Application of statistical design to optimize the preparation of ZnO nanoparticles via hydrothermal technique

Synthesis of ZnO nanoparticles was carried out by hydrothermal technique in the presence of hexamethylenetetramine (HMTA) as a surfactant. Statistical design was used to investigate the effect of main parameters (i.e., surfactant concentration, time and temperature) on ZnO particle size and morphology. The results indicated that the formation of ZnO nanoparticles was confirmed, using XRD and SEM, at 100 °C and their crystallinity was improved with temperature rise from 100 to 200 °C. Particle size of ZnO in the range of 55–110 nm is achieved using this technique.     

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.     

Facile and controlled synthesis of FeCo nanoparticles via a hydrothermal method

Magnetic FeCo alloy nanoparticles have been synthesized by reduction of FeSO₄ and CoCl₂ with hydrazine in concentrated alkaline media via a hydrothermal route. The size could be controlled by synthetic conditions such as reaction time and temperature, respectively. The obtained samples were characterized by XRD, SEM, TEM, and VSM techniques. Magnetic investigations show the ferromagnetic behavior with saturation magnetization higher than 148.2 emu/g and maximum coercivity up to 411.0 Oe at room temperature. The present method is simple, inexpensive, surfactant-free, and may stimulate technological interests. Such FeCo alloy nanoparticles may have potential applications in biomedical field and magnetic storage devices.     

Epitaxial growth of ZnO nanorods on electrospun ZnO nanofibers by hydrothermal method

In this paper, we report a new ZnO nanofibers-nanorods structure which was successfully prepared by the electrospun ZnO nanofibers as seed to guide hydrothermal epitaxial growth of the ZnO nanorods. The structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). The XRD results indicate that ZnO nanofibers obtained at 600° have high crystallinity with a typical hexagonal wurtzite structure. Furthermore compared with the strongest diffraction of ZnO nanofibers in (101) plane, the diffraction from (002) plane of ZnO nanofibers-nanorods becomes the strongest. The SEM shows that the diameters of epitaxial-grown ZnO nanorods on ZnO nanofibers were approximately 100–200?nm. The PL spectrum shows that the ZnO nanofibers-nanorods have a broad green-yellow emission around 537?nm, in contrast to that of ZnO nanofibers, the peak had obvious redshift about 24?nm and the luminous intensity weakened.     

Single-crystalline ZnO nanowires on zinc substrate by a simple hydrothermal synthesis method

A simple synthesis route to long ZnO nanowires with high aspect ratio of up to ∼ 1000 on zinc substrate in the NaOH aqueous solution was reported, without the assistance of any catalyst, templates or high temperature. We studied the key influencing factors including the reaction time and the solution concentration. With the increase of reaction time from 12 h to 24 h, the average length of ZnO nanowires would increase correspondingly. Through this synthesis route, we can obtain a mass of products and the method is both convenient and reproducible. The as-grown ZnO nanowires are single crystalline with a wurtzite structure.     

水热法可控合成ZnO微纳米结构及其光致发光性能研究

以锌金属片作为源物,卤族元素的碱金属盐溶液作为添加剂,采用水热法合成了氧化锌(ZnO)的管簇状、片簇状、棱柱状和多足状等微纳米结构.采用扫描电子显微镜(SEM),X射线衍射(XRD)表征了其形貌及晶体结构.详细研究了不同卤族元素离子对氧化锌形貌的影响,并研究了其生长机理.利用荧光光谱仪测试了不同形貌ZnO微纳米结构的光...     

Controllable synthesis of ZnO with various morphologies by hydrothermal method

ZnO microstructures with various morphologies have been controllably synthesized by hydrothermal route using different precipitant and zinc source in liquid solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the ZnO2, Zn(OH)2 and ZnO structures to understand the role of precipitant and precursors in the growth of various morphologies. The nucleation and growth process can regulate by changing the precipitant. When H2O2 was used as precipitant, ZnO particles with a rather uniform particle size of -500 nm and a rather rough surface was obtained. While, ZnO synthesized in this polyvinyl pyrrolidone (PVP) solution has the same granular morphology with particle size of 300-1000 nm. In contrast, ZnO sunflower and polyhedron aggregates composed of several smaller polyhedron were formed, when ammonium hydroxide and NH4HCO3 was applied, respectively. Meanwhile, precursors play an important role in the determination of the morphology of ZnO. Sunflower and dumbbell like ZnO composed of nanosheets were obtained, when different centrifugal component of Zn(OH)2 suspension was applied as zinc source. In contrast, sunflower and dumbbell like ZnO composed of nanorods and ZnO rods were obtained, when different centrifugal components of ZnO2 suspension were used as zinc sources. The growth mechanism of ZnO nanostructures fabricated by the hydrothermal process using different zinc sources was tentatively investigated.     

A task specific basic ionic liquid for synthesis of flower-like ZnO by hydrothermal method

Flower-like ZnO morphology, with different shapes, have been successfully synthesized via a novel and environment-friendly hydrothermal method using zinc acetate and a task specific dicationic dibasic ionic liquid, [mmpim]₂[OH]₂, which plays an important role in fabrication of ZnO structure. The structure and morphology of the product were characterized by X-ray diffraction and scanning electron microscopy, which show different flower-like morphologies. Photoluminescence spectrum of the product exhibits a strong ultraviolet emission at 391 nm and two weak blue-green emissions at about 450 and 500 nm.     

Synthesis of ZnO nanoparticles through the impregnated layer combustion synthesis process

Zinc oxide nanopowders were synthesized by a solution combustion technique named impregnated layer combustion synthesis (ILCS), involving the impregnation of an active layer with the reactant solution and subsequently the combustion of the impregnated system. In this work three different organic fuels and two different ignition modes were tested in order to optimize the final microstructure and specific surface area (SSA) of the ZnO nanopowders. In particular, the ignition mode was found to significantly affect the final products, discriminating between an explosion procedure (flame combustion) and a self-propagating mode (smoldering combustion). The nitrate–glycine mixture and the smoldering combustion way were found to be the most suitable conditions, giving rise to softly agglomerated nanopowders with an average size of 20 nm and a very high SSA, without the need of any further crystallization treatment.     

水热法制备菜花状氧化锌

以Zn(NO3)2.6H2O和N2H4.H2O为原料,采用水热法在180℃制备了菜花状的氧化锌(ZnO)纳米棒束、不规则的长短棒晶须体以及柱状晶须束。用XRD、SEM、FE-SEM及HR-TEM对样品进行了表征。具有六方纤维锌矿结构的ZnO棒或柱的直径分别在100、200nm和1μm左右。以负离子配位多面体生长基元理论讨论了ZnO晶体的生长过程及N2H4.H2O浓度对ZnO形貌的影响。     

Low-temperature direct synthesis of CeO2-ZrO2 solid solution nanoparticles by a hydrothermal method

Well-crystallized CeO2-ZrO2 solid solution nanoparticles were successfully prepared by a hydrothermal method in a single step at 120 degrees C, for 6 h without any post heat treatment. The particle sizes of 6 +/- 3 nm by surface area measurements are in good agreement with crystallite sizes of 6 +/- 3 nm by X-ray diffraction. Transmission microscopy also confirmed the formation of crystals of 5-8 nm in the products. In the formation of the homogeneous solid solutions the complete oxidation of Ce3+ to Ce4+ in the precipitated gels seems to be one of the important steps. The solid solutions contained several wt % water, but it was expelled by calcining > or = 600 degrees C. The heating of the samples brought about grain growths, but did not change the phases. The specific areas of 120-200 m2/g of as-prepared samples were decreased to 4-14 m2/g by heating at 900 degrees C for 4 h.     

Microwave-assisted hydrothermal synthesis and photocatalytic activity of ZnO

The effect of synthesis temperature on the morphology of fine zinc oxide powders prepared by microwave-assisted hydrothermal processing of Zn(OH)₂ suspensions has been studied using x-ray diffraction and low-temperature nitrogen BET measurements. The photocatalytic activity of the powders for Methyl Orange photodegradation has been assessed as a function of synthesis temperature. The results indicate that the specific surface of ZnO powders plays a key role in determining their photocatalytic activity.     

Supercritical hydrothermal synthesis of organic-inorganic hybrid nanoparticles

We have developed supercritical hydrothermal synthesis method of metal oxide nanoparticles where metal salt aqueous solution is mixed with high temperature water to rapidly increase the temperature of the metal salt solution and thus reduce the reactions and crystallizations during the heating up period. By using this method, we succeeded in the continuous and rapid production of metal oxide nanocrystals. A new method proposes to synthesize organic-inorganic fused materials based on the methods of supercritical hydrothermal synthesis. By introducing organic materials in a reaction atmosphere of supercritical hydrothermal synthesis, we successfully synthesized metal oxide nanoparticles whose surface was modified with organic materials. In supercritical state, water and organic materials form a homogeneous phase, which provides an excellent reaction atmosphere for the organic modification of nanoparticles. Modification with bio-materials including amino acids was also possible. By changing organic modifiers, particle morphology and crystal structure were changed. This organic surface modification provides a various unique characteristics for the nanoparticles: Dispersion of nanoparticles in aqueous solutions, organic solvents or in liquid polymers can be controlled by selecting hydrophilic or hydrophobic modifiers.     

简单水热法制备棒状纳米氧化锌及其表征

以Zn(NO3)2和NaOH为原料,在不使用任何添加剂的条件下,采用水热合成法在不同的合成时间和合成温度下制备棒状纳米ZnO颗粒。通过X射线衍射(XRD)、透射电镜(TEM)、光致发光谱(PL)、电导率测试对样品进行表征。结果表明,所制备的纳米ZnO粉末具有六方红锌矿结构并沿(101)面择优生长;随着合成时间和温度的增加,样品的纯度逐渐增加;合成时间为25h,温度为200℃时,样品的结晶最好,样品基本成棒状,平均直径约为30～40nm,长度约为300～400nm、电阻率最大,且在376nm和500～600nm处有明显发射现象。深入分析了上述结果的形成原因。     

Controlled growth of ZnO nanomaterials via hydrothermal method: effect of buffer layer

We report a facile solution-based method for the controlled growth of ZnO nanomaterials on an AIN/Si substrate. A ZnO buffer layer was coated on the substrate before growing the ZnO nano-materials. The shape of the ZnO nanomaterials changed from nanosheet to nanorod as the thickness of the ZnO buffer layer increased. Doping of the buffer layer with Ga decreased the average grain size of the ZnO buffer layer, which resulted in the growth of longer and thinner ZnO nanorods on the buffer layer. The UV sensing results of the ZnO nanorod-based device revealed that the aspect ratio of the ZnO nanorods is crucial for enhancing the performance of the device.     

A two-step method for synthesis of micron sized nanoporous silver powder and ZnO nanoparticles

Micron-sized nanoporous silver powder with pore size of ～100–160 nm and specific surface area of ～4.7–5.5 m²/g was synthesized from three mechanically alloyed Ag-Zn powders (composition: 25, 50 and 75 at.% Zn). Dealloying was carried out at free corrosion conditions in NaOH, HCl and AgNO₃ solutions. Both partial and complete dealloying were obtained by suitable choice of electrolyte and time of exposure. Zn in the solution after dealloying was recovered in the form of ZnO nanoparticles with particle size of 55.7 ± 18 nm. The effect of composition and electrolyte on the degree of dealloying was also studied.     

Statistical optimization of experimental parameters for synthesis of manganese carbonate and manganese oxide nanoparticles

Taguchi robust design was used for optimization of direct precipitation reaction conditions in order to simple and fast synthesis of manganese carbonate nanoparticles. Manganese carbonate nanoparticles were synthesized in this study by addition of manganese ion solution to the aqueous carbonate reagent. Effects of several reaction variables, such as manganese and carbonate concentrations, flow rate of reagent addition and temperature on particle size of prepared manganese carbonate were investigated. The significance of these parameters in tuning the size of manganese carbonate particles was quantitatively evaluated by analysis of variance. The results showed that manganese concentration and carbonate concentration in the solutions and also flow rate have significant effects in preparation of manganese carbonate nanoparticles. Also, optimum conditions for synthesis of manganese carbonate nanoparticles via precipitation reaction were proposed. Analysis of variance showed that under the optimum condition, the size of manganese carbonate nanoparticles will be about 54 ± 12 nm. In another part of this study, solid state thermal decomposition reaction of precursor was used for preparation of Mn₂O₃ nanoparticles. The results showed that Mn₂O₃ nanoparticles synthesized via thermal decomposition of manganese carbonate nanoparticles have average size of 90 nm.     

Surfactant-assisted hydrothermal synthesis of titania nanoparticles for solar cell applications

Nanostructured anatase TiO₂ powders (~7 nm) with different microstructures have been successfully synthesized using surfactant-assisted hydrothermal route. It can be seen that different morphologies of sphere, flower petal and cauliflower were appeared for the anatase powders formed at hydrothermal temperature 100 °C for 24 h without and with sodium dodecyl sulfate (SDS) and cetyl trimethyl-ammonium bromide (CTAB) as anionic and cationic surfactants, respectively. The specific surface area S_BET was increased from 77.14 m²/g without surfactant to 177.19 m²/g in the presence of SDS as anionic surfactant. The optical properties were measured and the band gap energy of the obtained powders was ~3.3 eV. The UV-absorption band of the anatase phase was at near 295 nm without other observable bands, which proved to exhibit high optical property and might have potential application in solar cells devices.     

The structural and optical properties of ZnO nanowire arrays prepared by hydrothermal synthesis method

ZnO nanowire arrays have been grown on the ZnO film-coated silicon (100) substrates by hydrothermal method, and the deposited nanowires are found to have a uniform size distribution with sharp hexagonal-shaped tips. The structural and optical properties of the nanowires were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) techniques. The XRD and SEM results demonstrate that the well-aligned ZnO nanowires are single crystalline structure formed along the c-axis orientation. TEM analysis further confirms that the ZnO nanowires are highly preferred grown along the (002) crystal plane. The spacing between adjacent (002) lattice planes is estimated as 0.52 nm. The optical properties of the nanowires were measured using CL after annealing in oxygen and nitrogen atmospheres at 550 °C for various times. The CL spectra in the visible spectrum exhibit two weak deep-level emission bands that may be attributed to the intrinsic or extrinsic defects. It can be observed that the ZnO nanowires show different optical behaviors after various annealing times. The dependence of the optical properties on the annealing conditions is also discussed.     

Improved UV resistance in wood through the hydrothermal growth of highly ordered ZnO nanorod arrays

In this study, wood materials with significantly improved UV resistance were successfully fabricated by growing highly ordered ZnO nanorod arrays on wood surfaces using a facile one-pot hydrothermal method. The resultant samples were characterized via scanning electron microscopy (SEM), X-ray diffraction, and attenuated total reflectance-Fourier transformation infrared (ATR–FTIR) techniques. The SEM images clearly show the highly ordered and well-aligned ZnO nanorod arrays directly grown onto the wood surface. ATR–FTIR spectra demonstrate that stable chemical bonds between the hydroxyl groups of the ZnO nanorod array film and the wood surface were formed at the interface of the two materials. An accelerated aging test was used to measure the UV resistance of the original wood and the ZnO/wood composite. The experimental results indicate that the ZnO/wood samples exhibited a more superior UV resistance than the original wood. This significantly improved UV resistance is mainly attributed to the excellent UV absorption of the well-aligned ZnO nanorod arrays grown on the wood surface.