Metal Hydroxide Surfaces Research Articles

Study on the Influence of Metal Ions on the Dispersion of Fine Calcium Gangue Minerals.

In this study, the calcium gangue material calcite (-10 μm) was used to investigate the effects of different kinds of metal ions and dosages on the dispersion behavior of calcite. The test results showed that the dispersion behavior of calcite was poor under strongly alkaline conditions without the addition of metal ions, and the reason for that was calcite dissolved ions. The degree of influence of different metal ions on calcite dispersion behavior was Fe3+ > Mg2+ > Na+. The three metal ion dosage tests showed that the dispersion behavior of calcite became poorer with the increase of metal ion dosage. This mainly showed that with the increase of Na+ dosage, the trend of the dispersion behavior of calcite was not obvious, but with the increase of Fe3+ and Mg2+ dosage, the trend of calcite dispersion behavior changed more. The dispersion behavior of calcite was devastated by 5 × 10-4 mol/L Fe3+ at pH = 4-12. The different mechanisms of the three metal ions were identified by zeta potential, solution chemistry, and XPS analysis. Na+ only changed the zeta potential value of the calcite surface, which acted as a compressed electric double layer. However, the formation of metal hydroxide species or metal hydroxide surface precipitation due to the adsorption of Fe3+ and Mg2+ on the mineral surface resulted in the change of the dispersion behavior of calcite.

Polydopamine‐induced nano‐coating layer for high stability of nickel‐rich cathode in secondary batteries

High-Ni layered-oxide cathodes are the most prospective cathode materials for next-generation Li-ion batteries (LIBs) in electric vehicles (EVs) owing to their high specific capacity. However, High-Ni layered-oxide cathode materials exhibit inferior cyclability and low thermal stability owing to the side reaction between Ni4+ and the electrolytes. To solve these surface-related problems, we proposed a strategy for forming LiNbO3 (LNO)—with outstanding thermal stability and ionic conductivity—on a Ni-rich layered-oxide surface using polydopamine (PDA). The PDA formed on the transition metal hydroxide surface has copious catechol OH groups, which attract the Nb ions in the solution to form a LNO coating layer during the calcination process. The LiNi0.8Co0.1Mn0.1O2 (pristine LNCM) electrode experiences enormous degradation when cycled after being subjected to severe conditions—such as a full charge and a 60°C storage test—but the LiNbO3-coated LNCM (LNO-LNCM) electrode exhibits particularly stable cycling performance. Furthermore, differential scanning calorimetry (DSC) results exhibited that the LNO coating notably ameliorated the thermal stability of the cathode material. As a result, our experimental results suggest that the development of cathode materials that can withstand greatly oxidized states and high-temperature environments is achievable.

Crystal Facet-Manipulated 2D Pt Nanodendrites to Achieve an Intimate Heterointerface for Hydrogen Evolution Reactions.

Despite the Pt-catalyzed alkaline hydrogen evolution reaction (HER) progressing via oxophilic metal-hydroxide surface hybridization, maximizing Pt reactivity alongside operational stability is still unsatisfactory due to the lack of well-designed and optimized interface structures. Producing atomically flat two-dimensional Pt nanodendrites (2D-PtNDs) through our 2D nanospace-confined synthesis strategy, this study tackles the insufficient interfacial contact effect during HER catalysis by realizing an area-maximized and firmly bound lateral heterointerface with NiFe-layered double hydroxide (LDH). The well-oriented {110} crystal surface exposure of Pt promotes electronic interplay that bestows strong LDH binding. The charge-relocated interfacial bond in 2D-PtND/LDH accelerates the hydrogen generation steps and achieves nearly the highest reported Pt mass activity enhancement (∼11.2 times greater than 20 wt % Pt/C) and significantly improved long-term operational stability. This work uncovers the importance of the shape and facet of Pt to create heterointerfaces that provide catalytic synergy for efficient hydrogen production.

Structure, Properties, and Phase Transformations of Water Nanoconfined between Brucite-like Layers: The Role of Wall Surface Polarity.

The interaction of water with confining surfaces is primarily governed by the wetting properties of the wall material—in particular, whether it is hydrophobic or hydrophilic. The hydrophobicity or hydrophilicity itself is determined primarily by the atomic structure and polarity of the surface groups. In the present work, we used molecular dynamics to study the structure and properties of nanoscale water layers confined between layered metal hydroxide surfaces with a brucite-like structure. The influence of the surface polarity of the confining material on the properties of nanoconfined water was studied in the pressure range of 0.1–10 GPa. This pressure range is relevant for many geodynamic phenomena, hydrocarbon recovery, contact spots of tribological systems, and heterogeneous materials under extreme mechanical loading. Two phase transitions were identified in water confined within 2 nm wide slit-shaped nanopores: (1) at p1 = 3.3–3.4 GPa, the liquid transforms to a solid phase with a hexagonal close-packed (HCP) crystal structure, and (2) at p2 = 6.7–7.1 GPa, a further transformation to face-centered cubic (FCC) crystals occurs. It was found that the behavior of the confined water radically changes when the partial charges (and, therefore, the surface polarity) are reduced. In this case, water transforms directly from the liquid phase to an FCC-like phase at 3.2–3.3 GPa. Numerical simulations enabled determination of the amount of hydrogen bonding and diffusivity of nanoconfined water, as well as the relationship between pressure and volumetric strain.

Comparative Study on Electrochemical Treatment of Arsenite: Effects of Process Parameters, Sludge Characterization and Kinetics

This study involves the application of electrocoagulation process to remove arsenite from simulated groundwater using steel, aluminium, platinum and glassy carbon in a 2-L batch reactor setup. It was observed that arsenite was initially oxidized to arsenate. In the case of glassy carbon and platinum electrodes, arsenate build-up was found in the solution due to the lack of floc formation. However, in the case of steel and aluminium electrodes, the flocs generated effectively adsorbed the arsenate produced. Parametric studies reveal the highest removal efficiency of arsenite at low pH, high current and low concentration, with the optimum removal according to surface response methodology achieved at pH 4, 1.2 A and 10 ppm. Electrical energy consumption evaluation shows that operating at the optimum conditions, 653.33 kWh/kg is required to achieve WHO limit from an initial arsenite concentration of 10 ppm. Kinetic studies indicate that the rate is best described by first-order model. The sludges obtained after the electrocoagulation process using the steel and aluminium electrodes further reveal the adsorption of arsenic species onto the metal hydroxide surfaces.

Rapid Fabrication of Metal–Organic Framework Films from Metal Substrates Using Intense Pulsed Light

In this article, we demonstrate an innovative approach for the fabrication of uniform metal–organic framework (MOF) films on Cu or Zn metal substrates by using intense pulsed light (IPL). The metal substrates are first treated with a strong oxidizing agent to convert the metal to the corresponding metal hydroxide, then MOF films are prepared by in situ growth over the metal hydroxide surface with an organic ligand by multiple IPL irradiations at room temperature and ambient conditions. The metal hydroxide absorbs the light from IPL, which discharges an excessive energy with relatively short pulse duration (milliseconds), then converts the light to thermal energy. Four well-known MOF compounds, Cu-BTC, Cu-BDC, ZIF-8, and MOF-5 film, are successfully synthesized and characterized by scanning electron microscopy and X-ray diffraction analysis. The effects of organic ligand concentration and IPL exposure time on MOF film synthesis are systematically investigated. The innovative fabrication method presented in...

Carbon Nanotube Web with Carboxylated Polythiophene "Assist" for High-Performance Battery Electrodes.

A carbon nanotube (CNT) web electrode comprising magnetite spheres and few-walled carbon nanotubes (FWNTs) linked by the carboxylated conjugated polymer, poly[3-(potassium-4-butanoate) thiophene] (PPBT), was designed to demonstrate benefits derived from the rational consideration of electron/ion transport coupled with the surface chemistry of the electrode materials components. To maximize transport properties, the approach introduces monodispersed spherical Fe3O4 (sFe3O4) for uniform Li+ diffusion and a FWNT web electrode frame that affords characteristics of long-ranged electronic pathways and porous networks. The sFe3O4 particles were used as a model high-capacity energy active material, owing to their well-defined chemistry with surface hydroxyl (-OH) functionalities that provide for facile detection of molecular interactions. PPBT, having a π-conjugated backbone and alkyl side chains substituted with carboxylate moieties, interacted with the FWNT π-electron-rich and hydroxylated sFe3O4 surfaces, which enabled the formation of effective electrical bridges between the respective components, contributing to efficient electron transport and electrode stability. To further induce interactions between PPBT and the metal hydroxide surface, polyethylene glycol was coated onto the sFe3O4 particles, allowing for facile materials dispersion and connectivity. Additionally, the introduction of carbon particles into the web electrode minimized sFe3O4 aggregation and afforded more porous FWNT networks. As a consequence, the design of composite electrodes with rigorous consideration of specific molecular interactions induced by the surface chemistries favorably influenced electrochemical kinetics and electrode resistance, which afforded high-performance electrodes for battery applications.

Inhibition of Flash Rusting of HY80 By a Mussel Adhesive Protein: Characterizing the Interaction of MAP-5 with a High Strength Low Alloy Steel

A proteinaceous biopolymer, mussel adhesive protein #5, isolated from the common blue mussel (Mytilus edulis L) has been investigated as a model for designing an aqueously soluble candidate corrosion inhibitor system that is non-toxic and environmentally friendly and that could inhibit the flash rusting of exposed high strength low alloy steel surfaces during the paint removal process. It was found that a significant amount of corrosion inhibition is possible (100% inhibition after 7 days) on HY80 steel in a 100% relative humidity environment at 95°F. Indeed, these results were shown to surpass the performance of a commercially available flash rust inhibitor (90% inhibition after 7 days) currently in use on maritime vessels. These results indicated that it is possible to utilize the biochemistry of a naturally occurring biopolymer isolated from the marine mussel, Mytilus edulis (L), to develop a non-toxic and environmentally friendly corrosion inhibitor. This protein is unique in containing 27% L-Dopa and 20% lysine, two unique amino acids containing catecholic and primary amine functional groups, respectively. Currently, characterization of the interaction of the MAP-5 biopolymer on the steel substrate is underway to better understand its mechanism of corrosion inhibition. Energy dispersive spectroscopy (EDS) findings indicate that iron content is highest where the MAP-5 biopolymer is adsorbed onto the steel substrate at pH 5.5, twice the content of the iron on the steel surface alone. When the biopolymer is enzymatically cross-linked on the steel surface at pH 5.5, the iron content is decreased by 1/3 of that of the adsorbed biopolymer. These results suggest that the iron at the steel surface is undergoing complexation and possible metal-mediated cross-linking, whereas the enzyme cross-linked protein on the steel surface complexes less of the iron. Further EDS analysis indicates that when the biopolymer is first dissolved in acetic acid and then phosphate buffer added and placed on the HY80 surface, the same amount of iron is present for all conditions indicating that the presence of acetate or a more acidic pH inhibits any complexation of the iron by the biopolymer as well as any enzymatic cross-linking. Fourier transform infrared (FTIR) spectroscopy using attenuated total reflectance (ATR) and nanoscale IR spectroscopy of the MAP-5 adsorbed onto the steel substrate indicates that the peaks associated with the L-Dopa catecholic hydroxyl groups (-OH) present are very much diminished on the HY80 substrate vs on glass, whereas the aromatic benzene ring peak assignment of the catechol is present on both substrates, confirming the complexation of the surface iron atoms. However, the primary amine (NH3+) functional group present in the amino acid lysine is present in numerous peak assignments on both substrates, with deformation and scissoring, indicating their orientation at the metal surface. It has been suggested that the primary amine may allow for displacement of hydroxyl groups on a metal hydroxide surface, thus allowing the formation of a bi-dentate catechol complex by the L-Dopa amino acids present within the proteinaceous polymer.

Influence of coating bath chemistry on the deposition of 3-mercaptopropyl trimethoxysilane films deposited on magnesium alloy

Magnesium alloys have a low specific density and a high strength to weight ratio. This makes them sought after light weight construction materials for automotive and aerospace applications. These materials have also recently become of interest for biomedical applications. Unfortunately, the use of magnesium alloys in many applications has been limited due to its high susceptibility to corrosion. One way to improve the corrosion resistance of magnesium alloys is through the deposition of protective coatings. Many of the current pretreatments/coatings available use toxic chemicals such as chromates and hydrofluoric acid. One possible environmentally friendly alternative is organosilane coatings which have been shown to offer significant corrosion protection to both aluminum alloys and steels. Organosilanes are ambifunctional molecules that are capable of covalent bonding to metal hydroxide surfaces. In order for covalent bonding to occur, the organosilane must undergo hydrolysis in the coating bath followed by a condensation reaction with the surface. There are a number of factors that influence the rates of these reactions such as pH and concentration of reactants. These factors can also influence competing reactions in solution such as oligomerization. The rates of hydrolysis and condensation of 3-mercaptopropyltrimethoxy silane in methanol have been analyzed with 1H NMR and ATR–FTIR. The results indicate that organosilane oligomers begin to form in solution before the molecules are fully hydrolyzed. The organosilane films deposited on magnesium alloy AZ91 at a variety of concentrations and pre-hydrolysis times were characterized with a combination of ATR–FTIR, ellipsometry and SEM/EDS. The results show that both organosilane film thickness and uniformity are affected by the chemistry occurring in the coating bath prior to deposition.

The formulation and modeling of the anodic dissolution of zinc through adsorbed intermediates

Dissolution mechanisms suggested for Zn have been discussed. It has been shown that the anions adsorbed on the metal or metal hydroxide surfaces play an important role in the dissolution process, therefore involvement of anions in the charge and mass balance cannot be neglected. An attempt has been made to demonstrate that without taking into account the real meaning of charge transfer processes, the application of the suggested mechanism and the relevant kinetic equations may lead to serious problems in the interpretation of the experimental results.

Relative dominance of physical versus chemical effects on the transport of adhesion-deficient bacteria in intact cores from South Oyster, Virginia.

Bacterial transport experiments were conducted using intact sediment cores collected from sites on the Delmarva Peninsula near South Oyster, VA, to delineate the relative importance of physical and chemical heterogeneity in controlling transport of an adhesion-deficient bacterial strain. Electron microscopy revealed that the sediments consisted of quartz and feldspar with a variable amount of clay and iron and aluminum hydroxide coatings on the grains. A nonmotile, gram-negative indigenous groundwater strain, designated as Comamonas sp. DA001, was injected into the cores along with a conservative tracer bromide (Br). DA001 cells were 1.2 x 0.6 microm in size with a hydrophilic surface and a slightly negative surface charge. Bacterial breakthrough preceded that of Br. This differential advection phenomenon can be accounted for by reduction of the effective porosity for the bacteria relative to Br. The distribution of cells remaining in the core as determined by scintillation counting and phosphor imaging techniques was variable, ranging from nearly uniform concentrations throughout the core to exponentially decreasing concentrations with distance from the point of injection. The fraction of bacterial retention in the core was positively correlated with the abundance of the metal hydroxides and negatively correlated with grain size. Because grain size was inversely correlated with the abundance of the metal hydroxide coatings, it was necessary to separate the effects of grain size and mineralogy. The fraction of the bacterial retention accounting for the effect of grain size, the collision efficiency, exhibited no correlation with the abundance of the metal hydroxides, indicating that the bacterial retention was primarily controlled by grain size. Reasons for the lack of influence of mineralogy on bacterial transport include (i) the slightly negatively charged bacterial surfaces; (ii) an insufficient heterogeneity of sediment surface properties; and (iii) the masking of the positive charge of the metal hydroxide surfaces by adsorbed organic carbon (up to 1180 ppm). This study demonstrates that the laboratory-based bacterial transport experiments are effective in delineating physical versus chemical controlling factors and provide an important link to field-based bacterial transport studies.

Lignin demethylation and polysaccharide decomposition in spruce sapwood degraded by brown rot fungi

The organic residues produced in the brown-rot (BR) of wood by many basidiomycetes fungi are ubiquitous on most coniferous forest floors. This degraded wood tissue is characterized by low levels of polysaccharides and a high proportion of demethylated lignin with minor glycerol side chain oxidation. Because of the selective enrichment in an aromatic dihydroxy-rich lignin residue, the chemical and biological reactivity of BR degraded wood will be distinctly different from white rot, the other primary class of fungal wood decay, which typically produces oxidized, lignin-depleted residues. The biochemical mechanism by which BR fungi perform this distinctive degradative chemistry is only starting to become known, and molecular studies which examine the chemical changes imparted to lignin over the long-term decay process are lacking. Using 13C-labeled tetramethylammonium hydroxide thermochemolysis (13C-TMAH) and solid state 13C NMR, we investigated the relationship between lignin oxidation/demethylation and polysaccharide metabolism in a 32-week time series study of spruce sapwood inoculated with either of two BR fungi (Postia placenta and Gloeophyllum trabeum). Our findings demonstrate a close relationship between lignin demethylation and polysaccharide loss and suggest demethylation may play a mechanistic role in polysaccharide loss, possibly by assisting in Fenton reactions where catechol/quinone oxidation and cycling aids in iron reduction. The residue remaining after 16 weeks of decay is devoid of polysaccharides, in contrast to the 68% polysaccharide carbon present in the initial spruce, and exhibits an increased aromatic dihydroxy content (resulting from demethylation of the 3-methoxyl carbon) of up to 22% of the lignin, as determined by 13C-TMAH thermochemolysis. In a typical soil or porewater environment these chemical changes would make BR residues highly reactive toward redox sensitive polyvalent metals (e.g. ferric iron) and likely to adsorb to metal hydroxide surfaces.