C. Muthamizhchelvan

Morphology-directed synthesis of ZnO nanostructures and their antibacterial activity

Zinc oxide (ZnO) nanostructures of various morphologies were produced in an aqueous system, with pyridine as a shape-directing agent. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) revealed hexagonal wurtzite crystal structure. Variation in surface morphology was analyzed using transmission electron microscopy (TEM). Changes in surface morphology were attributed to the absence of steric stabilization in pyridine during synthesis process. Pyridine concentration affected morphology and optical properties. Fourier transform infrared spectroscopy (FTIR) confirmed the presence/absence of pyridine on the surface of ZnO nanostructures (ZnO-NSs). Optical measurements carried out using UV-visible spectrophotometer (UV-vis) and photoluminescence (PL) indicated the presence of defects. All the samples exhibited two PL peaks, at 350-370 nm and 560-624 nm. Variation in the intensities of PL peaks corresponded to the changes in the surface morphology from nanoparticles to rods and origin of deep-level defect luminescence is attributed to surface recombination. The toxicity of the nanostructures was tested on model Gram-negative and Gram-positive pathogens. Smaller nanorods were most toxic among the nanostructures tested.

Amino acid-mediated synthesis of zinc oxide nanostructures and evaluation of their facet-dependent antimicrobial activity

ZnO nanostructures (ZnO-NSs) of different morphologies are synthesized with the amino acids L-alanine, L-threonine, and L-glutamine as capping agents. X-ray diffraction (XRD) shows the formation of a crystalline wurtzite phase of ZnO-NSs. The surface modification of ZnO-NSs due to the capping agents is confirmed using Fourier transform infrared (FTIR) spectroscopy. Photoluminescence spectroscopy reveals that the concentration of surface defects correlates positively with the number of polar facets in ZnO-NSs. The antimicrobial activity of the ZnO-NSs has been tested against Escherichia coli and the common pathogens Staphylococcus aureus, Klebsiella pneumoniae, and Bacillus subtilis. Culture-based methods in rich medium show up to 90% growth inhibition, depending on the ZnO-NSs. Flow cytometry analyses indicate that the reactive oxygen species (ROS) generated by ZnO-NSs contribute mostly to the antibacterial activity. Control experiments in minimal medium show that amino acids and other reducing agents in Luria-Bertani (LB) medium quench ROS, thereby decreasing the antimicrobial activity of the ZnO-NSs.

Enhanced visible light induced photocatalytic activity on the degradation of organic pollutants by SnO nanoparticle decorated hierarchical ZnO nanostructures

One (1D) and two-dimensional (2D) nanostructures of zinc oxide and tin oxide (ZnO/SnO) nanocomposites were synthesized by a hydrothermal method using ethylenediamine (EDA) as a capping ligand. The effect of Sn concentration on the morphology of the nanocomposites has been investigated. X-ray diffraction analysis indicated good crystallinity of samples with the presence of both ZnO and SnO phases. The morphological analysis revealed the morphological transformation from ZnO nanorods to ZnO/SnO nanosheets by adding Sn. X-ray photoelectron spectra analyses showed significant peak shift in the electronic state of Zn at the higher concentration of Sn. Elemental mapping results clearly evidenced that both ZnO and SnO moieties were uniformly distributed in the nanosheets. Photocatalytic degradation of methylene blue using as-prepared ZnO/SnO nanocomposites was nine times faster than that of pure ZnO under visible light irradiation. It could be attributed to the formation of a hetero-junction between ZnO and SnO. Our experimental results revealed that photogenerated superoxide (O2−˙) radicals were the main reactive species for the degradation of MB. The maximum degradation efficiency was observed for the sample with 1 wt% of tin chloride, the MB related absorption peak completely disappeared after 6 min of irradiation. ZnO/SnO composites extended the light absorption spectra of ZnO to a visible light region and enhanced the visible light photocatalytic activity.

Highly efficient dye-sensitized solar cell performance from template derived high surface area mesoporous TiO2 nanospheres

High surface area mesoporous anatase TiO2 spheres are synthesized using ethylene glycol as a template by a solvothermal method. Electron microscopy studies revealed the formation of smooth surfaced mesoporous spheres with uniform size. A high surface area of 221.52 m2 g−1 is obtained for the titanium tetraisopropoxide concentration of 0.5 mL. X-Ray diffraction and Raman analyses revealed the formation of anatase phase TiO2. Uniform deposition of a mesoporous film for a photoanode was achieved by an optimized spray deposition method. The effects of the ruthenium dye-sensitizer N719 and indoline dye-sensitizer D205 on the dye sensitized solar cell performance are investigated. Maximum efficiencies of 8.96 and 9.02% are achieved using the sensitizers N719 and D205, respectively; from the mesoporous anatase TiO2 sphere coated DSSC. IPCE analyses revealed that the mesoporous spheres efficiently collected the incident photons and achieved a conversion efficiency over 80% by internal reflections and a scattering process.

Effect of organic-ligands on the toxicity profiles of CdS nanoparticles and functional properties.

CdS nanoparticles are one among the most promising agents for fluorescent imaging. Hence, it is essential to develop new strategies to overcome the cytotoxicity of these nanoparticles. Surface modification is one of the simplest and effective techniques. This paper assesses the effect of surface modification on toxicity of the CdS nanoparticles. Unmodified CdS and surface-modified CdS nanoparticles were synthesized in an aqueous medium using a wet chemical route at room temperature. The surface modification of the CdS nanoparticles with polyvinylpyrrolidone (PVP) and cysteine was confirmed using infrared absorption studies. The diameters of unmodified CdS, PVP-modified CdS, and cysteine-modified CdS nanoparticles were determined using HRTEM. They exhibited luminescence in the range from 500 to 800 nm. The cytotoxic effects of these CdS nanoparticles were investigated in cultures of Vero cells. The results indicated that Vero cell viability was higher for the surface-modified CdS nanoparticles than for the unmodified CdS nanoparticles. The reduction in the toxicity was related to the nature of the capping agents used for the surface modification, and the particle size.

Fabrication of bistable switching device using CdS nanorods embedded in PMMA (polymethylmethacrylate) nanocomposite

Abstract An organic bistable memory device was fabricated using CdS NR’s/PMMA (polymethylmethacrylate) nanocomposite sandwiched between ITO and Al thin film. XRD analysis confirmed that CdS NR’s reveals wurtzite hexagonal phase. FESEM and TEM images showed the monodispersed rod-like morphology. The nanorods were uniformly dispersed in the PMMA (polymethylmethacrylate) layer. EDX spectrum confirms that the product consists of only Cd and S elements. No other impurities were found. UV–visible absorption of CdS NR’s showed a slight blue shift. The photoluminescence spectra of CdS NR’s spectra showed surface defects which may be due to sulfur vacancies in surface of nanorods. The CdS NR’s polymer nanocomposite showed better thermal stability. The current–voltage (C–V) measurement of ITO/CdS NR’s/Al showed a clockwise hysteresis with flatband shift voltage in C–V curve for the device.

Ultrathin layered MoS2 nanosheets with rich active sites for enhanced visible light photocatalytic activity

Edge-rich active sites of ultrathin layered molybdenum disulphide (MoS2) nanosheets were synthesized by a hydrothermal method. The effect of pH on the formation of MoS2 nanosheets and their photocatalytic response have been investigated. Structural and elemental analysis confirm the presence of S–Mo–S in the composition. Morphological analysis confirms the presence of ultrathin layered nanosheets with a sheet thickness of 10–28 nm at pH 1. The interplanar spacing of MoS2 layers is in good agreement with the X-ray diffraction and high-resolution transmission electron microscopy results. A comparative study of the photocatalytic performance for the degradation of methylene blue (MB) and rhodamine B (RhB) by ultrathin layered MoS2 under visible light irradiation was performed. The photocatalytic activity of the edge-rich ultrathin layered nanosheets showed a fast response time of 36 min with the degradation rate of 95.3% of MB and 41.1% of RhB. The photocatalytic degradation of MB was superior to that of RhB because of the excellent adsorption of MB than that of RhB. Photogenerated superoxide radicals were the key active species for the decomposition of organic compounds present in water, as evidenced by scavenger studies.

Enhanced biocidal activity and optical properties of zinc oxide nanoneedles

Zinc oxide nanoneedles were successfully synthesized by simple wet chemical method. X-ray diffraction studies reveal the formation of wurtzite-type of ZnO. Optical studies indicate the presence of defects in the form of oxygen vacancies and zinc interstitials. As an application study, this sample was tested for its antibacterial activity. These nanoneedles were found to exhibit excellent biocidal activity against both gram positive and gram negative bacteria.

SYNTHESIS AND CHARACTERAIZATION OF Fe3O4 NANOPARTICLES FOR MAGNETIC HYPERTHERMIA APPLICATION

The superparamagnetic magnetite (Fe3O4) nanoparticles were synthesized by microemulsion technique. The synthesized nanoparticles were 10 nm with good crystalline nature. The superparamagnetic property was observed from vibrating sample magnetometer study. Specific absorption (SAR) of the Fe3O4 nanoparticles were calculated for different AC magnetic field amplitude at constant frequency. Calculated SAR was found to be square field dependent.The superparamagnetic magnetite (Fe3O4) nanoparticles were synthesized by microemulsion technique. The synthesized nanoparticles were 10 nm with good crystalline nature. The superparamagnetic property was observed from vibrating sample magnetometer study. Specific absorption (SAR) of the Fe3O4 nanoparticles were calculated for different AC magnetic field amplitude at constant frequency. Calculated SAR was found to be square field dependent.