Microwave synthesis and characterization of ZnO with various morphologies

ZnO micro- and nanostructures with a variety of morphologies have been synthesized using Zn(NO₃)₂·6H₂O and pyridine by a microwave-assisted aqueous solution method at 90 °C for 10 min. The pyridine has a significant influence on the morphology of ZnO. Various morphologies of ZnO (hexagonal columns, linked hexagonal needles, hollow structures, and hexagonal nanorings) were obtained by adjusting the concentration of pyridine. The effect of the type of other alkaline additive (aniline and triethanolamine) on the morphology of ZnO was also investigated. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM).     

ZnO nanostructures for efficient perovskite solar cells

Controlled ZnO nanostructures were synthesized via spin-coating and in situ thermal decomposition processing using ZnO paster with/without zinc acetate as precursor. The perovskite CH₃NH₃PbI₃ solar cells (PSCs) based on these ZnO nanostructures were fabricated and their photovoltaic performances have also been investigated. Effects of zinc acetate concentration on morphologies of ZnO nanostructures and the photovoltaic properties of corresponding PSCs have been discussed. Interestingly, the morphologies of ZnO nanostructures were varied from separate nanoparticles to interconnect net-like nanostructures and the space of ZnO nanoparticles became large when the concentration of zinc acetate was increased from 0 to 0.13 M. The space and the connection degree of ZnO nanostructure obtained from 0.05 M zinc acetate are the best choice for perovskite infiltration and charge transport, which leads to corresponding cells have highest power conversion efficiencies (PCE) of 9.30 %. Post-treatment of ZnO nanostructures improved further Voc and FF, leading to PCE to 13.1 %.     

Hydrothermal controllable synthesis to convert ZnO hexagonal nanotubes to hexagonal nanorods and their photocatalytic application

Zinc oxide (ZnO) thick films were analyzed by high-resolution X-ray diffraction (HR-XRD), field emission scanning electron microscopy, and photoluminescence (PL) spectroscopy at room temperature. The films were grown on glass substrates using different molar concentrations of aqueous solution (0.02, 0.04, and 0.06 M) via a simple hydrothermal method. This method uses glass bottles with rubber caps as reactor vessels (100 mL) and, thus, is classified as a green chemistry technique. Hexahedral zinc nitrate (Zn (NO₃)₂·6H₂O), hexamethylenetetramine (C₆H₁₂N₄), and deionized water were used as starting materials and were reacted in the presence of heat. HR-XRD measurements confirmed that the diffraction peaks of the polycrystalline structure films can be assigned to the hexagonal-shaped wurtzite ZnO. In addition, the PL spectra show that the integrated intensity decreases with the increase in ZnO content. The SEM images also revealed the existence of hexagonal ZnO nanotubes in the 0.02 M sample, and these nanotubes are gradually converted into hexagonal nanorods with the increase in ZnO content. Moreover, the photocatalytic activity of both nanostructures was measured based on the degradation of methyl blue (MB) by using ultraviolet light (λ = 366 nm). Results showed that the ZnO nanotubes degraded MB more effectively than the nanorods.     

Morphological evolution in single-crystalline Bi2Te3 nanoparticles, nanosheets and nanotubes with different synthesis temperatures

A general surfactant-assisted wet chemical route has been developed for the synthesis of a variety of bismuth telluride (Bi₂Te₃) single-crystalline nanostructures with varied morphologies at different temperatures in which hydrazine hydrate plays as an important solvent. Bi₂Te₃ sheet grown nanoparticles, nanosheets and nanotubes have been synthesized by a simplest wet chemical route at 50, 70 and 100 °C within 4 h. Bi₂Te₃ sheet grown nanoparticles are obtained in agglomerate state and they are found with many wrinkles. Various types of Bi₂Te₃ nanotubes are also found which are tapered with one end open and the other closed. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern and energy dispersive X-ray (EDX) spectroscopy were employed to characterize the powder product. It is found that all nanoparticles, nanosheets and nanotubes are well-crystallized nanocrystals and morphologies of the powder products are greatly affected by different synthesis temperatures. The formation mechanisms of bismuth telluride nanostructures are also discussed.     

Effect of Eu doping concentration on the morphologies and optical properties of ZnO film prepared by ultrasonic spray pyrolysis

In this paper, we report a new and simple method to prepare different concentrations in molarities Eu-doped ZnO films on the ITO glass substrates by ultrasonic spray pyrolysis. The morphologies, crystal structures and optical properties were investigated by using scanning electro microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL). The SEM images show that the morphologies of Eu doping concentrations 3 and 9 at.% of ZnO films are lamellae. When the Eu doping concentration in molarities is 6 at.%, the morphology of films are graininess and dense, particle diameter is about 200–250 nm. The XRD results indicate that when the Eu doping concentration is 6 at.%, the structure of Eu-doped ZnO films have better hexagonal polycrystalline structure, and characteristic diffraction peak of Eu₂O₃ was appeared at 2θ = 50.47°. The PL spectra of different concentrations Eu-doped ZnO films show that for the Eu doping concentration 6 at.%, ZnO film has a stronger red emission at 613 nm with excitation wavelength at 280 nm.     

Fabrication of three-dimensional snowflake-like bismuth sulfide nanostructures by simple refluxing

Three-dimensional snowflake-like bismuth sulfide nanostructures were successfully synthesized by simple refluxing at 160 °C in ethylene glycol, using bismuth citrate and thiourea as reactants. The crystal structures and morphologies of the products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX). The Bi₂S₃ nanostructure was built up by highly ordered one-dimensional Bi₂S₃ nanorods, which was aligned in an orderly fashion. Ethylene glycol plays a critical role in the creation of bismuth sulfide three-dimensional nanostructures, which serves as an excellent solvent and structure director. Bismuth citrate, a linear polymer, also makes for the formation of the three-dimensional nanostructures.     

Fabrication of novel hierarchical ZnO via ultrasonic assisted hydrothermal route and their gas sensing property

Novel hierarchical ZnO nanomaterials with castellated and turriform morphologies were successfully synthesized by ultrasonic assisted hydrothermal route. The morphology and structure of products were characterized by scanning electron microscopy and X-ray diffraction, respectively. The results show that as-prepared castellated ZnO microrods have six-equal axis symmetry features with the length of 2–4 μm and the diameter of about 1 μm, and ZnO with turriform morphology has radical branch structure with the diameter ranging from 500 to 700 nm. It is found that initial alkaline concentration of the solution plays a crucial role in determining two kinds of hierarchical morphologies by etching ZnO crystal during hydrothermal process. A possible formation mechanism of castellated and turriform ZnO microstructures is also proposed. Gas sensing of hierarchical ZnO to different gases was also examined. The result indicates turriform ZnO sensor has fast response properties and excellent selective resolution capability to C₂H₅OH gas.     

Hydrothermal synthesis of transition metal oxide nanomaterials in HEPES buffer solution

Various transition metal oxide (Co₃O₄, Mn₃O₄ and ZnO) nanostructures were readily synthesized in HEPES buffer solution (200 mmol/L, pH 7.40) via a simple hydrothermal method. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX). It was found that the morphologies of the as-obtained transition metal oxide nanostructures were affected by the reaction temperature, HEPES/metal salt molar ratio and metal precursor. HEPES with two free nitrogen atoms (piperazine group) and terminal hydroxyl groups plays a critical role as a reactant and surfactant to prevent the transition metal oxide nanomaterials from aggregation.     

A simple route to V2O5·xH2O bundle-like nanostructures

V₂O₅·xH₂O bundle-like nanostructures composed of nanobelts have been synthesized by a simple hydrothermal method with the aid of Co²⁺. The widths, thickness and lengths of V₂O₅·xH₂O nanobelts are 80–100 nm, 10–20 nm, and several micrometers, respectively. The morphologies and the crystallographic structures of the V₂O₅·xH₂O bundle-like nanostructures were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and electron diffraction (ED). The effects of the inorganic ions and reaction temperature on the morphologies of the resulting products have been investigated.     

Improved performance of ZnO thin film solar cells by doping magnesium ions

This study investigates the effect of magnesium doping on the performance of nanocrystalline zinc oxide (ZnO) thin film solar cells. Mg_xZn_1?xO (x = 0.00, 0.05, 0.075 and 0.1 %) nanoparticles were prepared by simple precipitation method. The crystallinity and morphology of the photo-anode was characterized by X-ray diffraction analysis and scanning electron microscopy. The effect of various concentrations of magnesium ions on the structural and optical properties of ZnO nanoparticles was examined. Doping of magnesium ions helps the ZnO nanoparticles to grow larger in size with rod like surface morphologies. Solar cell with 0.075 % magnesium doped ZnO electrode exhibits an enhanced short-circuit current density of 3.36 mA/cm², open-circuit photo voltage of 0.79 V, fill factor of 0.73, and overall power conversion efficiency of 2.1 %.     

Chemical vapor deposition-based growth of aligned ZnO nanowires on polycrystalline Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn substrates

ZnO nanowires have been grown on polycrystalline Zn₂GeO₄:Mn substrates for the first time using a chemical vapor deposition method. Both Zn and ZnO sources were used to supply Zn vapor in the growth process of ZnO nanowires. The Zn₂GeO₄:Mn substrates were prepared using solid-state ceramic synthesis methods, and average grain sizes of ~1 μm were achieved. The nanowires of diameters in the range of 100–200 nm and length of ~30 μm were observed. In addition to nanowires, other morphologies of ZnO nanostructures, such as ZnO tetrapods, were observed when Zn powder was used as the source for the CVD growth. The results reveal that polycrystalline substrates are also promising as novel alternative substrates for growth of ZnO nanostructures. The as-synthesized ZnO nanowire/Zn₂GeO₄:Mn composites are being developed for future electroluminescent devices.     

Synthesis of porous ZnO nanostructures using bamboo fibers as templates

In this study, we fabricated ZnO nanostructures using bamboo fibers as templates. The starting material used was zinc acetate, and the nanostructures were synthesized by soaking and calcining the bamboo fibers. The fabricated nanostructures were characterized using X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometry. The results showed that the size of the ZnO nanoparticles was approximately 20–100 nm. When the ZnO nanoparticles were used as the catalyst in the photodegradation of methyl orange, the dye degraded by 95.98 % in 80 min. The response and recovery times of a gas sensor based on the ZnO nanoparticles were 25 and 24 s, respectively, during the detection of C₂H₅OH in a concentration of 10 ppm at 270 °C.     

Synthesis and photo-catalytic degradation property of nanostructured-ZnO with different morphology

ZnO nanostructures with different morphology have been successfully fabricated by a simple relative low temperature approach at 90 °C for 5 h without surfactant assistance. These structures can be easily tailed using varied concentrations of sodium hydroxide (NaOH) and different amounts of the hydrazine hydrate (N₂H₄·H₂O). X-ray diffraction (XRD) result proves the formation of ZnO with wurtzite structure. Microstructure as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicates that the rod-like and chrysanthemum-like ZnO nanostructures contain many radial nanorods, which grow along the [0001] direction. Furthermore, the as-prepared ZnO nanomaterials exhibit high activity on the photo-catalytic degradation of typical persistent organic pollutants (POPs), indicating that they are promising as semiconductor photo-catalysts.     

Dendritic and epitaxial growths of ZnO particle-rod and rod-rod nanostructures with quasi-one-dimensional and two-dimensional configurations

Quasi-one-dimensional and two-dimensional ZnO nanostructures have been fabricated through thermal evaporation approach. The microstructures of the ZnO nanostructures have been studied using scanning electron microscopy and high-resolution electron microscopy. Quasi-one-dimensional ZnO nanostructures are formed by dendritic growths of ZnO nanoparticles from the stem nanorods surfaces, forming particle-rod nanostructures. While epitaxial growths of branch nanorods from the stem nanorods configure two-dimensional ZnO nanostructures. The epitaxial growth orientation relationship can be described as [2? 110]_R1 || [2? 110]_R2 and (0001) _R1 || (011?0)_R2. The growth mechanism of the quasi-one-dimensional and two-dimensional ZnO nanostructures has been discussed.     

表面活性剂对纳米氧化锌形貌和发光性能的影响

以二水合乙酸锌和氢氧化钠为原料,分别以表面活性剂十六烷基三甲基溴化铵(CTAB)和聚乙烯吡咯烷酮(PVP)为结构导向剂,采用简单的水热法制备了不同形貌的纳米氧化锌。研究了两种表面活性剂对纳米氧化锌形貌和光致发光性能的影响,并探讨了表面活性剂的作用机理。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和室温光致发光光谱(PL)等测试方法对样品的结构、形貌和发光性能进行了表征。结果表明:添加了表面活性剂后,样品形貌和尺寸都更加均匀,紫外发射峰强度相对增加。     

Structural and morphological studies of zinc oxide incorporating single-walled carbon nanotubes as a nanocomposite thin film

Pure zinc-oxide and a composition of zinc oxide-single walled carbon nanotubes (ZnO-SWCNTs) thin films were prepared by using a sol–gel doctor blade technique. A precursor of zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O), absolute ethanol (C₂H₅OH) and triethanolamine were mixed in one solution. Non-acid treatment SWCNTs were doped in the prepared solution. Structural and morphological properties of ZnO and ZnO-SWCNTs thin films were studied by means of X-ray diffractometer (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). XRD measurements indicated that the crystallite size of ZnO was bigger than the crystallite size of ZnO-SWCNTs; 0.4331 and 0.3386 nm, respectively. The FESEM images showed the hexagonal and nanorod structures of ZnO thin film and a broccoli-like ZnO nanostructures coated with CNTs for ZnO-SWCNTs thin film. The AFM analysis revealed smoother surface morphology of ZnO-SWCNTs thin film compared to the surface of pure ZnO thin film. TEM results captured the inner structures of ZnO and ZnO-SWCNTs. Inner and outer diameter of non-acid treatment SWCNTs were recorded about 5.09 and 14.95 nm, respectively. Photovoltaic performance of ZnO-SWCNTs based dye-sensitized solar cell (DSSC) showed high power conversion efficiency of 0.102 % compared to ZnO based DSSC (0.019 %). This study suggests that SWCNTs should be acid-treated to produce highly porous structure and greater surface area for better photovoltaic performance of the DSSCs.     

Solvothermal synthesis of Ag/ZnO micro/nanostructures with different precursors for advanced photocatalytic applications

Micro/nanostructured systems based on metallic oxide (ZnO) with noble metal (Ag) on the surface (Ag/ZnO) are synthesized by solvothermal method from zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O), zinc acetylacetonate hydrate (Zn(C₅H₇O₂)₂·xH₂O) and silver nitrate (Ag(NO₃)) as precursors. In these systems, polyvinylpyrrolidone (PVP) is used as surfactant for controlling particle morphology, size and dispersion. The obtained materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV–vis diffuse reflectance spectroscopy (DRS), N₂ gas adsorption–desorption (BET) and Raman spectroscopy (RS). By XRD results, all major peaks are indexed to the hexagonal wurtzite-type structure of the ZnO and samples with noble metal, extra diffraction peaks are detected which correspond to the face-centered-cubic (fcc) structure of the metallic Ag. Depending on used precursor, different morphologies have been obtained. Mainly, ZnO prims-like rods – NRs (with 0.8 ? aspect ratio ? 3.4) – have been observed. Quasi-spherical particles of metallic Ag (with diameters between 558 ± 111 μm and 22 ± 1 nm) have been detected on the ZnO surface. Photocatalytic results (all samples studied >30% MB degradation) verify the important effect of surfactant and the viability of synthesized Ag/ZnO micro/nanocomposites for environmental applications.     

ZnO nanoparticles: hydrothermal synthesis and 4-nitrophenol sensing property

In this paper reports a facile hydrothermal synthesis, characterization and sensing application of zinc oxide (ZnO) nanostructures. ZnO nanostructures were synthesized by mixing triethylamine (TEA) with zinc nitrate at 60?°C followed by calcination at 650?°C for 6 h. The detailed characterizations conformed the synthesized ZnO nanostructures. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectral analysis confirmed the formation of hexagonal ZnO. Band gap of the ZnO nanoparticles was determined by UV–visible absorption spectroscopy. Morphology and size of the sample was examined by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). It shows that the sample has rod and hexagonal morphology. Elemental composition was determined by energy dispersive X-ray (EDX) spectroscopy. The ZnO was coated on glassy carbon electrode (ZnO/GCE) and it was utilized as an electrochemical sensor for 4-nitrophenol (4-Np). Sensitivity and detection limit of ZnO/GCE towards 4-Np was found to be 0.04 µA/mM and 2.09?×?10^?5 M. The result suggests that ZnO has suitable sensor detection of 4-Np.     

Solvent directed fabrication of Bi2WO6 nanostructures with different morphologies: Synthesis and their shape-dependent photocatalytic properties

In this work, Bi₂WO₆ with complex morphologies, namely, flower-like, pancake-like, and tubular shapes have been controllably synthesized by a facile solvothermal process. The as-obtained samples are systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). The effects of solvents on the morphologies of Bi₂WO₆ nanostructures are systematically investigated. According to the time-dependent experiments, a two-step growth mode basing on Ostwald ripening process and self-assembly has been proposed for the formation of the flower-like and pancake-like Bi₂WO₆ nanostructures. The photocatalytic properties of Bi₂WO₆ nanostructures are strongly dependent on their shapes, sizes, and structures for the degradation of rhodamine B (RhB) under visible-light irradiation. The deduced reasons for the differences in the photocatalytic activities of these Bi₂WO₆ nanostructures are further discussed.     

Controllable synthesis of flower- and rod-like ZnO nanostructures by simply tuning the ratio of sodium hydroxide to zinc acetate

A controlled synthesis of flower-?and rod-like ZnO nanostructures in a hydrothermal phase has been realized in the absence of an additional template. The well-defined morphologies are obtained by simply tuning the ratio of sodium hydroxide to zinc acetate in a narrow range. The products are characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The growth mechanism is suggested to be that the supersaturation of the precursor Zn(OH)(4)(2-) results in various nucleation habits, which induce the ZnO nanostructures with different morphologies.