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Cr doped Zn 0.96 Cu 0.04 O nanopowders with different Cr concentrations from 0% to 4% were successfully synthesized by a simple co-precipitation method. X-ray diffraction patterns revealed that all the samples had hexagonal crystal structure and co-doping could not alter its hexagonal structure. The dielectric dispersion and dielectric loss were increased with Cr concentrations due to the increase of charge carrier density, dipoles and vacancies within the grains. At higher frequency, the dielectric loss was found to be low because of the inhibition of domain wall motion. The low dielectric constant and dielectric loss at high frequency region makes it to be a suitable material for high frequency applications. The conductivity was increased by Cr-doping due to the enhanced transition of charge carriers between the grains. The strong suppression of ultraviolet emission at higher Cr revealed the promotion of non-radiative recombination. A broad defect-related visible luminescence band gave evidence for an increase in optically active deep level defects with increased Cr doping level. The combined effect of intrinsic defects and exchange interactions involving Cr ions substituted for Zn in the Zn-Cu-O lattice were responsible for the observed room temperature ferromagnetism. The saturation magnetization of the Cu doped ZnO was decreased by Cr co-doping, which occurred due to the antiferromagnetic coupling of neighboring Cu-Cu ions and Cr-Cr ions. The segregation of spinel ZnCr 2 O 4 phase is responsible for the enhanced coercivity at higher Cr concentration (4%). [ABSTRACT FROM AUTHOR]

Abstract: Zn0.96−xCu0.04CrxO nanoparticles with different Cr concentrations from 0 to 4% were successfully synthesized by co-precipitation method. The X-ray diffraction pattern showed the crystalline nature with hexagonal wurtzite structure. The diminution in activation energy and the enhanced strain by Cr-doping from 0 to 3% reduced the average crystal size from 27 to 23.8nm while the formation of secondary phase such as spinel ZnCr2O4 enhanced it to 25.6nm after Cr=3% via increasing the activation energy. The solubility limit of Cr in the present system is fixed as 3%. The energy dispersive X-ray spectra confirmed the presence of Cu and Cr in Zn-O. The optical absorption spectra showed the three distinct bands corresponding to UV region (305–324nm) due to electronic transition between the bands; blue region (382–386nm) mainly due to the Zn/Cr interstitials and bluish green (481–482nm) region due oxygen vacancies and interstitials. The noticed poor transmittance throughout the region and the broader absorption bands in Cr=1% doped Zn0.96Cu0.04O confirmed that it had more defects such as oxygen vacancies, Zn interstitials and other defects. The blue shift of energy gap from 3.68eV (Cr=0%) to 3.71eV (Cr=1%) was due to the creations of more defects. The red shift of Eg from 3.71eV (Cr=1%) to 3.6eV (Cr=3%) was explained by sp–d exchange interactions between the band electrons and the localized d-electrons of the Cr3+ ions. Presence of chemical bonding was confirmed by FTIR spectra. [Copyright &y& Elsevier]

Abstract: Effective fluidization of materials present in the reactor bed is critical for optimizing reaction conditions in a fluidized-bed gasifier. An improper fluidization leads to inefficient conversion due to many reasons such as low heat and mass transfers, ineffective gas–solid phase reactions, and uneven reactor temperature in autothermal gasification. The objective of this study was to investigate effect of reactor bed composition, i.e. a mixture of gasifier solid residues (GSR), switchgrass, and inert material, on fluidization using a 0.25m i.d. transparent column. In this cold-flow study, the amount of inert material, i.e. silica sand, in the bed was held at 20kg. The switchgrass in the mixture ranged from 0.17 to 5% of the sand quantity while the GSR ranged from 5 to 35% of the switchgrass. The particle geometric sizes by mass of sand, GSR and switchgrass were 348±1.6μm, 80±2.6μm, and 10.3±1.7mm, respectively. For all conditions, with an increase in gas superficial velocity, i.e. ratio of volumetric gas flow and bed cross-sectional area, the pressure drop across the bed increased reaching a maximum level at the minimum fluidization condition. Results showed that when the bed consisted of only GSR and sand, with an increase in the GSR from 5% to 35%, the gas superficial velocity at minimum fluidization condition, called minimum fluidization velocity (U mf), decreased significantly (p <0.05); however, corresponding bed pressure drop (dPmf) remained constant. When the bed consisted of GSR, switchgrass and sand, there were significant effects (p <0.001) of GSR, switchgrass and their interaction (GSR*Switchgrass) on U mf and dPmf. Fluidization improved with an increase in GSR up to 35% in the mixture. Overall, both U mf and dPmf increased with an increase in levels of GSR (5 to 35%) and switchgrass (0.17 to 3%) in the mixture. Fluidization characteristics were found to be strongly dependent upon mixture''s effective properties, which were determined using properties of all mixture components. Correlations available in literature were used to predict U mf using effective properties of tertiary mixture with GSR, switchgrass and sand. Prediction of U mf from all selected correlations did not match well with the experimental data for the entire range of tertiary mixture compositions. Fluidization of bed materials sustained up to 3% level of switchgrass. However, segregation of bed materials and in-bed channelization caused ineffective fluidization at 5% level of switchgrass in the mixture. [Copyright &y& Elsevier]

Abstract: ZnO nanomaterials have been synthesized by simple precipitation technique using polyvinylpyrrolidone (PVP) as surfactant, followed by calcination. The products were characterized by various techniques such as X-ray diffraction studies (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible spectroscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), etc. Effective photosensitizers of porphyrin derivative, meso-tetra (4-sulfonatophenyl) porphyrin (TSPP) have been encapsulated into the ZnO nanomaterials to increase the generation of singlet oxygen. Efficiency of singlet oxygen (1O2) generation was detected by optical method and EPR–spin trapping technique. Encapsulated TSPP has generated more singlet oxygen compared to that of ZnO nanospheres. Optical spectroscopic studies have indicated that 1O2 generation was involved via fluorescence resonance energy transfer which was responsible for photodynamic action. The antimicrobial activity of the ZnO nanomaterials encapsulated TSPP was also tested against the Gram-negative bacterium Escherichia coli as well as Gram-positive bacterium Staphylococcus aureus and the effect was more pronounced with Gram-positive than with Gram-negative bacteria. ZnO-TSPP has low photodynamic inactivation (PDI) of bacteria under dark conditions but high PDI under visible light irradiation. The result has indicated that TSPP loaded ZnO nanomaterials, can be used as a nanocarrier for antimicrobial photodynamic therapy (aPDT). [Copyright &y& Elsevier]