The ‘dolomite problem’, the scarcity of present-day dolomite formation near the Earth’s surface, has attracted much attention over the past century. Solving this problem requires having reliable data ...on the stability and kinetics of formation of this mineral. Toward this goal, the solubility of natural dolomite (CaMg(CO3)2) has been measured from 50 to 253 °C in 0.1 mol/kg NaCl solutions using a hydrogen electrode concentration cell (HECC). The obtained apparent solubility products (Kapp-sp-dol), for the reaction: CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32−, were extrapolated to infinite dilution to generate the solubility product constants for this reaction (Ksp°-dol). The derived equilibrium constants were fit and can be accurately described by log10Ksp°-dol = a + b/T (K) + cT (K) where a = 17.502, b = −4220.119 and c = −0.0689. This equation and its first and second derivatives with respect to T were used together with corresponding aqueous species properties to calculate the revised standard state thermodynamic properties of dolomite at 25 °C and 1 bar, yielding a Gibbs energy of formation (ΔfG298.15∘) equal to −2160.9 ± 2 kJ/mol, (log10Ksp°-dol = −17.19 ± 0.3); an enthalpy of formation (ΔfH298.15∘) of −2323.1 ± 2 kJ/mol, an entropy (S298.15∘) of 156.9 ± 2 J/mol/K and heat capacity (Cp298.15∘) of 154.2 ± 2 J/mol/K (uncertainties are 3σ). The dolomite solubility product derived in this study is nearly identical to that computed using SUPCRT92 (Johnson et al., 1992) at 200 °C, but about one order of magnitude higher at 50 and 25 °C, suggesting that dolomite may be somewhat less stable than previously assumed at ambient temperatures.
Understanding the role of citrate in the crystallization kinetics of amorphous calcium carbonate (ACC) is essential to explain the formation mechanisms, stabilities, surface properties, and ...morphologies of CaCO3 biominerals. It also contributes to deeper insight into fluid–mineral interactions, both in nature and for industrial processes. In this study, ACC formation and its crystallization are monitored in real time as a function of citrate (CIT) concentration in solution. Additionally, synchrotron radiation pair distribution function analyses combined with solid‐state, spectroscopic, and microscopic techniques are used to determine the effect of CIT on ACC structure, composition, and size. Results show an increase in ACC lifetime coupled with an increase in CIT uptake by ACC and slight changes in ACC atomic structure with an increase in CIT concentration. ACC does not form at concentrations ≥ 75% CIT/Ca and vaterite is absent in all cases where CIT is present. These findings can be explained by CIT binding with Ca ions, thereby forming Ca–CIT complexes in solution and decreasing ACC and calcite saturation levels. The formation of CIT‐bearing ACC with calcitic structure and the absence of vaterite formation suggest that these solution complexes form a calcite‐type atomic arrangement while CIT probably also acts as a growth inhibitor.
The addition of citrate to solutions supersaturated with respect to
amorphous calcium carbonate (ACC) leads to more stable ACC with modified structure and composition and direct crystallization to calcite via a spherulitic growth mechanism. At citrate/Ca ratio ≥ 0.75, ACC formation is inhibited and calcite spherulites form directly from solution.
A new type of solid‐state molecular junction is introduced, which employs reduced graphene oxide as a transparent top contact that permits a self‐assembled molecular monolayer to be photoswitched in ...situ, while simultaneously enabling charge‐transport measurements across the molecules. The electrical switching behavior of a less‐studied molecular switch, dihydroazulene/vinylheptafulvene, is described, which is used as a test case.
Porous organic polymers from triazatriangulenium salts (TAPOPs) were developed
via
oxidative polymerization. FeCl
3
-caused chlorination on the triazatriangulenium core was observed, which has a ...pronounced impact on the photophysical properties and porosity of the polymers. Optimization of reaction conditions affords TAPOPs with a Brunauer–Emmett–Teller specific surface area as high as 940 m
2
g
−1
and a carbon dioxide uptake capacity up to 15.4 wt% at 273 K and 1.0 bar. Furthermore, the reversible and preferred adsorption of TAPOPs toward carbon dioxide over nitrogen is not only demonstrated by gas sorption experiments but also gas–sorbent interaction measurements through recording the emission change of TAPOPs under different gas atmospheres using fluorescence microscopy.
Semiconductor nanowires (NWs) are gaining significant importance in various biological applications, such as biosensing and drug delivery. Efficient and controlled immobilization of biomolecules on ...the NW surface is crucial for many of these applications. Here, we present for the first time the use of the CuI‐catalyzed alkyne–azide cycloaddition and its strain‐promoted variant for the covalent functionalization of vertical NWs with peptides and proteins. The potential of the approach was demonstrated in two complementary applications of measuring enzyme activity and protein binding, which is of general interest for biological studies. The attachment of a peptide substrate provided NW arrays for the detection of protease activity. In addition, green fluorescent protein was immobilized in a site‐specific manner and recognized by antibody binding to demonstrate the proof‐of‐concept for the use of covalently modified NWs for diagnostic purposes using minute amounts of material.
Click on nanowires: A method for highly reproducible, covalent functionalization of oxidized semiconductor nanowires with peptides and proteins is reported. The method combines silanization with the CuI‐catalyzed and strain‐promoted alkyne–azide cycloaddition (CuAAC and SPAAC) reactions. A protease FRET substrate and green fluorescent protein were site‐specifically immobilized on GaAs nanowires.
Transition metal oxides exhibit a rich collection of electronic properties and have many practical applications in areas such as catalysis and ultra-high-density magnetic data storage. Therefore the ...development of switchable molecular transition metal oxides has potential for the engineering of single-molecule devices and nanoscale electronics. At present, the electronic properties of transition metal oxides can only be tailored through the irreversible introduction of dopant ions, modifying the electronic structure by either injecting electrons or core holes. Here we show that a molybdenum(VI) oxide 'polyoxometalate' molecular nanocluster containing two embedded redox agents is activated by a metallic surface and can reversibly interconvert between two electronic states. Upon thermal activation two electrons are ejected from the active sulphite anions and delocalized over the metal oxide cluster cage, switching it from a fully oxidized state to a two-electron reduced state along with the concomitant formation of an S-S bonding interaction between the two sulphur centres inside the cluster shell.
The presence of adsorbed ions on calcite surfaces can significantly affect the adsorption and desorption of organic molecules, which is critical for oil recovery and biomineralization. In this study, ...the structure of calcite–artificial seawater interfaces from 25 to 80 °C was experimentally and theoretically investigated by surface X–ray scattering and molecular dynamics simulations, respectively. The small difference in the CTR scattering profiles at different temperatures could be attributed to the relaxed outermost calcite surface. The electron density profile of the NaCl solution (0.5 mol/kg) exhibits peaks near the calcite surfaces. The two peaks closest to the surface can be interpreted as adsorbed water molecules, inner–sphere Na+ complexes, and inner– and outer–sphere Cl− complexes. Thus, the adsorbed Cl− formed two peaks near the calcite’s surface, while Na+ formed a single peak as an inner–sphere complex. It should be noted that there was no strong covalent bond between these inner–sphere complexes and the calcite surface. These structural differences between adsorbed cations and anions could be explained by the balance of the interactions between the surface Ca2+ and CO32−, adsorbed ions, and the surrounding water molecules. The presence of inner–sphere Cl− complexes destabilizes surface Ca2+, whereas Na+ has an insignificant effect on the structure of surface CO32−. Adding a small amount (0.045 mol/kg) of Mg2+ and SO42− appears to enhance the relaxation of the interfacial structure.
This study examines the transport and retention of colloidal particles and heavy ions in porous sand, focusing on the environmental risks associated with waste from oil and gas drilling. Experimental ...and numerical models assess the influence of flow rate, external filter cake layer, and ionic strength on bentonite clay particles and heavy ions, such as cadmium (Cd) and lead (Pb), in near-wellbore (high-flux) and far-field (low-flux) scenarios. Colloidal filtration theory and the one-dimensional convection-dispersion equation with two-site kinetic model for attachment and detachment were utilized to calibrate and predict the transport of colloidal suspension in porous media. The research investigates the role of internal and external filter cakes on sand column pressure distribution and heavy ion absorption. Results indicate that the mobility of colloids and heavy ions is influenced by the ionic strength and pH of the carrying fluid. Colloidal clay suspensions show a higher affinity for Pb (II) absorption, while Cd (II) exhibits increased mobility in both clean sand and colloidal environments. Notably, the formation of an external filter cake significantly delays the breakthrough of heavy ions, up to four times longer than in clean sand, and reduces Cd (II) and Pb (II) outlet concentrations by 86% and 93%, respectively. This cake also limits clay concentration and particle size passage. High clay concentrations or injections under high ionic conditions induce clay bridging in pore throats, enhancing internal filtration and heavy ion retention. Conversely, low clay fluxes allow freer particle passage, increasing heavy ion loads and outlet concentrations.
Display omitted
•Transport and hydrodynamic studies determined colloids' retention profile.•Clay particles bridging across pore voids reduce heavy ion mobility.•An external filter cake can decrease heavy ion output concentration by 90%.•In a cotransport system, ionic strength and pH retain clay and restrict heavy ion movement.
The addition of dairy ingredients (buttermilk powder and/or sodium caseinate) to the cheese feed before spray drying, as well as the age of the cheese used as raw material on reconstitution behavior ...of cheese powder without emulsifying salt were studied. Cheese powders made with addition of 2% sodium caseinate plus 2% buttermilk powder showed increased wettability and the lowest amount of fat on the surface, but a delayed dispersibility. Powders made using only buttermilk powder (4%) and powders produced with 45 weeks old cheese exhibited faster dispersibility, but reduced total rehydration. Reconstituted powders produced with 16 weeks old cheese showed the best total rehydration. The amount of surface fat, lactose, and protein interactions with water in the cheese casein network are pointed to be the main reasons for the differences observed, as they affect particle size distribution or ability of the powder components to interact with the water.
•Adding both buttermilk powder and sodium caseinate improved wettability.•Wettability was correlated with the N/C ratio on the powder surface.•Cheese powders produced with 45 weeks old cheeses had faster dispersibility.•Dispersibility decreased when buttermilk powder and sodium caseinate were added.•Powders produced with 16 weeks old cheeses showed better total rehydration.
Fe(II)-carbonates, such as siderite, form in environments where O2 is scarce, e.g., during marine sediment diagenesis, corrosion and possibly CO2 sequestration, but little is known about their ...formation pathways. We show that early precipitates from carbonate solutions containing 0.1M Fe(II) with varying pH produced broad peaks in X-ray diffraction and contained dominantly Fe and CO3 when probed with X-ray photoelectron spectroscopy. Reduced pair distribution function (PDF) analysis shows only peaks corresponding to interatomic distances below 15Å, reflecting a material with no long range structural order. Moreover, PDF peak positions differ from those for known iron carbonates and hydroxides. Mössbauer spectra also deviate from those expected for known iron carbonates and suggest a less crystalline structure. These data show that a previously unidentified iron carbonate precursor phase formed. Its coherent scattering domains determined from PDF analysis are slightly larger than for amorphous calcium carbonate, suggesting that the precursor could be nanocrystalline. Replica exchange molecular dynamics simulations of Fe-carbonate polynuclear complexes yield PDF peak positions that agree well with those from experiments, offering the possibility that the material is a condensate of such complexes, assembled in a relatively unorganised fashion. If this is the case, the material could be nearly amorphous, rather than being composed of well defined nanocrystals. PDF measurements of samples ageing in solution coupled with refinement with the software PDFgui show that the material transforms to siderite or siderite/chukanovite mixtures within hours and that the transformation rate depends on pH. The identified Fe-carbonate precursor may potentially form during anaerobic corrosion or bacterial Fe reduction.
PDF
