2D/2D Heterojunctions for Catalysis

Mechanistic insight into sp-hybridized carbon-induced dual electronic 'push effect' in Pt/graphdiyne/graphene for boosting oxidase-like activity

Efficient oxidase-mediated oxidation is pivotal for environmental remediation and energy conversion application, yet natural enzymes require artificial alternatives due to inherent instability. Cofactors are essential in natural oxidase catalysis, interacting with the active centre to induce an electronic 'push effect' that propels the catalytic process. While efforts to mimic cofactors in nanozyme often involve sophisticated designs and complex synthesis. This study presents a scalable material engineering approach to mimic cofactor functionality using platinum nanoparticles (Pt NPs) supported on an ultrathin graphdiyne/graphene (GDY/G) composite (Pt/GDY/G), in which the sp-hybridized carbon (sp-C) in GDY induces a dual electronic 'push effect'. The unique sp-C structure in GDY imparts semiconductor characteristics and a low work function, this induces an interfacial electrostatic potential between GDY and Pt, which enables unidirectional electron transfer from GDY to Pt, thereby enhancing the electron density at Pt sites. Moreover, the sp-C sites in GDY act as oxygen (O2) adsorption centres, forming a spCOO-Pt bridge that facilitates electron transfer from GDY to O2. This sp-C induced dual electronic 'push effect' significantly reduces the energy barrier for OO bond cleavage, resulting in a 3.4-fold enhancement of the oxidase-like (OXD-like) activity of Pt/GDY/G compared to Pt NPs alone. This work provides mechanistic insights into the design of OXD-like nanozymes, offering a promising strategy to boost O2 activation and OO bond cleavage. The superior catalytic performance of Pt/GDY/G highlights its potential for dye and microplastics degradation, contributing to sustainable environmental remediation.

Unveiling Mechanically Driven Catalytic Processes: Beyond Piezocatalysis to Synergetic Effects

Mechanically driven catalysis (MDC) has emerged as an effective strategy for environmental remediation, renewable energy conversion, and cancer therapy; this functions by converting mechanical forces to drive catalytic reactions. This review examines four primary mechanisms, namely, piezocatalysis, flexocatalysis, tribocatalysis, and sonocatalysis, each involving specific catalytic pathways for harnessing mechanical energy at the nanoscale. However, significant challenges arise in decoupling the effects related to each individual mechanism in order to better understand and manipulate their synergies. In this review, the fundamental principles underpinning MDC are systematically interpreted. Beyond mechanistic insights, recent advancements in performance enhancement strategies for these catalysts are highlighted. Potential applications using these mechanistic approaches in environmental remediation (pollutant and antibiotic degradation and microbial disinfection), renewable energy conversion (hydrogen production and greenhouse gas conversion), and biomedical treatments (particularly cancer therapy) are discussed. Finally, the mechanistic synergies and limiting factors are explored, addressing challenges related to the overlooked combined effects of ultrasound as the activation source, complexities in mechanical force interactions at the nanoscale, and the need for targeted application strategies. Additionally, the industrial potential of these catalytic processes with consideration to scalability and practical deployment is evaluated. While challenges remain, this review provides a roadmap for advancing mechanically driven catalyst design and implementation toward real-world applications, offering potential into its future trajectory and transformative impact across numerous fields.

Heterogeneous Interface Engineering of 2D Black Phosphorus-Based Materials for Enhanced Photocatalytic Performance

Photocatalysis has garnered significant attention as a sustainable approach for energy conversion and environmental management. 2D black phosphorus (BP) has emerged as a highly promising semiconductor photocatalyst owing to its distinctive properties. However, inherent issues such as rapid recombination of photogenerated electrons and holes severely impede the photocatalytic efficacy of single BP. The construction/stacking mode of BP with other nanomaterials decreases the recombination rate of carriers and extend its functionalities. Herein, from the perspective of atomic interface and electronic interface, the enhancement mechanism of photocatalytic performance by heterogeneous interface engineering is discussed. Based on the intrinsic properties of BP and corresponding photocatalytic principles, the effects of diverse interface characteristics (point, linear, and planar interface) and charge transfer mechanisms (type I, type II, Z-scheme, and S-scheme heterojunctions) on photocatalysis are summarized systematically. The modulation of heterogeneous interfaces and rational regulation of charge transfer mechanisms can enhance charge migration between interfaces and even maximize redox capability. Furthermore, research progress of heterogeneous interface engineering based on BP is summarized and their prospects are looked ahead. It is anticipated that a novel concept would be presented for constructing superior BP-based photocatalysts and designing other 2D photocatalytic materials.

Chemically-Linked Heterostructures of Palladium Nanosheets and 2H-MoS2

The burgeoning field of 2D heterostructures targets the combination of 2D materials with 3D, 1D, or 0D nanomaterials. Among the most popular 2D materials, the 2H polytype of molybdenum disulfide (MoS2) features a well-defined bandgap that becomes direct at the monolayer level, which can be exploited for photodetection. A notable limitation of 2H-MoS2 is its curtailed absorbance beyond the visible range. Here, a covalently-linked Pd nanosheet (PdNS)/functionalized MoS2 (f-MoS2) heterostructure is introduced, leveraging PdNS infrared-absorbing properties to surmount this constraint. A bifunctional molecule, featuring a maleimide for attachment to MoS2 and a phenyl bromide for connection to PdNS, enables the synthesis of the heterostructure. Comprehensive spectroscopic and microscopic characterization shed light on the structure of PdNS@f-MoS2 and the electronic interaction between its components. Prototype devices show an enhancement in the width and intensity of the optoelectronic response of PdNS@f-MoS2 in the infrared, up to 1700 nm. In comparison, a van der Waals heterostructure with the same components shows poorer photoresponse. The results prove that the covalent linkage of metal nanostructures to 2D materials is a promising approach to build mixed-dimensional heterostructures.

DFT-Based Mechanistic Exploration and Application in Photocatalytic Heterojunctions

Density functional theory (DFT) is one of the most widely used methods in the field of computational materials and has become an important research method for photocatalytic heterojunctions. Based on the research progress of DFT in the field of photocatalytic heterojunctions, this review introduces three kinds of heterojunction modeling in detail as well as the problems encountered in the construction process and the solutions. It provides a comprehensive review of the calculation methods of important parameters related to photocatalytic heterojunctions. Comparison, analysis, and discussion were conducted on some functional selections and calculation results based on experimental data. Finally, the limitations and shortcomings of DFT in the field of photocatalytic heterojunctions are pointed out. This review will provide valuable guidance for the calculation and analysis of the performance of photocatalytic heterojunctions and help promote the wider application of DFT in the field of photocatalysis.

GeSe/WSe2 mixed dimensional p-n junction photoelectric properties

Heterojunctions prepared utilizing diverse 2D materials enhance a variety of optoelectronic devices. Here, we present GeSe/WSe2 mixed-dimensional p-n heterojunctions, which broaden the possibility of material combination and selection in 2D/layered heterojunction devices, while also providing material parameters to facilitate the development of optoelectronic devices based on 2D/layered semiconductor materials.

Comparative study of the photocatalytic activity of g-C3N4/MN4 (M = Mn, Fe, Co) for water splitting reaction: A theoretical study

In this study, nanocomposites of g-C3N4/MN4 (where M is Mn, Fe and Co) have been designed using advanced density functional theory (DFT) calculations. A comprehensive analysis was conducted on the geometry, electronic, optical properties, work function, charge transfer interaction and adhesion energy of the g-C3N4/MN4 heterostructures and concluded that g-C3N4/FeN4 and g-C3N4/CoN4 heterojunctions exhibit higher photocatalytic performance than individual units. The better photocatalytic activity can be attributed mainly by two facts; (i) the visible light absorption of both g-C3N4/FeN4 and g-C3N4/CoN4 interfaces are higher compared to its isolated analogs and (ii) a significant enhancement of band gap energy in g-C3N4/FeN4 and g-C3N4/CoN4 heterostructures limited the electron-hole recombination significantly. The potential of the g-C3N4/MN4 heterojunctions as a photocatalyst for the water splitting reaction was assessed by examining its band alignment for water splitting reaction. Importantly, while the electronic and magnetic properties of MN4 systems were studied, this is the first example of inclusion of MN4 on graphene-based material (g-C3N4) for studying the photocatalytic activity. The state of the art DFT calculations emphasis that g-C3N4/FeN4 and g-C3N4/CoN4 heterojunctions are half metallic photocatalysts, which is limited till date.

ZnO quantum dots decorated BaTiO3 for cancer sonodynamic therapy

Sonodynamic therapy depending on ultrasound irradiation, which generates reactive species to kill cancer cells, has attracted considerable attention due to the deep tissue penetration depth. However, the insufficient separation of electron/hole pairs induces its limited therapeutic efficiency. Herein, we use oxygen vacancy and ZnO quantum dots decoration techniques to enhance electron/hole separation and reactive species production. In oxygen vacancy-engineered BaTiO3, the higher oxygen vacancy concentration leads to more efficient adsorption of activate O2 and thus results in production of more radicals. In BaTiO3/ZnO heterostructures, the built-in electric field further improves separation of electron/hole pairs. The separated electron/hole react with O2/H2O to produce reactive species of •OH/∙O2- and kill cancer cells upon ultrasound irradiation. The work provides a guidance for sonosensitizers to tumor therapy.

A review on recent advances in g-C3N4-MXene nanocomposites for photocatalytic applications

The solutions for environmental remediation and renewable energy generation have intensified the exploration of efficient photocatalytic materials. Recently, the composites of g-C3N4and MXene have gained considerable interest for their potential applications in photocatalysis. In the g-C3N4-MXene composite, the g-C3N4possesses unique physical, chemical, and optical properties to increase visible light absorption. At the same time, MXene improves conductivity, adsorption of reactant molecules or the active sites, and charge transfer properties. Combining the unique physico-chemical properties of MXene and g-C3N4, the resulting composite exhibits superior photo-responsive behavior and is critical in photocatalytic reactions. Furthermore, the g-C3N4-MXene composite exhibits stability and recyclability, making it a promising candidate for sustainable and scalable photocatalytic material in environmental remediation. This review offers an in-depth analysis of the development and design of g-C3N4-MXene composites through diverse synthesis procedures and a comprehensive analysis of their application in carbon dioxide (CO2) reduction, photocatalytic degradation, water splitting processes, mainly hydrogen (H2) generation, H2O2production, N2fixation, and NOxremoval. The charge transfer mechanism of g-C3N4-MXene composite for photocatalytic application has also been discussed. This review provides insights into the photocatalytic capabilities of g-C3N4-MXene composites, showing their potential to address current environmental challenges and establish a robust foundation for sustainable energy conversion technologies.

Ultrathin and Conformal Depletion Layer of Core/Shell Heterojunction Enables Efficient and Stable Acidic Water Oxidation

Ru-based electrocatalysts hold great promise for developing affordable proton exchange membrane (PEM) electrolyzers. However, the harsh acidic oxidative environment of the acidic oxygen evolution reaction (OER) often causes undesirable overoxidation of Ru active sites and subsequent serious activity loss. Here, we present an ultrathin and conformal depletion layer attached to the Schottky heterojunction of core/shell RuCo/RuCoOx that not only maximizes the availability of active sites but also improves its durability and intrinsic activity for acidic OER. Operando synchrotron characterizations combined with theoretical calculations elucidate that the lattice strain and charge transfer induced by Schottky heterojunction substantially regulate the electronic structures of active sites, which modulates the OER pathway and suppresses the overoxidation of Ru species. Significantly, the closed core/shell architecture of the RuCo/RuCoOx ensures the structure integrity of the Schottky heterojunction under acidic OER conditions. As a result, the core/shell RuCo/RuCoOx Schottky heterojunction exhibits an unprecedented durability up to 250 0 h at 10 mA cm-2 with an ultralow overpotential of ∼170 mV at 10 mA cm-2 in 0.5 M H2SO4. The RuCo/RuCoOx catalyst also demonstrates superior durability in a proton exchange membrane (PEM) electrolyzer, showcasing the potential for practical applications.

Unveiling Versatile Electronic Properties and Contact Features of Metal-Semiconductor Graphene/γ-Ge2SSe van der Waals Heterostructures

Recently, searching for a metal-semiconductor junction (MSJ) that exhibits low-contact resistance has received tremendous consideration, as they are essential components in next-generation field-effect transistors. In this work, we design a MSJ by integrating two-dimensional (2D) graphene as the metallic electrode and 2D Janus γ-Ge2SSe as the semiconducting channel using first-principles simulations. All the graphene/γ-Ge2SSe MSJs are predicted to be energetically, mechanically, and thermodynamically stable, characterized by the weak van der Waals (vdW) interactions. The graphene/γ-SGe2Se MSJ-vdWH form the n-type Schottky contact (SC), while the graphene/γ-SeGe2S MSJ-vdWH form the p-type one, suggesting that the switching between p-type and n-type SC in the graphene/γ-Ge2SSe MSJ-vdWHs can occur spontaneously by simply altering the stacking patterns, without requiring any external conditions. Notably, the contact features, including contact types and barriers of the graphene/γ-Ge2SSe MSJs are significant in versatility and can be altered by applying electric gating and adjusting interlayer spacing. Both the applied electric gating and strain engineering induce switchability between p- and n-type and SC to OC in the graphene/γ-Ge2SSE MSJs. This versatility underscores the potential of the graphene/γ-Ge2SSe MSJ for next-generation applications that require low-contact resistance and high performance.

Discovery of Self-Assembled 2D Ru/Si Superlattices Boosting Hydrogen Evolution

2D heterostructuring is a versatile methodology for designing nanoarchitecture catalytic systems that allow for reconstruction and modulation of interfaces and electronic structures. However, catalysts with such structures are extremely scarce due to limited synthetic strategies. Here, a highly ordered 2D Ru/Si/Ru/Si… nano-heterostructures (RSHS) is reported by acid etching of the LaRuSi electride. RSHS shows a superior electrocatalytic activity for hydrogen evolution with an overpotential of 14 mV at 10 mA cm-2 in alkaline media. Both experimental analyses and first-principles calculations demonstrate that the electronic states of Ru can be tuned by strong interactions of the interfacial Ru-Si, leading to an optimized hydrogen adsorption energy. Moreover, due to the synergistic effect of Ru and Si, the energy barrier of water dissociation is significantly reduced. The well-organized superlattice structure will provide a paradigm for construction of efficient catalysts with tunable electronic states and dual active sites.

Enhanced Uranium Extraction via Charge Dynamics and Interfacial Polarization in MoS2/GO Heterojunction Electrodes

The removal of uranyl ions (UO2 2+) from water is challenging due to their chemical stability, low concentrations, complex water matrix, and technical limitations in extraction and separation. Herein, a novel molybdenum disulfide/graphene oxide heterojunction (MoS2/GO-H) is developed, serving as an effective electrode for capacitive deionization (CDI). By combining the inherent advantages of electroadsorption and electrocatalysis, an innovative electroadsorption-electrocatalysis system (EES) strategy is introduced. This system utilizes interface polarization at the MoS2 and GO interface, creating an additional electric field that significantly influences carrier behavior. The MoS2/GO-H electrode, with its extraordinary adsorption capacity of 805.57 mg g-1 under optimal conditions, effectively treated uranium-laden wastewater from a mine, achieving over 90% removal efficiency despite the presence of numerous competing ions at concentrations significantly higher than UO2 2+. Employing density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, it is found that the MoS2/GO-H total charge density at the Fermi level, enhanced by interfacial polarization, surpasses that of separate MoS2 and GO, markedly boosting conductivity and electrocatalytic effectiveness.

Two-dimensional architecture of N,S-codoped nanocarbon composites embedding few-layer MoS2 for efficient lithium storage

The exploration and advancement of highly efficient anode materials for lithium-ion batteries (LIBs) are critical to meet the growing demands of the energy storage market. In this study, we present an easily scalable synthesis method for the one-pot formation of few-layer MoS2 nanosheets on a N,S dual-doped carbon monolith with a two-dimensional (2D) architecture, termed MoS2/NSCS. Systematic electrochemical measurements demonstrate that MoS2/NSCS, when employed as the anode material in LIBs, exhibits a high capacity of 681 mA h g-1 at 0.2 A g-1 even after 110 cycles. The exceptional electrochemical performance of MoS2/NSCS can be attributed to its unique porous 2D architecture. The few-layer MoS2 sheets with a large interlayer distance reduce ion diffusion pathways and enhance ion mobility rates. Additionally, the N,S-doped porous carbon matrix not only preserves structural integrity but also facilitates electronic conductivity. These combined factors contribute to the reversible electrochemical activities observed in MoS2/NSCS, highlighting its potential as a promising anode material for high-performance LIBs.

Modification Strategies of Hexagonal Boron Nitride Nanomaterials for Photocatalysis

Although hexagonal boron nitride (h-BN) was initially considered a less promising photocatalyst due to its large band gap and apparent chemical inertness, its unique two-dimensional lamellar structure coupled with high stability and environmental friendliness, as the second largest van der Waals material after graphene, provides a unique platform for photocatalytic innovation. This review not only highlights the intrinsic qualities of h-BN with photocatalytic potentials, such as high stability, environmental compatibility, and tunable bandgap through various modification strategies but also provides a comprehensive overview of the recent advances in h-BN-based nanomaterials for environmental and energy applications, as well as an in-depth description of the modification methods and fundamental properties for these applications. In addition, we discuss the challenges and prospects of h-BN-based nanomaterials for future photocatalysis.

Vacancy-and doping-mediated electronic and magnetic properties of PtSSe monolayer towards optoelectronic and spintronic applications

Developing new multifunctional two-dimensional (2D) materials with two or more functions has been one of the main tasks of materials scientists. In this work, defect engineering is explored to functionalize PtSSe monolayer with feature-rich electronic and magnetic properties. Pristine monolayer is a non-magnetic semiconductor 2D material with a band gap of 1.52(2.31) eV obtained from PBE(HSE06)-based calculations. Upon creating single Pt vacancy, the half-metallic property is induced in PtSSe monolayer with a total magnetic moment of 4.00 μ B. Herein, magnetism is originated mainly from S and Se atoms around the defect site. In contrast, single S and Se vacancies preserve the non-magnetic nature. However, the band gap suffers of considerable reduction of the order of 67.11% and 48.68%, respectively. The half-metallicity emerges also upon doping with alkali metals (Li and Na) with total magnetic moment of 1.00 μ B, while alkaline earth impurities (Be and Mg) make new diluted magnetic semiconductor materials from PtSSe monolayer with total magnetic moment of 2.00 μ B. In these cases, magnetic properties are produced mainly by Se atoms closest to the doping site. In addition, doping with P and As atoms at chalcogen sites is also investigated. Except for the half-metallic AsSe system (As doping at Se site), the diluted magnetic semiconductor behavior is obtained in the remaining cases. Spin density results indicate key role of the VA-group impurities in magnetizing PtSSe monolayer. In these cases, total magnetic moments between 0.99 and 1.00 μ B are obtained. Further Bader charge analysis implies the charge loser role of all impurities that transfer charge to the host monolayer. Results presented in this work may suggest promises of the defected and doped Janus PtSSe structures for optoelectronic and spintronic applications.

Fenton-Like Reaction: Recent Advances and New Trends

The Fenton reaction refers to the reaction in which ferrous ions (Fe2+) produce hydroxyl radicals and other reactive oxidizing substances by decomposing hydrogen peroxide (H2O2). This paper reviews the mechanism, application system, and materials employed in the Fenton reaction including conventional homogeneous and non-homogeneous Fenton reactions as well as photo-, electrically-, ultrasonically-, and piezoelectrically-triggered Fenton reactions, and summarizes the applications in the degradation of soil oil pollutions, landfill leachate, textile wastewater, and antibiotics from a practical point of view. The mineralization paths of typical pollutant are elucidated with relevant case studies. The paper concludes with a summary and outlook of the further development of Fenton-like reactions.

Electron Storage in Monolayer Tungstate Nanosheets Produced via a Scalable Exfoliation Method

Inorganic nanosheet materials with atomic thinness have been widely studied as (photo)catalytic materials due to their unique electronic states and surface structures. One scalable and reproducible method of producing monolayer nanosheets is a top-down approach based on the exfoliation of layered parent compounds using an alkylammonium solution as a surfactant. However, H2W2O7 layered tungstates dissolve in basic aqueous solutions, making them unsuitable for the exfoliation process. This work proposes a scalable method to obtain monolayer WO3 nanosheets with a very high external field responsiveness. This work shows that H2W2O7 topochemically swells in a concentrated octylamine (C8N17NH2) aqueous solution with a concentration above the solubility of octylamine in water. Water was added for exfoliation of the liquid crystalline phase into isolated W2O72- nanosheets with octylammonium (C8N17NH3+) protection. Crystalline WO3 nanosheets on the n-Si substrate obtained with calcination exhibited electron richness in the conduction band due to static electron transfer at the interface.

Achieving Clearance of Drug-Resistant Bacterial Infection and Rapid Cutaneous Wound Regeneration Using an ROS-Balancing-Engineered Heterojunction

Intractable infected microenvironments caused by drug-resistant bacteria stalls the normal course of wound healing. Sono-piezodynamic therapy (SPT) is harnessed to combat pathogenic bacteria, but the superabundant reactive oxygen species (ROS) generated during SPT inevitably provoke severe inflammatory response, hindering tissue regeneration. Consequently, an intelligent nanocatalytic membrane composed of poly(lactic-co-glycolic acid) (PLGA) and black phosphorus /V2C MXene bio-heterojunctions (2D2-bioHJs) is devised. Under ultrasonication, 2D2-bioHJs effectively eliminate drug-resistant bacteria by disrupting metabolism and electron transport chain (ETC). When ultrasonication ceases, they enable the elimination of SPT-generated ROS. The 2D2-bioHJs act as a "lever" that effectively achieves a balance between ROS generation and annihilation, delivering both antibacterial and anti-inflammatory properties to the engineered membrane. More importantly, in vivo assays corroborate that the nanocatalytic membranes transform the stalled chronic wound environment into a regenerative one by eradicating the bacterial population, dampening the NF-κB inflammatory pathway and promoting angiogenesis. As envisaged, this work demonstrates a novel tactic to arm membranes with programmed antibacterial and anti-inflammatory effects to remedy refractory infected wounds from drug-fast bacteria.

Advances in Heterostructures for Optoelectronic Devices: Materials, Properties, Conduction Mechanisms, Device Applications

Atomically thin 2D transition metal dichalcogenides (TMDs) have recently been spotlighted for next-generation electronic and photoelectric device applications. TMD materials with high carrier mobility have superior electronic properties different from bulk semiconductor materials. 0D quantum dots (QDs) possess the ability to tune their bandgap by composition, diameter, and morphology, which allows for a control of their light absorbance and emission wavelength. However, QDs exhibit a low charge carrier mobility and the presence of surface trap states, making it difficult to apply them to electronic and optoelectronic devices. Accordingly, 0D/2D hybrid structures are considered as functional materials with complementary advantages that may not be realized with a single component. Such advantages allow them to be used as both transport and active layers in next-generation optoelectronic applications such as photodetectors, image sensors, solar cells, and light-emitting diodes. Here, recent discoveries related to multicomponent hybrid materials are highlighted. Research trends in electronic and optoelectronic devices based on hybrid heterogeneous materials are also introduced and the issues to be solved from the perspective of the materials and devices are discussed.

Study on synergistic effects of 4f levels of erbium and black phosphorus/SnNb2O6 heterostructure catalysts by multiple spectroscopic analysis techniques

Lanthanide single atom modified catalysts are rarely reported because the roles of lanthanide in photocatalysis are difficult to explain clearly. Based on the construction of Er single atom modified black phosphorus/SnNb2O6 (BP/SNO) heterojunctions, the synergistic effect of 4f levels of Er and heterostructures was studied by combining steady-state, transient, and ultrafast spectral analysis techniques with DFT theoretical calculations. According to the Judd-Ofelt theory of lanthanide ions, the CO2 photoreduction test under single wavelength excitation verifies that the 4F7/2/2H11/2 → 4I15/2 emissions of Er in BPEr/SNOEr can be more easily absorbed by SNO and BP, further proving the role of the 4f levels. As a result, the CO and CH4 yields of BPEr/SNOEr-10 under visible light irradiation are 10.7 and 10.1 times higher than those of pure BP, respectively, and 3.4 and 1.5 times higher than those of SNO. The results of DFT calculations show that the Er single atoms can cause surface reconstruction, regulate the active sites of BP, and reduce the energy change value in the key steps (CO2* + H+ + e- → COOH* and COOH* → CO* + H2O). This work provides novel insights into the design of lanthanide single atom photocatalysts for CO2 reduction.

Boosting the photocatalytic activity of β-FeOOH catalyst for toluene oxidation by constructing internal electric field at 0D/1D homojunction interfaces

Photocatalytic degradation is considered as the most energy-efficient, environmentally benign, and effective method for treating low fraction organic contaminants. However, the photocatalysts still suffer from low utilization efficiency of visible-light and severe carrier recombination. Heterojunctions can resolve these two main problems in some extent but still be restrained by the low quality of hetero-interface. In this study, homojunction was constructed of β-FeOOH quantum dots and nanorods with the same lattice by a two-step precipitation method, to avoid the heterointerface with too many defects and possess good charge separation as a consequence. The catalysts were characterized by activity test, electron spin resonance, Mott-Schottky plots, photocurrent density tests and open-circuit potential measurements, etc. The results revealed that a strong internal electric fields (IEFs) was created at the interface of catalyst. Beneficently, the electron rearrangement leads to a more rational distribution of oxygen vacancies in the catalyst, resulting in more efficient dissociation of oxygen molecules and formation of active radicals, thus facilitating the efficient degradation of toluene. This study proposes a novel strategy to boosting the photocatalytic activity of low dimensional semiconductors via forming homojunction interfaces to improve their charge transfer.

Modification engineering of TiO2-based nanoheterojunction photocatalysts

Titanium dioxide (TiO2)-based photocatalysts have gained increasing attention for their versatile applications in organic degradation, hydrogen production, air purification, and CO2 reduction. Various TiO2-based heterojunction structures, including type I, type II, Schottky junction, Z-scheme, and S-scheme, have been extensively studied. The current research frontier is centered on the engineering modifications of TiO2-based nanoheterojunction photocatalysts, such as defect engineering, morphological engineering, crystal phase/facet engineering, and multijunction engineering. These modifications enhance carrier transport, separation, and light absorption, thereby improving the photocatalytic performance. Remarkably, this aspect has been less addressed in existing reviews. This review aims to fill this gap by focusing on the engineering modifications of TiO2-based nanoheterojunction photocatalysts. We delve into specific topics like oxygen vacancies, n-p homojunctions, and double defects. The review also systematically discusses the applications of multidimensional heterojunctions and examines carrier transport pathways in heterophase/facet junctions and their interactions with heterojunctions. A comprehensive summary of multijunction systems, including multi-Schottky junctions, semiconductor-based heterojunction-attached Schottky junctions, and multisemiconductor-based heterojunctions, is presented. Lastly, we outline future perspectives in this promising research field. This paper will assist researchers in constructing more efficient TiO2-based nanoheterojunction photocatalysts.

Nano-Scale Engineering of Heterojunction for Alkaline Water Electrolysis

Alkaline water electrolysis is promising for low-cost and scalable hydrogen production. Renewable energy-driven alkaline water electrolysis requires highly effective electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, the most active electrocatalysts show orders of magnitude lower performance in alkaline electrolytes than that in acidic ones. To improve such catalysts, heterojunction engineering has been exploited as the most efficient strategy to overcome the activity limitations of the single component in the catalyst. In this review, the basic knowledge of alkaline water electrolysis and the catalytic mechanisms of heterojunctions are introduced. In the HER mechanisms, the ensemble effect emphasizes the multi-sites of different components to accelerate the various intermedium reactions, while the electronic effect refers to the d-band center theory associated with the adsorption and desorption energies of the intermediate products and catalyst. For the OER with multi-electron transfer, a scaling relation was established: the free energy difference between HOO* and HO* is 3.2 eV, which can be overcome by electrocatalysts with heterojunctions. The development of electrocatalysts with heterojunctions are summarized. Typically, Ni(OH)2/Pt, Ni/NiN3 and MoP/MoS2 are HER electrocatalysts, while Ir/Co(OH)2, NiFe(OH)x/FeS and Co9S8/Ni3S2 are OER ones. Last but not the least, the trend of future research is discussed, from an industry perspective, in terms of decreasing the number of noble metals, achieving more stable heterojunctions for longer service, adopting new craft technologies such as 3D printing and exploring revolutionary alternate alkaline water electrolysis.

Constructing α-Fe2O3/g-C3N4/SiO2 S-scheme-based heterostructure for photo-Fenton like degradation of rhodamine B dye in aqueous solution

This work successfully fabricated graphitic carbon nitride and magnetically recoverable α-Fe2O3/g-C3N4/SiO2 photo-Fenton catalysts using thermal polycondensation and in situ-simple precursor drying-calcination process, respectively, was examined for model synthetic rhodamine B (RhB) dye in the presence of H2O2 and acidic pH under simulated visible light irradiation. An aqueous suspension of the reaction mixture of dye-containing wastewater was fully degraded and reached 97% of photo-Fenton degradation efficiency within 120 min followed by the production of hydroxyl radical (•OH). The dominant hydroxyl radical position generated surface charge, electrostatic potential distribution, and average local ionization potential, which contributed to the complete mineralization of RhB dye, according to the density functional theory (DFT) calculations. HPLC and GCMS experiments were performed to examine the degradation fragments of RhB and draw a plausible mechanistic pathway which showed that RhB degradation generated a series of N-deethylated products, followed by a one-time ring-opening, which indicated that photosensitization induced a photocatalysis reaction mechanism.

Ultra-fast synthesis of three-dimensional porous Cu/Zn heterostructures for enhanced carbon dioxide electroreduction

The construction of metal hetero-interfaces has great potential in the application of electro-catalytic carbon dioxide reduction (ECR). Herein, we report a fast, efficient, and simple electrodeposition strategy for synthesizing three-dimensional (3D) porous Cu/Zn heterostructures using the hydrogen bubble template method. When the deposition was carried out at -1.0 A for 30 s, the obtained 3D porous Cu/Zn heterostructures on carbon paper (CP) demonstrated a nearly 100% CO faradaic efficiency (FE) with a high partial current density of 91.8 mA cm-2 at -2.1 V vs. Ag/Ag+ in the mixed electrolyte of ionic liquids/acetonitrile in an H-type cell. In particular, the partial current density of CO could reach 165.5 mA cm-2 and the FE of CO could remain as high as 94.3% at -2.5 V vs. Ag/Ag+. The current density is much higher than most reported to date in an H-type cell (Table S1). Experimental and density functional theory (DFT) calculations reveal that the outstanding electrocatalytic performance of the electrode can be ascribed to the formation of 3D porous Cu/Zn heterostructures, in which the porous and self-supported architecture facilitates diffusion and the Cu/Zn heterostructures can reduce the energy barrier for ECR to CO.

Synergistically Enhanced Photocatalytic Degradation by Coupling Slow-Photon Effect with Z-Scheme Charge Transfer in CdS QDs/IO-TiO2 Heterojunction

Lower light absorption and faster carrier recombination are significant challenges in photocatalysis. This study introduces a novel approach to address these challenges by anchoring cadmium sulfide quantum dots (CdS QDs) on inverse opal (IO)-TiO₂, which increases light absorption and promotes carriers' separation by coupling slow-photon effect with Z-scheme charge transfer. Specifically, the IO-TiO₂ was created by etching a polystyrene opal template, which resulted in a periodic structure that enhances light absorption by reflecting light in the stop band. The size of CdS quantum dots (QDs) was regulated to achieve appropriate alignment of energy bands between CdS QDs and IO-TiO₂, promoting carrier transfer through alterations in charge transfer modes and resulting in synergistic-amplified photocatalysis. Theoretical simulations and electrochemical investigations demonstrated the coexistence of slow-photon effects and Z-scheme transfer. The system's photodegradation performance was tested using rhodamine B as a model. This novel hierarchical structure of the Z-scheme heterojunction exhibits degradability 7.82 and 4.34 times greater than pristine CdS QDs and IO-TiO₂, respectively. This study serves as a source of inspiration for enhancing the photocatalytic capabilities of IO-TiO₂ and broadening its scope of potential applications.

Nanoscale Ni-NiO-ZnO Heterojunctions for Switchable Dehydrogenation and Hydrogenation through Modulation of Active Sites

Catalysts consisting of metal-metal hydroxide/oxide interfaces are highly in demand for advanced catalytic applications as their multicomponent active sites will enable different reactions to occur in close proximity through synergistic cooperation when a single component fails to promote it. To address this, herein we disclosed a simple, scalable, and affordable method for synthesizing catalysts consisting of nanoscale nickel-nickel oxide-zinc oxide (Ni-NiO-ZnO) heterojunctions by a combination of complexation and pyrolytic reduction. The modulation of active sites of catalysts was achieved by varying the reaction conditions of pyrolysis, controlling the growth, and inhibiting the interlayer interaction and Ostwald ripening through the efficient use of coordinated acetate and amide moieties of Zn-Ni materials (ZN-O), produced by the reaction between hydrazine hydrate and Zn-Ni-acetate complexes. We found that the coordinated organic moieties are crucial for forming heterojunctions and their superior catalytic activity. We analyzed two antagonistic reactions to evaluate the performance of the catalysts and found that while the heterostructure of Ni-NiO-ZnO and their cooperative synergy were crucial for managing the effectiveness and selectivity of the catalyst for dehydrogenation of aryl alkanes/alkenes, they failed to enhance the hydrogenation of nitro arenes. The hydrogenation reaction was influenced by the shape, surface properties, and interaction of the hydroxide and oxide of both zinc and nickel, particularly accessible Ni(0). The catalysts showed functional group tolerance, multiple reusabilities, broad substrate applicability, and good activity for both reactions.

Efficient visible-light-driven S-scheme AgVO3/Ag2S heterojunction photocatalyst for boosting degradation of organic pollutants

The traditional semiconductor photocatalysts for solving the related environmental aggravation are often challenged by the recombination of photogenerated carriers. Designing an S-scheme heterojunction photocatalyst is one of the keys to tackling its practical application problems. This paper reports an S-scheme AgVO₃/Ag₂S heterojunction photocatalyst constructed via a straightforward hydrothermal approach that exhibits outstanding photocatalytic degradation performances to the organic dye Rhodamine B (RhB) and antibiotic Tetracycline hydrochloride (TC-HCl) driven by visible light. The results show that AgVO₃/Ag₂S heterojunction with a molar ratio of 6:1 (V6S) possesses the highest photocatalytic performances, 99% of RhB can be almost degraded by 0.1 g/L V6S within 25 min light illumination, and about 72% of TC-HCl can be photodegraded with the act of 0.3 g/L V6S under 120 min light irradiation. Meanwhile, the AgVO₃/Ag₂S system exhibits superior stability and maintains high photocatalytic activity after 5 repeated tests. Moreover, the EPR measurement and radical capture test identify that superoxide radicals and hydroxyl radicals mainly contribute to the photodegradation process. The present work demonstrates that constructing an S-scheme heterojunction can effectively inhibit the recombination of carriers, providing insights into the fabrication of applied photocatalysts for practical wastewater purification treatment.

Enhancement of Charge Separation and NIR Light Harvesting through Construction of 2D-2D Bi4 O5 I2 /BiOBr:Yb3+ , Er3+ Z-Scheme Heterojunctions for Improved Full-Spectrum Photocatalytic Performance

Developing full-spectrum photocatalysts with simultaneous broadband light absorption, excellent charge separation, and high redox capabilities is becoming increasingly significant. Herein, inspired by the similarities in crystalline structures and compositions, a unique 2D-2D Bi4 O5 I2 /BiOBr:Yb3+ ,Er3+ (BI-BYE) Z-scheme heterojunction with upconversion (UC) functionality is successfully designed and fabricated. The co-doped Yb3+ and Er3+ harvest near-infrared (NIR) light and then convert it into visible light via the UC function, expanding the optical response range of the photocatalytic system. The intimate 2D-2D interface contact provides more charge migration channels and enhances the Förster resonant energy transfer of BI-BYE, leading to significantly improved NIR light utilization efficiency. Density functional theory (DFT) calculations and experimental results confirm that the Z-scheme heterojunction is formed and that this heterojunction endows the BI-BYE heterostructure with high charge separation and strong redox capability. Benefit from these synergies, the optimized 75BI-25BYE heterostructure exhibits the highest photocatalytic performance for Bisphenol A (BPA) degradation under full-spectrum and NIR light irradiation, outperforming BYE by 6.0 and 5.3 times, respectively. This work paves an effective approach for designing highly efficient full-spectrum responsive Z-scheme heterojunction photocatalysts with UC function.

Improving the intrinsic activity of ultrathin 2D-2D heterostructures by bridge-bonded Ni-O-Ti ligands for efficient oxygen evolution

The integration of ultrathin two-dimensional (2D) semiconductors with other conductive 2D materials to form hybrid electrocatalysts with abundant heterointerfaces can enhance the electrocatalytic activity by facilitating interfacial charge transfer. However, the hybrid electrocatalysts with weak interfacial bonding have limited effect on the electrocatalytic performance because the intrinsic activity of interfacial sites cannot be altered by weak interfacial interactions. As a proof-of-concept, we design ultrathin 2D-2D heterostructures with bridge-bonded Ni-O-Ti ligands based on single-layered Ti₃C₂T_xMXene and metal hydroxides, and further reveal the structure-activity correlation between interfacial bonding and electrocatalytic oxygen evolution reaction by combining theoretical and experimental studies. Density functional theory calculations reveal the modulation of the electronic structure of interfacial metal sites after the formation of bridged interfacial Ni-O-Ti bonding. Compared with the hydrogen-bond-linked heterostructure, the ultrathin 2D-2D heterostructure with bridge-bonded Ni-O-Ti ligands shows enhanced intrinsic activity and stability towards electrocatalytic oxygen evolution with a very low overpotential of 205 mV at 10 mA cm^-2and the long-term durability. This work provides a new understanding and approach for the design and development of 2D hybrid catalysts with highly efficient electrocatalytic activity.

BiOCl Heterojunction photocatalyst: Construction, photocatalytic performance, and applications

BiOCl semiconductors have attracted extensive amounts of attention and have substantial potential in alleviating energy shortages, improving sterilization performance, and solving environmental issues. To improve the optical quantum efficiency of layered BiOCl, the lifetimes of photogenerated electron-hole pairs, and BiOCl reduction capacity. During the past decade, researchers have designed many effective methods to weaken the effects of these limitations, and heterojunction construction is regarded as one of the most promising strategies. In this paper, BiOCl heterojunction photocatalysts designed and synthesized by various research groups in recent years were reviewed, and their photocatalytic properties were tested. Among them, direct Z-scheme and S-scheme photocatalysts have high redox potentials and intense redox capabilities. Hence, they exhibit excellent photocatalytic activity. Furthermore, the applications of BiOCl heterojunctions for pollutant degradation, CO2 reduction, water splitting, N2 fixation, organic synthesis, and tumor ablation are also reviewed. Finally, we summarize research on the BiOCl heterojunctions and put forth new insights on overcoming their present limitations.

Interface Engineering in 2D/2D Heterogeneous Photocatalysts

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

Fully Flexible MXene-based Gas Sensor on Paper for Highly Sensitive Room-Temperature Nitrogen Dioxide Detection

Flexible chemiresistive gas sensors have attracted growing interest due to their capability in real-time and rapid detection of gas. However, the performance of gas sensors has long been hindered by the poor charge transfer ability between the conventional metal electrode and gas sensing semiconductors. Herein, for the first time, a fully flexible paper-based gas sensor integrated with the Ti₃C₂T_x-MXene nonmetallic electrode and the Ti₃C₂T_x/WS₂ gas sensing film was designed to form Ohmic contact and Schottky heterojunction in a single gas sensing channel. Ti₃C₂T_x/WS₂ has outstanding physical and chemical properties for both Ti₃C₂T_x and WS₂ nanoflakes, showing high conductivity, effective charge transfer, and abundant active sites for gas sensing. The response of the gas sensor to NO₂ (1 ppm) at room temperature is 15.2%, which is about 3.2 and 76.0 times as high as that of the Au interdigital electrode integrated with the Ti₃C₂T_x/WS₂ sensor (4.8%) and the MXene electrode integrated with the Ti₃C₂T_x sensor (0.2%), respectively. Besides, this design performed at a limit of detection with 11.0 ppb NO₂ gas and displayed excellent stability under high humidities. Based on first-principles density functional theory calculation results, the improvement of the gas sensing performance can be mainly attributed to the heterojunction regulation effect, work function matching, and suppressing metal-induced gap states. This work provides a new approach for the design of flexible gas sensors on paper with MXene-based conductive electrodes and gas sensing materials.

Design and analysis of in-plane and out-of-plane heterostructures based on monolayer tri-G with enhanced photocatalytic property for water splitting

Photocatalytic water splitting is considered to be a promising renewable solution to the energy crisis and environmental problems as an inexhaustible clean energy source. Graphene has an ultrahigh carrier mobility, but the zero gap limits its practical application in the photocatalysis field. Graphane has a wider band gap and retains a high carrier mobility, which demonstrates its great potential in this field. However, the broad band gap results in low photocatalytic efficiency. In this work, we propose two effective ways to modulate its electronic structure, modifying the structure of graphane and constructing a heterojunction using density functional calculations. We systematically investigated four trilayer graphane (tri-G) conformers and designed in-plane (lateral) and out-of-plane (vertical) heterojunctions with tri-G and chair-G (cha-G), the two most stable graphanes, with theoretical prediction. The results show that tri-G not only has a smaller band gap, falling in the ultraviolet range, which enhances the UV-light catalytic performance, but also has tunable band edge positions, locating outside the reduction potential of hydrogen and oxidation potential of water. Furthermore, the calculated electron effective mass for the tri-G conformers is smaller than that of cha-G. What's more, the band gap, band edge position, and photocatalytic efficiency are further optimized by constructing heterojunctions. In particular, both the in-plane and out-of-plane tri-G-C/cha-G heterostructures are confirmed as direct band gap semiconductors and type-I heterostructures exhibiting special band alignment, meanwhile satisfying the requirements for water splitting. And the band gaps of the heterostructures are further reduced. In addition, metal doping is expected to further optimize their electronic structure. These results provide theoretical support and a feasible modulation strategy for developing graphane as an effective photocatalyst for water splitting.

Design of the Synergistic Rectifying Interfaces in Mott-Schottky Catalysts

The functions of interfacial synergy in heterojunction catalysts are diverse and powerful, providing a route to solve many difficulties in energy conversion and organic synthesis. Among heterojunction-based catalysts, the Mott-Schottky catalysts composed of a metal-semiconductor heterojunction with predictable and designable interfacial synergy are rising stars of next-generation catalysts. We review the concept of Mott-Schottky catalysts and discuss their applications in various realms of catalysis. In particular, the design of a Mott-Schottky catalyst provides a feasible strategy to boost energy conversion and chemical synthesis processes, even allowing realization of novel catalytic functions such as enhanced redox activity, Lewis acid-base pairs, and electron donor-acceptor couples for dealing with the current problems in catalysis for energy conversion and storage. This review focuses on the synthesis, assembly, and characterization of Schottky heterojunctions for photocatalysis, electrocatalysis, and organic synthesis. The proposed design principles, including the importance of constructing stable and clean interfaces, tuning work function differences, and preparing exposable interfacial structures for designing electronic interfaces, will provide a reference for the development of all heterojunction-type catalysts, electrodes, energy conversion/storage devices, and even super absorbers, which are currently topics of interest in fields such as electrocatalysis, fuel cells, CO₂ reduction, and wastewater treatment.

Hydroxyl-/Carboxyl-Rich Graphitic Carbon Nitride/Graphene Oxide Composites for Efficient Photodegradation of Reactive Red 195 and Antibacterial Applications

In this work, a protonated graphitic carbon nitride (P-g-C₃N₄)-coated graphene oxide (GO) composite (GO/P-g-C₃N₄) was prepared via wet-chemistry exfoliation, followed by a freeze-drying process. The GO/P-g-C₃N₄ composite was found to have an outstanding photodegradation performance effect on the reactive red 195 (RR195) dye and very strong antibacterial properties. Both the GO structure and the dispersed state of P-g-C₃N₄ were found to play a significant role in enhancing the photocatalytic activity of GO/P-g-C₃N₄. The GO/P-g-C₃N₄ obtained via freeze-drying retained a large number of oxygen-containing groups and showed higher catalytic activity and reusability than the reduced GO (rGO)/g-C₃N₄ obtained via thermal reduction. Characterization of the samples indicates that GO/P-g-C₃N₄ has a higher specific surface area and photocurrent density than rGO/g-C₃N₄; it is likely that these properties lead to the superior photocatalytic activity observed in GO/P-g-C₃N₄. Adsorption energy calculations indicate that O₂ can be readily adsorbed onto the GO surface, which results in stronger oxidizing superoxide anion radicals (^•O₂^-) and holes (h⁺); these active radicals can rapidly degrade RR195 dyes. Moreover, broad-spectrum antibacterial activity (demonstrated against Staphylococcus aureus and Escherichia coli) was observed in the case of the GO/P-g-C₃N₄ composite irradiated with visible light. This work offers new insights into the design of cost-effective g-C₃N₄-based photocatalysts for environmental remediation.

Synthesis and Application of Liquid Metal Based-2D Nanomaterials: A Perspective View for Sustainable Energy

With the continuous exploration of low-dimensional nanomaterials, two dimensional metal oxides (2DMOs) has been received great interest. However, their further development is limited by the high cost in the preparation process and the unstable states caused by the polarization of surface chemical bonds. Recently, obtaining mental oxides via liquid metals have been considered a surprising method for obtaining 2DMOs. Therefore, how to scientifically choose different preparation methods to obtain 2DMOs applying in different application scenarios is an ongoing process worth discussing. This review will provide some new opportunities for the rational design of 2DMOs based on liquid metals. Firstly, the surface oxidation process and in situ electrical replacement reaction process of liquid metals are introduced in detail, which provides theoretical basis for realizing functional 2DMOs. Secondly, by simple sticking method, gas injection method and ultrasonic method, 2DMOs can be obtained from liquid metal, the characteristics of each method are introduced in detail. Then, this review provides some prospective new ideas for 2DMOs in other energy-related applications such as photodegradation, CO₂ reduction and battery applications. Finally, the present challenges and future development prospects of 2DMOs applied in liquid metals are presented.

2D-2D heterostructure g-C3N4-based materials for photocatalytic H2 evolution: Progress and perspectives

Photocatalytic hydrogen generation from direct water splitting is recognized as a progressive and renewable energy producer. The secret to understanding this phenomenon is discovering an efficient photocatalyst that preferably uses sunlight energy. Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄)-based materials are promising for photocatalytic water splitting due to special characteristics such as appropriate band gap, visible light active, ultra-high specific surface area, and abundantly exposed active sites. However, the inadequate photocatalytic activity of pure 2D layered g-C₃N₄-based materials is a massive challenge due to the quick recombination between photogenerated holes and electrons. Creating 2D heterogeneous photocatalysts is a cost-effective strategy for clean and renewable hydrogen production on a larger scale. The 2D g-C₃N₄-based heterostructure with the combined merits of each 2D component, which facilitate the rapid charge separation through the heterojunction effect on photocatalyst, has been evidenced to be very effective in enhancing the photocatalytic performance. To further improve the photocatalytic efficiency, the development of novel 2D g-C₃N₄-based heterostructure photocatalysts is critical. This mini-review covers the fundamental concepts, recent advancements, and applications in photocatalytic hydrogen production. Furthermore, the challenges and perspectives on 2D g-C₃N₄-based heterostructure photocatalysts demonstrate the future direction toward sustainability.

Engineered 2D Metal Oxides for Photocatalysis as Environmental Remediation: A Theoretical Perspective

Modern-day society requires advanced technologies based on renewable and sustainable energy resources to meet environmental remediation challenges. Solar-inspired photocatalytic applications such as water splitting, hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO2RR) are unique solutions based on green and efficient technologies. Considering the special electronic features and larger surface area, two-dimensional (2D) materials, especially metal oxides (MOs), have been broadly explored for the abovementioned applications in the past few years. However, their photocatalytic potential has not been optimized yet to the level required for practical and commercial applications. Among many strategies available, defect engineering, including cation and anion vacancy creations, can potentially boost the photocatalytic performance of 2D MOs. This mini-review covers recent advancements in 2D engineered materials for various photocatalysis applications such as H2O2 oxidation, HER, and CO2RR for environmental remediation from theoretical perspectives. By thoroughly addressing the fundamental aspects, recent developments, and associated challenges—the author’s recommendations in compliance with future challenges and prospects will pave the way for readers.

Constructing Fast Transmembrane Pathways in a Layered Double Hydroxide Nanosheets/Nanoparticles Composite Film for an Inorganic Anion-Exchange Membrane

Anion-exchange membranes (AEMs) with high conductivity are crucial for realizing next-generation energy storage and conversion systems in an alkaline environment, promising a huge advantage in cost reduction without using precious platinum group metal catalysts. Layered double hydroxide (LDH) nanosheets, exhibiting a remarkably high hydroxide ion (OH^-) conductivity approaching 10^-1 S cm^-1 along the in-plane direction, may be regarded as an ideal candidate material for the fabrication of inorganic solid AEMs. However, two-dimensional anisotropy results in a substantially low conductivity of 10^-6 S cm^-1 along the cross-plane direction, which poses a hurdle to achieve fast ion conduction across the membrane comprising restacked nanosheets. In the present work, a composite membrane was prepared based on mixing/assembling micron-sized LDH nanosheets with nanosized LDH platelets (nanoparticles) via a facile vacuum filtration process. The hybridization with nanoparticles could alter the orientation of LDH nanosheets and reduce the restacking order, forming diversified fast ion-conducting pathways and networks in the composite membrane. As a result, the transmembrane conductivity significantly improved up to 1000-fold higher than that composed of restacked nanosheets only, achieving a high conductivity of 10^-2 to 10^-1 S cm^-1 in both in-plane and cross-plane directions.

Rational Design and Preparation of Pt-LDH/CeO2 Catalyst for High-Efficiency Photothermal Catalytic Oxidation of Toluene

Volatile organic compounds (VOCs) are attracting much more attention due to their contributions to air pollution and human health problems. Photothermal catalytic oxidation is considered as an energy-saving method for the removal of VOCs. However, the efficiency of the photothermal catalytic system is still suffering from the low activity of the catalyst due to its poor response to visible light and low efficiency of charge separation. Here, few-layer CoAl-LDH (layered double hydroxide) was prepared as an advantageous support for loading Pt nanoparticles to obtain Pt-LDH, which were coated on CeO₂ nanoparticles. Type II heterojunctions were formed on the interface of LDH and CeO₂. In photocatalysis, the hot electrons will move to CeO₂, which is better at the activation of O₂ molecules, and holes will concentrate on the LDHs, which have plenty of hydroxyls to generate •OH radicals. Furthermore, the Schottky heterojunctions between LDH and Pt nanoparticles benefit the improvement of light absorption by the localized surface plasmon resonance of Pt nanoparticles. As a consequence, a high removal rate of toluene (75.7%) at a weight-hourly space velocity of 23340 mL/(g·h) under visible light irradiation (160 mW/cm², λ > 400 nm) at room temperature was achieved over the Pt-LDH/CeO₂ catalyst. The catalyst design provides a useful method to prepare high-efficiency photothermal catalysts.

g-C3N4/TiO2-B{100} heterostructures used as promising photocatalysts for water splitting from a hybrid density functional study

Fabrication of heterostructures has been shown to be a good strategy to improve photocatalytic performance. By using first-principles calculation based on hybrid density functionals, the photocatalytic mechanism of g-C₃N₄/TiO₂-B{100} heterostructures is investigated to understand the process of water decomposition. We find that the reduction of the band gap of g-C₃N₄/TiO₂-B{100} heterostructures enhances the visible light response range. g-C₃N₄/TiO₂-B{100} heterostructures have direct band gaps, staggered band alignment, electron flow from g-C₃N₄ to TiO₂-B{100} surfaces and straddling water decomposition potential, and are potential Z-scheme photocatalysts. Photoinduced carriers can be effectively separated using the Z-scheme photocatalytic mechanism. Our results demonstrate that g-C₃N₄/TiO₂-B{100} heterostructures can enhance light absorption, prolong the life of photoinduced carriers, and further improve the photocatalytic activity. We believe that our findings can provide a reference for explaining the enhancement mechanism of the g-C₃N₄/TiO₂ photocatalyst as observed in the experiment.

Recent advances and challenges in 2D/2D heterojunction photocatalysts for solar fuels applications

Although photocatalytic technology has emerged as an effective means of alleviating the projected future fuel crisis by converting sunlight directly into chemical energy, no visible-light-driven, low-cost, and highly stable photocatalyst has been developed to date. Due to considerably higher interfacial contact with numerous reactive sites, effective charge transmission and separation ability, and strong redox potentials, the focus has now shifted to 2D/2D heterojunction systems, which have exhibited effective photocatalytic performance. The fundamentals of 2D/2D photocatalysis for different applications and the classification of 2D/2D materials are first explained in this paper, followed by strategies to improve the photocatalytic performance of various 2D/2D heterojunction systems. Following that, current breakthroughs in 2D/2D metal-based and metal-free heterojunction photocatalysts, as well as their applications for H₂ evolution via water splitting, CO₂ reduction, and N₂ fixation, are discussed. Finally, a brief overview of current constraints and predicted results for 2D/2D heterojunction systems is also presented. This paper lays out a strategy for developing efficient 2D/2D heterojunction photocatalysts and sophisticated technology for solar fuel applications in order to address the energy issue.