Qiang Chen

Oxygen (O₂) helicon plasmas in multiple wave modes were excited by a right-helical antenna with an upper metal endplate at low pressure. Mode transitions were observed at increasing input power or magnetic field, characterized by obvious jumps of plasma parameters. Blue Core appears at high magnetic fields (∼700 G) and input powers (∼1700 W), with a large radial gradient of plasma density, ion line intensity, and electron temperature. Emission spectra demonstrate that the blue lights originate from O II lines. We found that the intensity ratio of O II to O I of Blue Core in O₂ is lower by one order than that in N₂ or Ar despite their similar ionization rates and plasma densities in the Blue Core area. A high-temperature B-dot probe together with a waveform fitting procedure was used to present the measured oscillating waveforms of m = +1 helicon waves, showing distinct wave structures of different eigenmodes. Cavity mode resonance is suggested to be responsible for the formation of standing waves of discrete eigenmodes. A pressure balance model was developed to estimate the species densities around the central area in different modes, showing massive dissociation of O₂ molecules and high density of O atoms locally, so that O₂ helicon plasma behaves as a species feature of monatomic gas discharge. The obviously low intensity of the O II lines compared to the O I lines of Blue Core in O₂ is related to the quite high excitation threshold of O⁺ ions (∼30 eV) although electron density and temperature are relatively high. The combined effects of dispersed reaction energy distribution, massive molecule dissociation and negative ion creation are considered to be the main causes for the requirement of much higher RF power and magnetic field for Blue Core formation in O₂ helicon plasma than that in Ar. The calculated radial profiles of power deposition and the captured plasma morphology confirm that the dominant central electron heating is the essential reason for the large radial gradients of plasma density and electron temperature which contribute to the serious neutral depletion and Blue Core formation.

The prevention and treatment of organic pollutants in wastewater have attracted extensive attention because they threaten ecological balance and human health. Traditional wastewater treatment technologies, such as physical, chemical, biological methods, etc., are still limiting and challenging due to some factors, such as high energy consumption, chemical agents, low efficiency, and secondary pollution. At present, gliding arc plasma, based on equilibrium/non-equilibrium in plasma temperature, demonstrates itself to be one of the most promising technologies for the degradation of refractory organics with its fast degradation rates, no secondary contamination, high efficiency, and so on. The theoretical mechanisms and typical applications of gliding arc plasma degradation of wastewater are introduced in detail in this paper. The physical and chemical characteristics of gliding arc plasma and the role of the reactive species in the plasma are reviewed.

Manganese nitride films have been successfully fabricated by the technique of plasma enhanced atomic layer deposition (PEALD). The process employed bis(N,N'-di-tert-butylacetamidinate)manganese [Mn(amd)2] as manganese precursor and ammonia plasma as a coreactant. With a typical PEALD process cycle of 5 s Mn(amd)2 pulse, 10 s Ar purge pulse, 10 s NH3 plasma exposure, 10 s Ar purge pulse, 80 °C deposition temperature, and 60 W input power, the deposited film is continuous and smooth with a growth rate is 0.037 nm/cycle. Based on x-ray diffraction measurement, the film is determined to be η-Mn3N2 crystal structure. The primary deposition mechanism has been investigated by in situ optical emission spectroscopy and quartz crystal microbalance. The deposited manganese nitride film shows an excellent barrier performance against copper diffusion at insulator/copper interface.

A novel plasma-assisted fluidized-bed atomic layer deposition process to synthesize Pd-Cu bimetallic nanoparticles is reported, using palladium hexafluoroacetylacetonate, copper(I)-N, N′-di-iso-propylacetamidinate and H₂ plasma. The process allows us to uniformly deposit Pd-Cu nanoparticles in porous powder, which is a mixture of γ-Al₂O₃ (30 wt%), amorphous aluminum silicate (50 wt%) and molecular sieve (20 wt%) (ASM). With metal loadings of 13.1 and 2.5 mg g⁻¹ for Pd and Cu, respectively, the afforded 13.1Pd-2.5Cu catalyst shows excellent catalytic performance for the hydrogenation of CO₂ in a dielectric barrier discharge reactor with no intentional heating. Under the condition of discharge input power of 24.6 W, H₂-to-CO₂ ratio of 4 in feed gas, and gas hourly space velocity of 7595 h⁻¹, the conversion of CO₂ can reach as high as 38.0%, with the CH₄ and CH₃OH product selectivities of 6.7% and 12.8%, respectively. Density functional theory calculations are further employed to understand the associated CH₃OH formation mechanism.

In order to study the characteristics of radio frequency dielectric barrier discharge (RF-DBD) using argon doped with nitrogen at atmospheric pressure, electrical and optical diagnoses of the discharge with different nitrogen ratios from 1% to 100% were carried out, and the self-organizing form of the filamentous plasma was studied through a transparent water electrode. At the same time, an ICCD camera was used to study the spatiotemporal evolution filamentous discharge during one cycle. Different from discharge using pure argon, using argon doped with nitrogen made the discharge change from glow discharge to filamentous discharge when the voltage increased to a certain value, and a higher nitrogen ratio made the filaments thicker and more sparsely arranged. Under different input power and nitrogen content conditions, several forms of glow discharge, hexagonal/irregularly arranged filamentous discharge and local filamentous discharge were obtained, all of which have potential applications to reduce the high cost of using inert gases.

Perfluorooctanoic acid (PFOA) is an artificially synthesized perfluorinated chemical widely used in industries. It is often released into the environment without treatment, which causes pollution in groundwater. Recently, we have reported a rapid and efficient removal of PFOA in aqueous solution by using a fountain-strip dielectric barrier discharge reactor (SF-DBD). This design allows for the gaseous–liquid interaction to happen in a large space at atmospheric pressure, so it is a promising method to efficiently remove PFOA from water. Recently, we reported the effects of the process parameters, including power mode, pulse time, sinusoidal wave discharge, the discharge gas, initial concentration, pH, conductivity, and positive and negative discharges, on the efficiency of this method for PFOA degradation. Understanding the reaction mechanism is key to further improve the efficiency of the system. In this work, we reported the decomposition mechanism of the SF-DBD for PFOA degradation. The mass spectrum (MS) showed that PFOA was degraded to perfluoroheptanoic acid, perfluorohexanoic acid, perfluoropentanoic acid, perfluorobutanoic acid, perfluoropropionic acid, and trifluoroacetic acid after the plasma treatment. The optical emission spectroscope (OES) and the radical scavenger experiments indicated that the excited argon atoms and hydroxyl radicals played a major role in PFOA degradation, while the contributions from the solvated electrons (e⁻_aq), superoxide anion radical (·O²⁻), and singlet oxygen (1O₂) were negligible in initiating the cleavage reaction.

A fluidized-bed plasma-enhanced atomic layer deposition (FP-ALD) process is reported to fabricate Pd nanoparticles using palladium hexafluoroacetylacetonate and H2 plasma. The process successfully deposits Pd nanoparticles over porous γ-Al2O3 (30 wt. %), amorphous aluminum silicate (50 wt. %), and molecular sieve (20 wt. %) (ASM) powders. Pd loading on ASM is increased linearly with increasing the number of FP-ALD cycle with a growth rate of 0.34 mg/1 g ASM/cycle. Transmission electron microscopy reveals that high-density Pd nanoparticles are uniformly distributed over the entire ASM powders and the average Pd particle size is sensitive to the number of FP-ALD cycle. By increasing the number of FP-ALD cycles from 25 to 150, the average Pd particle size rises from 0.9 to 5.8 nm, indicating the particle size can be tuned easily by varying the number of FP-ALD cycles. The catalytic activities of different particle sizes and Pd loading samples are evaluated for CO oxidation. With the metal loading amount of 2% for Pd and the average particle size of 2.9 nm, the deposited Pd/ASM sample shows an excellent catalytic activity for the oxidation of CO. Under the condition of a gas mixture of 0.5 vol. % CO and 21 vol. % O2 balanced with N2, and gas hourly space velocity of 24 000 h−1, 100% CO conversion temperature is as low as 140 °C.

Perfluorooctanoic acid (PFOA) is an artificially synthesized per-fluorinated chemical widely used in industry. It is often released into the environment without treatment and causes pollution in groundwater. In this paper, we employed a strip fountain dielectric barrier discharge (SF-DBD) plasma source to degrade PFOA from the water. The effects of power supply mode, discharge gases, pH, the conductivity of the solution, concentration, etc., on the degradation efficiency were studied. For a 200 mL sample of 75 mg/L PFOA, a 99% degradation efficiency with a 204.5 μg/kJ energy production rate was achieved using an average power of 43 W negative pulse argon plasma for 50 min at atmospheric pressure. The total organic carbon concentration (TOC) decreased by 63% after a 60 min treatment. The SF-DBD proves to be a promising and energy-saving technique to efficiently remove PFOA from water.

The study of aggregation-induced emission luminogens (AIEgens) shows promising perspectives explored in lighting, optical sensors, and biological therapies. Due to their unique feature of intense emissions in aggregated solid states, it smoothly circumvents the weaknesses in fluorescent dyes, which include aggregation-caused quenching of emission and poor photobleaching character. However, our present knowledge of the AIE phenomena still cannot comprehensively explain the mechanism behind the substantially enhanced emission in their aggregated solid states. Herein, to systematically study the mechanism, the typical AIEgens tetraphenylethene (TPE) was chosen, to elucidate its photophysical properties, the TPE in THF/H₂O binary solvents, TPE in THF solvents depending on concentration, and the following direct conversion from a dissolved state to a precipitated solid state were analyzed. Moreover, the TPE derivatives were also investigated to supply more evidence to better decipher the generally optical behaviors of TPE and its derivatives. For instance, the TPE derivative was homogeneously dispersed into tetraethyl orthosilicate to monitor the variance of photophysical properties during sol–gel processing. Consequently, TPE and its derivatives are hypothesized to abide by the anti-Kasha rule in dissolved states. In addition, the factors primarily influencing the nonlinear emission shifting of TPE and its derivatives are also discussed.