Ozonation of azo dye in a semi-batch reactor: a determination of the molecular and radical contributions

Azo dye ozonation was carried in a semi-batch reactor to evaluate both the molecular and radical contributions of ozone on the dye decay. From two mass balance equations, the simultaneous determination of mass transfer, self-decomposition and solubility parameters of ozone were determinated; thus establishing the steady state conditions in the experimental system. The results of kinetic studies showed that the decay of azo dye was a pseudo-first-order reaction with respect to dye concentration and the overall rate constant increased with an increase in the pH, however declined with an increase in the dye concentration. Furthermore, from the overall rate constants obtained at various pH values a mathematical analysis of dye decay was performed, which provides a practical new method to quantify the radical and molecular contributions in the ozonation of azo dyes.     

Enhanced ozonation of dichloroacetic acid in aqueous solution using nanometer ZnO powders

Nanometer zinc oxide (ZnO) powders were used as a catalyst to enhance the ozonation for the degradation of dichloroacetic acid (DCAA) in aqueous solution. The batch experiments were carried out to investigate the e ects of key factors such as catalyst dosage, ozone dosage, solution pH and tert-butyl alcohol (t-BuOH) on the degradation e ciency of DCAA. Density functional theory (DFT) was adopted to explore the mechanism of generating hydroxyl radical (.OH) on the ZnO surface. The results showed that adsorption and ozonation processes were not e ective for DCAA removal, and the addition of ZnO catalyst improved the degradation e ciency of DCAA during ozonation, which caused an increase of 22.8% for DCAA decomposition compared to the case of ozonation alone after 25 min. Under the same experimental conditions, the DCAA decomposition was enhanced by increasing catalyst dosage from 100 to 500 mg/L and ozone dosage from 0.83 to 3.2 mg/L. The catalytic ozonation process is more pronounced than the ozonation process alone at pH 3.93, 6.88, and 10. With increasing the concentration of t-BuOH from 10 to 200 mg/L, the degradation of DCAA was significantly inhibited in the process of catalytic ozonation, indicating that ZnO catalytic ozonation followed .OH reaction mechanism. Based on the experimental results and DFT analysis, it is deduced that the generation of .OH on the ZnO surface is ascribed to the adsorption of molecule ozone followed by the interaction of adsorbed ozone with active sites of the catalyst surface. It is also concluded that ZnO may be an e ective catalyst for DCAA removal, which could promote the formation of .OH derived from the catalytic decomposition of ozone.     

Study on superoxide and hydroxyl radicals generated in indirect electrochemical oxidation by chemiluminescence and UV-Visible spectra

The generation and transformation of radicals on the cathode of indirect electrochemical oxidation were studied by chemilumines- cence(CL)and UV-Visible spectra in the reactor with a salt bridge that connected the separated chambers.The CL intensity of 4×10~(-9)mol/L luminol on the cathode with bubbling oxygen was about seven times that of the intensity without it,which was because of the generation of reactive oxygen species(ROS).The existence of ROS,especially the generation of the superoxide radical,c...     

Detection of hydroxyl radical in plasma reaction on toluene removal

A new method was introduced to detect the concentration of OH radical in dielectric barrier discharge(DBD)reaction.A film, which was impregnated with salicylic acid,was used to detect OH radical in plasma reaction at room temperature and atmospheric pressure.Salicylic acid reacts with OH radical and produces 2,5-dihydroxybenzoic acid(2,5-DHBA).Then,a high performance liquid chromatography(HPLC)was carried out to detect the concentration of 2,5-DHBA.Therefore,OH radical in nonthermal plasma reaction could be...     

含碳酸盐水溶液中扑热息痛的光解研究

采用动力学方法研究了环境浓度范围内的扑热息痛在含碳酸盐溶液中的光解,比较了碳酸盐自由基和羟基自由基对扑热息痛的光解效果,探讨了pH值、硝酸根离子、腐殖质、氯化钠、钙镁离子等因素对扑热息痛光解的影响.利用GC/MS技术鉴定了扑热息痛的光解产物,并探讨了扑热息痛在碳酸根体系中可能的光解途径.结果表明,扑热息痛与碳酸盐自由基反应的二级反应速率常数为 k.=5.0×107L·(mol·s)-1,低于与羟基自由基反应的二级反应速率常数kb=8.1×109L·(tool·s)-1,但是由于天然水体中碳酸盐自由基的稳态浓度较高,所以碳酸盐自由基对扑热息痛光解的影响和羟基自由基大致相当.提高体系pH值,加入硝酸根离子、氯化钠或者钙镁离子都会加快扑热息痛的光解速率;而加入Suwannee河富里酸则会降低光解速率.     

Effect of illumination intensity and light application time on secondary organic aerosol formation from the photooxidation of α-pinene

Secondary organic aerosol (SOA) formation from hydroxyl radical (OH.) initiated photooxidation of α-pinene was investigated in a home-made smog chamber. The size distribution of SOA particles was measured using aerodynamic particle sizer spectrometer. The effects of illumination intensity and light application time on SOA formation for α-pinene were evaluated. Experimental results show that the concentration of SOA particles increased significantly with an increasing of illumination intensity, and the light...     

Simultaneous oxidation of NO, SO2 and Hg0 from flue gas by pulsed corona discharge

A process capable of oxidizing NO, SO2 and Hg0 was proposed simultaneously, which utilized a high-voltage and short-duration positive pulsed corona discharge. By focusing on NO, SO2, and Hg0 oxidation efficiencies, the influences of pulse peak voltage, pulse frequency, initial concentration, electrode number, residence time and water vapor addition were investigated. The results indicate that NO, SO2 and Hg0 oxidation efficiencies depend primarily on the radicals (OH, HO2, O) and the active species (O3, H2O2), etc. produced by the pulsed corona discharge. The NO, SO2 and Hg0 oxidation efficiencies improved as increasing pulse peak voltage, pulse frequency, electrode number and residence time, while they are reduced with an increasing initial concentration. By adding water vapor, SO2 oxidation efficiency is improved remarkably, while NO oxidation efficiency is decreased slightly. In our experiments, the simultaneous NO, SO2, and Hg0 oxidation efficiencies reached to 40%, 98% and 55% with the initial concentrations 479 mg/m3, 1040 mg/m3, and 15.0 ug/m3, respectively.     

蜂窝陶瓷催化臭氧化苯乙酮的研究

研究了蜂窝陶瓷对臭氧化降解苯乙酮效率的影响.结果表明,蜂窝陶瓷显著提高了臭氧化降解苯乙酮的效率,叔丁醇的试验表明该体系遵循.OH氧化机理.蜂窝陶瓷催化臭氧化降解苯乙酮的动力学可分为2个阶段,第一阶段的表观动力学常数为8.77×10-4s-1,Rct为10.34×10-10;第二阶段的表观动力学常数为4.63×10-3s-1,Rct为172.34×10-10.基于降解过程的色度变化和水样原子吸收的分析结果,结合降解动力学可以推测:降解过程中蜂窝陶瓷催化剂中Ti4+的溶出是苯乙酮降解效率提高的主导因素.     

Using polarized muons as ultrasensitive spin labels in free radical chemistry

In a chemical sense, the positive muon is a light proton. It is obtained at the ports of accelerators in beams with a spin polarization of 100%, which makes it a highly sensitive probe of matter. The muonium atom is a light hydrogen isotope, nine times lighter than H, with a muon as its nucleus. It reacts the same way as H, and by addition to double bonds it is implemented in free radicals in which the muon serves as a fully polarized spin label. It is reviewed here how the muon can be used to obtain information about muonium and radical reaction rates, radical structure, dynamics, and local environments. It can even tell us what a fragrance molecule does in a shampoo.     

等离子体引发自由基增强光催化降解医用PVC的研究

研究了等离子体引发的自由基对锐钛矿TiO₂光催化降解医用聚氯乙烯（PVC）的影响.等离子体改性前后PVC的表面特性通过接触角、表面张力、X-光电子能谱（XPS）、电子自旋共振（ESR）表征.结果表明,等离子体改性后PVC的表面自由能和润湿性增强,水、丙三醇、硫代双乙醇的接触角减小.ESR表明等离子体改性后PVC表面的自由基增加了10倍.此外,通过重量损失和扫描电镜（SEM）对比了PVC-TiO₂和等离子体改性PVC-TiO₂的光催化降解,紫外光照60 h后,等离子体改性PVC-TiO₂的失重率比PVC-TiO₂增加了27.4%,SEM显示光照后等离子体改性PVC-TiO₂的表面有大量的裂纹.等离子体改性后PVC的光催化降解加剧.