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Plasma bubbles are regarded as a promising means of interacting plasma discharges and liquids due to their high efficiency in the generation of reactive species. The discharge mode and characteristics are significant factors that should be considered. In this study, the plasmas are initially generated in the gas phase and then driven by the gas flow to diffuse into the solution through the two holes at the lower part of the quartz tube to form plasma bubbles. The discharge modes, characteristics, and plasma–liquid interactions in two different configurations, i.e., bare electrode and dielectric-coated electrode, are investigated. It is found that the discharge mode induced for the two structures is different, with a hybrid-mode operating in the bare electrode design and a filamentary mode operating in the dielectric design. When the applied voltage is increased, a filamentary-to-spark transition occurs in the bare structure, while the discharge remains relatively stable in the dielectric design. Direct and intense contact between the discharge and the solution in the bare structure greatly promotes the physio-chemical reactions and results in obvious changes in H2O2 concentration, solution pH, conductivity, and temperature. This study provides insights into hybrid gas–liquid discharges and reactor design for plasma bubble generation. [ABSTRACT FROM AUTHOR]

Solution pH is a significant parameter that affects the electrical characteristics of gas–liquid discharges and thus potentially produces different plasma chemistries for different plasma-engineered applications. In this study, the discharge characteristics and long-lived aqueous reactive species under different initial pH conditions were investigated. It was found that the discharge contained three phases in one pulse cycle, which occurred at the pulse rising edge, the falling edge, and between the rising and falling edges. The discharge intensity and average power at an initial solution pH of 7.0 are much lower than those obtained at an initial solution pH of 5.0 and 9.0. In contrast, the density ratio of N2 (C3Πu, v = 1)/N2 (C3Πu, v = 0) is much higher under neutral solution conditions, indicating that the relatively high vibrational energy was obtained in the gas–liquid discharge plasma. Concentrations of aqueous species H2O2, NO2–, and NO3– are higher at the initial pH of 9.0, indicating that different plasma intensities and chemical compositions (H+ and OH–) are involved in their generation and consumption processes. This study provides insights into understanding and controlling the characteristics of the gas–liquid discharge under different solution conditions. [ABSTRACT FROM AUTHOR]

• New approach for clean hydrogen energy and smart nano-carbons production. • Effective bioresource conversion using new pulsed plasma modes. • Catalyst-free, plasma conversion of ethanol at near-room temperature. • Towards full bioresource utilization: carbon for carbon, hydrogen for hydrogen. Selective conversion of bio-renewable ethanol under mild conditions especially at room temperature remains a major challenge for sustainable production of hydrogen and valuable carbon-based materials. In this study, adaptive non-thermal plasma is applied to deliver pulsed energy to rapidly and selectively reform ethanol in the absence of a catalyst. Importantly, the carbon atoms in ethanol that would otherwise be released into the environment in the form of CO or CO 2 are effectively captured in the form of carbon dots (CDs). Three modes of non-thermal spark plasma discharges, i.e. single spark mode (SSM), multiple spark mode (MSM) and gliding spark mode (GSM), provide additional flexibility in ethanol reforming by controlling the processes of energy transfer and distribution, thereby affecting the flow rate, gas content, and energy consumption in H 2 production. A favourable combination of low temperature (<40 °C), attractive conversion rate (gas flow rate of ~120 mL/min), high hydrogen yield (H 2 content >90%), low energy consumption (~0.96 kWh/m3 H 2) and the effective generation of photoluminescent CDs (which are applicable for bioimaging or biolabelling) in the MSM indicate that the proposed strategy may offer a new carbon-negative avenue for comprehensive utilization of alcohols and mitigating the increasingly severe energy and environmental issues. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate that atmospheric air plasma bubbles are an effective, energy‐efficient, residue‐free alternative to current decontamination techniques. Five to fifteen minutes of plasma‐bubble treatments of inoculated chicken skin led to a significant reduction in colony‐forming units (CFUs). We show that the activation efficiency is dependent on the plasma discharge frequency, with a higher one (2,000 Hz) leading to a higher CFU reduction (1.4 log) as compared with a lower (0.3 log) reduction at 1,000 Hz. Scanning electron microscopy pictures of treated bacteria reveal damage to the cells. An evaluation of the physicochemical properties of the generated plasma‐activated water revealed an increase in conductivity and in ozone, nitrite, nitrate, hydroxyl, and peroxide concentrations with higher frequencies, all contributing to the observed antimicrobial effect. [ABSTRACT FROM AUTHOR]

Interactions of cold atmospheric‐pressure plasma jets (APPJs) and water are important for water purification, chemical synthesis, medicine, and biotechnology. However, the reactivity and bactericidal effects of water activated with jets of different ionized gases remain unclear, especially in the commonly used helium (He)‐ and argon (Ar)‐APPJ systems. Here, He and Ar are used as working gases to produce APPJ for comparing the plasma‐induced aqueous reactive species and bacteria inactivation effects in solutions. Experimental results indicate that the Ar plasma jet shows a quicker propagation velocity and higher concentrations of gaseous reactive species, and the gas and electron temperature are different for the He and Ar plasma. Moreover, the higher concentration of aqueous reactive species, such as ∙OH, ∙O2−/ONOOH, H2O2, NO2−, and NO3−, and better bacterial inactivation effects are achieved by the Ar plasma treatment. Water deformation induced from plasma water is found as the reason for the different reactivity and bactericidal effects. Further validation experiments using a film with different pore diameters confirm that the molecular weight of the working gas influences the shape and stability of the cavity induced by the gas flow in the plasma jet, and plays a vital role in the production of aqueous reactive species with variable concentrations. [ABSTRACT FROM AUTHOR]

• New plasma-enhanced electrolytic oxidizing water sterilization method. • Decoupling anodic and cathodic reactions using an ion-exchange membrane. • Effective control of free chlorine and other reactive species by the plasma polarity. • Green, efficient, and stable plasma-electrified multipurpose water treatment approach. Pathogenic microorganisms pose a global threat to public health and environment. Common antibacterial chemicals produce toxic residues, inevitably harming the environment. Electrolyzed oxidizing water (EOW), a promising environment-friendly alternative disinfectant, still lacks effective production processes, sufficient bactericidal efficacy and stability, while the enabling physico-chemical mechanisms remain unclear. Here, we report, for the first time, an effective hybrid plasma electrochemical EOW production process and reveal the mechanisms by combining nonthermal plasmas and a two-chamber electrochemical cell separated by a cation exchange membrane (CEM) for decoupling the chemical reactions during the plasma treatment of water. Experimental results demonstrate that combined chlorine (chloramine) was the main chlorine product in the plasma-enhanced EOW (P-EOW) without a membrane, owing to the consumption of free chlorine (Cl 2 , HOCl, ClO−) by plasma-generated reactive nitrogen species. With a CEM in the plasma electrolysis system and through controlling the plasma discharge polarity, the production of free chlorine and other reactive species can be selectively controlled, with the highest concentration of free chlorine obtained in the negative plasma-enhanced EOW (NP-EOW). According to the transportation of cations by the CEM, the high concentrations of free chlorine may be attributed to the higher consuptions of H+ in cathode cell of negative plasma. The study of antibacterial ability of EOW produced under different conditions revealed that Staphylococcus aureus cells were best inactivated by the NP-EOW with CEM, which is mainly attributed to the higher concentration of free chlorine. This study demonstrates the feasibility of plasma-enhanced microbial electrolytic disinfection and offers new insights into the fundamental aspects of P-EOW chemistries for the future development of sustainable, efficient, and cost-effective multipurpose sustainable chemical technologies for water research and treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • New heavy oil processing approach through liquid-phase methane bubble discharge. • A competitive mechanism for radical hydrogenation and recombination is proposed. • High H density in CH 4 plasma contributes to the hydrogenation of aromatic rings. • The H density can be tuned by changing the bubble properties. Hydrogenation, an alternative to conventional cracking, is poised to revolutionize heavy oil upgrading by raising the hydrogen-to-carbon ratio at lower process pressures and temperatures. The emerging low-temperature plasma-enabled hydrogenation is an effective, fast, and environment-friendly process; however, the conversion rate and energy efficiency are still insufficient. To address these limitations, here we propose an innovative bubble-assisted methane plasma-liquid process for heavy oil processing (using ethylbenzene as a model compound) and offer new insights into radical-assisted hydrogenation. Results from the plasma kinetics modeling and density functional theory calculations indicate that ·H and ·CH 3 radicals generated by CH 4 plasma are two main drivers for ethylbenzene hydrogenation, and their chemical reaction rates with ethylbenzene molecules strongly depend on their spatial distribution in bubbles, which further govern the reaction direction towards ethylbenzene hydrogenation or free radical recombination. Moreover, it is found that by controlling the bubble numbers and plasma parameters, the H density can increase by an order of magnitude from 1.4 × 1020 to 3.88 × 1021 m−3, while the number of hydrogenated aromatic rings increases by ∼ 58%, which further confirms the excellences of the proposed plasma-bubble technology in chemical regulation and feasible processing. In addition, the feasibility of the plasma-enabled hydrogenation has been verified by the experiment, which highlighted the competition between the radical recombination and radical-aromatic ring interactions. Overall, the revealed interaction mechanisms between the plasma-generated radicals and ethylbenzene provide new insights and guiding principles for the future upgrading of heavy oils and other industrial hydrocarbon products. [ABSTRACT FROM AUTHOR]

Transitions between the streamer and spark modes affect the stability of gas–liquid discharges, limiting their practical applications, while the nature of such transitions is poorly understood. Here we clarify the often neglected effect of a dielectric on the gas–liquid discharge stability, using direct and indirect grounding configurations. Discharge modes and plasma characteristics in these two configurations are investigated. The discharge appears in a transient spark mode in the direct grounding while in a streamer mode in the indirect case. It is shown that the dielectric significantly improves the discharge stability. The gas temperature and electron density in the transient spark are 380 K and 1017/cm3 with a 30 kV pulse voltage, respectively, which are higher than those in the streamer mode. [ABSTRACT FROM AUTHOR]

Homogeneous penetration of atmospheric pressure uniform air plasma (APUAP) into thin gaps is highly warranted for multipurpose processing of materials. Here, we report APUAP generation in a 7 mm discharge gap with ambient air as the working gas, well beyond the presently maximum achievable 4 mm. Driven by a short pulse high voltage power, a 7 mm wide and 60 mm long uniform air plasma sheet is generated. The discharge is robust and the uniformity is not affected by the complex and variable components of ambient air, as is the case for most plasma discharges in air. Ultrafast photography shows that, different from previous reports, the discharge initiates in the whole air gap simultaneously and brightens quickly with the fast rise of the pulsed voltage. The generation of uniform plasma is mainly attributed to the high density of seed electrons and the reduced number density of molecules in air. Moreover, the achievable gas temperature of up to 1300 K indicates that this type of plasma is suitable for processing of a broad range of materials. [ABSTRACT FROM AUTHOR]

• HDP reactor formed plasma discharges in both electrodes with a single power source. • PAW was generated with high energy efficiency and a very fast inactivation rate. • Decreasing the orifice diameter of the HPD reactor increased the energy efficiency. • Increasing salinity enhanced the energy efficiency to 0.181 mol·kW−1·h−1. • 5.18-log 10 reduction of Escherichia coli inactivation was achieved in 30 s. Plasma-activated water (PAW), an emerging and cost-effective disinfectant produced from the interaction between non-thermal plasma and water, was generated with a newly designed hybrid plasma discharge (HPD) reactor. The HPD reactor produces two simultaneous plasma discharges within one power source, one from the high-voltage electrode above the liquid surface, and the other from the ground electrode enclosed in a quartz tube, allowing the air to flow through the side of the ground electrode and injecting plasma bubbles into the liquid. The simulated distributions of electric field indicated that high electric fields were induced around both the high voltage and ground electrodes, at high input voltages, explaining the plasma discharges observed on both electrodes. The PAW generated via the HPD reactor achieved a high RONS energy efficiency of 1.81 × 10-1 mol·kW−1·h−1 and a high inactivation against Escherichia coli of 5.18-log 10 reduction in 30 s of contact time, outperforming reported literature studies, which require minutes or hours to achieve similar inactivation. The effect of the number and size of orifices in the bubble column of the HPD reactor was studied, as well as the effect of the liquid volume (from 0.5 to 2 L), and salinity (from 0 to 8 mM NaCl). The Escherichia coli in PAW was further analysed by TEM and DNA leakage showing that PAW damaged the cell membrane. This hybrid plasma discharge reactor can be the base of producing disinfectant PAW in larger volume for the agriculture, biomedical, food and water treatment industries. [ABSTRACT FROM AUTHOR]