Facile synthesis and investigation of NiO–ZnO–Ag nanocomposites as efficient photocatalysts for degradation of methylene blue dye

In the present study, NiO–ZnO–Ag photocatalytic nanocomposites were synthesized using two-stage precipitation method. The synthesized composite powders were investigated and characterized using different techniques including XRD, FESEM, FT-IR, TGA and UV–Vis. XRD results showed that by increasing the Ag content, the crystallite size of ZnO decreased. FESEM micrographs showed that addition of Ag could lead to formation of more uniform particles in the size range of 30–500 nm. Diffuse reflectance spectroscopy results confirmed that addition of Ag nanoparticles led to the increase of light absorption, which was attributed to the plasmon surface resonance of Ag. Band gap energies of NiO–ZnO, NiO–ZnO–5%Ag, NiO–ZnO–3%Ag, NiO–ZnO–1%Ag and ZnO–1%Ag were estimated to be 3.13, 3.14, 3.147, 3.19 and 3.17 eV, respectively. Investigation of degradation process showed that by adding up to 1 wt% Ag to NiO–ZnO composite led to the increase of methylene blue degradation from 67% to 94%, but further addition resulted in decrease of degradation.     

Synthesis and characterization of chlorapatite–ZnO composite nanopowders

The influence of zinc oxide content on the formation of chlorapatite-based composite nanopowders in the mechanically alloyed CaO–CaCl₂–P₂O₅–ZnO system was studied. To mechanosynthesize composite nanopowders, different amounts of hydrothermally synthesized zinc oxide nanoparticles (0–10 wt%) were mixed with ingredients and then were mechanically activated for 5 h. Results showed that in the absence of zinc oxide, high crystalline chlorapatite nanopowder was obtained after 5 h of milling. In the presence of 4 and 7 wt% zinc oxide, the main product of milling for 5 h was chlorapatite–zinc oxide composite nanopowder. On increasing the zinc oxide content to 10 wt%, composite nanopowder was not formed due to improper stoichiometric ratio of the reactants. The crystallite size, lattice strain, volume fraction of grain boundary, and crystallinity degree of the samples fluctuated significantly during the milling process. In the presence of 7 wt% zinc oxide, the crystallite size and crystallinity degree reached 51±2 nm and 79±2%, respectively. During annealing at 900 °C for 1 h, the crystallization of composite nanopowder occurred and as a result the crystallinity degree rose sharply to 96±3%. In addition, the crystallite size increased to 77±2 nm after annealing at 900 °C. According to SEM and TEM images, the composite nanopowder was composed of both ellipse-like and polygonal particles with a mean size of about 98 nm.     

Growth and characterization of the Al-doped and Al–Sn co-doped ZnO nanostructures

In the present work, well-dispersed structures of spherical-like pure ZnO, Al doped ZnO (AZO) and Al, Sn co-doped ZnO (ATZO) nanocrystals were successfully synthesized by using zinc acetate dihydrate as the starting material and also the low temperature hydrothermal process without any additional surfactant or catalytic agent. The ZnO structures were characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The XRD results revealed that ZnO powders have a hexagonal crystal structure and the TEM indicated that the nanoparticles self-aggregate. An X-ray photoelectron spectroscopy (XPS) study confirmed the substitution of Zn²⁺ by Sn and Al ions. Optical properties of the ZnO structures were investigated by Raman spectroscopy and room-temperature photoluminescence (PL) spectroscopy. The Raman spectroscopy results demonstrated that the doped ZnO nanoparticles had a higher crystalline quality than that of pure ZnO. Room-temperature PL spectra of these structures showed a strong UV emission peak and a relative weak green emission peak, and the UV peak of the doped ZnO nanoparticles was blue-shifted with respect to that of the undoped ZnO nanoparticles.     

A green and facile one-pot synthesis of Ag–ZnO/RGO nanocomposite with effective photocatalytic activity for removal of organic pollutants

In this study, Ag–ZnO/reduced graphene oxide (Ag–ZnO/RGO) composite was synthesized by a green and facile one-step hydrothermal process. Aqueous suspension containing Ag and ZnO precursors with graphene oxide (GO) sheets was heated at 140 °C for 2 h. The morphology and structure of as-synthesized particles were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and Photoluminescence (PL) spectroscopy which revealed the formation of composite of metal, metal oxide and RGO. It was observed that the presence of Ag precursor and GO sheets in the hydrothermal solution could sufficiently decrease the size of ZnO flowers. The hybrid nanostructure, with unique morphology, obtained from this convenient method (low temperature, less time, and less number of reagents) was found to have good photocatalytic and antibacterial activity. The perfect recovery of catalyst after reaction and its unchanged efficiency for cyclic use showed that it will be an economically and environmentally friendly photocatalyst.     

Preparation and properties of nano ZnO toughed phenol–urea-formaldehyde foam

Urea formaldehyde (UF) and phenol formaldehyde (PF) foam possess outstanding flame-retardant properties, excellent insulation, and low thermal conductivity. These properties make them suitable for thermal insulation in buildings. However, the mechanical properties still need to be improved. In this study, orthogonal test was designed to optimize the level components of PF/UF composite foam first, then nano ZnO was added to the PF/UF composite foam to improve its toughness. The effects of nano ZnO on the morphology, apparent density, pulverization rate, thermal conductivity and thermal degradation property, flame retardancy, and mechanical properties of the ZnO/PF/UF nanocomposite foam were studied. The addition of nano ZnO improved the bending and compressive strength and decreased the pulverization rate of the composite foam significantly. The ZnO/PF/UF nanocomposite foam also presented better flame retardant properties than PF/UF composite foam. The largest oxygen index values of ZnO/PF/UF nanocomposite foam could reach 39.31%, while the thermal conductivity and the maximum rate of weight loss temperature were increased to 0.036 W/(m∙K) and 279°C, respectively. Moreover, ZnO/PF/UF nanocomposite foam showed low apparent density property (0.27 g/cm³).     

Synthesis of Ag3PO4–ZnO nanorod composites with high visible-light photocatalytic activity

Ag₃PO₄ nanoparticles with 50–100 nm in size distributed on the surface of ZnO nanorods with ca. 20 nm in diameter and 1–2 μm in length have been synthesized by a facile method. The Ag₃PO₄–ZnO nanorod composites had much higher photocatalytic activity toward degradation of Rhodamine B (RhB) under visible light irradiation than pure ZnO nanorods, and had better recyclability and stability than pure Ag₃PO₄ nanoparticles. The Ag₃PO₄–ZnO nanorod composite with the molar ratio of Ag₃PO₄:ZnO = 1:40 exhibited the highest photodegradation efficiency of RhB (93%), which was 1.5 times of pure ZnO nanorods.     

Effect of Zr–Al Co-Doping on Structure and Photocatalytic Performance of ZnO Photocatalyst

利用水热处理结合焙烧的方法分别制备了Zr、Al掺杂及Zr–Al共掺的ZnO光催化剂。研究了制备的光催化剂样品的相结构和光谱性能;以紫外光（λ=254nm）为光源,酸性橙Ⅱ为降解对象,进行光催化活性测试;考察了Zr、Al掺杂对ZnO光催化剂反应活性的影响。研究表明,制备的产物均为六方晶系纤锌矿结构的ZnO;Zr、Al掺杂及Zr–Al共掺的ZnO样品的光催化活性相对于纯ZnO均有较大程度的提高,而且Zr–Al共掺的ZnO的光催化性能明显优于单一掺杂的。Zr–Al共掺可以明显改善ZnO表面状态,使ZnO具有更丰富的表面羟基,同时可以抑制光生电子–空穴对的复合,从而有利于光催化活性和稳定性的提高。     

Atomic Layer Deposition of ZnO on Multi-walled Carbon Nanotubes and Its Use for Synthesis of CNT–ZnO Heterostructures

In this article, direct coating of ZnO on PECVD-grown multi-walled carbon nanotubes (MWCNTs) is achieved using atomic layer deposition (ALD). Transmission electron microscopy investigation shows that the deposited ZnO shell is continuous and uniform, in contrast to the previously reported particle morphology. The ZnO layer has a good crystalline quality as indicated by Raman and photoluminescence (PL) measurements. We also show that such ZnO layer can be used as seed layer for subsequent hydrothermal growth of ZnO nanorods, resulting in branched CNT–inorganic hybrid nanostructures. Potentially, this method can also apply to the fabrication of ZnO-based hybrid nanostructures on other carbon nanomaterials.     

Physical and Electrical Performance of Vapor–Solid Grown ZnO Straight Nanowires

Physical and electrical properties of wurtzitic ZnO straight nanowires grown via a vapor–solid mechanism were investigated. Raman spectrum shows four first-order phonon frequencies and a second-order Raman frequency of the ZnO nanowires. Electrical and photoconductive performance of individual ZnO straight nanowire devices was studied. The results indicate that the nanowires reported here are n-type semi-conductors and UV light sensitive, and a desirable candidate for fabricating UV light nanosensors and other applications.     

Hollow mesoporous silica spheres supported Ag and Ag–Au catalyzed reduction of 4-nitrobenzo-15-crown

Hollow mesoporous silica (HMS) spheres of size within the range 120–220 nm have been prepared using propanol–water solvent as template and cetyltrimethylammonium bromide (CTAB) as stabilizer. HMS supported silver and silver–gold catalysts were prepared by impregnating metal nanoparticles on HMS and were characterized by ultraviolet–visible spectroscopy (UV–vis), dynamic light scattering (DLS), optical microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductive coupled plasma optical emission spectroscopy (ICP-OES) and N₂ adsorption–desorption. The reduction of 4-nitrobenzo-15-crown (4-NB-15-C) was compared using HMS supported silver and silver–gold nanocatalysts varying experimental parameters. Bimetallic Ag–Au/HMS nanocatalysts was found to be more active than monometallic Ag/HMS nanocatalyst.     

One-pot fabrication of Ag–SrTiO3 nanocomposite and its enhanced thermoelectric properties

Ag–SrTiO₃ ceramic nanoparticles were fabricated by doping SrTiO₃ with various contents (0.5, 1, 3, and 5%, in mass ratio) of Ag. Composite samples were prepared through a one-pot solvothermal method and sintering process. The temperature-dependent thermoelectric properties of these sample were measured from 300 K to 500 K. The maximum power factor (843.3 μ·W/m·K²) at 500 K, which is ∼3.96 times higher than that of the pristine SrTiO₃ ceramics, was obtained for the Ag–SrTiO₃ composite sample with 1% of Ag. In addition, the thermal conductivity of the composites decreased due to the phonon scattering effect. The maximum thermoelectric figure of merit (ZT), i.e., ∼0.09, which was achieved with 1% of Ag at 500 K, yielded an enhanced power factor and a reduced thermal conductivity. This ZT value was ∼4.27 times larger than that of pristine SrTiO₃ at the same temperature.     

Microstructure and electrical characteristics of ZnO–B2O3–PbO–V2O5–MnO2 ceramics prepared from ZnO nanopowders

A peculiar kind of ZnO–B₂O₃–PbO–V₂O₅–MnO₂ ceramics was produced from the ZnO nanopowders directly co-doped with the oxides instead of lead zinc borate frit in this investigation. The 8 wt.% (PbO+B₂O₃) co-doped ceramics sintered at 950 °C for 2 h displayed the optimum electrical properties, that is, leakage current density J_L=6.2×10⁻⁶ A/cm², nonlinear coefficient α=22.8 and breakdown voltage V_BK=331 V/mm. The co-doping of 8 wt.% (PbO+B₂O₃) resulted in an increase in nonlinear coefficient and a decrease in leakage current density of the ZnO–V₂O₅ varistors while the sintering temperature showed no evident influence on nonlinear coefficient and leakage current density at the range of 800–950 °C.     

Glucose sensing,photocatalytic and antibacterial properties of graphene–ZnO nanoparticle hybrids

A simple and efficient approach was developed to uniformly decorate graphene nanosheets with zinc oxide (ZnO) nanoparticles. A single source precursor, zinc benzoate dihydrazinate complex, has been used for the in situ generation of ZnO nanoparticles onto graphene at a relatively low temperature, 200 °C. Physico chemical analyses such as X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy revealed that ZnO nanoparticles were finely dispersed on the surface of graphene. ZnO–graphene hybrids were further characterized by Raman spectroscopy and ultraviolet visible spectroscopy and room-temperature photoluminescence. The materials exhibited excellent photocatalytic activity as evident from the degradation of methylene blue in ethanol under UV irradiation. An electrochemical glucose biosensor was fabricated by immobilization of glucose oxidase on the ZnO–graphene hybrids. This biosensor showed improved sensitivity towards glucose as compared to graphene. Also, the hybrids showed significant antibacterial activity against E. coli, gram negative bacteria. This simple and economical preparation strategy may be extended for the preparation of other graphene-based hybrids.     

Electrochemical synthesis and surface characterization of hexagonal Cu–ZnO nano-funnel tube films

An electrochemical deposition technique was used to synthesis hexagonal nano-funnel tube films on zinc foil, utilizing an electrolyte of ZnCl₂+H₂O₂ under ambient conditions. The structures, morphologies, chemical compositions, and optical properties of the synthesized films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectrometry (UV-vis-DRS), photoluminescence (PL) spectrometry, and energy-dispersive X-ray spectrometry (EDS) techniques. The XRD pattern showed a set of diffraction peaks that were indexed to the ZnO, Zn(OH)₂, and Cu phases. The SEM observations revealed a cauliflower-like morphology consisting of branches in the form of nano-funnel tubes. The TEM results demonstrated that the synthesized film was comprised of several branches. The EDS studies confirmed the presence of only Cu, Zn, and O atoms. The UV-vis-DRS spectrum showed the onset of the band gap absorption peak at ～375 nm. The PL studies evaluated various emission bands that originated from different defect mechanisms. In addition, the hexagonal nano-funnel tube film showed a good superhydrophobicity, with a water contact angle of ～153°.     

Preparation and corrosion resistance of nanostructured PVC/ZnO–polyaniline hybrid coating

ZnO–polyaniline nanocomposite with core–shell nanostructure was prepared by in situ polymerization of aniline monomer in the presence of ZnO nanoparticles. Fourier transform infrared spectroscopy, X-ray diffraction patterns, field emission scanning electron microscopy and transmission electron microscopy techniques were used to characterize the composition and structure of ZnO–polyaniline nanocomposite. d.c. electrical conductivity measurement showed that the electrical conductivity of ZnO–polyaniline nanocomposite pellets is higher than that of pristine polyaniline and ZnO nanoparticles pellets. The addition of ZnO nanoparticles causes to the increasing of polyaniline electrical conductivity. ZnO–polyaniline nanocomposite was mixed with polyvinyl chloride (PVC) through a solution mixing method and the three components PVC/ZnO–polyaniline hybrid material was applied as coating on iron coupon by the solution casting method. Corrosion protection efficiency of PVC/ZnO–polyaniline hybrid coating on iron coupons was studied by open circuit potential and Tafel techniques in 3.5% NaCl solution as corrosive environment. According to the results, PVC/ZnO–polyaniline hybrid nanocomposite coating showed dramatically increased corrosion protection effect on iron samples compared to that of uncoated iron coupon and pure polyaniline anticorrosive coating. It was found that ZnO nanoparticles improve the barrier and electrochemical anticorrosive properties of polyaniline and the addition of polyvinyl chloride increases the barrier effect of polyaniline coating.     

Growth and optical properties of ZnO–In2O3 heterostructure nanowires

ZnO–In₂O₃ heterostructure nanowires were grown on a Si (111) substrate using the thermal evaporation method. Scanning electron microscopy results showed that the ZnO nanowires had spherical caps. The X-ray diffraction (XRD) pattern and energy-dispersive X-ray (EDX) spectrum indicated that these caps were In₂O₃. An analysis of the early growth process revealed that indium oxide might have played a self-catalytic role. Therefore, it was plausible that the vapor–liquid–solid mechanism (VLS) was responsible for the growth of the ZnO–In₂O₃ heterostructure nanowires. The optical properties of the products were characterized using a photoluminescence (PL) technique. The PL results for the ZnO–In₂O₃ heterostructure nanowires showed a strong peak in the ultraviolet region as a result of the near band emission and a negligible peak for the visible emissions that occurred as a result of the defects. Based on these PL results, it was found that the In₂O₃ nanostructures not only introduced the caps at the tips of the ZnO nanowires but also partially passivated the nanowire surfaces, leading to an improved near band edge emission and the suppression of the defect luminescence.     

Surface characterization of Au–ZnO nanowire films

Au–ZnO nanowire films have been synthesized by annealing Zn foils coated with a thin layer of gold. An X-ray diffraction study found that the synthesized ZnO consists mainly of a hexagonal wurtzite structure along with a small amount of AuZn₃ phase. Scanning electron images showed that the ZnO wires extend to several microns in length. X-ray photoelectron spectroscopy studies confirmed the oxidation states of Au and Zn. An asymmetric O 1s peak indicates the presence of oxygen in an oxide layer and O–H groups on the films surfaces. Photoluminescence (PL) spectra showed different visible peaks for pre-annealed films, while for annealed films an UV peak appeared. In addition, the PL analysis showed that the overall intensity of photoluminescence decreased significantly after the films were annealed. Raman spectroscopy results also indicated that the crystalline quality of the films improved with annealing. This could be attributed to a decrease in oxygen vacancies and/or absorption of O–H groups on the surface of ZnO film. The highly hydrophilic surface with a water contact angle of ∼155° was obtained after annealing in air.     

Fabrication and Characterization of Pure and Pb-doped ZnO Thin Films Prepared by Sol–Gel and Dip-coeting Method

In this paper, undoped and Pb-doped ZnO thin films have been prepared by sol gel method and deposited on glass substrate using dip-coating technique. The structural, morphological, and optical properties of the films were investigated as a function of Pb doping. The results of the structural tests showed that these films are of a polycrystalline hexagonal structure with a preferred orientation in the (002) direction. The grain size values of Pb-doped films were lower than that of pure ZnO, but the strain and the dislocation density values inecrease with increase Pb doping ratio. The atomic force microscopy (AFM) images showed that the particle size and Root Mean Square (RMS) of ZnO decrease with increasing Pb doping. The optical band gap values were found to increase from (3.19 to 3.30 eV) and the Urbach energy decrease from (322 to 313 meV). PL spectra exhibit an increased amount of defects with increasing Pb, which leads to a red shift in the UV region.

     

Preparation of Ag–Cu bimetallic dendritic nanostructures and their hydrogen peroxide electroreduction property

In this work, dendritic silver–copper (Ag–Cu) nanostructures were synthesised on a copper foil by electrodeposition and subsequently galvanic displacement reaction without any surfactant. The crystalline nature of the nanostructures was examined by X-ray diffraction, and the morphology of the material was investigated by field-emission scanning electron microscopy. The applied potential, displacement reaction time, and silver nitrate solution concentration exerted different effects on the nanoparticle shape. And a possible growth mechanism of the Ag–Cu dendrites was proposed based on the experimental results. The electrochemical properties of the Ag–Cu dendrite-modified electrode were characterised by linear sweep voltammetry. The reduction peak potential of hydrogen peroxide (H₂O₂) was about ?0.25 V (vs. a saturated calomel electrode), which indicated that the as-synthesised Ag–Cu dendrites had favourable electroreduction activity towards hydrogen peroxide. At the same time, we found that the solution pH also affected the electrocatalytic ability of the dendrites for H₂O₂ reduction, which was important for the design of a NaBH₄–H₂O₂ battery.