Microwave-Assisted Hydrothermal Preparation, Characterization and Photocatalytic Properties of a Chrysanthemum-Shaped ZnWO4 Photocatalyst

A novel chrysanthemum-shaped monocline ZnWO₄ photocatalyst was synthesized by microwave-assisted hydrothermal method with Na₂WO₄·2H₂O and Zn(NO₃)₂·6H₂O as raw materials at different reaction temperatures. The prepared ZnWO₄ photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy, Photoluminescence spectrum (PL) and UV–Vis absorption spectrum (UV–Vis). The photocatalytic property of the prepared chrysanthemum-shaped monocline ZnWO₄ photocatalyst was evaluated by the degradation of Rhodamine B (RhB) in aqueous solution. The effects of reaction temperature on the photocatalytic degradation efficiency of RhB were investigated. The results indicated that the chrysanthemum-shaped monocline ZnWO₄ photocatalyst is prepared by foliated powders with the sizes of about 30 nm and 500 nm respectively at 160 and 220 °C. The PL relative intensity of prepared ZnWO₄ photocatalyst is apparently intensifying with increasing temperature. The photocatalytic property decreases with the increasing recombination probability of the excited electrons and holes. The chrysanthemum-shaped monocline ZnWO₄ photocatalyst prepared at 160 °C possesses the best photocatalytic property, and the degradation efficiency of RhB at 180 min UV-light irradiation is achieved 75 %. The ZnWO₄ has good reusability property on degradation of RhB and the degradation rate is still higher than 65 % after three cycles.     

Characterizations of white-light ZnWO4 phosphor prepared by blending complementary phosphor

In the preparation of ZnWO₄ phosphor, crystalline ZnWO₄ was created, even though the concentration of WO₃ was only 10 mol%. ZnWO₄ was the dominant crystallization phase when the concentration of WO₃ exceeded 40 mol%. The optimal crystallization of ZnWO₄ phosphor was obtained when the composition molar ratio of ZnO to WO₃ was 1:1, and sintering was carried out at 1,100°C for 3 h. In this condition, a bluish-green emission with a peak at 460 nm was observed. For Y₂O₃:Eu³⁺,Li⁺, the complementary phosphor of ZnWO₄, the Li flux improved phosphor crystallization. The red emission peak of the Y₂O₃:Eu³⁺,Li⁺ phosphor was measured at about 612 nm. The optimal photoluminescence intensity of the Y₂O₃:Eu³⁺,Li⁺ phosphor was obtained when it was sintered at 1,200°C for 5 h and was mixed with 11 mol% Eu₂O₃ and 70 mol% Li₂CO₃. When the weight ratio of Y₂O₃:Eu³⁺,Li⁺ to ZnWO₄ was 1:4, the Y₂O₃:Eu³⁺,Li⁺-blended ZnWO₄ phosphor showed white-light emission with Commission Internationale de l’Eclairage coordinates at (0.34, 0.30). The luminance of the white-light phosphor excited by a 6-W UV lamp was around 160 cd/m².     

Novel Green Route of Synthesis of ZnO Nanoparticles by Using Natural Biodegradable Polymer and Its Application as a Catalyst for Oxidation of Aldehydes

ZnO nanoparticles have been synthesized by using biodegradable natural biopolymer viz. Gum Tragacanth. This single step approach is very cost effective and reproducible. The reaction time and concentration of precursor zinc acetate play a major role in the nature and growth of ZnO nanoparticles. ZnO nanoparticles were characterized by X-ray diffraction, SEM, FTIR, EDAX, UV-visible spectroscopy and TEM. ZnO nanoparticles with 20-30 nm in diameter and hexagonal morphology were found; dispersed uniformly. Raman spectrum shows the mode E₂ high at 437 cm^?1 that is related to the vibration of wurtzite Zn-O bond in crystal structure of ZnO. The space between adjacent lattice fringes is ～ sharp 2.42 Å. UV-visible absorption spectrum shows the sharp absorption band at 308 nm assigned to the intrinsic transition from valance band to conduction band. The ZnO nanoparticles display superior catalytic activity of conversion of aldehyde to acid as compared to bulk-ZnO material, because of high surface area of ZnO nanoparticles. A trace amount of ZnO nanoparticles catalyst required for organic conversion. The ZnO nanoparticles as catalyst are highly stable, recyclable and efficient in its activity.     

ZnO nanoparticles and poly(acrylic) acid-based polymer gel electrolyte for photo electrochemical cell

This work presents a photo electrochemical cell based on zinc oxide (ZnO) nanoparticles and poly(acrylic) acid (PAA) doped with sodium iodide (NaI) and iodine (I₂) polymer gel electrolyte. The ZnO powders were synthesized by sol–gel storage and sol–gel centrifugation. The ZnO powder synthesized via sol–gel centrifugation showed the optimal structural properties, with largest crystallite sizes of 58 nm, average particles size between 20 and 80 nm and indirect band gap energy of 3.20 eV. The highest conductivity [(8.0 ± 0.1) × 10^?2 S cm^?1] was obtained for PAA + 0.8 M NaI + 0.02 M I₂. This sample achieved the lowest activation energy (0.029 eV) and electrochemical stability at 1.6 V. The ZnO powder synthesized via sol–gel centrifugation and PAA + 0.8 M NaI + 0.02 M I₂ was fabricated as a Cu–ZnO/PAA + 0.8 M NaI + 0.02 M I₂/C-ITO photo electrochemical cell.     

Calcination temperature-dependent morphology of photocatalytic ZnO nanoparticles prepared by an electrochemical–thermal method

ZnO nanoparticles (NPs) with tunable morphologies were synthesized by a hybrid electrochemical–thermal method at different calcination temperatures without the use of any surfactant or template. The NPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, dynamic light scattering, thermogravimetry–differential thermal analysis, scanning electron microscope and N₂ gas adsorption–desorption studies. The FT-IR spectra of ZnO NPs showed a band at 450 cm^?1, a characteristic of ZnO, which remained fairly unchanged at calcination temperatures even above 300 °C, indicating complete conversion of the precursor to ZnO. The products were thermally stable above 300 °C. The ZnO NPs were present in a hexagonal wurtzite phase and the crystallinity of ZnO increased with an increasing calcination temperature. The ZnO NPs calcined at lower temperature were mesoporous in nature. The surface areas of ZnO NPs calcined at 300 and 400 °C were 51.10 and 40.60 m² g^?1, respectively, which are significantly larger than commercial ZnO nanopowder. Surface diffusion has been found to be the key mechanism of sintering during heating from 300 to 700 °C with the activation energy of sintering as 8.33 kJ mol^?1. The photocatalytic activity of ZnO NPs calcined at different temperatures evaluated by photocatalytic degradation of methylene blue under sunlight showed strong dependence on the surface area of ZnO NPs. The ZnO NPs with high surface area showed enhanced photocatalytic activity.     

室温一步固相反应合成纳米氧化锌的表征、光催化性能及动力学

以七水硫酸锌、氢氧化钠为原料,采用室温一步固相反应合成ZnO纳米粒子,并分别利用X射线衍射分析（XRD）、傅里叶变换红外光谱分析（FTIR）、热重分析（TG）、扫描电子显微分析（SEM）、透射电子显微分析（TEM）、N₂吸附-脱附、紫外可见漫反射光谱分析（UV-Vis DRS）等方法对ZnO纳米粒子进行表征。实验结果表明：不需任何添加剂,室温下可通过一步固相反应合成ZnO纳米粒子,其形成过程首先是ZnSO₄·7H₂O和NaOH充分接触,然后反应形成Zn₄SO₄（OH）₆·5H₂O,最后NaOH的溶解热可使Zn₄SO₄（OH）₆·5H₂O转变为ZnO并逐渐长大形成纳米粒子。同时以甲基橙为降解对象评价了ZnO纳米粒子的光催化活性,实验结果表明：紫外光照射下,该方法合成的ZnO纳米粒子对甲基橙具有较好的光催化活性,且光催化动力学方程符合准一级反应动力学。     

Fe-lactate mediated formation of ZnO sols and self-organized nanorod assemblies

Hot ethanolic mixtures of hydrated Zn(II)- and Fe(II)-carboxylates (acetate and lactate) react to form yellow-orange colored Fe(III)_xZn_yO_zOH_w heteroclusters showing pronounced electronic resonances in the optical UV absorption spectra. On the addition of LiOH to these polymolecular sols, stable nanoparticulate Fe(III)–ZnO colloids are formed. During colloidal growth, 2–4 nm sized weakly crystallized Wurtzite nanoparticles are exclusively formed even in the presence of high Fe content up to 20 at.%. The presence of Fe(III) in the ZnO condensation process retards the nanoparticle growth and blocks the thermal crystallization and size enhancement up to 250 °C. The produced 0.5 M Fe(III)–ZnO sols are useful for film formation processes. From atomic force microscopy-AFM, scanning electron microscopy-SEM and X-ray diffraction-XRD studies, we note important differences in shape and morphology of the thermally annealed Fe(III)–ZnO layers depending on the iron carboxylate employed. Surprisingly, Fe(II)-lactate derived coatings are carrying vertically oriented cone-shaped aggregates composed of 60–120 nm long primary nanorods. Contrary, Fe(II)-acetate based synthesis gave sand-dune like film morphologies containing spherical 12 nm sized nanocrystallites. All film samples possess mesoporosity with pore size ranging between 5 and 20 nm.     

Influence of sodium dodecyl sulfate on the fabrication of zinc oxide nanoparticles

Dispersive ZnO nanoparticles with a primary particle size of about 70 nm and an average agglomerate size of about 2.0 ??m were synthesized via the precipitation-thermal decomposition route using ZnSO₄ and Na₂CO₃ as the reactants and sodium dodecyl sulfate (SDS) as the surface modification agent. The presence of minor amounts of SDS in the formation of hydrozicite (Zn₅(CO₃)₂(OH)₆) precursor changed the agglomeration size of ZnO from 9.7 to 2.0 ??m and the primary particle size of ZnO from about 45 to 70 nm. Molecular simulation based on the DISCOVER model and COMPASS force field indicated that SDS was adsorbed on the surface of Zn₅(CO₃)₂(OH)₆ mainly via the coulomb and hydrogen bond interactions.     

Preparation and characterization of novel polyimide/functionalized ZnO bionanocomposite for gas separation and study of their antibacterial activity

In the present investigation novel Polyimide/functionalized ZnO (PI/ZnO) bionanocomposites containing amino acid (Methionine) and benzimidazole pendent groups with different amounts of modified ZnO nanoparticles (ZnO NPs) were successfully prepared through ultrasonic irradiation technique. Due to the high surface energy and tendency for agglomeration, the surface ZnO NPs was modified by a coupling agent as 3- methacryloxypropyl-trimethoxysilane (MPS) to form MPS-ZnO nanoparticles. The ultrasonic irradiation effectively changes the rheology and the glass transition temperature and the crystallinity of the composite polymer. PI/ZnO nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM analysis showed that the modified ZnO nanoparticles were homogeneously dispersed in polymer matrix. The TGA results of PI/ZnO nanocomposites showed that the thermal stability is obviously improved the presence of MPS-ZnO NPs in comparison with the pure PI and that this increase is higher when the NP content increases. The permeabilities of pure H₂, CH₄, O₂, and N₂ gases through prepared membranes were determined at room temperature (25 °C) and 20 bar feed pressure. The membranes having 20% ZnO showed higher values of H₂ permeability, and H₂/CH₄ and H₂/N₂ ideal selectivities (the ratio of pair gas permeabilities) compared with other membranes. The antibacterial activity of bionanocomposite films was tested against gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). Further, it was observed that antibacterial activity of the resulting hybrid biofilms showed somewhat higher for gram-positive bacteria compared to gram-negative bacteria.     

Synergistic Effect of SnO2/ZnWO4 Core–Shell Nanorods with High Reversible Lithium Storage Capacity

High reversible lithium storage capacity is obtained from novel SnO₂/ZnWO₄ core–shell nanorods. At C/20 (20 h per half cycle) rate, the reversible capacity of SnO₂/ZnWO₄ core–shell nanorods is as high as 1000 mAh g^?1, much higher than that of pure ZnWO₄, SnO₂, or the traditional theoretical result of the simple mixture. Such performance can be attributed to the synergistic effect between the nanostructured SnO₂ and ZnWO₄. The distinct electrochemical activity of ZnWO₄ nanorods probably activates the irreversible capacity of the SnO₂ nanoparticles. These results indicate that high‐performance lithium ion batteries can be realized by introducing the synergistic effect of one‐dimensional core–shell nanocomposites.     

Synthesis and Characterization of Zinc Oxide Nano-particles by Solid State Chemical Reaction Method

Several important synthetic parameters such as precursor concentration, reaction time are found to determine the growth of ZnO nanostructures. These reaction parameters can be tuned to produce a variety size of nanostructures. In this work we show the importance of these parameters on the size of synthesized zinc oxide nano-powders. ZnO nanoparticles are synthesized by the solid-state reaction using ZnSO₄·7H₂O and NaOH as the reagents. In this method Zn(OH)₂ is the intermediate product of the reaction, we show that by adjusting the molar ratio of the reagents and grinding time, we can be removed this unwanted component in the final product so for obtaining pure ZnO nanostructures the calcinations process is not necessary, also we can tune the size of ZnO nanoparticles. XRD spectra of the nanoparticles demonstrate typical diffraction peaks of a well-crystalline Wurtzite ZnO structure transmission electron microscopic observations show that these nanoparticles are of hexagonal phase ZnO mostly in round shapes and he composition analysis by EDX indicate that final product is pure ZnO. In the optimum conditions by XRD analysis we see that the mean grain size of synthesized zinc oxide nano-particles is about 44 nm.     

Photocatalytic studies of silver doped ZnO nanoparticles synthesized by chemical precipitation method

Ag-doped ZnO nanoparticles (Zn_1?xAg_xO; where x = 0.00–0.05) were synthesized by chemical precipitation method. The synthesized products were characterized by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–Vis spectrometer. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology and the measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge after Ag doping. The band gap values of as prepared undoped and doped with silver samples were found to decrease with increase in temperature from 300 to 800 °C. Photocatalytic activities of ZnO and Ag doped ZnO were evaluated by irradiating the sample solution to ultraviolet light by taking methylene blue as organic dye. The experiment demonstrated that the photo-degradation efficiency of 1 mol% Ag-doped ZnO was significantly higher than that of undoped and 2–5 mol% Ag doped ZnO under ultraviolet light irradiation.     

Reactivity of nanoparticles; interaction between zinc and copper oxide nanoparticles and iron ions in an alkaline medium

The reactivity of zinc and copper oxide nanoparticles was investigated upon their interaction with iron oxides. It was ascertained that, depending on the reaction conditions, nanoparticles of zinc and copper ferrites (ZnFe₂O₄ and CuFe₂O₄) or core/shell nanoparticles (Fe₃O₄/ZnO) are produced. Size, composition, and structure of the resulting nanoparticles were determined by transmission electron microscopy and X-ray diffraction analysis. The average size of zinc and copper ferrite nanoparticles was ascertained to be 9–10 and 2–3 nm, respectively. For core/shell Fe₃O₄/ZnO nanoparticles, the average size is 20 nm. It was experimentally proved that the photoluminescence radiative characteristics of ZnO nanoparticles are retained in core/shell Fe₃O₄/ZnO nanoparticles.     

Au Nanoparticles Supported Nanoporous ZnO Sphere for Enhanced Photocatalytic Activity Under UV-Light Irradiation

Monodispersed 200 nm-sized ZnO spheres (SPs) with porous structure emanating from 8 nm zinc oxide nanoparticles (NPs) composing the SPs were synthesized by dissolving zinc acetate dihydrate in diethylene glycol at 160 °C. The prepared SPs were employed in fabricating the gold (Au) loaded ZnO (Au/ZnO SP) composite materials, exhibiting high photocatalytic activity in decomposing salicylic acid under UV-light irradiation. It is deduced that its high catalytic activity originates from the charge separation by transferring photoinduced electrons from the conduction band (CB) of ZnO to Au, since the CB level of ZnO (?0.5 V vs. NHE) is located more negative side than that of Au (+0.5 V vs. NHE). The evidence for the charge separation was provided by monitoring^.OH radical with bare ZnO SPs and Au/ZnO SP produced in the solution which readily react with 1,4-terephthalic acid (TA) inducing 2-hydroxy terephthalic acid (TAOH) that shows unique fluorescence peak at 426 nm.     

Photocatalytic Degradation of 2-Propanol and Phenol Using Au Loaded MnWO4 Nanorod Under Visible Light Irradiation

Single crystalline MnWO₄ nanorod has been prepared by low temperature hydrothermal reaction at 180 °C. The prepared MnWO₄ possesses band gap of 2.63 eV. Photochemical decomposition method has been followed to disperse Au nanoparticles onto MnWO₄ nanorod. The prepared Au loaded MnWO₄ nanorod demonstrated greatly enhanced photocatalytic activity in decomposing 2-propanol and evolving CO₂ in gas phase and phenol in aqueous phase compared to bare MnWO₄ and commercial TiO₂ nanoparticles (Degussa P25) under visible light (λ ≥ 420 nm) irradiation. The Au loading was optimized to 3.79 wt% for the highest efficiency. The enhanced photocatalytic activity originates from the absorption of visible light by MnWO₄ as well as the introduction of nanoparticulate Au on the surface of MnWO₄ as cocatalyst to impede the recombination of photogenerated charge-carriers.     

Different morphologies of ZnO nanostructures via polymeric complex sol–gel method: synthesis and characterization

Various morphologies of ZnO nanostructures, such as nanoparticles, nanorods and nanoflowers have been achieved controllably by polymeric sol–gel method. In this approach, zinc nitrate Zn(NO₃)₂·6H₂O, citric acid and ethylene glycol were used as the source of Zn²⁺, the chelating agent and the solvent agent, respectively. The microstructure of the ZnO nanostructures was characterized by X-ray diffractometry, scanning electron microscopy with the energy dispersive X-ray spectroscopy, transmission electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. The effect of ethylene glycol to citric acid mole ratio on the morphology and structure of the products was discussed. The ZnO nanoparticles with diameter between 24 ± 2 nm was obtained with EG:CA mole ratio equal to 2:1. The optical properties of as-obtained power were investigated by ultraviolet–visible spectroscopy.     

Co-doped ZnO nanoparticles synthesized by an adapted sol–gel method: effects on the structural,optical, photocatalytic and antibacterial properties

Pure and Co-doped ZnO nanoparticles were synthesized with different cobalt levels (1–10 mol%) via adapted sol–gel method using water as solvent and characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and photoacoustic absorption spectroscopy. The results showed that all the samples have hexagonal wurtzite structure, with no evidence of any secondary phases until 10 mol% of the dopant. The average crystallite size of the samples was in the range of 25–50 nm, do not showing significant differences with the increase of the dopant level. However, the band gap energy of the nanoparticles decreases from 2.98 eV (pure ZnO) to 1.95 eV (10 mol% of Co). The photocatalytic activity of the samples was evaluated on the removal of methylene blue under visible light irradiation, which revealed an efficiency reduction by Co-doping ZnO. The antibacterial property was carried out indicating activity of the prepared samples against gram-positive bacteria.     

Structure,optical and magnetic properties of LaFeO3 nanoparticles prepared by polymerized complex method

This work reports the study the structure, optical and magnetic properties of LaFeO₃ nanoparticles synthesized by the polymerized complex method. The LaFeO₃ nanoparticles were successfully obtained from calcination of the precursor at different temperatures from 750 to 1,050 °C in air for 2 h. The calcined LaFeO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and vibrating sample magnetometry. The XRD and TEM results showed that all LaFeO₃ samples had a single phase nature with the orthorhombic structure. The estimated crystallite sizes were in the range of 44.5 ± 2.4–74.1 ± 4.9 nm. UV–Vis spectra showed strong UV and Vis absorption with small band gap energy. The valence states of Fe ions were in the Fe³⁺ and Fe⁴⁺ state, as confirmed by XPS and XANES results. The weak ferromagnetic behavior with specific saturation magnetization of 0.1 emu/g at 10 kOe was obtained for the small particle of 44.5 ± 2.4 nm. The uncompensated spins at the surface was proposed as playing a part in the magnetic properties of small sized LaFeO₃.     

A polyacrylamide gel route to different-sized CaTiO3 nanoparticles and their photocatalytic activity for dye degradation

Calcium titanate (CaTiO₃) nanoparticles with different average sizes were prepared by a polyacrylamide gel route, where the particle size was tailored by using different chelating agents. Scanning electron microscope observation shows that the samples prepared by using the chelating agents EDTA, acetic acid, tartaric acid, and citric acid have an average particle size of 25, 33, 36, and 55 nm, respectively. All the particles are regularly shaped like spheres. The bandgap energy of the four samples is measured to be 3.66–3.59 eV by ultraviolet (UV)–visible diffuse reflectance spectroscopy. The photocatalytic activity of the prepared CaTiO₃ samples was evaluated by the degradation of methyl orange under 254 nm UV irradiation, revealing that they exhibit a good photocatalytic activity. Hydroxyl radicals are revealed, by the photoluminescence technique using terephthalic acid as a probe molecule, to be produced on the irradiated CaTiO₃ nanoparticles and suggested to be the primary active species toward the dye degradation.