O12 nanofiber composite with a synergistic effect on visible light photocatalysis

CaCu3Ti4O12 (CCTO)–polyaniline (PANI) nanofiber composites with different ratios of PANI/CCTO were successfully prepared by in situ polymerization and were shown to be active photocatalysts under irradiation with visible light. The as-synthesized samples were characterized by XRD, SEM, TEM, FTIR, UV-visible spectrophotometry and TGA/DSC. Significant adsorption was observed for anionic dyes because the negatively charged groups or the electron-rich groups of these dyes interacted chemically with the positively charged backbone of PANI. Photocatalytic experiments showed that PANI/CCTO nanofibers with a weight ratio of 7 : 3 showed the highest photocatalytic activity for the degradation of Congo red and methyl orange under visible light irradiation. The synergistic effect in the PANI/CCTO nanofiber composites results in a reduction of the photoinduced electron–hole recombination rate, giving a high photocatalytic activity for the degradation of the dyes under visible light irradiation. The intense photocatalytic activity can be attributed to the photogenerated electrons in PANI, which can directly transfer to the LUMO of CCTO, and the photogenerated holes in the HOMO of CCTO, which can migrate to the valance band of PANI, efficiently inhibiting direct recombination of the charge carriers.

Enormous energy harvesting and storage potential in multiferroic epitaxial thin film hetrostructures: an unforeseen era

This work propounds the competence of epitaxial multiferroic thin-film heterostructures for low-grade thermal energy harvesting using Olsen cycle and ultra-high density capacitor applications. Our investigation (based on well-reported experiments in the literature) reveals that this class of materials shows a giant energy storage density as well as colossal energy harnessing possibilities. Indeed, the energy storage capability of these films is found to be 1.6 times the already existing giant value (alkali free glasses: 35 MJ m−3). On the other hand, the energy harnessing plausibility is found to be four orders of magnitude higher than the reported values to date.

Enhanced electrocatalytic performance of perovskite supported iron oxide nanoparticles for oxygen reduction reaction

Perovskite oxide based materials have drawn considerable amount of attention as non-precious, non-noble cathode catalysts in oxygen reduction reactions for fuel cell and battery applications. High efficiency of perovskite catalysts often suffers due to instability and poor conductivity issues. Thus, the integration of these perovskite materials with other active catalysts is be of great interest. In this article, a series of new nanocomposites of perovskite–iron oxide with different molar ratios has been developed by hydrothermal method. We have shown that double perovskite calcium copper titanate CaCu3Ti4O12 (CCTO) supported iron oxide (Fe2O3) catalysts exhibit excellent activity as cathode catalyst for oxygen reduction reactions in fuel cells. Three different composites of CaCu3Ti4O12 (CCTO) with Fe2O3 were prepared and the composites were analysed by various structural and microstructural characterization methods, such as XRD and FESEM. Microstructural investigations revealed cubic shaped iron oxide nanoparticles decorated over CCTO particles. Electrochemical analysis showed that the performance of composites improved drastically with increase in the amount of CCTO. Kinetic studies by rotating ring disc electrode method revealed that the composites exhibit four electron pathway for oxygen reduction reaction and generate hydrogen peroxide as an intermediate. This work demonstrates a new type of efficient metal oxide–perovskite composite for oxygen redution catalysis.

Label free selective detection of estriol using graphene oxide-based fluorescence sensor

Water-soluble and fluorescent Graphene oxide (GO) is biocompatible, easy, and economical to synthesize. Interestingly, GO is also capable of quenching fluorescence. On the basis of its fluorescence and quenching abilities, GO has been reported to serve as an energy acceptor in a fluorescence resonance energy transfer (FRET) sensor. GO-based FRET biosensors have been widely reported for sensing of proteins, nucleic acid, ATP (Adenosine triphosphate), etc. GO complexes with fluorescent dyes and enzymes have been used to sense metal ions. Graphene derivatives have been used for sensing endocrine-disrupting chemicals like bisphenols and chlorophenols with high sensitivity and good reproducibility. On this basis, a novel GO based fluorescent sensor has been successfully designed to detect estriol with remarkable selectivity and sensitivity. Estriol is one of the three estrogens in women and is considered to be medically important. Estriol content of maternal urine or plasma acts as an important screening marke...

Effect of Sr2TiMnO6 fillers on mechanical, dielectric and thermal behaviour of PMMA polymer

Composites of poly(methyl methacrylate) (PMMA) and Sr2TiMnO6 (STMO) were fabricated via melt mixing followed by hot pressing technique. These were characterized using X-ray diffraction (XRD), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), thermo mechanical analysis (TMA) and impedance analyser for their structural, thermal and dielectric properties. The coefficient of thermal expansion (CTE) was measured between 40°C and 100°C for pure PMMA is 115.2 ppm/°C, which was decreased to 78.58 ppm/°C when the STMO content was increased to 50 wt.% in PMMA. There was no difference in the glass transition (Tg) temperature of the PMMA polymer and their composites. However, the FTIR analysis indicated possible interaction between the PMMA and STMO. The density and the hardness were increased as the STMO content increased in the PMMA matrix. Permittivity was found to be as high as 30.9 at 100 Hz for the PMMA+STMO-50 wt.% composites, indicating the possibility of using these materials for capacitor applications. The thermal stability of polymer was enhanced by incorporation of STMO fillers.

Highly efficient visible light mediated azo dye degradation through barium titanate decorated reduced graphene oxide sheets

This study investigates BaTiO3 decorated reduced graphene oxide sheets as a potential visible light active catalyst for dye degradation (Rhodamine B). The composites were prepared through conventional hydrothermal synthesis technique using hydrazine as a reducing agent. A number of techniques have been employed to affirm the morphology, composition and photocatalytic properties of the composites; these include UV-visible spectrophotoscopy that assisted in quantifying the concentration difference of Rhodamine B. The phase homogeneity of the composites was examined through x-ray powder diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) was employed to confirm the orientation of the BaTiO3 particles over the reduced graphene oxide sheets. Photoluminescence (PL) emission spectra assisted in determining the surface structure and excited state of the catalyst. Fourier transformed-infrared (FTIR) spectra investigated the vibrations and adsorption peak of the composites, thereby ascertaining the formation of reduced graphene oxide. In addition, diffuse reflectance spectroscopy (DRS) demonstrated an enhanced absorption in the visible region. The experimental investigations revealed that graphene oxide acted as charge collector and simultaneously facilitated surface adsorption and photo-sensitization. It could be deduced that BaTiO3-reduced graphene oxide composites are of significant interest the field of water purification through solar photocatalysis.

Giant energy harvesting potential in (100)-oriented 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 with Pb(Zr0.3Ti0.7)O3/PbOx buffer layer and (001)-oriented 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 thin films

This work emphasis on the competence of (100)-oriented PMN–PT buffer layered (0.68PbMg1/3Nb2/3O3–0.32PbTiO3 with Pb(Zr0.3Ti0.7)O3/PbOx buffer layer) and (001)-oriented PMN–PT (0.67PbMg1/3Nb2/3O3–0.33PbTiO3) for low grade thermal energy harvesting using Olsen cycle. Our analysis (based on well-reported experiments in literature) reveals that these films show colossal energy harnessing possibility. Both the films are found to have maximum harnessable energy densities (PMN–PT buffer layered: 8 MJ/m3; PMN–PT: 6.5 MJ/m3) in identical ambient conditions of 30–150°C and 0–600 kV/cm. This energy harnessing plausibility is found to be nearly five times higher than the previously reported values to date.

Visible light driven multifunctional photocatalysis in TeO 2 -based semiconductor glass ceramics

Abstract. Photocatalytic xCaCu3Ti4O12−(100−x)TeO2 (x=0.25  mol% to 3 mol%), glass nanocomposites were fabricated and investigated for wastewater treatment, self-cleaning surfaces, and photocatalytic hydrogen evolution. Visible light active crystals of Cu-doped TiO2 and TiTe3O8 were grown by optimized crystallization of as-quenched glasses. The visible light photocatalytic activity of glass samples was investigated for estrogenic pharmaceutical pollutants, and the degradation rate was obtained as 168.56  min−1 m−2. A higher photocatalytic H2 production rate was observed (135  μmole h−1 g−1) for the crystallized CaCu3Ti4O12-TeO2 (x=3. 0) glass plate under visible light. The self-cleaning performance was observed using contact angle measurements for water under dark and light conditions. These visible light active glass ceramics are a cost effective sustainable solution for water treatment and self-cleaning applications.