Gliding arc plasma processing of CO2 conversion

Conversion of carbon dioxide (CO2) using gliding arc plasma was performed. The research was done to investigate the effect of variation of total gas flow rates and addition of auxiliary gases--N2, O2, air, water--to the CO2 conversion process. This system shows higher power efficiency than other nonthermal plasma methods. Experiment results indicate the conversion of CO2 reaches 18% at total gas flow rate of 0.8 L/min and produces CO and O2 as the main gaseous products. Among auxiliary gases, only N2 gives positive effect on CO2 conversion and the power efficiency at N2 concentration of 95% and total gas flow rate of 2 L/min increases about three times compared to pure CO2 process.     

采用真空电弧源镀制纳米TiO2薄膜研究

在真空条件下利用真空电弧源在不同基底材料上镀制了TiO2薄膜.对影响镀膜过程和膜层质量的氧气工作压强和偏压等因素进行了研究.X射线衍射结构分析结果显示TiO2薄膜主要以锐钛矿相为主及少量的金红石相.对TiO2薄膜的物理性质、化学性质进行了初步检测.     

Investigation on the sonocatalytic degradation of parathion in the presence of nanometer rutile titanium dioxide (TiO2) catalyst

The nanometer rutile titanium dioxide (TiO2) powder was adopted to act as the sonocatalyst after treatment of high-temperature activation and the ultrasound of low power was used as an irradiation source to induce heat-treated TiO2 powder performing sonocatalytic degradation of parathion. Although there are many factors influencing sonocatalytic degradation of parathion, the experimental results demonstrate that the optimal degradation condition of parathion can be obtained when the experimental conditions such as initial concentration of 50 mg/L parathion, addition amount of 1000 mg/L nanometer rutile TiO2, ultrasonic of 30-50 kHz frequency and 50 W output power, acidity of pH 10.0 and temperature of 20 degrees C are adopted. The degradation ratio of parathion surpassed 90% within 120 min ultrasonic irradiation in these optimal experiment conditions. The total degradation process of parathion has been monitored by UV-vis spectra and ion chromatography. At last, the parathions in aqueous solution are completely degraded and become some simple inorganic ions such as NO3(-), PO4(3-), SO4(2-), etc. In addition, the sonocatalytic activities of reused TiO2 catalysts were also studied and found to decline gradually along with the reused times. In this paper, the research on sonocatalytic degradation kinetics was also been performed and found to follow pseudo first-order reaction. All experiments indicated that the sonocatalytic method in the presence of nanometer rutile TiO2 powder was an advisable choice for the treatments of non- or low-transparent organic wastewaters in future.     

采用真空电弧源镀制纳米TiO2薄膜研究

在真空条件下利用真空电弧源在不同基底材料上镀制了TiO2薄膜.对影响镀膜过程和膜层质量的氧气工作压强和偏压等因素进行了研究.X射线衍射结构分析结果显示TiO2薄膜主要以锐钛矿相为主及少量的金红石相.对TiO2薄膜的物理性质、化学性质进行了初步检测.     

Synthesis of Mn-Al alloy nanoparticles by plasma arc discharge

Alloy nanoparticles in the Mn-Al system were prepared by the plasma arc discharge method. The influence of process parameters on the vaporization rate, composition, particle size, and magnetic properties of the as-produced nanoparticles was investigated. The Mn content was found to be higher in the nanoparticles than in the corresponding mother alloy, although the difference diminished with the reaction time. With increasing H₂ content in the reaction gas, both vaporization rate and particle size increased. With 30 at.% Mn, the average particle diameter in pure Ar was 35.2 nm, whereas that in an atmosphere with Ar:H₂ = 60:40 was 95.4 nm. With the addition of a small amount of carbon, ε-phase nanoparticles were synthesized. After heat treatment in a vacuum for 30 min at 400-600 °C, the nonmagnetic ε-phase was transformed into the ferromagnetic τ-phase and a very high coercivity of about 446 kA/m was achieved.     

Controlling diameter distribution of catalyst nanoparticles in arc discharge

It is demonstrated that the diameter distribution of catalyst nanoparticles in arc discharge can be controlled by a magnetic field. The magnetic field affects the arc shape, shortens the diffusing time of the catalyst nanoparticles through the nucleation zone, and consequentially reduces the average diameters of nanoparticles. The average diameter is reduced from about 7.5 nm without magnetic field to about 5 nm is the case of a magnetic field. Decrease of the catalyst nanoparticle diameter with magnetic field correlates well with decrease in the single-wall carbon nanotube and their bundles diameters.     

Photocatalytic decolorization and degradation of dye solutions and wastewaters in the presence of titanium dioxide

In this study, the photocatalytic degradation of two commercial azo dyes in the presence of TiO(2) suspensions as photocatalyst has been investigated. The degradation of the dyes follows a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. Under the certain experimental conditions, in the presence of TiO(2) P-25 decolorization is achieved within 100 min of illumination, while in the presence of TiO(2) Hombikat UV-100 complete color disappearance is accomplished in less than 50 min of light exposure. The influence of various parameters, such as the type and mass of the catalyst, the initial concentration of the dye, etc. on the degradation process was examined. The mineralization of organic carbon was also evaluated by measuring the dissolved organic carbon (DOC) of the dye solutions. Moreover, the toxic properties of the dye solutions treated by photocatalysis were examined by the use of a Microtox bioassay (Vibrio fischeri). Finally, experiments using real textile wastewater were also carried out, in order to examine the effectiveness of the method to a more complex substrate.     

Enhancement in the microhardness of arc plasma melted tungsten carbide

Microhardness is found to increase significantly in arc plasma melted tungsten carbide. To understand the mechanism for such increase, tungsten carbide powder was mixed with tungsten metal powder to prepare mixtures of seven different compositions. The mixtures with varying WC/W ratio were pelletized and melted in an arc plasma followed by cooling in the furnace. It is observed that microhardness value enhances in the product when WC/W₂C ratio becomes high. Based on our microstructural finding of <100> WC hard faces and lamellar/acicular structures (due to martensite transformation) carried out by XRD, optical microscope and SEM, an attempt has been made to understand the reason behind the enhancement in microhardness.     

Optimized photocatalytic degradation of Alcian Blue 8 GX in the presence of TiO2 suspensions

The photocatalytic degradation of Alcian Blue 8 GX, a cationic copper phthalocyanine dye, has been investigated in aqueous suspensions containing the commercial catalyst TiO(2) P-25. The photodegradation of the organic molecule follows approximately a pseudo-first kinetic order, according to the Langmuir-Hinshelwood model. The effect of catalyst concentration, pH of the initial solution and the H(2)O(2) concentration upon the reaction rate was ascertained. It was shown that the photocatalytic degradation reaction can be mathematically described as a function of parameters such as pH, H(2)O(2) concentration and irradiation time, being modeled by the use of the response surface methodology. Optimized values for oxidizing agent, concentration, pH and UV exposure time for the studied system were determined.     

电气石/TiO2复合体系光催化降解苯酚溶液的反应动力学

采用电气石微粒表面钛盐水解包覆纳米TiO2的方法,在不同条件下构建电极性矿物/TiO2体系,分别采用扫描电子显微镜、傅里叶红外吸收光谱、高效液相色谱仪等对催化体系进行了表征。以苯酚溶液为目标物,考察了动态条件下催化体系对苯酚的去除效果,结果表明复合光催化体系对苯酚具有良好的分解性能,当比例为0.2时,催化效果增长的趋势非常明显,当反应时间为120min时,降解率达到了96.29%,高出了纯相TiO2的70%降解率将近26个百分点;在苯酚浓度不断变化时的速率常数从-0.0012～-0.0503变化,证明在苯酚浓度变化的条件下对催化剂的催化效率有明显的影响。在加入的催化剂量不断变化时的催化速率常数从-0.0105～-0.0051,降解苯酚符合Langmuir-Hinshelwood动力学方程。     

Treatment of textile wastewaters by electrocoagulation using iron and aluminum electrodes

Treatment of textile wastewaters by electrocoagulation using iron and of aluminum electrode materials has been investigated in this paper. The effects of relevant wastewater characteristics such as conductivity and pH, and important process variables such as current density and operating time on the chemical oxygen demand (COD) and turbidity removal efficiencies have been explored. Furthermore, the electrode and energy consumptions for each electrode have been calculated. The results show that iron is superior to aluminum as sacrificial electrode material, from COD removal efficiency and energy consumption points.     

Decolorization of Acid Orange 7 solution by gas-liquid gliding arc discharge plasma

The decolorization of 180 microM aqueous solutions of Acid Orange 7 (AO7) by means of a non-thermal plasma technique (i.e., the gas-liquid gliding arc discharge, which is generated between at least two metal electrodes with AC high voltage) was investigated in this paper. The effects of the plasma treatment time and the type of feeding gas, including air, oxygen, nitrogen and argon of the dye removal were determined. It is found that the voltage cycles of the gas-liquid gliding arc discharge are characterized by a moderate increase in the tension which is represented by a peak followed by an abrupt decrease and a current peak in the half period (10 ms); the concentration of AO7 solution decreases exponentially to reach 58.9, 77.4, 89.1, 95.1 and 99% in 25, 50, 75, 100 and 125 min, respectively, and the ln(Ct/C0) varies linearly with the treatment time t, indicating that decolorization reaction follow first pseudo-order kinetics with a constant rate of 0.03327 min(-1) when air was used as feeding gas; the decolorization rate during the plasma treatment is the greatest for oxygen as the feeding gas, in turn followed by air and argon, and was the least when using nitrogen. The variations of pH and conductivity and the formations of hydrogen peroxide and ozone are measured.     

Sustainable treatment of wastewaters resulted in the textile dyeing industry

Adsorption on fly-ash-based substrates is discussed as a possible alternative to the industrial processes used for the treatment of wastewaters resulted in the dyeing industry. Three samples, containing four dyes and one conditioner, were collected from the dyeing and rinsing baths in a textile company. Adsorption on fly ash was comparatively discussed with adsorption and photocatalysis, both on fly ash and a mixed suspension with TiO₂. The fly-ash crystalline substrates are characterized by X-ray diffraction (XRD) and morphology studies were done using atomic force microscopy. The wastewater, before and after treatment is characterized by quality indicators (pH, TDS, BOD₅, COD, TOC, color, and total chromium content). The studies allow to calculate the efficiency of the dyes removal process and the kinetic parameters, for the pseudo-second order mechanism. The results show that, in designing an industrial wastewater treatment process, the results obtained in the investigations on single-dye solutions must be completed with data specifically obtained on industrial wastewaters. The data also support the assumption of competitive adsorption, between the initial components and between these and the possible by-products resulted after photocatalysis.     

Photocatalytic degradation of model textile dyes in wastewater using ZnO as semiconductor catalyst

Semiconductor photocatalysis often leads to partial or complete mineralization of organic pollutants. Upon irradiation with UV/visible light, semiconductors catalyze redox reactions in presence of air/O2 and water. Here, the potential of a common semiconductor, ZnO, has been explored as an effective catalyst for the photodegradation of two model dyes: Methylene Blue and Eosin Y. A 16 W lamp was the source of UV-radiation in a batch reactor. The effects of process parameters like, catalyst loading, initial dye concentration, airflow rate, UV-radiation intensity, and pH on the extent of photo degradation have been investigated. Substantial reduction of COD, besides removal of colour, was also achieved. A rate equation for the degradation based on Langmuir-Hinshelwood model has been proposed.     

Producing of aluminum boride in plasma of high-current impulse arc discharge

The experimental investigations were conducted on producing ultradisperse materials in a beam of electrodischarge plasma that contained aluminum and boron. A beam is generated by a high-current impulse accelerator of plasma and flows into an inert atmosphere (argon). According to the quality X-ray diffraction analysis, the produced powder material consists of aluminum and aluminum boride α-AlB₁₂.     

Spectroscopic diagnostics of a pulsed arc plasma in the presence of acetylene

Plasma fluxes for deposition of diamond-like carbon films were generated by the four-electrode device with graphite cathode in vacuum as well as in acetylene atmosphere at pressure of 0.2–2 Pa. Optical emission spectra of the cathodic-arc carbon plasma in a wavelength range of 400–1000 nm were studied. For observation along the plasma flow at acetylene pressures of 0.2, 0.5 and 1.0 Pa the intensity of the C₂ molecular band at 563.55 nm increases by a factor of 6, 8 and 11, respectively, in comparison with values for a vacuum discharge. When displacing the observation line from the discharge axis a sharp decrease of carbon ion emission is detected while radiation of C₂ molecules remains approximately the same. For observation across the plasma flux the emission of C₂ molecular bands predominates over carbon ions both for the vacuum discharge and the discharge in acetylene. However on acetylene addition the intensities of carbon ions and hydrogen spectral lines increase by 1.5–3 times. It was found that the gas-kinetic temperature of the plasma is about 0.1 eV.     

Photocatalytic degradation of methyl red by TiO2: comparison of the efficiency of immobilized nanoparticles versus conventional suspended catalyst

The photocatalytic efficiency of supported TiO2 nanoparticles (mean size 6 nm), immobilized onto the inner walls of a cylindrical glass photoreactor was compared versus the performance of conventional TiO2 Degussa P25 catalyst. For this purpose the degradation of methyl red dye was used as evaluation test. The obtained results showed that the TiO2 Degussa P25 catalyst is more efficient than the supported nanoparticles. The poorer performance of the nanosized catalyst can be ascribed to the fact that the immobilization procedure turns out, in spite of the extremely high surface to volume ratio, in an overall reduction of active surface area available for target molecule adsorption, due to the low porosity of the supported catalyst layer. The kinetics of the investigated processes were monitored and a study on the reaction products and intermediates was carried out in order to evaluate possible difference in the reaction pathway in presence of immobilized nanoparticles versus suspended catalyst. The results demonstrate that the mechanisms of parent dye degradation in presence of supported TiO2 nanoparticles are the same as those occurring in presence of TiO2 Degussa P25 catalyst. The present work describe the results obtained on the feasibility of scaling up the colloidal nanocrystal-based photocatalysis experiment: the comparison with a well standardized degradation method performed with a known material can allow a realistic evaluation of the advantages and the limits of the investigated nanoparticle towards the ultimate technology transfer.     

Photocatalytic degradation of methylene blue in TiO2 aqueous suspensions using microwave powered electrodeless discharge lamps

Photocatalytic degradation of methylene blue (MB) in TiO(2) aqueous suspensions using microwave (MW) powered electrodeless discharge lamps (EDLs) was studied. MB of initial concentration 100 mg/l was mainly decomposed in the process of photocatalytic degradation using EDLs (PCD/EDLs) after 15 min of irradiation. The corresponding mineralization efficiency was 45%. The influence of factors as EDLs, solution volume and TiO(2) catalyst dosage on the decomposition of MB in the PCD/EDLs process was also investigated. The optimal decomposition efficiency was observed when EDLs-4 (four 10 mm x 50 mm EDLs), solution volume of 50 ml and TiO(2) catalyst dosage of 1-4 g/l were used in the study. The PCD/EDLs process was promising in treating MB polluted water.