Tuning Of The Reducibility In Ti₃C₂ Mxene Quantum Dots And Its Effect On The Fluorescence Detection Of Mn（Ⅶ）

MXenes are an emerging kind of two-dimensional layered structure materials,which possess a high specific surface area,abundant active sites,excellent hydrophilicity and metallic conductivity.Therefore,they have attracted more and more attentions in recent years.However,MXene materials generally exhibit low photoluminescence(PL)properties in aqueous solutions,thus limiting their applications in the areas of optical detection imaging and labeling.Recent studies found that when the lateral size of MXenes was reduced below 10 nm,fluorescence was generated due to the quantum confinement and edge effects,which expanded the development of MXenes in the optics field.Although there are related reports proving that MXenes have intrinsic reducibility,the reducing capacity in MXene quantum dots(MQDs)has been rarely studied.It is still a challenging research to tune the reducibility of MQDs and explore its influence on the properties and applications of MQDs.Based on the above problems,we regulated the reducibility of MQDs through different oxidation pathways,and investigated its effect on the fluorescence detection performance of MQDs towards Mn(VII).The main work of this thesis is as follows:1.Ti3C2 MXene was obtained by HF selective etching Ti3AlC2 and then the reduced Ti3C2 MXene quantum dots(r-MQDs)was synthesized by one-step hydrothermal treatment of Ti3C2 MXene and ethanediamine(EDA)at 120℃for 8h.The r-MQDs had an average particle size of 3.62 nm with amino,hydroxyl and amide functional groups on the surface.It showed the strongest PL emission under 320 nm excitation,the position of emission peak was 474 nm.On account of the redox reaction between r-MQDs and Mn(Ⅶ)with the resulted fluorescence quenching,ultra-sensitive detection of Mn(Ⅶ)was realized(linear range of 0-1.7μM,detection limit as low as 5.2 nM).2.The oxidized Ti3C2 MXene quantum dots(o-MQDs)was prepared by adding H2O2 into the aqueous solution of r-MQDs and then through a one-step hydrothermal method at 120℃ for 8 h.The o-MQDs had an average particle size of 3.05 nm with amino,hydroxyl and amide functional groups on the surface.Because of the oxidation,the content of Ti in o-MQDs reduced and the O content was increased.It showed the strongest PL emission under 340 nm excitation,the position of emission peak was 445 nm,Meanwhile,o-MQDs had a selective fluorescence quenching response to Mn(Ⅶ),with a linear range of 0-200μM and a detection limit of 260nM.Compared with the above r-MQDs,o-MQDs had a wider detection range and the fluorescence response mechanism converted to internal filtration effect(IFE).3.The partially oxidized Ti3C2 MXene quantum dots(p-MQDs)was synthesized by aerating of O2 in r-MQDs aqueous solution and then hydrothermally treated at 120℃for 8 h.The p-MQDs had an average particle size of 3.14 nm with amino,hydroxyl and amide functional groups on the surface.It showed the strongest PL emission under 350 nm excitation,and the emission peak position was 445 nm.Its fluorescence could still be selectively quenched by Mn(Ⅶ),with a linear range of 0-4μM and a detection limit of 50 nM.The linear range and detection limit of p-MQDs were both between those of r-MQDs and o-MQDs.