Chronoamperometric study of elemental sulphur (S) nanoparticles (NPs) in NaCl water solution: new methodology for S NPs sizing and detection

Abstract

BackgroundElemental sulfur (S) persists in natural aquatic environment in a variety of forms with different size distributions from dissolved to particulate. Determination of S speciation mainly consists of the application of chromatographic and electrochemical techniques while its size determination is limited only to the application of microscopic and light scattering techniques. S biological and geochemical importance together with recent increases of S industrial applications requires the development of different analytical tools for S sizing and quantification. In recent years the use of electrochemical measurements as a direct, fast, and inexpensive technique for the different nanoparticles (NPs) characterization (Ag, Au, Pt) is increasing. In this work, electrochemical i.e. chronoamperometric measurements at the Hg electrode are performed for determination of the size distribution of the S NPs.ResultsS NPs were synthesized in aqueous medium by sodium polysulphide acidic hydrolysis. Chronoamperometric measurements reveal the polydisperse nature of the formed suspension of S NPs. The electrochemical results were compared with dynamic light scattering measurements parallel run in the same S NPs suspensions. The two methods show fairly good agreement, both suggesting a log-normal size distribution of the S NPs sizes characterized by similar parameters.ConclusionsThe preliminary results highlight the amperometric measurements as a promising tool for the size determination of the S NPs in the water environment.

Oxidation of arsenite to arsenate on birnessite in the presence of light

“…This lack of quantifiable adsorbed arsenic could be due to the Na-birnessite sample possessing a small concentration of cation vacancies, which is the favored site for metal ions to sorb [ 39 , 57 ]. This observation agrees with a recent study that investigated As(III) oxidation on different manganese oxides in which the experimental observation that crystalline triclinic birnessite did not adsorb observable amounts of As was also made [ 14 ]. Results from a different batch of Na-birnessite synthesized in our laboratory exhibited a higher surface area (HSA birnessite, 23.10 m 2 g −1 ) and led to an increased amount of As(V) adsorption during the As(III) oxidation reaction.…”

“…The simulated light intensity used in this study is comparable to the light intensity experienced by the Earth’s surface environment (i.e., 1.45 suns). The photochemical pathways presented in this contribution are informed by the many prior studies that have investigated the adsorption and oxidation of As(III) on birnessite [ 4 , 14 , 23 – 27 ] under dark conditions. We propose that the creation of the hole-electron pair during the irradiation of the small band-gap semiconductor drives the oxidation chemistry; the valence band hole leads to the oxidation of As(III) and the conduction band electron leads to the reduction of Mn(IV)/Mn(III) and the formation of Mn(II) product.…”

“…Unlike TiO 2 and iron oxyhydroxides, birnessite, the focus of the current study, can facilitate the oxidation of As(III) to As(V) in the absence of light [ 4 , 14 ]. Birnessite, a layered manganese oxide containing both Mn 3+ and Mn 4+ within its structure, is composed of edge sharing MnO 6 octahedra arranged into stacked sheets that are separated by cations [ 4 , 14 ]. Depending on the position of the Mn 3+ within the structure, triclinic or hexagonal birnessite can result.…”

“…Interlayer regions can also contain Mn(II), other metal cations (M + /M 2+ ) and H 2 O [ 17 – 19 ]. Both of these phases of birnessite have been found to facilitate the oxidation of As(III) to As(V) in the absence of light [ 4 , 14 , 20 – 27 ] as presented in the following composite reaction: …”

Bio‐inspired synthesis of sulphur nanoparticles using leaf extract of four medicinal plants with special reference to their antibacterial activity

“…They reported monoclinic spherical sulphur nanoparticles with average crystallite size 20 nm. There are different techniques for synthesis of nanoparticles: for example, by using sodium polysulphide hydrolysis method [15], unique membrane‐assisted precipitation technique [5], water‐in‐oil microemulsion method [16], liquid phase precipitation method [17] etc. Most of the above techniques involve chemical and physical approaches, but the green biological methods have attracted the attention of researchers towards the development of an eco‐friendly, unique biological approach for rapid and mass level synthesis of sulphur nanoparticles.…”