Effect Of ZnO Nanostructures Research Articles

Effect of ZnO nanostructures on the performance of dye sensitized solar cells

Development of cost effective and easily scalable energy systems for harvesting renewable solar energy is attractive proposal for future. This work presents facile synthesis of ZnO nanostructures with different morphologies simply providing different solvating conditions in a hydrothermal process, for their subsequent use in dye sensitized solar cell (DSSC) device. ZnO nanoprisms were obtained in aqueous solution where addition of methanol/ethanol resulted in formation of hollow nanoprism while methanol in alkaline solution yield ZnO nanorice morphology. The obtained nanostructures were characterized for structural, morphological, elemental, optical and surface area analysis. Then devices were fabricated using the grown nanostructure and tested their response under 1 sun conditions for dye sensitized solar cells with N719 dye-loading. Among different nanostructure morphologies, ZnO nonorice showed superior performance reaching the maximum conversion efficiency. We attribute this to large surface area, better conductivity, and enhanced dye adsorption of nanorice in comparison to other synthesized ZnO nanostructures.

Controlled degradability of PCL-ZnO nanofibrous scaffolds for bone tissue engineering and their antibacterial activity

Up to date, tissue regeneration of large bone defects is a clinical challenge under exhaustive study. Nowadays, the most common clinical solutions concerning bone regeneration involve systems based on human or bovine tissues, which suffer from drawbacks like antigenicity, complex processing, low osteoinductivity, rapid resorption and minimal acceleration of tissue regeneration. This work thus addresses the development of nanofibrous synthetic scaffolds of polycaprolactone (PCL) - a long-term degradation polyester - compounded with hydroxyapatite (HA) and variable concentrations of ZnO as alternative solutions for accelerated bone tissue regeneration in applications requiring mid- and long-term resorption. In vitro cell response of human fetal osteoblasts as well as antibacterial activity against Staphylococcus aureus of PCL:HA:ZnO and PCL:ZnO scaffolds were here evaluated. Furthermore, the effect of ZnO nanostructures at different concentrations on in vitro degradation of PCL electrospun scaffolds was analyzed. The results proved that higher concentrations ZnO may induce early mineralization, as indicated by high alkaline phosphatase activity levels, cell proliferation assays and positive Alizarin-Red-S-stained calcium deposits. Moreover, all PCL:ZnO scaffolds particularly showed antibacterial activity against S. aureus which may be attributed to release of Zn2+ ions. Additionally, results here obtained showed a variable PCL degradation rate as a function of ZnO concentration. Therefore, this work suggests that our PCL:ZnO scaffolds may be promising and competitive short-, mid- and long-term resorption systems against current clinical solutions for bone tissue regeneration.

Effect of ZnO nanostructures on the optical properties of white light-emitting diodes.

White light produced by blue LEDs with yellow phosphor is the most widely used methods, but it results in poor quality in angular CCT uniformity. In this work, a novel technique was introduced to solve this problem by integrating different ZnO nanostructures into white light-emitting diodes. The experiment of ZnO doped films and the simulation of Finite-Difference Time-Domain (FDTD) were carried out. The result indicated scattering effect of ZnO nanoparticles could improve uniformity of scattering energy effectively. Moreover, the effect of ZnO nanostructures on white light-emitting diodes (wLEDs) devices was also investigated. The CCT deviation of wLEDs devices would decrease from 3455.49 K to 96.30 K, 40.03 K and 60.09 K when the node-like (N-ZnO), sheet-like (S-ZnO) and rod-like ZnO (R-ZnO) respectively applied. The higher CCT uniformity and little luminous flux dropping were achieved when the optimal concentrations of N-ZnO, S-ZnO, and R-ZnO nanostructures were 0.25%, 0.75%, and 0.25%. This low-cost and green manufacturing method has a great impact on development of white light-emitting diodes.

Enhanced biostability and cellular uptake of zinc oxide nanocrystals shielded with a phospholipid bilayer.

The widespread use of ZnO nanomaterials for biomedical applications, including therapeutic drug delivery or stimuli-responsive activation, as well as imaging, imposes a careful control over the colloidal stability and long-term behaviour of ZnO in biological media. Moreover, the effect of ZnO nanostructures on living cells, in particular cancer cells, is still under debate. This paper discusses the role of surface chemistry and charge of zinc oxide nanocrystals, of around 15 nm in size, which influence their behaviour in biological fluids and effect on cancer cells. In particular, we address this problem by modifying the surface of pristine ZnO nanocrystals (NCs), rich of hydroxyl groups, with positively charged amino-propyl chains or, more innovatively, by self-assembling a double-lipidic membrane, shielding the ZnO NCs. Our findings show that the prolonged immersion in simulated human plasma and in the cell culture medium leads to highly colloidally dispersed ZnO NCs only when coated by the lipidic bilayer. In contrast, the pristine and amine-functionalized NCs form huge aggregates after already one hour of immersion. Partial dissolution of these two samples into potentially cytotoxic Zn2+ cations takes place, together with the precipitation of phosphate and carbonate salts on the NCs' surface. When exposed to living HeLa cancer cells, higher amounts of lipid-shielded ZnO NCs are internalized with respect to the other samples, thus showing a reduced cytotoxicity, based on the same amount of internalized NCs. These results pave the way for the development of novel theranostic platforms based on ZnO NCs. The new formulation of ZnO shielded with a lipid-bilayer will prevent strong aggregation and premature degradation into toxic by-products, and promote a highly efficient cell uptake for further therapeutic or diagnostic functions.

Nanostructural Effect of ZnO on Light Extraction Efficiency of Near-Ultraviolet Light-Emitting Diodes

The effect of ZnO nanostructures on the light output power of 375 nm near-ultraviolet light-emitting diodes (NUV-LEDs) was investigated by comparing one-dimensional (1D) nanorods (NR-ZnO) with two-dimensional (2D) nanosheets (NS-ZnO). ZnO nanostructures were grown on a planar indium tin oxide (ITO) by solution based method at low temperature of 90°C without degradation of the forward voltage. At an injection current of 100 mA, the light output efficiency of NUV-LED with NR-ZnO was enhanced by around 30% compared to the conventional NUV-LEDs without ZnO nanostructures. This improvement is due to the formation of a surface texturing, resulting in a larger escape cone and a multiple scattering for the photons in the NUV-LED, whereas the light output efficiency of NUV-LED with NS-ZnO was lower than that of the conventional NUV-LEDs due to the internal reflection and light absorption in the defective sites of NS-ZnO.

Antibacterial activity of ZnO nanorods prepared by a hydrothermal method

We investigated antibacterial activity of ZnO nanorods prepared by a hydrothermal method against a gram-negative bacterium Escherichia coli and a gram-positive bacterium Bacillus atrophaeus. Antibacterial activity of ZnO nanorod coatings was studied on solid substrates covered with nutrient agar, as well as in liquid nutrient broth for different concentrations of ZnO nanorods, nanoparticles, and powder. ZnO exhibited antibacterial activity against both E. coli and B. atrophaeus, but it was considerably more effective in the latter case (at 15 mM vs. 5 mM concentration, respectively, showing zero viable cell count). For both organisms, damage of the cell membranes was found, and the effect was more pronounced for B. atrophaeus. Chemiluminescence analysis has been used to detect the release of hydrogen peroxide from ZnO structures, and the effect of H 2O 2 on the E. coli and B. atrophaeus was studied. Since significant differences were observed in the effect of ZnO nanostructures and H 2O 2 on B. atrophaeus, it can be concluded that there are other mechanisms contributing to the antibacterial activity of ZnO nanostructures.

Effect of ZnO Nanostructures on 2-Dimensional Random Lasing Properties

We show results on how the morphology of a ZnO layer can have a big impact on the random lasing threshold of the material. Plasma-enhanced chemical vapor deposition method is used to grow ZnO layers on sapphire substrates. The morphologies and structures of ZnO are observed to undergo transition when growth temperature decreases from 750 to 100 °C: the deposited ZnO changes from crystalline films to nanocrystalline films with columnar-shaped grains, then to well-aligned ZnO nanorods, and finally to randomly oriented irregular-shaped grains. ZnO nucleation and surface diffusion rates, coalescence between crystal grains, and preferential growth along c-axis play important roles in this transition from continuous films to nanorods. Random lasing properties of our ZnO films and nanorods are studied. The scattering ability of ZnO is critical to control the lasing properties. The lowest lasing thresholds are observed for ZnO films grown between 500 and 600 °C when the films have columnar-shaped grains and not at 750 °C when the ZnO layer has a continuous crystalline film. Calculations based on quasi-2D random lasing are consistent with the experimental results of lasing threshold measurements.