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Graphene quantum dots (GQDs) were synthesized by a facile one-step wet chemically derived from carbon fibers. A novel, sensitive, simple, and convenient method for the detection of tert-butylhydroquinone (TBHQ) was established based on GQDs and silver nanoparticle (AgNP) modified electrode. The modified electrode exhibited excellent electrocatalytic performance toward the electrochemical detection of TBHQ. Meanwhile, a possible reaction mechanism related to the oxidation of TBHQ was proposed. The electron transfer number and electron transfer coefficient were found to be 3.05 and 0.40. The surface concentration of TBHQon GQD/AgNP-modified electrode was calculated as 2.62 x [10.sup.-10] mol [cm.sup.-2]. Under the optimum conditions, a good linear relationship between peak current and the concentration of TBHQ was obtained in the range of 0.15-300 [micro]mol [L.sup.-1] with a detection limit of 0.07 [micro]mol [L.sup.-1] (S/N =3). The proposed method was successfully applied for the detection of TBHQin edible vegetable oil. Key words: graphene quantum dots, silver nanoparticles, tert-butylhydroquinone, modified electrode, edible vegetable oil. Nous avons synthetise des boites quantiques de graphene a partir de fibres de carbone par un procede chimique humide en une etape facile. Nous avons etabli une nouvelle methode sensible, simple et pratique pour la detection de la tert-butylhydroquinone (TBHQ) au moyen d'une electrode modifiee a base de boites quantiques de graphene et de nanoparticules d'argent. Nous avons observe que la performance electrocatalytique de l'electrode modifiee pour la detection electrochimique de la TBHQ etait excellente. Parallelement, nous avons propose un mecanisme de reaction possible pour l'oxydation de la TBHQ. Nous avons obtenu un nombre de transferts d'electrons de 3,05 et un coefficient de transfert d'electrons de 0,40. La concentration de TBHQ a la surface de l'electrode modifiee a base de boites quantiques de graphene et de nanoparticules d'argent a ete calculee a 2,62 x [10.sup.-10] mol [cm.sup.-2]. En conditions optimales, nous avons obtenu une bonne linearite entre le courant de pic et la concentration de TBHQ dans l'intervalle de 0,15 a 300 [micro]mol [L.sup.-1], avec une limite de detection de 0,07 [micro]mol [L.sup.-1] (rapport signal/bruit = 3). La methode proposee a ete appliquee avec succes a la detection de la TBHQ dans l'huile vegetale comestible. [Traduit par la Redaction] Mots-cles: boites quantiques de graphene, nanoparticules d'argent, tert-butylhydroquinone, electrode modifiee, huile vegetale comestible., Introduction Graphene quantum dots (GQDs), graphene sheets with lateral sizes less than 100 nm, have several unique properties over micrometre-sized graphene and graphene oxide sheets. (1) As a new type [...]

Abstract: Free radicals play an important role in the oxidizing power of polluted air, the development of aging‐related diseases, the formation of ozone, and the production of secondary particulate matter. The high variability of peroxyl radical concentration has prevented the detection of possible trends or distributions in the concentration of free radicals. We present a new method, free radical reaction combined with liquid chromatography photodiode array detection, for identifying and quantifying peroxyl radicals in polluted air. Functionalized graphene was used for loading peroxyl radicals and reactive molecules in air sampling system, which can facilitate reaction kinetics (charge transfers) between peroxyl radicals and reaction molecules. Separation was performed with and without a preliminary exposure of the polluted air sample to reactive molecule(s) system. The integral chromatographic peak areas before and after air sampling are used to quantify the atmospheric peroxyl radicals in polluted air. The utility of the new technique was tested with measurements carried out in the field. [ABSTRACT FROM AUTHOR]

A novel screening method was developed for the detection and identification of radical scavenging natural antioxidants based on a free radical reaction combined with liquid chromatography with tandem mass spectrometry. Functionalized graphene quantum dots were prepared for loading free radicals in the complex screening system. The detection was performed with and without a preliminary exposure of the samples to specific free radicals on the functionalized graphene quantum dots, which can facilitate charge transfer between free radicals and antioxidants. The difference in chromatographic peak areas was used to identify potential antioxidants. This is a novel approach to simultaneously evaluate the antioxidant power of a component versus a free radical, and to identify it in a vegetal matrix. The structures of the antioxidants in the samples were identified using tandem mass spectrometry and comparison with standards. Fourteen compounds were found to possess potential antioxidant activity, and their free radical scavenging capacities were investigated. The order of scavenging capacity of 14 compounds was compared according to their free radical scavenging rate. 4′,5,6,7-Tetrahydroxyflavone (radical scavenging rate: 0.05253 mL mg−1 s−1) showed the strongest capability for scavenging free radicals. [ABSTRACT FROM AUTHOR]

Abstract: A graphene sheets (GS), ionic liquid (IL) and chitosan (CS) modified electrode was fabricated and the modified electrode displayed excellent electrochemical catalytic activities toward guanine and adenine. The transfer electron number (n) and the charge transfer coefficient (α) were calculated with the result as n =2, α =0.58 for guanine, and n =2, α =0.51 for adenine, which indicated the electrochemical oxidation of guanine and adenine on GS/IL/CS modified electrode was a two-electron and two-proton process. The oxidation overpotentials of guanine and adenine were decreased significantly compared with those obtained at the bare glassy carbon electrode and multi-walled carbon nanotubes modified electrode. The modified electrode exhibited good analytical performance and was successfully applied for individual and simultaneous determination of guanine and adenine. Low detection limits of 0.75μM for guanine and 0.45μM for adenine were obtained, with the linear calibration curves over the concentration range 2.5–150μM and 1.5–350μM, respectively. At the same time, the proposed method was successfully applied for the determination of guanine and adenine in denatured DNA samples with satisfying results. Moreover, the GS/IL/CS modified electrode exhibited good sensitivity, long-term stability and reproducibility for the determination of guanine and adenine. [Copyright &y& Elsevier]

We load the natural active molecules onto the spin film in an array using electrospinning techniques. The electrospun active molecular membranes we obtain in optimal parameters exhibit excellent capacity for scavenging radical. The reaction capacity of three different membranes for free radicals are shown as follow, glycyrrhizin acid membrane > quercetin membrane > α-mangostin membrane. The prepared active molecular electrospun membranes with a large specific surface area and high porosity could increase the interaction area between active molecules and free radicals. Additionally, it also has improved anti-airflow impact strength, anti-contaminant air molecular interference ability, and the ability to capture free radicals. [ABSTRACT FROM AUTHOR]

Abstract Atmospheric particulate pollution in China has attracted much public attention. Occasionally, the particle number concentration increases sharply in a short time period, which is defined as a "particulate matter explosive increase". Heavy particulate matter pollution not only reduces visibility but also has an adverse effect on human health. Hence, there is an urgent need to discover the causes of particulate matter explosive increase. During this campaign, the particle number concentration and free radicals were measured at a tall building on the campus of Lanzhou University of Technology. Additionally, we examined a series of chemicals to reproduce the observed particulate matter explosive increase in a smog chamber to determine its potential factors. Then, we analyzed the mechanism of particulate matter explosive increase in the presence of free radicals. We found that, among the potential inorganic and organic sources analyzed, a mixture of organic and SO 2 in the research region had a major effect on particulate matter explosive increase. Moreover, free radical oxidation has a large effect, especially in the formation of organic particulates. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Free radicals are the most important chemical intermediate or agent of the atmosphere and influenced by thousands of reactants. The free radicals determine the oxidizing power of the polluted air. Various gases present in smog or haze are oxidants and induce organ and cellular damage via generation of free radical species. At present, however, the high variability of total free radicals in polluted air has prevented the detection of possible trends or distributions in the concentration of those species. The total free radicals are a kind of contaminants with colorless, tasteless characteristics, and almost imperceptible by human body. Here we present total free radical detection and distribution characteristics, and analyze the effects of total free radicals in polluted air on human health. We find that the total free radical values can be described by not only a linear dependence on ozone at higher temperature period, but also a linear delay dependence on particulate matter at lower temperature period throughout the measurement period. The total free radical species distribution is decrease from west to east in Lanzhou, which closely related to the distribution of the air pollutants. The total free radical oxidation capacity in polluted air roughly matches the effects of tobacco smoke produced by the incomplete combustion of a controlled amount of tobacco in a smoke chamber. A relatively unsophisticated chromatographic fingerprint similarity is used for indicating preliminarily the effect of total free radicals in polluted air on human health. [ABSTRACT FROM AUTHOR]

The hydroxyl radical (•OH) has a crucial function in the oxidation and removal of many atmospheric compounds that are harmful to health. Nevertheless, high reactivity, low atmospheric abundance, determination of hydroxyl, and hydroperoxyl radical's quantity is very difficult. In the atmosphere and troposphere, hydroperoxyl radicals (HO 2) are closely demanded in the chemical oxidation of the troposphere. But advances in technology have allowed researchers to improve the determination methods on the research of free radicals through some spectroscopic techniques. So far, several methods such as laser-induced fluorescence (LIF), high-performance liquid chromatography (HPLC), and chemical ionization mass spectroscopy have been identified and mostly used in determining the quantity of hydroxyl and hydroperoxyl radicals. In this systematic review, we have advised the use of scavenger as an advance for further researchers to circumvent some of these problems caused by free radicals. The primary goal of this review is to deepen our understanding of the functions of the most critical free radical (•OH, HO 2) and also understand the currently used methods to quantify them in the atmosphere and troposphere. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Hydroxyl free radicals (OH radicals) play the main role in atmospheric chemistry and their involving reactions are the dominant rate determining step in the formation of secondary fine particulate matter and in the removal of air pollutants from the atmosphere. In this paper, we studied the seasonal variation characteristics of OH radicals during the daytime in Lanzhou and explored the potential formation mechanism of high concentration OH radicals. We found that the OH radicals in four seasons was 2.7 × 106, 2.6 × 106, 3.1 × 106, and 2.2 × 106 cm−3, respectively. Since the rainfall was concentrated in summer, the wet deposition had a significant effect on removing OH radicals. Among the four pollutants (including ozone (O 3), volatile organic compounds (VOCs), nitrogen dioxide (NO 2) and fine particulate matter (PM 2.5)), the variation of OH radicals were closely related to ozone concentration especially in spring and summer. In autumn, the correlation between PM 2.5 and OH radicals were the closest among the observing pollutants and its formation mechanism was different conventional regeneration pathway. In Event 1, high concentration of ozone was the main source of OH radicals; under the high humidity condition, except for ozone, the multiple factors including VOCs, NO 2 and PM 2.5 interplayed and leaded to the Event 2. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In the troposphere, the knowledge about nitrous acid (HONO) sources is incomplete. The missing source of sulfate and fine particles cannot be explained during haze events. Air quality models cannot predict high levels of secondary fine-particle pollution. Despite extensive studies, one challenging issue in atmospheric chemistry is identifying the source of HONO. Here, we present direct ab initio molecular dynamics simulation evidence and typical air pollution events of the formation of gaseous HONO, nitrogen dioxide/hydrogen sulfite (HOS(O)2-NO 2 or NO 2 -HSO 3 ) from nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), water (H 2 O), and ammonia (NH 3 ) molecules in a proportion of 2:1:3:3. The reactions show a new mechanism for the formation of HONO and NO 2 -HSO 3 in the troposphere, especially when the concentration of NO 2 , SO 2 , H 2 O, and NH 3 is high (e.g., 2:1:3:3 or higher) in the air. Contrary to the proportion NO 2 , SO 2 , H 2 O, and NH 3 equaling to 1:1:3:1 and 1:1:3:2, the proportion (2:1:3:3) enables barrierless reactions and weak interactions between molecules via the formation of HONO, NO 2 -HSO 3 , and NH 3 /H 2 O. In addition, field observations are carried out, and the measured data are summarized. Correlation analysis supported the conversion of NO 2 to HONO during observational studies. The weak interactions promote proton transfer, resulting in the generation of HONO, NO 2 -HSO 3 , and NH 3 /H 2 O pairs.