Synergetic Exfoliation and Lateral Size Engineering of MoS2 for Enhanced Photocatalytic Hydrogen Generation

Engineering Injectable Coassembled Hydrogel by Photothermal Driven Chitosan-Stabilized MoS2 Nanosheets for Infected Wound Healing

The application of enzyme-like molybdenum disulfide (MoS2) in tissue repair was confronted with stable dispersion, solubilization, and biotoxicity. Here, the injectable self-healing hydrogel was successfully designed using a step-by-step coassembly of chitosan and MoS2. Polyphenolic chitosan as a "structural stabilizer" of MoS2 nanosheets reconstructed well-dispersed MoS2@CSH nanosheets, which improved the biocompatibility of traditional MoS2, and strengthened its photothermal conversion and enzyme-like activities, guaranteeing highly efficient radical scavenging and antimicrobial properties. Furthermore, the polyphenol chitosan was employed again as a "molecular cross-linking agent" to form the injectable NIR-responsive MoS2@CSH hydrogel by accelerating hydrogen-bond interaction among chitosan and the multicross-linking reaction among polyphenols. The rapid self-healing ability was conducive to wound closure and dynamic adaptability. An experimental study on infected wound healing demonstrated that MoS2@CSH hydrogel could substantially eradicate bacteria and accelerate the angiogenesis of infected wounds. The photothermal-driven coassembly of MoS2 and polycation provided an alternative strategy for infected wound healing.

Recent developments, advances and strategies in heterogeneous photocatalysts for water splitting

Photocatalytic water splitting (PWS) is an up-and-coming technology for generating sustainable fuel using light energy. Significant progress has been made in the developing of PWS innovations over recent years. In addition to various water-splitting (WS) systems, the focus has primarily been on one- and two-steps-excitation WS systems. These systems utilize singular or composite photocatalysts for WS, which is a simple, feasible, and cost-effective method for efficiently converting prevalent green energy into sustainable H2 energy on a large commercial scale. The proposed principle of charge confinement and transformation should be implemented dynamically by conjugating and stimulating the photocatalytic process while ensuring no unintentional connection at the interface. This study focuses on overall water splitting (OWS) using one/two-steps excitation and various techniques. It also discusses the current advancements in the development of new light-absorbing materials and provides perspectives and approaches for isolating photoinduced charges. This article explores multiple aspects of advancement, encompassing both chemical and physical changes, environmental factors, different photocatalyst types, and distinct parameters affecting PWS. Significant factors for achieving an efficient photocatalytic process under detrimental conditions, (e.g., strong light absorption, and synthesis of structures with a nanometer scale. Future research will focus on developing novel materials, investigating potential synthesis techniques, and improving existing high-energy raw materials. The endeavors aim is to enhance the efficiency of energy conversion, the absorption of radiation, and the coherence of physiochemical processes.

Precise Tuning of Bilayer Ultrasmall MoS2 Featuring Inhibition of Carrier Recombination and Fast Surface Chemistry for Green H2 Evolution

Achieving water splitting to produce green H2 , using the noble-metal-free MoS2 , has attracted huge interest from researchers. However, tuning the number of MoS2 layers precisely while obtaining small lateral sizes to surge the H2 -evolution rate is a tremendous challenge. Here, a bottom-up strategy is designed for the in situ growth of ultrasmall lateral-sized MoS2 with tunable layers on CdS nanorods (CN) by controlling the decomposition temperature and concentration of substrate seed (NH4 )2 MoS4 . Here, the bilayer MoS2 and CN coupling (2L-MoS2 /CN) exhibits the optimum photocatalytic activity. Compared to thicker MoS2 , the 2L-MoS2 has sufficient reduction capacity to drive photocatalytic H2 evolution and the ultrasmall lateral size provides more active sites. Meanwhile, the indirect bandgap, in contrast to the direct bandgap of the monolayer MoS2 , suppresses the carrier recombination transferred to 2L-MoS2 . Under the synergistic effect of both, 2L-MoS2 /CN has fast surface chemical reactions, resulting in the photocatalytic H2 -evolution rate of up to 41.86 mmol g-1 h-1 . A novel strategy is provided here for tuning the MoS2 layers to achieve efficient H2 evolution.

All-inorganic lead halide perovskites for photocatalysis: a review

Nowadays, environmental pollution and the energy crisis are two significant concerns in the world, and photocatalysis is seen as a key solution to these issues. All-inorganic lead halide perovskites have been extensively utilized in photocatalysis and have become one of the most promising materials in recent years. The superior performance of all-inorganic lead halide perovskites distinguish them from other photocatalysts. Since pure lead halide perovskites typically have shortcomings, such as low stability, poor active sites, and ineffective carrier extraction, that restrict their use in photocatalytic reactions, it is crucial to enhance their photocatalytic activity and stability. Huge progress has been made to deal with these critical issues to enhance the effects of all-inorganic lead halide perovskites as efficient photocatalysts in a wide range of applications. In this manuscript, the synthesis methods of all-inorganic lead halide perovskites are discussed, and promising strategies are proposed for superior photocatalytic performance. Moreover, the research progress of photocatalysis applications are summarized; finally, the issues of all-inorganic lead halide perovskite photocatalytic materials at the current state and future research directions are also analyzed and discussed. We hope that this manuscript will provide novel insights to researchers to further promote the research on photocatalysis based on all-inorganic lead halide perovskites.

Preparation of Structure Vacancy Defect Modified Diatomic-Layered g-C3 N4 Nanosheet with Enhanced Photocatalytic Performance

Structure self-modification of graphitic carbon nitride (g-C3 N4 ) without the assistance of other species has attracted considerable attention. In this study, the structure vacancy defect modified diatomic-layered g-C3 N4 nanosheet (VCN) is synthesized by thermal treatment of bulk g-C3 N4 in a quartz tube with vacuum atmosphere that will generate a pressure-thermal dual driving force to boost the exfoliation and formation of structure vacancy for g-C3 N4 . The as-prepared VCN possesses a large specific surface area with a rich pore structure to provide more active centers for catalytic reactions. Furthermore, the as-formed special defect level in VCN sample can generate a higher exciton density at photoexcitation stage. Meanwhile, the photogenerated charges will rapidly transfer to VCN surface due to the greatly shortened transfer path resulting from the ultrathin structure (≈1.5 nm), which corresponds to two graphite carbon nitride atomic layers. In addition, the defect level alleviates the drawback of enlarged bandgap caused by the quantum size effect of nano-scaled g-C3 N4 , resulting in a well visible-light utilization. As a result, the VCN sample exhibits an excellent photocatalytic performance both in hydrogen production and photodegradation of typical antibiotics.

Ni-doped MoS2 embedded in natural wood containing porous cellulose for piezo-catalytic degradation of tetracycline

Wood is a natural material with low cost and easy recovery, which porous, layered, excellent structure and mechanical properties make it possible to apply in wastewater treatment. We have successfully grown MoS₂ on natural wood containing porous cellulose and introduced the high conductivity circuit path provided by Ni nanoparticles to construct a new piezoelectric three-dimensional wood block for the efficient degradation of tetracycline. Ni/MoS₂/Wood exhibited excellent piezo-catalytic degradation performance, and the degradation rate of tetracycline reached 95.96 % (k = 0.0411 min^-1) under ultrasonic vibration. After 5 cycles, the degradation rate still reached 90.20 %. In addition, Ni/MoS₂/Wood was used as the reactor filler to degrade tetracycline through piezoelectric response triggered by hydrodynamic force, and the degradation rate reached 90.27 % after 60 min. Further, the mechanism and the possible degradation pathways of tetracycline degradation were proposed. This low-cost, recyclable and stable three-dimensional wood block piezoelectric material provides a new idea for the practical application of wastewater treatment.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion

Artificial photosynthetic solar-to-chemical cycles enable an entire environment to operate in a more complex, yet effective, way to perform natural photosynthesis. However, such artificial systems suffer from a lack of well-established photocatalysts with the ability to harvest the solar spectrum and rich catalytic active-site density. Benefiting from extensive experimental and theoretical investigations, this bottleneck may be overcome by devising a photocatalytic platform based on metal sulfides with predominant electronic, physical, and chemical properties. These tunable properties can endow them with abundant active sites, favorable light utilization, and expedited charge transportation for solar-to-chemical conversion. Here, it is described how some vital lessons extracted from previous investigations are employed to promote the further development of metal sulfides for artificial photosynthesis, including water splitting, CO₂ reduction, N₂ reduction, and pollutant removal. Their functions, properties, synthetic strategies, emerging issues, design principles, and intrinsic functional mechanisms for photocatalytic redox reactions are discussed in detail. Finally, the associated challenges and prospects for the utilization of metal sulfides are highlighted and future development trends in photocatalysis are envisioned.

Preparation and characterization of ZnO/graphene/graphene oxide/multi-walled carbon nanotube composite aerogels

ZnO/Graphene (G)/Graphene Oxide (GO)/Multi-walled Carbon Nanotube (MCNT) composite aerogels with a three-dimensional porous structure were prepared by the sol-gel method under average temperature and alkaline conditions, combined with freeze-drying process and heat treatment process. The photocatalytic degradation of Rhodamine B (RhB) was mainly studied. The scanning electron microscope (SEM) test results showed that the morphology uniformity of the ZnO/G/GO/MCNT composite aerogel was significantly enhanced, which effectively solving the agglomeration problem of MCNT and ZnO. The photocatalytic degradation test results of RhB show that due to the synergistic effect of physical adsorption and photocatalytic degradation, the total degradation efficiency of RhB by ZnO/G/GO/MCNT could reach 86.8%, which is 3.3 times higher than that of ZnO. In addition, the synergistic effect of ZnO and G effectively hinders the recombination of photo-generated electron-hole pairs and enhances photocatalytic activity. The ZnO/G/GO/MCNT composite aerogel can be applied in the visible light catalytic degradation of water pollution.

Promoting Charge Separation in Hollow-Structured C/MoS2@ZnIn2S4/Co3O4 Photocatalysts via Double Heterojunctions for Enhanced Photocatalytic Hydrogen Evolution

A reasonable design of samples with efficient spatial separation for photoinduced electron-hole pairs toward the photocatalytic hydrogen evolution reaction (HER) has gained significant attention. Herein, a new C/MoS₂@ZnIn₂S₄/Co₃O₄ composite with a core-shell structure is designed toward photocatalytic hydrogen production on C/MoS₂ and Co₃O₄ dual electron collectors. Co₃O₄ nanoparticles as the co-catalyst would form a Schottky junction with ZnIn₂S₄ nanosheets while the C/MoS₂ hollow core would form the step-scheme (S-scheme) heterojunction with ZnIn₂S₄ sheets, which provides a dual photogenerated electron transfer pathway during the light irradiation process. In addition, the unique core-shell architecture offers large contact interfaces favoring the exposure of rich active sites, which facilitated the separation and the transfer of charges. Consequently, all these factors endowed the C/MoS₂@ZnIn₂S₄/Co₃O₄ composite with enhanced light absorption ability and an increased hydrogen evolution rate of 6.7 mmol·g^-1·h^-1 under 420 nm light irradiation, which is about 23.4- and 4.5-fold that of ZnIn₂S₄ and CMZ, respectively. This work offers a guideline for designing efficient composite photocatalysts toward the photocatalytic HER.

Synergistic Promotion Effect of ZnCoS Solid Solution and Co1-xS on Photocatalytic Hydrogen Production of the CdS Composite

Photocatalytic reactions over effective photocatalysts are attractive to explore clean hydrogen energy from water with the utilization of solar energy. Ternary Co_1-xS@ZnCoS/CdS (ZCS/CdS) composites are constructed as photocatalysts through the hydrothermal formation of Co_1-xS and ZnCoS nanoparticles on CdS nanorods. Superior to the binary Co_1-xS/CdS composite, ZCS/CdS shows the improved photocatalytic activity with a hydrogen production rate of 58.4 mmol·g^-1·h^-1, which is 31.4 and 2.1 times higher than those of CdS and Co_1-xS/CdS, respectively. Different from binary Co_1-xS/CdS, the participation of a small amount of zinc favors the formation of ZnCoS solid solution in ZCS/CdS. A synergistic promotion effect of ZnCoS and Co_1-xS is confirmed due to tight heterojunctions among Co_1-xS, ZnCoS, and CdS in ZCS/CdS. The unique heterostructure of ZCS/CdS benefits its enhanced absorption ability of visible light, accelerating the separation of photoinduced electron-hole pairs and the electron transfer. ZCS/CdS exhibits the strong reduction ability and superior photocatalytic stability due to the role of double Z-scheme electron transfer pathways in the ternary composite. This work provides a suitable way to tune noble metal-free composite photocatalysts for efficient H₂ production.

Synergetic Advantages of Atomically Coupled 2D Inorganic and Graphene Nanosheets as Versatile Building Blocks for Diverse Functional Nanohybrids

2D nanostructured materials, including inorganic and graphene nanosheets, have evoked plenty of scientific research activity due to their intriguing properties and excellent functionalities. The complementary advantages and common 2D crystal shapes of inorganic and graphene nanosheets render their homogenous mixtures powerful building blocks for novel high-performance functional hybrid materials. The nanometer-level thickness of 2D inorganic/graphene nanosheets allows the achievement of unusually strong electronic couplings between sheets, leading to a remarkable improvement in preexisting functionalities and the creation of unexpected properties. The synergetic merits of atomically coupled 2D inorganic-graphene nanosheets are presented here in the exploration of novel heterogeneous functional materials, with an emphasis on their critical roles as hybridization building blocks, interstratified sheets, additives, substrates, and deposited monolayers. The great flexibility and controllability of the elemental compositions, defect structures, and surface natures of inorganic-graphene nanosheets provide valuable opportunities for exploring high-performance nanohybrids applicable as electrodes for supercapacitors and rechargeable batteries, electrocatalysts, photocatalysts, and water purification agents, to give some examples. An outlook on future research perspectives for the exploitation of emerging 2D nanosheet-based hybrid materials is also presented along with novel synthetic strategies to maximize the synergetic advantage of atomically mixed 2D inorganic-graphene nanosheets.

Simultaneous Enhancement of Charge Separation and Hole Transportation in a W:α-Fe2O3/MoS2 Photoanode: A Collaborative Approach of MoS2 as a Heterojunction and W as a Metal Dopant

In this study, a facile approach has been successfully applied to synthesize a W-doped Fe₂O₃/MoS₂ core-shell electrode with unique nanostructure modifications for photoelectrochemical performance. A two-dimensional (2D) structure of molybdenum disulfide (MoS₂) and tungsten (W)-doped hematite (W:α-Fe₂O₃) overcomes the drawbacks of the α-Fe₂O₃ and MoS₂ semiconductor through simple and facile processes to improve the photoelectrochemical (PEC) performance. The highest photocurrent density of the 0.5W:α-Fe₂O₃/MoS₂ photoanode is 1.83 mA·cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE) under 100 mW·cm² illumination, which is higher than those of 0.5W:α-Fe₂O₃ and pure α-Fe₂O₃ electrodes. The overall water splitting was evaluated by measuring the H₂ and O₂ evolution, which after 2 h of irradiation for 0.5W:α-Fe₂O₃/MoS₂ was determined to be 49 and 23.8 μmol.cm^-2, respectively. The optimized combination of the heterojunction and metal doping on pure α-Fe₂O₃ (0.5W:α-Fe₂O₃/MoS₂ photoanode) showed an incident photon-to-electron conversion efficiency (IPCE) of 37% and an applied bias photon-to-current efficiency (ABPE) of 26%, which are around 5.2 and 13 times higher than those of 0.5W:α-Fe₂O₃, respectively. Moreover, the facile fabrication strategy can be easily extended to design other oxide/carbon-sulfide/oxide core-shell materials for extensive applications.

One-pot synthesis of S-scheme MoS2/g-C3N4 heterojunction as effective visible light photocatalyst

Despite pioneering as the holy grail in photocatalysts, abundant reports have demonstrated that g-C₃N₄ performs poor photocatalytic activity due to its high recombination rate of photo-induced charge carriers. Many efforts have been conducted to overcome this limitation in which the semiconductor-semiconductor coupling strategies toward heterojunction formation were considered as the easiest but the most effective method. Herein, a one-pot solid-state reaction of thiourea and sodium molybdate as precursors at different temperatures under N₂ gas was applied for preparing composites of MoS₂/g-C₃N₄. The physicochemical characterization of the final products determines the variation in contents of components (MoS₂ and g-C₃N₄) via the increase of synthesis temperature. The enhanced photocatalytic activity of the MoS₂/g-C₃N₄ composites was evaluated by the degradation of Rhodamine B in an aqueous solution under visible light. Therein, composites synthesized at 500 °C showed the best photocatalytic performance with a degradation efficiency of 90%, much higher than that of single g-C₃N₄. The significant improvement in photocatalytic performance is attributed to the enhancement in light-harvesting and extension in photo-induced charge carriers' lifetime of composites which are originated from the synergic effect between the components. Besides, the photocatalytic mechanism is demonstrated to well-fit into the S-scheme pathway with apparent evidences.

Aqueous Adsorption of Heavy Metals on Metal Sulfide Nanomaterials: Synthesis and Application

Heavy metals pollution of aqueous solutions generates considerable concerns as they adversely impact the environment and health of humans. Among the remediation technologies, adsorption with metal sulfide nanomaterials has proven to be a promising strategy due to their cost-effective, environmentally friendly, surface modulational, and amenable properties. Their excellent adsorption characteristics are attributed to the inherently exposed sulfur atoms that interact with heavy metals through various processes. This work presents a comprehensive overview of the sequestration of heavy metals from water using metal sulfide nanomaterials. The common methods of synthesis, the structures, and the supports for metal sulfide nano-adsorbents are accentuated. The adsorption mechanisms and governing conditions and parameters are stressed. Practical heavy metal remediation application in aqueous media using metal sulfide nanomaterials is highlighted, and the existing research gaps are underscored.

Electroforming-free nonvolatile resistive switching of redox-exfoliated MoS2nanoflakes loaded polystyrene thin film with synaptic functionality

Here, we report robust and highly reproducible nonvolatile resistive switching (RS) devices with artificial synaptic functionalities utilizing redox-exfoliated few-layered 2H-MoS₂nanoflakes. Advantageous polar solvent compatibility of 2D MoS₂from this method were utilized to fabricate thin film devices very easily and cost-effectively using polystyrene as matrix. Prominent RS property of polystyrene thin film devices with varying MoS₂concentrations strongly favors electroforming-free operation. The conduction band position of 2D MoS₂nanosheet in combination with the work functions of chosen electrodes looks alleviating to switch the current from low to high at a suitable positive bias voltage. We further confirmed the mechanism of charge transport through fitting the results with theoretical models, say injection-dominated Schottky emission model for low-conducting states and space-charge-limited current mechanism for the high-conducting state. Interestingly, a relatively high current On/Off ratio 10²was recorded during the pump-probe testing to show resistive random-access memory (ReRAM) application. Finally, artificial synaptic functionalities- the building blocks of neuromorphic computing architectures is also illustrated by considering the robust RS property and ReRAM application.

0D, 1D, 2D molybdenum disulfide functionalized by 2D polymeric carbon nitride for photocatalytic water splitting

Photocatalytic activity of molybdenum disulfide structures with different dimensions (0D, 1D and 2D) functionalized with polymeric carbon nitride (PCN) is presented. MoS₂nanotubes (1D), nanoflakes (2D) and quantum dots (0D, QDs) were used, respectively, as co-catalysts of PCN in photocatalytic water splitting reaction to evolve hydrogen. Although, 2D-PCN showed the highest light absorption in visible range and the most enhanced photocurrent response after irradiation with light from 460 to 727 nm, QDs-PCN showed the highest photocatalytic efficiency. The detailed analysis revealed that the superior photocatalytic activity of QDs-PCN in comparison with other structures of MoS₂arose from (i) the most effective separation of photoexcited electron-hole pairs, (ii) the most enhanced up-converted photoluminescence (UCPL), (iii) the highest reactivity of electrons in conduction band. Moreover, a narrowed size of QDs affected shorter diffusion path of charge carriers to active reaction sites, higher number of the sites and higher interfacial area between molybdenum disulfide and PCN.

Light-Induced In Situ Formation of a Nonmetallic Plasmonic MoS2/MoO3-x Heterostructure with Efficient Charge Transfer for CO2 Reduction and SERS Detection

Low-cost and abundant reserved nonmetallic plasmonic materials have been regarded as a promising substitute of noble metals for photocatalysis and surface-enhanced Raman scattering (SERS). In this paper, a MoS₂/MoO_3-x heterostructure was synthesized by light-induced in situ partial oxidation of MoS₂ nanosheets, exhibiting strong surface plasmon resonance (SPR) in a vis-near-infrared (NIR) region. Continuously plasmon-induced hot electrons boost CO₂ reduction to CO due to efficient photoelectron injection from MoS₂ to MoO_3-x. Under UV-vis-NIR irradiation, the CO generation rate reached 32.4 μmol g^-1 h^-1 with a selectivity of 94.1%, which was much higher than that of single MoS₂ or MoO_3-x. Furthermore, the plasmonic MoS₂/MoO_3-x heterostructure exhibits superior SERS performance for sensitive rhodamine 6G detection (10^-9 M) with an enhancement factor of ∼10⁶ because of the synergy between SPR and charge transfer effect. This work provides one novel mild synthetization of a plasmonic heterostructure and demonstrates its potential in plasmon-enhanced CO₂ reduction and SERS detection.

Donor–acceptor covalent organic framework/g-C3N4 hybrids for efficient visible light photocatalytic H2 production

A donor–acceptor type covalent organic framework (COF) was used to construct TBTA/g-C₃N₄ hybrids for photocatalytic H₂ evolution. Under visible light irradiation, the hybrids exhibited an optimized H₂ evolution rate of 11.73 mmol g⁻¹ h⁻¹ without Pt.

Lamellar flower-like porous MoS2 as an efficient cocatalyst to boost photocatalytic hydrogen evolution of CdS

A lamellar flower-like porous MoS₂ cocatalyst with the synergistic role of porous and lamellar structures was configured to boost photocatalytic performance of CdS in hydrogen evolution reaction.

Ultrasonically prepared photocatalyst of W/WO3 nanoplates with WS2 nanosheets as 2D material for improving photoelectrochemical water splitting

A sonochemical treatment has been an emerged technique as an interesting method for fabricating different photocatalysts with unique photoelectrochemical (PEC) properties. This study investigated the PEC performance of WO3 with WS2 nanosheets as a 2D material before calcination (WO3/WS2-90) and after calcination (WO3/WS2-450) prepared with sonochemical treatment. The WS2 nanosheets were prepared from a liquid exfoliation phase with few-layer nanosheets, approximately 6.5 nm in thickness. The nanosheets were confirmed by UV-Vis spectroscopy and atomic force microscopy. Further, XPS, RAMAN, and SEM-EDAX analyses indicated that, following calcination of the WO3/WS2 electrode, the WS2 nanosheets initially transformed to 2D-WO3. After depositing the WS2 nanosheets on the WO3, the photocurrent density increased substantially. The WO3/WS2-450 films after calcination showed a photocurrent density of 5.6 mA.cm-2 at 1.23 V vs. Ag/AgCl, which was 3.1 and 7.2 times higher, respectively than those of the WO3/WS2-90 before calcination and pure WO3. Mott-Schottky and electrochemical impedance spectroscopy analyses confirmed the fabrication of the WO3/WS2 photoanode after calcination. The deposition of WS2 nanosheets onto pure WO3 increased the donor concentration (24-fold), reduced the space charge layer (4.6-fold), and decreased the flat band potential (1.6-fold), which could all help improve the photoelectrochemical efficiency. Moreover, the incorporation of WO3 with WS2 nanosheets as a 2D material (WO3/WS2-450) enhanced the incident photon current efficiency (IPCE) by 55%. In addition, the applied-bias photon-to-current conversion efficiency of the WO3/WS2-450 films was approximately 2.26% at 0.75 V (vs. Ag/AgCl), which is 5.6 and 9 times higher, respectively than those of WO3/WS2-90 and pure WO3.

Topology of transition metal dichalcogenides: the case of the core-shell architecture

Non-planar architectures of the traditionally flat 2D materials are emerging as an intriguing paradigm to realize nascent properties within the family of transition metal dichalcogenides (TMDs). These non-planar forms encompass a diversity of curvatures, morphologies, and overall 3D architectures that exhibit unusual characteristics across the hierarchy of length-scales. Topology offers an integrated and unified approach to describe, harness, and eventually tailor non-planar architectures through both local and higher order geometry. Topological design of layered materials intrinsically invokes elements highly relevant to property manipulation in TMDs, such as the origin of strain and its accommodation by defects and interfaces, which have broad implications for improved material design. In this review, we discuss the importance and impact of geometry on the structure and properties of TMDs. We present a generalized geometric framework to classify and relate the diversity of possible non-planar TMD forms. We then examine the nature of curvature in the emerging core-shell architecture, which has attracted high interest due to its versatility and design potential. We consider the local structure of curved TMDs, including defect formation, strain, and crystal growth dynamics, and factors affecting the morphology of core-shell structures, such as synthesis conditions and substrate morphology. We conclude by discussing unique aspects of TMD architectures that can be leveraged to engineer targeted, exotic properties and detail how advanced characterization tools enable detection of these features. Varying the topology of nanomaterials has long served as a potent methodology to engineer unusual and exotic properties, and the time is ripe to apply topological design principles to TMDs to drive future nanotechnology innovation.

A Mini Review of the Preparation and Photocatalytic Properties of Two-Dimensional Materials

The successful preparation and application of graphene shows that it is feasible for the materials with a thickness of a single atom or few atomic layers to exist stably in nature. These materials can exhibit unusual physical and chemical properties due to their special dimension effects. At present, researchers have made great achievements in the preparation, characterization, modification, and theoretical research of 2D materials. Because the structure of 2D materials is often similar, it has a certain degree of qualitative versatility. Besides, 2D materials often carry good catalytic performance on account of their more active sites and adjustable harmonic electronic structure. In this review, taking 2D materials as examples [graphene, boron nitride (h-BN), transition metal sulfide and so on], we review the crystal structure and preparation methods of these materials in recent years, focus on their photocatalyst properties (carbon dioxide reduction and hydrogen production), and discuss their applications and development prospects in the future.

Theoretical study on the photocatalytic properties of 2D InX(X = S, Se)/transition metal disulfide (MoS2 and WS2) van der Waals heterostructures

Harvesting solar energy for artificial photosynthesis is an emerging field in alternative energy research. In this work, the photocatalytic properties of InX(X = S, Se)/transition metal disulfide (MoS₂ and WS₂) van der Waals heterostructures have been investigated. The calculation results indicate that these heterostructures exhibit improved photocatalytic performance over that of isolated InX or transition metal disulfide monolayers. The studied heterostructures all have type-II band alignment with holes and electrons located at the TMD and InX side, respectively. This facilitates the spatial separation of photogenerated carriers and improves the photocatalytic efficiency. The carrier mobility of the designed heterostructures can be boosted compared with the isolated monolayers, thus enhancing the carrier transport properties. Moreover, the strain-tuned heterostructures can prominently manipulate the light-harvesting capability especially from the visible light to infrared light range. Among the studied heterostructures, InSe/MoS₂ with the suitable band edge positions, excellent transport properties and strain tolerance, and the lowest overpotential for oxygen evolution, stands out as the most promising candidate for photocatalytic applications. This work opens an avenue for the design of highly efficient heterostructure photocatalysts for solar-to-energy applications.

Confining Mo-activated CoSx active sites within MCM-41 for highly efficient dye-sensitized photocatalytic H2 evolution

Although transition-metal-based sulfides have been identified as efficient catalysts to replace expensive noble metal catalysts for photocatalytic H₂ evolution reaction (HER), their activities are still unsatisfied and could be further improved by controlling their microstructures and electronic structures. Herein, we present an effective strategy to confine highly active Mo-activated CoS_x (Mo-CoS_x) active sites within MCM-41 frameworks by sulfurization of Co-doped MCM-41 during the in situ photoreduction of [MoS₄]^2- in Erythrosin B-triethanolamine (ErB-TEOA) system. It is found that Co-MCM-41 offers not only abundant coordinatively unsaturated Co sites to be activated by Mo and S but also large surface area to effectively disperse the in situ generated amorphous Mo-CoS_x active sites. Under 520 nm irradiation, the most efficient Mo-CoS_x/MCM-41-100 (Si/Co = 100) catalyst exhibits ~7, 3, and 4 times higher H₂ evolution activity than free MoS_x, free Mo-CoS_x, and CoS_x/MCM-41-100, respectively, and an apparent quantum yield (AQY) of 12.3% for H₂ evolution. Furthermore, when Mo-CoS_x/MCM-41-100 was sensitized with a more stable fluorescein (FL) dye, the photocatalytic system shows a sustainable H₂ evolution activity in a 20 h reaction, showing the good stability of Mo-CoS_x/MCM-41-100 catalyst. This work provides a new insight into the design and development of highly active hybrid H₂ evolution catalysts based on transition metals for highly efficient and large-scale solar energy conversion to clean H₂ energy.

S-Edge-rich MoxSy arrays vertically grown on carbon aerogels as superior bifunctional HER/OER electrocatalysts

Molybdenum disulfide (MoS₂) is a potential earth-abundant electrocatalyst for the hydrogen evolution reaction (HER), but the lack of in-depth understanding of its intrinsic activity still impedes the further optimization and design of MoS₂-based electrocatalysts. Herein, we report a facile in situ hydrothermal synthetic method to prepare vertical Mo_xS_y arrays grown on guar gum-derived carbon aerogels (GCA), termed Mo_xS_y@GCA. The obtained well-assembled Mo_xS_y@GCA architectures consist of uniform, few-layered and S-edge-rich Mo_xS_y nanoflakes with a length of approximately 100 nm, which effectively prevent the inherent stacking among Mo_xS_y layers and connect the charge transfer path between interlayers, thus endowing Mo_xS_y@GCA with a huge number of active sites and high conductivity. Benefitting from all these advantages, the optimal Mo₄S₁₆@GCA exhibited extraordinary HER/OER performances, including a low onset potential for both the HER (24.28 mV) and OER (1.53 V), and a low overpotential at 10 mA cm^-2 for the HER (54.13 mV) and OER (370 mV), which are both extremely close to that of the noble Pt/C. Furthermore, a series of operando Raman spectroscopy measurements on Mo₄S₁₆@GCA were conducted to identify the intrinsic HER/OER-active sites during the HER and OER process. The results show that the S-H bond is generated simultaneously as HER/OER excitation, indicating the rich S-edge may be the intrinsic active site, which will accelerate the HER/OER kinetic process. Density functional theory (DFT) calculations revealed that the observed superb HER/OER activity can be attributed to the synergistic effect of rich S-edge of Mo_xS_y and confinement effect of GCA, which collaboratively promote the proton adsorption and electrocatalytic kinetics. Reasonably, this study will have profound guiding value for the rational tailoring of the microstructure and size of transition metal electrocatalysts via hierarchical porous carbon aerogels.

A Critical Review on Enhancement of Photocatalytic Hydrogen Production by Molybdenum Disulfide: From Growth to Interfacial Activities

Ultrathin 2D molybdenum disulfide (MoS₂ ), which is the flagship of 2D transition-metal dichalcogenide nanomaterials, has drawn much attention in the last few years. 2D MoS₂ has been banked as an alternative to platinum for highly active hydrogen evolution reaction because of its low cost, high surface-to-volume ratio, and abundant active sites. However, when MoS₂ is used directly as a photocatalyst, contrary to public expectation, it still performs poorly due to lateral size, high recombination ratio of excitons, and low optical cross section. Besides, simply compositing MoS₂ as a cocatalyst with other semiconductors cannot satisfy the practical application, which stimulates the pursual of a comprehensive insight into recent advances in synthesis, properties, and enhanced hydrogen production of MoS₂ . Therefore, in this Review, emphasis is given to synthetic methods, phase transitions, tunable optical properties, and interfacial engineering of 2D MoS₂ . Abundant ways of band edge tuning, structural modification, and phase transition are addressed, which can generate the neoteric photocatalytic systems. Finally, the main challenges and opportunities with respect to MoS₂ being a cocatalyst and coherent light-matter interaction of MoS₂ in photocatalytic systems are proposed.

Tailoring the physicochemical properties of solution-processed transition metal dichalcogenides via molecular approaches

In this Feature Article we highlight the tremendous progress in solution-processed transition metal dichalcogenides and the molecular approaches employed to finely tune their physicochemical properties.

Doping engineering and functionalization of two-dimensional metal chalcogenides

Two-dimensional (2D) layered metal chalcogenides (MXs) have significant potential for use in flexible transistors, optoelectronics, sensing and memory devices beyond the state-of-the-art technology. To pursue ultimate performance, precisely controlled doping engineering of 2D MXs is desired for tailoring their physical and chemical properties in functional devices. In this review, we highlight the recent progress in the doping engineering of 2D MXs, covering that enabled by substitution, exterior charge transfer, intercalation and the electrostatic doping mechanism. A variety of novel doping engineering examples leading to Janus structures, defect curing effects, zero-valent intercalation and deliberately devised floating gate modulation will be discussed together with their intriguing application prospects. The choice of doping strategies and sources for functionalizing MXs will be provided to facilitate ongoing research in this field toward multifunctional applications.

MOF-templated in situ fabrication of surface-modified Ni/graphitic carbon nitride with enhanced photocatalytic hydrogen evolution

Surface-modified Ni species derived from 2D Ni-MOFs were loaded on g-C₃N₄ with high dispersion by the in situ calcination method.

Construction of Acetaldehyde-Modified g-C3N4 Ultrathin Nanosheets via Ethylene Glycol-Assisted Liquid Exfoliation for Selective Fluorescence Sensing of Ag. ACS APPLIED MATERIALS & INTERFACES 2018;10:44624-44633. [PMID: 30511564 DOI: 10.1021/acsami.8b15501]

We successfully prepared acetaldehyde-modified graphitic carbon nitride (g-C₃N₄) ultrathin nanosheets (ACNNSs) by a simple ethylene glycol-assisted liquid exfoliation method. The introduction of acetaldehyde regulated the surface energy of g-C₃N₄ to better match with that of water, which improved the exfoliation efficiency. Moreover, acetaldehyde introduces defects into the g-C₃N₄ structure, which can act as excitation energy traps and cause considerable variation in the fluorescence emission. Benefiting from the stable photoluminescence emission, good water solubility, and biocompatibility, the obtained ACNNSs showed a selective fluorescent response to Ag⁺ in both aqueous solution and living cells. The strong absorption and intimate contact with Ag⁺ and its appropriate redox potential of ACNNSs contributed to this excellent fluorescent response. A simple and environmental friendly approach was proposed to simultaneously achieve modification and exfoliation of g-C₃N₄ in aqueous solution. These findings might lead to wider applications of carbon-based nanomaterials as active materials for fluorescence detection in the environment.

Conductive Molybdenum Sulfide for Efficient Electrocatalytic Hydrogen Evolution

Molybdenum sulfide (MoS₂ ) is a layered material with high activity for electrocatalytic hydrogen evolution reaction (HER). In conventional MoS₂ , the high electrical resistance between the layers hampers the bulk charge transfer and therefore greatly limits its performance in electrolysis. Herein, ultrathin MoS₂ nanosheets with bent layers on reduced graphene oxide (RGO) are reported. In sharp contrast to the bulk MoS₂ , the resulting MoS₂ has mostly 1 or 2 layers, and the layer distance is significantly expanded to ≈1 nm. From computational studies, the prepared MoS₂ with limited layer numbers and expanded layer distances has similar physical and chemical features with single-layer MoS₂ . Importantly, the bent single layer is electrically conductive and is intrinsically more active than a normal flat single layer. In addition, the unusual features of confined sizes and distorted lattices in the prepared MoS₂ can bring about plentiful active sites and are beneficial for mass diffusion during electrocatalysis. The hybrid material exhibits high activity for electrocatalytic HER, affording a current density of 10 mA cm^-2 at a low overpotential of 66 mV.