Enhancing toluene removal in a plasma photocatalytic system through a black TiO_2 photocatalyst

An efficient toluene removal in air using a plasma photocatalytic system(PPS) not only needs favorable surface reactions over photocatalysts under the action of plasma,but also requires the photocatalysts to efficiently absorb light emitted from the discharge for driving the photocatalytic reactions. We report here that the PPS constructed by integrating a black titania(B-TiO_2)photocatalyst with a dielectric barrier discharge(DBD) can effectively remove toluene with above 70% CO_2 selectivity and remarkably reduced the concentration of secondary pollutants of ozone and nitrogen oxides at a specific energy input of 1500 J·l~(-1),while exhibiting good stability. Photocatalyst characterizations suggest that the B-TiO_2 provides a high concentration of oxygen vacancies for the surface oxidation of toluene in DBD,and efficiently absorbs ultraviolet–visible light emitted from the discharge to induce plasma photocatalytic oxidation of toluene. The presence of B-TiO_2 in the plasma region also results in a high discharge efficiency,facilitating the generation of large numbers of reactive species and thus the oxidation of toluene towards CO_2. The greatly enhanced performance of the PPS integrated with B-TiO_2 in toluene removal offers a promising approach to efficiently remove refractory volatile organic compounds from air at low temperatures.     

Physicochemical study on supercritical fluids and their industrial use

In this study, we confirm a tetrahedral structure for a Co²⁺ complex in supercritical water instead of the octahedral structure in normal water. The absorption spectra of Ru²⁺ complexes were observed for only stable species such as [Ru(phen)₃]²⁺ in supercritical water. The photochemistry of uranyl(VI)-tributylphosphate(TBP) complex in supercritical carbon dioxide(scCo₂) was studied in the pressure range of 8-40 MPa and from 289 to 336K. In order to examine the hydrogen-bond structures and molecular motions of supercritical water and non-aqueous solvents, their ¹H spin-lattice relaxation times were measured under sub- and supercritical conditions by using high-pressure NMR. NiMo/Al₂O₃ was chosen as a catalyst because of its catalytic activity for hydrocracking aromatic structures.     

Hydrochlorination of acetylene over the Ru-based catalysts treated by plasma under different atmospheres

Ru-based catalysts modified in different atmospheres by plasma technology were prepared to catalyze the acetylene hydrochlorination reaction. The (Ru/AC)-N₂ (AC = activated carbon) catalyst yielded by the plasma modification of Ru/AC catalyst in N₂ atmosphere exhibits the best catalytic performance with a stable C₂H₂ conversion of 87.2%; a relative increase of 27.1% in C₂H₂ conversion was achieved compared with that of the untreated Ru/AC catalyst. The results of the analysis revealed that the modification produced a mutual effect between the generated function groups on carrier AC and the active components, which can disperse and yield more active species in the fresh catalysts. These are benefits of enhancing the activity of the catalysts. Moreover, the modification can restrain coke formation and inhibit the loss of active species in the reaction, as well as strengthen the adsorption ability of reactants on the catalysts. These are benefits of improving the catalysts’ performance.     

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O₂ is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O₂ contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O₂, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O₂⁻, which promotes the filamentary formation. While, in AC DBD, the added O₂ can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T_e drops quickly with the addition of O₂ both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_e and n_e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.     

Plasma-catalytic degradation of tetracycline hydrochloride over Mn/γ-Al2O3 catalysts in a dielectric barrier discharge reactor

A coaxial dielectric barrier discharge (DBD) reactor was used for plasma-catalytic degradation of tetracycline hydrochloride over a series ofMn/γ-Al₂O₃ catalysts prepared by the incipient wetness impregnation method. The combination of plasma and theMn/γ-Al₂O₃ catalysts significantly enhanced the degradation efficiency of tetracycline hydrochloride compared to the plasma process alone, with the 10%Mn/γ-Al₂O₃ catalyst exhibiting the best tetracycline hydrochloride degradation efficiency. A maximum degradation efficiency of 99.3% can be achieved after 5 min oxidation and a discharge power of 1.3 W, with only 69.7% by a single plasma process. The highest energy yield of the plasma-catalytic process is 91.7 gkWh⁻¹. Probable reaction mechanisms of the plasma-catalytic removal of tetracycline hydrochloride were also proposed.     

Photon-induced impurity production in TEXTOR

Analysis of the residual neutral gas during plasma discharges in the tokamak TEXTOR shows considerable amounts of neutral CO and CO₂. Details of these observations have suggested that the CO₂ and part of the CO neutral gas is released from the surfaces by photon-stimulated desorption processes. To prove this suggestion additional mass-spectroscopic measurements have been performed in a chamber vacuum-sealed from the TEXTOR vacuum by a MgF₂-window which is transparent for wavelengths above about 110 nm. It has been confirmed that CO₂ and CO molecules together with H₂ are released from the walls of the chamber by the photons penetrating from the TEXTOR plasma through the window. The overall desorption rate has been estimated to be between 10⁻⁴ and 10⁻⁵ molecules/photon and a linear relation between the amount of desorbed molecules and the total radiation from the plasma has been found. The results are discussed in view of the overall impurity release from the walls and limiters of TEXTOR.     

赣杭构造带某铀矿区地下水中铀的存在形式研究北大核心CSCD

为研究铀矿区地下水化学性质对铀的存在形式的影响,本文以赣杭构造带某铀矿区地下水为研究对象,在对9个典型采样点地下水化学成分分析的基础上,采用数理统计软件SPSS 18.0和地球化学模拟软件PHREEQC及llnl.dat数据库,探究了研究区内地下水水化学特征及U的存在形式。结果表明:本研究区地下水水化学类型以HCO_(3)-Na与HCO_(3)-Na·Ca为主,U含量与Ca^(2+)和Mg^(2+)浓度体现出较强正相关性,与SO_(4)^(2-)的相关性次之;地下水中U元素主要以六价为主,几乎占100%,主要存在形式依次为UO_(2)(CO_(3))_(2)^(2-)、UO_(2)(CO_(3))_(3)^(4-)、UO_(2)CO_(3)、UO_(2)(OH)2、UO_(2)(OH)_(3)^(-)、UO_(2)OH^(+)等6种,其中UO_(2)(CO_(3))_(2)^(2-)占绝对优势,整体以碳酸铀酰形式为主,这也与研究区地下水酸碱性相对应。     

Time-Resolved Optical Emission Spectroscopy Diagnosis of CO2 Laser-Produced SnO2 Plasma

The spectral emission and plasma parameters of SnO_2 plasmas have been investigated.A planar ceramic SnO_2 target was irradiated by a CO2 laser with a full width at half maximum of 80 ns.The temporal behavior of the specific emission lines from the SnO_2 plasma was characterized.The intensities of Sn I and Sn II lines first increased,and then decreased with the delay time.The results also showed a faster decay of Sn I atoms than that of Sn II ionic species.The temporal evolutions of the SnO_2 plasma parameters(electron temperature and density) were deduced.The measured temperature and density of SnO_2 plasma are 4.38 eV to0.5 eV and 11.38×10~(17) cm~(-3) to 1.1×10~(17) cm~(-3),for delay times between 0.1 μs and 2.2 μs.We also investigated the effect of the laser pulse energy on SnO_2 plasma.     

应用于等离子体排灰气处理的甲烷水汽重整反应的热力学分析

Tokamak装置中的等离子体反应一段时间后,需对产生的排灰气进行净化处理,以回收其中的氘氚。目前拟采用甲烷水汽重整反应将化合态的氘氚转化为单质并回收。本文运用Gibbs自由能最小化方法,对应用于等离子体排灰气处理的水汽重整反应进行热力学分析,考查反应温度、原料比例、反应压力、O₂、CO₂、H₂、CO等因素对反应平衡的影响,确定了适宜的反应条件,即反应温度范围650～700 ℃,压力1×105 Pa,水碳比1.5～2.0。此外,原料气中O₂或CO₂的存在有利于减少积碳的生成量,并获得较高的氢同位素平衡转化率;H₂的存在对重整反应的热力学平衡无明显影响;CO的存在会使积碳量增加,对反应产生不利影响,在进入重整反应器前应将其去除。     

Application of dielectric barrier discharge (DBD) plasma packed with glass and ceramic pellets for SO2 removal at ambient temperature: optimization and modeling using response surface methodology

Air pollution is a major health problem in developing countries and has adverse effects on human health and the environment. Non-thermal plasma is an effective air pollution treatment technology. In this research, the performance of a dielectric barrier discharge (DBD) plasma reactor packed with glass and ceramic pellets was evaluated in the removal of SO₂ as a major air pollutant from air in ambient temperature. The response surface methodology was used to evaluate the effect of three key parameters (concentration of gas, gas flow rate, and voltage) as well as their simultaneous effects and interactions on the SO₂ removal process. Reduced cubic models were derived to predict the SO₂ removal efficiency (RE) and energy yield (EY). Analysis of variance results showed that the packed-bed reactors (PBRs) studied were more energy efficient and had a high SO₂ RE which was at least four times more than that of the non-packed reactor. Moreover, the results showed that the performance of ceramic pellets was better than that of glass pellets in PBRs. This may be due to the porous surface of ceramic pellets which allows the formation of microdischarges in the fine cavities of a porous surface when placed in a plasma discharge zone. The maximum SO₂ RE and EY were obtained at 94% and 0.81 g kWh⁻¹, respectively under the optimal conditions of a concentration of gas of 750 ppm, a gas flow rate of 2 l min⁻¹, and a voltage of 18 kV, which were achieved by the DBD plasma packed with ceramic pellets. Finally, the results of the model's predictions and the experiments showed good agreement.     

Radiation shielding design of the CFETR polarimeter interferometer and CO2 dispersion interferometer

A three-wave based laser polarimeter/interferometer and a CO₂ laser dispersion interferometer are used to determine the electron and current density profiles on a Chinese fusion engineering test reactor (CFETR). Radiation shielding is designed for the combination of polarimeter/interferometer and CO₂ dispersion interferometer. Furthermore, neutronics models of the two systems are developed based on the engineering-integrated design of CFETR polarimeter/interferometer and CO₂ dispersion interferometer and the major material components of CFETR. The polarimeter/interferometer and CO₂ dispersion interferometer's neutron and photon transport simulations were performed using the Monte Carlo neutral transport code to determine the energy deposition and neutron energy spectrum of the optical mirrors. The energy depositions of the first mirrors on the polarimeter/interferometer are reduced by three orders with the whole shielding. Since the mirrors of CO₂ dispersion interferometer are very close to the diagnostic first wall, shielding space is limited and the CO₂ dispersion interferometer energy deposition is higher than that of the polarimeter/interferometer. The dose rate after shutdown 10⁶ s in the back-drawer structure has been estimated to be 83 μSv h⁻¹ when the radiation shield is filled in the diagnostic shielding modules, which is below the design threshold of 100 μSv h⁻¹. Radiation shielding design plays a key role in successfully applying polarimeter/interferometer and CO₂ dispersive interferometer in CFETR.     

Exploring the cooperation effect of DBD byproducts and Ag/TiO2 catalyst for water treatment in an APPJ system

In this paper,the collective effects of combining heterogeneous Ag/TiO_2 nanocomposite catalyst with the byproducts(primarily the irradiation and the O_3 species) of an atmospheric pressure plasma jet(APPJ) system on the degradation of methyl orange(MO) were explored.The heterostructured Ag/TiO_2 nanocomposite was achieved via decorating the Ag quantum dots(QDs) on the commercially available TiO_2catalyst(P25) through a hydrothermal method.The x-ray diffraction analysis of the nanocomposite catalyst showed the diffraction peaks at 44.3°,64.4°,and 77.5°,corresponding to the Ag planes of(200),(220) and(311),respectively.The high resolution transmission electron microscope characterization of the nanocomposite catalyst indicated that the Ag QDs with an average diameter of 5 nm were homogeneously distributed on the P25 surface.The experimental results on the MO photodegradation showed that the APPJ irradiation had a marginal effect on the cleavage of the MO molecules.When the Ag/TiO_2 nanocomposite catalyst was used,the photodegradation rate of MO increased about 5 times.When both the APPJ byproducts and the Ag/TiO_2 nanocomposite catalyst were used,however,over 90% of the MO in the tested solution was cleaved within 15 min,and the energy efficiency was about 0.6 g/k W h.Moreover,an optimal Ag dosage value was determined(6 wt%).The catalytic results indicated that combining the DBD plasma byproducts with heterogeneous nanocomposite catalysts may be an effect protocol for decreasing the application cost of the DBD system and mitigating the environment pollution by organic dyes in the textile industry.     

Study on the properties of a ε-Fe3N-based magnetic lubricant prepared by DBD plasma

The ε-Fe₃N-based magnetic lubricant which is stable and high saturation magnetization has been prepared by a homemade DBD device under the atmospheric pressure. The results show that the NH3 flow rate, the applied peak-to-peak voltage and the mass ratio of surfactant and carrier lubricant have important effects on the phase structure, the magnetic properties, the size of ferroparticles and the stability of the ε-Fe3N-based magnetic lubricant. TEM images show the ε-Fe₃N ferroparticles are dispersed in the carrier lubricant homogeneously, and the cluster phenomenon is not observed. The stable ε-Fe3N-based magnetic lubricant with the saturation magnetization of 50.11 mT and the mean ferroparticle size of 11 nm is prepared successfully. The main particles of the atmospheric-pressure Ar/NH3/Fe(CO)5 DBD plasma are NH, N, N⁺, Fe, N₂, Ar, H_α, and CO; NH is a decomposition product of NH₃. Fe and N active radicals are two elementary species in the preparation of the ε-Fe3N-based magnetic lubricant in the atmospheric-pressure DBD plasma. There are two discharge modes for DBD plasma, namely, multi-pulse APGD and filamentary discharge. By increasing the applied peak-to-peak voltage from 4600 to 7800 V, the discharge mode is changed from single-pulse APGD with filamentary discharge to two-pulse APGD with filamentary discharge, and the Lissajous figure also converts from a quadrilateral with one step to two steps on the right-hand side.     

Naphthalene oxidation by different non-thermal electrical discharges at atmospheric pressure

Gaseous naphthalene has been removed by air plasma generated by pulsed corona discharges at 100°C (LSPM) and dielectric barrier discharges (DBD) up to 250 °C (LPGP) in different reactors geometries. Naphthalene has been chosen as one of unburned hydrocarbon present in exhaust gas engine during the cold start of vehicles. The comparison between the different discharge geometries has been possible using the specific input energy (SIE) as relevant parameter for pollutant removal process control considering the differences in the electrical characteristics and the differences of gas flow. The best naphthalene degradation is obtained in the wire-to cylinder (WTC) corona discharge and the stem-to-cylinder DBD with an energy cost β respectively of 10 and 20 J L ^-1. The main by-products issues of the naphthalene oxidation are CO₂ and CO reaching 45% in Multi-Pin-to-Plan corona discharge. We detected polyaromatic hydrocarbons in the gas phase (few ppm) and in the solid phase deposited in the reactors. The introduction of water in the discharges promotes the naphthalene degradation by OH-atom, which has better oxidising power than O-atom in dry air.     

Plasma-assisted Co/Zr-metal organic framework catalysis of CO_2 hydrogenation:influence of Co precursors

In this study, Co/Zr-metal organic framework(MOF) precursors were obtained by a roomtemperature liquid-phase precipitation method and the equivalent-volume impregnation method,respectively, using a Zr-MOF as the support, and Co/Zr-MOF-M and Co/Zr-MOF-N catalysts were prepared after calcination in a hydrogen–argon mixture gases(V_(Ar):V_(H_2)= 9: 1) at 350 °C for 2 h. The catalytic activities of the prepared samples for CO_2 methanation under atmosphericpressure cold plasma were studied. The results showed that Co/Zr-MOF-M had a good synergistic effect with cold plasma. At a discharge power of 13.0 W, V_(H_2):V_(CO_2)= 4: 1 and a gas flow rate of 30 ml·min~(-1), the CO_2 conversion was 58.9% and the CH_4 selectivity reached 94.7%,which was higher than for Co/Zr-MOF-N under plasma(CO_2 conversion 24.8%, CH_4 selectivity 9.8%). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N_2 adsorption and desorption(Brunauer–Emmett–Teller) and x-ray photoelectron spectroscopy analysis results showed that Co/Zr-MOF-M and Co/Zr-MOF-N retained a good Zr-MOF framework structure, and the Co oxide was uniformly dispersed on the surface of the Zr-MOF. Compared with Co/Zr-MOF-N, the Co/Zr-MOF-M catalyst has a larger specific surface area and higher Co~(2+)/Cototaland Co/Zr ratios. Additionally, the Co oxide in Co/ZrMOF-M is distributed on the surface of the Zr-MOF in the form of porous particles, which may be the main reason why the catalytic activity of Co/Zr-MOF-M is higher than that of Co/ZrMOF-N.     

Fast and low-temperature elimination of organic templates from SBA-15 using dielectric barrier discharge plasma

Organic templates P-123 of mesoporous SBA-15 can be effectively removed in a few minutes (4min) by using the dielectric-barrier discharge (DBD) plasma technique at ambient pressure and low gas temperature (around 130°C). The mesoporous SBA-15 was characterized by FT-IR, ²⁹ Si solid sate NMR, TEM, XRD, TGA and N₂ adsorption/desorption isotherms. The as-made SBA-15 treated with DBD plasma exhibited a larger surface area of 790 m ²·g ⁻¹ with larger pores and microspore volume than samples prepared by using the conventional thermal calcination method (550 °C and 5h, 660 m ²·g ⁻¹ ). In addition to less shrinkage of the silica framework, the DBD-prepared SBA-15 showed significantly increased weight loss of 8.3% about 200 °C as compared with that of conventional calcination (5.5%), which is attributed mainly to the dehydroxylation by condensation of silanol groups.     

Evaluation of trans-ferulic acid degradation by dielectric barrier discharge plasma combined with ozone in wastewater with different water quality conditions

In this study, dielectric barrier discharge plasma and ozone(O_3) were combined to synergistically degrade trans-ferulic acid(FA), and the effect of water quality on FA degradation was studied. The results showed that 96.9% of FA was degraded after 40 min treatment by the plasma/O_3 process. FA degradation efficiency increased with the p H values. The presence of suspended solid and humic acid inhibited FA degradation. FA degradation efficiency increased as the water temperature increased to 30 °C. However, the further increase in water temperature was adverse for FA degradation. Effects of common inorganic ions on FA degradation were also investigated. The addition of Cl~- inhibited the FA degradation, whileCO_3~(2-) had both negative and positive influences on FA degradation.NO_3~- andSO_4~(2-) did not have significant effect on FA degradation. Fe~(3+)and Cu~(2+)benefited FA degradation through the Fenton-like and catalytic ozonation reactions.     

CO_2 conversion by thermal plasma with carbon as reducing agent: high CO yield and energy efficiency

A key problem in CO_2 conversion by thermal plasma is suppressing the inverse reactions,CO?+?O?→?CO_2 and CO?+?0.5O_2?→?CO_2, to simultaneously obtain high CO yield and energy efficiency. This can be done by quickly quenching the decomposed gas or rapidly taking away free oxygen from decomposed gas. In this paper, experiments of CO_2 conversion by thermal plasma with carbon as a reducing agent are presented. Carbon quickly devoured free oxygen in thermal plasma decomposed gas, and not only is the inverse reaction completely suppressed, but the discharge energy to form oxygen atoms, oxygen molecular, and thermal energy is also reused.A CO_2 conversion rate of 67%–94% and the corresponding electric energy efficiency of about 70% are achieved, both are much higher than that seen so far by other plasma implementations.     

Numerical simulation of plasma-assisted combustion of methane-air mixtures in combustion chamber

A two-dimensional mathematical model was developed to investigate the effects of dielectric barrier discharge (DBD) plasma on CH₄-air mixtures combustion at atmospheric pressure. Considering the physical and chemical processes of plasma-assisted combustion (PAC), plasma discharge, heat transfer and turbulent were simultaneously coupled into simulation of PAC. This coupling model consists of DBD kinetic model and methane combustion model. By comparing simulations and the original reference’s results, a high-accuracy of this model was validated. In addition, the effects of PAC actuation parameters on combustion characteristics were studied. Numerical simulations show that with an inlet airflow velocity of 10 ms ^-1, a CH₄-air mixtures’ equivalence ratio of 0.5, an applied voltage of 10 kV, a frequency of 1200 kHz, compared to conventional combustion (CC), the highest flame temperature rises by 32 K; outlet temperature distribution coefficient drops by 2.3%; the maximum net reaction rate of CH₄ and H₂O increase by 11.22% and 12.80% respectively; the maximum CO emission index decreases by 14.61%; the mixing region turbulence mixing time reduces by 89 ms.     

Analysis of the critical active species for methylene blue decoloration in a dielectric barrier discharge plasma system

In the paper, a hybrid gas–liquid dielectric barrier discharge (DBD) plasma system was set up to treat a methylene blue (MB) solution. The effects of the change of the carrier gas, the gas bubbling rate and different kinds of scavenger addition, including sodium carbonate (Na₂CO₃), para benzoquinone (p-BQ), triethylenediamine and sodium dihydrogen phosphate (NaH₂PO₄), on the MB decoloration were reviewed to clarify the critical active species for the dye decoloration in the DBD plasma system. The obtained results show that higher decoloration of the MB solution could be achieved when O₂ was used as the carrier gas, which could be 100% after 20 min discharge treatment, and the result confirmed the crucial effect of O₃ in the MB decoloration. Based on the experiments of the scavenger addition, it could be concluded that O₂⁻ and ¹O₂ were two other important reactive oxygen species (ROS) for the MB decoloration. The results of the higher chemical oxygen demand removal and faster disappearance of the characteristic peak of the MB from the UV–vis analysis under O₂ bubbling conditions also proved the critical effect of the ROS formed by O₂ on the MB decoloration.