A derivative absorption spectroscopic method is used in situ to simultaneously trace and quantify the aqueous peroxide (H2O2), nitrate () and nitrite () generated during plasma–liquid interactions. The results indicate that the time evolutions of H2O2, and generated from the plasma–liquid interactions strongly depend on the solution’s pH value, which varies with the plasma treatment. The concentrations of aqueous H2O2, and increase independently from each other during the plasma treatment when the solution’s pH value is higher than 3.0. However, when the solution’s pH value is less than 3.0, most of the aqueous (~71.5%) will exist in the form of molecular nitrous acid since the pKa of nitrous acid is 3.4, the aqueous is mainly formed from the reaction between H2O2 and as well as the decomposition of molecular HNO2, which leads to a continuous increase of concentration and an appearance of the maximum concentrations of H2O2 and as the pH value of the solution reaches 3.0.

Hydroxyl (OH) radical is the most important reactive species produced by the plasmaliquid interactions, and the OH in the liquid phase (dissolved OH radical, OHdis) takes effect in many plasma-based applications due to its high reactivity. Therefore, the quantification of the OHdis in the plasma-liquid system is of great importance, and a molecular probe method usually used for the OHdis detection might be applied. Herein we investigate the validity of using the molecular probe method to estimate the [OHdis] in the plasma-liquid system. Dimethyl sulfoxide is used as the molecular probe to estimate the [OHdis] in an air plasma-liquid system, and the partial OHdis is related to the formed formaldehyde (HCHO) which is the OHdis-induced derivative. The analysis indicates that the true concentration of the OHdis should be estimated from the sum of

Silver nanoparticles (AgNPs) are synthesized in a plasma electrochemical system with an aqueous solution of AgNO 3 as anode. 5-Bromouracil, ethanol and dimethyl sulfoxide are added to the solutions for tuning the plasma-induced liquid chemistry. The characteristic localized surface plasmon resonance of the AgNPs is used to investigate the AgNPs formation process. The results indicate that there exists Ag + reduction and Ag oxidation simultaneously during the AgNPs formation, and the hydrated electrons formed by the dissolution of plasma electrons are the main reducing agents for the Ag + reduction, while the hydrogen peroxide produced by the plasma-liquid interactions plays a role in etching the formed AgNPs to Ag + .

Due to the complicated nature of carbon dots (CDs), fluorescence mechanism of red fluorescent CDs is still unrevealed and features highly controversial. Reliable and effective strategies for manipulating the red fluorescence of CDs are urgently needed. Herein, CDs with one‐photon excited (622 nm, QYs ≈ 17%) and two‐photon (629 nm) excited red fluorescence are prepared by acidifying o‐phenylenediamine‐based reaction sediments. Systematic analysis reveals that the protonation of amino groups increases the particle surface potential, disperse the bulk sediments into nano‐scale CDs. In the meanwhile, amino protonation of pyridinic nitrogen (–N=) structure inserts numerous n orbital energy levels between the π → π* transition, narrows the gap distance for photon transition, and induces red fluorescence emission on CDs. Present research reveals an effective pathway to activate CDs reaction sediments and trigger red emission, thus may open a new avenue for developing CDs with ideal optical properties and promising application prospects.

Based on the Stark broadening method and the imaging method, the electron densities of the plasma generated at different pulse frequencies, gap distances and inner diameters of the electrodes are diagnosed. The experimental results indicate that reducing the pulse frequency, shortening the gap distance between the electrodes, and using thinner diameter electrode are all in favor of enhancing the electron density. With the help of the global model, we perform the numerical simulation to explore the factors that influence the variation of the electron density. According to the simulations results, we find that the reduced discharge volume results in the increase of electron density with the increase of pulse frequency. When the gap distance between the electrodes is reduced, although the increased absorbed power and the reduced discharge volume both have an effect on the electron density, the reduced discharge volume plays a decisive role in these two factors. Moreover, using a thinner inner diameter electrode can also reduce the discharge volume, which is of benefit to obtaining the plasma with high electron density.

Treatment of methyl orange (MO) synthetic wastewater by air discharge plasma was investigated, and the solution's pH value was found to be a key parameter of influencing the treatment efficiency. The results indicate that lower pH value can induce production of high reactive species, NO+ and peroxynitrous acid, which can contribute to the MO decomposition. When the appropriate amount of Fe2+ ions is present in the MO solution, the MO decomposition can be promoted by Fenton's reaction (Fe2+ reacts with H2O2 produced from the plasma–liquid interaction). Furthermore, the lower pH value is also beneficial for the Fenton's reaction by avoiding an appearance of Fe(OH)3 precipitate that can reduce the treatment efficiency.

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An efficient microplasma chemistry method to synthesize highly stable Ag nanoparticles (AgNPs) that can be stored for 2 months is presented. The sucrose, maltose, lactose, and glucose are applied to stablize the produced AgNPs, respectively, and the pH value of the solution is controlled by using NaHCO 3 with different concentrations. It can be concluded that AgNPs with different sizes can be achieved by selecting different stabilizers and adjusting the pH value of solution. Finally, by checking the UV absorbance of AgNPs solution within 2 months, the stability of the AgNPs is investigated. It is found that the stability of AgNPs in water solution can also be improved by changing the pH of the solution and the kind of colloidal stabilizer.