Green Construction Of Xylan Carbon Points-based Nanocomposites And Their Sensing Applications

Carbon quantum dots as a kind of"zero"carbon nanomaterials,attracted much attention in recent years,it is usually below 10 nm in diameter,because of the unique fluorescent,oxidizing reducing,electron transfer properties,water solubility and biocompatibility,the fluorescence imaging,catalysis,drug delivery,biological sensor has a broad application prospect.As the main component of hemicellulose,xylan has a higher hydrothermal carbonization efficiency than hexose sugars.So it is a good carbon source for the preparation of carbon quantum dots.However,the fluorescence and electrochemical properties of xylan carbon dots are not strong enough,and their applications are limited.This research through the other fluorescent dye,and the ability of using xylan carbon point reduction at the same time the introduction of inorganic nanomaterials,solve the xylan carbon point on the construction of new biological sensors performance of a single,detecting the effect not beautiful,expanded the xylan carbon point on the analysis of the test in the field of application scope,xylan resources high assignment transformation is realized.The main research contents are as follows:1.Research on Fe³⁺sensing based on proportional fluorescence rodamine B-CQDs integrated paper base platform for mobile phoneXylan carbon dot has excellent optical properties and unique charm in the detection of metal ions.In this work,an optical sensor based on proportional fluorescence was established,and a fluorescent paper piece combined with a smart phone was further designed for visualization,field and quantitative detection of Fe³⁺.The fluorescence of the sensor is produced by mixing the blue fluorescent carbon dots with rhodamine B red fluorescent dye in a certain proportion,which is synthesized by xylan as carbon source in sodium hydroxide/urea system by hydrothermal method.In the sensor,the launch of the red fluorescence intensity constant rhodamine B as a background reference,due to ferric iron ions can be quenched xylan point carbon blue fluorescence,the fluorescence intensity of xylan carbon points as signal report unit,according to the generated image of red(R)and blue(B)the ratio of the quantitative detection of Fe³⁺,the mechanism of Fe³⁺quenching carbon spot fluorescence was further studied.In the concentration range of10-180?m,the Fe³⁺concentration and R/B value conform to the equation:Y(R/B)=0.00975C+0.850796,and the detection limit is 98.2 n M.The sensor,portable and practical,has a broad application prospect in the real-time monitoring of environmental protection.2.Highly sensitive electrochemical sensor based on xylan-based Ag@CQDs-rGO nanocomposite for dopamine detectionIt was found that xylan carbon dot not only has good fluorescence properties,but also has excellent electrical conductivity and unique reducibility.Using the xylan carbon dots as reducing agent and stabilizer,Ag@CQDs and CQDS-rGO nanocomposites were rapidly synthesized by microwave reaction under optimized conditions.By simple physical mixing and stirring Ag@CQDs and CQDS-rGO,the nano-composites were prepared.Nanocomposite materials were directly dropped on the surface of glassy carbon electrode,and an economical,practical,easy to operate and sensitive electrochemical sensor for detecting dopamine content was constructed.It is worth noting that the carbon quantum dots can not only improve the conductivity of the electrode,but also realize the highly selective detection of dopamine through the electrostatic interaction between the carboxyl group and the amine functional group of dopamine.In addition,silver nanoparticles can enhance the sensitivity of the sensor by increasing the electrocatalytic activity of dopamine and improving the conductivity of the electrode.At the same time,the reduction of GO and dopamine can form?-?conjugation,which enables dopamine to reach the electrode surface more easily than some interferences to enhance the selectivity of dopamine detection.Under optimal conditions,the sensor was responsive to dopamine concentration with a linear range of 0.1 to 300?m and a detection limit of 1.59 n M(S/N=3).This sensor has been successfully applied to the determination of dopamine in real samples with good recovery rate and satisfactory results.In addition,the sensor based on Ag@CQDs-rGO broadens the application of polysaccharid-based CQDS in electrochemical sensors.3.Green one-pot synthesis of Au@CQDs-Mxene nanocomposite as electrochemical sensors for sensitive detection of nitriteIn order to further simplify the preparation process of constructing the electrical sensor,this study synthesized Au@CQDs-Mxene nanocomposite material by one-pot method using xylan carbon dots as reducing agent and stabilizer,and directly dropped it on the glassy carbon electrode to construct an electrochemical sensor sensitive to the detection of NO^2-content in water.Mxene has the advantages of large specific surface area,excellent metal conductivity,hydrophilicity and more active sites,so it was first used in the sensing detection of nitrite in this study.Mxene acted as an effective matrix for the growth of gold nanoparticles,and the stable reduction of gold nanoparticles by xylan carbon points also effectively prevented the agglomeration of Mxene.Due to the large specific surface area,good electrical conductivity and the synergistic catalytic action of each component,Au@CQDs-Mxene nanocomposite exhibits excellent catalytic activity for NO^2-electrooxidation.The sensor is sensitive to nitrite concentration with a linear range of 1 to 500?M and 500 to 3200?M,and a detection limit of 0.078?m.This work provides not only a kind of used for precious metals-2 d sheet general one pot synthesis methods of nanometer complex compound,but also provides using nanometer complex compound as the reinforcing material to make electrochemical nitrite sensor as an example,it is easy to implement and can be further extended to other sensors,is of great importance to food testing field.