Search results for "OXIDATION"
showing 10 items of 1913 documents
Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna's emissions
2011
A major uncertainty regarding the environmental impacts of volcanic Hg is the extent to which Hg is deposited locally or transported globally. An important control on dispersion and deposition is the oxidation state of Hg compounds: Hg(0) is an inert, insoluble gas, while Hg(II) occurs as reactive gases or in particles, which deposit rapidly and proximally, near the volcanic vent. Using a new high temperature thermodynamic model, we show that although Hg in Etna's magmatic gases is almost entirely Hg(0) (i.e., gaseous elemental mercury), significant quantities of Hg(II) are likely formed at Etna's vents as gaseous HgCl2, when magmatic gases are cooled and oxidised by atmospheric gases. Thes…
Persistence of oxidation state III of gold in thione coordination
2017
Ligands N,N'-tetramethylthiourea and 2-mercapto-1-methyl-imidazole form stable Au(III) complexes [AuCl3(N,N'-tetramethylthiourea)] (1) and [AuCl3(2-mercapto-1-methyl-imidazole)] (2) instead of reducing the Au(III) metal center into Au(I), which would be typical for the attachment of sulfur donors. Compounds 1 and 2 were characterized by spectroscopic methods and by X-ray crystallography. The spectroscopic details were explained by simulation of the UV-Vis spectra via the TD-DFT method. Additionally, computational DFT studies were performed in order to find the reason for the unusual oxidation state in the crystalline materials. The preference for Au(III) can be explained via various weak in…
Degradation of Antibiotic Vancomycin by UV Photolysis and Pulsed Corona Discharge Combined with Extrinsic Oxidants
2023
Antibiotics are the most frequently detected pharmaceuticals in the environment creating conditions for the development of resistant genes in bacteria. Degradation and mineralization of glycopeptide antibiotic vancomycin (VMN) were examined by UV photolysis, pulsed corona discharge (PCD), and their combinations with extrinsic oxidants, hydrogen peroxide (HP), peroxydisulfate (PDS), and peroxymonosulfate (PMS). Both combinations were effective in VMN degradation and faster at pH 11 than in acidic or neutral media. Combined with the UV photolysis, HP showed a higher oxidation rate than other oxidants, whereas PMS and PDS proved to be more efficient in combinations with PCD. In contrast to low…
A synergic nanoantioxidant based on covalently modified halloysite–trolox nanotubes with intra-lumen loaded quercetin
2016
We describe the preparation and properties of the first example of a synergic nanoantioxidant, obtained by different functionalizations of the external surface and the inner lumen of halloysite nanotubes (HNTs). Trolox, a mimic of natural α-tocopherol, was selectively grafted on the HNT external surface; while quercetin, a natural polyphenolic antioxidant, was loaded into the inner lumen to afford a bi-functional nanoantioxidant, HNT–Trolox/Que, which was investigated for its reactivity with transient peroxyl radicals and a persistent 1,1-diphenyl-2-picrylhydrazyl (DPPH˙) radical in comparison with the corresponding mono-functional analogues HNT–Trolox and HNT/Que. Both HNT–Trolox and HNT/Q…
Oxidation-Induced Changes in the ALD-Al2O3/InAs(100) Interface and Control of the Changes for Device Processing
2018
InAs crystals are emerging materials for various devices like radio frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We have characterized atomic-layer-deposition (ALD) grown Al2O3/InAs interfaces, preoxidized differently, with synchrotron hard X-ray photoelectron spectroscopy (HAXPES), low-energy electron diffraction, scanning tunneling microscopy, and time-of-flight elastic recoil detection analysis. The chemical environment and core-level shifts are clarified for w…
Reduction-oxidation dynamics of oxidized graphene: Functional group composition dependent path to reduction
2018
Micrometer-sized oxidation patterns containing varying composition of functional groups including epoxy, ether, hydroxyl, carbonyl, carboxyl, were created in chemical vapor deposition grown graphene through scanning probe lithography and pulsed laser two-photon oxidation. The oxidized graphene films were then reduced by a focused x-ray beam. Through in-situ x-ray photoelectron spectroscopy measurement, we found that the path to complete reduction depends critically on the total oxygen coverage and concentration of epoxy and ether groups. Over the threshold concentrations, a complex reduction-oxidation process involving conversion of functional groups of lower binding energy to higher bindin…
Revealing lattice disorder, oxygen incorporation and pore formation in laser induced two-photon oxidized graphene
2019
Abstract Laser induced two-photon oxidation has proven to be a reliable method to pattern and control the level of oxidation of single layer graphene, which in turn allows the development of graphene-based electronic and optoelectronic devices with an all-optical method. Here we provide a full structural and chemical description of modifications of air-suspended graphene during the oxidation process. By using different laser irradiation doses, we were able to show via transmission electron microscopy, electron energy loss spectroscopy, electron diffraction and Raman spectroscopy how graphene develops from its pristine form up to a completely oxidized, porous and amorphous carbon layer. Furt…
Mechanistic Origins of the pH Dependency in Au-Catalyzed Glycerol Electro-oxidation: Insight from First-Principles Calculations
2021
Electrocatalytic oxidation of glycerol (EOG) is an attractive approach to convert surplus glycerol to value-added products. Experiments have shown that EOG activity and selectivity depend not only on the electrocatalyst but also on the electrode potential, the pH, and the electrolyte. For broadly employed gold (Au) electrocatalysts, experiments have demonstrated high EOG activity under alkaline conditions with glyceric acid as a primary product, whereas under acidic and neutral conditions Au is almost inactive producing only small amounts of dihydroxyacetone. In the present computational work, we have performed an extensive mechanistic study to understand the pH and potential dependency of …
Effect of ozone and hydrogen peroxide on off-flavor compounds and water quality in a recirculating aquaculture system
2022
The recirculating aquaculture system (RAS) is an ever-developing technology for producing fish with a low environmental impact. However, off-flavors can be a major problem in RAS fish production. Off-flavor compounds are of microbial origin and are accumulated in fish flesh. They typically cause a musty and earthy taste and odor, which consumers find unacceptable. Here we hypothesized that oxidizing compounds such as ozone (O3), hydrogen peroxide (H2O2), and their combinations, referred to as advanced oxidation processes (AOP)s, can remove or decrease these compounds in water and prevent their accumulation in fish. In this study, four different oxidative treatments (O3 low (0.4 mg O3 L−1), …
Elementary steps in heterogeneous catalysis: The basis for environmental chemistry
2017
Kataliza stała się obecnie alternatywnym sposobem na natychmiastowe tworzenie produktu chemicznego z uwagi na niższą barierę energetyczną (między cząsteczkami a katalizatorami). Kataliza heterogenna obejmuje przyspieszenie reakcji chemicznej poprzez oddziaływanie cząsteczek związanych z powierzchnią ciała stałego. Jest to dyscyplina, która obejmuje różne aspekty chemii: chemię nieorganiczną i analityczną w celu scharakteryzowania katalizatorów i form tych katalizatorów. Chemia przemysłowa następnie łączy te wszystkie zagadnienia razem, aby zrozumieć chemiczną manipulację ciał stałych, reakcję chemiczną i inżynierię energetyczną oraz przenoszenie ciepła i masy w tych procesach katalitycznych…