沉淀法合成纳米氧化锌的工艺比较

本研究分别采用尿素均匀沉淀法和草酸直接沉淀法制备了纳米氧化锌粉体;并用XRD,SEM和激光粒度仪等对纳米ZnO的形貌和粒度进行表征.在此基础上,本文比较了不同的制备方法及不同煅烧条件对产品性能的影响.结果表明:两种方法均可制备得到粒径小于40nm的ZnO纳米粉体,所用工艺过程简单,产品性能较好.     

Preparation of nanosized TiO2 particles via ultrasonic irradiation and their photocatalytic activity on the decomposition of 4-nitrophenol

TiO₂ nanoparticles were prepared by hydrolysis of TTIP (titanium tetraisopropoxide) using an ultrasonication technique coupled with a sol-gel method. The physical properties of nanosized TiO₂ were investigated. The photocatalytic degradation of 4-nitrophenol was studied by using a batch reactor in the presence of UV light. The crystallite size of the anatase phase is increased with an increase of R_EtOH ratio (EtOH/H₂O molar ratio). The particles’ crystallite size prepared with and without ultrasonic irradiation is marginally different. Those particles prepared with ultrasonic irradiation show a higher activity on the photocatalytic decomposition of 4-nitrophenol compared to those prepared without ultrasonic irradiation. The photocatalytic activity decreases with an increase of R_EtOH ratio. In addition, the photocatalytic activity shows the highest value on the titania particle calcined at 500 ‡C. This paper was presented at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4,2004.     

Studies on the gas sensing behaviour of nanosized CuNb2O6 towards ammonia, hydrogen and liquefied petroleum gas

Appreciable changes in resistance of polycrystalline nanosized CuNb₂O₆ upon exposure to reducing gases like hydrogen, liquefied petroleum gas (LPG) and ammonia in ambient atmosphere recognize the material as a gas sensor. Nanosized CuNb₂O₆ synthesized by thermal decomposition of an aqueous precursor solution containing copper nitrate, niobium tartrate and tri-ethanol amine (TEA), followed by calcination at 700 °C for 2 h, has been characterized using X-ray diffraction (XRD) study, transmission electron microscopy (TEM), field-emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX) analysis and Brunauer–Emmett–Teller (BET) surface area measurement. The synthesized CuNb₂O₆ exhibits monoclinic structure with crystallite size of 25 nm, average particle size of 25–40 nm and specific surface area of 55 m² g⁻¹.     

Characterization and electrochemical studies of Nafion/nano-TiO2 film modified electrodes

A nano-TiO₂ film from stable aqueous dispersion has been modified on a glassy carbon electrode (GCE), and was characterized by scanning electron microscopy (SEM) and surface-enhanced Raman spectroscopy (SERS). This nanostructured film exhibits an ability to improve the electron-transfer rate between electrode and dopamine (DA), and electrocatalyze the redox of DA. The electrocatalytical behavior of DA was examined by cyclic voltammetry (CV). Combined with Nafion, the bilayer-modified electrode (N/T/GCE) gives a sensitive voltammetric response of DA regardless of excess ascorbic acid (AA). Electrochemical impedance spectroscopy (EIS) at a fixed potential was performed at variously treated GCEs. The mechanism of the electrode reaction of DA at N/T/GCE and the equivalent circuits of different GCEs have been proposed.     

Acute and chronic nephrotoxicity of platinum nanoparticles in mice

Platinum nanoparticles are being utilized in various industrial applications, including in catalysis, cosmetics, and dietary supplements. Although reducing the size of the nanoparticles improves the physicochemical properties and provides useful performance characteristics, the safety of the material remains a major concern. The aim of the present study was to evaluate the biological effects of platinum particles less than 1 nm in size (snPt1). In mice administered with a single intravenous dose of snPt1, histological analysis revealed necrosis of tubular epithelial cells and urinary casts in the kidney, without obvious toxic effects in the lung, spleen, and heart. These mice exhibited dose-dependent elevation of blood urea nitrogen, an indicator of kidney damage. Direct application of snPt1 to in vitro cultures of renal cells induced significant cytotoxicity. In mice administered for 4 weeks with twice-weekly intraperitoneal snPt1, histological analysis of the kidney revealed urinary casts, tubular atrophy, and inflammatory cell accumulation. Notably, these toxic effects were not observed in mice injected with 8-nm platinum particles, either by single- or multiple-dose administration. Our findings suggest that exposure to platinum particles of less than 1 nm in size may induce nephrotoxicity and disrupt some kidney functions. However, this toxicity may be reduced by increasing the nanoparticle size.     

Synthesis of functional nanocrystallites through reactive thermal plasma processing

A method of synthesizing functional nanostructured powders through reactive thermal plasma processing has been developed. The synthesis of nanosized titanium oxide powders was performed by the oxidation of solid and liquid precursors. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, were used to vary the quench rate, and therefore the particle size, of the resultant powders. The experimental results are well supported by numerical analysis on the effects of the quench gas on the flow pattern and temperature field of the thermal plasma as well as on the trajectory and temperature history of the particles. The plasma-synthesized TiO₂ nanoparticles showed phase preferences different from those synthesized by conventional wet-chemical processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via reactive thermal plasma processing.     

Microwave-assisted synthesis of LiCoO2 and LiCo1−xGaxO2: Structural features,magnetism and electrochemical characterization

Nanocrystalline (between 30 and 40 nm) LiCoO₂ and LiCo_1−xGa_xO₂ (0 ≤ x ≤ 0.15) powders have been prepared by using a standard microwave furnace.     

Effects of nanosized constriction on thermal transport properties of graphene

Thermal transport properties of graphene with nanosized constrictions are investigated using nonequilibrium molecular dynamics simulations. The results show that the nanosized constrictions have a significant influence on the thermal transport properties of graphene. The thermal resistance of the nanosized constrictions is on the order of 10⁷ to 10⁹ K/W at 150 K, which reduces the thermal conductivity by 7.7% to 90.4%. It is also found that the constriction resistance is inversely proportional to the width of the constriction and independent of the heat current. Moreover, we developed an analytical model for the ballistic thermal resistance of the nanosized constrictions in two-dimensional nanosystems. The theoretical prediction agrees well with the simulation results in this paper, which suggests that the thermal transport across the nanosized constrictions in two-dimensional nanosystems is ballistic in nature.

PACS

65.80.CK; 61.48.Gh; 63.20.kp; 31.15.xv     

Production of hydrogen from methane decomposition using nanosized carbon black as catalyst in a fluidized-bed reactor

Nanosized carbon black (NCB) was employed as catalyst for methane decomposition to produce hydrogen in a fluidized-bed reactor. The carbon atoms of the surface defects of NCB act as active sites in this reaction. The activity of NCB is improved after more defects in the surface of NCB are generated after the treatment in nitric acid and calcination in nitrogen gas. The loading of small amounts of Ni and Co can obviously increase the initial activity of NCB, however, their activity deceases very quickly after the reaction begins due to the encapsulation of the corresponding metal particles inside amorphous carbon produced from methane decomposition. After reaction, the formed carbon was found to grow into carbon flakes and cover the surface of NCB. The investigation with TEM and SEM indicates that they may form from a new carbon crystallite, not build upon the existing hexagon layer in the surface defects of NCB.     

Synthesis and Characterization of Nanoscale Mullite Powder

Nanoscale mullite powder were synthesized via solgel-SCFD and middle temperature treatment by using AIP (aluminum-isopropoxde)and TEOS(tetraethyl orthosilicate) as starting materials.Both of the binary aerogel of alumina-silica and calcined nanoscale materials were investigated by using TG-DSC(thermogravimetry-differential scanning calorimeter),TEM(transmission electron microscope),XRD(X-Ray diffractometer)and specific surface area and porosimetry.TG-DSC indicated the removal of most of the volatiles,i.e.15.98% up to about 700℃,and in the DSC curve,existence of two exothermic peak at about 445℃ and 1015℃ may be due to the crystallization of Si-O-Al-O in diphasic gels and mullitization and a small endothermic peak at about 805℃ indicated the decomposition of structural water molecules.On the colligation of the results of TG-DSC,XRD and TEM,the beginning temperature of mullitization in Al2O3-SiO2 aerogel system can be confirmed at about 1015℃.XRD results also showed the formation of mullite at the range 1100-1200℃.TEM and surface area and porosimetry results showed that the nanosized mullite were calcinated at 1100 and 1200℃ exhibited size 30nm and 50nm,specific surface area 138.91m^2/g and 95.81m^2/g.