Thermal hazard evaluation of carbon nanotubes with sulfuric acid by DSC

Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics regarding stability would represent potential hazards during the production or utilization stage and could be determined by calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate the thermokinetic parameters for MWNTs at various compositions. Thermoanalytical curves showed that the average heat of decomposition (ΔH _d) of the MWNTs samples in a manufacturing process was about 31,723 J g⁻¹, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence of sulfuric acid (H₂SO₄). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch addition with reactants of H₂SO₄. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation or accident.     

The study of self-assembled films of triazole on iron electrodes using electrochemical methods,XPS, SEM and molecular simulation

3-Alkyl-4-amino-5-mercapto-1,2,4-triazole (AAMT) has been evaluated as corrosion inhibition for iron in 0.1 M H₂SO₄ when the films of AAMT were self-assembled on the surface of iron. The films of AAMT inhibitor were characterized by electrochemical impedance spectroscopy, electrochemical polarization curves Results revealed that AAMT performed excellently as a corrosion inhibitor for iron in H₂SO₄ solution. Surface analysis was carried out using X-ray photoelectron spectroscopy and scanning electron microscope. The mechanism of adsorption was discussed using molecular simulation.     

Preparation of iron oxides using ammonium iron citrate precursor: Thin films and nanoparticles

Ammonium iron citrate (C₆H₈O₇·nFe·nH₃N) was used as a precursor for preparing both iron-oxide thin films and nanoparticles. Thin films of iron oxides were fabricated on silicon (111) substrate using a successive-ionic-layer-adsorption-and-reaction (SILAR) method and subsequent hydrothermal or furnace annealing. Atomic force microscopy (AFM) images of the iron-oxide films obtained under various annealing conditions show the changes of the micro-scale surface structures and the magnetic properties. Homogenous Fe₃O₄ nanoparticles around 4 nm in diameter were synthesized by hydrothermal reduction method at low temperature and investigated using transmission electron microscopy (TEM).     

The effect of electrochemically treated glassy carbon on the activity of supported Pt catalyst in methanol oxidation

Effect of electrochemical oxidation of glassy carbon on deposition of platinum particles and electrocatalytic activity of platinum supported on oxidized glassy carbon (Pt/GC_OX) were studied for methanol oxidation in H₂SO₄ solution. Platinum was potentiostatically deposited from H₂SO₄ + H₂PtCl₆ solution. Glassy carbon was anodically polarised in 0.5 M H₂SO₄ at 2.25 V vs. saturated calomel electrode (SCE) during 35 s. Electrochemical treatment of GC support, affecting not significantly the real Pt surface area, leads to a better distribution of platinum on the substrate and has remarkable effect on the activity. The activity of the Pt/GC_OX electrode for methanol oxidation is larger than polycrystalline Pt and for more than one order of magnitude larger than Pt/GC electrode. This increase in activity indicates the pronounced role of organic residues of GC support on the properties of Pt particles deposited on glassy carbon.     

Effect of H2SO4 Solution Treatment on Adhesion,Charge Transfer,and Catalytic Performance of Screen-Printed PEDOT:PSS

Post-treatment was performed for poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films screen-printed on fluorine-doped tin oxide (FTO) substrates, to improve their charge transfer efficiency. Different H₂SO₄ solutions, including concentrated H₂SO₄ and H₂SO₄ diluted with H₂O or dimethyl sulfoxide (DMSO), were adopted during the post-treatment. The adhesion of the as-treated films was evaluated by adhesive tape peeling tests, the surface morphology and vertical charge transfer from the films to the substrates were investigated by current-sensing atomic force microscopy, and the catalytic activities toward I₃⁻ reduction of PEDOT:PSS films were characterized by electrochemical measurements. It is discovered that selecting proper H₂SO₄ solutions is crucial to improve the charge transfer efficiency and catalytic performance while maintaining reliable adhesion of the film on the substrates, with H₂SO₄/DMSO performing best as the solution for post-treatment. A mechanistic explanationis proposed based on different interactions among solution, PEDOT:PSS, and the substrate for various post-treatment solutions.     

Decoration of carbon nanotubes with iron oxide

A magnetic composite of multiwalls carbon nanotubes (MWNTs) decorated with iron oxide nanoparticles was synthesized successfully by a simple and effective chemistry precipitation method. The composite was characterized by X-ray diffraction analysis (XRD), Mössbauer spectrum (MS), transmission electron microscopy (TEM), and Fourier transform spectroscopy (FTIR) techniques. The patterns of XRD and MS indicated that MWNTs, γ-Fe₂O₃, and Fe₃O₄ coexisted in the composite. The TEM observation indicated that the nanoparticles of iron oxide were attached on the surface of the MWNTs, and the sizes of the particles ranged from 25 to 80 nm. FTIR spectra showed that SO₄⁻ functional groups existed on the surface of MWNTs after modification by sodium dodecylbenzene sulfonic acid (SDBS), which could immobilize Fe³⁺ ions onto the MWNTs. The hysteresis loops of the MWNTs and decorated MWNTs were measured by vibrating sample magnetometer (VSM), and the results showed that the composite was ferromagnetism with the saturated magnetization of 20.07 emu/g, and the coercive of 163.44 Oe.     

稀碱溶液中水热法制备柔性TiO2纳米须薄膜的生长机制及表征

以柔性不锈钢基底上经磁控溅射沉积的钛膜为钛源, 在1 mol·L^-1的低浓度NaOH溶液中水热法制备了朝基底上方取向生长的大长径比柔性TiO₂纳米须薄膜, 考察了钛膜沉积条件对纳米须薄膜的影响, 系统研究了水热反应条件对薄膜生长过程的影响及TiO₂纳米须薄膜的形成机制. 通过场发射扫描电镜(FESEM)、X射线能谱仪(EDS)、高分辨透射电子显微镜(HRTEM)、X射线衍射仪(XRD)等对样品进行了表征. 结果表明, 与室温沉积的钛膜相比, 600 ℃下沉积的钛膜水热后得到的纳米线薄膜与基底的附着力更好. 所得TiO₂纳米须为单晶锐钛矿, 经由Na₂Ti₂O₄(OH)₂、H₂Ti₂O₅·H₂O转变而来. 纳米须形成于水热阶段, 平行于Na₂Ti₂O₄(OH)₂的(100)晶面择优取向生长, 纳米须经历了纳米片→纳米线束→纳米线的裂解生长过程. 朝基底上方取向生长的纳米须薄膜的形成是低浓度NaOH溶液与较高水热温度(220 ℃)协同作用的结果. 进一步在Na₂SO₄溶液中研究了薄膜电极的光电化学性能, 结果表明, TiO₂纳米须薄膜的光电性能明显优于零维纳米颗粒薄膜和二维纳米片薄膜, 显示了良好的应用前景.     

Application of Tri-n-octylamine for the substoichiometric separation of chromium(VI) in activation analysis

A method has been developed for the substoichiometric separation of Cr(VI) by extraction with tri-n-octylamine solution in benzene from 0.1M H₂SO₄ solution. The method has been applied to the determination of chromium in silicon and aluminium by the neutron activation method.     

Growth of vertically aligned carbon nanotubes on carbon fiber: thermal and electrochemical treatments

Composite electrodes of vertically aligned carbon nanotubes (VACNT) were synthesized on carbon fiber (CF) substrate by pyrolysis of camphor/ferrocene using a SiO₂ interlayer as a barrier against metal diffusion into the substrate. Two treatments were used to remove iron from CF/VACNT structure: thermal annealing at high temperature under inert atmosphere and electrochemical oxidation in H₂SO₄ solution. The composites were characterized by scanning electron microscopy and Raman scattering spectroscopy. Besides, the electrochemical behavior of CF/VACNT was analyzed by cyclic voltammetry and charge/discharge tests. CF/VACNT composite submitted to the electrochemical oxidation showed the best electrochemical performance, with high specific capacitance, which makes it very attractive as electrode for supercapacitors.     

Effect of TiOSO4 hydrothermal hydrolysis conditions on TiO2 morphology and gas-phase oxidative activity

The effect of synthesis conditions on morphology and catalytic activity has been studied for hydrothermal preparation of TiO₂ from acidified aqueous TiOSO₄ solution. It was found that the increase in TiOSO₄ and H₂SO₄ concentration results in the increase of photocatalytic activity of produced TiO₂, as it was revealed by steady-state gas-phase oxidation of acetone and ethanol vapors in a flow-circulating reactor. TiOSO₄ concentration exerts strong influence on the shape of the produced TiO₂ particles. At TiOSO₄ concentration less than 0.1 wt%, hydrolysis gives rise to hedgehog-like agglomerates consisting of spliced-blade TiO₂ nanocrystals. At higher concentration of TiOSO₄, the resultant TiO₂ consists of round agglomerates of 5–10 nm primary particles. The size of secondary particles depends mainly on the H₂SO₄ concentration. The increase of the time of hydrothermal treatment results in the enhancement of TiO₂ photocatalytic activity that reaches a maximum. Among different acids (HCl, HClO₄, HNO₃, H₃PO₄ and CH₃COOH) added during hydrolysis of TiOSO₄, sulfuric and acetic acids had the best effect on photocatalytic activity of TiO₂. The results obtained can help to finely tune this TiO₂ preparation method in order to obtain desirable particles size, shape and activity.     

Effect of Zirconia Precursor on the Properties of ZrO2-SiO2 Sol-Gel Oxides

Sol-gel zirconia-silica oxides were synthesized with two zirconium precursors, zirconium n-butoxide and zirconium acetylacetonate, and two different hydrolysis catalysts, HCl and H₂SO₄. The samples prepared with HCl were additionally sulfated with a 1 M solution of H₂SO₄. Characterization was performed with FTIR and ²⁹Si-MAS-NMR spectroscopy, as well as with nitrogen adsorption. Because zirconium and silicon alkoxides have different hydrolysis rates, it was necessary to perform a pre-hydrolysis of the silicon alkoxide before mixing. The atom distribution in the ZrO₂-SiO₂ system depended on the zirconium precursor, which also determined the zirconium incorporation in the silica lattice, which was greater for zirconium acetylacetonate. The zirconium precursor also was responsible for the silanol concentration, which increases when samples were sulfated. Sulfating stabilizes the specific surface area. On sulfate samples calcined at 800°C BET areas larger than 500 m²/g were obtained.     

Quantitative estimations of ferric iron by phosphoric acid in aqueous-alcoholic medium

Summary The only method recommended for the direct estimation of ferric iron in presence of HCl is to reduce the ferric iron to ferrous iron and then to titrate against KMnO₄ solution by adding Reinhardt-Zimmermann reagent (MnSO₄ + H₂SO₄ + H₃PO₄). The solubility of the phosphato complexes of ferric chloride and phosphoric acid is much reduced by adding a nonaqueous solvent, ethyl alcohol or acetone. This property has been availed of to find out a method of estimating ferric iron directly against standard solution of phosphoric acid in aqueous-nonaqueous medium using K₄Fe(CN)₆ or cupferron as external indicators. A slight discrepancy at the end point, however, exists in the direct titration but it can be removed by applying a correction factor determined from the estimated results.     

Variation of the capacity characteristics of a composite material consisting of acetylene black and polytetrafluoroethylene and of its wettability with an aqueous solution under the action of anodic current

The effect exerted by treatment with cyclic anodic current in 1 M H₂SO₄ in the interval 0.0–2.0 V on electrodes made of a porous (55 vol %) composite material consisting of A-437E acetylene black and polytetrafluoroethylene (60 wt %) was studied. The cyclic volt–ampere curves were recorded in 3 M KOH and 1 M H₂SO₄ to determine the double layer capacity. The anodic treatment leads to an increase in the volume of pores filled with the electrolyte and in the electrical capacity of the electrode due both to an increase in the area of the surface wetted with the electrolyte and to the pseudocapacity caused by oxidation of the carbon black surface.     

六方相WO3纳米带的制备与表征

以Na2WO4、K2SO4和H2C2O4为原料,采用两步水热合成法制备了六方相WO3纳米带.首先,在探索pH值、K2SO4加入量、反应温度和时间以及表面活性剂等因素对WO3纳米带的前驱物钨酸盐形貌的影响后,给出了前驱物钨酸盐纳米带的合成条件,并讨论了纳米带的形成机理;然后,在180℃的水热条件下对前驱物再处理48 h获得六方相WO3纳米带.测试结果表明,WO3纳米带的形貌保持较好,宽度在100～300 nm间,长度可达数微米,沿纳米带长轴方向为[001]方向.     

氧化钌/石墨纳米片复合阵列电极的制备及其电容性能

通过电化学剥离法在石墨棒表面构筑了层数不等、彼此平行且垂直于基底的二维石墨纳米片(GNS)阵列, 而后采用阴极还原电沉积法在GNSs 表面均匀地包覆了一层氧化钌(RuO₂·xH₂O)薄膜, 形成了RuO₂·xH₂O/GNS 复合阵列电极. 电化学测试表明, RuO₂·xH₂O/GNS 复合阵列电极具有优良的超电容性能, 在0.5mol·L^-1 H₂SO₄电解质溶液中, 扫描速率为5 mV·s^-1, 电位窗口为0.9 V时, 其比电容高达4226 F·m^-2, 并且具有优异的循环性能, 经过20000圈充放电循环后, 电容保持率高达94.18%.     

Effect of nitrogen-containing groups on enhanced capacitive behaviors of multi-walled carbon nanotubes

In this work, electrochemical properties of surface treated multi-walled carbon nanotubes (MWNTs) are studied in supercapacitors. Nitrogen and oxygen functional groups containing MWNTs are prepared by urea and acidic treatments, respectively. The surface properties of the MWNTs are confirmed by X-ray photoelectron spectroscopy (XPS) and zeta-potential measurements. The textural properties are characterized by N₂ adsorption/desorption isotherm at 77 K using the BET eqaution, BJH method, and HK method. The electrochemical properties of the MWNTs are accumulated by cyclic voltammetry, impedance spectra, and charge-discharge cycling performance in 1 M H₂SO₄ at room temperature. As a result, the functionalized MWNTs lead to an increase in capacitance as compared with pristine MWNTs. It suggests that the pyridinic and pyridinic-N-oxides nitrogen species have effects on the specific capacitance due to the positive charge, and thus an improved electron transfer at high current loads results, the most important functional groups affecting capacitive behaviors.     

Separation of yttrium(III) from iron(III) through liquid membrane impregnated with di(2-ethylhexyl)phosphoric acid

The selective transport of yttrium(III) in the presence of iron(III) through a supported liquid membrane (SLM) has been investigated by using di(2-ethylhexyl)phosphoric acid (DEHPA) as a mobile carrier. Yttrium(III) with fast kinetics was preferentially transported from the feed solution of dilute acid into the product solution of 1M H₂SO₄, while most of iron(III) with slow kinetics remained in the feed solution. The effective separation of yttrium(III) from a large amount of iron(III) was accomplished by the selective transport of yttrium(III) through the SLM.     

[Fe(N2H5)2(SO4)2]n的合成、结构和磁性质

采用水热合成方法得到一例新的过渡金属铁(Fe)的含肼硫酸盐: [Fe(N₂H₅)₂(SO₄)₂]_n (1). 用单晶X射线衍射的方法对其晶体结构进行了表征. 结果表明, 该化合物以硫酸根为桥连配体, 质子化的肼分子为端基配体, 形成一维(1D)链状结构. 肼分子和硫酸根形成的链间氢键, 将1D链进一步扩展成三维(3D)结构. 磁性测试表明化合物在低温下显示出反铁磁有序的磁行为.     

Mechanism of synthesis of anatase TiO2 pigment from low concentration of titanyl sulfuric–chloric acid solution under hydrothermal hydrolysis

In order to investigate the influence of Cl⁻/SO₄²⁻ molar ratios and hydrolysis temperature on the hydrolysis process and TiO₂ pigment, H₂TiO₃ was prepared with a low concentration of titanyl sulfuric–chloric acid solution by hydrothermal hydrolysis. Under the optimal hydrolysis conditions, 1.5–2.2 μm of H₂TiO₃ samples were achieved. After doping and calcination, anatase TiO₂ pigments demonstrated excellent performance: the achromic ability of tinctorial strength (TCS) and blue phase index (SCX) were 1,429 and 4.07, respectively. As hydrolysis was a significant step in the process, the structure was simplified to a periodic structure of Ti[OH](H₂O)₃Cl(SO₄) to simulate the cluster structures. Based on experimental results and density functional theory (DFT) calculation, the hydrolysis mechanism was presumed to be a process of anionic (OH⁻, Cl⁻ and SO₄²⁻) competition reaction to explain the formation of anatase-type H₂TiO₃, and the crystal growth direction of H₂TiO₃ was also confirmed to be a (OA) and b (OB).     

Composite film of carbon nanotubes and chitosan for preparation of amperometric hydrogen peroxide biosensor

A new amperometric biosensor for hydrogen peroxide was developed based on cross-linking horseradish peroxidase (HRP) by glutaraldehyde with multiwall carbon nanotubes/chitosan (MWNTs/chitosan) composite film coated on a glassy carbon electrode. MWNTs were firstly dissolved in a chitosan solution. Then the morphology of MWNTs/chitosan composite film was characterized by field-emission scanning electron microscopy. The results showed that MWNTs were well soluble in chitosan and robust films could be formed on the surface. HRP was cross-linked by glutaraldehyde with MWNTs/chitosan film to prepare a hydrogen peroxide biosensor. The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for H₂O₂ in the absence of a mediator. The linear range of detection towards H₂O₂ (applied potential: −0.2 V) was from 1.67 × 10⁻⁵ to 7.40 × 10⁻⁴ M with correction coefficient of 0.998. The biosensor had good repeatability and stability for the determination of H₂O₂. There were no interferences from ascorbic acid, glucose, citrate acid and lactic acid.