Browsing by Author "Pradhan, A. C."

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    Electrospun mesoporous composite CuO−Co3O4/N‐ TiO2 nanofibers as efficient visible light photocatalysts
    (Wiley-Blackwell, 2017-08) Pradhan, A. C.; Senthamizhan A.; Uyar, Tamer
    One-dimensional mesoporous composite CuO−Co3O4 /N-TiO2 nanofibers (CuCoNT NFs) have been fabricated by in situ sol−gel electrospinning technique. In our approach, both polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) are used as dual polymeric carrier matrix for the fabrication of electrospun CuCoNT NFs. PVP chains assist the electrospinning of the uniform composite nanofibers whereas PEG is responsible for mesoporosity which is confirmed by N2 sorption analyses. Along with CuCoNT NFs, other nanofiber samples (TiO2 NFs, N-TiO2 NFs, CuO/N-TiO2 NFs, Co3O4/N-TiO2 NFs) have also been fabricated for comparative studies. The morphology and composition of the NFs have been confirmed by the HR-TEM and XPS analyses. The red shifting of band gap energy from anatase TiO2 NFs to composite CuCoNT NFs (1.57 eV) is suggesting formation of visible light response. Oxygen vacancies in CuCoNT NFs, leads to lowering the e− − h+ recombination. The lowering of photoluminescence spectrum and high photocurrent response in CuCoNT NFs makes CuO as low cost cocatalyst. The composite CuCoNT NFs is treated as an efficient photocatalyst for swift degradation of mixed dyes in visible light, an exemplary move. Exactly, 100% mixed dyes (30 mg/L) degradation is achieved at pH 10 in just 60 minutes.
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    Fabrication of mesoporous CuO/ZrO2-MCM-41 nanocomposites for photocatalytic reduction of Cr(VI)
    (Elsevier, 2017) Nanda, B.; Pradhan, A. C.; Parida, K. M.
    Mesoporous nanocomposites of CuO/ZrO2–MCM-41 (CuO@ZM-41) was designed by incorporating mesoporous ZrO2 (Z) into the high surface area MCM-41 (M-41) framework followed by loading CuO by wetness impregnation method keeping Si/Zr ratio 10. The nanocomposites were studied under PXRD, N2 sorption, DRS spectra, FTIR, XPS, NMR, HRTEM and PL to evaluate structural, morphological, optical properties and also the mesoporosity nature of the samples. The photo-reduction of Cr6+ was performed over CuO@ZM-41 by varying pH, substrate concentration, and irradiation time and catalyst dose. Among all the catalysts, 2 CuO@ZM-41 was found to be efficient photocatalyst for the photo-reduction of Cr6+. Nearly 100% reduction of Cr6+ has been achieved by 2 CuO@ZM-41 within 30 min. Intra-particle mesoporosity, high surface area, presence of CuO nanorods and electron transfer properties are the key factors for enhancing the photo-reduction activity of 2CuO@ZM-41.
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    Morphological control of mesoporosity and nanoparticles within Co3O4-CuO electrospun nanofibers: quantum confinement and visible light photocatalysis performance
    (American Chemical Society, 2017-09) Pradhan, A. C.; Uyar, Tamer
    The one-dimensional (1D) mesoporous and interconnected nanoparticles (NPs) enriched composite Co3O4-CuO nanofibers (NFs) in the ratio Co:Cu = 1/4 (Co3O4-CuO NFs) composite have been synthesized by electrospinning and calcination of mixed polymeric template. Not merely the mesoporous composite Co3O4-CuO NFs but also single mesoporous Co3O4 NFs and CuO NFs have been produced for comparison. The choice of mixed polymer templates such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) for electrospinning is responsible for the formation of 1D mesoporous NFs. The HR-TEM result showed evolution of interconnected nanoparticles (NPs) and creation of mesoporosity in all electrospun NFs. The quantum confinement is due to NPs within NFs and has been proved by the surface-enhanced Raman scattering (SERS) study and the UV-vis-NRI diffuse reflectance spectra (DRS). The high intense photoluminescence (PL) spectra showing blue shift of all NFs also confirmed the quantum confinement phenomena. The lowering of PL spectrum after mixing of CuO in Co3O4 nanofibers framework (Co3O4-CuO NFs) proved CuO as an efficient visible light response low cost cocatalyst/charge separator. The red shifting of the band gap in composite Co3O4-CuO NFs is due to the internal charge transfer between Co2+ to Co3+ and Cu2+, proved by UV-vis absorption spectroscopy. Creation of oxygen vacancies by mixing of CuO and Co3O4 also prevents the electron-hole recombination and enhances the photocatalytic activity in composite Co3O4-CuO NFs. The photocurrent density, Mott-Schottky (MS), and electrochemical impedance spectroscopy (EIS) studies of all NFs favor the high photocatalytic performance. The mesoporous composite Co3O4-CuO NFs exhibits high photocatalytic activity toward phenolic compounds degradation as compared to the other two NFs (Co3O4 NFs and CuO NFs). The kinetic study of phenolic compounds followed first order rate equation. The high photocatalytic activity of composite Co3O4-CuO NFs is attributed to the formation of mesoporosity and interconnected NPs within NFs framework, quantum confinement, extended light absorption property, internal charge transfer, and effective photogenerated charge separations.
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    Topotactic transformation of solvated MgCr-LDH nanosheets to highly efficient porous MgO/MgCr2O4 nanocomposite for photocatalytic H2 evolution
    (American Chemical Society, 2018) Nayak, S.; Pradhan, A. C.; Parida, K. M.
    The hybrid structure of nanoparticles (NPs) with nanosheets has the advantage of both anisotropic properties of NPs and large specific surface areas of nanosheets, which is desirable for many technological applications. In this study, MgCr2O4 spinel NPs decorated on highly porous MgO nanosheets forming MgO/MgCr2O4(x) nanocomposites were synthesized by a one pot coprecipitation method followed by a heat treatment process of the solvated wet gel of MgCr-LDH with polar solvent N,N-dimethylformamide (DMF) at 400 °C. This novel synthetic methodology generates materials consisting of porous metal oxides nanosheets adhered with spinel phase NPs due to the slow generation of gases such as H2O, CO2, and NH3 under moderate temperature during the heat treatment process. The synergistic effect of much wider band gap MgO nanosheets and narrow band gap MgCr2O4 NPs added increased stability due to the stronger bonding coordination of MgCr2O4 NPs with MgO nanosheets. The obtained MgO/MgCr2O4(x) nanocomposites possess large specific surface areas, highly porous structure, and excellent interface between MgCr2O4 NPs and MgO nanosheets, which proved from N2 sorption isotherm, TEM, HR-TEM study. With metallic ratio of MgCr3:1, MgO/MgCr2O4(MgCr3:1) nanocomposites exhibit highest H2 evolution rate of 840 μmolg-12h-1, which was 2 times higher than that of pure MgCr2O4(420 μmolg-12h-1). The LSV measurement study of MgO/MgCr2O4 (MgCr3:1) nanocomposite shows an enhancement of light current density of 0.22 μA/cm2 at potential bias of -1.1 V. The Mott-Schottky analysis suggested the band edge positions of the n-type constituents and formation of n-n type heterojunctions in MgO/MgCr2O4 (MgCr3:1) nanocomposite, which facilitates the flow of charge carriers. The EIS and Bode phase plot of MgO/MgCr2O4 (MgCr3:1) nanocomposite signifies the lower interfacial charge transfer resistance and higher lifetime of electrons (2.7 ms) for enhanced H2 production. Lastly, the enhanced photocatalytic H2 production activity and long-term stability of MgO/MgCr2O4(MgCr3:1) could be attributed to maximum specific surface area, porous structure, close intimacy contact angle between two cubic phases of MgCr2O4 NPs and MgO nanosheets, abundant oxygen vacancies sites, reduced charge transfer resistance and suitable band edge potential to drive the thermodynamic energy for H2 production. This work highlighted an effective strategy for the synthesis of cost-effective 2D porous heterojunctions nanocomposite photocatalyst for promising applications in the field of clean H2 production utilizing abundant solar energy. Copyright