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Perfluorooctanoic acid (PFOA) is a kind of persistent and refractory organic pollutants with high concern in recent years. In this work, a new treatment method-microwave discharge plasma in liquid (MDPL) is used to study the defluorination and degradation characteristics of PFOA. The effects of discharge parameters and solution conditions on the defluorination of PFOA are investigated in detail. The results show that the degradation and defluorination of PFOA by MDPL are excellent, with a removal of 98.6 % and a defluorination of 58.0 % in 100 min. And MDPL is innovatively combined with catalytic ions. The efficient degradation of PFOA by MDPL is attributed to its high mass transfer efficiency. The catalytic ion (Fe2+) is introduced to MDPL for synergistic degradation of PFOA. Under the synergistic catalysis of Fe2+, PFOA is almost completely removed and the defluorination is 82.9 %. The defluorination increased by 24.9 %, the synergistic factor reaches 2.41. In addition, the characteristics of intermediates and free radicals in the process of defluorination are discussed. It is confirmed that e aq - is the key reactive species that initiates the decomposition of PFOA, and hydroxyl radical (· OH) also plays an important role in the subsequent decomposition of PFOA. Finally, the decomposition mechanism of PFOA is analyzed, the degradation pathway of the reaction processes is given. This work proves that MDPL is efficient for the defluorination of PFOA, which also provides a new insight for the control of PFOA pollution. • A new technology-microwave discharge plasma in liquid (MDPL) was used to degrade PFOA, the removal can be more than 99 %. • MDPL can make PFOA efficiently defluorinated without secondary contamination, the highest defluoridation was up to 82.9 %. • It is found that e aq - is the key reactive species to open the decomposition of PFOA, and then·OH also plays a role. [ABSTRACT FROM AUTHOR]

Improved hydrogen production efficiency by microwave liquid-phase discharge plasma reforming of methanol solution without catalyst is investigated in this study. The ethanol solution was added to the methanol solution as accelerator for plasma reforming hydrogen production. The features of radicals and gas-phase products generated by discharge in different mixed solutions were studied by the optical emission spectrum (OES) and gas chromatography (GC). The study found that adding a small amount of ethanol to methanol solution could promote the production of hydrogen by microwave liquid-phase discharge plasma reforming of alcohols. The maximum flow rate of total gas was 30.8 NL/min when discharge in a mixed solution of S e t h / m e t h 1 : 4 , which was 11.6% higher than discharge in S m e t h 1 : 1 . • Ethanol was used as a promoter for hydrogen production by plasma reforming methanol. • Flow rate of total gas production increased by 11.6%. • The highest energy yield of hydrogen production was 0.78 Nm3/kWh. [ABSTRACT FROM AUTHOR]

• Effect of dissolved oxygen (DO) on CH 4 reforming was studied by liquid discharge. • Reducing DO can improve the discharge stability. • DO can affect the relative intensity of radicals generated in the discharge. • Reducing DO can increase the hydrogen yield and hydrogen production efficiency. In this paper, in order to improve hydrogen production, the effect of dissolved oxygen (DO) on methane (CH 4) reforming was studied by liquid phase microwave discharge firstly. DO was reduced by deducing pressure and gas replacement, and the reaction mechanism was researched by radical detection. It was revealed that reducing DO can improve hydrogen (H 2) yield and H 2 selectivity and energy efficiency of hydrogen production. When microwave power was 900 W and the DO was decreased from 4.82 mg/L to 0.65 mg/L, the production and selectivity of H 2 increased by 21.3 % and 22.6 % respectively, and the energy efficiency of hydrogen production increased by 33.1 %. Through the study on the characteristics of discharge radicals, it was concluded that ∙H extraction and ∙H coupling reaction and ∙OH oxidation ∙CH X are the main ways to produce hydrogen. The existence of DO affects the formation of H 2 by limiting the decomposition of water molecules. In addition, the reduction of DO can improve the stability of discharge. These results indicate that reducing the DO can be a simple, effective and energy conservation method to increase the selectivity of target products in the liquid phase discharge reforming of CH 4. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new and high performance technology-microwave discharge plasma in liquid (MDPL) is used to degrade PFOA and PFOS. • The defluorination of PFOA and PFOS by MDPL is excellent, with the defluorination of 82.9%, and 52.6%. • Adding Fe2+ to synergistic degradation, the synergistic factor of PFOA and PFOS reached 2.18 and 2.37. • The defluorination energy consumption efficiency of PFOA processed by MDPL technology is 741.5 mg/kWh, and PFOS is 459.5 mg/kWh. Per-fluorinated compound (PFC) is a kind of persistent and refractory organic pollutants with high concerns in recent years. Perfluorooctane sulphonate (PFOS) and Perfluorooctanoic acid (PFOA) are the most typical per-fluorinated compounds in the water environment. In this work, a new treatment method-microwave discharge plasma in liquid (MDPL) is used to study the defluorination of PFOA and PFOS. The effects of initial concentration of pollutants, microwave input power, distance between electrode and liquid according to the characteristics of pollutants on the defluorination rate are studied. The results show that the defluorination of PFOA and PFOS by MDPL is excellent, with the defluorination of 58.4% and 26.8%. Because MDPL has high mass transfer efficiency and the discharge process is accompanied by the production of ultraviolet light and reactive species. Adding Fe2+ to synergistic degradation, the defluorination of PFOA is 82.9%, PFOS is 52.6%. The defluorination increased by 24.5% and 25.8%, the synergistic factor reached 2.18 and 2.37. Reactive species experiments confirms that e aq - is the key reactive species that initiates the decomposition of PFOA and PFOS. In addition, the characteristics of intermediates and free radicals in the process of defluorination are discussed. Reactive species experiments confirms that e aq - is the key reactive species that initiates the decomposition of PFOA and PFOS. Finally, the decomposition mechanism of PFOA and PFOS are analyzed and the degradation pathway of the reaction processes is given. This work proves that MDPL is efficient for the defluorination of PFOA and PFOS, which also provides a new insight for the treatment of PFC pollution. [ABSTRACT FROM AUTHOR]

Carbon nanoparticles produced from alcohols by pulsed spark discharge in liquid (PSDL) was investigated in this work. The spherical carbon particles with about 10 nm diameter can be produced by PSDL, which were similar to the commercial carbon particles. With the increase of discharge power, the mean diameter of carbon particles was decreased and the size distribution was more uniform. Meanwhile, the yield of carbon produced from ethanol was more than from methanol that may be attributed to the more carbon atoms in ethanol compared with the same volume of methanol. In addition, the mechanism of carbon produced from alcohols by PSDL was also analyzed. The possible reactions were given according to the production analysis. This work presents a new method for carbon nanoparticles production and the results can play a guidance role in producing nanometer materials by plasma reforming. [ABSTRACT FROM AUTHOR]

Hydrogen, as an attractive energy carrier, is regarded as one of the best environmentally-friendly energy sources in the future. In the paper, it was reported that hydrogen was produced by 2.45 GHz microwave discharge in low carbon alcohol (methanol and ethanol) solution. The effects of microwave input power and concentration of alcohol solution on hydrogen production were studied. All results corresponded to the non-equilibrium plasma at reduced pressure (3000Ра). The gaseous products of microwave discharge in alcohol solution mainly included hydrogen, carbon monoxide, acetylene and carbon dioxide. The flow rates of total gaseous products and hydrogen increased with the increasing of power, while that increased firstly and then decreased with the increasing of concentration of alcohol solution. The percentage concentrations of hydrogen and carbon monoxide increased with the increasing of power, and when the concentration of alcohol solution was 8% v/v, the percentage concentrations of hydrogen and carbon monoxide reached a maximum value. As the power increased, the energy efficiency of hydrogen production improved significantly, and the energy efficiency of hydrogen produced from ethanol solution was higher than that from methanol solution with the same power. The energy efficiency of hydrogen production increased firstly and then decreased with the increasing of concentration of alcohol solution. In the paper, the best results of flow rate of hydrogen, percentage concentration of hydrogen and energy efficiency were 401.00 mL/min, 64.55% and 137.63 NL/kWh, respectively. [ABSTRACT FROM AUTHOR]

Discharge plasma reforming of methane to produce hydrogen has been a hotspot in recent years. At present, there is no report on liquid-phase discharge for methane reforming. In this paper, directly coupled liquid-phase microwave discharge plasma (LPMDP) is used for the first time to realize liquid-phase methane wet reforming to produce hydrogen. When methane gas is injected into the water in the reactor, plasma is generated in the water by microwave discharge. The type and relative intensity of active radicals produced during discharge are detected by emission spectroscopy. Methane gas is introduced into the reactor through two electrode structures. When the microwave power was 900 W, the optimal methane conversion rate reached 94.3%, and the highest concentration of hydrogen reached 74.0%. In addition, through the optimization of the electrode structure, while improving the stability of the plasma system, the higher yield of hydrogen and energy efficiency of hydrogen production were obtained, and the highest energy efficiency of hydrogen production was approximately 0.92 mmol/kJ. This investigation provides a new method for hydrogen production by liquid-phase plasma methane wet reforming. • Liquid-phase microwave discharge plasma is applied to methane reforming to produce hydrogen for the first time. • The main products are H 2 , CO and CO 2 , the highest concentration of hydrogen reaches 74%. • Compared with the peripheral inlet electrode, the central inlet electrode is more conductive to methane conversion. • While the peripheral inlet electrode is more conductive for water to participate in the reforming reaction. [ABSTRACT FROM AUTHOR]

• Liquid products and syngas from ethanol solution by microwave discharge were studied. • There were highly correlated relationships between the acetaldehyde and hydrogen. • Possible reaction pathway of microwave discharge in ethanol solution was analyzed. Microwave discharge in ethanol solution to produce hydrogen can obtain optimistic flow rate of hydrogen, because of the high mass transfer efficiency and water participation in the reaction. In this work, combined with liquid and gas products analysis, the main aim is to identify the reaction pathways of hydrogen production by microwave discharge plasma in ethanol-water mixtures. The features of radicals, gas-phase and liquid-phase products were investigated by the optical emission spectrum (OES) and gas chromatography (GC). The experimental results showed the gas-phase products included: H 2 , CO, CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , and CO 2 , and the liquid-phase products primarily included CH 3 CHO and CH 3 OH. By analysis, it is found that the amount of hydrogen production is closely related to the production of the intermediate product CH 3 CHO, and the OH radicals can inhibit the formation of solid carbon and by-product (C 2 H 2), also promote the generation of hydrogen. [ABSTRACT FROM AUTHOR]

The ethanol decomposition process for hydrogen-rich gas synthesis via microwave discharge in ethanol-water mixtures was investigated in this study. Excited active species and gas-phase products based on ethanol's varying volume fraction were detected via optical emission spectroscopy (OES) and mass spectrometry (MS). The correlation between the spectrum signal of the active species and the mass spectrum signal of the gas phase products was quantitatively analyzed. The experimental results showed that the intermediate active species mainly consisted of OH, C 2 , CH 2 , CH, C, and H, and the gas phase products mainly included H 2 , CH 4 , C 2 H 2 , CO, C 2 H 4 , and CO 2. There were significantly positive linear relationships between H or CH 2 and H 2 , demonstrating that both H and CH 2 were important radicals for generating H 2. Based on the experimental results and analyzed from the perspective of thermodynamics, the reactions of H + H (+M) → H 2 (+M) and H + H + H 2 →H 2 + H 2 , H + H + H 2 O → H 2 + H 2 O, CH 2 + CH 2 → H 2 + C 2 H 2 were all likely to produce hydrogen. • There were significantly positive linear relationships between H or CH 2 and H 2. • H and CH 2 were important radicals for generating H 2. • Possible reaction path of microwave discharge in ethanol solution was given. [ABSTRACT FROM AUTHOR]

• This paper first uses plasma technology for H 2 from simulated seawater. • Conductivity significantly affected the discharge characteristic. • The plasma reaction was limited by the optimum conductivity. • This method can achieve efficient and stable hydrogen production. Given the current shortage of freshwater resources and the global energy trend is changing to clean and efficient energy, this paper first attempts to use microwave plasma technology for hydrogen production from simulated seawater. The purpose is to build a plasma reactor with unique characteristics of stable operation, which provides the possibility of direct hydrogen production from seawater using plasma technology. To increase hydrogen production and overcome the problem of unstable discharge of pure water, methane (CH 4) is introduced into the liquid to realize the gas–liquid two-phase discharge. At different conductivity and CH 4 feed flow, the performance of the reactor was evaluated by hydrogen production, hydrogen production energy efficiency, and energy conversing efficiency. The plasma reaction was limited by the optimum conductivity of the solution. At conductivity of 1800 μS/cm, the discharge product was mainly hydrogen, the hydrogen production can reach 2202.3 mL/min, and energy efficiency of hydrogen production and energy conversion efficiency were also increased by 59.6% and 64.8% compared with the pure water experiment. It showed that the change of conductivity significantly affected the plasma chemical reaction. This difference is mainly related to the change of conductivity affecting the number of charges in the solution and and the catalysis of chloride ions. In addition, the optical characteristics and bubble dynamics during the discharge process were also studied to better understand the complex behavior of the plasma reactor. This method proves the huge potential of the reactor for hydrogen production from seawater without a catalyst and provides a new reference for the subsequent hydrogen production industry. [ABSTRACT FROM AUTHOR]

In situ hydrogen production technologies have attracted attentions because of hydrogen storage and transportation safety issues. Discharge plasma technology for hydrogen production is of fast response, large capacity, small scale and portability, which is suitable for automobiles and ships. In this paper, a method for producing hydrogen by microwave discharge in ethanol solution was introduced. A microwave discharge reactor of direct standing wave coupling (MDRSWC) was designed, which was suitable for on-board hydrogen production. The characteristics of large capacity hydrogen production by applying MDRSWC in liquid ethanol were investigated. Depending on the experimental conditions of ethanol concentration and microwave power, the flow rate of hydrogen production was achieved ranging from 28.93 to 72.48 g/h. In addition to main hydrogen and carbon dioxide, a small amount of methane and acetylene as by-products were detected. By optimizing the experimental conditions, the experimental results showed that the flow rate of hydrogen, the percentage concentration of hydrogen and the energy yield of hydrogen production were 72.48 g/h, 58.1% and 48.32 g/kWh respectively. This work could provide a potentially effective hydrogen production method for on-board hydrogen utilization device. [ABSTRACT FROM AUTHOR]

• The effect of auxiliary gases on CH 4 reforming was studied by liquid plasma firstly. • The auxiliary gas can successfully activate of CH 4 and H 2 O to improve H 2 production. • Compared with N 2 , the addition of Ar showed better auxiliary performance. Given the excited state species generated by the discharge gas can activate CH 4 in gas-phase discharge and water in liquid-phase discharge. In this work, to make full use of the activation of auxiliary gases and maximize the energy utilization in liquid-phase discharge, the microwave liquid-phase plasma technology was used to study the activation of the CH 4 -H 2 O system by auxiliary gases for the first time, the photoelectric characteristics of discharge and discharge plasma parameters were analyzed. N 2 and Ar were selected as auxiliary gases. The results showed that auxiliary gas could also activate CH 4 and H 2 O in addition to the effective dissociation of reactants by electron collision, and the discharge gas-phase products were mainly H 2. Compared with the discharge in the pure CH 4 -H 2 O system, under N 2 and Ar atmosphere, the hydrogen production energy efficiency increased by 43.0% and 72.8%, respectively. This difference is mainly related to the selectivity of the active species produced by the two auxiliary gases to the original reactants and radicals. This study provides a simple and efficient method for plasma-assisted CH 4 activation for hydrogen production. [ABSTRACT FROM AUTHOR]

In order to further improve the hydrogen production efficiency of microwave liquid-phase discharge, a three-electrode reactor was designed and a suspended electrode was added. The internal structure of the three-electrode reactor was optimized. The formation of bubbles during the discharge and the change characteristics of plasma morphology were studied after adding the suspended electrode. In addition to investigating the physical influence of the suspended electrode on the discharge plasma, the influences of the different electrode materials and specific surface area of the suspension electrode on the composition of the gas products, the hydrogen flow rate and the hydrogen energy yield were also investigated. The experimental results show that the suspended electrode can increase the formation time of plasma and bubble. In this study, the highest flow rate of total gas is 29.5 NL/min with the 80 PPI-Cu foamed metal suspended electrode which is an increase of 31.5% than no suspended electrode. • Suspended electrode with high specific surface area is used. • The effect of suspended electrode on bubble residence time is discussed. • The energy yield of hydrogen production increased by 34.6%. [ABSTRACT FROM AUTHOR]