In Situ Growth of MAPbBr3 Nanocrystals on Few‐Layer MXene Nanosheets with Efficient Energy Transfer

The performance of perovskite nanocrystals (NCs) in optoelectronics and photocatalysis is severely limited by the presence of large amounts of crystal boundaries in NCs film that greatly restricts energy transfer. Creating heterostructures based on perovskite NCs and 2D materials is a common approach to improve the energy transport at the perovskite/2D materials interface. Herein, methylamine lead bromide (MAPbBr₃, MA: CH₃NH₃⁺) perovskite NCs are homogeneously deposited on highly conductive few‐layer MXene (Ti₃C₂T_x) nanosheets to form heterostructures through an in situ solution growth method. An optimal mixed solvent ratio is essential to realize the growth of perovskite NCs on Ti₃C₂T_x nanosheets. Time‐resolved photoluminescence spectroscopy, transient absorption spectroscopy, and the photoresponse of electron‐ and hole‐only photoelectric conversion devices reveal the interfacial energy transfer behavior within MAPbBr₃/Ti₃C₂T_x heterostructures. The present investigation may provide a useful guide toward use of halide perovskite/2D material heterostructures in applications such as photocatalysis as well as optoelectronics.     

Enhanced Photocarrier Generation with Selectable Wavelengths by M‐Decorated‐CuInS2 Nanocrystals (M = Au and Pt) Synthesized in a Single Surfactant Process on MoS2 Bilayers

A facile approach for the synthesis of Au‐ and Pt‐decorated CuInS₂ nanocrystals (CIS NCs) as sensitizer materials on the top of MoS₂ bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS₂ bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20–40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS₂ bilayers‐based photodetectors. Remarkably, by using Pt‐ or Au‐decorated CIS NCs, the photocurrent enhancement of MoS₂ photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS₂‐based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.     

Recent Advances in Rolling 2D TMDs Nanosheets into 1D TMDs Nanotubes/Nanoscrolls

Transition metal dichalcogenides (TMDs) van der Waals (vdW) 1D heterostructures are recently synthesized from 2D nanosheets, which open up new opportunities for potential applications in electronic and optoelectronic devices. The most recent and promising strategies in regards to forming 1D TMDs nanotubes (NTs) or nanoscrolls (NSs) in this review article as well as their heterostructures that are produced from 2D TMDs are summarized. In order to improve the functionality of ultrathin 1D TMDs that are coaxially combined with boron nitride nanotubes and single-walled carbon nanotubes. 1D heterostructured devices perform better than 2D TMD nanosheets when the two devices are compared. The photovoltaic effect in WS₂ or MoS₂ NTs without a junction may exceed the Shockley–Queisser limit for the above-band-gap photovoltage generation. Photoelectrochemical hydrogen evolution is accelerated when monolayer WS₂ or MoS₂ NSs are incorporated into a heterojunction. In addition, the photovoltaic performance of the WSe₂/MoS₂ NSs junction is superior to that of the performance of MoS₂ NSs. The summary of the current research about 1D TMDs can be used in a variety of ways, which assists in the development of new types of nanoscale optoelectronic devices. Finally, it also summarizes the current challenges and prospects.     

Aqueous Phase Exfoliating Quasi‐2D CsPbBr3 Nanosheets with Ultrahigh Intrinsic Water Stability

All‐inorganic cesium lead halide perovskite nanocrystals (NCs) have emerged as attractive optoelectronic materials due to the excellent optical and electronic properties. However, their environmental stability, especially in the presence of water, is still a significant challenge for their further commercialization. Here, ultrahigh intrinsically water‐stable all‐inorganic quasi‐2D CsPbBr₃ nanosheets (NSs) via aqueous phase exfoliation method are reported. Compared to conventional perovskite NCs, these unique quasi‐2D CsPbBr₃ nanosheets present an outstanding long‐term water stability with 87% photoluminescence (PL) intensity remaining after 168 h under water conditions. Moreover, the photoluminescence quantum yields (PLQY) of quasi‐2D CsPbBr₃ NSs is up to 82.3%, and these quasi‐2D CsPbBr₃ NSs also present good photostability of keeping 85% PL intensity after 2 h under 365 nm UV light. Evidently, such quasi‐2D perovskite NSs will open up a new way to investigate the intrinsic stability of all‐inorganic perovskites and further promote the commercial development of perovskite‐based optoelectronic and photovoltaic devices.     

Self‐Assembly of Transition Metal Oxide Nanostructures on MXene Nanosheets for Fast and Stable Lithium Storage

Recently, a new class of 2D materials, i.e., transition metal carbides, nitrides, and carbonitrides known as MXenes, is unveiled with more than 20 types reported one after another. Since they are flexible and conductive, MXenes are expected to compete with graphene and other 2D materials in many applications. Here, a general route is reported to simple self‐assembly of transition metal oxide (TMO) nanostructures, including TiO₂ nanorods and SnO₂ nanowires, on MXene (Ti₃C₂) nanosheets through van der Waals interactions. The MXene nanosheets, acting as the underlying substrate, not only enable reversible electron and ion transport at the interface but also prevent the TMO nanostructures from aggregation during lithiation/delithiation. The TMO nanostructures, in turn, serve as the spacer to prevent the MXene nanosheets from restacking, thus preserving the active areas from being lost. More importantly, they can contribute extraordinary electrochemical properties, offering short lithium diffusion pathways and additional active sites. The resulting TiO₂/MXene and SnO₂/MXene heterostructures exhibit superior high‐rate performance, making them promising high‐power and high‐energy anode materials for lithium‐ion batteries.     

Cu2MoS4/Au Heterostructures with Enhanced Catalase‐Like Activity and Photoconversion Efficiency for Primary/Metastatic Tumors Eradication by Phototherapy‐Induced Immunotherapy

Photoimmunotherapy can not only effectively ablate the primary tumor but also trigger strong antitumor immune responses against metastatic tumors by inducing immunogenic cell death. Herein, Cu₂MoS₄ (CMS)/Au heterostructures are constructed by depositing plasmonic Au nanoparticles onto CMS nanosheets, which exhibit enhanced absorption in near‐infrared (NIR) region due to the newly formed mid‐gap state across the Fermi level based on the hybridization between Au 5d orbitals and S 3p orbitals, thus resulting in more excellent photothermal therapy and photodynamic therapy (PDT) effect than single CMS upon NIR laser irradiation. The CMS and CMS/Au can also serve as catalase to effectively relieve tumor hypoxia, which can enhance the therapeutic effect of O₂‐dependent PDT. Notably, the NIR laser‐irradiated CMS/Au can elicit strong immune responses via promoting dendritic cells maturation, cytokine secretion, and activating antitumor effector T‐cell responses for both primary and metastatic tumors eradication. Moreover, CMS/Au exhibits outstanding photoacoustic and computed tomography imaging performance owing to its excellent photothermal conversion and X‐ray attenuation ability. Overall, the work provides an imaging‐guided and phototherapy‐induced immunotherapy based on constructing CMS/Au heterostructures for effectively tumor ablation and cancer metastasis inhibition.     

Ligand-free Au nanoclusters/g-C3N4 ultra-thin nanosheets composite photocatalysts for efficient visible-light-driven photocatalytic H2 generation

In this paper, we report the synthesis of ligand-free Au nanoclusters (NCs)/g-C₃N₄ ultra-thin nanosheets (NSs) composite via a facile wet-impregnation method with post-annealing. On the one hand, post-annealing was used for the exfoliation of multi-layered g-C₃N₄ to obtain ultra-thin NSs; on the other hand, after Au₂₅(Cys)₁₈ NCs were loaded, post-annealing was further adopted to remove the ligands to obtain clean surface on Au NCs. It is demonstrated that the loaded Au NCs were aggregating resistant by post-annealing. Constructing heterojunctions with appropriate inter-band structures between the ligand-free Au NCs and the ultra-thin g-C₃N₄ NSs, along with the mono-distribution of the Au NCs and their intimate contact with g-C₃N₄ NSs ensured the smooth interfacial charge transfer. As a result, the composite photocatalysts exhibited efficient visible-light-induced photocatalytic H₂ generation, mainly due to the local electric field enhancement induced by excitation of Au NCs under visible light and the improved charge separation in g-C₃N₄. This work provides a general strategy for the synthesis of noble metal NCs based composites with clean surface as the efficient photocatalysts for solar energy conversion.

Graphical Abstract

A stepwise post-annealing strategy is exploited to prepare g-C₃N₄ ultra-thin nanosheets modified with highly dispersed ligand-free Au nanoclusters for efficient photocatalytic hydrogen production.

     

Probing Bidirectional Plasmon-Plasmon Coupling-Induced Hot Charge Carriers in Dual Plasmonic Au/CuS Nanocrystals

Heterostructured Au/CuS nanocrystals (NCs) exhibit localized surface plasmon resonance (LSPR) centered at two different wavelengths (551 and 1051 nm) with a slight broadening compared to respective homostructured Au and CuS NC spectra. By applying ultrafast transient absorption spectroscopy we show that a resonant excitation at the respective LSPR maxima of the heterostructured Au/CuS NCs leads to the characteristic hot charge carrier relaxation associated with both LSPRs in both cases. A comparison of the dual plasmonic heterostructure with a colloidal mixture of homostructured Au and CuS NCs shows that the coupled dual plasmonic interaction is only active in the heterostructured Au/CuS NCs. By investigating the charge carrier dynamics of the process, we find that the observed interaction is faster than phononic or thermal processes (< 100 fs). The relaxation of the generated hot charge carriers is faster for heterostructured nanocrystals and indicates that the interaction occurs as an energy transfer (we propose Landau damping or interaction via LSPR beat oscillations as possible mechanisms) or charge carrier transfer between both materials. Our results strengthen the understanding of multiplasmonic interactions in heterostructured Au/CuS NCs and will significantly advance applications where these interactions are essential, such as catalytic reactions.     

Strongly Coupled g‐C3N4 Nanosheets‐Co3O4 Quantum Dots as 2D/0D Heterostructure Composite for Peroxymonosulfate Activation

The development of effective approaches for the preparation of 0D quantum dots (QDs)/2D nanosheets (NSs) heterostructures, which have been proven to be favorable for heterogeneous catalysis, is highly desirable but remains a great challenge. Herein, 0D metal oxide nanocrystals–2D ultrathin g‐C₃N₄ nanosheets (Co₃O₄/CNNS) heterostructures are synthesized via a facile chemical reaction, followed by annealing in air. Ultrafine Co₃O₄ QDs (≈2.2–3.2 nm) are uniformly and tightly attached on the surface of g‐C₃N₄ nanosheets. Detailed characterization reveals that the specially designed unique 0D/2D structure is critical to the high photocatalytic performance for the degradation of tetracycline (TC) via peroxymonosulfate (PMS) activation. The optimal catalyst, namely, Co₃O₄/CNNS‐1100, exhibits excellent performance and ≈98.7% TC can be degraded under visible light irradiation. Moreover, TC degradation is almost completely insusceptible to several real water samples. Meanwhile, other dye pollutants can also be efficiently degraded by the Co₃O₄/CNNS‐1100/PMS/vis system. The quenching tests display that that the h⁺, ?OH, O₂^??, and SO₄^?? are responsible for TC removal. The improved photocatalytic performance can be attributed to the synergistic effect of the photocatalytic‐ and chemical‐processes in the PMS activation. This work gives an insight into the development of multifunctional 0D/2D nanocomposites for further potential applications which are not limited to environmental purification.     

High Detectivity and Transparent Few‐Layer MoS2/Glassy‐Graphene Heterostructure Photodetectors

Layered van der Waals heterostructures have attracted considerable attention recently, due to their unique properties both inherited from individual two‐dimensional (2D) components and imparted from their interactions. Here, a novel few‐layer MoS₂/glassy‐graphene heterostructure, synthesized by a layer‐by‐layer transfer technique, and its application as transparent photodetectors are reported for the first time. Instead of a traditional Schottky junction, coherent ohmic contact is formed at the interface between the MoS₂ and the glassy‐graphene nanosheets. The device exhibits pronounced wavelength selectivity as illuminated by monochromatic lights. A responsivity of 12.3 mA W^?1 and detectivity of 1.8 × 10¹⁰ Jones are obtained from the photodetector under 532 nm light illumination. Density functional theory calculations reveal the impact of specific carbon atomic arrangement in the glassy‐graphene on the electronic band structure. It is demonstrated that the band alignment of the layered heterostructures can be manipulated by lattice engineering of 2D nanosheets to enhance optoelectronic performance.     

Heterostructures of 2D Molybdenum Dichalcogenide on 2D Nitrogen-Doped Carbon: Superior Potassium-Ion Storage and Insight into Potassium Storage Mechanism

Constructing 2D heterostructure materials by stacking different 2D materials can combine the merits of the individual building blocks while eliminating their shortcomings. Dichalcogenides are attractive anodes for potassium-ion batteries (KIBs) due to their high theoretical capacity. However, the practical application of dichalcogenide is greatly hampered by the poor electrochemical performance due to sluggish kinetics of K⁺ insertion and the electrode structure collapse resulting from the large K⁺ insertion. Herein, heterostructures of 2D molybdenum dichalcogenide on 2D nitrogen-doped carbon (MoS₂, MoSe₂-on-NC) are prepared to boost their potassium storage performance. The unique 2D heterostructures possess built-in heterointerfaces, facilitating K⁺ diffusion. The robust chemical bonds (C S, C Se, C Mo bonds) enhance the mechanical strength of electrodes, thus suppressing the volume expansion. The 2D N-doped carbon nanosheets interconnected as a 3D structure offer a fast diffusion path for electrons. Benefitting from these merits, both the MoS₂-on-NC and the MoSe₂-on-NC exhibit unprecedented cycle life. Moreover, the electrochemical reaction mechanism of MoSe₂ is revealed during the process of potassiation and depotassiation.     

Novel SiQDs–MoS<Subscript>2</Subscript> heterostructures with increasing solar absorption for the photocatalytic degradation of malachite green

Novel heterostructures based on silicon quantum dots and molybdenum disulfide nanosheets (SiQDs–MoS₂) were synthesized by a hydrothermal method, in which the introduced SiQDs play a determining role in manipulating the morphology, phase and band structure of MoS₂. The resultant SiQDs–MoS₂ is uniform flowerlike 3D microspheres assembled from petallike 2D MoS₂ nanosheets anchored with 0D SiQDs, possessing abundant active sites. Besides, the primary MoS₂ nanosheets consist of both semiconductive 2H and metallic 1T phases accompanied with intralayer mesopores and expanded interlayer spacing, endowing the resulting architectures with effective electron transfer. Significantly, the as-synthesized SiQDs–MoS₂ exhibits intense full solar-spectrum absorption, indicating efficient solar energy harvesting. First-principles calculations simulate similar increased spectral absorption of monolayer MoS₂ adhered with a Si cluster, suggesting the existence of new energy states associated with the integration of SiQDs and MoS₂ nanosheets as evidenced by photoluminescence (PL) spectral analysis. As expected, the current SiQDs–MoS₂ heterostructures demonstrate substantial photocatalytic activity even under visible and near-infrared (NIR) light on degradation of malachite green (MG). The type II electronic structure of SiQDs–MoS₂ was proposed, enabling sufficient photogenerated electrons and holes for the photocatalytic reactions. This study may establish a new frontier on the rational design and feasible development of the hybrid structures with the desirable morphologies, phase compositions and band structures for the catalysis and beyond.     

Stabilizing MoS2 Nanosheets through SnO2 Nanocrystal Decoration for High‐Performance Gas Sensing in Air

The unique properties of MoS₂ nanosheets make them a promising candidate for high‐performance room temperature sensing. However, the properties of pristine MoS₂ nanosheets are strongly influenced by the significant adsorption of oxygen in an air environment, which leads to instability of the MoS₂ sensing device, and all sensing results on MoS₂ reported to date were exclusively obtained in an inert atmosphere. This significantly limits the practical sensor application of MoS₂ in an air environment. Herein, a novel nanohybrid of SnO₂ nanocrystal (NC)‐decorated crumpled MoS₂ nanosheet (MoS₂/SnO₂) and its exciting air‐stable property for room temperature sensing of NO₂ are reported. Interestingly, the SnO₂ NCs serve as strong p‐type dopants for MoS₂, leading to p‐type channels in the MoS₂ nanosheets. The SnO₂ NCs also significantly enhance the stability of MoS₂ nanosheets in dry air. As a result, unlike other MoS₂ sensors operated in an inert gas (e.g. N₂), the nanohybrids exhibit high sensitivity, excellent selectivity, and repeatability to NO₂ under a practical dry air environment. This work suggests that NC decoration significantly tunes the properties of MoS₂ nanosheets for various applications.     

Substrate‐Friendly Growth of Large‐Sized Ni(OH)2 Nanosheets for Flexible Electrochromic Films

Large‐area, 2D, anisotropic, direct growth of nanostructures is considered an effective and straightforward way to readily fulfill transparent, flexible technology requirements. In addition, formation of thin hybrid structures by combining with another 2D material brings about dimensional advantages, such as intimate heterostructure functionalities, large specific area, and optical transparency. Here, we demonstrate 2D planar growth of thin Ni(OH)₂ nanosheets on arbitrary rigid and soft supports, by exploiting the growth strategies of oriented attachment induced by interfacial chemistry and the intrinsic driving force of layered structure constitution. Moreover, large‐scale 2D heterohybrids have successfully been prepared by direct conformal growth of Ni(OH)₂ nanosheets overlying MoO₃ nanobelts. Unlike the exfoliation and transfer of 2D materials technique, this approach minimizes multiple process contamination and physical‐handling structural defects. Accordingly, proof‐of‐concept flexible electrochromism is demonstrated in view of its prerequisite to the access of a large homogeneous material coating. The as‐synthesized 2D layered structure affirms its optical and electrochemical superiority through the display of wide optical modulation, high coloration efficiency, good cyclic stability, and flexibility.     

Engineering Gold Nanorod–Copper Sulfide Heterostructures with Enhanced Photothermal Conversion Efficiency and Photostability

Plasmonic gold nanorods (Au NRs)–copper sulfide heterostructures have recently attracted much attention owing to the synergistically enhanced photothermal properties. However, the facile synthesis and interface tailoring of Au NRs–copper sulfide heterostructures remain a formidable challenge. In this study, the rational design and synthesis of Au NRs–Cu₇S₄ heterostructures via a one‐pot hydrothermal process is reported. Specifically, core–shell and dumbbell‐like Au NRs–Cu₇S₄ heterostructures are obtained with well‐controlled interfaces by employing the Au NRs with different aspect ratios. Both core–shell and dumbbell‐like Au NRs–Cu₇S₄ have proven effective as photothermal therapy agents, which offer both high photothermal stability and significant photothermal conversion efficiency up to 62%. The finite‐difference time domain simulation results confirm the coupling effect that leads to the enhanced local field as well as the optical absorption at the heterostructure interface. Importantly, these Au NRs–Cu₇S₄ heterostructures can be compatibly used as an 808 nm laser‐driven photothermal therapy agents for the efficient photothermal therapy of cancer cells in vitro. This study will provide new insight into the design of other noble metal–semiconductor heterostructures for a broad range of applications utilizing surface plasmon resonance enhancement phenomena.     

Elaborately Designed Hierarchical Heterostructures Consisting of Carbon‐Coated TiO2(B) Nanosheets Decorated with Fe3O4 Nanoparticles for Remarkable Synergy in High‐Rate Lithium Storage

The capacity and conductivity deficiencies of TiO₂(B) are addressed simultaneously through a smart morphological and compositional design. Elaborately designed hierarchical heterostructures are reported, consisting of carbon‐coated TiO₂(B) nanosheets decorated with Fe₃O₄ nanoparticles, based on a facile self‐assembly strategy. The novel hierarchical heterostructures exhibit a remarkable synergy by bridging the intriguing functionalities of TiO₂(B) nanosheets (high safety and durability), Fe₃O₄ nanoparticles (high theoretical capacity), and carbon coatings (high conductivity), which results in significantly improved cycle and rate performances. A startlingly high reversible capacity of 763 mA h g⁻¹ is delivered at 500 mA g⁻¹ after 200 charging−discharging cycles. Even when the current density is as high as 10 000 mA g⁻¹, the reversible capacity is still up to 498 mA h g⁻¹. This smart morphological and compositional design opens up new opportunities for developing novel, multifunctional hierarchical heterostructures as promising anode materials for next‐generation, high‐power lithium‐ion batteries.     

Heterostructured TiO2 Spheres with Tunable Interiors and Shells toward Improved Packing Density and Pseudocapacitive Sodium Storage

Insertion‐type anode materials with beneficial micro‐ and nanostructures are proved to be promising for high‐performance electrochemical metal ion storage. In this work, heterostructured TiO₂ shperes with tunable interiors and shells are controllably fabricated through newly proposed programs, resulting in enhanced pseudocapacitive response as well as favorable Na⁺ storage kinetics and performances. In addition, reasonably designed nanosheets in the extrinsic shells are also able to reduce the excess space generated by hierarchical structure, thus improving the packing density of TiO₂ shperes. Lastly, detailed density functional theory calculations with regard to sodium intercalation and diffusion in TiO₂ crystal units are also employed, further proving the significance of the surface‐controlled pseudocapacitive Na⁺ storage mechanism. The structure design strategies and experimental results demonstrated in this work are meaningful for electrode material preparation with high rate performance and volume energy density.     

Sonoelectrochemical synthesis of chitosan/gold nanocomposites for application in removing toxic materials in mainstream smokes

In this work, chitosan (Ch)-capped gold nanoparticles (NPs) were prepared in aqueous solutions by electrochemical methods. First, Ch-capped Au cations were prepared by dissolving Au substrates via electrochemical treatments of oxidation-reduction cycles. Then the Ch-capped Au cations were reduced via sonoelectrochemical reductions to synthesize Ch/Au nanocomposites (NCs). The particle size of prepared Au NPs with predominant (1 1 1) face on Ch is ca. 15 nm. Ch on the prepared Ch/Au NCs can easily react with acetaldehydes in mainstream smokes to form Schiff bases. Then catalysts of Au NPs can instantaneously decompose capped acetaldehydes and oxidize CO into CO₂ to protect people from poisoning in the mainstream smokes.     

Nitrogen Boosts Defective Vanadium Oxide from Semiconducting to Metallic Merit

2D metal oxide nanosheets have attracted substantial attention for various applications owing to their appealing advantages. Yet, the exploration of effective methodology for fabrication of metallic 2D metal oxides with a high concentration of N dopants in a scalable manner remains challenging. Herein, a topochemical strategy is demonstrated on vanadium oxide nanosheets by combining 2D nanostructuring, heteroatom‐doping, and defect engineering for modulating their intrinsic electronic structure and greatly enhancing their electrochemical property. O vacancies and N dopants (V? O? N and V? N bonds) are in situ formed in vanadium oxide via nitridation and lead to semiconductive‐to‐metallic phase transformation evidenced by experimental results and theoretical calculation. Overall, the N‐VO_0.9 nanosheets exhibit a metallic electron transportation behavior and excellent electrochemical performance. These findings shed light on the rational design and electron structure tuning of 2D nanostructures for energy and electronics applications.     

0D Cs3Cu2X5 (X = I,Br, and Cl) Nanocrystals: Colloidal Syntheses and Optical Properties

0D lead‐free metal halide nanocrystals (NCs) are an emerging class of materials with intriguing optical properties. Herein, colloidal synthetic routes are presented for the production of 0D Cs₃Cu₂X₅ (X = I, Br, and Cl) NCs with orthorhombic structure and well‐defined morphologies. All these Cs₃Cu₂X₅ NCs exhibit broadband blue‐green photoluminescence (PL) emissions in the range of 445–527 nm with large Stokes shifts, which are attributed to their intrinsic self‐trapped exciton (STE) emission characteristics. The high PL quantum yield of 48.7% is obtained from Cs₃Cu₂Cl₅ NCs, while Cs₃Cu₂I₅ NCs exhibit considerable air stability over 45 days. Intriguingly, as X is changed from I to Br and Cl, Cs₃Cu₂X₅ NCs exhibit a continuous redshift of emission peaks, which is contrary to the blueshift in CsPbX₃ perovskite NCs.