Calcite precipitation plays a significant role in processes such as geological carbon sequestration and toxic metal sequestration and, yet, the rates and mechanisms of calcite growth under close to equilibrium conditions are far from well understood. In this study, a quartz crystal microbalance with dissipation (QCM-D) was used for the first time to measure macroscopic calcite growth rates. Calcite seed crystals were first nucleated and grown on sensors, then growth rates of calcite seed crystals were measured in real-time under close to equilibrium conditions (saturation index, SI = log (Ca2+/CO32−/Ksp) = 0.01–0.7, where i represent ion activities and Ksp = 10−8.48 is the calcite thermodynamic solubility constant). At the end of the experiments, total masses of calcite crystals on sensors measured by QCM-D and inductively coupled plasma mass spectrometry (ICP-MS) were consistent, validating the QCM-D measurements. Calcite growth rates measured by QCM-D were compared with reported macroscopic growth rates measured with auto-titration, ICP-MS, and microbalance. Calcite growth rates measured by QCM-D were also compared with microscopic growth rates measured by atomic force microscopy (AFM) and with rates predicted by two process-based crystal growth models. The discrepancies in growth rates among AFM measurements and model predictions appear to mainly arise from differences in step densities, and the step velocities were consistent among the AFM measurements as well as with both model predictions. Using the predicted steady-state step velocity and the measured step densities, both models predict well the growth rates measured using QCM-D and AFM. This study provides valuable insights into the effects of reactive site densities on calcite growth rate, which may help design future growth models to predict transient-state step densities.

Phosphate is commonly added to drinking water to inhibit lead release from lead service lines and lead-containing materials in premise plumbing. Phosphate addition promotes the formation of lead phosphate particles, and their aggregation behaviors may affect their transport in pipes. Here, lead phosphate formation and aggregation were studied under varied aqueous conditions typical of water supply systems. Under high aqueous PO4/Pb molar ratios (>1), phosphate adsorption made the particles more negatively charged. Therefore, enhanced stability of lead phosphate particles was observed, suggesting that although addition of excess phosphate can lower the dissolved lead concentrations in tap water, it may increase concentrations of particulate lead. Adsorption of divalent cations (Ca2+ and Mg2+) onto lead phosphate particles neutralized their negative surface charges and promoted their aggregation at pH 7, indicating that phosphate addition for lead immobilization may be more efficient in harder waters. The presence of natural organic matter (NOM, ≥ 0.05 mg C/L humic acid and ≥ 0.5 mg C/L fulvic acid) retarded particle aggregation at pH 7. Consequently, removal of organic carbon during water treatment to lower the formation of disinfection-byproducts (DBPs) may have the additional benefit of minimizing the mobility of lead-containing particles. This study provided insight into fundamental mechanisms controlling lead phosphate aggregation. Such understanding is helpful to understand the observed trends of total lead in water after phosphate addition in both field and pilot-scale lead pipe studies. Also, it can help optimize lead immobilization by better controlling the water chemistry during phosphate addition.

Phosphate is added to Pb-contaminated soils to induce lead immobilization through lead phosphate precipitation. Organic coatings on soils, which may affect heterogeneous lead phosphate nucleation, can impact the effectiveness of lead immobilization. Here, SiO2 surfaces were coated with silanol self-assembled thin films terminated with −COOH and −OH functional groups to act as model organic coatings on soil particles. Using grazing incidence small-angle X-ray scattering (GISAXS), heterogeneous lead phosphate nucleation on coatings was measured from mixed Pb(NO3)2 and Na2HPO4/NaH2PO4 solutions at pH 7 with varied ionic strengths (IS = 0.58, 4, and 11 mM). Raman spectroscopy identified the homogeneous precipitates in solution as hydroxylpyromorphite (Pb5(PO4)3OH). The smallest lead phosphate nuclei (4.5 ± 0.5 nm) were observed on −COOH coatings, which resulted from the highest level of lead and phosphate ion adsorption on −COOH coatings. The IS of the solution also affected the sizes of the heterogeneous precipitates on −COOH coating, with smaller nuclei (1.3 ± 0.4 nm) forming under higher IS (4 and 11 mM). This study provided new findings that can improve our understanding of lead immobilization in contaminated soil environments.

Abstract Planar alignment of disc-like nanomaterials is required to transfer their superior anisotropic properties from microscopic individual structures to macroscopic collective assemblies. However, such alignment by electrical or magnetic field is challenging due to their additional degrees of orientational freedom compared to that of rod-like nanostructures. Here, the realization of planar alignment of suspended graphene sheets using a rotating magnetic field produced by a pair of small NdFeB magnets and subsequent demonstration of high optical anisotropy and potential novel device applications is reported. Compared to partially aligned sheets with a static magnetic field, planar aligned graphene suspensions exhibit a near-perfect order parameter, much higher birefringence and anisotropic absorption/transmission. A unique feature of discotic nanomaterial assemblies is that the observed order parameter and optical property can vary from isotropic to partial and complete alignment depending on the experimental configuration. By immobilizing and patterning aligned graphene in a UV-curable polymer resin, we further demonstrated an all-graphene permanent display, which exhibits wide-angle, high dark-bright contrast in either transmission or reflection mode without any polarizing optics. The ability to control and pattern graphene orientation in all three dimensions opens up new exploration and broad device applications of graphene.

The leakage of low and intermediate level radioactive wastes from cementitious barriers at disposal sites can pose long-term environmental threats. In this study, cementitious materials were modified with hematite nanoparticles at 1.0%, 3.0%, and 5.0% by mass to enhance uranium immobilization for the first time. After curing the specimens for 28 days, leaching experiments were carried out at 90 °C up to 28 days. The leached uranium and sodium ions in solutions were quantified, and the effects of hematite nanoparticles on the physicochemical and mechanical properties of cementitious materials were studied. The experimental results revealed that the addition of 1.0%, 3.0% and 5.0% hematite nanoparticles all significantly reduced uranium leaching, which is partially due to uranium adsorption onto hematite nanoparticles. Interestingly, the slowest uranium leaching was found in the specimens with 1.0% hematite nanoparticles. The leaching results were complemented by isothermal calorimetry measurements, mercury intrusion porosimetry, chemical analysis, and compression tests, which showed that hematite nanoparticles increased the cement hydration rate and degree, affected cementitious material pore structure development, decreased leachability, and increased compressive strength. These effects were found to be the strongest in specimens containing 1.0% hematite nanoparticles. This study provides new insights into the modification of cementitious materials with hematite nanoparticles for enhanced cement hydration and uranium immobilization. It suggests an economical strategy for the long-term disposal of low and intermediate level radioactive wastes.

For safer geologic CO2 sequestration (GCS), it is important to understand CO2-brine-cement interactions, which affect wellbore integrity. However, potential effects of sulfate and magnesium ions on cement degradation under GCS conditions are not well understood. Here Class H Portland cement were reacted in brines containing 0.05M sulfate and/or magnesium ions under both GCS (50°C and 100atm CO2) and control (50°C and atmospheric pressure) conditions. Using optical microscopy and scanning electron microscope coupled with energy dispersive spectrometry and electron back scattered electron (SEM-EDS/BSE), slower cement carbonation rates were observed in the presence of sulfate under GCS conditions, because of gypsum precipitation on cement surfaces. Calcite rather than gypsum formed in both the inner layers of cement samples reacted under GCS conditions, and on cement surfaces reacted under atmospheric pressure conditions. Under GCS conditions, the dissolved CO2 lowered the pH of the solution surrounding cement surfaces, thus favoring the formation of gypsum over calcite on cement surfaces; while the high pH condition in pore solution inside cement favors the formation of calcite over gypsum. The presence of magnesium had no significant effect on cement degradation under GCS conditions, as brucite, magnesium carbonates and magnesium calcite did not form, due to the low pH at cement surface and the limited diffusion of Mg into cement inner layers.

Ferrihydrite, as one of the most common naturally occurring iron oxides, can sequester toxic metals through co-precipitation. In this study, using grazing-incidence small-angle X-ray scattering, the heterogeneous precipitation of pure, Ni-, and Cd-bearing ferrihydrite on quartz was quantified in 0.1 mM Fe3+ solutions in the absence and presence of 1 mM Ni2+ or Cd2+ (pH 3.8 ± 0.1). Under acidic condition, the limited hydrolysis of metal ions resulted in their small amounts of incorporation in ferrihydrite lattices (<0.1%), several orders of magnitude lower than those reported at neutral and alkaline pH conditions. The presence of Ni2+ or Cd2+ did not significantly affect the surface charges of either ferrihydrite pre-nucleation clusters (PNCs) or quartz surfaces. Therefore, with similar electrostatic interactions between PNCs and quartz, similar initial heterogeneous precipitation rates of pure and Ni- and Cd-bearing ferrihydrite on quartz were observed. Later on, continuous heterogeneous nucleation and growth of ferrihydrite nanoparticles resulted in their increased polydispersity, and the size-dependent solubility of ferrihydrite nanoparticles caused the Ostwald ripening process. The presence of Ni and Cd was found to retard the recrystallization of ferrihydrite, probably as a result of their structural incorporation, which could inhibit the dissolution of ferrihydrite. This study provided new kinetic and mechanistic insights for understanding the effects of metal ions on the heterogeneous precipitation and recrystallization processes of ferrihydrite nanoparticles on mineral surfaces, which can better predict the fate and transport of heavy metals.

Silica aerogel, with mesoporous structure and high hydrophobicity, is a promising adsorbent for oil spill clean-up. To make it economic and environmental-friendly, hydrocarbon desorption and silica aerogel regeneration were investigated. After hydrocarbon desorption at 80°C, silica aerogel maintained its hydrophobicity. After toluene, petrol, and diesel desorption, shrinkage of mesopores (from 19.9 to 16.8, 13.5, and 13.4nm) of silica aerogels occurred, causing decreased adsorption capacities (from 12.4, 11.2, and 13.6 to 12.0, 6.5, and 2.3g/g). Low surface tension of petrol caused high stress on mesopores during its desorption, resulting in significant pore shrinkage. For diesel, its incomplete desorption and oxidation further hindered the regeneration. Therefore, diesel desorption was also conducted at 200°C. Severe diesel oxidation occurred under aerobic condition and destroyed the mesopores. Under anaerobic condition, no diesel oxidation occurred and the decreases in pore size (to 13.2nm) and adsorption efficiency (to 10.0g/g) of regenerated silica aerogels were much less, compared with under aerobic condition. This study provided new insights on silica aerogel regeneration for oil spill clean-up.

The adsorption of Cr(III) or Cr(VI) in the absence and presence of Cu(II) onto kaolin was investigated under pH 2.0–7.0. Results indicated that the adsorption rate was not necessarily proportional to the adsorption capacity. The solutions’ pH values played a key role in kaolin zeta potential , especially the hydrolysis behavior and saturation index of heavy metal ions. In the presence of Cu(II), reached the maximum adsorption capacity of 0.73 mg·g−1 at pH 6.0, while the maximum adsorption capacity for the mixed Cr(VI) and Cu(II) system () was observed at pH 2.0 (0.38 mg·g−1). Comparing the adsorption behaviors and mechanisms, we found that kaolin prefers to adsorb hydrolyzed products of Cr(III) instead of Cr3+ ion, while adsorption sites of kaolin surface were occupied primarily by Cu(II) through surface complexation, leading to Cu(II) inhibited Cr(VI) adsorption. Moreover, Cr(III) and Cr(VI) removal efficiency had a positive correlation with distribution coefficient . Cr(III) and Cr(VI) removal efficiency had a positive correlation with distribution coefficient and that of adsorption affinities of Cr(III) or Cr(VI) on kaolin was found to be Cr(III) < Cr(III)-Cu(II) and Cr(VI) > Cr(VI)-Cu(II).

To improve the efficiency of TiO₂ as a photocatalyst for contaminant degradation, a novel nanocomposite catalyst of (N, Fe) modified TiO₂ nanoparticles loaded on bentonite (B-N/Fe-TiO₂) was successfully prepared for the first time by sol-gel method. The synthesized B-N/Fe-TiO₂ catalyst composites were characterized by multiple techniques, including scanning electron microscope (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), X-ray fluorescence (XRF), nitrogen adsorption/desorption, UV-Vis diffuse reflectance spectra (DRS), and electron paramagnetic resonance (EPR). The results showed that bentonite significantly enhanced the dispersion of TiO₂ nanoparticles and increased the specific surface area of the catalysts. Compared with nondoped TiO₂, single element doped TiO₂, or unloaded TiO₂ nanoparticles, B-N/Fe-TiO₂ had the highest absorption in UV-visible region. The photocatalytic activity of B-N/Fe-TiO₂ was also the highest, based on the degradation of methyl blue (MB) at room temperature under UV and visible light irradiation. In particular, the synthesized B-N/Fe-TiO₂ showed much greater photocatalytic efficiency than N/Fe-TiO₂ under visible light, the newly synthesized B-N/Fe-TiO₂ is going to significantly increase the photocatalytic efficiency of the catalyst using sun light.

The fluorine content of coal has been well documented, while such data of coal spoil are limited. In the present paper, fluorine in coal spoils and its releasing behavior were studied via leaching and combustion tests, as well as field investigation. Fluoride pollution in groundwater and soil occurred in the air depositing areas of coal spoils. The average content of fluorine in coal spoils was 525mg/kg with the highest value of 1885mg/kg. The only XRD detectable inorganic fluorine phase was fluorphlogopite. The absence of major fluorine bearing minerals in coal spoils suggested that bulk fluorine, rather than trace phases, resided in the mineral matrix. The major extracted species were water soluble fluorine and exchangeable fluorine in the coal spoils. Batch leaching tests illustrated that the leachable fluoride in coal spoils was widely distributed, ranging from 2.0 to 108.4mg/kg. Column leaching tests showed a clear pH-dependent leaching behavior of fluorine: lower pH situation led to fluorine release from the mineral matrix; the loosely bound or easily exchangeable fluorine was also flushed out of the column. The higher ion strength or alkaline bicarbonate/carbonate rich leaching solution tended to free more fluorine into the acidic aqueous solution. The leachable fluorine in coal spoils was estimated as ca. 6%, based on the results of leaching tests. Also, our research found that over 90% of fluorine in coal spoils could be released into the atmosphere as a result of spontaneous combustion, accounting for over 40% of the total atmospheric fluorine emissions in northern China. Our investigation suggests that it is urgent to conduct comprehensive studies to assist the management and control of fluorine pollution at coal spoil banks.

{ Barium sulfate (BaSO4) is a common scale-forming mineral in natural and engineered systems, yet the rates and mechanisms of heterogeneous BaSO4 nucleation are not understood. To address these, we created idealized interfaces on which to study heterogeneous nucleation rates and mechanisms, which also are good models for organic–water interfaces: self-assembled thin films terminated with different functional groups (i.e., −COOH, −SH, or mixed −SH & COOH) coated on glass slides. BaSO4 precipitation on coatings from Barite-supersaturated solutions (saturation index

The formation of (Fe, Cr)(OH)3 nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small-angle X-ray scattering, precipitation rates of (Fe, Cr)(OH)3 nanoparticles in solution and on quartz were quantified from 0.1 mM Fe(III) solutions containing 0–0.25 mM Cr(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr(III)/Fe(III) controlled the chemical composition (x) of (Fex, Cr1–x)(OH)3 precipitates, solutions’ supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, the aqueous Cr(III)/Fe(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fex, Cr1–x)(OH)3 through different mechanisms. The sequestration mechanisms of Cr(III) in precipitates were also investigated. In solutions with high aqueous Cr(III)/Fe(III) ratios, surface enrichment of Cr(III) on the precipitates occurred, resulting in slower particle growth in solutions. From solutions with 0–0.1 mM Cr(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fex, Cr1–x)(OH)3 nanoparticles, which can help determine the fate of Cr in aquatic environments.

Microscopic understanding of interaction between H2O and MAPbI3 (CH3NH3PbI3) is essential to further improve efficiency and stability of perovskite solar cells. A complete picture of perovskite from initial physical uptake of water molecules to final chemical transition to its monohydrate MAPbI3·H2O is obtained with in situ infrared spectroscopy, mass monitoring, and X-ray diffraction. Despite strong affinity of MA to water, MAPbI3 absorbs almost no water from ambient air. Water molecules penetrate the perovskite lattice and share the space with MA up to one H2O per MA at high-humidity levels. However, the interaction between MA and H2O through hydrogen bonding is not established until the phase transition to monohydrate where H2O and MA are locked to each other. This lack of interaction in water-infiltrated perovskite is a result of dynamic orientational disorder imposed by tetragonal lattice symmetry. The apparent inertness of H2O along with high stability of perovskite in an ambient environment provides a solid foundation for its long-term application in solar cells and optoelectronic devices.

Understanding the interactions between natural organic matter (NOM) and zero-valent iron nanoparticles (nano-Fe0) and magnetite nanoparticles (nano-Fe3O4) is essential for evaluating their performance in pollutant remediation, as well as determining their fate and transport in the environment. Batch experiments were performed to investigate the sorption/desorption behaviors of humic acid (HA) on commercially available nano-Fe0 and nano-Fe3O4. The sorption/desorption of HA on nano-Fe0 and nano-Fe3O4 were well described by both the Langmuir model and the modified Langmuir model. The adsorption capacities of HA were 8.77 ± 0.31 mg C/g and 10.05 ± 0.95 mg C/g for nano-Fe0 and nano-Fe3O4, respectively. The interactions of HA with nano-Fe0 and nano-Fe3O4 were highly pH-dependent. On one hand, nano-Fe0 had its maximum adsorption of 11.0 mg C/g HA at pH = 3, which decreased to 0.6 mg C/g when pH increased to 11.9; on the other hand, alkaline condition enhanced HA desorption greatly. At pH = 10.1, after 24 h desorption experiments, nearly 80% of initially adsorbed HA desorbed from the nanoparticles. The interactions of HA with nano-Fe0 and nano-Fe3O4 were also influenced by different ion compositions in solution. Divalent cations (e.g. Ca2+, Mg2+) enhanced HA adsorption significantly, while phosphate nearly eliminated HA adsorption and promoted significantly HA desorption.

Fe(III) hydroxide nanoparticles are an essential carrier for aqueous heavy metals. Particularly, iron hydroxide precipitation on mineral surfaces can immobilize aqueous heavy metals. Here, we used grazing-incidence small-angle X-ray scattering (GISAXS) to quantify nucleation and growth of iron hydroxide on quartz in 0.1 mM Fe(NO3)3 solution in the presence of Na+, Cu2+, Pb2+, or Cr3+ at pH = 3.7 ± 0.1. In 30 min, the average radii of gyration (Rg) of particles on quartz grew from around 2 to 6 nm in the presence of Na+ and Cu2+. Interestingly, the particle sizes remained 3.3 ± 0.3 nm in the presence of Pb2+, and few particles formed in the presence of Cr3+. Quartz crystal microbalance dissipation (QCM-D) measurements showed that only Cr3+ adsorbed onto quartz, while Cu2+ and Pb2+ did not. Cr3+ adsorption changed the surface charge of quartz from negative to positive, thus inhibiting the precipitation of positively charged iron hydroxide on quartz. Masses and compositions of the precipitates were also quantified. This study provided new insights on interactions among quartz, iron hydroxide, and metal ions. Such information is helpful not only for environmental remediation but also for the doping design of iron oxide catalysts.

Heterogeneous coprecipitation of iron and aluminum oxides is an important process for pollutant immobilization and removal in natural and engineered aqueous environments. Here, using a synchrotron-based small-angle X-ray scattering technique, we studied heterogeneous nucleation and growth of Fe(III) (hydr)oxide on quartz under conditions found in acid mine drainage (at pH = 3.7 ± 0.2, [Fe3+] = 10–4 M) with different initial aqueous Al/Fe ratios (0:1, 1:1, and 5:1). Interestingly, although the atomic ratios of Al/Fe in the newly formed Fe(III) (hydr)oxide precipitates were less than 1%, the in situ particle size and volume evolutions of the precipitates on quartz were significantly influenced by aqueous Al/Fe ratios. At the end of the 3 h experiments, with aqueous Al/Fe ratios of 0:1, 1:1, and 5:1, the average radii of gyration of particles on quartz were 5.7 ± 0.3, 4.6 ± 0.1, and 3.7 ± 0.3 nm, respectively, and the ratio of total particle volumes on quartz was 1.7:3.4:1.0. The Fe(III) (hydr)oxide precipitates were poorly crystallized, and were positively charged in all solutions. In the presence of Al3+, Al3+ adsorption onto quartz changed the surface charge of quartz from negative to positive, which caused the slower heterogeneous growth of Fe(III) (hydr)oxide on quartz. Furthermore, Al affected the amount of water included in the Fe(III) (hydr)oxides, which can influence their adsorption capacity. This study yielded important information usable for pollutant removal not only in natural environments, but also in engineered water treatment processes.

To predict the fate of aqueous pollutants, a better understanding of heterogeneous Fe(III) (hydr)oxide nucleation and growth on abundant mineral surfaces is needed. In this study, we measured in situ heterogeneous Fe(III) (hydr)oxide nucleation and growth on quartz, muscovite, and corundum (Al2O3) in 10–4 M Fe(III) solution (in 10 mM NaNO3 at pH = 3.7 ± 0.2) using grazing incidence small-angle X-ray scattering (GISAXS). Interestingly, both the fastest heterogeneous nucleation and slowest growth occurred on corundum. To elucidate the mechanisms, zeta potential and water contact angle measurements were conducted. Electrostatic forces between the charged Fe(III) (hydr)oxide polymeric embryos and substrate surfaces—which affect local saturations near the substrate surfaces—controlled heterogeneous growth rates. Water contact angles (7.5° ± 0.7, 22.8° ± 1.7, and 44.8° ± 3.7 for quartz, muscovite, and corundum, respectively) indicate that corundum has the highest substrate–water interfacial energy. Furthermore, a comparison of structural mismatches between the substrates and precipitates indicates a lowest precipitate–substrate interfacial energy for corundum. The fastest nucleation on corundum suggests that interfacial energies in the solution–substrate–precipitate system controlled heterogeneous nucleation rates. The unique information provided here bolsters our understanding of nanoparticle–mineral surface interactions, mineral surface modification by iron oxide coating, and pollutant transport.

The precipitation of carbonate minerals—mineral trapping—is considered one of the safest sequestration mechanisms ensuring long-term geologic storage of CO2. However, little is known about the thermodynamic factors controlling the extent of heterogeneous nucleation at mineral surfaces exposed to the fluids in porous reservoirs. The goal of this study is to determine the thermodynamic factors controlling heterogeneous nucleation of carbonate minerals on pristine quartz (100) surfaces, which are assumed representative of sandstone reservoirs. To probe CaCO3 nucleation on quartz (100) in solution and with nanoscale resolution, an in situ grazing incidence small-angle X-ray scattering technique has been utilized. With this method, a value of α′ = 36 ± 5 mJ/m2 for the effective interfacial free energy governing heterogeneous nucleation of CaCO3 has been obtained by measuring nucleation rates at different solution supersaturations. This value is lower than the interfacial energy governing calcite homogeneous nucleation (α ≈ 120 mJ/m2), suggesting that heterogeneous nucleation of calcium carbonate is favored on quartz (100) at ambient pressure and temperature conditions, with nucleation barriers between 2.5% and 15% lower than those expected for homogeneous nucleation. These observations yield important quantitative parameters readily usable in reactive transport models of nucleation at the reservoir scale.

For sustainable geologic CO2 sequestration (GCS), a better understanding of the effects of brine cation compositions on mica dissolution, surface morphological change, and secondary mineral precipitation under saline hydrothermal conditions is needed. Batch dissolution experiments were conducted with biotite under conditions relevant to GCS sites (55–95 °C and 102 atm CO2). One molar NaCl, 0.4 M MgCl2, or 0.4 M CaCl2 solutions were used to mimic different brine compositions, and deionized water was used for comparison. Faster ion exchange reactions (Na+–K+, Mg2+–K+, and Ca2+–K+) occurred in these salt solutions than in water (H+–K+). The ion exchange reactions affected bump, bulge, and crack formation on the biotite basal plane, as well as the release of biotite framework ions. In these salt solutions, numerous illite fibers precipitated after reaction for only 3 h at 95 °C. Interestingly, in slow illite precipitation processes, oriented aggregation of hexagonal nanoparticles forming the fibrous illite was observed. These results provide new information for understanding scCO2–brine–mica interactions in saline aquifers with different brine cation compositions, which can be useful for GCS as well as other subsurface projects.