Template free fabrication of hollow hematite spheres via a one-pot polyoxometalate-assisted hydrolysis process

Uniform hollow hematite (α-Fe₂O₃) spheres with diameter of about 600-700 nm and shell thickness lower than 100 nm are obtained by direct hydrothermal treatment of dilute FeCl₃ and tungstophosphoric acid H₃PW₁₂O₄₀ solution at 180 °C. The hollow spheres are composed of robust shells with small nanoparticles standing out of the surface and present a high-surface area and a weak ferromagnetic behavior at room temperature. The effect of concentration of H₃PW₁₂O₄₀, reaction time and temperature for the formation of the hollow spheres are investigated in series of experiments. The formation of the hollow spheres may be ascribed to a polyoxometalte-assisted forced hydrolysis and dissolution process.     

Template-free polyoxometalate-assisted synthesis for ZnO hollow spheres

ZnO hollow spheres with diameters ranging from 400 to 600 nm and the thickness of shell approximate 80 nm were synthesized by a simple polyoxometalate-assisted solvothermal route without using any templates. The effect of polyoxometalate concentration, reaction time and temperature on the formation of the hollow spheres was investigated. The results indicated that the hollow spheres were composed of porous shells with nanoparticles and polyoxometalate play a key role in controlling morphology of ZnO. A possible growth mechanism based on polyoxometalate-assisted assembly and slow Ostwald ripening dissolution in ethanol solution is tentatively proposed. In addition, the room temperature photoluminescence spectrum showed that the ZnO hollow spheres exhibit exciting emission features with wide band covering nearly all the visible region.     

Preparation and properties of nitrogen-containing hollow carbon nanospheres by pyrolysis of polyaniline-lignosulfonate composites

Polyaniline-lignosulfonate composite hollow spheres were synthesized by using one-step unstirred polymerization of aniline in the presence of lignosulfonate. Novel nitrogen-containing hollow carbon nanospheres were prepared by direct pyrolysis of the polyaniline-lignosulfonate composite spheres at different temperatures under a nitrogen atmosphere. Thermal behavior of the polyaniline-lignosulfonate composite spheres was studied by TG-DTG, FTIR and element analyze instruments. The resultant carbon spheres were characterized by SEM, XRD and nitrogen adsorption-desorption measurement. It was found that the pyrolysis products of the polyaniline-lignosulfonate composite spheres were made up of uniform hollow carbon nanospheres with an average diameter of 135 nm. Furthermore, the hollow carbon nanospheres exhibit high BET surface area range from 381.6 m² g⁻¹ to 700.2 m² g⁻¹. The hollow carbon nanospheres could be used as adsorbents of papain. The papain adsorption capacity for the carbon spheres prepared at 1200 °C was up to 1161 mg g⁻¹ at an initial papain concentration of 10 mg mL⁻¹ at 25 °C.     

Architecture of micron-scale hollow spheres composed of silica nanoparticles and approach to luminescent spheres

Micron-scale hollow spheres were successfully constructed with silica nanoparticles by templating of polymer spheres. Subsequently, the use of 3-aminopropyltriethoxysilane (APTES) introduces carbon and oxygen defects in the silica nanoparticles resulting from calcination of the aminopropyl group. In this approach, the template of micron-scale polymer spheres was prepared from dispersion polymerization. Subsequent St?ber process results in the formation of a silica layer attached to the polymer sphere surfaces. After calcination, the obtained micron-scale hollow silica spheres were then studied on the relationship between the particle diameter and the surface morphology. The luminescence of hollow spheres was prepared through using APTES in St?ber process, and which of related the appearance of luminescence to the APTES concentration and calcination temperature. The results of this study can provide useful information for the structure of micron-scale hollow spheres and their application to luminescent materials.     

Mesoscale assembly of NiO nanosheets into spheres

NiO solid/hollow spheres with diameters about 100 nm have been successfully synthesized through thermal decomposition of nickel acetate in ethylene glycol at 200 °C. These spheres are composed of nanosheets about 3-5 nm thick. Introducing poly(vinyl pyrrolidone) (PVP) surfactant to reaction system can effectively control the products’ morphology. By adjusting the quantity of PVP, we accomplish surface areas-tunable NiO assembled spheres from ∼70 to ∼200 m² g⁻¹. Electrochemical tests show that NiO hollow spheres deliver a large discharge capacity of 823 mA h g⁻¹. Furthermore, these hollow spheres also display a slow capacity-fading rate. A series of contrastive experiments demonstrate that the surface area of NiO assembled spheres has a noticeable influence on their discharge capacity.     

A one-pot synthetic approach to prepare palladium nanoparticles embedded hierarchically porous TiO2 hollow spheres for hydrogen peroxide sensing

A simple one-step method to fabricate hierarchically porous TiO₂/Pd composite hollow spheres without any template was developed by using solvothermal treatment. Pd nanoparticles (2-5 nm) were well dispersed in the mesopores of the TiO₂ hollow spheres via in-situ reduction. In our experiment, polyvinylpyrrolidone played an important role in the synthetic process as the reducing agent and the connective material between TiO₂ and Pd nanoparticles. HF species generated from solvothermal reaction leaded to the formation of TiO₂ hollow spheres and Ostwald ripening was another main factor that affected the size and structure of the hollow spheres. The as-prepared TiO₂/Pd composite hollow spheres exhibited high electrocatalytic activity towards the reduction of H₂O₂. The sensitivity was about 226.72 μA mM⁻¹ cm⁻² with a detection limit of 3.81 μM at a signal-to-noise ratio of 3. These results made the hierarchically porous TiO₂/Pd composite a promising platform for fabricating new nonenzymic biosensors.     

Preparation and properties of Nafion/hollow silica spheres composite membranes

In present work, hollow silica spheres (HSS)/Nafion^® composite membranes were prepared by solution casting. The thermal properties, water retention, swelling behavior and proton conductivity of the composite membranes were explored. It was found that HSS dispersed well at micrometer scale in the obtained composite membranes by SEM and TEM observation. Thermal properties of composite membranes were improved than that of recast Nafion^® membrane. Compared with the recast Nafion^® membrane, the composite membranes showed higher water uptake and lower swelling degree at the temperature range from 40 to 100 °C. At the same HSS loading, the smaller the diameter of HSS in composite membranes, the more the water uptake, however, the swelling degree of composite membranes was increased. The proton conductivity of the composite membrane with 3–5 wt.% HSS (120 and 250 nm) increased distinctively at above 60 °C, reached the optimal value at 100 °C, and decreased slowly when the temperature exceeded 100 °C.     

Synthesis of poly(o-phenylenediamine) hollow spheres and nanofibers using different oxidizing agents

Poly(o-phenylenediamine) (PoPD) hollow spheres (ca. 800 nm in outer diameter) were synthesized by a simple solution route using ammonium persulfate (APS) as the oxidizing agent, whereas PoPD nanofibers (0.5-2 μm in width and more than 100 μm in length) and gold nanoparticles (200-500 nm) were obtained when changing the oxidizing agent of APS to chlorauric acid (HAuCl₄). The chemical structures of PoPD hollow spheres and nanofibers were characterized by FTIR and XRD spectra. When using HAuCl₄ as the oxidizing agent, the products of PoPD nanofibers and gold nanoparticles could be separated by chemical methods. The monomer droplets were proposed to act as template to the formation of polymer hollow spheres while the oriented growth of polymer nanofibers might be catalyzed by gold nanoparticles.     

Hydrothermal synthesis of nanocrystalline ZnSe: An in situ synchrotron radiation X-ray powder diffraction study

The hydrothermal synthesis of nanocrystalline ZnSe has been studied by in situ X-ray powder diffraction using synchrotron radiation. The formation of ZnSe was studied using the following starting mixtures: Zn+Se+H₂O (route A) and ZnCl₂+Se+H₂O+Na₂SO₃ (route B). The route A experiment showed that Zn powder starts reacting with water at 134 °C giving ZnO and H₂ followed by the formation of ZnSe which takes place in temperature range from 167 to 195 °C. The route B experiment shows a considerably more complex reaction path with several intermediate phases and in this case the formation of ZnSe starts at 141 °C and ZnSe and Se were the only crystalline phases observed at the end of the experiment where the temperature was 195 °C. The sizes of the nanocrystalline particles were determined to 18 and 9 nm in the route A and B experiments, respectively. Nanocrystalline ZnSe was also synthesized ex situ using the route A and B methods and characterized by conventional X-ray powder diffraction and transmission electron microscopy. An average crystalline domain size of ca. 8 nm was determined by X-ray powder diffraction in fair agreement with TEM images, which showed larger aggregates of nanoparticles having approximate diameters of 10 nm. Furthermore, a method for purification of the ZnSe nanoparticles was developed and the prepared particles showed signs of anisotropic size broadening of the diffraction peaks.     

Mechanism for the formation of tin oxide nanoparticles and nanowires inside the mesopores of SBA-15

The formation of polycrystalline tin oxide nanoparticles (NP) and nanowires was investigated using nanocasting approach included solid-liquid strategy for insertion of SnCl₂ precursor and SBA-15 silica as a hard template. HR-TEM and XRD revealed that during the thermal treatment in air 5 nm tin oxide NP with well defined Cassiterite structure were formed inside the SBA-15 matrix mesopores at 250 °C. After air calcination at 700 °C the NP assembled inside the SBA-15 mesopores as polycrystalline nanorods with different orientation of atomic layers in jointed nanocrystals. It was found that the structure silanols of silica matrix play a vital role in creating the tin oxide NP at low temperature. The pure tin chloride heated in air at 250 °C did not react with oxygen to yield tin oxide. Tin oxide NP were also formed during the thermal treatment of the tin chloride loaded SBA-15 in helium atmosphere at 250 °C. Hence, it is well evident that silanols present in the silica matrix not only increase the wetting of tin chloride over the surface of SBA-15 favoring its penetration to the matrix pores, but also react with hydrated tin chloride according to the proposed scheme to give tin oxide inside the mesopores. It was confirmed by XRD, N₂-adsorption, TGA-DSC and FTIR spectra. This phenomenon was further corroborated by detecting the inhibition of SnO₂ NP formation at 250 °C after inserting the tin precursor to SBA-15 with reduced silanols concentration partially grafted with tin chloride.     

Photochemical preparation of CdS hollow microspheres at room temperature and their use in visible-light photocatalysis

CdS hollow microspheres have been successfully prepared by a photochemical preparation technology at room temperature, using polystyrene latex particles as templates, CdSO₄ as cadmium source and Na₂S₂O₃ as both sulphur source and photo-initiator. The process involved the deposition of CdS nanoparticles on the surface of polystyrene latex particles under the irradiation of an 8 W UV lamp and the subsequent removal of the latex particles by dispersing in dichloromethane. Photochemical reactions at the sphere/solution interface should be responsible for the formation of hollow spheres. The as-prepared products were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Such hollow spheres could be used in photocatalysis and showed high photocatalytic activities in photodegradation of methyl blue (MB) in the presence of H₂O₂. The method is green, simple, universal and can be extended to prepare other sulphide and oxide hollow spheres.     

Synthesis of nickel nanoparticles and carbon encapsulated nickel nanoparticles supported on carbon nanotubes

Nickel nanoparticles were prepared and uniformly supported on multi-walled carbon nanotubes (MWCNTs) by reduction route with CNTs as a reducing agent at 600 °C. As-prepared nickel nanoparticles were single crystalline with a face-center-cubic phase and a size distribution ranging from 10 to 50 nm, and they were characterized by transmission electron microscopy (TEM), high-resolution TEM and X-ray diffraction (XRD). These nickel nanoparticles would be coated with graphene layers, when they were exposed to acetylene at 600 °C. The coercivity values of nickel nanoparticles were superior to that of bulk nickel at room temperature.     

Thermal behavior of aluminum powder and potassium perchlorate mixtures by DTA and TG

In this work the thermal decomposition characteristics of micron sized aluminum powder + potassium perchlorate pyrotechnic systems were studied with thermal analytical techniques. The results show that the reactivity of aluminum powder in air increases as the particle size decreases. Pure aluminum with 5 μm particle size has a fusion temperature about 647 °C, but this temperature for 18 μm powder is 660 °C. Pure potassium perchlorate has an endothermic peak at 300 °C corresponding to a rhombic-cubic transition, a fusion temperature around 590 °C and decomposes at 592 °C. DTA curves for Al₅/KClO₄ (30:70) mixture show a maximum peak temperature for thermal decomposition at 400 °C. Increasing the particle size of aluminum powder increases the ignition temperature of the mixture. The oxidation temperature increased by enhance in the aluminum content of the mixture.     

Thermo-Raman spectroscopy in situ monitoring study of solid-state synthesis of NiO-Al2O3 nanoparticles and its characterization

Hyphenation of thermogravimetric analyzer (TGA) and thermo-Raman spectrophotometer for in situ monitoring of solid-state reaction in oxygen atmosphere forming NiO-Al₂O₃ catalyst nanoparticles is investigated. In situ thermo-Raman spectra in the range from 200 to 1400 cm⁻¹ were recorded at every degree interval from 25 to 800 °C. Thermo-Raman spectroscopic studies reveal that, although the onset of formation is around 600 °C, the bulk NiAl₂O₄ forms at temperatures above 800 °C. The X-ray diffraction (XRD) spectra and the scanning electron microscopy (SEM) images of the reaction mixtures were recorded at regular temperature intervals of 100 °C, in the temperature range from 400 to 1000 °C, which could provide information on structural and morphological evolution of NiO-Al₂O₃. Slow controlled heating of the sample enabled better control over morphology and particle size distribution (∼20-30 nm diameter). The observed results were supported by complementary characterizations using TGA, XRD, SEM, transmission electron microscopy, and energy dispersive X-ray analysis.     

Shape evolution and thermal stability of Ag nanoparticles on spherical SiO2 substrates

In this paper, the shape evolution and thermal stability of Ag nanoparticles (NPs) on spherical SiO₂ substrates were investigated by means of in situ transmission electron microscopy (TEM) imaging and differential scanning calorimetry (DSC). The initial Ag NPs at room temperature were semispherical-like, with an average size of 9 nm in half-height width, well-dispersed on spherical SiO₂ substrates. No obvious shape change was observed when the semispherical NPs of Ag were heated at temperature lower than 550 °C. The shape of the semispherical Ag NPs changed gradually into a spherical one in the temperature range of 550-700 °C, where surface diffusion and surface premelting took place. When the heating temperature was increased up to 750 °C, the spherical Ag NPs were found to desquamate from the substrates due to the decreases of the contact area and the binding force between Ag NPs and SiO₂ substrates. A possible mechanism for the desquamation of Ag NPs from the SiO₂ sphere surface is proposed according to the results of in situ TEM observation and DSC analysis.     

交联度对原位聚合法制备聚合物胶束性质的影响及相应的空心球制备

用原位聚合法成功地制备出不同响应温度的温敏性聚乳酸/聚(异丙基丙烯酰胺-co-丙烯酰胺)[P(D,L-LA)/P(NIPAM-co-AM)]核壳胶束. 实验中发现, 壳层的交联剂含量对粒子的尺寸有很大的影响, 当交联剂的摩尔分数从5%提高到15%时, 粒子在25 ℃时的流体力学直径从170.2 nm增加到886.5 nm. 通过对胶束粒子的核进行生物降解, 方便地得到了相应的空心球. 用FTIR监测核的降解过程, 用SEM和AFM检测核降解完全后粒子的外在形貌和内在结构变化. DLS结果表明, 空心球粒子同样具有良好的温度响应性, 其响应温度可通过改变原位聚合时单体AM的含量加以调节.     

A new low temperature methodology to obtain pure nanocrystalline nickel borate

The present study focuses on the development of a new route for the synthesis of pure nickel borate nanoparticles using reverse micellar route. Nickel borate nanoparticles (25 nm) were synthesized from a precursor (obtained by reverse micellar route) containing both nickel and boron (nickel nitrate and sodium borohydride as starting materials). Decomposition of the precursor at a temperature of ∼800 °C yielded pure nickel borate nanoparticles. This was confirmed by powder X-ray diffraction and transmission electron microscopy. These nanoparticles show an antiferromagnetic ordering with N?el temperature of 47 K.     

A new general-purpose isothermal microcalorimeter for use at temperatures up to 200 °C

The design and some properties of a new general-purpose isothermal microcalorimeter are reported. The instrument is a twin thermopile heat conduction calorimeter, which is designed for use up to 200 °C. The calorimetric units and surrounding heat sink are suspended inside a hollow aluminium construction, which is thermostated. Above that unit a second thermostated block is positioned and the whole assembly is suspended inside a Dewar vessel. When the instrument is used at room temperature and below, the thermostated units are cooled by use of an insertion Peltier effect cooler. The instrument can be used with a wide range of different reaction vessels (diameter 14 mm). Baseline experiments have been conducted in the temperature range 15-200 °C. Typical values obtained during 10 h periods at 200 °C are ±3 and ±10 nW for the baseline drift and baseline fluctuations, respectively. The heat detection limit, determined by release of electrical energy, is about 2 μJ. Preliminary stability measurements have been conducted at 100 °C on samples of stabilised and non-stabilised polyamide film.     

Sonochemical Method for the Preparation of Hollow SnO2 Microspheres

A simple sonochemical route has been successfully developed to synthesize SnO_2 hollow microspheres.Theobtained sample is characterized by XRD,TEM,XPS and UV-visible spectrophotometer.The TEM image of thesample at high magnification shows that the shell of the hollow sphere is composed of 3-5 nm SnO_2 nanoparticles.A possible formation mechanism of the hollow spheres is briefly discussed.     

Facile solvent-free synthesis of pure-phased AlN nanowhiskers at a low temperature

Pure hexagonal aluminum nitride (AlN) nanowhiskers have been successfully synthesized by directly reacting AlCl₃ with NaN₃ in non-solvent system at the low temperature of 450 °C for 24 h. The obtained products are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction, which show that the obtained products are hexagonal phase AlN nanowhiskers with width from 10 to 80 nm and length up to several micrometers. The influencing factors of the formation of AlN nanowhiskers were discussed and a possible growth mechanism for AlN nanowhiskers was proposed. Additionally, the study on the corresponding optical properties and catalytic properties is also carried out.