Molecular investigation of water adsorption on MoS 2 and graphene surfaces

MoS2 and MoS2 Nanocomposites for Adsorption and Photodegradation of Water Pollutants: A Review

The need for fresh and conveniently treated water has become a major concern in recent years. Molybdenum disulfide (MoS₂) nanomaterials are attracting attention in various fields, such as energy, hydrogen production, and water decontamination. This review provides an overview of the recent developments in MoS₂-based nanomaterials for water treatment via adsorption and photodegradation. Primary attention is given to the structure, properties, and major methods for the synthesis and modification of MoS₂, aiming for efficient water-contaminant removal. The combination of MoS₂ with other components results in nanocomposites that can be separated easily or that present enhanced adsorptive and photocatalytic properties. The performance of these materials in the adsorption of heavy metal ions and organic contaminants, such as dyes and drugs, is reviewed. The review also summarizes current progress in the photocatalytic degradation of various water pollutants, using MoS₂-based nanomaterials under UV-VIS light irradiation. MoS₂-based materials showed good activity after several reuse cycles and in real water scenarios. Regarding the ecotoxicity of the MoS₂, the number of studies is still limited, and more work is needed to effectively evaluate the risks of using this nanomaterial in water treatment.

2D/2d heterojunction of MoS2/g-C3N4 nanoflowers for enhanced visible-light-driven photocatalytic and electrochemical degradation of organic pollutants

Photodegradation of toxic pollutants is a promising approach to deal with wastewater management. In this regard, MoS₂/g-C₃N₄ (MSC) derived composites with varying weight-ratios were prepared via fast (30 min) one step microwave-assisted method. The materials were characterized by XRD, XPS, EDS, FESEM and HRTEM to validate their flower-like and sheet-like morphologies. The PL and UV-vis DRS spectra exhibited low recombination-rate and band-gap (1.7 eV), which is appropriate for an effective visible-light degradation. Photocatalytic performance of the catalysts was analyzed by investigating the degradation of methylene blue (MB) as well as pesticide fipronil. Best results were obtained by 5:1 MSC (98.7% degradation efficacy; rate constant 0.0261 min^-1) in 80 min under the sunlight. The effects of solution pH, catalyst-dose, scavengers and illumination-area were also explored. The catalyst was reusable as confirmed by degradation studies (~82% efficiency) even after 5-cycles. The photocatalytic treatment of real industrial-wastewater was also conducted. The TOC and COD analysis validated that the treatment by as-prepared catalyst is more proficient for effluent-treatment than the industrial physico-chemical treatments. Electrochemical degradation of MB was also investigated using the glassy carbon electrode modified with different MSC-ratios. The electrode modified with 5:1 MSC at pH 7 manifested the maximum peak current. The plausible mechanisms for photocatalytic and electrochemical degradations were proposed, which suggested the remarkable potential the prepared nanocomposites for wastewater treatment.

How pressure affects confine water inside different nanoslits

Nanoslits composed of different layered nanomaterials attract great attention in the theoretical and experimental investigations of nanofluidic devices due to their geometric simplicity and unique surface properties. Although many efforts have witnessed simulations of water molecules inside slit-like nanochannels formed by graphenes, the thermodynamic properties and transport behavior of water inside nanoslits formed by different two-dimensional materials are seldom investigated. In this paper, we choose nanoslits formed by graphene, boron nitride (hBN), and molybdenum disulfide (MoS₂) as models, and study the water properties inside these nanoslits using traditional molecular dynamics simulations at different pressures. It is shown that water molecules can form a planar square at high pressure (10 kbar) in all three types of nanoslit. The nanoslits affect diffusion coefficient, orientation of water molecules, number of hydrogen bonds and life-time of hydrogen bonding significantly. The self-diffusion coefficients of water molecules in different nanoslits are all lower than that of bulk water. The diffusion coefficients are significantly affected by the special ordered structure of water, which is caused by the unique surface structure of the nanoslit. The results of the present work will be helpful to understand the unique behavior of confined water in nanoslits composed of different nanomaterials and provide theoretical guidance for many applications, such as desalination and nano-energy conversion.

Pressure significantly affects thermodynamic and diffusion properties of water confined in different nanoslits. This difference is caused by the competition of interaction between water–water and water–wall.

Formation and stability of water clusters at the molybdenum disulfide interface: a molecular dynamics simulation investigation

In this work structural properties and dynamic behavior of a water nano droplet on the molybdenum disulfide were considered. The simulation results show that water molecules form polygon clusters on the interface, and most of which are hexagonal. Structures of water clusters at the interface are seen in two forms of curved and flattened polygons, which result in the formation of hydrogen bonds between and in the adjacent layers, respectively. Most of the clusters have circular flattened structures. Calculations of the lifetime of hydrogen bonds of water molecules at the interface also show that hydrogen bonds between water molecules at the interface have a low stability. This leads to the permanent formation and breaking down of hydrogen bonds of water molecules which can cause movement of water molecules and, consequently, the displacement of the center of mass and droplet motion. Considering the changes in the center of mass of a water droplet at the MoS₂ interface display, the water droplet has a significant spontaneous motion.

Structural and dynamical characterization of water on the Au (100) and graphene surfaces: A molecular dynamics simulation approach

The positioning, adsorption, and movement of water on substrates is dependent upon the chemical nature and arrangement of the atoms of the surface. Therefore the behavior of water molecules on a substrate is a reflection of properties of the surface. Based on this premise, graphene and gold substrates were chosen to study this subject from a molecular perspective. In this work, the structural and dynamical behaviors of a water nanodroplet on Au (100) and the graphene interfaces have been studied by molecular dynamics simulation. The results have shown how the structural and dynamical behaviors of water molecules at the interface reflect the characteristics of these surfaces. The results have demonstrated that residence time and hydrogen bonds' lifetime at the water-Au (100) interface are bigger than at the water-graphene interface. Energy contour map analysis indicates a more uniform surface energy on graphene than on the gold surface. The obtained results illustrate that water clusters on gold and graphene form tetramer and hexamer structures, respectively. Furthermore, the water molecules are more ordered on the gold surface than on graphene. The study of hydrogen bonds showed that the order, stability, and the number of hydrogen bonds is higher on the gold surface. The positioning pattern of water molecules is also similar to the arrangement of gold atoms while no regularity was observed on graphene. The study of dynamical behavior of water molecules revealed that the movement of water on gold is much less than on graphene which is in agreement with the strong water-gold interaction in comparison to the water-graphene interaction.