Intercalation of dodecylamine into kaolinite and its layering structure investigated by molecular dynamics simulation

Effects of Typical Solvents on the Structural Integrity and Properties of Activated Kaolinite by Wet Ball Milling

The influence of organic solvents on the structural integrity and properties of activated kaolinite were compared and analyzed via characterization techniques and molecular dynamics (MD) simulation. The results revealed that the organic intercalators can be easily inserted into the interlayer spaces of activated kaolinite within a short time of the wet ball milling. The DMSO intercalated kaolinites maintained structural integrity due to the high intercalation rate and the excellent buffering effect against the crushing force of milling during the delamination/exfoliation process. The delaminated layers of the DMSO-kaolinite complex exhibited a high specific surface area of 99.12 m²/g and a low average thickness of 35.21 nm. The calculated elastic properties of the organo-kaolinite complex manifested the intercalation of DMSO into a kaolinite interlayer, which could improve the compressibility and structural integrity of kaolinite nanosheets. The DMSO-kaolinite complex was easier to peel off when compared to the other organic intercalators due to its more intercalated molecules.

Atomic-Scale Intercalation of Graphene Layers into MoSe2 Nanoflower Sheets as a Highly Efficient Catalyst for Hydrogen Evolution Reaction

MoSe₂ is an efficient catalyst for the hydrogen evolution reaction (HER) and can potentially replace conventional catalysts composed of noble metals such as Pt. The HER activity of MoSe₂ originates mainly from the edge sites of Se atoms, but the low concentration of Se exposed to the electrolyte hampers the performance. Hence, activating a larger portion of the basal plane of Se atoms is an effective way to improve the HER properties. Herein, a 3D hierarchic nanoflower structure comprising MoSe₂ with atomic-scale interlayered graphene layers in the nanosheets is designed and prepared to improve the electron conductivity and decrease the proportions of inactive basal planes. Raman scattering, transmission electron microscopy, and energy-dispersive X-ray spectroscopy verify effective insertion of graphene layers in MoSe₂, and the HER characteristics are improved as exemplified by a small overpotential of 175 mV at 10 mA cm^-2, small Tafel slope of 58 mV dec^-1, and excellent durability with only small deterioration of 10 mV after 10,000 cycles. First-principles density functional theory and finite element method calculations corroborate the experimental results, revealing better conductivity and hydrogen adsorption/desorption ability rendered by the graphene layers. Our results reveal a new and effective strategy to optimize the structure and composition and reduce the hydrogen adsorption energy barrier in the pursuit of high-efficiency non-noble metal catalysts.

Enhanced interlayer trapping of Pb(II) ions within kaolinite layers: intercalation, characterization, and sorption studies

Lead (Pb(II)) pollution in water poses a serious threat to human health in many parts of the world. In the past decades, research has been aimed at developing efficient and cost-effective methods to address the problem. In this study, dimethyl sulfoxide (DMSO) and potassium acetate (K-Ac) intercalated kaolinite complexes were synthesized and subsequently utilized for Pb(II) removal from water. The intercalation of kaolinite with DMSO was found to be useful for expanding the interlayer space of the clay mineral from 0.72 to 1.12 nm. Kaolinite intercalation with K-Ac (KDK) increased the interlayer space from 1.12 to 1.43 nm. The surface area of KDK was found to be more than threefold higher as compared to natural kaolinite (NK). Batch experimental results revealed that the maximum Pb(II) uptake capacity of KDK was 46.45 mg g^-1 which was higher than the capacity of NK (15.52 mg g^-1). Reusability studies showed that KDK could be reused for 5 cycles without substantially losing its adsorption capacity. Furthermore, fixed-bed column tests confirmed the suitability of KDK in continuous mode for Pb(II) removal. Successful application of intercalated kaolinite for Pb(II) adsorption in batch and column modes suggests its application in water treatment (especially removal of divalent metals).

Efficient preparation of kaolinite/methanol intercalation composite by using a Soxhlet extractor

Kaolinite/methanol intercalation composite (KMe) is a key precursor for preparing clay-based inorganic/organic hybrid materials and kaolinite nanoscrolls. However, synthesis of KMe is a time and methanol dissipative process and the complexity of this process also limits its further applications. In this study, Soxhlet extractor was introduced to synthesize an intercalation composite and KMe was efficiently synthesized in a Soxhlet extractor through a continuous displacement process by using kaolinite/DMSO intercalation composite (KD) as a precursor. The formation process of kaolinite/methanol intercalation composite was studied by X-ray diffraction (XRD) and infrared spectroscopy (IR). The results showed that the DMSO in kaolinite could be completely displaced by methanol in this process and the preparation of KMe could be completed in 8 hours, which was far faster than the reported methods. Moreover, methanol used in this process could be recycled. Furthermore, the resulting material could be successfully used to prepare kaolinite nanoscrolls in high yield.

Mechanism Responsible for Intercalation of Dimethyl Sulfoxide in Kaolinite: Molecular Dynamics Simulations

Intercalation is the promising strategy to expand the interlayer region of kaolinite for their further applications. Herein, the adaptive biasing force (ABF) accelerated molecular dynamics simulations were performed to calculate the free energies involved in the kaolinite intercalation by dimethyl sulfoxide (DMSO). Additionally, the classical all atom molecular dynamics simulations were carried out to calculate the interfacial interactions between kaolinite interlayer surfaces and DMSO with the aim at exploring the underlying force that drives the DMSO to enter the interlayer space. The results showed that the favorable interaction of DMSO with both kaolinite interlayer octahedral surface and tetrahedral surface can help in introducing DMSO enter kaolinite interlayer. The hydroxyl groups on octahedral surface functioned as H-donors attracting the S=O groups of DMSO through hydrogen bonding interaction. The tetrahedral surface featuring hydrophobic property attracted the methyl groups of DMSO through hydrophobic interaction. The results provided a detailed picture of the energetics and interlayer structure of kaolinite-DMSO intercalate.

Synthesis of TiO2@α-Fe2O3 core–shell heteronanostructures by thermal decomposition approach and their application towards sunlight-driven photodegradation of rhodamine B

TiO₂@α-Fe₂O₃ core–shell heteronanostructures that act as a good photocatalyst for the degradation of RhB were synthesized by a novel thermal decomposition approach.

Thermodynamic Mechanism and Interfacial Structure of Kaolinite Intercalation and Surface Modification by Alkane Surfactants with Neutral and Ionic Head Groups

Intercalation and surface modification of clays with surfactants are the essential process to tailor the clays' surface chemistry for their extended applications. A full understanding of the interaction mechanism of surfactants with clay surfaces is crucial to engineer clay surfaces for meeting a particular requirement of industrial applications. In this study, the thermodynamic mechanism involved in the intercalation and surface modification of methanol preintercalated kaolinite by three representative alkane surfactants with different head groups, dodecylamine, cetyltrimethylammonium chloride (CTAC), and sodium stearate, were investigated using the adaptive biasing force accelerated molecular dynamics simulations. In addition, the interaction energies of surfactants with an interlayer environment (alumina surface, siloxane surface, and interlayer methanol) of methanol preintercalated kaolinite were also calculated. It was found that the intercalation free energy of CTAC with a cationic head group was relatively larger than that of stearate with an anionic head group and dodecylamine with a neutral head group. The attractive electrostatic and van der Waals interactions of surfactants with an interlayer environment contributed to the intercalation and surface modification process with the electrostatic force playing the significant role. This study revealed the underlying mechanism involved in the intercalation and surface modification process of methanol preintercalated kaolinite by surfactants, which can help in further design of kaolinite-based organic clays with desired properties for specific applications.

Mechanism Associated with Kaolinite Intercalation with Urea: Combination of Infrared Spectroscopy and Molecular Dynamics Simulation Studies

Intercalation of urea in kaolinite was investigated using infrared spectroscopy and molecular dynamics simulation. Infrared spectroscopic results indicated the formation of hydrogen bonds between urea and siloxane/alumina surfaces of kaolinite. The carbonyl group (-C=O) of urea acted as H-acceptors for the hydroxyl groups on alumina surfaces. The amine group (-NH₂) of urea functioned as H-donors interacting with basal oxygens on siloxane surfaces and/or the oxygens of hydroxyl groups on alumina surfaces. The H-bonds of urea formed with kaolinite surfaces calculated directly from molecular dynamics simulation was consistent with the infrared spectroscopic results. Additionally, MD simulations further provided insight into the interaction energies of urea with the kaolinite interlayer environment. The calculated interaction energies of urea molecules with kaolinite alumina and siloxane surfaces suggest that the intercalation of urea within kaolinite interlayers is energetically favorable. The interaction energy of urea with alumina surfaces was greater than that with siloxane surfaces, indicating that the alumina surface plays a primary role in the intercalation of kaolinite by urea. The siloxane surfaces function as H-acceptors to facilitate the intercalation of urea. The present study offers a direct view of the specific driving force involved in urea intercalation in kaolinite. The results obtained can help develop appropriate protocol to intercalate and delaminate clay layers for clay-based applications and products.

Long-chain amine-templated synthesis of gallium sulfide and gallium selenide nanotubes

We describe the soft chemistry synthesis of amine-templated gallium chalcogenide nanotubes through the reaction of gallium(iii) acetylacetonate and the chalcogen (sulfur, selenium) using a mixture of long-chain amines (hexadecylamine and dodecylamine) as a solvent. Beyond their role as solvent, the amines also act as a template, directing the growth of discrete units with a one-dimensional multilayer tubular nanostructure. These new materials, which broaden the family of amine-stabilized gallium chalcogenides, can be tentatively classified as direct large band gap semiconductors. Their preliminary performance as active material for electrodes in lithium ion batteries has also been tested, demonstrating great potential in energy storage field even without optimization.

Lamellar supramolecular materials based on a chelated metal complex for organic dye adsorption

The industrial poisonous waste chelated copper complex can be made into recyclable lamellar supramolecular materials which display excellent adsorption ability towards organic dyes.

Investigation of Hexagonal Mesoporous Silica-Supported Composites for Trace Moisture Adsorption

Moisture control is an important part of effective maintenance program for gas-insulated switchgear (GIS). Herein, hexagonal mesoporous silica (HMS) materials were synthesized by adopting dodecylamine as a structure directing agent, which was then employed as a host for supporting polyethylenimine (PEI) without further calcinations or extraction treatment. The physicochemical properties of the silica support and composites were characterized, and the moisture adsorption capacity of these composites was determined. The reserved template agents resulted in a dramatic improvement in moisture adsorption amount. Among them, 50PEI/DHMS showed the highest adsorption value. The enhanced adsorption could be attributed to the generated hydrogen bonding between amino groups and H2O molecules and the improved diffusion of moisture into the bulk networks of PEI polymers due to its better spatial dispersion imposed by the long alkyl chains of template agents, which was confirmed by thermogravimetry results and hydrogen efficiency analysis. Moreover, the maintained terminal amino groups of templates could also function as active sites for moisture adsorption. The results herein imply that the PEI/DHMS composites could be appealing materials for capturing moisture in GIS.