Friction-Induced Enhancements for Photocatalytic Degradation of MoS2@Ti3C2 Nanohybrid

Enhancement of Peroxydisulfate Activation for Complete Degradation of Refractory Tetracycline by 3D Self-Supported MoS2/MXene Nanocomplex

Antibiotic abuse, particularly the excessive use of tetracycline (TC), a drug with significant environmental risk, has gravely harmed natural water bodies and even posed danger to human health. In this study, a three-dimensional self-supported MoS2/MXene nanohybrid with an expanded layer spacing was synthesized via a facile one-step hydrothermal method and used to activate peroxydisulfate (PDS) for the complete degradation of TC. The results showed that a stronger •OH signal was detected in the aqueous solution containing MoS2/MXene, demonstrating a superior PDS activation effect compared to MoS2 or Ti3C2TX MXene alone. Under the conditions of a catalyst dosage of 0.4 g/L, a PDS concentration of 0.4 mM, and pH = 5.0, the MoS2/MXene/PDS system was able to fully eliminate TC within one hour, which was probably due to the presence of several reactive oxygen species (ROS) (•OH, SO4•-, and O2•-) in the system. The high TC degradation efficiency could be maintained under the influence of various interfering ions and after five cycles, indicating that MoS2/MXene has good anti-interference and reusability performance. Furthermore, the possible degradation pathways were proposed by combining liquid chromatography-mass spectrometry (LC-MS) data and other findings, and the mechanism of the MoS2/MXene/PDS system on the degradation process of TC was elucidated by deducing the possible mechanism of ROS generation in the reaction process. All of these findings suggest that the MoS2/MXene composite catalyst has strong antibiotic removal capabilities with a wide range of application prospects.

Controllable interface-tailored strategy to reduce the nanotribological properties of Ti3C2Txby depositing MoS2using atomic layer deposition

Ti3C2TxMXene has attracted widespread attention in lubrication owing to its unique structure and surface properties. However, the inferior nanotribological properties of Ti3C2Txstill limit its applications in nano lubricants. Herein, we propose a controllable interface-tailored strategy to reduce the nanotribological properties of Ti3C2Txby depositing MoS2nano-sheet on its surface using atomic layer deposition (ALD). The nanotribological properties of the MoS2/Ti3C2Txnanocomposites synthesized by ALD are studied by atomic force microscope for the first time. At the optimal 20 ALD MoS2cycles, the nanofriction of MoS2/Ti3C2Txhas been reduced by 57%, 46%, and 44% (at 5, 10, and 15 nN load, respectively), while the adhesion has been reduced by 59%, compared to the original Ti3C2Tx. The results can contribute to understanding of the nanotribological mechanisms of Ti3C2Txcomposites and provide the potential prospects for Ti3C2Txas a nanoscale adjustable lubricant.

Recent advancements in MXene-based nanocomposites as photocatalysts for hazardous pollutant degradation - A review

The recent expeditious industrialization and urbanization showcase the increasing need for renewable and non-renewable energy and the severe environmental crisis. In this regard, numerous 2-dimensional (2D) nanomaterials have been developed as a facile approach to meet the futuristic energy essentials and to resolve the crisis. In contrast, the newly explored 2D MXenes (transition metal carbide/nitrides/carbonitride) have been employed as an intriguing material for various environmental applications. This development is accredited to their unique properties, which include a vast surface area, strong electrical conductivity, fascinating photophysical properties, high mechanical properties, stability in an aqueous medium, high hydrophilicity, biocompatibility, ease of functionalization, and excellent thermal properties. MXenes act as a potential candidate in water desalination, energy storage devices such as electrodes of Li-ion batteries and pseudo capacitors, hydrogen production, sensors, and wastewater treatment. This review article deliberates the synthesis of MXene and nanocomposites of MXene and their photo-catalytic actions against various toxic pollutants such as organic dyes and heavy metals in wastewater. This review also precises the various preparation methods of MXene-based photocatalyst and the enhanced photocatalytic activity of MXene and MXene-based nanocomposites in wastewater treatment. Also, it details the attempts made to improve the photocatalytic activity of MXene-based nanocomposites in terms of their structural compositions. In addition, the merits and demerits of the MXene-based photocatalysts are deliberated, which may pave the way for future research in this arena.

Interface Engineering in 2D/2D Heterogeneous Photocatalysts

Assembling different 2D nanomaterials into heterostructures with strong interfacial interactions presents a promising approach for novel artificial photocatalytic materials. Chemically implementing the 2D nanomaterials' construction/stacking modes to regulate different interfaces can extend their functionalities and achieve good performance. Herein, based on different fundamental principles and photochemical processes, multiple construction modes (e.g., face-to-face, edge-to-face, interface-to-face, edge-to-edge) are overviewed systematically with emphasis on the relationships between their interfacial characteristics (e.g., point, linear, planar), synthetic strategies (e.g., in situ growth, ex situ assembly), and enhanced applications to achieve precise regulation. Meanwhile, recent efforts for enhancing photocatalytic performances of 2D/2D heterostructures are summarized from the critical factors of enhancing visible light absorption, accelerating charge transfer/separation, and introducing novel active sites. Notably, the crucial roles of surface defects, cocatalysts, and surface modification for photocatalytic performance optimization of 2D/2D heterostructures are also discussed based on the synergistic effect of optimization engineering and heterogeneous interfaces. Finally, perspectives and challenges are proposed to emphasize future opportunities for expanding 2D/2D heterostructures for photocatalysis.

A Review on MXene Synthesis, Stability, and Photocatalytic Applications

Photocatalytic water splitting, CO₂ reduction, and pollutant degradation have emerged as promising strategies to remedy the existing environmental and energy crises. However, grafting of expensive and less abundant noble-metal cocatalysts on photocatalyst materials is a mandatory practice to achieve enhanced photocatalytic performance owing to the ability of the cocatalysts to extract electrons efficiently from the photocatalyst and enable rapid/enhanced catalytic reaction. Hence, developing highly efficient, inexpensive, and noble-metal-free cocatalysts composed of earth-abundant elements is considered as a noteworthy step toward considering photocatalysis as a more economical strategy. Recently, MXenes (two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides) have shown huge potential as alternatives for noble-metal cocatalysts. MXenes have several excellent properties, including atomically thin 2D morphology, metallic electrical conductivity, hydrophilic surface, and high specific surface area. In addition, they exhibit Gibbs free energy of intermediate H atom adsorption as close to zero and less than that of a commercial Pt-based cocatalyst, a Fermi level position above the H₂ generation potential, and an excellent ability to capture and activate CO₂ molecules. Therefore, there is a growing interest in MXene-based photocatalyst materials for various photocatalytic events. In this review, we focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of MXenes, and MXene-based photocatalysts for H₂ evolution, CO₂ reduction, and pollutant degradation. The existing challenges and the possible future directions to enhance the photocatalytic performance of MXene-based photocatalysts are also discussed.

Emerging architecture titanium carbide (Ti3C2Tx) MXene based photocatalyst toward degradation of hazardous pollutants: Recent progress and perspectives

MXenes family has aroused marvelous consideration as a frontier photoactive candidate for solar energy transformation and environmental remediation. 2D Ti₃C₂ exhibit a unique layered microstructure, large surface functional groups (-F, -OH, -O), substantial sorption selectivity, superior reduction efficiency, and electrical conductivity. Electronically conductive Ti₃C₂T_x with tunable energy band gap (0.92-1.75eV) makes it one of the most potential photoactive materials for photodegradation. The present review paper aims to design cost-effective heterojunctions and Schottky junctions of Ti₃C₂ with transition metal oxides, sulfides, g-C₃N₄, and other organic frameworks. The discussion mainly involves different aspects related to its tunable electronic structure, stability problems, and surface morphology control. In addition, the advantages of Ti₃C₂ in fabricating highly efficient Ti₃C₂ based catalytic junctions exhibiting suppressed charge carrier recombination are discussed with particular emphasis on their adsorption and redox properties for the removal of toxic dyes, heavy metal ions, and various pharmaceuticals. Finally, current challenges and research directions are outlined and prospected for the future development of Ti₃C₂ based photocatalytic systems.

MXenes based nano-heterojunctions and composites for advanced photocatalytic environmental detoxification and energy conversion: A review

Extensive research is being done to develop multifunctional advanced new materials for high performance photocatalytic applications in the field of energy production and environmental detoxification, MXenes have emerged as promising materials for enhancing photocatalytic performance owing to their excellent mechanical properties, appropriate Fermi levels, and adjustability of chemical composition. Numerous experimental and theoretical research works implied that the dimensions of MXenes have a significant impact on their performance. For photocatalysis to thrive in the future, we must understand the current state of the art for MXene in different dimensions. Using MXene co-catalysts in widely used in photocatalytic applications such as CO₂ reduction, hydrogen production and organic pollutant oxidation, this study focuses on the most recent developments in MXenes based materials, structural modifications, innovations in reaction and material engineering. It has been reported that using 5 mg of CdS-MoS₂-MXene researchers were able to generate as high as 9679 μmol/g/h hydrogen under visible light. The MXenes based heterojunction photocatalyst Co₃O₄/MXene was utilized to degrade 95% bisphenol A micro-pollutant in just 7 min. Numerous novel materials, their preparations and performances have been discussed. Depending upon the nature of MXene-based materials, the synthesis techniques and photocatalytic mechanism of MXenes as co-catalyst are also summarized. Finally, some final thoughts and prospects for developing highly efficient MXene-based photocatalysts are provided which will indeed motivate researchers to design novel hybrid materials based on MXenes for sustainable solutions to energy and pollution issues.

Accelerating Surface Photoreactions Using MoS2-FeS2 Nanoadsorbents: Photoreduction of Cr(VI) to Cr(III) and Photodegradation of Methylene Blue

Nanocubic MoS₂-FeS₂, as a photocatalyst, was synthesized with high catalytic active edges and high specific surface areas with the capability of absorbing visible light. The results showed that the photocatalytic efficiency of nanocubic MoS₂-FeS₂ for adsorption/degradation of methylene blue (MB) as well as the reduction of Cr(VI) was high. The adsorption process was found to follow a kinetic model of a pseudo-second-order kind (Q_e.cal = 464 mg g^-1) along with an isotherm described by the Langmuir model with Q_e.cal = 340 mg g^-1. The photodegradation process was achieved by holes. It was found that the photodegradation rate constant of MB by MoS₂-FeS₂ (0.203 min^-1) was about 22 times higher than that of MoS₂ (0.0091 min^-1). The percent apparent quantum yield for photoreduction of Cr(VI) to Cr(III) using MoS₂-FeS₂ (5.7%) was about 33 times higher than utilizing MoS₂ (0.1709%). Therefore, the synergistically prolonged visible-light harvesting as well as the photocarrier diffusion length proved that MoS₂-FeS₂ nanotubes can effectively be utilized in environmental pollutant's remediation.

Hierarchical MXene/transition metal chalcogenide heterostructures for electrochemical energy storage and conversion

MXenes have gained rapidly increasing attention owing to their two-dimensional (2D) layered structures and unique mechanical and physicochemical properties. However, MXenes have some intrinsic limitations (e.g., the restacking tendency of the 2D structure) that hinder their practical applications. Transition metal chalcogenide (TMC) materials such as SnS, NiS, MoS₂, FeS₂, and NiSe₂ have attracted much interest for energy storage and conversion by virture of their earth-abundance, low costs, moderate overpotentials, and unique layered structures. Nonetheless, the intrinsic poor electronic conductivity and huge volume change of TMC materials during the alkali metal-ion intercalation/deintercalation process cause fast capacity fading and poor-rate and poor-cycling performances. Constructing heterostructures based on metallic conductive MXenes and highly electrochemically active TMCs is a promising and effective strategy to solve these problems and enhance the electrochemical performances. This review highlights and discusses the recent research development of MXenes and hierarchical MXene/TMC heterostructures, with a focus on the synthesis strategies, surface/heterointerface engineering, and potential applications for lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, electrocatalysis, and photocatalysis. The critical challenges and perspectives of the future development of MXenes and hierarchical MXene/TMC heterostructures for electrochemical energy storage and conversion are forecasted.

Photocatalytic Fuel Cell-Assisted Molecularly Imprinted Self-Powered Sensor: A Flexible and Sensitive Tool for Detecting Aflatoxin B1

The self-powered electrochemical sensor has gained big achievements in energy and devices, but it is challenging in analytical application owing to its low energy conversion efficiency and limited selectivity caused by the plentiful interference in actual samples. Herein, a new self-powered biosensor was constructed by the integration of a photocatalytic fuel cell (PFC) with a molecular imprinting polymer (MIP) to achieve sensitive and specific detection of aflatoxin B1 (AFB₁). Compared with other fuel cells, the PFC owns the advantages of low cost, high energy, good stability, and friendly environment by using light as the excitation source. MoS₂-Ti₃C₂T_x MXene (MoS₂-MX) served as the photoanode material for the first time by forming a heterojunction structure, which can enhance the photocurrent by about 3-fold and greatly improve the photoelectric conversion efficiency. Aiming at the poor selectivity of the self-powered sensor, the MIP was introduced to achieve the specific capture and separation of targets without sample pretreatment. Using the MIP and PFC as recognition and signal conversion elements, respectively, the proposed self-powered biosensor showed a wide dynamic range of 0.01-1000 ng/mL with a detection limit of 0.73 pg/mL, which opened opportunities to design more novel self-powered biosensors and promoted its application in food safety and environmental monitoring.

Alkyl-Ethylene Amines as Effective Organic Friction Modifiers for the Boundary Lubrication Regime

With the pursuit of fuel economy in the automotive industry, recently low-viscosity lubricant technology has been widely improved. The present work has systematically discussed a series of sulfur- and phosphorus-free organic friction modifiers (FMs)-alkyl-ethylene amines-by alkyl substitution from ethylene amines with various nitrogen-atom numbers and molecular configurations. Herein, the pin-on-flat reciprocation friction tests have exhibited that the addition of the novel alkyl-ethylene amines into base oil led to significant reductions in the friction coefficient (up to 23%). Further investigations of tribological properties at elevated temperatures demonstrated that the increased number of nitrogen atoms and the regular linear atomic arrangement contributed to an improvement of friction reduction (up to 66%) compared to the neat base oil. Notably, results of water contact angle measurement and infrared spectroscopy (IR) have provided favorable evidence that the novel FMs have adsorbed on the metal surface leading to the formation of a tribofilm, whereby the tribofilm prevented the sliding surfaces from direct asperity contact and markedly improved the tribological performance, as seen from the composition analysis of the worn surfaces by an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and confocal Raman spectroscopy. Therefore, the present work can provide a practical reference for molecular structure design through investigation of structure-performance relations of lubricant additives.