介孔碳CMK-3对苯酚的吸附动力学和热力学研究

研究了介孔碳CMK-3对苯酚的吸附性能, 与传统商用活性碳(CAC)进行了比较, 结果表明, CMK-3比CAC的吸附量大、吸附速率快、达到平衡时间短, 是一种较好的吸附剂. 同时探讨了介孔碳CMK-3对苯酚的吸附热力学和动力学特征. CMK-3对苯酚的吸附行为可用Langmuir和Freundlich等温式进行描述, 相关性都较好, 但更符合Freundlich经验公式. 分别采用模拟一阶反应和二阶反应模型考察了吸附动力学, 并计算了这些动力学模型的速率常数. 模拟二级反应模型和实验数据之间有较好的相关性. 分别计算了热力学参数ΔG0, ΔS0和ΔH0, 结果表明, CMK-3对苯酚的吸附过程是吸热和自发的.     

Base-catalyzed hydroxymethylation of phenol by formaldehyde: Continuous process in a cascade of stirred tank reactors

The kinetic equations relating to the hydroxymethylation stage in base-catalyzed phenol-formaldehyde condensation have been developed as functions of the free phenol concentration. The same kinetic model was applied to the calculation of a continuous process carried out in a cascade of stirred tank reactors. The results obtained in batch and continuous experiments at 70, 80 and 90° were compared with the corresponding calculated values.     

Carbon felt electrode design: application to phenol electrochemical determination by direct oxidation

In this paper, electrochemical behaviour of phenol in a carbon felt electrode is studied. An adsorption process on electrode surface that inhibits polymer formation after oxidation of phenol was confirmed. In this work we propose a phenol determination method based on direct electrochemical oxidation on carbon felt electrodes after an accumulation process.     

Unbiased spectrophotometric method for estimating phenol or o-cresol in unknown water samples

The generalised H-point standard addition method (GHPSAM) was applied to quantify phenol and o-cresol in waters and compared with other analytical approaches. The method is based on spectroscopic and kinetic measurement of the formation of derivatives with p-aminophenol and KIO(4) in presence of NaOH. First, pseudo-first order kinetic behaviour of the reaction products was demonstrated. The unbiased formation rate constants of phenol and o-cresol derivatives were calculated. The analytical figures of merit were determined using the GHPSAM as calibration method. Detection limits achieved were 0.2 microg L(-1) of phenol and 0.2 microg L(-1) of o-cresol using a preconcentration factor of 10. Styrene-divinyl benzene cartridges were used in the preconcentration step. Repeatability values were 3.7% for phenol and 2.0% for o-cresol; reproducibility values were 6.9% and 3.5%, respectively. Accurate and precise results were obtained when the method was applied to real samples of natural water.     

乙酰苯胺修饰的吸附树脂对苯酚和对氯苯酚的吸附研究

通过Friedel-Crafts后交联及化学修饰反应,合成了乙酰苯胺基修饰的超高交联吸附树脂ZH-05,通过红外光谱(IR)和比表面及孔径分析(BET)对其结构进行表征.以Amberlite XAD-4树脂作为参照,通过等温吸附实验和吸附动力学实验探讨了ZH-05树脂对水溶液中苯酚和对氯苯酚的吸附性能和机理.结果表明,与XAD-4树脂相比,ZH-05树脂对苯酚和对氯苯酚均具有更佳的吸附性能.Langmuir和Freundlich方程均能较好拟合ZH-05树脂对苯酚和对氯苯酚的吸附等温线.ZH-05树脂对苯酚和对氯苯酚的吸附以焓推动的自发物理吸附过程为主,吸附过程放热;吸附符合准一级动力学吸附方程,颗粒内扩散是吸附过程的主要控制步骤.     

Electrochemical properties of exfoliated graphite affected by its two-step modification

Exfoliated graphite (EG) was modified by a two-stage process consisting of electrochemical oxidation followed by the thermal treatment. Within the former one, the process of re-intercalation of H₂SO₄ into the EG by linear sweep voltammetry was carried out. Thus, obtained re-intercalated EG underwent heat treatment at 800 °C in order to synthesize re-exfoliated EG (re-EG). The electrochemical features of the re-EG were examined in the model process of phenol electrooxidation carried out by cyclic voltammetry technique in alkaline solution with and without phenol addition. Taking into account the anodic charges as a main criterion of electrochemical activity, it was found that the modification of EG caused over twofold improvement of its electrochemical activity. This behavior is related with the changes within the chemical composition of modified EG surface and on much smaller scale with the modification of its structure. The degree of electrochemical activity improvement depends on the conditions under which the processes of re-intercalation and re-exfoliation were performed. The results of Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis supported by the data of the Brunauer-Emmett-Teller (BET) surface area and scanning electron microscope (SEM) observations allow an understanding of the physicochemical properties of re-exfoliated EG and enhancement of its electrochemical activity.     

丹皮酚的电化学氧化及其反应机理研究

研究了在碱性磷酸盐缓冲溶液体系中,丹皮酚在固体电极上的电化学吸附氧化行为。与苯酚的电化学性质比较表明,碱性溶液中丹皮酚在电极表面上发生类似的不可逆的氧化。氧化产物发生随后化学反应,在电极表面生成致密的不导电聚合物膜。利用超微电极技术研究了丹皮酚电化学氧化的动力学过程,并用时间分辨快速扫描现场红外光谱电化学证明了电极表面的聚合物膜是芳醚类聚合物。     

Synthesis, characterization and adsorption performance of a novel post-crosslinked adsorbent

In this paper a post-crosslinked polymeric adsorbent PDHT-2 with high specific surface area was prepared by Friedel-Crafts reaction of the pendant vinyl groups without an externally added crosslinking agent. It was obvious that both the specific surface area and the pore volume of starting copolymer PDHT-1 increased significantly after post-crosslinking. Batch adsorption runs of phenol from aqueous solution onto adsorbent PDHT-1 and PDHT-2 were researched, and commercial macroporous resin XAD-4 was chosen for comparison purpose. Experimental results showed that the adsorption isotherms could be fitted by Langmuir model and Freundlich model and the adsorption capacity onto PDHT-2 was much larger than that onto PDHT-1 and XAD-4 with respect to phenol and phenolic compound, which possibly resulted from its larger specific surface area. The adsorption process for phenol onto the three adsorbents was proved to be exothermic and spontaneous in nature. The thermodynamic parameters such as Gibb's free energy (ΔG), change in enthalpy (ΔH) and change in entropy (ΔS) had been calculated. The adsorption kinetic curves obeyed the pseudo-second order model and the intraparticle diffusion process was the rate-controlling step.     

苯酚的电极过程吸附和氧化研究

应用循环伏安法测试了1mol·L-1硫酸水溶液和含苯酚的1molL-1硫酸水溶液体系的电化学行为,分析电极过程中苯酚及其中间产物在电极表面的吸附特征以及苯酚氧化的可逆性及其反应步骤;提出了特性吸附电位Ead;当电极电位大于Ead时,不同的氧化产物开始生成.     

Mechanism Studies on Water Sorption and Permeation in Epoxy Resin by Impedance Spectroscopy. II. Cure Kinetics of O-Cresol Novolac Resin with Esterfied Phenol Novolac Resin

Abstract

To study the effect of water affinity of the cured epoxy resin on water sorption and permeation in the cured epoxy resin, a novel hardener (esterfied phenol novolac was synthesized and used for obtaining the cured product without free hydroxyl group. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FT-IR) were used to study the cure kinetics of o-cresol novolac epoxy resin using esterfied phenol novolac resin as curing agent in the presence of 2-methylimidazole as accelerator. Some kinetic parameters of the curing reaction such as the reaction order, activation energy, and frequency factor were obtained in the temperature range studied. The results show that this curing process is a first-order kinetic mechanism, which was different with that cured with phenol novolac resin.     

Kinetics and mechanistic study of the reaction of cyclic anhydrides with substituted phenols. Structure-reactivity relationships

[reaction: see text] The kinetic of the reactions of phthalic and maleic anhydrides with different substituted phenols (Z-PhOH with Z = H, m-CH(3), p-CH(3), m-Cl, p-Cl, and m-CN) were studied in aqueous solution. Two kinetic processes well separated in time were observed. The fast one is attributed to the formation of the aryl ester in equilibrium with the anhydride and allows the determination of the rate of nucleophilic attack of the phenol on the anhydride (k(-)(A)). From the slow kinetic process, the equilibrium constant for this reaction was determined. The Bronsted-type plots for the nucleophilic attack of substituted phenols on the anhydrides were linear with slopes beta(Nuc) of 0.45 and 0.56 for phthalic and maleic anhydride, respectively. The results are consistent with a mechanism involving rate-determining nucleophilic attack and also with a concerted mechanism. The calculated effective charge on the atoms involved in the reactions and the Bronsted beta values are consistent with a mechanism involving a concerted or enforced concerted mechanism where a tetrahedral intermediate with significant lifetime is not formed along the reaction coordinate. The latter mechanism is preferred over the stepwise process.     

Regeneration of expanded graphite electrodes by joined electrochemical and ozone treatment in liquid phase

The researches presented in this work were devoted to electrochemico-chemical regeneration of exhausted electrode made of expanded graphite (EG). The aimed process was conducted by electrochemical treatment and ozone flow performed together in wet environment. EG was covered with insoluble products of incomplete oxidation of phenol formed during cyclic voltammetry measurement. The same electrochemical technique was applied for evaluation of regeneration efficiency. To understand the process of EG regeneration, the electrode was characterized by calculating of BET surface, FTIR and XPS analysis. Moreover, SEM images of the investigated samples were also done. Obtained results have showed the success of regeneration treatment, which led to significant enhancement of electrode activity compared to original EG. The present work also revealed that the mechanism of phenol electrooxidation is changed after the regeneration treatment of electrode material. This effect is probably caused by the modification of chemical composition of EG surface due to its interactions with OH radicals intensively generated during the process of regeneration.

     

Effect of Ethanedioic Acid Additives on the Dissolution of Manganese Oxides in Sulfuric Acid Solution

The effect of ethanedioic acid additives on the rate of manganese(IV) oxide dissolution in sulfuric acid solutions was studied by kinetic and electrochemical methods. Interaction modes were established, and some details of the studied process mechanism were elucidated. Interaction schemes corresponding to the observed kinetic dependences were proposed.     

磷酸铈对磷化镍催化苯酚转移加氢的促进作用

通过氢气原位程序升温还原法制备了一系列不同Ce/Ni摩尔比的CePO₄-Ni₃P及Ni₃P催化剂, 考察了其在苯酚催化转移加氢反应的催化性能. 研究了Ce/Ni摩尔比、 供氢溶剂、 反应温度和反应时间对催化剂性能的影响, 并初步考察了苯酚转移加氢的反应动力学. 研究结果表明, CePO₄的加入能显著提升体相Ni₃P催化苯酚转移加氢的转化率, 且Ce/Ni摩尔比为0.2时促进作用最显著; 在所考察的供氢溶剂中异丙醇展现出最好的性能; 使用CePO₄(0.2)-Ni₃P作为反应催化剂, 异丙醇作为供氢溶剂, 220 ℃下反应6 h, 苯酚转化率和环己醇选择性分别可达93.1%和92.0%.     

Synthesis and Temperature-dependent Electrochemical Properties of Boron-doped Diamond Electrodes on Titanium

On the sand-blasting-treated titanium(Ti) substrate, the boron-doped diamond(BDD) electrodes with a wide potential window were prepared by microwave plasma chemical vapor deposition(MPCVD). The electrochemical oxidation ratios of phenol at BDD/Ti electrodes at elevated temperatures(from 20 ℃ to 80 ℃) were examined by the chemical oxygen demand(COD) of phenol electrolyte during electrolysis. The results show that the COD removal was increased at high temperatures and the optimized temperature for enhancing the electrochemical oxidation ratio of phenol is 60 ℃. The mechanism for the temperature-dependent electrochemical oxidation ratios of phenol at the electrodes was investigated. The study would be favorable for further improving the performance of BDD/Ti electrodes, especially working at high temperatures.     

Oxygen Reduction Reaction on a Rotating Ag/GC Disk Electrode in Acidic Solution

Finding an appropriate mechanism of oxygen reduction reaction, without having kinetic parameters and intermediate species at hand, is an impossible task. In view of the fact that this reaction is one of the important reactions, it was tried to overcome this problem through computing the kinetic parameters by means of Ag/GC rotating disc electrode in an acidic solution. Using this electrode, two values were obtained for electron transfer coefficient and reaction order was calculated through relative equations. Based on this information, an ECE (electrochemical chemical electrochemical) mechanism has been proposed.     

靛蓝胭脂红的光谱电化学研究 II. 靛蓝胭脂红复相电子转移动力学

报道了靛蓝胭脂红在SnO_2透光电极上的复相电子转移动力学参数。由光谱电化学和电化学两种实验方法测定。前一方法为单电位阶跃计时吸收法((SPS/CA)。后一方法为循环伏安法。两种方法的数据处理中均应用了计算机拟合, 较之文献中常规的工作曲线法更为简便、正确。两种方法测定的结果十分一致。进一步的研究表明, 动力学参数值与靛蓝胭脂红的浓度和溶液pH有关, 为靛蓝胭脂红在水溶液中的状态提供了重要信息。     

PANI膜电聚合过程及电控分离苯酚的EQCM研究

通过电沉积方法在镀铂石英晶片上制备了导电聚苯胺(PANI)膜,采用电化学石英晶体微天平(EQCM)技术探讨了苯胺聚合机制及在苯酚溶液中的氧化还原特性.在0.5 mol/L硫酸溶液中结合循环伏安法考察了PANI膜在完全还原态(L)-半氧化态(E)-完全氧化态(P)之间的电活性和稳定性;在不同浓度的苯酚溶液中结合恒电压阶跃...     

二氧化钛纳米管阵列光电催化同时降解苯酚和Cr(VI)

采用电化学阳极氧化法在纯钛箔基底上制备了TiO2纳米管阵列,并运用X射线衍射、扫描电镜和电化学工作站对其进行了表征.结果表明,所制样品是锐钛矿相,管径约为100nm,管长约为2μm,在0.5V偏压下光电流最大.以苯酚和Cr(VI)混合溶液为目标污染物,考察了TiO2纳米管阵列光电催化同时去除苯酚和Cr(VI)的反应性能...     

Traitement électrochimique d' eaux usées chargées de phénol : étude comparative sur des électrodes de dioxyde de plomb et de platine

Electrochemical treatment of waste water containing phenol: a comparative study on lead dioxide and platinum electrodes. The objective of this work was to study the efficiency of the Pb/PbO₂ electrode for decomposing the molecule of phenol, then to compare it to a platinum model electrode. Preliminary investigations by cyclic voltammetry showed that the Pb/PbO₂ anode presents a good chemical and electrochemical stability and possesses a high oxygen overvoltage. The study also showed that the electrochemical oxidation of phenol on Pt and PbO₂ in acidic media is a complex process. Long-time electrolysis was carried out using a three potential-plateau program with different values of the oxidation potentials and different concentrations of phenol. The obtained results showed that the transformation of phenol is total on the Pb/PbO₂ anode and that it is partial on Pt. On the other hand an increase in the phenol concentration decreases the rate of its conversion on the electrodes.