Synthesis of N-doped ZnO nanoparticles with improved photocatalytical activity

ZnO nanoparticles with diameters of 20–50 nm were initially prepared by solvothermal route using ZnCl₂ and ethylene glycol as raw materials. With the as-prepared ZnO nanoparticles as precursor and melamine as N source, N-doped ZnO nanoparticles were then successfully obtained by a simple, efficient, and environmentally-friendly vacuum atmosphere method. Both the undoped and N-doped ZnO nanoparticles have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectrometry. The N-doped ZnO nanoparticles were found to exhibit obviously improved photocatalytic performance for the degradation of methyl orange under simulated daylight irradiation in comparison with the undoped ZnO nanoparticles. The extending light absorption towards the visible-light region and increased crystallinity of the N-doped ZnO nanoparticles contribute equally to the improved photocatalytic performance. The present vacuum atmosphere method opens up a new strategy for preparing other N-doped oxide semiconductors such as TiO₂.     

Characterization and composition evolution of multiple-phase nanoscaled ceramic powders produced by laser ablation

Nanosized ceramic powder was prepared by laser ablation under different atmospheres using a ceramic target composed of ZrO₂, TiO₂, ZnO and Al₂O₃. Physical characteristics and microstructure of nanoparticles, including particle morphology, phase transformation, powder compositions and far-infrared emissivity, have been investigated. The laser-ablated nanoparticles exhibit two kinds of particle size distribution with 7-15 (70-90%) and 40-100 nm (10-30%). Nanoparticles synthesized at lower laser fluences show poor crystallinity but rich Zn composition. While increasing laser fluence, better crystalline nanoparticles with rich Zr composition were obtained. It was found that both composition and morphology of nanoparticles change with laser fluence. The average far-infrared emissivity of the nanoparticles varies with crystallinity of nanoparticles.     

Microwave-assisted synthesis of ZnO doped CeO2 nanoparticles as potential scaffold for highly sensitive nitroaniline chemical sensor

Herein, we report the successful fabrication of highly sensitive, reproducible and reliable nitroaniline chemical sensor based on ZnO doped CeO₂ nanoparticles. The ZnO doped CeO₂ nanoparticles were synthesized through a simple, facile and rapid microwave-assisted method and characterized by several techniques. The detailed characterizations confirmed that the synthesized nanoparticles were monodisperse and grown in high density and possessing good crystallinity. Further, the synthesized ZnO doped CeO₂ nanoparticles were used as efficient electron mediators for the fabrication of high sensitive nitroaniline chemical sensors. The fabricated nitroaniline chemical sensor exhibited very high sensitivity of 550.42 μA mM⁻¹ cm⁻² and experimental detection limit of 0.25 mM. To the best of our knowledge, this is the first report in which CeO₂–ZnO nanoparticles were used as efficient electron mediators for the fabrication of nitroaniline chemical sensors. Thus, presented work demonstrates that ZnO doped CeO₂ nanoparticles are potential material to fabricate highly efficient and reliable chemical sensors.     

Effect of Calcination Temperature on the Structural and Optical Properties of (ZnO)0.8 (ZrO2)0.2 Nanoparticles

Calcination temperature has influenced the structural and optical features of nanocrystalline (ZnO)_0.8 (ZrO₂)_0.2 series. Indeed, at present, general research in the approach to synthesis of (ZnO)_0.8 (ZrO₂)_0.2 nanoparticles by combustion using zinc nitrate hexahydrate (Zn (NO₃)₂·6H₂O) and zirconium (11) nitrate pentahydrate (Zr (NO₃)₂·5H₂O) is still in its infancy. A Thermogravimetric (TG) assessment was performed to determine the precursor of the conduction. Characterizations such as energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible, Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) spectroscopy were carried out. The crystallite size of the binary oxides (ZnO)_0.8 (ZrO₂)_0.2 on the maximum expansion of ZnO–ZrO₂ nanoparticle was studied using Scherrer’s equation. Due to calcination, significant modifications were observed in terms of the size of the particles, the absorption spectra, and the intensity of the photoluminescence. In the XRD result, an increment in crystallinity was observed from 10.20 nm to 28.00 nm while the FTIR findings showed the removal of the polymer as well as the presence of nanoparticles metals. The optical band gap results indicated a decline in energy band gap between (3.27 and 3.12) eV for (ZnO)_0.8 and (4.89–4.51) eV for (ZrO₂) _0.2 nanoparticles. A photoluminescence result showed two individual peaks at 655 nm (1.89 eV) and 715 nm (1.73 eV) respectively. The study also showed the application which can be a suitable choice to be used in solar cell applications.

     

Antibacterial performance of TiO2 ultrafine nanopowder synthesized by a chemical vapor condensation method: Effect of synthesis temperature and precursor vapor concentration

TiO₂ nanoparticles were synthesized using a chemical vapor condensation (CVC) method, and their physicochemical properties were characterized to optimize the synthesis conditions for antibacterial activity. The antibacterial activities of CVC-TiO₂ nanoparticles and commercialized TiO₂ nanoparticles (P25, Deggusa) were investigated according to UV exposure time and amount of photocatalyst. We found that the specific surface area and the crystallinity of CVC-TiO₂ nanoparticles were varied depending on synthesis temperature and precursor vapor concentration. As a result, the CVC-TiO₂ nanoparticles showed a higher specific surface area and better crystallinity than that of P25TiO₂. More importantly, CVC-TiO₂ nanoparticles generated a larger amount of hydroxyl radicals than P25TiO₂. Consequently CVC-TiO₂ nanoparticles were more effective as an antibacterial photocatalyst than P25TiO₂ under irradiation with UV light. Based-on these results, the optimum synthetic conditions of CVC-TiO₂ nanoparticles for bactericidal effect were found.     

Direct writing polyvinylidene difluoride thin films by intercalation of nano-ZnO

Polyvinylidene fluoride (PVDF) is a preeminent pyrolytic and piezoelectric polymer. It has been widely studied as an ideal material for wearable flexible sensors or low-power electronic equipment. PVDF/ZnO thin films were prepared by direct writing method, which promoted the ordered arrangement of PVDF molecular chains under the action of electric field and thus improved the crystallinity of the β phase. Meanwhile, the effects of intercalation of ZnO nanoparticles on the crystallinity of PVDF thin films were explored. The results show that appropriate addition of nano-ZnO as nucleating agent can induce the crystallinity of the PVDF film obviously. While the additive amount of nanoparticles was 0.02 wt%, the relative β phase content of the PVDF film can reach 88.92%. Under the double action of adding ZnO nanoparticles and electric field assistance, the dielectric constant of the composite film increases from 6.9 (pure PVDF) to 12.4 (0.03 wt% ZnO) at a frequency of 1 kHz. The d₃₃ value of the film without polarization is up to −9.1 pC/N, the output voltage is increased to 351 mV, and the conductivity of the composite film has been improved.     

Synthesis and Characterization of Anti-fungus,Anti-corrosion and Self-cleaning Hybrid Nanocomposite Coatings Based on Sol–Gel Process

Anti-corrosion, anti-fungus, and self-cleaning properties of coatings containing ZnO–TiO₂, SiO₂–TiO₂ and SiO₂/TiO₂/ZnO nanoparticles synthesized based on sol–gel precursors using tetra methoxysilane, 3-glycidoxypropyl trimethoxysilane, tetra (n-butyl orthotitanate) and zinc acetate dihydrate were investigated by FESEM, EDAX and TEM analyses. Results indicated uniform dispersion of inorganic nanoparticles in the range of 20–40 nm in size. Anti-corrosion property of the hybrid coating was characterized by EIS measurements and parametrically analyzed in an equivalent circuit when the coating was exposed to salt solution. Results showed that, ZnO and TiO₂ nanoparticles enhance anti-corrosion property of the hybrid coatings. Anti-fungus and anti-bacterial properties of the coatings were determined by diameter of inhibition zone and inhabitation of bacterial growth, respectively. The coating containing ZnO and TiO₂ nanoparticles showed anti-fungus and anti-bacterial properties which were related to their photocatalytic properties. Degradation of methylene blue in aqueous solution was determined by UV–Visible tests which indicated self-cleaning property of the coatings containing ZnO and TiO₂ nanoparticles.     

Growth temperature dependent properties of ZnO nanorod arrays on glass substrate prepared by wet chemical method

In this work, ZnO nanorod arrays were grown on glass substrate by the wet chemical method, and the effect of synthesis temperature on the properties was investigated. The grown nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman and Photoluminescence (PL) measurements. XRD pattern showed that nanorod prepared at 80 °C and 90 °C has high crystallinity with wurtzite structure and orientated along the c-axis. However, nanorods were not formed at 60 °C and 70 °C due to less energy supply for the growth of the ZnO. FE-SEM results showed that the morphology and the size of ZnO can be effectively controlled. In particular, as the temperature increased, diameter of the nanorod was increased while length decreased. Raman scattering spectra of ZnO nanorod arrays revealed the characteristic E₂^high mode that is related to the vibration of oxygen atoms in the wurtzite ZnO. Room-temperature PL spectra of the ZnO nanorods revealed a near-band-edge (NBE) emission peak. The NBE (UV light emission) band at ~383 nm might be attributed to the recombination of free exciton. The narrow full-width at half-maximum (FWHM) of the UV emission indicated that ZnO nanorods had high crystallinity.     

Facile synthesis of ZnO nanostructures and enhancement of their sinterability via short-time cryo-milling

Zinc oxide (ZnO), a wide band-gap semiconductor, has received a great interest due to its potential applications in various fields both as nanostructures and as sintered compacts. In this study, we report on the synthesis of the ZnO nanostructures and facilitation of their sintering for the production of fine-grained dense compacts. The facile synthesis of gram scale ZnO nanostructures was achieved by thermal decomposition of zinc acetate dihydrate (Zn(Ac)₂·2H₂O) or Zn(Ac)₂·2H₂O/graphite mixtures at 300 °C for 12 h. Thermal decomposition of Zn(Ac)₂ resulted in the formation of mostly ZnO nanoparticles with wurtzite structure along with ZnO nanorods, while the addition of graphite significantly promoted the growth of ZnO nanowires. Microstructural and phase properties of the obtained ZnO nanostructures were determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) techniques, all of which revealed the successful synthesis of high quality ZnO nanostructures. In addition to synthesis and characterization of the ZnO nanostructures, we report on the enhancement of their sinterability by a subsequent cryogenic milling for a short duration of 5 min. As a result of the applied cryo-milling, fabrication of highly dense (96.2%) sintered compacts with fine grain sizes (572 nm) could be achieved after pressureless sintering at 1000 °C for 2 h.     

Glass forming,crystallization, and physical properties of MgO-Al2O3-SiO2-B2O3 glass-ceramics modified by ZnO replacing MgO

This study focused on the glass forming, crystallization, and physical properties of ZnO doped MgO-Al₂O₃-SiO₂-B₂O₃ glass-ceramics. The results show that the glass forming ability enhances first with ZnO increasing from 0 to 0.5 mol%, and then weakens with further addition of ZnO which acted as network modifier. No nucleating agent was used and the crystallization of studied glasses is controlled by a surface crystallization mechanism. The predominant phase in glass-ceramics changed from α-cordierite to spinel/gahnite as ZnO gradually replaced MgO. The phase type did not change; however, the crystallinity and grain size in glass-ceramics increased when the glasses were treated from 1030 °C to 1100 °C. The introduction of ZnO can improve the thermal, mechanical, and dielectric properties of the glass-ceramics. The results reveal a rational mechanism of glass formation, crystal precipitation, and evolution between structure and performance in the xZnO-(20-x)MgO-20Al₂O₃-57SiO₂-3B₂O₃ (0 ≤ x ≤ 20 mol%) system.     

Surface and grain boundary excess of ZnO-doped TiO2 anatase nanopowders

In this study, TiO₂ nanoparticles containing 0–10?mol% ZnO were synthesized using the polymeric precursor method. The surface excess of ZnO on the TiO₂ surface was measured by the selective lixiviation method, and the grain boundary (GB) excess was calculated considering the total amount of ZnO and its solubility in the TiO₂ bulk. The results showed that ZnO segregates on both the surface and GBs of the TiO₂ nanopowder and that the GBs are richer in ZnO at high ZnO concentrations. X-ray photoelectron spectroscopy (XPS) analysis confirmed that ZnO segregated on the TiO₂ surface. However, after acid lixiviation, the same analysis showed a considerable reduction of the surface concentration of ZnO. A systematic reduction in the crystallite size and an increase in the specific surface area of TiO₂ were observed when increasing the ZnO concentration, which confirms the nanoparticle stability provided by the interfaces enrichment with ZnO. By measuring the electrophoretic mobility, it was possible to show the changes to the surface composition of the TiO₂ nanoparticles and the pH for ZnO solubilization.     

Tuning of dielectric properties of (ZnO)x-(CuTl-1223) nanoparticles-superconductor composites

Zinc oxide (ZnO) nanoparticles and Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ (CuTl-1223) superconducting phase were prepared separately by sol–gel and solid-state reaction, respectively. ZnO nanoparticles were mixed with CuTl-1223 to get (ZnO)_x-(CuTl-1223); x=0, 0.5, 1.0 and 1.5 wt% nanoparticles-superconductor composites, which were characterized by different experimental techniques. There was no change observed in crystal structure of host CuTl-1223 phase after addition of ZnO nanoparticles, which provide a clue about the occupancy of these nanoparticles at the grains-boundaries. The inclusion of ZnO nanoparticles was found to reduce the voids and to improve the inter-grains connectivity in the host CuTl-1223 phase. The zero resistance critical temperature {T_c(R=0)(K)} was increased by increasing wt% addition of ZnO nanoparticles in CuTl-1223 matrix. The dielectric properties of these samples i.e. dielectric constants (ε′_r ε′′_r), and dielectric loss (tan δ), were determined by experimentally measuring the capacitance (C) and conductance (G) as a function of frequency at different operating temperatures. The values of dielectric parameters were decreased with the increase of frequency and become constant at certain higher frequency values, while the values of these parameters were increased with the increase of operating temperature values. So, we can tune the dielectric properties of CuTl-1223 superconducting phase by varying the content of ZnO nanoparticles, frequency and operating temperature.     

The effect of ageing time on co-precipitated Cu/ZnO/ZrO2 catalysts used in methanol synthesis from CO2 and H2

The effect of suspension ageing time during the catalyst precipitation process on the performance of co-precipitated Cu/ZnO/ZrO₂ catalysts in methanol synthesis from CO₂ and H₂ has been studied. The ageing time influenced greatly the physical and chemical characteristics of the catalysts as well as their activity in the methanol synthesis. Prolonged ageing was advantageous, mainly due to both lower sodium contents and enhanced crystallinity of the catalysts.     

Photocatalytic hydrogen generation of ZnO rod–CdS/reduced graphene oxide heterostructure prepared by Pt-induced oxidation and light irradiation-assisted methods

A synthesis method including Pt-induced oxidation and light irradiation-assisted routes has been developed to prepare a ZnO rod–CdS/reduced graphene oxide (RGO) heterostructure. Here, graphene oxide nanosheets are reduced and loaded onto the surface of Zn spheres using a redox process. ZnO rods are generated from Zn spheres by a Pt-induced oxidation method, and CdS nanoparticles are then loaded onto the surface of RGO via a light irradiation-assisted method. The ZnO rod–CdS/RGO heterostructure exhibits 3.8 times higher photocatalytic hydrogen generation rate from an aqueous solution containing Na₂S/Na₂SO₃ than the reference ZnO rod–CdS heterostructure under simulated solar light irradiation. The optimal contents of RGO nanosheets and CdS nanoparticles are 2 wt% and 20 at.%, respectively.     

Thermal,thermomechanical, and morphological characterization of poly(vinyl chloride) (PVC)/ZnO nanocomposites: PVC molecular weight effect

Poly(vinyl chloride) (PVC)‐based nanocomposites containing 2 wt% zinc oxide (ZnO) nanoparticles were prepared by solution casting and the effect of the PVC molecular weight (MW) on the morphology, thermal properties, and thermogravimetric behavior was studied. The addition of ZnO nanoparticles to PVCs of different MWs increased the glass transition temperature (T_g) of the resulting nanocomposites, the extent of which was dependent upon the MW of the PVC matrix. The nanocomposite samples exhibited broadened transition zones as compared with their unfilled PVC matrices. The extent of transition zone broadening was also controlled by the MW of the PVC matrix in the nanocomposites. In the absence of ZnO nanoparticles, the increase in MW of PVC had no effect on the breadth of the transition zone. The TGA results showed that the incorporation of ZnO nanoparticles into PVC matrices of different MWs accelerated the first stage weight loss via the nanoparticle catalytic effect through removal of HCL from the polymeric chains. The presence of ZnO nanoparticles lowered the second stage weight loss, and the char yield obtained for nanocomposites samples was significantly greater than that obtained for neat PVC samples. At low MWs, the presence of ZnO nanoparticles had no effect on the first stage of thermal degradation process. The presence of ZnO nanoparticles in the matrix in different nanocomposites was revealed by SEM observations, and the EDX analysis demonstrated a progressive improvement in the distribution and dispersion state of ZnO nanoparticles in the PVC‐based nanocomposites as the MW of PVC matrix gradually increased. J. VINYL ADDIT. TECHNOL., 25:E63–E71, 2019. © 2018 Society of Plastics Engineers     

A novel thermal decomposition method for the synthesis of ZnO nanoparticles from low concentration ZnSO4 solutions

In this research work, ZnO nanoparticles were prepared by direct thermal decomposition method with Zn₄(SO₄)(OH)₆·0.5 H₂O as a precursor. The precursor was calcinated in air for 1 h at 825 °C. Samples were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), infrared spectrum (IR), and scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD, EDS, and IR results indicated that the ZnO nanoparticles were pure. The average crystallite and particle size of the ZnO nanoparticles were estimated to be 87 nm and 92 nm by XRD and TEM, respectively. The SEM and TEM images showed that the ZnO nanoparticles were of spherical shape. The simplicity of the present method suggests its potential application at industrial scale as a cheap and convenient way to produce pure ZnO nanoparticles from low concentration ZnSO₄ solutions.     

Preparation of CeO2/ZnO nanostructured microspheres and their catalytic properties

CeO₂/ZnO nanostructured microspheres with an average diameter of about 3.8 μm were synthesized by a solid-stabilized emulsion route. The CeO₂/ZnO nanostructured microspheres were characterized with SEM, XRD, CO₂-TPD, BET measurement and size analysis. Based on the oxidative coupling reaction of methane with carbon dioxide as an oxidant, the catalytic performance of the CeO₂/ZnO nanostructured microspheres was evaluated and compared with that of the CeO₂/ZnO nanoparticles. The results showed that the surfaces of the CeO₂/ZnO nanostructured microspheres consisted of petal-like structures with a petal thickness of about 90 nm and a petal depth of 0.4 μm to 0.9 μm. Using CeO₂/ZnO nanostructured microspheres as catalysts for the oxidative coupling of methane with carbon dioxide, the conversion of methane corresponded with that using the CeO₂/ZnO nanoparticles, while the CeO₂/ZnO nanostructured microspheres had much longer operating life.     

Sol‐Gel‐Derived Sb‐Doped SnO2 Nanoparticles Controlled in Size by Nb2O5

Nanocrystalline Sb‐doped SnO₂ particles were prepared by sol‐gel and their particle growth was controlled by niobium oxide. In the present synthesis, SnCl₄ and SbCl₃, as precursors, were dissolved and hydrolyzed in ethylene glycol at 80–120 °C, and further 0.1 mol.‐% Nb₂O₅ through its precursor NbCl₅ was mixed to the above solution. The mixture was then dried at 120–150 °C and calcinated at 600 °C for 2 hours. By XRD and TEM, Sb‐doped SnO₂ nanoparticles were highly crystalline and their mean crystal size was ca.10–20 nm with narrow particle size distribution. As the addition of antimony increased, the crystallinity and particle size distribution of SnO₂ particles had the trend to decrease.     

Characterization and property of bifunctional Zn-incorporated TiO2 micro-arc oxidation coatings: The influence of different Zn sources

In the present work, Zn-incorporated TiO₂ coatings are prepared through a one-step micro-arc oxidation (MAO) method on a grade 4 pure titanium with the addition of either Na₂Zn-EDTA solution or ZnO nanoparticles (NPs) as Zn sources. The microstructural features of both Zn-incorporated TiO₂ coatings were systematically examined. It is revealed that different Zn sources result in significant difference of phase component, chemical state, composition and morphology between the resultant Zn-incorporated MAO coatings. Zn species could be present as ZnO and Zn(OH)₂ in the coating when Na₂Zn-EDTA was used as Zn source whereas the presence of ZnO nano-clusters is obvious on the coating surface with ZnO NPs as Zn source. The addition of ZnO NPs during the MAO process also leads to a lower Zn content of the resultant coating, which is more defective with increased thickness in comparison to that of Na₂Zn-EDTA. Further, antibacterial property and osteogenic activity of both Zn-incorporated coatings were examined. Both Zn-incorporated coatings exhibit favourable bacterial inhibition ability and bone formability, suggesting the successful synthesis of bifunctional coatings through the facile one-step micro-arc oxidation method.     

A new synergistic effect in one step sputtered ZnO/Zn2SnO4 heterojunction films for H2 sensing related to crystal structure and film compactness

In this paper, ZnO/Zn₂SnO₄ heterojunction films were one step fabricated by magnetron sputtering and the dependence of crystal structures, film compactness and H₂ sensing properties on annealing process were investigated and discussed. The results showed that three typical surface morphologies can be controlled by adjusting annealing temperatures and periods. The films annealed at the temperature of 550 °C for 6 h showed the best H₂ sensing properties. It exhibited a response (R_a/R_g) of 28.3–100 ppm H₂ at the temperature of 230 °C and the detection limit is 30.2 ppb. Meanwhile, it also showed a good selectivity and long-term stability to H₂. The H₂ sensing mechanism is attributed to the synergistic effect between ZnO (0001) signal crystal facets and ZnO/Zn₂SnO₄ heterojunction structures which enhanced the gas reactivity and resistance modulation range. On the contrary, insufficient annealing restricts the film crystallinity and the growth of hexagonal ZnO while undue annealing destroys the compactness of the films, leading to poor H₂ sensing properties.