Research On Preparation And Photoluminescence Properties Of Graphene-Like Quantum Dots

The graphene-like quantum dots are a new class of quantum dot materials with similar structures and properties to graphene quantum dots.This type of quantum dot not only retains the original properties of its two-dimensional layered structure material,but also exhibits a series of new or superior physicochemical properties,especially stable photoluminescence properties and biocompatibility.It has attracted wide attention in biomedical fields such as biosensing,cell imaging,and cancer treatment.It is found that the performance of materials depends mainly on their special structure and preparation methods.The size,morphology and structure of quantum dots can significantly affect their fluorescence properties and cytotoxicity.At present,most of the research on quantum dots of new two-dimensional materials have the shortcomings such as low yield,use of toxic solvents in the preparation process,uncontrollable size and morphology,poor optical properties of products,and less cytotoxicity research,which greatly limits their practical application.Therefore,how to improve and develop the preparation technology of graphene-like quantum dots,realize the controllable preparation of quantum dot structure,improve its optical properties and biocompatibility,and obtain a wider range of applications,are still of great significance.Based on the above reasons,this paper proposes a simple,green and efficient solvothermal method.By optimizing the experimental conditions,the molybdenum disulfide?MoS₂?,boron nitride?h-BN?and tungsten oxide?WO₃?quantum dot materials with excellent fluorescence properties were prepared.The morphologies,structures,optical properties and cytotoxicity were investigated and discussed.The fluorescence imaging of cells and detection of metal ions with the as-prepared quantum dot were further studied.The main results are summarized as follows:?1?A facile one-step,low cost and green method is developed to produce molybdenum disulfide quantum dots?MoS₂ QDs?by solvothermal treatment in the presence of NaOH.The morphologies and structure of the materials were studied by several microscopic and spectroscopic techniques,and the results indicated the high crystallinity and narrow particle size distribution of the as-prepared MoS₂ QDs.The as-prepared MoS₂ QDs have a size of 3-9 nm and an average size of 5.5 nm.They can exhibited bright blue luminescence under UV light irradiation with high crystallinity and excellent photoluminescence properties.The quantum yield was 7.5%.By being directly applied for bio-imaging of HeLa cells,MoS₂ QDs showed bright luminescence,low toxicity and excellent biocompatibility.This convenient process represents a potential advancement for large-scale production.In addition,this work may provide an alternative facile approach to synthesize the quantum dots of other graphene-like quantum dots on a large scale.?2?A simple route for the synthesis of boron nitride nanosheets?BNNSs?and boron nitride quantum dots?BNQDs?simultaneously was demonstrated in this study.The synthesis is accomplished by a solvothermal alkaline intercalation method with anhydrous ethanol as solvent.The morphology and properties of the formed BNNSs and BNQDs were characterized by several microscopic and spectroscopic techniques.The results show that the thickness of the as-prepared BNNSs is about 1 nm,indicating that the bulk h-BN can be efficiently exfoliated to a single layer or a small layer of nanosheet structure.The as-prepared BNQDs have an average size of 5.1 nm,showing good biocompatibility and have variable fluorescence emission characteristics,with a quantum yield of 15.7%.Based on this feature,it was successfully applied to the multicolor fluorescent labeling of HeLa cells as a bioimaging probe.The excellent water solubility of BNNSs and the stable fluorescence of BNQDs make nano boron nitride have great potential for development in biological applications.?3?tungsten oxide quantum dots?WO₃ QDs?fluorescent nanoprobe for Fe³⁺detection and fluorescence imaging were was synthesized by solvothermal method.The as-prepared WO₃ QDs exhibited outstanding photoluminescence properties and high fluorescence stability,with a quantum yield of 13.6%.The MTT results show that the material has low cytotoxicity and can be applied to fluorescence imaging of cells in vitro.At the same time,fluorescence quenching occurs when it is in contact with Fe³⁺,which shows highly selectivity and sensitivity,and can successfully achieve fast,efficient and sensitive detection of Fe³⁺.This work set up a new method for the analysis and determination of Fe³⁺.The WO₃ QDs fluorescent probe is expected to be used for Fe³⁺monitoring in more practical environments and biomedical fields.?4?A simple hydrothermal method was proposed to synthesis ultra-small tungsten oxide quantum dots with oxygen deficiency(WO_3-x-x QDs)by using ammonium tungstate hydrate as the tungstate source and polyvinyl pyrrolidone?PVP?as reductant and organic modification regent.The results show that the as-prepared WO_3-x-x QDs exhibit good photoluminescence and photochromic properties.When the sample was irradiated by UV light or sunlight,the as-prepared WO_3-x-x QDs can rapidly undergo photochromic reaction.The solution can quickly change from light yellow to dark blue within 5 min.When storage in dark environment,the sample can change back to the original light yellow solution within 5min,and the process of color change is completely reversible.This high-efficiency photochromic performance,excellent reversibility and good cycling stability make WO_3-x QDs have great practical potential in the field of sensing and photochromic materials.