Mechanism of surface reactions and dissolution of fluorite surface in an aqueous electrolyte solution

2019 ◽  
Vol 16 (7) ◽  
pp. 529
Author(s):  
Tin Klačić ◽  
Marko Tomić ◽  
Danijel Namjesnik ◽  
Borna Pielić ◽  
Tajana Begović
Keyword(s):  
Reaction Mechanism ◽  
Colloidal Particles ◽  
Rate Coefficient ◽  
Aqueous Electrolyte ◽  
Mineral Dissolution ◽  
Interfacial Region ◽  
Surface Groups ◽  
Mineral Surfaces ◽  
Fluoride Ions ◽  
Single Crystal Electrode

Environmental contextSolubility and dissolution rates of mineral surfaces depend on both the surface properties of the mineral and the composition of the aqueous solution. We investigated the link between the interfacial reactions and dissolution of a fluorite crystal. The study provides a detailed microscopic picture of the dissolution phenomena at the fluorite surface, and the results have wider application to general mineral dissolution processes taking place in the environment. AbstractDissolutions of the fluorite (111) crystallographic plane and fluorite (CaF2) colloidal particles were studied as a function of pH. The process was examined by measuring the concentration of released fluoride and calcium ions by ion-selective electrodes. Additionally, electrokinetic and inner surface potentials were measured by means of electrophoresis and a fluorite single crystal electrode respectively. The rate of fluorite dissolution was analysed assuming a reaction mechanism with a series of elementary steps, which included the reaction of surface groups with H+ ions, the formation of F− vacancies, the dissociation of surface groups and the release of calcium and fluoride ions into the interfacial region as well as the diffusion of ions from the interfacial region. The proposed reaction mechanism indicates that H+ ions play a necessary role in allowing the dissolution to take place, a concept not possible to confirm by looking at the overall equation of fluorite dissolution. The order of the total reaction with respect to H+ ions was found to be 0.37, which is in good accordance with the value derived from the reaction mechanism (1/3). The experimentally determined rate coefficient of fluorite dissolution was found to be kdis=9×10−6mol2/3dmm−2s−1.

scholarly journals Highly efficient water oxidation via a bimolecular reaction mechanism on rutile structured mixed-metal oxyfluorides

2021 ◽  
Author(s):  
Zahra Gohari-Bajestani ◽  
Xiao Wang ◽  
Amandine Guiet ◽  
Romain Moury ◽  
Jean-Marc Grenèche ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Water Oxidation ◽  
Active Sites ◽  
Catalyst Surface ◽  
Coupling Reaction ◽  
Bimolecular Reaction ◽  
Fluoride Ions ◽  
Mixed Metal ◽  
Beneficial Effects ◽  
Catalytic Sites

Mixed-metal oxides are generally considered to be the highest-performance catalysts for alkaline water oxidation. Despite significant efforts dedicated to understanding and accelerating their efficiency, most works have been limited investigations of Ni, Co, and Fe oxides, thus overlooking beneficial effects of hetero-anion incorporation. To this end, we report on the development of Co0.5Fe0.5O0.5F1.5 oxyfluoride materials featuring a rutile crystal structure and porous morphology via a scalable and green synthetic route. The catalyst surface, enhanced through electron withdrawing effects imparted by the fluoride ions, give rise to highly effective catalytic sites for electrochemical water oxidation. In particular, their performance across metrics of Tafel slope (27 mV/dec), mass activity (846 A/g at 1.53 V vs. RHE), turnover frequency (21/s at 1.53 V vs. RHE), overpotential (220 mV for 10 mA/cm2), and stability (27 days of continuous operation) largely surpasses most known Co-based catalysts. Mechanistic studies suggest that this performance is driven by a bimolecular, oxygen coupling reaction mechanism through proximal active sites on the catalyst surface, thus enabling a new avenue for achieving accelerated oxygenic electrocatalysis.

scholarly journals Reviews and syntheses: Biological weathering and its consequences at different spatial levels – from nanoscale to global scale

2020 ◽  
Vol 17 (6) ◽  
pp. 1507-1533 ◽  
Author(s):  
Roger D. Finlay ◽  
Shahid Mahmood ◽  
Nicholas Rosenstock ◽  
Emile B. Bolou-Bi ◽  
Stephan J. Köhler ◽  
...  
Keyword(s):  
Biological Activity ◽  
Chemical Processes ◽  
Mineral Dissolution ◽  
Biological Processes ◽  
Mineral Surfaces ◽  
Long Distance ◽  
Microbial Decomposition ◽  
Nutrient Mobilisation ◽  
Physical And Chemical

Abstract. Plant nutrients can be recycled through microbial decomposition of organic matter but replacement of base cations and phosphorus, lost through harvesting of biomass/biofuels or leaching, requires de novo supply of fresh nutrients released through weathering of soil parent material (minerals and rocks). Weathering involves physical and chemical processes that are modified by biological activity of plants, microorganisms and animals. This article reviews recent progress made in understanding biological processes contributing to weathering. A perspective of increasing spatial scale is adopted, examining the consequences of biological activity for weathering from nanoscale interactions, through in vitro and in planta microcosm and mesocosm studies, to field experiments, and finally ecosystem and global level effects. The topics discussed include the physical alteration of minerals and mineral surfaces; the composition, amounts, chemical properties, and effects of plant and microbial secretions; and the role of carbon flow (including stabilisation and sequestration of C in organic and inorganic forms). Although the predominant focus is on the effects of fungi in forest ecosystems, the properties of biofilms, including bacterial interactions, are also discussed. The implications of these biological processes for modelling are discussed, and we attempt to identify some key questions and knowledge gaps, as well as experimental approaches and areas of research in which future studies are likely to yield useful results. A particular focus of this article is to improve the representation of the ways in which biological processes complement physical and chemical processes that mobilise mineral elements, making them available for plant uptake. This is necessary to produce better estimates of weathering that are required for sustainable management of forests in a post-fossil-fuel economy. While there are abundant examples of nanometre- and micrometre-scale physical interactions between microorganisms and different minerals, opinion appears to be divided with respect to the quantitative significance of these observations for overall weathering. Numerous in vitro experiments and microcosm studies involving plants and their associated microorganisms suggest that the allocation of plant-derived carbon, mineral dissolution and plant nutrient status are tightly coupled, but there is still disagreement about the extent to which these processes contribute to field-scale observations. Apart from providing dynamically responsive pathways for the allocation of plant-derived carbon to power dissolution of minerals, mycorrhizal mycelia provide conduits for the long-distance transportation of weathering products back to plants that are also quantitatively significant sinks for released nutrients. These mycelial pathways bridge heterogeneous substrates, reducing the influence of local variation in C:N ratios. The production of polysaccharide matrices by biofilms of interacting bacteria and/or fungi at interfaces with mineral surfaces and roots influences patterns of production of antibiotics and quorum sensing molecules, with concomitant effects on microbial community structure, and the qualitative and quantitative composition of mineral-solubilising compounds and weathering products. Patterns of carbon allocation and nutrient mobilisation from both organic and inorganic substrates have been studied at larger spatial and temporal scales, including both ecosystem and global levels, and there is a generally wider degree of acceptance of the “systemic” effects of microorganisms on patterns of nutrient mobilisation. Theories about the evolutionary development of weathering processes have been advanced but there is still a lack of information connecting processes at different spatial scales. Detailed studies of the liquid chemistry of local weathering sites at the micrometre scale, together with upscaling to soil-scale dissolution rates, are advocated, as well as new approaches involving stable isotopes.

n-Butylamine Adsorption onto Amorphous Silica

1972 ◽  
Vol 50 (6) ◽  
pp. 907-911 ◽  
Author(s):  
Colin Clark-Monks ◽  
Bryan Ellis
Keyword(s):  
Elevated Temperature ◽  
Reaction Mechanism ◽  
Ethylene Oxide ◽  
Hydroxyl Groups ◽  
Surface Groups ◽  
Vicinal Surface ◽  
Surface Hydroxyl ◽  
Surface Hydroxyl Groups ◽  
Strong Adsorption ◽  
Oxide Vapor

Gravimetric and infrared spectroscopic observations of n-butylamine adsorption onto silica have shown that strong adsorption is associated primarily with isolated surface hydroxyl groups and also with some vicinal surface groups. Adsorbed material can be totally removed from the surface by outgassing at elevated temperature (to 200 °C) without irreversible changes to the underlying surface. The interaction between adsorbed amine and ethylene oxide vapor has been investigated and a possible reaction mechanism is presented.

The Reaction of O(3P) with C2Cl4

1974 ◽  
Vol 52 (23) ◽  
pp. 3870-3878 ◽  
Author(s):  
Eugenio Sanhueza ◽  
Julian Heicklen
Keyword(s):  
Reaction Mechanism ◽  
Quantum Yield ◽  
Chain Length ◽  
Rate Coefficient ◽  
Chain Process ◽  
Reaction Conditions ◽  
Text Production ◽  
Competitive Kinetics ◽  
A Chain ◽  
Cl Atom

The reaction of O(3P), prepared from Hg photosensitization of N2O with C2Cl4 was studied at 25 °C. The exclusive products of the reaction in the absence of O2 were CCl2O and polymer (as well as N2 from the N2O). The quantum yield of CCl2O production, Φ{CCl2O}, was 0.19 independent of the C2Cl4 pressure or the absorbed intensity, Ia. There was no evidence for CO, Cl2, c-C3Cl6, CCl3CCl(O), or [Formula: see text] production. The reaction mechanism is[Formula: see text]with k12a/k12 = 0.19. The CCl2 radical dimerizes and the energetic C2Cl4O* intermediate polymerizes. By competitive kinetics, the ratio k12/k13 was found to be 0.10, where k12 ≡ k12a + k12b and k13 is the rate coefficient of the O(3P) + C2F4 reaction.In the presence of O2, a chain process is involved in which CCl3CCl(O) and CCl2O are the major products. They are formed in a ratio of 2.0 independent of reaction conditions, but the chain length is proportional to [C2Cl4]/Ia1/2. Also produced is CO with a quantum yield of ∼0.18. The ratio Φ{CCl3CCl(O)}/Φ{CCl2O} = 2.0 is similar to that of 2.5 found in the Cl atom initiated oxidation. This result is interpreted to mean that chlorine atoms are involved in the chain. The reaction which initiates monoradicals in the system is[Formula: see text]

scholarly journals Charge regulation of colloidal particles in aqueous solutions

2020 ◽  
Vol 22 (42) ◽  
pp. 24712-24728 ◽  
Author(s):  
Amin Bakhshandeh ◽  
Derek Frydel ◽  
Yan Levin
Keyword(s):  
Aqueous Solutions ◽  
Colloidal Particles ◽  
Aqueous Electrolyte ◽  
Electrolyte Solutions ◽  
Charge Regulation ◽  
Aqueous Electrolyte Solutions

We study the charge regulation of colloidal particles inside aqueous electrolyte solutions.

A view of reactions at mineral surfaces from the aqueous phase

2001 ◽  
Vol 65 (3) ◽  
pp. 323-337 ◽  
Author(s):  
W. H. Casey
Keyword(s):  
Exchange Reaction ◽  
Ligand Exchange ◽  
Reaction Rates ◽  
Mineral Dissolution ◽  
Mineral Surfaces ◽  
Exchange Reactions ◽  
Ligand Exchange Reaction ◽  
Molecular Information ◽  
Aqueous Complexes ◽  
Oxygen Bond

AbstractThe processes by which a metal–oxygen bond dissociates in aqueous complexes are discussed and the reactions related to more complicated pathways of mineral dissolution. The dissolution of oxide minerals, and in fact many other classes of surface reactions, can be viewed as a ligand-exchange reaction because the bridging oxygens that link the metal to the mineral are progressively replaced by non-bridging functional groups. These ligand-exchange reactions are accelerated by protonations, hydroxylations and ligand substitutions that modify the lability of surface oxygens, but always at specific sites. Molecular information is important because reactions at some sites retard rates while reaction at other sites enhance them. Virtually all of the important variables that affect these reaction rates are local.

scholarly journals Electrochemical performance and reaction mechanism investigation of V2O5 positive electrode material for aqueous rechargeable zinc batteries

2021 ◽  
Author(s):  
Qiang Fu ◽  
Jiaqi Wang ◽  
Angelina Sarapulova ◽  
Lihua Zhu ◽  
Alexander Missyul ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Electrochemical Performance ◽  
Electrode Material ◽  
Aqueous Electrolyte ◽  
Positive Electrode ◽  
Charge Capacity ◽  
Initial Discharge ◽  
Positive Electrode Material

The electrochemical performance and reaction mechanism of orthorhombic V2O5 in 1 M ZnSO4 aqueous electrolyte are investigated. V2O5 nanowires exhibit an initial discharge and charge capacity of 277 and 432...

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