辉光放电中处理聚四氟乙烯表面：Ⅱ,ESR研究PTFE膜自由基

在外部电极电容耦合式反应装置中,对聚四氟乙烯(PTFE)膜进行了辉光放电处理。通过电子自旋共振(ESR)谱研究了PTFE在处理过程中所产生的自由基,着重讨论了温度对ESR谱的影响。最后,以DPPH为内标,测定了处理后PTFE膜的自由基浓度,并考察了自由基在空气中的衰减情况。     

γ辐射引发淀粉目由基衰减的动力学研究

用ESR方法研究了红薯淀粉在y射线预辐照下,产生的淀粉自由基特性及其室温下的自由基衰减动力学反应。结果表明在室温条件下,淀粉自由基的相对浓度随辐射剂量的增大而增加。自由基相对浓度的室温衰减用二级反应动力学处理,求得了衰减速率常数和淀粉自由基反应的半衰期。     

γ辐射引发淀粉目由基衰减的动力学研究

用ESR方法研究了红薯淀粉在γ射线预辐照下,产生的淀粉自由基特性及其室温下的自由基衰减动力学反应。结果表明在室温条件下,淀粉自由基的相对浓度随辐射剂量的增大而增加。自由基相对浓度的室温衰减用二级反应动力学处理,求得了衰减速率常数和淀粉自由基反应的半衰期。     

苯在铂电极上溴代反应的共焦显微拉曼光谱研究

本文主要利用共焦显微拉曼技术检测KBr溶液中苯在光滑铂电极上的取代反应。结果表明 ,苯在 1 2V时将和溴离子在氧化产生的溴自由基发生溴代反应 ,与氯代反应相比 ,溴代反应更剧烈、产物更复杂、更容易受光照影响     

紫外光诱导下的固体胆红素自由基性质的ESR研究

利用电子自旋共振方法对固体胆红素及其自由基在紫外照射下的变化进行了研究,发现在紫外光下仅引起胆红素超氧自由基及半醌自由基浓度的增加,而没有新的自由基形式生成,指出Foote提出的光氧化机理假说的中间体自由基即是由上述两种自由基构成,并通过电子计算机对ESR谱的摸拟,提出了紫外辐照下的胆红素自由基形成机理,推测胆红素光化学反应的途径及产物与这两种自由基浓度及在不同环境下的反应活性有关.     

茶多酚及其单体结构自由基的ESR研究

通过ESR检测方法研究了邻苯三酚、茶多酚及其四种单体的自氧化醌类自由基的ESR波谱信号,系统阐明了这几种物质的内在结构联系.     

某些酸性磷(膦)酸酯VO(Ⅱ)配合物在四氢呋喃中的氧化过程的ESR研究

本文用电子顺磁共振法对某些酸性磷(膦)酸酯VO(Ⅱ)配合物在四氢呋中的氧化过程进行了动力学研究,研究了温度、浓度和配合物性质对反应速度及反应可逆性的影响,并计算得到动力学参数-氧化反应级数,反应速度常数和反应的表观活化能。     

某些酸性磷(膦)酸酯VO(Ⅱ)配合物在四氢呋喃中的氧化过程的ESR研究

本文用电子顺磁共振法对某些酸性磷(膦)酸酯VO(Ⅱ)配合物在四氢呋中的氧化过程进行了动力学研究,研究了温度、浓度和配合物性质对反应速度及反应可逆性的影响,并计算得到动力学参数-氧化反应级数,反应速度常数和反应的表观活化能。     

芳胺-二苯酮光化夺氢反应活泼自由基的ESR研究

本文用自由基捕捉剂与ESR相结合的方法系统研究了各种取代苯胺与二苯酮光化夺氢反应中的活泼自由基。找出了形成N-中心及C-中心自由基的条件:即当芳胺有N上氢和α-C上氢时,优先形成N-中心自由基;仅当无N上氢时,才形成C-中心自由基。     

标准曲线法测定煤中自由基含量

自由基在煤变质过程、煤自燃反应及煤热解和液化中发挥着重要作用,准确测量煤中自由基总量对于研究上述煤的反应机理具有一定的理论意义. 由于单点法测量煤中自由基含量的准确度及精确度不够,该文通过考察ESR测定自由基含量的稳定性和重复性,尝试建立了标准曲线方法测定煤中的自由基含量,得到了满意的结果. 稳定性实验的相对标准偏差（RSD）＜4%,重复性实验的相对准偏差（RSD）＜3%,自由基含量在本实验范围（6.12×10¹⁵~1.47×10¹⁷）内线性关系良好,相关系数＞0.99. 实验结果表明,该方法对煤中自由基含量测定有很好的精密度和准确性.     

ESR法考察龙胆酸的氧化——柞蚕茧丝中龙胆酸的鉴定

本文用电子自旋共振波谱法研究了龙胆酸在碱性水溶液中的氧化,发现了一种新的自由基谱,通过自旋密度和超精细偶合常数的计算,给出了该自由基物种的结构模式,推测出龙胆酸在碱性水溶液中的氧化过程。作为柞蚕茧中龙胆酸的ESR检测方法,对测定的条件和一些影响因素进行了考察、     

Surface modification and characterization of Jordanian kaolinite: Application for lead removal from aqueous solutions

Kaolinite clay was tested for removal of lead ions from aqueous solution. This clay was washed with sulfuric acid solution followed by chemical surface modification using 3-chloropropyltriethoxysilane and sodium hydroxide. XRF results showed that silica to alumina ratio was 2.8:1 for the treated sample compared to 1.6:1 for the raw one.XRD analysis displayed different distinct kaolinite and quartz peaks before treatment while kaolinite peaks were diminished after the treatment. SEM morphology indicated that the raw kaolinite appears as plate structure with no local pores on the plates. However, after treatment the surface was found to have micropores.Different adsorption isotherm models were applied to the experimental data and found that Shawabkeh-Tutunji equation best fit these data adequately. It was also found that chemisorption took place at the surface of the modified kaolinite with maximum adsorption capacity of 54.35 mg/g.     

Preparation and Properties of Water-Soluble Sodium Polyacrylates

Butyl acrylate-acrylic acid copolymer and poly (butyl acrylate) were synthesized via suspension polymerization by using butyl acrylate as the main monomer and acrylic acid as a secondary monomer. Then these polymers were swollen in ethanol and hydrolyzed in an aqueous solution of sodium hydroxide. Finally, water-soluble sodium polyacrylates were obtained by washing and drying the hydrolyzed resultant. The influence of the mass fraction of acrylic acid in the monomer feed ratio, swelling time, and hydrolysis time on hydrophilicity, solubility, and absolute viscosity of the prepared sodium polyacrylates was researched. In addition, an Ubbelohde viscometer was used to determine the intrinsic viscosity of the aqueous solutions of the prepared sodium polyacrylates. The Mark–Houwink equation was applied to calculate their viscosity average molecular weight. Finally, their chemical structures and heat resistance properties were analyzed by using nuclear magnetic resonance spectroscopy and thermogravimetric analysis; additionally, the changes of the surface elements before and after hydrolysis were researched by using X-ray photoelectron spectroscopy.     

pH-dependent color change of colloidal dispersions of gold nanoclusters: Effect of stabilizer

Gold nanoclusters protected by 3-mercaptopropionic acid (MPA-Au nanoclusters) were prepared by citrate-reduction of hydrogen tetrachloroaurate(III) in the presence of sodium 3-mercaptopropionate. Color of the dispersions of MPA-Au nanoclusters changed from red to purple by addition of hydrochloric acid and returned from purple to red by addition of an aqueous sodium hydroxide solution. This reversible response can be attributed to synchronized changes between dispersion and ordering of MPA-Au nanoclusters, determined by transmission electron microscopy. Gold nanoclusters protected by poly(acrylic acid) (PAA-Au nanoclusters) were prepared by UV irradiation of an aqueous solution of hydrogen tetrachloroaurate(III) in the presence of poly(sodium acrylate). The pH-dependent spectral change observed for MPA-Au was not observed for PAA-Au. UV-Vis absorption spectra of colloidal dispersions of PAA-Au nanoclusters after addition of hydrochloric acid and an aqueous sodium hydroxide solution were in good agreement with each other, suggesting the stability of PAA-Au nanoclusters to pH change. Received 18 October 2000 and Received in final form 10 April 2002     

Time resolved ESR study of the oxidation of the ascorbic Acid/Ascorbate system by the isopropylol radical in aqueous solution

(CH₃)₂COH was generated photolytically in aqueous solution in the pH range 1.0 to 7.3 in presence of ascorbic acid. It reacts with ascorbate to yield the ascorbate radical anion. The kinetics of this oxidation and of the radical termination reactions were measured using time resolved ESR. It is shown that the ascorbate anion reacts faster than the neutral molecule by a factor of 20. This is ascribed to differences in the free energies of reaction.     

Surfactant-assisted organic reactions in water. Effect of ultrasound on condensation reactions between active methylene compounds and arylaldehydes

A series of quaternary ammonium salts has been tested as phase transfer agents to promote condensation reactions in an aqueous solution of sodium hydroxide in the absence of any organic solvent. Methyltrioctylammonium chloride (Aliquat 336) emerges as the most efficient catalyst. Sonication of the reaction media has a poor but positive kinetic effect.     

Influence of ionic dopants on the conductivity of electrochemically synthesized polypyrrole

Comparison of elemental analytical, XPS and SIMS data allows a semi-quantitative assessment of the dopant and oxidation states of polypyrrole synthesized using a variety of potentials and electrolyte concentrations. Studies of polypyrrole grown in aqueous solution indicate, contrary to previous reports, that a maximum in the conductivity is observed for films grown close to the oxidation-reduction potential and in agreement with our previous observations on organically grown polypyrrole.Treatment of electrochemically synthesized polypyrrole with sodium hydroxide leads to a reduction in the electrical conductivity by three orders of magnitude and similarly the addition of hydrochloric acid causes an increase in the electrical conductivity by several orders of magnitude. It was found, by comparison of films of different thicknesses that the initial time lag in the decrease in the conductivity on exposure to sodium hydroxide is a result of diffusion controlled deprotonation, whereas the protonation reaction causes an almost instantaneous increase in the electrical conductivity.     

Optimization of the alkali treatment process of date palm fibres for polymeric composites

The global interest in environmentally friendly material over the past few years has led to the development of new research areas in the field of renewable materials and biocomposites. Within this scope, several researches have been conducted to modify natural fibres aiming at an improved compatibility with polymeric matrices. In this study, fibres from the spadix stem of the date palm tree were treated with sodium hydroxide over different times. The effect of the alkali treatment on the structure, thermal and mechanical behaviour of the fibres was verified through chemical analysis, FTIR spectroscopy, TGA, and tensile testing. Comparing the different alkalisation parameters, promising results are obtained with a 2% sodium hydroxide solution over a treatment time of 2 h.     

Effect of acids on the gamma-radiolysis of frozen aqueous systems of some organic compounds

Abstract

ESR spectra of γ-irradiated frozen aqueous solutions of a number of organic compounds such as alcohols, ether, acetone and tetrahydrofurans have been examined in the presence and absence of mineral acids such as H₂SO₄. The presence of the acid is found to cause an intensification of the organic radical ESR spectra as compared with the acid free solutions. Also, the presence of the organic compounds in frozen aqueous H₂SO₄ suppresses the formation of both H-atoms and SO₄ ^? radical ions. These results have been explained on the basis of reactions of the electrons and holes, or excitons, primarily formed by the action of radiation on the substrate ice.     

Passivating oxide film and growing characteristics of anodic coatings on aluminium alloys

The paper studies some aspects of the behaviour of four aluminium alloys under chemical etching by sodium hydroxide solution and during their subsequent anodizing in sulphuric acid solution. A correspondence is seen between etching rate, thickness of the passivating oxide film and porosity of the anodic layer. The possibility of an influence on these properties of precipitates and micro-heterogeneities in the metallic surface is suggested.