PAN纤维热稳定化过程中环化反应对氧化反应的影响

在惰性气氛中制备了不同环化程度的聚丙烯腈(PAN)热稳定化纤维,并将其在含氧气氛中进一步氧化处理,通过差示扫描量热仪(DSC)、傅立叶变换红外(FT-IR)和元素分析(EA)等方法研究了PAN纤维热稳定化过程中环化反应对氧化反应的影响。结果表明,与环化反应相比,氧化反应可在更低的温度下进行;对于环化程度越高的PAN热稳定化纤维,在含氧气氛中经相同条件热处理后氧含量越高,即氧化反应程度越高,故环化反应对氧化反应具有促进作用。     

亚硫酸钙氧化为石膏的研究

进行了亚硫酸钙氧化为二水石膏的研究 ,考察了初始 p H值、反应温度、空塔气速、固含量和停留时间对氧化率的影响 ,给出了适宜的反应条件 .在这些条件下 ,氧化率达 96 %以上     

Ti40合金的高温氧化动力学研究

为了准确预测外界环境对Ti40合金氧化反应的影响规律,利用一种新的气固反应动力学模型对阻燃钛合金Ti40合金在773~1 273 K范围内的恒温氧化行为进行研究。发现Ti40合金在773~873 K时的氧化主要受内扩散控制,活化能为262.20 k J/mol;在973~1 273 K时的氧化主要受界面反应控速,其活化能为155.67 k J/mol。另外,通过模型预测了各因素(氧气分压、温度、目标氧化厚度等)对其氧化反应分数ξ、特征时间tc和转化速率dξ/dt的影响规律。     

完全氧化和部分氧化反应中CuMnO_x的不同活性相

完全氧化和部分氧化反应的目标产物完全不同,而铜锰复合氧化物催化剂(CuMnO_x)不仅可以催化燃烧挥发性有机物(VOCs)这样的完全氧化反应,也可以催化醇类选择氧化制醛酮这样的部分氧化反应。CuMnO_x结构复杂,且对制备方法具有高度敏感性,制备方法的微小差别就可导致催化剂结构的显著差异。CuMnO_x中存在不同价态的CuO_x 、MnO_x 物种,还可生成尖晶石型或者无定形的铜锰复合氧化物。CuMnO_x中的这些物种在完全氧化反应和部分氧化反应中都可能存在一定的催化活性,研究者对CuMnO_x的活性相还没有完全统一的认识。在醇类部分氧化反应中,CuMnO_x所含的尖晶石型铜锰复合氧化物能提供移动性强的表面吸附氧物种、具有吸附-活化分子氧功能的表面氧空位以及晶格氧等多种活性氧物种。在VOCs完全氧化反应中,富含具有吸附反应物能力的Mn~(4+)的尖晶石型铜锰复合氧化物,具有较强的氧化还原能力,表现出高催化活性。含有丰富的Mn~(3+)的无定形铜锰复合氧化物也具有高催化活性,无定形铜锰复合氧化物表面发生Cu~(2+)+Mn~(3+)→Cu++Mn~(4+)氧化还原反应是其具有高催化活性的原因。尖晶石型铜锰复合氧化物和氧化铜/氧化锰形成的复合物也可能是完全氧化反应的活性相,其中MnO_x 由于具备较强的储氧/释氧能力可以为尖晶石型铜锰复合氧化物提供充足的氧物种,而高度分散的CuO_x 能提高活化分子氧的能力,从而提高催化剂在完全氧化反应中的催化能力。本文归纳了CuMnO_x在部分氧化醇类及完全氧化VOCs反应中的活性相的研究进展,对尖晶石Cu_xMn_(3-x)O_4物种作为部分氧化醇类活性相进行介绍,并分析其在部分氧化反应中的氧化机理。分别对无定形Cu-Mn-O物种在完全氧化反应中的作用、尖晶石Cu_xMn_(3-x)O_4物种在完全氧化反应中的作用、尖晶石Cu_xMn_(3-x)O_4物种和氧化铜或氧化锰的复合体在完全氧化反应中的作用进行介绍,为开发高效的完全氧化和部分氧化催化剂提供参考。     

光敏氧化反应的工业化应用研究

有机合成化学工业为人类社会创造了无数的奇迹,氧化反应是有机合成化学中最为重要的反应类型之一,其实现依赖于三氧化铬、重铬酸盐、高锰酸盐等重金属氧化剂的使用,由此带来的重金属废弃物的大量排放已经给环境造成了极大的污染,开发洁净环保的绿色氧化技术势在必行。光敏氧化反应是利用光子和氧气来实现物质的氧化。光子和氧气是两种特殊的化学试剂,它们不仅本身环境友好,参与氧化反应后不存在重金属排放问题,而且光敏氧化反应多在室温常压的温和反应条件下进行,反应后目标产物的分离过程也极为简单方便。因此作为一项绿色氧化技术,深入开…     

SiC涂层/三维碳纤维编织体的氧化动力学和机理研究

采用原位反应法在三维碳纤维编织体(简称:RB)的纤维表面制得SiC涂层,通过 XRD、SEM、等温氧化失重和非等温热重分析等测试手段研究了制备方法对SiC涂层均匀性 的影响,并对SiC涂层／碳纤维编织体(简称:CB)材料在等温和非等温条件下,氧化反应的 动力学和反应机理进行了研究.结果表明:SiC涂层均匀、完整地涂覆于编织体内外各纤维表 面;材料等温氧化反应的机理为第一阶段反应控制,第二阶段扩散和反应共同控制;材料的非 等温氧化过程呈现自催化特征,氧化机理为随机成核,氧化动力学参数为:lgA=9.615min^-1; E_a=201.73kJ·mol^-1.     

2,5-二巯基-1,3,4-噻二唑的合成及电化学性能

以二硫化碳和水合肼为原料合成了2,5-二巯基-1,3,4-噻二唑(DMcT),并采用元素分析、Raman光谱和红外(IR)光谱对DMcT的结构进行了表征.DMcT的循环伏安曲线表明,在室温下DMcT的氧化还原反应速度很慢,且酸碱条件对DMcT氧化还原反应有很大的影响.加入三乙胺之后,DMcT的氧化反应更加容易,还原峰电流增大,但对还原峰电位的影响不大;相反,当甲磺酸存在时,DMcT的氧化反应更难进行,而还原反应变得更加容易.     

油脂的等离子体氧化研究

本文利用氧等离子体制对油脂进行氧化，考察了等离子体放电电压和氧化反应温度对过程的影响，得出了工频条件下等离子氧化的最佳条件；反应温度７０℃、空气流量１００ｍｌ／ｈ、放电电压２１ＫＶ。同时将等离子氧化与催化氧化的结果进行了比较，认为前者反应过程简单、反应速度更快     

热解碳涂层的烧蚀行为

研究涂复热解碳(PC)的石墨材料的氧化侵蚀作用,对其实际应用十分重要,然而至今为止,对这样腐蚀的研究进行得还很不够。一般地说,多晶石墨的氧化速度与其孔隙度、织态结构及石墨化程度紧密相关。随着石墨化程度的提高,由O_2和CO_2引起的氧化反应的速度相应降低。在氧化反应过程中,氧化剂首先对晶体的棱状边缘进行作用。900℃左右温度时,氧化反     

空气湿度对聚丙烯腈纤维稳定化过程的影响

空气湿度是影响聚丙烯腈(PAN)纤维预氧化过程中的重要环境因素之一,通过考察空气湿度对预氧化过程中纤维收缩率、预氧丝单丝直径、体密度及预氧丝力学性能的影响,结果表明空气湿度对预氧化过程有两种作用机制,一方面起塑化作用,有利于纤维在张力作用下的择优取向,有利于纤维单丝直径的细化,对双扩散有促进作用;另一方面则起钝化作用,阻碍大分子链段的构象调整,对预氧化反应有延迟作用,使预氧化反应以反应控制的方式进行,有利于均质预氧化纤维的形成。高温下空气相对湿度较之温度影响很小。     

Activated carbon/iron oxide composites for the removal of atrazine from aqueous medium

The adsorption features of activated carbon and the oxidation properties of iron oxides were combined in a composite to produce new materials for atrazine removal from aqueous medium. Activated carbon/iron oxide composites were prepared at 1/1 and 5/1 mass ratios and characterized with powder X-ray diffractometry (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and nitrogen adsorption measurements. The adsorption and oxidation processes were evaluated in batch experiments, in order to monitor the atrazine removal capacity of these composites. The main iron oxide actually present in the composites was goethite (alpha-FeOOH). Impregnation with iron oxide reduced the surface area by its deposition in the activated carbon pores. However, a higher iron concentration promoted a higher oxidation rate, indicating that the efficiency of the oxidation reaction is related with the iron content and not with the pre-concentration of the contaminant on the carbon surface through adsorption process.     

Treatment of petroleum refinery sourwater by advanced oxidation processes

The performance of several oxidation processes to remove organic pollutants from sourwater was investigated. Sourwater is a specific stream of petroleum refineries, which contains slowly biodegradable compounds and toxic substances that impair the industrial biological wastewater treatment system. Preliminary experiments were conducted, using the following processes: H2O2, H2O2/UV, UV, photocatalysis, ozonation, Fenton and photo-Fenton. All processes, except Fenton and photo-Fenton, did not lead to satisfactory results, reducing at most 35% of the sourwater dissolved organic carbon (DOC). Thus, further experiments were performed with these two techniques to evaluate process conditions and organic matter removal kinetics. Batch experiments revealed that the Fenton reaction is very fast and reaches, in a few minutes, an ultimate DOC removal of 13-27%, due to the formation of iron complexes. Radiation for an additional period of 60 min can increase DOC removal up to 87%. Experiments were also conducted in a continuous mode, operating one 0.4L Fenton stirred reactor and one 1.6L photo-Fenton reactor in series. DOC removals above 75% were reached, when the reaction system was operated with hydraulic retention times (HRT) higher than 85 min. An empirical mathematical model was proposed to represent the DOC removal kinetics, allowing predicting process performance quite satisfactorily.     

Controlled multistep purification of single-walled carbon nanotubes

A controlled and scalable multistep purification method has been developed to remove iron impurity and nonnanotube carbon materials from raw single-walled carbon nanotubes (SWNTs) produced in the HiPco (high-pressure CO) process. In this study, iron nanoparticles, coated by carbon, are exposed and oxidized by multiple step oxidation at increasing temperatures. To avoid catalytic oxidation by iron oxide of carbon nanotubes, the exposed and oxidized iron oxide is deactivated by reaction with C(2)H(2)F(4) or SF(6). The iron fluorides are removed by a Soxhlet extraction with a 6 M HCl solution. The purity and quality of each sample were determined by thermogravimetric analysis (TGA), Raman spectrometry, ultraviolet-visible-near-IR (UV-vis-near-IR) spectrometry, fluorescence spectrometry, and transmission electron microscope (TEM) spectroscopy. The purity and yield of SWNTs are improved due to reduced catalytic activity of the iron oxide. Greater iron oxide removal also resulted from oxidation at higher temperatures.     

Steel dust catalysis for Fenton-like oxidation of polychlorinated dibenzo-p-dioxins

An advanced oxidation process (AOP) for degrading toxic contaminants, specifically polychlorinated dibenzo-p-dioxins (PCDDs), was developed to utilize steel dust, a steel industry by-product, as the heterogenous catalyst for a Fenton-like oxidation. The steel dust was treated using a chemical acid etchant (HCl) and ultrasound to remove surface anchored groups, reduce aggregation, and thereby increase the specific surface areas, resulting in increased access to catalytic sites. The removal of PCDD was optimized through various reaction conditions. The removal percentage of 1,2,3,4-tetrachlorintated dibenzo-p-dioxins (1,2,3,4-TCDD, 3.1 microM) after 3 h of Fenton-like oxidation under the conditions of 3 g/L (88 mM) H(2)O(2) and pH 3 was approximately 97% with 10 g/L of steel dust, compared to approximately 99% when 5 g/L metallic iron was used as a control. When a PCDD mixture (0.5-0.7 nM) was treated, 10 g/L (92 mM) steel dust achieved approximately 88% removal, comparable to the removal with 5 g/L (89 mM) Fisher iron with 3 g/L (88 mM) H(2)O(2.) These results indicate that the steel dust is a potentially viable catalyst for removing PCDDs from contaminated water.     

Synergistic effect of transition metal oxides and ozone on PCDD/F destruction

Catalytic oxidations of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) with ozone on the transition metal oxides (iron oxide or manganese oxide) at the temperature range of 120-180 degrees C were investigated. These two catalysts were prepared by precipitation methods. Iron oxide has a higher surface area (330 m(2)/g) than manganese oxide (53 m(2)/g). In the absence of ozone, the removal efficiencies of PCDD/Fs achieved with iron oxide or manganese oxide were between 83% and 85%, while the destruction efficiencies were only between 20% and 25% at 180 degrees C. It indicates that adsorption was the main removal mechanism of PCDD/Fs over these two catalysts. On the other hand, ozone addition greatly enhanced the catalytic activity of iron oxide or manganese oxide catalysts on the oxidation of gaseous PCDD/Fs. At 180 degrees C, the destruction efficiencies of gaseous PCDD/Fs achieved with iron oxide or manganese oxide with 100 ppm O(3) exceeded 90%. It indicates that catalytic ozonation achieved with iron oxide or manganese oxide is effective in decomposing PCDD/Fs and the application of ozone lowers the reaction temperature of PCDD/F oxidation below 200 degrees C. Furthermore, the synergistic effect of iron oxide and ozone is superior to that of manganese oxide due to the fact that the surface of iron oxide has more hydroxyl groups, which easily form hydrogen bonds with ozone and decompose to form atomic oxygen for the further reaction with dioxin molecules.     

Purification process for vertically aligned carbon nanofibers

Individual, free-standing, vertically aligned multiwall carbon nanotubes or nanofibers are ideal for sensor and electrode applications. Our plasma-enhanced chemical vapor deposition techniques for producing free-standing and vertically aligned carbon nanofibers use catalyst particles at the tip of the fiber. Here we present a simple purification process for the removal of iron catalyst particles at the tip of vertically aligned carbon nanofibers derived by plasma-enhanced chemical vapor deposition. The first step involves thermal oxidation in air, at temperatures of 200-400 degrees C, resulting in the physical swelling of the iron particles from the formation of iron oxide. Subsequently, the complete removal of the iron oxide particles is achieved with diluted acid (12% HCl). The purification process appears to be very efficient at removing all of the iron catalyst particles. Electron microscopy images and Raman spectroscopy data indicate that the purification process does not damage the graphitic structure of the nanotubes.     

Treatment of petroleum-hydrocarbon contaminated soils using hydrogen peroxide oxidation catalyzed by waste basic oxygen furnace slag

The contamination of subsurface soils with petroleum hydrocarbons is a widespread environmental problem. The objective of this study was to evaluate the potential of applying waste basic oxygen furnace slag (BOF slag) as the catalyst to enhance the Fenton-like oxidation to remediate fuel oil or diesel contaminated soils. The studied controlling factors that affect the removal efficiency of petroleum hydrocarbons included concentrations of H₂O₂, BOF slag dosages, types of petroleum hydrocarbons (e.g., fuel oil and diesel), and types of iron mineral. Experimental results indicate that oxidation of petroleum hydrocarbon via the Fenton-like process can be enhanced with the addition of BOF slag. Results from the X-ray powder diffraction analysis reveal that the major iron type of BOF slag/sandy loam system was iron mineral (e.g., α-Fe₂O₃ and α-FeOOH). Approximately 76% and 96% of fuel oil and diesel removal were observed (initial total petroleum hydrocarbon (TPH) concentration = 10,000 mg kg⁻¹), respectively, with the addition of 15% of H₂O₂ and 100 g kg⁻¹ of BOF slag after 40 h of reaction. Because BOF slag contains extractable irons such as amorphous iron and soluble iron, it can act as an iron sink to supply iron continuously for Fenton-like oxidation. Results demonstrate that Fenton-like oxidation catalyzed by BOF slag is a potential method to be able to remediate petroleum-hydrocarbon contaminated soils efficiently and effectively.     

Enhancing the efficiency of AuCl4 ion removal from aqueous solution using activated carbon and carbon nanomaterials

The removal of AuCl₄⁻ ion from acidic aqueous solutions is studied using a series of non-oxidized and surface oxidized carbon materials (activated carbon, carbon nanotubes, carbon-encapsulated iron nanoparticles and carbon black). The studied sorbents differ in crystallinity, porosity and morphology. In the case of non-oxidized carbon materials the maximum removal efficiency (74%) is found for activated carbon, whilst graphitized nanomaterials (i.e. carbon nanotubes and carbon-encapsulated iron nanoparticles) are able to remove 42–45% of gold ion from the solution. The oxidation in nitric acid significantly improves the removal efficiencies. The uptake of Au(III) increases two times (to 91–92%) for oxidized carbon nanotubes and carbon-encapsulated iron nanoparticles. The same oxidation procedure applied to activated carbon and carbon black moderately enhances the uptake efficiency to 88% and 55%, respectively. The observed substantially distinct uptakes are discussed in the frames of textural properties, morphology, surface chemistry characteristics and crystallinity of the studied carbon materials. Moreover, the possibility of a galvanic exchange reaction between AuCl₄⁻ and metallic Fe in the carbon encapsulate core is also evaluated.     

Hydrogen peroxide lifetime as an indicator of the efficiency of 3-chlorophenol Fenton's and Fenton-like oxidation in soils

In this work the possibility of using the hydrogen peroxide lifetime as indicator of the oxidation efficiency of Fenton's and Fenton-like processes for soil treatment was explored. A reactivity scale, in terms of the oxidizing power in the different tested operating conditions (pH, iron sulfate concentration and stabilizer concentration) was built for each soil as a function of the hydrogen peroxide lifetime. Its validity was then confirmed through 3-chlorophenol Fenton's and Fenton-like slurry-phase oxidation experiments. The proposed reactivity scale proved to be effective for comparing the different operating conditions for the same soil, but failed when used to compare the oxidation performances for different soils, since the different adsorptive behavior of the tested soils may have influenced the contaminant removal rate.     

Fenton-like oxidation of Rhodamine B in the presence of two types of iron (II,III) oxide

The catalytic efficiency of iron (II, III) oxide to promote Fenton-like reaction was examined by employing Rhodamine B (RhB) as a model compound at neutral pH. Two types of iron (II, III) oxides were used as heterogeneous catalysts and characterized by XRD, Mössbauer spectroscopy, BET surface area, particle size and chemical analyses. The adsorption to the catalyst changed significantly with the pH value and the sorption isotherm was fitted using the Langmuir model for both solids. Both sorption and FTIR results indicated that surface complexation reaction may take place in the system. The variation of oxidation efficiency against H₂O₂ dosage and amount of exposed surface area per unit volume was evaluated and correlated with the adsorption behavior in the absence of oxidant. The occurrence of optimum amount of H₂O₂ or of exposed surface area for the effective degradation of RhB could be explained by the scavenging effect of hydroxyl radical by H₂O₂ or by iron oxide surface. Sorption and decolourization rate of RhB as well as H₂O₂ decomposition rate were found to be dependent on the surface characteristics of iron oxide. The kinetic oxidation experiments showed that structural Fe^II content strongly affects the reactivity towards H₂O₂ decomposition and therefore RhB decolourization. The site density and sorption ability of RhB on surface may also influence the oxidation performance in iron oxide/H₂O₂ system. The iron (II, III) oxide catalysts exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle. The sorption on the surface of iron oxide with catalytic oxidation using hydrogen peroxide would be an effective oxidation process for the contaminants.