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Kumar D.P.,Yogi Vemana University | Reddy N.L.,Yogi Vemana University | Karthik M.,Energy Cooperative Research Center | Neppolian B.,SRM University | And 2 more authors.
Solar Energy Materials and Solar Cells | Year: 2016

Solar light harvesting nano-heterojunction p-Ag2O/n-TiO2 nanotube catalysts were successfully synthesized by a combination of hydrothermal and wet impregnation methods. The crystal structure and surface morphology analysis revealed that n-TiO2 composed of biphasic anatase-rutile with nano-tubular morphology. The X-ray photoelectron spectrum confirmed the presence of Ti4+ and Ag+ in the form of TiO2 and Ag2O, the results are in good agreement with TEM images. Moreover, DRS UV-Vis spectra and photocurrent density measurements indicated that Ag2O/TiO2 nanotubes have shown strong absorption in visible region and improved current production that indicates the hetero-junction properties. The Ag2O loaded (0.5-2.0 wt%) TiO2 nanotubes showed 26 folds enhanced photocatalytic hydrogen (H2) production in glycerol/water mixture than the standard TiO2 P-25 under solar light irradiation. Interestingly, the catalytic recyclability tests carried out in pure water and glycerol/water mixture exhibited similar rate of H2 production without significant loss in catalytic activity. Furthermore, the photocatalytic activity conducted in summer season exhibited higher rate of H2 production than the experiments conducted during winter season owing to the variation in solar flux. The high rate of H2 production can be attributed to the synergistic functions of 1-D nano-tubular morphology, hetero-junction formed between biphasic TiO2 photocatalyst and visible light active Ag2O as sensitizer. Based on the experimental results, a possible electron-hole transfer mechanism was also proposed. © 2016 Elsevier B.V. All rights reserved.

Mahalingam P.,Arignar Anna Government Arts College | Sivakumar N.,Chikkanna Government Arts College | Karthik M.,Energy Cooperative Research Center | Karthikeyan S.,Chikkanna Government Arts College
Asian Journal of Chemistry | Year: 2014

Magnetic metals Fe-Co encapsulated in multi-walled carbon nanotubes, were prepared by spray pyrolysis of methyl ester of Pongamia pinnata oil, a renewable carbon precursor, over Fe-Co catalyst supported on silica. Carbon nanostructures with different morphologies were obtained over Fe-Co catalyst supported on silica, with 20 mL/h feed rate of precursor at different temperatures (550, 650 and 750 °C). The products were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, thermogravimetry and vibrating sample magnetometer. The Fe-Co encapsulated in multi-walled carbon nanotubes was used as adsorbent for removal of As(V) ions from aqueous solution. Sorption experiments were conducted using batch system. The effect of pH on As(V) ions adsorption on the adsorbent, effect of initial As(V) ions concentration on adsorption by adsorbent and effect of temperature on As(V) ions removal were studied. The kinetics of As(V) ions adsorption on Fe-Co encapsulated in multi-walled carbon nanotubes was discussed.

Praveen Kumar D.,Yogi Vemana University | Lakshmana Reddy N.,Yogi Vemana University | Srinivas B.,Indian Institute of Chemical Technology | Durgakumari V.,Indian Institute of Chemical Technology | And 6 more authors.
Solar Energy Materials and Solar Cells | Year: 2016

The nanostructured TiO2 materials impregnated with Cu were prepared via a simple and eco-friendly preparation route. The materials are comprised of nano -tubes, -rods and -particles whose surfaces are modified by a fine dispersion of CuxO clusters (Cuo and Cu2O) as evidenced by TEM and XPS analysis. Structural and optical characterization ascertained the biphasic (anatase-rutile) crystal structure of TiO2 nano-objects. The presence of CuxO at the surface extends the absorption from the UV to the visible light range. In contrast to the pristine and calcined TiO2 nanotubes (TNT), the CuxO/TiO2 nanostructures (Cu1.5TNT) exhibit a prolonged life-time of photogenerated charge carriers and decreased surface area as confirmed by the photoluminescence spectra and surface area analysis, respectively. The prepared photocatalysts were tested for hydrogen (H2) production activity using water, mono and di-hydroxylic alcohols solutions under solar light irradiation. Surprisingly, Cu-modified TiO2 nanostructures (Cu1.5TNT) have shown an unusually high rate of H2 production of about 114.9±2 mmol h- 1 g-1 cat under a set of optimized experimental conditions. Among all of the studied photocatalysts, the Cu1.5TNT catalyst exhibits enhancements of 33 and 18 fold in the H2 production rate as compared to the commercial TiO2 nanoparticles (TNP) and calcined TNT, respectively. We report here on the highest known rate of H2 production using the nanostructured Cu-doped TiO2 photocatalyst (Cu1.5TNT) under solar light irradiation. This unprecedented H2 production is attributed to synergistic effects of nanocrystalline structures, morphology and copper oxide species (Cuo and Cu2O) present in the photocatalyst. © 2015 Elsevier B.V. All rights reserved.

Praveen Kumar D.,Yogi Vemana University | Lakshmana Reddy N.,Yogi Vemana University | Mamatha Kumari M.,Yogi Vemana University | Srinivas B.,Indian Institute of Chemical Technology | And 8 more authors.
Solar Energy Materials and Solar Cells | Year: 2015

Hydrogen trititanate (H2Ti3O7) nanorods were synthesized by using a hydrothermal method. The transformation of the crystal structure from H2Ti3O7 to TiO2 occurred into either single crystalline TiO2 (B) [calcined at 400 or 450 °C] or bicrystalline TiO2 (B) with anatase phases [calcined at 500 or 550°C] during a calcination process. Calcination temperature from 450 to 550°C induced both phase transformation and formation of large size nanocavities, and the changes in the nanorods morphology were confirmed using HRTEM/TEM images. Nanocomposites of Cu2O/TiO2 nanorods with different copper loading (CuxTNR) were prepared by using the wet impregnation method with TiO2 nanorods [calcined at 500°C] and copper nitrate as copper source. The structural, optical, surface elemental and morphological properties of the synthesized catalysts were extensively characterized. Solar photocatalytic hydrogen (H2) production experiment was carried out with aqueous-glycerol solution for 4 h. The photocatalytic activity of TiO2 nanorods that are calcined at 500°C exhibited very high rate of H2 production, is ascribed to the improved separation of electron/hole pairs and catalytic activity at bicrystalline TiO2 surface. For the first-time, we have achieved the higher rate of H2 (50,339 μmol h-1 g-1 cat) production under the set of the optimized conditions using Cu1.5TNR nanorods containing nanocavities as catalyst under solar irradiation. This enhancement in the activity can be attributed to the desirable absorption of UV-visible light in natural solar spectrum and minimization of the recombination of electron-hole pairs, multiple internal reflection of light within nanocavities, which improved the surface-interface reactions. The present study clearly demonstrated that Cu loaded on titania nanorods containing nanocavities were found to be more efficient and promising photocatalyst for H2 production under solar light irradiation. © 2015 Elsevier B.V. All rights reserved.

Calvet N.J.,French National Center for Scientific Research | Calvet N.J.,Energy Cooperative Research Center | Calvet N.J.,National Renewable Energy Laboratory | Py X.,French National Center for Scientific Research | And 11 more authors.
ACS National Meeting Book of Abstracts | Year: 2011

The PROMES-CNRS laboratory located in south of France proposed a new sustainable approach for Thermal Energy Storage materials to be used in Concentrated Solar Power Plants: the use of industrial waste treated at high temperature for sustainable energy storage. During the 20 th century 174 million tons of asbestos were used worldwide, principally for building insulation. In 1993 essentially all countries in the world forbid the use of asbestos because of its health hazards. These Asbestos Containing Wastes can be treated at high temperature (1400°C) by plasma torch to produce a totally inert ceramic called COFALIT®, commercially. This first good candidate is available in huge quantity, is very inexpensive (11 dollars/ton) and stable up to 1000°C. This paper presents the thermo-physical characterization of this material and the comparison with other available materials as molten salts, castable ceramics and high temperature concrete.

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