Preliminary Study of ZnO/GO Composite Preparation as Photocatalyst Material for Degradation Methylene Blue under Low UV-Light Irradiation

ZnO:Graphene Oxide composite nanopowders have been successfully prepared by sol-gel method. The study of composite preparation is discussed in this paper. Graphene oxide was added in two ways in order to study the mixed behaviour especially in photocatalytic properties. The degradation of methylene blue (MB) concentration in water was used to evaluate the photocatalytic property under low UV-light irradiation (14 μW/cm2). The results showed that all varian ZnO-GO composite samples have spherical morphology and hexagonal wurtzite crystal structure. An addition of graphene oxide (GO) in ZnO precursor solution during preparation shows a better photocatalytic property that related to reducing in particle size, thereby produce a large surface area and formed a better interfacing with GO/rGO. The existence of GO around ZnO nanoparticles gives some advantageous due to presences of hydroxyl component that directly relate to the increments in photocatalytic behavior. The photodegradation rate of MB in water using ZnO-GO composite as catalyst is significantly increase compared with pure ZnO.

Optical and Photocatalytic Properties of In-Situ Gr@ZnO Microspindle Composites Prepared by Hydrothermal Method

In-Situ composite materials of graphene (Gr) and ZnO microspindle with different Gr contents (1, 2 and 5 wt.%) were prepared via a facile one-step hydrothermal route with the assistance of hexamethylenetetramine. Graphene does not affect the hexagonal wurtzite crystal structure of composite materials but strongly affects the morphological, structural, optical and photocatalytic properties of composite materials. In detail, Gr causes a decrease in both the dimensions of ZnO microspindle and photoluminescence efficiency. The average crystalline size and microstrain first increase from 28.9 nm and 0.00394 to 49.5 nm and 0.00524 when Gr content increases from 0 to 1 wt.%, respectively; then decrease to 39.6 nm and 0.00404 when Gr content increase from 1 to 5 wt.%, respectively. Both pristine and composite materials show high photocatalytic activity with high methylene blue degradation efficiency?more than 90%-just after 40 min under UV irradiation. Composite material having a Gr content of 5 wt.% shows the highest degradation efficiency of 96.5% which confirms the role of Gr in enhancing the photocatalytic activity of ZnO.

Effect of Cd precursor on structure and optical properties of spin coated Zn0.9Cd0.1O films for optoelectronics applications

The development of transparent conducting oxide materials has gained an increased interest in the scientific community for developing efficient low cost optoelectronic devices. The effect of Cd precursor on structural and optical properties of sol-gel synthesized Zn0.9Cd0.1O nanostructured films has been studied by using XRD, AFM, optical absorption and emission spectroscopic techniques. X-ray diffraction confirms the hexagonal wurtzite crystal structure of the deposited films and the relative intensity of diffraction peaks has been observed with different cadmium salts. The granular surface morphology of the synthesized films has been observed from AFM measurements. The optical transmission, band gap and luminescence intensity was found to change for different cadmium salts. These results are very important for developing new materials for optoelectronic applications.

Histidine Decorated Nanoparticles of CdS for Highly Efficient H2 Production via Water Splitting

Pure cadmium sulfide and histidine decorated cadmium sulfide nanocomposites are prepared by the hydrothermal or solvothermal method. Scanning electron microscopy (SEM) analysis shows that the particle sizes of pure cadmium sulfide (pu/CdS) and histidine decorated cadmium sulfide prepared by the hydrothermal method (hi/CdS) range from 0.75 to 3.0 μm. However, when a solvothermal method is used, the particle size of histidine decorated cadmium sulfide (so/CdS) ranges from 50 to 300 nm. X-ray diffraction (XRD) patterns show that all samples (pu/CdS, hi/CdS and so/CdS) have a hexagonal wurtzite crystal structure but so/CdS has a poor crystallinity compared to the others. The as-prepared samples are applied to photocatalytic hydrogen production via water splitting and the results show that the highest H2 evolution rate for pu/CdS and hi/CdS are 1250 and 1950 μmol·g−1·h−1, respectively. On the other hand, the so/CdS sample has a rate of 6020 μmol·g−1·h−1, which is about five times higher than that of the pu/CdS sample. The increased specific surface area of so/CdS nanoparticles and effective charge separation by histidine molecules are attributed to the improved H2 evolution.

Enhancing crystal quality and optical properties of GaN nanocrystals by tuning pH of the synthesis solution

Gallium nitride nanocrystals as a wide bandgap semiconductor material for optoelectronic applications can be synthesized using chemical methods. In this research using co-precipitation and nitridation processes gallium nitride nanocrystals have been synthesized, and by tuning pH of the synthesis solution at the co-precipitation step, crystal quality and optical property of the resultant gallium nitride nanocrystals have been enhanced. Gallium nitride nanocrystal samples were synthesized using solutions with pH values of 2.1, 4.8, 7.8, and 9.0, and then nitridation at 950 °C under the flow of ammonia gas. The synthesized nanocrystal samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and photoluminescence techniques. The XRD data show that the nanocrystals have hexagonal wurtzite crystal structure, and using Scherer’s equation the sizes of the synthesized nanocrystals are 23.6, 26.6, 19.7, and 10.4 nm for the samples synthesized using the solutions with pH values of 2.1, 4.8, 7.8, and 9.0 respectively. The sizes of the nanocrystals obtained from SEM images are larger than the values obtained using Scherer’s equation, due to the aggregation of nanocrystals. EDX spectra show that pH of the synthesis solution affects the elemental stoichiometry of the gallium nitride nanocrystals. We obtained better stoichiometry for the nanocrystal sample synthesized using solution with the pH of 4.8. Photoluminescence spectra show that for this sample the emission intensity is higher than the others.

Chemically Synthesized Hierarchical Flower like ZnO Microstructures

In the present study, we have deposited hierarchical flower-like microstructured zinc oxide (ZnO) thin films directly on a glass substrate by using the simplistic aqueous chemical route for different concentrations of triethanolamine (TEA) which acted like a complexing agent. The as-synthesized ZnO thin films were subsequently annealed at 300 °C and are characterized with characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and electrical resistivity. The hexagonal wurtzite crystal structure of as-synthesized ZnO thin films was confirmed by their XRD patterns and the well-resolved ZnO flowers-like morphology was revealed from the FESEM micrographs. From FESEM images it can be seen that the ZnO flower is composed of dozens of nanorods originating from the same core in a symmetric fashion with an average diameter of around 180-300 nm. The flower-like morphology was obtained at 0.3 M TEA concentration. Due to its hierarchical structure, the deposited ZnO thin films were employed for multiple applications such as gas sensing and anti-microbial activity. The ZnO thin films with micro-flowers like morphology showed the maximum gas sensor sensitivity ∼64.50 at 150 °C for 100 ppm of NO2 gas. Moreover, the bacteria were completely destroyed in the presence of as-deposited ZnO thin films.

CATALYST–FREE GROWTH OF WELL–ALIGNED ZnO NANOWIRES ON GRAPHENE/Si SUBSTRATEBY THERMAL EVAPORATION

Vertically well–aligned ZnO nanowire (NW) arrays with high density were directly synthesized on graphene/Si substrate by thermal evaporation of zinc powder without catalysts or additives. The ZnO NWs were characterized by field emission scanning electron microscopy (FE–SEM), high resolution transmission electron microscopy (HRTEM), X–ray diffraction (XRD), photoluminescence (PL), and Raman spectroscopy. The results showed that the obtained ZnO NWs have diameters in the range of 300–350 nm with lengths of several tens micrometers. The prepared ZnO NWs are of a single crystal, which have a hexagonal wurtzite crystal structure with c–axis (002) orientation growth perpendicular to the substrate surface. The NW arrays had a good crystal quality with excellent optical properties, indicating a sharp and strong ultraviolet emission at 380 nm, and a weak visible emission at around 516 nm.

STUDY THE RESPONSE OF GAS SENSOR USING ZnO NANORODS SYNTHESIZED BY HYDROTHERMAL METHOD

Low-dimensional nano structures ZnO are potential material for optoelectronicand gas-sensing applications. The syntheses of a large quantity of ZnO nanostructures play an important role for practical applications for future. In the paper, we propose hydrothermal reduction method to synthesize large quantities ZnO nanorods under atmospheric pressure and without using any catalysts. As-prepared ZnO nanorods exhibited a hexagonal wurtzite crystal structure. For sensing properties, ZnO nanorods were coated on the Pt interdigitated microelectrodes arrays and examined at operating temperatures of 200 to 350 oC for the detection capacity of NO2 gas. The changes in response resistance revealed that the sensor exhibited a high sensing performance for low concentrations of NO2 gas (0.5 ppm). Additionally, the ZnO nanowires sensors have a good performance to ethanol.

Microstructure and optical properties of ZnO nanorods prepared by anodic arc plasma method

Introduction: A one-dimensional ZnO nanostructure is a versatile and multifunctional n-type semiconductor. In this paper, ZnO nanorods were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere. Methods: The composition, morphology, crystal microstructure, and optical properties of ZnO nanorods were characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and the corresponding selected-area electron diffraction (SAED), X-ray energy dispersive spectrometry (XEDS), ultraviolet-visible (UV-VIS) spectroscopy, Raman scattering spectrum (Raman), and photoluminescence spectrum (PL). Results: The experiment results show that ZnO nanorods synthesized by this method possess hexagonal wurtzite crystal structure with good crystallization, no other impurity phases are observed, the crystalline size is about 18 nm, and the lattice constant distortion occurs compared to that of bulk ZnO. The morphology of the sample is a rod-like shape, the length ranges from 100 nm to 300 nm, the average diameter is approximately 20 nm, and the aspect ratio is relatively high. The UV-VIS absorption spectrum occurs red shift, The Raman spectrum further demonstrates that the major peaks are assigned to ZnO optical vibrational modes, and the PL spectrum exhibits coexistence properties of ultraviolet (UV) and green emission. Conclusions: The results prove that ZnO nanorods with hexagonal wurtzite crystal structure were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere.

The Influence of Annealing Temperature on Structural Properties of Zinc Oxide Nanoparticles Synthesized by Precipitation Method

In the present work, the precipitation method was applied to prepare zinc oxide nanoparticles in the presence of zinc nitrate and potassium hydroxide as precursor solutions. The influence of annealing temperature on the properties such as structural and morphological of zinc oxide nanoparticles were performed by X-ray diffraction technique, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The effects of annealing temperature on the crystallite size of zinc oxide nanoparticles have investigated. The XRD results represented that the zinc oxide nanoparticles exhibits high crystallinity of hexagonal wurtzite crystal structure. The average crystallite size of nanoparticles increased from 18 to 31 nm when the annealing temperature had increased. The morphology images show that the nanoparticles in this work were spherical in shape. Raman and FT-IR spectra confirm that the quality of Zn-O vibrational mode is stronger at higher annealing temperature.