Controllable Preparation Of Coal-Based Carbon Quantum Dots And Their Fluorescence

Carbon quantum dots are a kind of fluorescent carbon nanomaterials which are widely studied at present.The advantages of low toxicity,good biocompatibility,adjustable wavelength of light,good light stability,easy functioning,and easy preparation make carbon quantum dots popular in luminescent materials,fluorescence sensing,environmental monitoring,biomedical and other fields.Coal has a high aromatic carbon content,a wide range of sources,and low cost,so it is a potential carbon quantum dots precursor.However,the existing methods of coal-based carbon quantum dots have disadvantages such as high energy consumption,large pollution,and single color of luminescence.Therefore,the"two-step"method of combining potassium ferrate pre-oxidation with hydrogen peroxide oxidation is used to make the preparation of coal-based carbon quantum dots convenient,fast and controllable.The fluorescence properties of carbon quantum dots are studied and applied to pH indicator and metal ion detection.The main research contents are as follows:?1?Using the Anthracite anthracite as the carbon source,carbon quantum dots with adjustable fluorescence color were prepared.Pre-oxidation of potassium ferrate could selectively oxidize fat side chains and weaken non-covalent interactions between coal molecules,form a large number of cracks or pores on the surface of coal particles,improve the wettability and reactivity of coal.Therefore,the time to prepare carbon quantum dots was shortened to 1 h.By controlling the hydrogen peroxide concentration to be 10%,20%,and 30%,coal-based carbon quantum dots with fluorescent colors of yellow,green,and blue,respectively,were obtained.The morphology,composition and fluorescence properties of carbon quantum dots were characterized.The results showed that the carbon quantum dots prepared by this method were smaller than 10 nm,with a narrow size distribution,high oxygen content and good water solubility.The blue fluorescence of the carbon quantum dots belonged to the eigenstate emission,while the yellow and green fluorescence was due to the formation of a new energy state in the band gap of the carbon quantum dots due to the oxygen-containing functional groups on the surface of the carbon quantum dots,which belongs to the defect state emission.?2?The effects of concentration and pH on the fluorescence properties of carbon quantum dots were investigated.The results showed that the change of solution concentration only affected the fluorescence intensity of the yellow fluorescent and green fluorescent carbon quantum dots without changing the emission wavelength,and the change of pH can not only change the fluorescence intensity but also the emission wavelength.A change occurs;for a carbon quantum dot that emited blue fluorescence,the result was just the opposite.The carbon quantum dots were applied to the detection of metal ions.The results showed that the carbon quantum dots could be quenched by specific fluorescence with Cu²⁺.The Cu²⁺concentration is in the range of 0.244-60?mol/L,and the quenching degree and Cu²⁺concentration of carbon quantum dots were good linear relationship.So it could be used as a nano fluorescent probe to detect Cu²⁺.?3?Using Hebi bituminous coal as carbon source,the fluorescence controllable carbon quantum dots were prepared by“two-step"method.When the reaction temperature was controlled at 60°C and 90°C,the fluorescence color was divided into orange and yellow carbon quantum.It proved that this method was also applicable to bituminous coal.The composition and fluorescence properties of carbon quantum dots were characterized.The results showed that the surface of the bituminous-based carbon quantum dots was rich in functional groups,water-soluble,and the fluorescence characteristics were not wavelength dependent.The surface nitrogen doping of bituminous coal-based carbon quantum dots shows thated the introduction of nitrogen could cause the fluorescence of the carbon quantum dots to shift blue.