Biodegradable Bi2O2Se Quantum Dots for Photoacoustic Imaging‐Guided Cancer Photothermal Therapy

As new 2D layered nanomaterials, Bi₂O₂Se nanoplates have unique semiconducting properties that can benefit biomedical applications. Herein, a facile top‐down approach for the synthesis of Bi₂O₂Se quantum dots (QDs) in a solution is described. The Bi₂O₂Se QDs with a size of 3.8 nm and thickness of 1.9 nm exhibit a high photothermal conversion coefficient of 35.7% and good photothermal stability. In vitro and in vivo assessments demonstrate that the Bi₂O₂Se QDs possess excellent photoacoustic (PA) performance and photothermal therapy (PTT) efficiency. After systemic administration, the Bi₂O₂Se QDs accumulate passively in tumors enabling efficient PA imaging of the entire tumors to facilitate imaging‐guided PTT without obvious toxicity. Furthermore, the Bi₂O₂Se QDs which exhibit degradability in aqueous media not only have sufficient stability during in vivo circulation to perform the designed therapeutic functions, but also can be discharged harmlessly from the body afterward. The results reveal the great potential of Bi₂O₂Se QDs as a biodegradable multifunctional agent in medical applications.     

Electrically Pumped White‐Light‐Emitting Diodes Based on Histidine‐Doped MoS2 Quantum Dots

MoS₂ quantum dots (QDs)‐based white‐light‐emitting diodes (QD‐WLEDs) are designed, fabricated, and demonstrated. The highly luminescent, histidine‐doped MoS₂ QDs synthesized by microwave induced fragmentation of 2D MoS₂ nanoflakes possess a wide distribution of available electronic states as inferred from the pronounced excitation‐wavelength‐dependent emission properties. Notably, the histidine‐doped MoS₂ QDs show a very strong emission intensity, which exceeds seven times of magnitude larger than that of pristine MoS₂ QDs. The strongly enhanced emission is mainly attributed to nitrogen acceptor bound excitons and passivation of defects by histidine‐doping, which can enhance the radiative recombination drastically. The enabled electroluminescence (EL) spectra of the QD‐WLEDs with the main peak around 500 nm are found to be consistent with the photoluminescence spectra of the histidine‐doped MoS₂ QDs. The enhanced intensity of EL spectra with the current increase shows the stability of histidine‐doped MoS₂ based QD‐WLEDs. The typical EL spectrum of the novel QD‐WLEDs has a Commission Internationale de l'Eclairage chromaticity coordinate of (0.30, 0.36) exhibiting an intrinsic broadband white‐light emission. The unprecedented and low‐toxicity QD‐WLEDs based on a single light‐emitting material can serve as an excellent alternative for using transition metal dichalcogenides QDs as next generation optoelectronic devices.     

Synthesis and characterisation of MoS2 quantum dots by liquid nitrogen quenching

Among transition metal dichalcogenides family, molybdenum disulphide (MoS₂) nanomaterial has a vital role in two-dimensional field due to its intrinsic optical and electronic properties. In this study, we report a new top-down approach for synthesising MoS₂ quantum dots (QDs). This strategy consists of liquid nitrogen (LN2) quenching of bulk MoS₂ material followed by two processes, probe sonication and ultra-centrifugation. This approach is simple, cost effective and eco-friendly. The structural, optical and morphological properties of obtained MoS₂ quantum dots were characterised. Photoluminescence spectra (PL) of the synthesised MoS₂ QDs show blue light emission when excited with ultraviolet radiation (365?nm). A significant observation in this study is that, the peak position of photoluminescence (PL) emission spectra is independent of excitation wavelength. In addition, a higher fluorescence quantum yield was obtained for the present MoS₂ QDs compared to MoS₂ QDs prepared by other methods.     

Controlled Synthesis of Ag2Te@Ag2S Core–Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near‐Infrared Window

Fluorescence in the second near‐infrared window (NIR‐II, 900–1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR‐II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag‐rich Ag₂Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag₂S shell to passivate the Ag₂Te core via a facile colloidal route, which greatly enhances the PLQY of Ag₂Te QDs and significantly improves the stability of Ag₂Te QDs. This strategy works well with different sized core Ag₂Te QDs so that the NIR‐II PL can be tuned in a wide range. In vivo imaging using the as‐prepared Ag₂Te@Ag₂S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag₂Te nanoprobes administrated, suggesting the success of the core–shell synthetic strategy and the potential biomedical applications of core–shell NIR‐II nanoprobes.     

One-step synthesis of water-soluble ZnSe quantum dots via microwave irradiation

A facile strategy has been developed for the synthesis of glutathione-capped ZnSe quantum dots (QDs) in aqueous media. The reaction was carried out in air atmosphere with a single step by using Na₂SeO₃, a stable and commercial Se source, to replace the commonly adopted NaHSe or H₂Se. Moreover, microwave irradiation improved the photoluminescence quantum yield (PLQY) as well as lowered the trap emission of as-prepared ZnSe QDs. The obtained QDs performed strong band-edge luminescence (PLQY reached 18%), narrow size distribution (full width at half maximum was 26-30 nm) and weak trap emission without post-treatments. The results of transmission electron microscopy and X-ray diffraction demonstrated the small particle size (2-3 nm), good monodispersity and ZnSe(S) alloyed structure of as-prepared QDs. The experimental variables including precursors and stabilizer amounts as well as pH value had significant influence on the PL properties of the ZnSe QDs.     

Ultrastable CsPbBr3 Perovskite Quantum Dot and Their Enhanced Amplified Spontaneous Emission by Surface Ligand Modification

The poor stability and aggregation problem of CsPbBr₃ quantum dots (QDs) in air are great challenges for their future practical application. Herein, a simple and effective ligand‐modification strategy is proposed by introducing 2‐hexyldecanoic acid (DA) with two short branched chains to replace oleic acid (OA) with long chains during the synthesis process. These two short branched chains not only maintain their colloidal stability but also contribute to efficient radiative recombination. The calculations show that CsPbBr₃ QDs with DA modification (CsPbBr₃‐DA QDs) have larger binding energy than CsPbBr₃ QDs with OA (CsPbBr₃‐OA QDs), resulting in significantly enhanced stability. Due to the strong binding energy between DA ligands and QDs, CsPbBr₃‐DA QDs exhibit no aggregation phenomenon even after stored in air for more than 70 d, and CsPbBr₃‐DA QDs films can maintain 94.3% of initial PL intensity after 28 d, while in CsPbBr₃‐OA QDs films occurs a rapid degradation of PL intensity. Besides, the enhanced amplified spontaneous emission (ASE) performance of CsPbBr₃‐DA QDs films has been demonstrated under both one‐ and two‐photon laser excitation. The ASE threshold of CsPbBr₃‐DA QDs films is reduced by more than 50% and their ASE photostability is also improved, in comparison to CsPbBr₃‐OA QDs films.     

Facile Synthesis,Silanization, and Biodistribution of Biocompatible Quantum Dots

A facile strategy for the synthesis of silica‐coated quantum dots (QDs) for in vivo imaging is reported. All the QD synthesis and silanization steps are conducted in water and methanol under mild conditions without involving any organometallic precursors or high‐temperature, oxygen‐free environments. The as‐prepared silica‐coated QDs possess high quantum yields and are extremely stable in mouse serum. In addition, the silanization method developed here produces nanoparticles with small sizes that are difficult to achieve via conventional silanization methods. The silica coating helps to prevent the exposure of the QD surface to the biological milieu and therefore increases the biocompatibility of QDs for in vivo applications. Interestingly, the silica‐coated QDs exhibit a different biodistribution pattern from that of commercially available Invitrogen QD605 (carboxylate) with a similar size and emission wavelength. The Invitrogen QD605 exhibits predominant liver (57.2% injected dose (ID) g^?1) and spleen (46.1% ID g^?1) uptakes 30 min after intravenous injection, whereas the silica‐coated QDs exhibit much lower liver (16.2% ID g^?1) and spleen (3.67% ID g^?1) uptakes but higher kidney uptake (8.82% ID g^?1), blood retention (15.0% ID g^?1), and partial renal clearance. Overall, this straightforward synthetic strategy paves the way for routine and customized synthesis of silica‐coated QDs for biological use.     

Au NPs@MoS2 Sub‐Micrometer Sphere‐ZnO Nanorod Hybrid Structures for Efficient Photocatalytic Hydrogen Evolution with Excellent Stability

MoS₂ shows promising applications in photocatalytic water splitting, owing to its uniquely optical and electric properties. However, the insufficient light absorption and lack of performance stability are two crucial issues for efficient application of MoS₂ nanomaterials. Here, Au nanoparticles (NPs)@MoS₂ sub‐micrometer sphere‐ZnO nanorod (Au NPs@MoS₂‐ZnO) hybrid photocatalysts have been successfully synthesized by a facile process combining the hydrothermal method and seed‐growth method. Such photocatalysts exhibit high efficiency and excellent stability for hydrogen production via multiple optical‐electrical effects. The introduction of Au NPs to MoS₂ sub‐micrometer spheres forming a core–shell structure demonstrates strong plasmonic absorption enhancement and facilitates exciton separation. The incorporation of ZnO nanorods to the Au NPs@MoS₂ hybrids further extends the light absorption to a broader wavelength region and enhances the exciton dissociation. In addition, mutual contacts between Au NPs (or ZnO nanorods) and the MoS₂ spheres effectively protect the MoS₂ nanosheets from peeling off from the spheres. More importantly, efficiently multiple exciton separations help to restrain the MoS₂ nanomaterials from photocorrosion. As a result, the Au@MoS₂‐ZnO hybrid structures exhibit an excellent hydrogen gas evolution (3737.4 μmol g^?1) with improved stability (91.9% of activity remaining) after a long‐time test (32 h), which is one of the highest photocatalytic activities to date among the MoS₂ based photocatalysts.     

Biocompatible Near‐Infrared Quantum Dots as Ultrasensitive Probes for Long‐Term in vivo Imaging Applications

A facile synthesis method to produce monodisperse, biocompatible, lysine crosslinked mercaptoundecanoic acid (MUA) CdSe_0.25Te_0.75/CdS near‐infrared (NIR) quantum dots and use them as probes to study their long term in vivo distribution, clearance, and toxicity is presented. Large signal enhancements are demonstrated by these quantum dots, which enables their use as efficient and sensitive probes for live‐animal imaging. An important finding is that mice intravenously injected with ≈10.5 mg kg^?1 of NIR QDs survive for more than three months without any apparent adverse effect to their health. Furthermore, it is determined that there is a significant reduction in the number of the QDs in the liver and spleen three months post injection. In addition, histological analysis of heart, kidney, liver, spleen, and lung tissue indicates that there are no acute toxic effects from these lysine cross‐linked MUA NIR QDs. This study suggests that these NIR QDs can be potentially used for long‐term targeted imaging and therapy studies in vivo.     

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

Generally, exfoliation is an efficient strategy to create more edge site so as to expose more active sites on molybdenum disulphide (MoS₂). However, the lateral sizes of the resultant MoS₂ monolayers are relatively large (≈50–500 nm), which retain great potential to release more active sites. To further enhance the catalytic performance of MoS₂, a facile cascade centrifugation‐assisted liquid phase exfoliation method is introduced here to fabricate monolayer enriched MoS₂ nanosheets with nanoscale lateral sizes. The as‐prepared MoS₂ revealed a high monolayer yield of 36% and small average lateral sizes ranging from 42 to 9 nm under gradient centrifugations, all exhibiting superior catalytic performances toward photocatalytic H₂ generation. Particularly, the optimized monolayer MoS₂ with an average lateral size of 9 nm achieves an apparent quantum efficiency as high as 77.2% on cadmium sulphide at 420 nm. This work demonstrates that the catalytic performances of MoS₂ could be dramatically enhanced by synergistic exfoliation and lateral size engineering as a result of increased density of active sites and shortened charge diffusion distance, paving a new way for design and fabrication of transition‐metal dichalcogenides‐based materials in the application of hydrogen generation.     

Molybdenum Disulfide Nanosheet/Quantum Dot Dynamic Memristive Structure Driven by Photoinduced Phase Transition

MoS₂ 2D nanosheets (NS) with intercalated 0D quantum dots (QDs) represent promising structures for creating low‐dimensional (LD) resistive memory devices. Nonvolatile memristors based 2D materials demonstrate low power consumption and ultrahigh density. Here, the observation of a photoinduced phase transition in the 2D NS/0D QDs MoS₂ structure providing dynamic resistive memory is reported. The resistive switching of the MoS₂ NS/QD structure is observed in an electric field and can be controlled through local QD excitations. Photoexcitation of the LD structure at different laser power densities leads to a reversible MoS₂ 2H‐1T phase transition and demonstrates the potential of the LD structure for implementing a new dynamic ultrafast photoresistive memory. The dynamic LD photomemristive structure is attractive for real‐time pattern recognition and photoconfiguration of artificial neural networks in a wide spectral range of sensitivity provided by QDs.     

Temperature-dependent resonance energy transfer from CdSe–ZnS core–shell quantum dots to monolayer MoS<Subscript>2</Subscript>

We investigated the temperature-dependent resonance energy transfer (ET) from CdSe–ZnS core–shell quantum dots (QDs) to monolayer MoS₂. QDs/MoS₂ structures were fabricated using a spin-coating method. Photoluminescence (PL) spectra and decay curves of the QDs/MoS₂ structures were measured in the temperature range of 80?400 K. The results indicate that the PL intensity of the QDs decreased approximately 81% with increasing temperature, whereas that of the MoS₂ increased up to a maximum of 78% at 300 K because of the combined effect of thermal quenching and the ET in the QDs/MoS₂ structures. The ET efficiency and ET rate also exhibited similar variation trends, both increased with increasing temperature from 80 to 260 K and then decreased until 400 K, resulting in a maximum ET efficiency of 22% and an ET rate of 1.17 ns^–1 at ~260 K. These results are attributed to the varied distribution of the localized excitons and free excitons in the QDs/MoS₂ structures with increasing temperature.

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Semiconductor Quantum Dots: An Emerging Candidate for CO2 Photoreduction

As one of the most critical approaches to resolve the energy crisis and environmental concerns, carbon dioxide (CO₂) photoreduction into value‐added chemicals and solar fuels (for example, CO, HCOOH, CH₃OH, CH₄) has attracted more and more attention. In nature, photosynthetic organisms effectively convert CO₂ and H₂O to carbohydrates and oxygen (O₂) using sunlight, which has inspired the development of low‐cost, stable, and effective artificial photocatalysts for CO₂ photoreduction. Due to their low cost, facile synthesis, excellent light harvesting, multiple exciton generation, feasible charge‐carrier regulation, and abundant surface sites, semiconductor quantum dots (QDs) have recently been identified as one of the most promising materials for establishing highly efficient artificial photosystems. Recent advances in CO₂ photoreduction using semiconductor QDs are highlighted. First, the unique photophysical and structural properties of semiconductor QDs, which enable their versatile applications in solar energy conversion, are analyzed. Recent applications of QDs in photocatalytic CO₂ reduction are then introduced in three categories: binary II–VI semiconductor QDs (e.g., CdSe, CdS, and ZnSe), ternary I–III–VI semiconductor QDs (e.g., CuInS₂ and CuAlS₂), and perovskite‐type QDs (e.g., CsPbBr₃, CH₃NH₃PbBr₃, and Cs₂AgBiBr₆). Finally, the challenges and prospects in solar CO₂ reduction with QDs in the future are discussed.     

Porous Hybrid Composites of Few‐Layer MoS2 Nanosheets Embedded in a Carbon Matrix with an Excellent Supercapacitor Electrode Performance

Porous hierarchical architectures of few‐layer MoS₂ nanosheets dispersed in carbon matrix are prepared by a microwave‐hydrothermal method followed by annealing treatment via using glucose as C source and structure‐directing agent and (NH₄)₂MoS₄ as both Mo and S sources. It is found that the morphology and size of the secondary building units (SBUs), the size and layer number of MoS₂ nanosheets as well as the distribution of MoS₂ nanosheets in carbon matrix, can be effectively controlled by simply adjusting the molar ratio of (NH₄)₂MoS₄ to glucose, leading to the materials with a low charge–transfer resistance, many electrochemical active sites and a robust structure for an outstanding energy storage performance including a high specific capacitance (589 F g⁻¹ at 0.5 A g⁻¹), a good rate capability (364 F g⁻¹ at 20 A g⁻¹), and an excellent cycling stability (retention 104% after 2000 cycles) for application in supercapacitors. The exceptional rate capability endows the electrode with a high energy density of 72.7 Wh kg⁻¹ and a high power density of 12.0 kW kg⁻¹ simultaneously. This work presents a facile and scalable approach for synthesizing novel heterostructures of MoS₂‐based electrode materials with an enhanced rate capability and cyclability for potential application in supercapacitor.     

Gram‐Scale Aqueous Synthesis of Stable Few‐Layered 1T‐MoS2: Applications for Visible‐Light‐Driven Photocatalytic Hydrogen Evolution

Most recently, much attention has been devoted to 1T phase MoS₂ because of its distinctive phase‐engineering nature and promising applications in catalysts, electronics, and energy storage devices. While alkali metal intercalation and exfoliation methods have been well developed to realize unstable 1T‐MoS₂, but the aqueous synthesis for producing stable metallic phase remains big challenging. Herein, a new synthetic protocol is developed to mass‐produce colloidal metallic 1T‐MoS₂ layers highly stabilized by intercalated ammonium ions (abbreviated as N‐MoS₂). In combination with density functional calculations, the X‐ray diffraction pattern and Raman spectra elucidate the excellent stability of metallic phase. As clearly depicted by high‐angle annular dark‐field imaging in an aberration‐corrected scanning transmission electron microscope and extended X‐ray absorption fine structure, the N‐MoS₂ exhibits a distorted octahedral structure with a 2a ₀ × a ₀ basal plane superlattice and 2.72 Å Mo–Mo bond length. In a proof‐of‐concept demonstration for the obtained material's applications, highly efficient photocatalytic activity is achieved by simply hybridizing metallic N‐MoS₂ with semiconducting CdS nanorods due to the synergistic effect. As a direct outcome, this CdS:N‐MoS₂ hybrid shows giant enhancement of hydrogen evolution rate, which is almost 21‐fold higher than pure CdS and threefold higher than corresponding annealed CdS:2H‐MoS₂.     

Coupling Interface Constructions of MoS2/Fe5Ni4S8 Heterostructures for Efficient Electrochemical Water Splitting

Water splitting is considered as a pollution‐free and efficient solution to produce hydrogen energy. Low‐cost and efficient electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are needed. Recently, chemical vapor deposition is used as an effective approach to gain high‐quality MoS₂ nanosheets (NSs), which possess excellent performance for water splitting comparable to platinum. Herein, MoS₂ NSs grown vertically on FeNi substrates are obtained with in situ growth of Fe₅Ni₄S₈ (FNS) at the interface during the synthesis of MoS₂. The synthesized MoS₂/FNS/FeNi foam exhibits only 120 mV at 10 mA cm^?2 for HER and exceptionally low overpotential of 204 mV to attain the same current density for OER. Density functional theory calculations further reveal that the constructed coupling interface between MoS₂ and FNS facilitates the absorption of H atoms and OH groups, consequently enhancing the performances of HER and OER. Such impressive performances herald that the unique structure provides an approach for designing advanced electrocatalysts.     

Responsive Porous Microcarriers With Controllable Oxygen Delivery for Wound Healing

Microcarriers with oxygen‐delivering capacity have attracted increasing interest in the field of tissue regeneration. Here, a kind of molybdenum disulfide quantum dots (MoS₂ QDs) integrated responsive porous microcarriers with controllable oxygen‐delivering ability for wound healing is presented. The specific gelatin methacryloyl (GelMa) porous microcarriers are derived from inverse opal microparticles which can be decorated with the oxygen‐carrying protein hemoglobin. Because of their characteristic porous structure, interconnected nanochannels, and excellent biocompatibility, the resultant microcarriers could carry oxygen extensively and provide support for tissue repair physically and biologically. Besides, since the typical photothermal effect of 2D materials and their derived 2D QDs, the inverse opal particles integrated with MoS₂ QDs are imparted with photo‐responsive capacity, which makes them able to release oxygen photo‐controllably. It is demonstrated that the designed microcarriers can promote the repair of abdominal wall defects effectively with their multifunctional features. These remarkable properties point to the potential value of the microcarriers in wound healing and tissue engineering.     

Plasmon‐Enhanced Photoelectrical Hydrogen Evolution on Monolayer MoS2 Decorated Cu1.75S‐Au Nanocrystals

Hydrogen production from water splitting through an efficient photoelectrochemical route requires photoinduced electron transfer from light harvesters to efficient electrocatalysts. Here, the plasmon‐enhanced photoelectrical nanocatalysts (NCs) have been successfully developed by coating a monolayer MoS₂ on the Cu_1.75S‐Au hetero‐nanoparticle for hydrogen evolution reaction (HER). The plasmonic NCs dramatically improve the HER, leading to 29.5‐fold increase of current under 650 nm excitation (1.0 W cm^?2). These NCs generate an exceptionally high current density of 200 mA cm^?2 at overpotential of 182.8 mV with a Tafel slope of 39 mV per decade and excellent stability, which is better than or comparable to the Pt‐free catalysts with carbon rod as counter electrode. The enhanced HER performance can be attributed to the significantly improved broad light absorption (400–3000 nm), more efficient charge separation and abundant active edge sites of monolayer MoS₂. The studies may provide a facile strategy for the fabrication of efficient plasmon‐enhanced photoelectrical NCs for HER.     

Microscopic Origin of the Fast Blue‐Green Luminescence of Chemically Synthesized Non‐oxidized Silicon Quantum Dots

The microscopic origin of the bright nanosecond blue‐green photoluminescence (PL), frequently reported for synthesized organically terminated Si quantum dots (Si‐QDs), has not been fully resolved, hampering potential applications of this interesting material. Here a comprehensive study of the PL from alkyl‐terminated Si‐QDs of 2–3 nm size, prepared by wet chemical synthesis is reported. Results obtained on the ensemble and those from the single nano‐object level are compared, and they provide conclusive evidence that efficient and tunable emission arises due to radiative recombination of electron–hole pairs confined in the Si‐QDs. This understanding paves the way towards applications of chemical synthesis for the development of Si‐QDs with tunable sizes and bandgaps.     

Preparation of MoS2‐Coated Three‐Dimensional Graphene Networks for High‐Performance Anode Material in Lithium‐Ion Batteries

A novel composite, MoS₂‐coated three‐dimensional graphene network (3DGN), referred to as MoS₂/3DGN, is synthesized by a facile CVD method. The 3DGN, composed of interconnected graphene sheets, not only serves as template for the deposition of MoS₂, but also provides good electrical contact between the current collector and deposited MoS₂. As a proof of concept, the MoS₂/3DGN composite, used as an anode material for lithium‐ion batteries, shows excellent electrochemical performance, which exhibits reversible capacities of 877 and 665 mAh g^?1 during the 50^th cycle at current densities of 100 and 500 mA g^?1, respectively, indicating its good cycling performance. Furthermore, the MoS₂/3DGN composite also shows excellent high‐current‐density performance, e.g., depicts a 10^th‐cycle capacity of 466 mAh g^?1 at a high current density of 4 A g^?1.