A. Chandra Bose

Flower-like hierarchical h-MoO3: new findings of efficient visible light driven nano photocatalyst for methylene blue degradation

Hexagonal molybdenum oxide (h-MoO3) nanocrystals with a flower-like hierarchical structure have been successfully synthesized by a solution based self assembly route. The as-synthesized h-MoO3 was recognized as a photocatalyst for the photocatalytic degradation of methylene blue (MB) under various experimental conditions. Initially, the as-synthesized h-MoO3 was characterized by different physico-chemical techniques in order to study and reveal the structural, functional, morphological, and optical properties. The results indicated that the photocatalyst has a hexagonal crystal structure with an average crystallite size of 46 nm. The morphology analysis has proved that the h-MoO3 comprises one dimensional (1D) rods with a hexagonal cross section. The possible formation mechanism is proposed as a self assembly process for nucleation and an Ostwald ripening mechanism for particle growth. The optical band gap investigation showed that the Eg value of h-MoO3 (2.94 eV) lies in the visible region and can be an appropriate candidate for visible light photocatalytic application. Furthermore, the experimental observations demonstrate an excellent photocatalytic performance of h-MoO3 in the degradation of MB under visible light irradiation.

Experimental Studies on Heat Transfer and Friction Factor Characteristics of Al2O3/Water Nanofluid in a Circular Pipe Under Transition Flow With Wire Coil Inserts

Heat transfer and friction factor characteristics in a circular tube fitted with wire coil inserts are investigated experimentally using Al2O3/water nanofluid as the working fluid. The effects of the pitch ratio and nanofluid on the Nusselt number and the friction factor are determined in a circular tube with fully developed transition flow for Reynolds number in the range of 2500 to 5000. The experiments were performed using wire coil inserts having different pitch ratios with Al2O3/water nanofluid having 0.1% volume concentration of nanoparticles as the working fluid. Experiments using the plain tube and with wire coil inserts were also carried out with distilled water as the working fluid for experimental setup validation and comparison. The experimental results reveal that the use of nanofluids increases the heat transfer rate with negligible increase in friction factor in the plain tube and the tube fitted with wire coil inserts. In addition, empirical correlations are proposed based on the experimental results of the present study, which are found to be sufficiently accurate for prediction of the heat transfer and friction factor characteristics.

Quantum confined CdS inclusion in graphene oxide for improved electrical conductivity and facile charge transfer in hetero-junction solar cell

We employed a simple mechanism in tuning the electrical conductivity of graphene oxide (GO) by the inclusion of nano cadmium sulphide (CdS) and thereby, utilized it in a pn hetero-junction based solar cell. Two different kinds of hetero-junction solar cell devices are fabricated; one with CdS acting as a separate buffer layer in GO and in another, the GO was functionalized with quantum confined CdS particles. In both kinds, the n-type junction was interfaced with the p-type semiconductor Rose Bengal (RB). The nano CdS has the ability to harvest a useful spectral range of the solar spectrum and to retard the recombination rate between the junction interfaces and hence, promote the facile charge carrier transport within the device. The CdS functionalized GO exhibited a remarkable short circuit current density (Jsc) of 4 mA cm−2, and an open circuit voltage (Voc) of 685 mV, giving rise to an enhanced power conversion efficiency (η) of 1.97% in comparison to the planar GO hetero-junction. The enhancement in power conversion efficiency and the influence of nano CdS inclusion is analyzed and interpreted on the basis of the electrical studies performed with cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS). From the electrical measurements, the charge storage capacitance of 138 F g−1 and the minimal resistance of 440 Ω are incurred in GO/CdS nanocomposites. The obtained results are further supported by the various physico-chemical characterizations such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), absorption and luminescence emission studies and demonstrate their significance in photovoltaic applications.

Role of synthesis variables on controlled nucleation and growth of hexagonal molybdenum oxide nanocrystals: investigation on thermal and optical properties

Solution based chemical precipitation route has been utilized for the controlled synthesis of novel and single phase three dimensional (3D) hierarchical flower-like microspheres of hexagonal molybdenum oxide (h-MoO3) nanocrystals. The nucleation, formation and the growth mechanism of h-MoO3 nanocrystals were examined as a function of synthesis variables such as the type of chemical oxidant, oxidant concentration, solvent medium, reaction time and reaction temperature. The growth mechanism was proposed and it involves four main consecutive stages: (1) homogeneous nucleation of h-MoO3via dissociation and association of precursors at a controlled reactant species, reactant concentration and solvent medium and (2) self-assembly process for the formation of anisotropic growth of hexagonal phase MoO3 nuclei (3) evaluation of 1D hexagonal rods through Ostwald ripening and (4) formation of 3D hierarchical flower-like microspheres via interparticle interaction with the assistance of reaction time and temperature. Among the various synthesis variables, the relative ratio of the oxidant to the chemical precursor (HNO3/AHM) and the nature of the solvent medium greatly influence the formation of h-MoO3 nanocrystals with a controlled morphology and reduced crystallite size. The results were supported with crystal phase analysis by X-ray diffraction (XRD), functional analysis by Fourier transform infrared spectroscopy (FT-IR), morphology and particle size analysis by scanning electron (SEM) and transmission electron microscopy (TEM). Further, the samples were characterized by thermogravimetric analysis (TGA) and diffuse reflectance spectroscopy (DRS) to analyze the thermal and optical properties. The results showed that the optical absorption of h-MoO3 nanocrystals were strongly dependent on the size and crystallinity. The as-synthesized h-MoO3 displayed an excellent visible light absorption. In addition, the reasons behind the bandgap tuning obtained under varying synthesis conditions were also discussed.

PVDF mixed matrix nano-filtration membranes integrated with 1D-PANI/TiO2 NFs for oil–water emulsion separation

The treatment of directly discharged oily waste water is difficult because of colloidal stability and the deformable nature of emulsified oil. In this work, one dimensional (1D) PANI/TiO2 nanofibers (NFs) were incorporated into polyvinylidene fluoride (PVDF) Mixed Matrix Membranes (MMMs) for the removal of oil and water droplets from oily waste water. The size of the 1D PANI/TiO2 (polyaniline/titanium dioxide) NFs ranged between 60 to 75 nm, as identified using transmission electron microscopy (TEM). Atomic force microscopy (AFM) analysis also revealed the significant decrease in the surface roughness of the membranes from 186 to 36 nm following the addition of 1D PANI/TiO2 NFs. Due to the hydrophilic property of the 1D PANI/TiO2 NFs, the contact angle, pure water flux and antifouling properties were increased for 1D PANI/TiO2 NF MMMs compared to the neat PVDF membrane. The pure water flux increased from 80 to 132 L m−2 h−1, which clearly indicates the impact of addition of the 1D PANI/TiO2 NFs. Among the MMMs, PT-4 exhibited the maximum oil rejection of 99% at a 5 bar operating pressure. Hence, the incorporation of PANI/TiO2 NFs in MMMs is proposed to enhance the oil rejection and fouling resistance of MMMs.

Impact of crystalline defects and size on X-ray line broadening: A phenomenological approach for tetragonal SnO2 nanocrystals

Nanocrystalline tin oxide (SnO2) powders with different grain size were prepared by chemical precipitation method. The reaction was carried out by varying the period of hydrolysis and the as-prepared samples were annealed at different temperatures. The samples were characterized using X-ray powder diffractometer and transmission electron microscopy. The microstrain and crystallite size were calculated for all the samples by using Williamson-Hall (W-H) models namely, isotropic strain model (ISM), anisotropic strain model (ASM) and uniform deformation energy density model (UDEDM). The morphology and particle size were determined using TEM micrographs. The directional dependant young’s modulus was modified as an equation relating elastic compliances (sij) and Miller indices of the lattice plane (hkl) for tetragonal crystal system and also the equation for elastic compliance in terms of stiffness constants was derived. The changes in crystallite size and microstrain due to lattice defects were observed while ...

BLUE EMISSION AND BANDGAP MODIFICATION IN N:ZnO NANORODS

Nanorods of nitrogen-doped ZnO(N:ZnO) are grown by hydrothermal chemical precipitation method. The average crystallite size, surface morphology, and particle size distribution are estimated and characterized from powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The characteristic vibration mode of metal-oxide is confirmed from Fourier transform infrared spectroscopy (FT-IR) study. The absorption spectra of N:ZnO in the ultraviolet visible (UV-vis) region and their variations are recorded as a function of dopant concentration. The Tauc plot elucidates that the bandgap of N:ZnO increases up to 6 atomic percent (at.%) of dopant concentration and then decreases for heavy doping. The widening and narrowing in bandgap is interpreted in terms of impurity induced absorption edge shift due to N doping. Photoluminescence (PL) spectra revealed the existence of visible band, arising from impurity related defects.

ESTIMATION OF LATTICE STRAIN, STRESS, ENERGY DENSITY AND CRYSTALLITE SIZE OF THE SPHERICAL YTTRIUM OXIDE NANOPARTICLES

Yttria nanoparticles are synthesized by co-precipitation method and as-prepared nanoparticles are annealed at various temperatures. The as-prepared and annealed particles are characterized by X-ray diffraction and transmission electron microscope (TEM). Here we estimated the lattice strain, crystallite size, deformation stress, and deformation energy density for annealed (800°C) yttrium oxide nanoparticles by Williamson-Hall-Isotropic Strain Model (W-H-ISM), W-H-Anisotropic Strain Model (W-H-ASM) and W-H-Energy Density Model (W-H-EDM) based on W-H plot from powder X-ray diffraction data. The shape and size of the nanoparticles are determined using TEM. The results of the estimated crystallite size of yttria nanoparticles by various methods agreed with the TEM results.

Dielectric relaxation behavior and electrical conduction mechanism in polymer-ceramic composites based on Sr modified Barium Zirconium Titanate ceramic

In this paper, we report the dielectric relaxation behavior and electrical conduction mechanism of Sr modified Barium Zirconium Titanate, (Ba1-xSrxZr0.1Ti0.9O3 (x = 0.1, 0.2, 0.3)) (BSZT) ceramic in the polyvinyl alcohol (PVA) matrix. The single phase BSZT ceramics are prepared by the conventional solid state route and are added to the polymer matrix at 25:75 volume percentage. Surface morphology of polymer ceramic composite identifies the uniform distribution of the ceramic particles in the polymer matrix. Dielectric and tangent loss spectrum of the composites indicates the distribution of relaxation time. Electric modulus analysis shows the relaxation peaks of bulk and interface properties, which follows the Arrhenius law. The ac conductivity spectrum of pure PVA obeys Jonchers power law and polymer composites obey the double power law which conduction mechanisms are explained by Jump Relaxation Model. The activation energy varies from the relaxation to conduction mechanism indicates that the different charge contributions are involved in both the processes.

Impedance and Electrical Modulus Study of Microwave-Sintered SrBi2Ta2O9 Ceramic

Bismuth layered structure SrBi2Ta2O9 ceramic is prepared by the microwave sintering technique via solid state route at 1100°C for 30 mins. X-ray diffraction analysis is used to analyze the phase purity, which identifies the orthorhombic structure with A21am space group. The fracture surface of the sintered pellet is visualized by scanning electron microscopy. Impedance spectroscopy is used to analyze the sample behavior as a function of frequency and temperature. Impedance and modulus study reveals the temperature-dependent non-Debye type relaxation phenomenon. The Nyquist plot shows a single arc representing the grain effect in the material, and the conductivity increases with increase in temperature. The Nyquist plot is fitted with an equivalent circuit, and the simulated parameters are well agreed with the calculated parameters. Arrhenius plot shows two different activation energies at below and above 300°C which identifies the phase transition of SrBi2Ta2O9 ceramic. The fatigue property is explained by the basis of activation energies, which shows that SBT sintered by microwave technique is more fatigue resistant than conventional sintering.