Chalcogen Vacancies as Key Drivers of Distinct Physicochemistry in MoS2, MoSe2, and MoTe2 for Selective Catalysis

The catalytic performance of Mo-based transition-metal-dichalcogenide (TMD) monolayers is intrinsically tied to their physicochemical properties. However, the limited chemical diversity among these materials constrains their versatility for key catalytic processes, including carbon dioxide (CRR), nitrogen (NRR), and oxygen (ORR) reduction reactions. This study employs density functional theory (DFT) calculations to investigate the impact of chalcogen vacancies on the properties ofMoS 2 ${{\rm{MoS}}_2 }$ ,MoSe 2 ${{\rm{MoSe}}_2 }$ , andMoTe 2 ${{\rm{MoTe}}_2 }$ , focusing on the adsorption behaviors of CO, NO, andNO 2 ${{\rm{NO}}_2 }$ . The findings reveal that chalcogen vacancies not only enhance surface reactivity but also impart distinctive physicochemical characteristics to each TMD. These effects arise from intrinsic bonding differences, resulting in distinct charge availability at exposed Mo atoms and variations in vacancy dimensions, which shape specific surface interactions. Hence, while adsorption differences between pristine surfaces are generally negligible for catalysis, vacancies amplify them by over an order of magnitude, resulting in pronounced material-specific behaviors. Moreover, varying vacancy dimensions affect how species incorporate into defects, further enhancing the differences. These characteristics unlock substantial potential of TMD sheets for distinct surface chemistries, transforming them from relatively similar to markedly different as defect density rises. Consequently, our findings provide insights for tailoring these materials toward applications in electro- and photocatalysis.

Nanoconfinement Effects in Electrocatalysis and Photocatalysis

Recently, the enzyme-inspired nanoconfinement effect has garnered significant attention for enhancing the efficiency of electrocatalysts and photocatalysts. Despite substantial progress in these fields, there remains a notable absence of comprehensive and insightful articles providing a clear understanding of nanoconfined catalysts. This review addresses this gap by delving into nanoconfined catalysts for electrocatalytic and photocatalytic energy conversion. Initially, the effect of nanoconfinement on the thermodynamics and kinetics of reactions is explored. Subsequently, the primary and secondary structures of nanoconfined catalysts are categorized, their properties are outlined, and typical methods for their construction are summarized. Furthermore, an overview of the state-of-the-art applications of nanoconfined catalysts is provided, focusing on reactions of hydrogen and oxygen evolution, oxygen reduction, carbon dioxide reduction, hydrogen peroxide production, and nitrogen reduction. Finally, the current challenges and future prospects in nanoconfined catalysts are discussed. This review aims to provide in-depth insights and guidelines to advance the development of electrocatalytic and photocatalytic energy conversion technology by nanoconfined catalysts.

Harnessing Dirac Semi-Metallicity in a Metal-Free Stand-alone Borophene Composite Electrode for High-Performance Supercapacitors

Borophene, a semimetallic Dirac material with exceptional mechanical and electronic properties, shows great energy storage potential but requires conductive substrates for stability. A strategy for fabricating flexible and conductive rGO-supported borophene supercapacitor electrodes is proposed, featuring a layered assembly of borophene nanosheets sandwiched between rGO layers. This architecture prevents rGO nanosheet restacking, maintaining interlayer spacing at 5.75 Å, which promotes rapid electrolyte ion diffusion and enhances electroactive site accessibility. The rGO/borophene electrode demonstrates a capacitance of 328 F g-1 at 1 A g-1 current density with excellent cycling stability. The flexible supercapacitor achieves an energy density of 24.3 Wh kg-1 at a power density of 600 W kg-1 and maintains stability even under bending angles of up to 180°. Density functional theory calculations indicate that boron and carbon contribute to an increase in electron density near the Fermi level, enabling semimetallic behavior which allows rapid electron transfer and high performance.

Superior selectivity for efficiently reductive degradation of hydrophobic organic pollutants in strongly competitive systems

Highly toxic halo-/nitro-substituted organics, often in low concentrations and with high hydrophobicity, make it difficult to obtain electrons for reduction when strongly electron-competing substances (e.g., O2, H+/H2O, NO3-) coexist. To address this barrier, we devised a new strategy to modify microscale zero-valent aluminum (mZVAl) with graphene (GE) by one-pot ball-milling for GE@mZVAl, which exhibits 99 % selective removal of halo-/nitro-substituted organic pollutants (e.g., carbon tetrachloride (CT), trichloroethylene (TCE), p-nitrophenol (PNP) and p-nitrochlorobenzene (p-NCB)) in the presence of multiple competing inorganics (O2, H+/H2O, Cr(VI), NO3- and BrO3-) and interfering ions (Cl-, CO32-, SO42- and PO43-). Notably, due to the fact that the side-reaction of H2 evolution and second-passivation are significantly suppressed, the electron utilization efficiency for organics degradation reaches an impressive 96 %, even under harsh pH conditions (3-11). GE@mZVAl contains an Al-C interface with a high concentration of C-O, which can form active sites for organics and perform selective electron transfer. Meanwhile, the organophilic catalyst GE also hinders the exposure of AlOH+/Al0 sites to shield the competing and interfering of inorganic substances. As a highly selective reduction system, this work may yield innovative insights for the selective removal of hydrophobic refractory pollutants in complex water matrices.

Stabilizing molecular catalysts on metal oxide surfaces using molecular layer deposition for efficient water oxidation

The stabilization of metal-oxide-bound molecular catalysts is essential for enhancing their lifetime and commercial viability in heterogeneous catalysis. This is particularly relevant in dye-sensitized photoelectrochemical cells (DSPECs), where the surface-bound chromophores and catalysts exhibit instability in aqueous environments, particularly at elevated pH levels. In this work, we have successfully employed molecular layer deposition (MLD) to stabilize ruthenium-based catalysts (RuCP(OH2)2+, denoted as RuCat). The application of polyimide (PI) via MLD onto the porous nanoITO surface significantly improved the stabilization of RuCat molecules for water oxidation. Additionally, time-resolved photoluminescence (TRPL) spectroscopy and femtosecond transient absorption spectroscopy (fs-TAS) results indicated that the MLD-deposited PI effectively preserved the robust redox capacity of the photogenerated electron-hole pairs associated with the catalyst molecules, thereby facilitating more efficient charge transfer. This research presents a novel approach for stabilizing surface-bound small molecules, which may contribute to advancements in heterogeneous catalysis and enhance its commercial viability.

Confined Synthesis of 2D Molybdenum Diphosphide Nanosheets via Gas-Solid Transformation

Molybdenum diphosphide (MoP2), a topological semimetal, possesses distinctive properties and applications in catalysis, energy storage, and condensed matter physics. However, synthesizing high-purity MoP2 is complex and often results in undesired stoichiometric by-products. Additionally, the intrinsic orthorhombic crystal structure makes it difficult to synthesize MoP2 in a 2D morphology, which is desirable for device and energy applications. Here, the robust synthesis of MoP2 with a well-defined 2D morphology is achieved using the confined gas-solid phosphorization of a MoS2 precursor on substrates. The use of 2D precursors and the surface confinement provided by the substrate maintain the 2D morphology and result in a thickness-dependent stoichiometry of the phosphorization products. The chemical composition and crystal structure of MoP2 nanosheets are comprehensively characterized. At room temperature, MoP2 nanosheets exhibit metallic transport with high conductivity over 5500 S cm-1. Furthermore, MoP2 nanosheets demonstrate excellent electrocatalytic activity and durability for hydrogen evolution in both neutral and acid mediums. Notably, MoP2 nanosheets possess better durability than amorphous Pt film and commercial Pt/C, positioning MoP2 as a promising catalyst for hydrogen evolution in neutral mediums. This work advances the synthetic chemistry of 2D MoP2 and provides 2D semimetals with a novel member for future explorations in diverse fields.

Two-Dimensional Catalysts: From Model to Reality

Two-dimensional (2D) materials have been utilized broadly in kinds of catalytic reactions due to their fully exposed active sites and special electronic structure. Compared with real catalysts, which are usually bulk or particle, 2D materials have more well-defined structures. With easily identified structure-modulated engineering, 2D materials become ideal models to figure out the catalytic structure-function relations, which is helpful for the precise design of catalysts. In this review, the unique function of 2D materials was summarized from model study to reality catalysis and application. It includes several typical 2D materials, such as graphene, transition metal dichalcogenides, metal, and metal (hydr)oxide materials. We introduced the structural characteristics of 2D materials and their advantages in model researches. It emphatically summarized how 2D materials serve as models to explore the structure-activity relationship by combining theoretical calculations and surface research. The opportunities of 2D materials and the challenges for fundamentals and applications they facing are also addressed. This review provides a reference for the design of catalyst structure and composition, and could inspire the realization of two-dimensional materials from model study to reality application in industry.

Highly Dispersed AuCu Nanoparticles Confined in Zr-MOFs for Efficient Methanol Synthesis from CO2 Hydrogenation

Making use of novel materials to develop efficient catalysts is one of the research hotspots for CO2 hydrogenation to methanol. Herein, UiO-66, a typical Zr-MOF, was modified by ethylene diamine tetraacetic acid (EDTA) to serve as a substrate for the synthesis of AuCu bimetallic catalysts. The resultant AuCu@UiO-66-EDTA catalyst exhibited a superior methanol production rate, which delivered a high space-time yield of methanol (3.34 gMeOH gmetal-1 h-1) at 250 °C and 3.0 MPa. The EDTA modification was found to effectively confine AuCu nanoparticles inside the framework of MOFs, which significantly reduced the metal particle size and enriched the oxygen vacancy concentration. As a consequence, more active sites were generated for methanol synthesis. Moreover, the AuCu@UiO-66-EDTA catalyst yielded more favorable reaction intermediates that could be converted to methanol at a faster rate. This work develops unique MOFs-encapsulated bimetallic catalysts and illuminates the positive effect of confinement.

Confinement Effects of Two-Dimensional Surfaces on Water Adsorption and Dissociation over Pt(111)

It has been established that the confined space created by stacking a two dimensional (2D) surface atop a metal catalyst serves as a nano-reactor. According to recent research, when a graphene (Gr) overlayer encloses a catalyst from above, the activation barrier for the water dissociation reaction, a process with major industrial significance, decreases. In order to investigate how the effect of confinement varies among different two-dimensional (2D) materials, we study the adsorption and dissociation barriers of water molecule on (111) under graphene, hexagonal boron nitride (h-BN), and heptazine-based graphitic carbon nitride (g-C3N4) layers using density functional theory calculations. Our findings reveal that the strength of adsorption does not decrease consistently with a reduction in the height of the 2D overlayer. Furthermore, a smaller barrier is not always the consequence of poorer adsorption of the reactant. We also examine the effect of confinement on the shape of the reaction path, on the frequencies of vibrational modes, and on the rate constants derived using the harmonic transition state theory. Overall, all three 2D surfaces cause a decrease in barrier height and a weakening of adsorption, though to differing degrees due to a mix of mechanical, geometric and electronic variables.

Microenvironment Control over Electrocatalytic Activity of g-C3N4/2H-MoS2 Superlattice-like Heterostructures for Hydrogen Evolution

Microenvironments in heterogeneous catalysis have been recognized as equally important as the types and amounts of active sites for regulating catalytic activity. Two-dimensional (2D) nanospaces between van der Waals (vdW) gaps of layered materials provide an ideal microenvironment to create novel functionalities. Here, we explore a facile method for fabricating g-C3N4/2H-MoS2 superlattice-like heterostructures based on thermochemical intercalation and polymerization reactions of formamide within enlarged vdW gaps of 2H-MoS2 nanosheets without any transfer process. DFT calculations demonstrate that the interlayer electron-electron correlations due to the intercalation effect of g-C3N4, rather than high-κ dielectric environments, lead to the improvement of intrinsic conductivity of 2H-MoS2 nanosheets. As the proof of concept in applications for the electrocatalysis field, the heterostructure for hydrogen electrochemical reaction (HER) exhibits high stability and catalytic activity in both acid and alkaline media, such as a quite low onset overpotential of 98 mV, a high exchange current density of 77.6 μA cm-2, and a small Tafel slope (52.9 mV dec-1) in an acid medium. The enhanced HER activity is attributed to the improved conductivity and nanoconfinement effect of 2D nanospaces that decrease the reaction activation energy and activate the inert basal planes.

Carbon encapsulated nanoparticles: materials science and energy applications

The technological implementation of electrochemical energy conversion and storage necessitates the acquisition of high-performance electrocatalysts and electrodes. Carbon encapsulated nanoparticles have emerged as an exciting option owing to their unique advantages that strike a high-level activity-stability balance. Ever-growing attention to this unique type of material is partly attributed to the straightforward rationale of carbonizing ubiquitous organic species under energetic conditions. In addition, on-demand precursors pave the way for not only introducing dopants and surface functional groups into the carbon shell but also generating diverse metal-based nanoparticle cores. By controlling the synthetic parameters, both the carbon shell and the metallic core are facilely engineered in terms of structure, composition, and dimensions. Apart from multiple easy-to-understand superiorities, such as improved agglomeration, corrosion, oxidation, and pulverization resistance and charge conduction, afforded by the carbon encapsulation, potential core-shell synergistic interactions lead to the fine-tuning of the electronic structures of both components. These features collectively contribute to the emerging energy applications of these nanostructures as novel electrocatalysts and electrodes. Thus, a systematic and comprehensive review is urgently needed to summarize recent advancements and stimulate further efforts in this rapidly evolving research field.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Covalently Linked 2D-Co3O4/GO Heterostructures: Catalytic and Electrochemical Properties

Covalently cross-linked 2D heterostructures may represent a ground-breaking approach to creating materials with multifunctionalities. To date, however, this field still remains relatively unexplored. In the present work, Co3O4/GO covalently linked heterostructures (Co3O4/GO-CL) were produced using 2D-Co3O4 functionalized with (3-aminopropyl)triethoxysilane (APTES) to react with the carboxyl groups of graphene oxide (GO). The surface and interface properties of the final material were assessed through electrochemical and catalytic studies. We found that the covalent bonds lead to a self-standing and ordered final structure, not observed for the noncovalent material (Co3O4/GO-nCL), also produced for comparison. The catalytic activity of Co3O4/GO-CL over the degradation of Rhodamine 6G showed great performance and the possibility of recycling the catalyst. Electrochemical evaluation stated higher specific capacitance for the covalently bonded material (468 F g-1 against 110 F g-1). Overall, results showed that the covalent bonds may be improving charge-transfer and interfacial area features, thus leading to enhanced catalytic and electrochemical performances.

WS2 with Controllable Layer Number Grown Directly on W Film

As a layered material with single/multi-atom thickness, two-dimensional transition metal sulfide WS2 has attracted extensive attention in the field of science for its excellent physical, chemical, optical, and electrical properties. The photoelectric properties of WS2 are even more promising than graphene. However, there are many existing preparation methods for WS2, but few reports on its direct growth on tungsten films. Therefore, this paper studies its preparation method and proposes an innovative two-dimensional material preparation method to grow large-sized WS2 with higher quality on metal film. In this experiment, it was found that the reaction temperature could regulate the growth direction of WS2. When the temperature was below 950 °C, the film showed horizontal growth, while when the temperature was above 1000 °C, the film showed vertical growth. At the same time, through Raman and band gap measurements, it is found that the different thicknesses of precursor film will lead to a difference in the number of layers of WS2. The number of layers of WS2 can be controlled by adjusting the thickness of the precursor.

Titanium carbide sealed cadmium sulfide quantum dots on carbon, oxygen-doped boron nitride for enhanced and durable photochemical carbon dioxide reduction

Despite great efforts that have been made, photocatalytic carbon dioxide (CO2) reduction still faces enormous challenges due to the sluggish kinetics or disadvantageous thermodynamics. Herein, cadmium sulfide quantum dots (CdS QDs) were loaded onto carbon, oxygen-doped boron nitride (BN) and encapsulated by titanium carbide (Ti3C2, MXene) layers to construct a ternary composite. The uniform distribution of CdS QDs and the tight interfacial interaction among the three components could be achieved by adjusting the loading amounts of CdS QDs and MXene. The ternary 100MX/CQ/BN sample gave a productive rate of 2.45 and 0.44 μmol g-1 h-1 for carbon monoxide (CO) and methane (CH4), respectively. This CO yield is 1.93 and 6.13 times higher than that of CdS QDs/BN and BN counterparts. The photocatalytic durability of the ternary composite is significantly improved compared with CdS QDs/BN because MXene can protect CdS from photocorrosion. The characterization results demonstrate that the excellent CO2 adsorption and activation capabilities of BN, the visible light absorption of CdS QDs, the good conductivity of MXene and the well-matched energy band alignment jointly promote the photocatalytic performance of the ternary catalyst.

In situ/Operando Synchrotron Radiation Analytical Techniques for CO2/CO Reduction Reaction: From Atomic Scales to Mesoscales

Electrocatalytic carbon dioxide/carbon monoxide reduction reaction (CO(2)RR) has emerged as a prospective and appealing strategy to realize carbon neutrality for manufacturing sustainable chemical products. Developing highly active electrocatalysts and stable devices has been demonstrated as effective approach to enhance the conversion efficiency of CO(2)RR. In order to rationally design electrocatalysts and devices, a comprehensive understanding of the intrinsic structure evolution within catalysts and micro-environment change around electrode interface, particularly under operation conditions, is indispensable. Synchrotron radiation has been recognized as a versatile characterization platform, garnering widespread attention owing to its high brightness, elevated flux, excellent directivity, strong polarization and exceptional stability. This review systematically introduces the applications of synchrotron radiation technologies classified by radiation sources with varying wavelengths in CO(2)RR. By virtue of in situ/operando synchrotron radiationanalytical techniques, we also summarize relevant dynamic evolution processes from electronic structure, atomic configuration, molecular adsorption, crystal lattice and devices, spanning scales from the angstrom to the micrometer. The merits and limitations of diverse synchrotron characterization techniques are summarized, and their applicable scenarios in CO(2)RR are further presented. On the basis of the state-of-the-art fourth-generation synchrotron facilities, a perspective for further deeper understanding of the CO(2)RR process using synchrotron radiation analytical techniques is proposed.

Unveiling Confinement Engineering for Achieving High-Performance Rechargeable Batteries

The confinement effect, restricting materials within nano/sub-nano spaces, has emerged as an innovative approach for fundamental research in diverse application fields, including chemical engineering, membrane separation, and catalysis. This confinement principle recently presents fresh perspectives on addressing critical challenges in rechargeable batteries. Within spatial confinement, novel microstructures and physiochemical properties have been raised to promote the battery performance. Nevertheless, few clear definitions and specific reviews are available to offer a comprehensive understanding and guide for utilizing the confinement effect in batteries. This review aims to fill this gap by primarily summarizing the categorization of confinement effects across various scales and dimensions within battery systems. Subsequently, the strategic design of confinement environments is proposed to address existing challenges in rechargeable batteries. These solutions involve the manipulation of the physicochemical properties of electrolytes, the regulation of electrochemical activity, and stability of electrodes, and insights into ion transfer mechanisms. Furthermore, specific perspectives are provided to deepen the foundational understanding of the confinement effect for achieving high-performance rechargeable batteries. Overall, this review emphasizes the transformative potential of confinement effects in tailoring the microstructure and physiochemical properties of electrode materials, highlighting their crucial role in designing novel energy storage devices.

A sensing platform for ascorbic acid based on the spatial confinement of covalent organic frameworks

Essential to many activities in our bodies, ascorbic acid is a small molecule essential to human health and physiological processes. In this study, a covalent organic framework called TpNda-COF was synthesized, which is composed of Tp (triformylephloroglucinol) and Nda (1, 5-napthalenediamine). This framework acts as a mimic enzyme and displays excellent oxidase-like activity when stimulated with purple light (at = 405 nm). It catalyzes the oxidation of 3,3',5,5'-tetramethylbenzydine (TMB) by generating O2- free radicals in the presence of oxygen. The resulting oxTMB shows a characteristic absorption peak at 652 nm. The biomimetic catalysis efficiency is significantly improved due to spatial restriction. By introducing ascorbic acid (AA) in the system, the blue oxTMB is reduced to colorless TMB. The decrease in absorption peak intensity can be quantitatively measured using a UV-Vis spectrophotometer, enabling the detection of AA. The sensing platform demonstrates excellent selectivity and sensitivity. It has a wide linear detection range from 5 μM to 50 μM, with a low detection limit of 1.44 μM. Advantages such as the easy control of light, high stability and efficient oxidation are provided by the TpNda-COF mimic oxidase. This innovative method presents a promising and cost-effective approach for rapid detection of ascorbic acid, with potential applications across various fields.

Toxicity of hexagonal boron nitride nanosheets to freshwater algae: Phospholipid membrane damage and carbon assimilation inhibition

Hexagonal boron nitride (h-BN) nanomaterials have attracted numerous attentions for application in various fields, including environmental governance. Understanding the environmental implications of h-BN is a prerequisite for its safe and sustainable use; nevertheless, information on the negative effect of h-BN on aquatic organisms and the underlying toxicity mechanisms is scarce. The present study found that low exposure doses (0.1-1 μg/mL) of micron-sized h-BN lamella apparently suppressed (maximally 45.3%) the growth of Chlorella vulgaris (a freshwater alga) via membrane damages and metabolic reprogramming. Experimental and simulation results verified that h-BN can penetrate into and then extract phospholipids from the cell membrane of algae due to the strong hydrophobic interactions between h-BN nanosheets and lipids, resulting in membrane permeabilization and integrity reduction. Oxidative stress-triggered lipid peroxidation also contributes to membrane destruction of algae. Metabolomics assay demonstrated that h-BN down-regulated the CO2-fixation associated Calvin cycle and glycolysis/gluconeogenesis pathways in algae, thereby inhibiting energy synthesis and antioxidation process. Despite releasing soluble B inside cells, the B species exhibited negligible toxicity. These findings highlight the phenomena and mechanisms of h-BN toxicity in photosynthetic algae, which have great implications for guiding their safe use under the scenarios of global carbon neutrality.

The growth of epitaxial graphene on SiC and its metal intercalation: a review

High-quality epitaxial graphene (EG) on SiC is crucial to high-performance electronic devices due to the good compatibility with Si-based semiconductor technology. Metal intercalation has been considered as a basic technology to modify EG on SiC. In the past ten years, there have been extensive research activities on the structural evolution during EG fabrication, characterization of the atomic structure and electronic states of EG, optimization of the fabrication process, as well as modification of EG by metal intercalation. In this perspective, the developments and breakthroughs in recent years are summarized and future expectations are discussed. A good understanding of the growth mechanism of EG and subsequent metal intercalation effects is fundamentally important.

Rational Design of Stimuli-Responsive Inorganic 2D Materials via Molecular Engineering: Toward Molecule-Programmable Nanoelectronics

The ability of electronic devices to act as switches makes digital information processing possible. Succeeding graphene, emerging inorganic 2D materials (i2DMs) have been identified as alternative 2D materials to harbor a variety of active molecular components to move the current silicon-based semiconductor technology forward to a post-Moore era focused on molecule-based information processing components. In this regard, i2DMs benefits are not only for their prominent physiochemical properties (e.g., the existence of bandgap), but also for their high surface-to-volume ratio rich in reactive sites. Nonetheless, since this field is still in an early stage, having knowledge of both i) the different strategies for molecularly functionalizing the current library of i2DMs, and ii) the different types of active molecular components is a sine qua non condition for a rational design of stimuli-responsive i2DMs capable of performing logical operations at the molecular level. Consequently, this Review provides a comprehensive tutorial for covalently anchoring ad hoc molecular components-as active units triggered by different external inputs-onto pivotal i2DMs to assess their role in the expanding field of molecule-programmable nanoelectronics for electrically monitoring bistable molecular switches. Limitations, challenges, and future perspectives of this emerging field which crosses materials chemistry with computation are critically discussed.

Confinement Accelerates Water Oxidation Catalysis: Evidence from In Situ Studies

Basic insight into the structural evolution of electrocatalysts under operating conditions is of substantial importance for designing water oxidation catalysts. The first-row transition metal-based catalysts present state-of-the-art oxygen evolution reaction (OER) performance under alkaline conditions. Apparently, confinement has become an exciting strategy to boost the performance of these catalysts. The van der Waals (vdW) gaps of transition metal dichalcogenides are acknowledged to serve as a suitable platform to confine the first-row transition metal catalysts. This study focuses on confining Ni(OH)2 nanoparticle in the vdW gaps of 2D exfoliated SnS2 (Ex-SnS2 ) to accelerate water oxidation and to guarantee long term durability in alkaline solutions. The trends in oxidation states of Ni are probed during OER catalysis. The in situ studies confirm that the confined system produces a favorable environment for accelerated oxygen gas evolution, whereas the un-confined system proceeds with a relatively slower kinetics. The outstanding OER activity and excellent stability, with an overpotential of 300 mV at 100 mA cm-2 and Tafel slope as low as 93 mV dec-1 results from the confinement effect. This study sheds light on the OER mechanism of confined catalysis and opens up a way to develop efficient and low-cost electrocatalysts.

Phase Engineering and Synchrotron-Based Study on Two-Dimensional Energy Nanomaterials

In recent years, there has been significant interest in the development of two-dimensional (2D) nanomaterials with unique physicochemical properties for various energy applications. These properties are often derived from the phase structures established through a range of physical and chemical design strategies. A concrete analysis of the phase structures and real reaction mechanisms of 2D energy nanomaterials requires advanced characterization methods that offer valuable information as much as possible. Here, we present a comprehensive review on the phase engineering of typical 2D nanomaterials with the focus of synchrotron radiation characterizations. In particular, the intrinsic defects, atomic doping, intercalation, and heterogeneous interfaces on 2D nanomaterials are introduced, together with their applications in energy-related fields. Among them, synchrotron-based multiple spectroscopic techniques are emphasized to reveal their intrinsic phases and structures. More importantly, various in situ methods are employed to provide deep insights into their structural evolutions under working conditions or reaction processes of 2D energy nanomaterials. Finally, conclusions and research perspectives on the future outlook for the further development of 2D energy nanomaterials and synchrotron radiation light sources and integrated techniques are discussed.

Controlling the spacing of the linked graphene oxide system with dithiol linkers under confinement

2D nanoscale confined systems exhibit behavior that is markedly different from that observed at the macroscale. Confinement can be tuned by controlling the interlayer spacing between confining layers using organic dithiol linkers. Adjusting spacing and selective intercalation have important impacts for catalysis, superconductivity, spin engineering, sodium ion batteries, 2D magnets, optoelectronics, and many other applications. In this study, we report how reaction conditions and organic linkers can be used to create variable, reproducible spacings between graphene oxide to provide confinement systems. We determined the conditions under which the spacing can be variably adjusted by the type of linker used, the concentration of the linker, and the reaction conditions. Employing dithiol linkers of different lengths, such as three (TPDT) and four (QPDT) aromatic rings, we can adjust the spacing between graphene oxide layers under varied reaction conditions. Here, we show that by varying dithiol linker length and using different reaction conditions, we can reproducibly control the spacing between graphene oxide layers from 0.37 nm to over 0.50 nm.

CeO2/Cu2O/Cu Tandem Interfaces for Efficient Water-Gas Shift Reaction Catalysis

Metal-oxide interfaces on Cu-based catalysts play very important roles in the low-temperature water-gas shift reaction (LT-WGSR). However, developing catalysts with abundant, active, and robust Cu-metal oxide interfaces under LT-WGSR conditions remains challenging. Herein, we report the successful development of an inverse copper-ceria catalyst (Cu@CeO₂), which exhibited very high efficiency for the LT-WGSR. At a reaction temperature of 250 °C, the LT-WGSR activity of the Cu@CeO₂ catalyst was about three times higher than that of a pristine Cu catalyst without CeO₂. Comprehensive quasi-in situ structural characterizations indicated that the Cu@CeO₂ catalyst was rich in CeO₂/Cu₂O/Cu tandem interfaces. Reaction kinetics studies and density functional theory (DFT) calculations revealed that the Cu⁺/Cu⁰ interfaces were the active sites for the LT-WGSR, while adjacent CeO₂ nanoparticles play a key role in activating H₂O and stabilizing the Cu⁺/Cu⁰ interfaces. Our study highlights the role of the CeO₂/Cu₂O/Cu tandem interface in regulating catalyst activity and stability, thus contributing to the development of improved Cu-based catalysts for the LT-WGSR.

Recent Advances in Confining Polyoxometalates and the Applications

Polyoxometalates (POMs) are widely used in catalysis, energy storage, biomedicine, and other research fields due to their unique acidity, photothermal, and redox features. However, the leaching and agglomeration problems of POMs greatly limit their practical applications. Confining POMs in a host material is an efficient tool to address the above-mentioned issues. POM@host materials have received extensive attention in recent years. They not only inherent characteristics of POMs and host, but also play a significant synergistic effect from each component. This review focuses on the recent advances in the development and applications of POM@host materials. Different types of host materials are elaborated in detail, including tubular, layered, and porous materials. Variations in the structures and properties of POMs and hosts before and after confinement are highlighted as well. In addition, an overview of applications for the representative POM@host materials in electrochemical, catalytic, and biological fields is provided. Finally, the challenges and future perspectives of POM@host composites are discussed.

The effects of intercalated environmental gas molecules on carrier dynamics in WSe2/WS2 heterostructures

Effective tuning of carrier dynamics in two-dimensional (2D) materials is significant for multi-scene device applications. Using first-principles and ab initio nonadiabatic molecular dynamics calculations, the kinetics of O₂, H₂O, and N₂ intercalation into 2D WSe₂/WS₂ van der Waals heterostructures and its effect on carrier dynamics have been comprehensively explored. It is found that the O₂ molecule prefers to dissociate into atomic O atoms spontaneously after intercalation of WSe₂/WS₂ heterostructures, whereas H₂O and N₂ molecules remain intact. O₂ intercalation significantly speeds up the electron separation process, while H₂O intercalation largely speeds up the hole separation process. The lifetime of excited carriers can be prolonged by O₂ or H₂O or N₂ intercalations. These intriguing phenomena can be attributed to the effect of interlayer coupling, and the underlying physical mechanism for tuning the carrier dynamics is fully discussed. Our results provide useful guidance for the experimental design of 2D heterostructures for optoelectronic applications in photocatalysts and solar energy cells.

Single-atom catalysts for hydroformylation of olefins

Hydroformylation is one of the most significant homogeneous reactions. Compared with homogeneous catalysts, heterogeneous catalysts are easy to be separated from the system. However, heterogeneous catalysis faces the problems of low activity and poor chemical/regional selectivity. Therefore, there are theoretical and practical significance to develop efficient heterogeneous catalysts. SACs can be widely applied in hydroformylation in the future, due to the high atom utilization efficiency, stable active sites, easy separation, and recovery. In this review, the recent advances of SACs for hydroformylation are summarized. The regulation of microstructure affected on the reactivity, stability of SACs, and chem/regioselectivity of SACs for hydroformylation are discussed. The support effect, ligand effect, and electron effect on the performance of SACs are proposed, and the catalytic mechanism of SACs is elaborated. Finally, we summarize the current challenges in this field, and propose the design and research ideas of SACs for hydroformylation of olefins.

Different Doping of VSe2 Monolayers as Adsorbent and Gas Sensing Material for Scavenging and Detecting SF6 Decomposed Species

The application of intrinsic and transition metals (TM)-doped VSe₂ monolayers for the detection of faulty gases in SF₆ electrical insulated equipment is investigated based on first-principles calculations. The electron density difference, density of state, and adsorption energy are analyzed to further clarify the reaction mechanism. The results show that the intrinsic VSe₂ monolayer has weak adsorption performance for SO₂ and SOF₂ molecules, but the adsorption properties of the system are significantly improved after doping TM atoms. Among them, the TM-doped VSe₂ monolayer has better sensing performance for SO₂ than for SOF₂ molecules. Furthermore, the modulating effect of biaxial strain on the gas-sensitive properties of TM-doped VSe₂ system is also analyzed. Finally, the recovery time of the gas molecules on the solid adsorbent is evaluated. The results confirm that the TM-doped VSe₂ monolayer can be used as a novel sensing material or scavenger to ensure the normal operation of SF₆ electrical insulated equipment. This will provide a prospective insight for experimenters to implement VSe₂-based sensing materials or scavengers.

Wearable chemical sensors based on 2D materials for healthcare applications

Chemical sensors worn on the body could make possible the continuous, noninvasive, and accurate monitoring of vital human signals, which is necessary for remote health monitoring and telemedicine. Attractive for creating high-performance, wearable chemical sensors are atomically thin materials with intriguing physical features, abundant chemistry, and high surface-to-volume ratios. These advantages allow for appropriate material-analyte interactions, resulting in a high level of sensitivity even at trace analyte concentrations. Previous review articles covered the material and device elements of 2D material-based wearable devices extensively. In contrast, little research has addressed the existing state, future outlook, and promise of 2D materials for wearable chemical sensors. We provide an overview of recent advances in 2D-material-based wearable chemical sensors to overcome this deficiency. The structure design, manufacturing techniques, and mechanisms of 2D material-based wearable chemical sensors will be evaluated, as well as their applicability in human health monitoring. Importantly, we present a thorough review of the current state of the art and the technological gaps that would enable the future design and nanomanufacturing of 2D materials and wearable chemical sensors. Finally, we explore the challenges and opportunities associated with designing and implementing 2D wearable chemical sensors.

Dynamic Construction and Maintenance of Confined Nanoregions via Hydrogen-Bond Networks between Acetylene Reactants and a Polyoxometalate-Based Metal-Organic Framework

The nanoconfinement effect in catalysis has attracted much attention because it provides a novel means of regulating the molecular properties and related reactions. Confined nanoregions composed of both reactants and catalysts through weak interactions are expected to improve the catalytic performance and promote the mass transport of relevant molecules simultaneously. However, at reaction temperatures, the structural variation of such confined spaces constructed via weak interactions remains unclear. Herein, through density functional theory calculations combined with ab initio molecular dynamics simulations, we have systematically investigated the dynamic structural evolution of the confined space constructed by acetylene reactants and a polyoxometalate-based metal-organic framework (POMOF) via hydrogen-bond networks. It is found that, at the reaction temperature of acetylene semihydrogenation, the hydrogen-bond networks and generated confined nanoregions are not rigid but are constantly changing and dynamically maintained. The steering role played by the O atoms at the surfaces of the polyoxometalate clusters is essential for generation of the hydrogen-bond networks and maintenance of the nanoregions. Upon confinement, the acetylene reactants can be better activated than those in an unconstrained atmosphere, which is reflected by the different dynamic distributions of the ∠CHC bending magnitude. Moreover, from a comparison of the distinct interaction characteristics between acetylene/ethylene and POMOF, the different manifestations in the adsorption energy variations of the confined molecules can be interpreted. This work helps to elucidate the underlying mechanisms of confined catalysis and may promote its application in practical catalytic processes.

Models for Reactions in Confined Space: Can Surface Science Contribute? A Review and Perspective

This paper reports and discusses some of our recent advances in surface science research on a silica film supported on a Ru(0001) substrate. This system is unique, as the silica is bound to the metal surface by dispersive forces only, and thus opens the possibility to study reactions in the confined space between the metal substrate and the silica film, acting as a permeable membrane. We demonstrate that this system allows for detailed insights into the complexity of reactions in confined space, including phenomena due to the response of the confined space to the presence of the reactants, and direct comparison to the situation when the same reaction occurs in open space.

A Sustainable Approach for Graphene Oxide-supported Metal N-Heterocyclic Carbenes Catalysts

Sustainable noble metal-N-heterocyclic carbenes (NHC's) are a topic of arising concern in both the chemical industry and the academic community due to a growing consciousness of environmental pollution and scarcity. Recovering and reusing homogeneous catalysts from the reaction mixture requires a tremendous amount of capital investment in the chemical manufacturing industry. Heterogeneous catalysts are proved to have better functional groups tolerance; however, catalysts support largely influences the active catalyst sites to affect catalyst efficiency and selectivity. Thus the, choice of catalyst supports plays an almost decisive role in this emerging area of catalysis research. Graphene oxide (GO)/reduced graphene oxide (rGO) support has a potential growth in heterogeneous catalysis owing to their commercial availability, considerably larger surface area, inert towards chemical transformations, and easy surface functionalization to attached metal complexes via covalent and non-covalent aromatic π-conjugates. To take advantage of two independently well-established research areas of noble metal-N-heterocyclic carbenes and GO/rGO support via covalent or non-covalent interactions approach would offer novel heterogeneous complexes with improved catalytic efficiency without sacrificing product selectivity. This unique concept of marrying metal-N-heterocyclic carbenes with GO/rGO support has potential growth in the chemical and pharmaceutical industry, however, limited examples are reported in the literature. In this perspective, a comprehensive summary of metal-NHC synthesis on GO/rGO support and synthetic strategies to graft M-NHC onto GO/rGO surface, catalytic efficiency, for the catalytic transformation are critically reviewed. Furthermore, a plausible mechanism for non-covalent grafting methodology is summarized to direct readers to give a better understanding of M-NHC@rGO complexes. This would also allow the designing of engineered catalysts for unexplored catalytic applications.

Design strategy of a Cu-based catalyst for optimizing the performance in the electrochemical CO2 reduction reaction to multicarbon alcohols

The electrochemical CO₂ reduction reaction (ECRR) is a promising method to reduce excessive CO₂ emissions and achieve a sustainable carbon cycle. Due to the high reaction kinetics and efficiency, copper-based catalysts have shown great application potential for preparing multicarbon (C₂₊) products. C₂₊ alcohols have high economic value and use-value, playing an essential role in modern industry. Therefore, we summarize the latest research progress of the ECRR to synthesize C₂₊ alcohols on Cu-based catalysts and discuss the state-of-the-art catalyst design strategies to improve CO₂ reduction performance. Moreover, we analyzed in detail the specific reaction pathways for the conversion of CO₂ to C₂₊ alcohols based on DFT calculations. Finally, we propose the problems and possible solutions for synthesizing C₂₊ alcohols with copper-based catalysts. We hope that this review can provide ideas for devising ECRR catalysts for C₂₊ alcohols.

Effect of temperature on CO oxidation over Pt(111) in two-dimensional confinement

Confined catalysis between a two-dimensional (2D) cover and metal surfaces has provided a unique environment with enhanced activity compared to uncovered metal surfaces. Within this 2D confinement, weakened adsorption and lowered activation energies were observed using surface science experiments and density functional theory (DFT) calculations. Computationally, the role of electronic and mechanical factors responsible for the improved activity was deduced only from static DFT calculations. This demands a detailed investigation on the dynamics of reactions under 2D confinement, including temperature effects. In this work, we study CO oxidation on a 2D graphene covered Pt(111) surface at 90 and 593 K using DFT-based ab initio molecular dynamics simulations starting from the transition state configuration. We show that CO oxidation in the presence of a graphene cover is substantially enhanced (2.3 times) at 90 K. Our findings suggest that 2D confined spaces can be used to enhance the activity of chemical reactions, especially at low temperatures.

Graphene as an Adsorption Template for Studying Double Bond Activation in Catalysis

Hydrogenated graphene (H-Gr) is an extensively studied system not only because of its capabilities as a simplified model system for hydrocarbon chemistry but also because hydrogenation is a compelling method for Gr functionalization. However, knowledge of how H-Gr interacts with molecules at higher pressures and ambient conditions is lacking. Here we present experimental and theoretical evidence that room temperature O2 exposure at millibar pressures leads to preferential removal of H dimers on H-functionalized graphene, leaving H clusters on the surface. Our density functional theory (DFT) analysis shows that the removal of H dimers is the result of water or hydrogen peroxide formation. For water formation, we show that the two H atoms in the dimer motif attack one end of the physisorbed O2 molecule. Moreover, by comparing the reaction pathways in a vacuum with the ones on free-standing graphene and on the graphene/Ir(111) system, we find that the main role of graphene is to arrange the H atoms in geometrical positions, which facilitates the activation of the O=O double bond.

Recent Progress in Phase Regulation, Functionalization, and Biosensing Applications of Polyphase MoS2

The disulfide compounds of molybdenum (MoS₂ ) are layered van der Waals materials that exhibit a rich array of polymorphic structures. MoS₂ can be roughly divided into semiconductive phase and metallic phase according to the difference in electron filling state of the 4d orbital of Mo atom. The two phases show completely different properties, leading to their diverse applications in biosensors. But to some extent, they compensate for each other. This review first introduces the relationship between phase state and the chemical/physical structures and properties of MoS₂ . Furthermore, the synthetic methods are summarized and the preparation strategies for metastable phases are highlighted. In addition, examples of electronic and chemical property designs of MoS₂ by means of doping and surface modification are outlined. Finally, studies on biosensors based on MoS₂ in recent years are presented and classified, and the roles of MoS₂ with different phases are highlighted. This review offers references for the selection of materials to construct different types of biosensors based on MoS₂ , and provides inspiration for sensing performance enhancement.

On-Site Synthesis and Characterizations of Atomically-Thin Nickel Tellurides with Versatile Stoichiometric Phases through Self-Intercalation

Self-intercalation of native metal atoms in two-dimensional (2D) transition metal dichalcogenides has received rapidly increasing interest, due to the generation of intriguing structures and exotic physical properties, however, only reported in limited materials systems. An emerging type-II Dirac semimetal, NiTe₂, has inspired great attention at the 2D thickness region, but has been rarely achieved so far. Herein, we report the direct synthesis of mono- to few-layer Ni-tellurides including 1T-NiTe₂ and Ni-rich stoichiometric phases on graphene/SiC(0001) substrates under ultra-high-vacuum conditions. Differing from previous chemical vapor deposition growth accompanied with transmission electron microscopy imaging, this work combines precisely tailored synthesis with on-site atomic-scale scanning tunneling microscopy observations, offering us visual information about the phase modulations of Ni-tellurides from 1T-phase NiTe₂ to self-intercalated Ni₃Te₄ and Ni₅Te₆. The synthesis of Ni self-intercalated Ni_xTe_y compounds is explained to be mediated by the high metal chemical potential under Ni-rich conditions, according to density functional theory calculations. More intriguingly, the emergence of superconductivity in bilayer NiTe₂ intercalated with 50% Ni is also predicted, arising from the enhanced electron-phonon coupling strength after the self-intercalation. This work provides insight into the direct synthesis and stoichiometric phase modulation of 2D layered materials, enriching the family of self-intercalated materials and propelling their property explorations.

Synergetic Catalysis of Magnetic Single-Atom Catalysts Confined in Graphitic-C3N4/CeO2(111) Heterojunction for CO Oxidization

Magnetic single-atom catalysts (MSAC), due to the intrinsic spin degree of freedom, are of particular importance relative to other conventional SAC for applications in various catalytic processes, especially in those cases that involve spin-triplet O₂. However, the bottleneck issue in this field is the clustering of the SAC during the processes. Here using first-principles calculations we predict that Mn atoms can be readily confined in the interface of the porous g-C₃N₄/CeO₂(111) heterostructure, forming high-performance MSAC for O₂ activation via a delicate synergetic mechanism of charge transfer, mainly provided by the p-block g-C₃N₄ overlayer mediated by the d-block Mn active site, and spin selection, preserved mainly through active participation of the f-block Ce atoms and/or g-C₃N₄, which effectively promotes the CO oxidization. Such a recipe is also demonstrated to be valid for V- and Nb-MSACs, which may shed new light on the design of highly efficient MSACs for various important chemical processes wherein spin-selection matters.

Porous Single-Crystalline Monolith to Enhance Catalytic Activity and Stability

Engineering the catalytic activity and stability of materials would require the identification of the structural features that can tailor active sites at surfaces. Porous single crystals combine the ordered lattice structures and disordered interconnected pores, and they would therefore provide the advantages of precise structure features to identify and engineer the active sites at surfaces. Herein, we fabricate porous single-crystalline vanadium nitride (VN) at centimeter scale and further dope Fe (Fe_0.1V_0.9N) and Co (Co_0.1V_0.9N) in lattice to engineer the active sites at surface. We demonstrate that the active surface is composed of unsaturated coordination of V-N, Fe-N, and Co-N structures which lead to the generation of high-density active sites at the porous single-crystalline monolith surface. The interconnected pores aid the pore-enhanced fluxion to facilitate species diffusion in the porous architectures. In the nonoxidative dehydrogenation of ethane to ethylene, we demonstrate the outstanding performance with ethane conversion of 36% and ethylene selectivity of 99% at 660°C. Remarkably stability as a result of their single-crystalline structure, the monoliths achieve the outstanding performance without degradation being observed even after 200 hours of a continuous operation in a monolithic reactor. This work not only demonstrates the effective structural engineering to simultaneously enhance the stability and overall performance for practically useful catalytic materials but also provide a new route for the element doping of porous single crystals at large scale for the potential application in other fields.

Visualizing the Anomalous Catalysis in Two-Dimensional Confined Space

Confined nanospaces provide a new platform to promote catalytic reactions. However, the mechanism of catalytic enhancement in the nanospace still requires insightful exploration due to the lack of direct visualization. Here, we report operando investigations on the etching and growth of graphene in a two-dimensional (2D) confined space between graphene and a Cu substrate. We observed that the graphene layer between the Cu and top graphene layer was surprisingly very active in etching (more than 10 times faster than the etching of the top graphene layer). More strikingly, at a relatively low temperature (∼530 °C), the etched carbon radicals dissociated from the bottom layer, in turn feeding the growth of the top graphene layer with a very high efficiency. Our findings reveal the in situ dynamics of the anomalous confined catalytic processes in 2D confined spaces and thus pave the way for the design of high-efficiency catalysts.

Selecting the Reaction Path in On-Surface Synthesis through the Electron Chemical Potential in Graphene

The organometallic on-surface synthesis of the eight-membered sp² carbon-based ring cyclooctatetraene (C₈H₈, Cot) with the neighboring rare-earth elements ytterbium and thulium yields fundamentally different products for the two lanthanides, when conducted on graphene (Gr) close to the charge neutrality point. Sandwich-molecular YbCot wires of more than 500 Å length being composed of an alternating sequence of Yb atoms and upright-standing Cot molecules result from the on-surface synthesis with Yb. In contrast, repulsively interacting TmCot dots consisting of a single Cot molecule and a single Tm atom result from the on-surface synthesis with Tm. While the YbCot wires are bound through van der Waals interactions to the substrate, the dots are chemisorbed to Gr via the Tm atoms being more electropositive compared to Yb atoms. When the electron chemical potential in Gr is substantially raised (n-doping) through backside doping from an intercalation layer, the reaction product in the synthesis with Tm can be tuned to TmCot sandwich-molecular wires rather than TmCot dots. By use of density functional theory, it is found that the reduced electronegativity of Gr upon n-doping weakens the binding as well as the charge transfer between the reaction intermediate TmCot dot and Gr. Thus, the assembly of the TmCot dots to long TmCot sandwich-molecular wires becomes energetically favorable. It is thereby demonstrated that the electron chemical potential in Gr can be used as a control parameter in an organometallic on-surface synthesis to tune the outcome of a reaction.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.