Selenium Nanowire Formation by Reacting Selenate with Magnetite

The mobility of ⁷⁹Se, a fission product of ²³⁵U and long-lived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se(VI)O₄^2-) and selenite (Se(IV)O₃^2-) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids. Here, we investigated the sorption and reduction capacity of synthetic nanomagnetite toward Se(VI) at neutral and acidic pH, under reducing, oxygen-free conditions. The additional presence of Fe(II)_aq, released during magnetite dissolution at pH 5, has an effect on the reduction kinetics. X-ray absorption spectroscopy analyses revealed that, at pH 5, trigonal gray Se(0) formed and that sorbed Se(IV) complexes remained on the nanoparticle surface during longer reaction times. The Se(0) nanowires grew during the reaction, which points to a complex transport mechanism of reduced species or to active reduction sites at the tip of the Se(0) nanowires. The concomitant uptake of aqueous Fe(II) and Se(VI) ions is interpreted as a consequence of small pH oscillations that result from the Se(VI) reduction, leading to a re-adsorption of aqueous Fe(II) onto the magnetite, renewing its reducing capacity. This effect is not observed at pH 7, where we observed only the formation of Se(0) with slow kinetics due to the formation of an oxidized maghemite layer. This indicates that the presence of aqueous Fe(II) may be an important factor to be considered when examining the environmental reactivity of magnetite.

Selenium and tellurium-based nanoparticles as interfering factors in quorum sensing-regulated processes: violacein production and bacterial biofilm formation

A cell-to-cell communication system called quorum sensing (QS) promotes the transcription of certain target genes in bacterial cells leading to the activation of different cellular processes, some of them related to bacterial biofilm formation. The formation of bacterial biofilms favours antibiotic resistance, which is nowadays a significant public-health problem. In this study, the effect of selenium (SeNPs) and tellurium (TeNPs) nanoparticles was examined in two bacterial processes mediated by QS: violacein production by Chromobacterium violaceum and biofilm formation by Pseudomonas aeruginosa. For this purpose, quantification of the pigment production in the presence of these nanoparticles was monitored using the C. violaceum strain. Additionally, a combination of different microscopical imaging techniques was applied to examine the changes in the 3D biofilm structure of P. aeruginosa, which were quantified through performing architectural metric calculations (substratum area, cell area coverage and biovolume). SeNPs produce an 80% inhibition in the violacein production by C. violaceum and a significant effect on the P. aeruginosa biofilm architecture (a reduction of 80% in the biovolume of the bacterial biofilm was obtained). TeNPs similarly affect violacein production and the P. aeruginosa biofilm structure but at lower concentration levels. The results obtained suggest an important disruption of the QS signalling system by SeNPs and TeNPs, supporting nanotechnology as a promising tool to fight against the emerging problem of bacterial resistance related to bacterial biofilm formation.

Fate and effect of in-house synthesized tellurium based nanoparticles on bacterial biofilm biomass and architecture. Challenges for nanoparticles characterization in living systems

The unexpected impact of nanoparticles on environment and human health remains as a matter of concern. In this sense, understanding the interaction between nanoparticles and biological indicators such as microorganism may help to understand their fate and effect in environmental systems. However, the adverse effect of nanoparticles greatly depends on their properties and, therefore, a precise evaluation of nanoparticles physicochemical characteristics is mandatory as the first step in accurately elucidating their behaviour in different ecosystems. Here in this work, in house-synthesized tellurium-based nanoparticles have been fully characterized for first time by means of a multi-method approach. Once characterized, the effect of these nanoparticles on Staphylococcus aureus and Escherichia coli biofilm biomass and structure was explored and quantified for first time. Moreover, the morphological transformations of tellurium based nanoparticles within the confines of a biofilm are also highlighted. Architectural metric calculations evidenced that nanoparticles were able to reduce the biovolume of the biofilm produced for both bacteria. Interestingly, the interaction between nanoparticles and bacterial communities led to the transformation of tellurium nanoparticles from sphere to rod-shaped nanoparticles. These findings open new insights into the behaviour of a type of uncommon nanoparticles such as tellurium-based nanoparticles on microbial communities.

Selenite reduction by the rhizobacterium Azospirillum brasilense, synthesis of extracellular selenium nanoparticles and their characterisation

Microbial reduction of selenium oxyanions has attracted attention in recent years. In this study, an original and simple method for the synthesis of extracellular selenium nanoparticles (Se NPs) of relatively uniform size has been developed using strains Sp7 and Sp245 of the ubiquitous plant-growth promoting rhizobacterium Azospirillum brasilense, both capable of selenite (SeO₃^2-) reduction. In addition, a reliable purification protocol for the recovery of the Se NPs has been perfected, which could be applied with minor modifications to cultures of other microbial species. Importantly, it was found that, by changing the conditions of bacterial reduction of selenite, extracellularly localised Se NPs can be obtained using bacteria which would otherwise produce intracellular Se NPs. In particular, bacterial cultures grown up to the end of the logarithmic growth phase, washed free of culture medium and then incubated with selenite, were used to obtain extracellular Se NPs. Their sizes depended on the initial selenite concentration (∼25-80 nm in diameter at 50-10 mM selenite, respectively). The Se NPs obtained were characterised by transmission electron microscopy (TEM), dynamic light scattering, as well as Raman and UV-vis spectroscopies. Their zeta potential was found to be negative (ca. minus 21-24 mV). Bacterial selenite reduction was also studied in the presence of the efflux pump inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP). In this case, TEM indicated the formation only of intracellular selenium crystallites. The data show that the formation of extracellular Se NPs requires normal bacterial metabolic activity, while CCCP evidently blocks the membrane export of Se⁰ nuclei.

Controlling the phase and morphology of amorphous Se nanoparticles: their prolonged stabilization and anticancer efficacy

Resolving issues related to the synthesis and stabilization of amorphous selenium nanoparticles: recycling of a matrix and promising biological applications.

Bond-Energy-Driven, Low- or High-Angle-Grain-Boundary-Movement-Mediated Synthesis of Porous Se-Te for Use in Water-Splitting Reactions

Herein, for the first time, we applied the metal-metal-bond-energy factor to the evolution of a porous Se-Te alloy. The porous Se-Te material has been prepared from the constituents' elemental states, through only a heating-cooling process in silicone oil without the use of any reagent, surfactant, or capping agent. Surprisingly, the reaction occurred at a much lower temperature (240 °C) than the mp (450 °C) of Te⁰. The reaction's nucleation and growth by means of varied bond energy have been clarified for the first time. A difference in the bond energies of a hetero metal-metal bond (Se-Te) and a homo metal-metal bond (Se-Se) directs nucleation and growth toward the fabrication of a porous structure, even from the constituents' elemental states, in which low-angle-grain-boundary (LAGB) and high-angle-grain-boundary (HAGB) movements play governing roles. Proper band-gap alignment of Se and Te makes the alloy composite applicable to water-splitting reactions under Xe-arc-lamp illumination. PEC efficiency of Se-Te was found to be higher than those reported for Se and other composite materials.

Dissolution behaviour and activation of selenium in phosphonium based ionic liquids

The dissolution behaviour of grey selenium in phosphonium based ionic liquids (ILs) has been investigated for the first time by ³¹P and ⁷⁷Se nuclear magnetic resonance (NMR) experiments.

In situ SeO2promoted synthesis of CdSe/PPy and Se/PPy nanocomposites and their utility in optical sensing for detection of Hg2+ions

The reaction of selenium dioxide, a mild oxidizing agent, leads to the initiation of polymerization of pyrrole. The presence of cadmium metal can generate CdSe/PPy nanocomposites however, without it, Se/ PPy composites have been isolated.

High-efficiency photocatalytic activity of type II SnO/Sn3O4 heterostructures via interfacial charge transfer

Flower-like hollow microspheres were synthesized on a large scale using a one-step hydrothermal route.