Synthesis Of Mxene Quantum Dots By Acid Assisted Ultrasound For Fluorescence And Colorimetry Detection Applications

Compared with other analytical methods,fluorescence and colorimetric detection methods do not require complex instruments,and are fast and simple to operate with visualization potential.They have been one of the research hotspots in the detection field.Quantum dots are widely used in the field of fluorescence and colorimetric detection because of their outstanding fluorescence properties and potential catalytic activity of nano-enzymes.Due to the poor water solubility and biocompatibility,the applications of traditional semiconductor quantum dots are limited.Therefore,the development of novel quantum dots has gradually attracted attentions.Among them,transition metal carbon/nitride（MXene）quantum dots not only have excellent optical properties,but also have good water solubility and biocompatibility,which can be widely used in environmental,biological detection and other fields.However,the main high-temperature treatment synthesis methods of MXene quantum dots,such as hydrothermal/solvothermal treatment,have the limitations of low fluorescence efficiency for products,easy oxidation and high operational risk.Meanwhile,fluorescent detection species and colorimetric detection applications for MXene quantum dots need to be further expanded.In view of the above problems,this research obtains nitrogen atom doped Ti₃C₂ MXene quantum dots by acid-assisted ultrasonic method at room temperature,and a series of fluorescence and colorimetric detection systems are constructed.The research of this paper can be divided into the following two parts:（1）At room temperature and in the presence of acid and ethylenediamine,nitrogen-doped Ti₃C₂ MXene quantum dots（N-MQDs）were obtained by cutting multilayer Ti₃C₂MXene by ultrasound.The as-prepared N-MQDs had an average particle size of 6.8 nm,and contained-OH,-NH and other polar functional groups on the surface.At the same time,N-MQDs had excellent fluorescence performance（fluorescence efficiency up to 20.35%）and light stability.These N-MQDs could achieve specific response and high sensitivity detection of Zn（Ⅱ）through fluorescence enhancement,with the detection limit as low as0.127μM,the linear range was 0-20μM.The response mechanism followed the intramolecular charge transfer.Then,by using the phenomenon that Zn（Ⅱ）enhanced fluorescence of N-MQDs,the composite nanostructure of N-MQDs/Zn（Ⅱ）was developed as a fluorescence quenching sensor for the detection of oxalic acid（OA）with a detection limit of 0.883μM in the linaear range of 0-20μM.The mechanism study showed that OA could quickly form complex with Zn（Ⅱ）,dissociating N-MQDs and restoring the fluorescence intensity.This fluorescence“off-on-off”probe had been applied to the detection in practical water and food samples.（2）Based on the nano-enzyme activity of N-MQDs,a simple and sensitive H₂O₂ and glutathione（GSH）colorimetric detection system was constructed.The optimal enzymatic reaction conditions（25℃,p H=4.0）were further investigated,and the reaction kinetics of N-MQDs nano-enzyme were studied.Then,researching the working curves for colorimetric detection of H₂O₂ and GSH,the detection limits and corresponding linear ranges were 1.15μM（25-1000μM）and 0.333μM（0.30-25μM）,respectively.The mechanism study showed that N-MQDs could catalyze the decomposition of H₂O₂ to produce hydroxyl radicals for oxidation of the chromogenic substrate,meanwhile GSH reduced oxidative chromogenic substrates,thus realizing qualitative and quantitative analysis of H₂O₂and GSH based on changes of solution’s color and absorbance.This colorimetric sensor had been successfully applied for the detection in actual food samples.