Dissolution Pathways Research Articles

Allotrope-dependent activity-stability relationships of molybdenum sulfide hydrogen evolution electrocatalysts

Molybdenum disulfide (MoS2) is widely regarded as a competitive hydrogen evolution reaction (HER) catalyst to replace platinum in proton exchange membrane water electrolysers (PEMWEs). Despite the extensive knowledge of its HER activity, stability insights under HER operation are scarce. This is paramount to ensure long-term operation of Pt-free PEMWEs, and gain full understanding on the electrocatalytically-induced processes responsible for HER active site generation. The latter are highly dependent on the MoS2 allotropic phase, and still under debate. We rigorously assess these by simultaneously monitoring Mo and S dissolution products using a dedicated scanning flow cell coupled with downstream analytics (ICP-MS), besides an electrochemical mass spectrometry setup for volatile species analysis. We observe that MoS2 stability is allotrope-dependent: lamellar-like MoS2 is highly unstable under open circuit conditions, whereas cluster-like amorphous MoS3-x instability is induced by a severe S loss during the HER and undercoordinated Mo site generation. Guidelines to operate non-noble PEMWEs are therefore provided based on the stability number metrics, and an HER mechanism which accounts for Mo and S dissolution pathways is proposed.

Molecular insight into the initial hydration of tricalcium aluminate

Portland cement (PC) is ubiquitously used in construction for centuries, yet the elucidation of its early-age hydration remains a challenge. Understanding the initial hydration progress of tricalcium aluminate (C3A) at molecular scale is thus crucial for tackling this challenge as it exhibits a proclivity for early-stage hydration and plays a pivotal role in structural build-up of cement colloids. Herein, we implement a series of ab-initio calculations to probe the intricate molecular interactions of C3A during its initial hydration process. The C3A surface exhibits remarkable chemical activity in promoting water dissociation, which in turn facilitates the gradual desorption of Ca ions through a metal-proton exchange reaction. The dissolution pathways and free energies of these Ca ions follow the ligand-exchange mechanism with multiple sequential reactions to form the ultimate products where Ca ions adopt fivefold or sixfold coordination. Finally, these Ca complexes reprecipitate on the remaining Al-rich layer through the interface-coupled dissolution-reprecipitation mechanism, demonstrating dynamically stable inner-sphere adsorption states. The above results are helpful in unmasking the early-age hydration of PC and advancing the rational design of cement-based materials through the bottom-up approach.

The initial stages of cement hydration at the molecular level

Cement hydration is crucial for the strength development of cement-based materials; however, the mechanism that underlies this complex reaction remains poorly understood at the molecular level. An in-depth understanding of cement hydration is required for the development of environmentally friendly cement and consequently the reduction of carbon emissions in the cement industry. Here, we use molecular dynamics simulations with a reactive force field to investigate the initial hydration processes of tricalcium silicate (C3S) and dicalcium silicate (C2S) up to 40 ns. Our simulations provide theoretical support for the rapid initial hydration of C3S compared to C2S at the molecular level. The dissolution pathways of calcium ions in C3S and C2S are revealed, showing that, two dissolution processes are required for the complete dissolution of calcium ions in C3S. Our findings promote the understanding of the calcium dissolution stage and serve as a valuable reference for the investigation of the initial cement hydration.

Insights into the Path-Dependent Charge of Iridium Dissolution Products and Stability of Electrocatalytic Water Splitting

The electrocatalytic stability of the oxygen evolution reaction (OER) is challenging for the storage of fluctuating renewable energies using polymer electrolyte membrane water electrolyzers (PEMWEs). Investigations are commonly conducted in so-called half-cell setups and different OER-related dissolution pathways have been proposed. However, the orders of magnitude difference in dissolution rate between half-cells and PEMWE using membrane electrode assemblies (MEA) is not well understood. In this work, the charge-related absorption affinity of Iridium (Ir) dissolution products, from both half-cell and MEA setups, is investigated, using cation and anion exchange materials. In the half-cell, a roughly constant ratio of cationic to anionic dissolution species is indicative of a single, dominant OER-related Ir dissolution pathway. While Ir dissolved in half-cells is mainly cationic, the Ir species from the MEA appear mainly in anionic form. This can be explained by the transport conditions of different Ir ions inside the catalyst layer, influenced by their ionomer absorption affinity and the migration driving force. Based on this understanding, key influences of electrocatalytic stability of MEAs, the effect of confinement of dissolved Ir species and the stability discrepancy to half-cells are discussed.

Sulfate enrichment in estuaries of the northwestern Gulf of Mexico: The potential effect of sulfide oxidation on carbonate chemistry under a changing climate

AbstractWater quality parameters from 2000 to 2020 were used to identify the spatial and temporal sulfate variations in estuaries of the northwestern Gulf of Mexico. Sulfate enrichment relative to conservative mixing was found to be associated with a low river discharge period from 2012 to 2014 in all estuaries. Based on reaction stoichiometry, sedimentary sulfide oxidation holds significant potential for reducing the alkalinity in estuarine waters. However, during this extreme drought, alkalinity enrichment was also occasionally observed in some of the southern estuaries along with sulfate enrichment, and when alkalinity depletion occurred, the magnitude of depletion was usually much less than what would be expected based on sulfide oxidation alone. This discrepancy can be partially explained by carbonate dissolution and other proton removal pathways (e.g., Fe‐oxide dissolution), and by the uncertainties in the model used to estimate alkalinity enrichment/depletion. Under a changing climate, the close coupling between river discharge variation and estuarine sulfate dynamics will significantly impact estuarine carbonate chemistry.

Atomic-Scale Site Characterization of Cu–Zn Exchange on Cu(111)

An accurate understanding of the physicochemical properties of bimetallic heterogeneous catalysts relies on atomic-scale knowledge of the surface morphology and the atomic distribution. Alloys of Cu and Zn created during catalyst operation are frequently studied and debated in relation to a description of the active phase of Cu/ZnO/Al2O3 methanol synthesis catalysts. This makes it relevant to build a better understanding of Zn dissolution pathways in Cu surfaces and the resulting surface morphology. Herein, we use scanning tunneling microscopy to investigate surface morphology and the distinct atom site configurations of Zn and Cu on Cu(111) resulting from room-temperature Zn exchange from a Zn monolayer into the topmost layer of Cu(111). A gradual dissolution of Zn islands induces an extensive element intermixing at room temperature, resulting in Zn alloying at Cu terrace lattice sites. In addition, we observe and address an interlayer element exchange between the Zn submonolayers in direct contact with Cu. The exchange process is driven by lattice strain and is strongly facilitated at the perimeter of Zn edges. The STM contrast associated with the resulting intermixed sites is reported together with the simulation of these sites based on density functional theory, showing that imaging of isolated Zn sites in Cu(111) is sensitive to the STM tip state. The findings provide new insight into the atomic-scale exchange for Zn/Cu bimetallic surfaces, which may be used onward for understanding the debated surface morphology that develops during reductive activation and alloy formation in the Cu/ZnO/Al2O3 methanol synthesis catalyst.

(Digital Presentation) Oxygen Evolution Reaction in Ru1-XMxO2 (M = Ti, Zr, Nb, Ta, Cr) Doped Catalysts: Activity and Stability Effects

The complex reaction mechanisms and dissolution pathways that drive oxygen evolution reaction on metal and metal oxide surfaces under acidic conditions challenge the development of a highly active, highly stable, and low cost catalyst for proton-exchange membrane (PEM) water electrolyzers. Currently, ruthenium-based materials present lower overpotentials, lower cost and higher global supply compared to iridium-based materials, though they are also considerably less stable. In order to elucidate a way to improve RuO2 stability under the harsh conditions during water electrolysis, we use a density functional theory (DFT) approach to investigate the effects on catalyst structure, OER activity and stability of transition metal substitution within Ru1-xMxO2 (M = Ti, Zr, Nb, Ta, Cr) at different atomic concentrations. Calculations show that M substitution within rutile RuO2 affects the electronic structure resulting in regions of electron accumulation and depletion at the surface and shifts the Ru d-band and O2p band centers, which are highly dependent on dopant characteristics and doped site. Moreover, dissolution calculations on the Ru1-xTixO2 surfaces show that Ti substitution alter the metal dissolution pathway energetics and thermodynamics bringing stability to the catalyst in terms of reducing material loss. Theoretical XRD patterns, Ru d-band and O p-band center calculations, and activation and reaction energy trends are in excellent agreement with experimental results that includes X-ray diffraction analysis, high resolution transmission electron microscopy images, X-ray photoelectron spectroscopy of core and valence bands, and rotating disk electrode measurements. In this presentation, we focus on the theoretical and computational aspects. The evaluation of the thermodynamics and kinetics of the water splitting, and oxygen evolution mechanism is done with spin-polarized plane-wave DFT calculations, while Ab Initio Molecular Dynamics (AIMD) simulations allow following and complementing the understanding of the dynamics of the initial steps of water dissociation on the various M and Ru sites. Electronic structure changes on the surface due to the presence of M before and during the reaction are analyzed based on the density of states and local magnetic moments, and the activation energies are obtained from the climbing Nudge Elastic Band method. Dissolution calculations are carried out with constrained-AIMD simulations using the slow-growth approach within the “Bluemoon ensemble” as implemented in VASP.

Influence of Amidation on the Release Profiles of Insulin Drug from Chitosan-Based Matrices

The present study deals with the comparative analysis of insulin drug release from pure chitosan (CS) and its crosslinked amide derivatives. The objective of this study was to investigate the influence of fatty acid derivatives on the release profiles of insulin drug from CS-based matrices. In order to form cross-linked CS-based amide derivatives, the CS biopolymer was reacted with four different fatty acids with varying amount of unsaturation, including stearic acid (SA), oleic acid (OA), linoleic acid (LA), and linolenic acid (LLA), and then subjected to cross-linking. Following this, the pure CS and cross-linked CS amide derivatives were loaded with insulin drug and were characterized thoroughly by making use of various instrumental techniques such as FTIR, UV–Vis, TGA, HRTEM, DLS, PDI, and zeta potential studies. In addition, the insulin release profiles were studied and compared between pure CS and CS amides at two different pHs, 7.4 and 1.2. Finally, the insulin drug release data was investigated with five different pharmacokinetic models (zero, first, Higuchi, Kersmeyer–Peppas, and Hixson models). From the analysis, the cross-linked CS amides was found to be superior to pure CS, and within the amide derivatives, the one with a high amount of unsaturation, LLA-derived CS biopolymer, was shown to be better for the release of insulin drug by means of the diffusion and dissolution pathways.

Performance and efficiency of methyl-cellulose polysaccharide as a green promising inhibitor for inhibition of corrosion of magnesium in acidic solutions

Gasometric and weight-loss systems was used for studying the corrosion inhibition of magnesium (Mg) in hydrochloric acid by methyl cellulose (MC) polysaccharide as carbohydrate polymer. The two techniques showed a comparable experimental data. The resulting inhibition data of MC on Mg metal surface was found to exhibit both Langmuir and Freundlich isotherms models. Influence of [H+] on the rates of corrosion indicates that the rates of corrosion depends on the rate of acid. This finding along with the first order found in [H+], suggests that the presence of hydrogen ions should be included at least in the rate-determining step in one of the dissolution pathways of Mg metal in the corrosive medium of HCl. The corrosion rate factors were investigated. Again, the inhibition efficiency increases with increasing the inhibitor concentration and temperature. The inhibition effect of the MC on the magnesium metal surface was confirmed by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) techniques to confirm the extent of corrosion and film formation of MC on the magnesium metal surface. Kinetic parameters were estimated and a suitable corrosion mechanism in good agreement with the kinetic results is suggested and discussed.

Impact of particle flocculation on the dissolution and bioavailability of injectable suspensions

Injectable suspensions occasionally exhibit variations in dissolution and bioavailability, which may impact the clinical outcome of the drug product. Here, variation in the injection method (i.e., applied shear) for triamcinolone acetonide (TA) injectable suspension (40 mg/mL) altered the flocculation state of the particles and subsequently their dissolution. Notably, TA suspensions contained primary particles of approximately 2 µm and secondary flocculates of tens of microns. The conversion between flocculated and deflocculated particles was rapid, reversible and highly shear dependent. As such, changing shear rates during laser diffraction (LD) measurement like stirring rate, sonication, and sample introduction method (micropipette vs 25-gauge needle) may result in variability in particle size distributions (PSD) that have the potential to alter drug dissolution. Furthermore, a non-sink, discriminatory in vitro release testing (IVRT) method was developed, which combined in-situ fiber optic UV with LD to simultaneously monitor the dissolution and changing PSD of the suspension. The simultaneously measured dissolution and PSD data showed that flocculated and deflocculated particles followed different dissolution pathways. Importantly, deflocculated particles dissolved up to six times faster than the flocculated particles. Similar shear-induced changes during injection could occur in a clinical setting and have implications for drug bioavailability.

Pore-scale dissolution mechanisms in calcite-CO2-brine systems: The impact of non-linear reaction kinetics and coupled ion transport

We simulate two sets of dissolution experiments in which CO2-saturated solutions are injected into calcite formations. We explore the impact of non-linear reaction kinetics and charge-coupled ion transport in systems representing different levels of flow and mineralogical complexity. First, we flow CO2-saturated water and brine through cylindrical channels drilled through solid calcite cores and compare directly with experimental dissolution rates. We find that simulations using a linear saturation model match experimental results much better than the batch-reactor-derived non-linear saturation model. The use of a coupled diffusion model causes only a very small increase in the overall dissolution rate compared to a single diffusion coefficient, due to the increase in transport rates of reaction products, particularly the highly charged Ca2+ ion. We also determine the relative importance of the two calcite dissolution pathways, with H+ and H2CO3, and conclude that the H2CO3 – calcite reaction is by far the more dominant, in contrast with common assumptions in the literature. Then, we compare to the experiments of Menke et al. (2015) in which CO2-saturated brine was injected into a microporous Ketton carbonate, and compare dissolution rates over time. We find that including non-linear saturation behaviour markedly changes the simulated dissolution rate, by up to a factor of 0.7 in the case of the experimentally derived saturation model of Anabaraonye (2017), however neither case matches the experimental result which is several times slower than the simulation. Including the effects of coupled ion transport lead to virtually no change in overall dissolution rate due to the convection dominated behaviour. The model also shows differences in the trend of the dissolution rate over time observed in Menke et al, with an approximately linear relationship with time compared to the experimental square-root dependence on time. We conclude that the geochemical model may need to include other effects such as dissolution inside microporous regions.

Using stable isotopes of Cu, Mo, S, and 87Sr/86Sr in hydrogeochemical mineral exploration as tracers of porphyry and exotic copper deposits

Groundwaters collected from the undisturbed Picaron Cu–Mo porphyry and exotic prospect (Atacama region, Chile) were analyzed for major and trace elements, along with isotopes of Cu, Mo, S, and 87Sr/86Sr. Sulfide minerals at Picaron have undergone oxidation by meteoric waters, resulting in the generation of acid and the lateral and downward migration of dissolved trace cations (Cd, Co, Cu, Ni, Pb, and Zn) and (oxy)anions (As, Mo, Sb, and Se). This paper presents a case study utilizing stable metal isotopes in hydrogeochemical mineral exploration to ascertain the possible hydrogeochemical footprints that can be detected around known mineralization. The groundwaters are weakly brackish (TDS < 3500 mg/L), reflected in relatively low trace metal concentrations. Despite this, the groundwaters reflect the dissolution of ore, as well as alteration and wall rock minerals proximal to porphyry mineralization with elevated dissolved concentrations of Ca, Mg, HCO3−, and SO42−. δ65Cu values range from 0.41 to 2.80‰, with values above 1‰ proximal to porphyry mineralization reflecting Cu fractionation during sulfide oxidation and the highest values (up to 2.80‰) proximal to exotic mineralization likely from Cu desorption. Downgradient, δ65Cu values decrease; possibility resulting from adsorption of the heavier 65Cu onto reactive surfaces or mixing with other sources. δ98Mo values proximal to porphyry mineralization (2.41 and 2.42‰) are much higher than the regional average for molybdenite reported in previous studies (0.11‰), suggesting acid neutralization and isotopic fractionation related to adsorption may be occurring close to the source. Much lower δ98Mo values downgradient (<1.0‰) are likely indicative of Mo input from surrounding country rocks. The hydrogeochemical trends observed in the Picaron groundwaters highlight the chemical processes of mineral dissolution, precipitation, and recharge pathways and indicate that the leaching of the porphyry mineralization could be the source of exotic mineralization. Ultimately, the results indicate the need for a multiple isotope approach to hydrogeochemical mineral exploration.

Bi-continuous porous structures from the selective dissolution of ionic solid solutions

Bi-continuous porous metal evolves from the selective dissolution of an alloy, a process known as dealloying. Here we report a similar observation in the selective dissolution of NaCl from a NaCl-AgCl solid solution. A procedure of simultaneous quenching and dissolution that retains the homogeneity of the solution is designed with the help of small-angle neutron scattering. The process in water creates bi-continuous porous AgCl of smooth ligaments and pores ~300 nm wide, which can coarsen up without altering the bi-continuous morphology. Post-mortem elemental analysis identifies a NaCl-compositional threshold at 35%, below which no dissolution occurs, a critical behavior suggestive of the need for percolating dissolution pathways. The work reveals intriguing similarities between the selective dissolutions of metallic and ionic solid solutions, bridging their mechanisms and promising new ways of fabricating functional porous materials.

The influence of chemical composition, aerosol acidity, and metal dissolution on the oxidative potential of fine particulate matter and redox potential of the lung lining fluid

Air pollution is a major environmental health risk and it contributes to respiratory and cardiovascular diseases and excess mortality worldwide. The adverse health effects have been associated with the inhalation of fine particulate matter (PM2.5) and induction of respiratory oxidative stress. In this work, we quantified the oxidative potential (OP) of PM2.5 from several Canadian cities (Toronto, Hamilton, Montreal, Vancouver) using a recently developed bioanalytical method which measures the oxidation of lung antioxidants, glutathione, cysteine, and ascorbic acid, the formation of glutathione disulfide and cystine, and the related redox potential (RP) in a simulated epithelial lining fluid (SELF). We evaluated the application of empirical SELF RP as a new metric for aerosol OP. We further investigated how PM2.5 chemical composition and OP are related across various emission source sectors and whether these features are linked to specific properties of aerosol aqueous phase, such as pH and metal-ligand complexation. The OP indicators including SELF RP were strongly correlated among each other, indicating that the empirical RP could be used as a reliable metric in future studies. OP based on ascorbic acid showed dependency on the emission source sectors, most likely due to variation in the solubility of Fe. Traffic emissions resulted in the highest OP, followed by industrial emissions and resuspended crustal matter. OP presented low correlation with PM2.5 concentrations, low-moderate correlation with the aerosol organic matter, and moderate-strong association with black carbon and transition metals across the sites. We did not find strong association between the concentration of biomass burning tracers and OP. Copper was the only metal that showed high association with OP across all sites, whereas the correlation with other metals, such as iron, manganese, and titanium, showed clear dependency on the source sectors. The aerosol pH correlated negatively with ambient temperature and positively with biomass burning tracers and the levels of nitrate, ammonium, and aerosol liquid water content. The solubility of Fe was associated with sulfate and aerosol pH at most sites, suggesting the involvement of proton-mediated dissolution pathway, while this was not visible at the site influenced by industrial emission, most likely due to the abundance of pyrogenic Fe. The effect of metal-ligand complexation on the solubility of transition metals, in particular Fe, was clearly observed at all sites, whereas a combined effect with aerosol pH, and a subsequent impact on OP, was only seen at the traffic site in Toronto. The enhanced solubility of Fe due to proton- and ligand-mediated dissolution pathways and subsequent formation of reactive oxygen species may in part explain the health effects of PM2.5 seen in previous epidemiological studies.

Bi-Continuous Porous Structures from the Selective Dissolution of Ionic Solid Solutions

Bi-continuous porous metal evolves from the selective dissolution of an alloy, a process known as dealloying. Here we report a similar observation in the selective dissolution of NaCl from a NaCl-AgCl solid solution. A procedure of simultaneous quenching and dissolution that retains the homogeneity of the solution is designed with the help of small-angle neutron scattering. The process in water creates bi-continuous porous AgCl of smooth ligaments and pores ~300 nm wide, which can coarsen up without altering the bi-continuous morphology. Post-mortem elemental analysis identifies a NaCl-compositional threshold at 35%, below which no dissolution occurs, a critical behavior suggestive of the need for percolating dissolution pathways. The work reveals intriguing similarities between the selective dissolutions of metallic and ionic solid solutions, bridging their mechanisms and promising new ways of fabricating functional porous materials.

Mobilization of co-occurring trace elements (CTEs) in arsenic contaminated aquifers in the Bengal basin

The mobilization of co-occurring trace elements (CTEs) in aquifers with known metal(loid) contamination may exacerbate potential human health threats where release mechanisms are not geochemically limited. This study investigates the co-mobilization of the potentially toxic CTEs antimony (Sb), molybdenum (Mo), vanadium (V), uranium (U), and selenium (Se) with arsenic (As) and iron (Fe) in contrasting high and low As aquifers surrounding the river Bhagirathi in Murshidabad, West Bengal, India. We sought to determine the dominant release mechanisms and fate of each CTEs as they relate to redox conditions, major element dissolution pathways, and characteristics of dissolved organic matter (DOM). Groundwater samples collected in 2013 and 2015 field campaigns across six villages in the Murshidabad district were analyzed for major and trace elements, as well as the quantity and optical properties of DOM. East of the river Bhagirathi, the Holocene aquifer contained groundwater with compositions reflective of carbonate mineral dissolution and silicate mineral weathering, along with clear signs of Fe reduction and associated mobilization of As, Sb, Mo, V, and U. Relatively oxic groundwater in the Pleistocene aquifer underlying the study sites on the west side of the river showed minimal Fe reduction and signatures of carbonate mineral dissolution and silicate mineral weathering (i.e., Nabagram), or evaporite mineral dissolution (i.e., Kandi). In groundwater samples from the more oxic Pleistocene aquifer, concentrations of As, Sb, Mo, and V were substantially lower than in the Holocene aquifer, however, U concentrations were relatively higher where carbonate mineral dissolution predominated (i.e., Nabagram). Compelling positive correlations between Fe and CTEs in the Holocene but not in the Pleistocene aquifer implicated Fe reductive processes as the probable pathway for CTEs release. The presence of humic-like DOM ligands and inorganic ions (i.e., Ca2+, CO32−) may also enhance CTEs mobility via aqueous complexation reactions, or possibly by inhibiting CTEs adsorption. We further hypothesize that carbonate mineral dissolution mobilizes U in the absence of Fe reduction, and that U solubility in the reducing Holocene aquifer may be facilitated by carbonate mineral dissolution products (e.g., Ca2+, HCO3−, CO32−) that promote U complexation and the inhibition of (bio)immobilization pathways. Conclusively, potentially toxic CTEs are being mobilized concomitantly with As in the Murshidabad district of West Bengal, probably by microbial Fe reduction. Because these aquifers still contain requisite organic matter and bulk sediment Fe required for Fe reductive processes, it follows that concentrations of CTEs may increase in the future. We therefore argue that despite moderately low concentrations of CTEs in the current study, mechanistic modeling efforts and more extensive monitoring of trace metal(loid)s should be performed to ensure that drinking water supplies do not pose additional health threats in the coming years.

Effect of dissolution pathways of polyacrylonitrile on the solution homogeneity: Thermodynamic- or kinetic-controlled dissolution

Dissolution behavior of polyacrylontrile (PAN) in N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO) is investigated in terms of dipole-dipole interactions at polymer-solvent interface. Fourier-transformed infrared (FTIR) imaging of polymer-solvent interface under static dissolution condition at 25 °C and 60 °C exhibits the gel-like swollen layer in the early stage of dissolution for both solvents. This layer readily disappears in PAN-DMSO and DMSO molecules penetrate deep into the polymer phase, whereas that in PAN-DMF is still observed until 12 h even at 60 °C. The better dissolving ability of DMSO is interpreted by higher intrinsic viscosity and lower Huggins’ constant. The solubility (solution homogeneity) is also evaluated by rheological analysis in a wide concentration range of 8–20 wt%. At above 15 wt%, DMSO produces homogeneous solution at 60 °C even without stirring, showing the lower Newtonian flow region. On the other hand, it is necessary to apply vigorous stirring and heating for PAN-DMF system in order to prepare concentrated solution. DMSO provides greater slope of the Cole-Cole plot by rheological measurement than DMF, indicating better solution homogeneity in PAN-DMSO. The FTIR spectra and 2D correlation analysis show that both DMSO and DMF dissolve PAN in a way of sequential contributions of enthalpic and entropic factors. However, DMSO exhibits predominant contribution by enthalpic factor, suggesting that enthalpy change of mixing is a driving force of PAN dissolution in DMSO, whereas dissolution of PAN-DMF is governed by kinetic control.

Competing Dissolution Pathways and Ligand Passivation-Enhanced Interfacial Stability of Hybrid Perovskites with Liquid Water.

Material instability issues, especially moisture degradation in ambient operating environments, limit the practical application of hybrid perovskite in photovoltaic and light-emitting devices. Very recent experiments demonstrate that ligand passivation can effectively improve the surface moisture tolerance of hybrid perovskites. In this work, the interfacial stability of as-synthesized pristine and alkylammonium-passivated methylammonium lead iodide (MAPbI3) with liquid water is systematically investigated using molecular dynamics simulations and reaction kinetics models. Interestingly, the more hydrophilic [PbI2]0 surface is more stable than the less hydrophilic [MAI]0 surface because of the higher polarity of the former surface. Linear alkylammoniums significantly stabilize the [MAI]0 surface with highly reduced (by 1-2 orders of magnitude) dissociation rates of both MA+ and ligands themselves, while branched ligands, surprisingly, lead to higher dissociation rates as the surface coverage increases. Such anomalous behavior is attributed to the aggregation-assisted dissolution of surfactant-like ligands as micelles during the degradation process. Short-chain linear alkylammonium at the full surface coverage is found to be the optimal ligand to stabilize the [MAI]0 surface. This work not only provides fundamental insights into the ionic dissolution pathways and mechanisms of hybrid perovskites in water but also inspires the design of highly stable hybrid perovskites with ligand passivation layers. The computational framework developed here is also transferrable to the investigation of surface passivation chemistry for weak ionic materials in general.

Structural Control of a Dissolution Network in a Limestone Reservoir Forced by Radial Injection of CO2 Saturated Solution: Experimental Results Coupled with X-ray Computed Tomography

This study was conducted in the framework of the PILOT CO2-DISSOLVED project, which provides an additional approach for CO2 sequestration, with the aims of capturing, injecting, and locally storing the CO2 after being dissolved in brine. The brine acidity is expected to induce chemical reactions with the mineral phase of the host reservoir. A set of continuous radial CO2 flow experiments was performed on cylindrical carbonate rock samples under geological storage conditions. The objective was to interpret the dissolution network morphology and orientation involved. To explore the three-dimensional architecture of dissolution arrays and their connection integrity within core samples, we used computed tomography. A structural investigation at different scales revealed the impact of the rock heterogeneity on the dissolution pathways. The initial strike of the observed mesoscopic wormholes appears to be parallel to dilatational fractures, with a subsequent change in major trends of dissolution along master shears or, more specifically, a combination of synthetic shears and secondary synthetic shears. Antithetic shears organize themselves as slickolitic surfaces, which may be fluid-flow barriers due to different mineralogy, thus affecting the permeability distribution-wormhole growth geometry induced by CO2-rich solutions.

Ab Initio Monte Carlo Simulations of the Acidic Dissolution of Stainless Steels Effect of Mechanical Deformation

This work is devoted to the Monte Carlo (MC) simulation of the acidic dissolution of mechanically deformed stainless steels (SS). Ab initio relaxation techniques are first used to calculate the bonding energies between atoms as a function of the interatomic distance. Dissolution kinetics of pre-deformed SS structures are then evaluated by means of an MC algorithm. Calculations show that the dissolution probability of surface atoms depends strongly on the strain field near the surface, compressed zones being found to dissolve more rapidly than extended ones. Mechanically induced defects, such as dislocation loops, were also investigated and shown to form preferential dissolution pathways due to the high levels of deformation and to significantly enhance the dissolution kinetics. Last, adding alloying elements is shown to increase the weakening effect of the strain field, regardless of the deformation mode. The addition of molybdenum for instance, known to improve the anodic dissolution resistance, may become less effective in deformed stainless steels.