High-pressure high-temperature (HPHT) nanodiamonds originate from grinding of diamond microcrystals obtained by HPHT synthesis. Here we report on a simple two-step approach to obtain as small as 1.1 nm HPHT nanodiamonds of excellent purity and crystallinity, which are among the smallest artificially prepared nanodiamonds ever shown and characterized. Moreover we provide experimental evidence of diamond stability down to 1 nm. Controlled annealing at 450 °C in air leads to efficient purification from the nondiamond carbon (shells and dots), as evidenced by X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and scanning transmission electron microscopy. Annealing at 500 °C promotes, besides of purification, also size reduction of nanodiamonds down to ∼1 nm. Comparably short (1 h) centrifugation of the nanodiamonds aqueous colloidal solution ensures separation of the sub-10 nm fraction. Calculations show that an asymmetry of Raman diamond peak of sub-10 nm HPHT nanodiamonds can be well explained by modified phonon confinement model when the actual particle size distribution is taken into account. In contrast, larger Raman peak asymmetry commonly observed in Raman spectra of detonation nanodiamonds is mainly attributed to defects rather than to the phonon confinement. Thus, the obtained characteristics reflect high material quality including nanoscale effects in sub-10 nm HPHT nanodiamonds prepared by the presented method.

The aqueous-phase chemistry of reactive chlorine species initiated in saline solution by the gas phase discharge plasma above the liquid surface was investigated. A micro-atmospheric pressure 13.56 MHz plasma jet operating with a 0.6% O 2 in He was used to promote reactions of plasmagenerated oxygen atoms with chloride anions at the gas-liquid interface. Physiological NaCl solution and phosphate buffered saline (PBS) were used. Three chlorine oxoacids or their conjugate bases were detected in the plasma treated saline: hypochlorites HOCl/OCl − , chlorites ClO 2 − , and chlorates ClO 3 − , being formed in the concentration ratio 4.5:1:1, respectively. In addition, chlorine dioxide ClO 2 was formed in minor amounts. The final pH value of the plasma treated saline was typically 10.2. The total hypochlorite production, [HOCl]+[OCl − ], was directly proportional to the initial NaCl concentration, supporting the idea of a direct reaction of Cl − with O atoms. Subsequent post-discharge chemical processes in the bulk plasma treated saline solution were found to lead to the disproportionation of hypochlorite into different oxidation states of chlorine with formation of ClO 3 − as the final product. The reactivity of O atoms in NaCl solution was studied using taurine and phenol as chemical probes. Experiments with 50 mM taurine revealed a very high initial formation rate of OCl − in PBS (up to 4 μM s −1 ). Chlorinated products of phenol (2and 4-chlorophenol) in addition to the hydroxylated products (hydroquinone and catechol) demonstrated chlorination of phenol by hypochlorite. The rate of Cl − oxidation by O atoms was estimated to be 2-3 orders slower than the reaction of O atoms with phenol.

Reactions accompanying the hypochlorite formation in Cl− solutions oxidized by plasma-supplied O atoms were studied. The concentration of oxychlorine compounds from reaction of O atoms with solutions of NaCl, NaOCl and NaClO2 was measured. The concentration dependence of O + Cl− reaction rate was evaluated using the simplified kinetic model leading to estimation of the 2nd order rate constant, k = 1.64 ± 0.01 × 105 M−1s−1. The limiting reaction rate at highly concentrated NaCl corresponds well with the delivery rate of O atoms to the gas-liquid interface calculated from the previously measured O concentration at the plasma jet outlet. Virtually all plasma-supplied O atoms can be captured by Cl− ions in highly concentrated solutions. The measurements confirmed the reactions O + OCl−, and O + ClO2 − as loss channels decreasing the hypochlorite production in O-treated Cl− solutions. These loss channels are less effective at more acidic pH, where the formation of ClO2 − is minimized and as a consequence, also the solution post-discharge reactivity. The validity of described reaction system was confirmed by chemical kinetics modelling. The fitted rate coefficients for the O reactions with ionic Cl forms were 3–4 orders of magnitude lower than those predicted in the literature.

The formation mechanisms of hydrogen peroxide due to the interaction of oxygen atom from the cold atmospheric plasmas in contact with water are not fully understood. Previous work on molecular dynamics (MD) simulations of interactions of O atoms in bulk water based on reactive force field and density-functional tight-binding method did not observe the formation of H 2 O 2 . In this work we applied density functional theory in MD simulations of 192 trajectories considering 63H 2 O−O system to explore the reaction mechanisms for atomic oxygen radical in water. Our calculations revealed that triplet (ground) state oxygen was not reactive. Oxywater-similar structure O − OH 2 was a transient product. Perhydroxyl anion O − OH − and its counterpart hydronium H 3 O + were formed. In most of simulated cases, hydrogen peroxide was observed as a final product. The formation pathways of hydrogen peroxide exhibited large complexities for the simple hydrogen bonded system. According to the sources and pathways of the hydrogen atom being bonded in hydrogen peroxide molecule, mechanisms can be classified into (1) hydrogen-abstraction, (2) hydrogen-transfer n (n = 3, 4, 5, 6, 7, 8), (3) proton-delivery n = 2, 3, (4) proton-transfer. It was confirmed that for correct prediction of reaction mechanisms is better to use quantum molecular dynamic simulations.

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We studied the chemical and bactericidal properties of plasma-modified amino acid leucine (Leu) treated in phosphate-buffered saline (PBS) using an atmospheric-pressure plasma jet operating with He/O2 gas. We determined the initial formation of hypochlorite by the reaction of plasma-supplied O atoms with chloride ions in PBS, followed by the subsequent chlorination of Leu. The principal chemical process involved the formation of Leu monochloramine and Leu dichloramine. The products of plasma-modified Leu further possessed post-discharge reactivity characterized by the decay of Leu chloramines to the secondary products, i.e. isovaleraldehyde, isovaleronitrile, and N-chloromethyl-3-butaldimine. Our study of the effects of Leu on the viability of Escherichia coli bacteria in the plasma-treated PBS solution demonstrated time-and pH-dependent cytotoxic behavior, which were associated with the formation of different reaction products. At shorter treatment times, the addition of Leu hindered the bactericidal properties of plasma-treated PBS caused by the consumption of bactericidal hypochlorite in reaction with Leu and formation of non-bactericidal Leu monochloramine. Acidification to pH = 3 and longer plasma treatment substantially enhanced the bactericidal effects of Leu solutions, which were tentatively assigned to the formation of Leu dichloramine.

Due to extraordinary properties and biocompatibility, diamond nanoparticles -nanodiamonds (NDs) are considered for various biomedical applications. Amongst other functional groups which may be grafted on the NDs surface, the amines (NH x ) are highly demanded linkers for biomolecules and dyes. In this regard, a non-destructive, non-hazardous and low-cost method of NDs amination would further accelerate their industrial applications in biomedicine and life science. Here we present a study on NDs treatment using diffuse coplanar surface barrier discharge in the gas mixture H 2 :N 2 ¼ 1:1 at the atmospheric pressure. Detonation and high pressure-high temperature nanoparticles (D-NDs and HPHT-NDs) were used either as-received or air-annealed. The FTIR spectra confirmed the presence of N-H stretching vibrations for all kinds of NDs after the treatment. It was revealed by XPS and FTIR measurements that both kinds of D-NDs (as-received and air-annealed) exhibited higher content of ÀNH 2 functions in the detected nitrogen groups than HPHT-NDs. The treatment of as-received D-NDs led to the conversion of ÀCOOH groups to amides. A large increase of C-H bonds after the discharge treatment was found, especially for the annealed NDs forms. Raman spectroscopy revealed a decrease of sp 2 carbon after the treatment of the as-received HPHT-NDs.

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