Mechanism And Application Of New Type Quantum Dots In Electrochemiluminesncence

Electrochemiluminescence(ECL)is the chemiluminescence(CL)phenomenon triggered by electrochemical method,which combines the merits of well spatial/temporal controllability in electrochemistry and low background signal in CL.Therefore,ECL technique has been developed significantly in recent decades,and the typical aqueous ECL system,Ruthenium(?)Tirs(2,2'-bipyridyl)[Ru(bpy)32+]/TPrA system,has been widely applied to in-vitro diagnostics,and environmental detection,etc.However,Ru(bpy)32+ is high priced,and TPrA is toxic,volatile,insoluble in water,which are urgent issues in ECL to be addressed.Recently,the boomingly developed nanomaterials show great prospects in ECL,and many researchers have been focused on nanomaterials-involved new ECL system,mechanism,and applications.Among various nanomaterials,quantum dots(QDs)have become a kind of star material as ECL luminophore or other roles due to the controllable optoelectronic performances and excellent physicochemical properties.Conventional quantum dots are the semiconductor nanostructure/nanomaterials typically smaller than 10 nm,in which excitons(electrons or holes)are confined at three arbitrary dimensional space.Semiconductor quantum dots generally classified as ?-? group(InP,GaAs),?-?/?-? group(CdSe,PbS),and ?-?-? group(CuInS2),which often contain hazardous elements(such as Pb,Cd,Hg,As,Se)and limit their bio-/eco-related application.Therefore,recently,some nontoxic and environmental-friendly new type quantum dots have got great attention and development,such as carbon(quantum)dots(CDs),carbon nitride quantum dots(CNQDs),graphene quantum dots(GQDs),which possess outstanding optoelectronic performance as well as rich surface chemical properties.Hence,the researches here are focused on the fabrication and regulation of new type quantum dots,and their mechanism and application in ECL.1.The annihilation ECL properties of carbon dots(CDs,less than 10 nm)have been investigated,and such kind of CDs was successfully fabricated via electrochemical etching strategy from graphite rods.Subsequently,a series of CDs were prepared through controlled surface engineering technique by wet chemical method,including the oxidized-CDs(oCDs),partially reduced-CDs(rCDs),and fully reduced-CDs(F-rCDs).In-depth characterizations including UV-vis,FT-IR,Raman,XPS,etc.revealed significant differences in features of these CDs,especially the condition of surface grafted oxygen containing functional groups.ECL results suggested that all the annihilation ECL of CDs,oCDs,and rCDs demonstrated stable positively charged luminophore(R+·)and unstable negatively charged luminophore(R-·)at the surface of GCE,and possessed 365 nm emission peak and consistent emission range from 550 nm to 850 nm.During further structural mode investigation and ECL properties simulation,the surface construction nature of CDs was speculated and significant role of oxygen containing groups in ECL behavior of CDs was also verified.According to the ECL behavior from all these samples,the probable ECL mechanism of CDs was then proposed,which further interpreted the indispensable contributions of oxygen containing functional groups to the ECL property of CDs.2.With the assistance of thermal reflux in excess TMAOH,well-defined Ti3C2Tx MXene Quantum Dots(MQDs)were successfully fabricated with high output(?60%).The as-prepared MQDs not only inherited the principal structure,component,and physicochemical property of parent Ti3C2Tx MXene,but also were bestowed with novel optoelectronic feature by introducing enlarged bandgap thanks to quantum confinement effect.The brightly green fluorescent MQDs possessed regular excitation-dependent photoluminescent(PL)behavior,performed quiet well in anti-photobleaching and maintained approvingly stable in ambient air for 10 days.Besides,the ECL properties of MQDs were investigated here for the first time,including annihilation ECL and coreactant(TPrA)enhanced(-29-fold)anode ECL,and the related ECL mechanism was also discussed in detail.Meanwhile,the long-term ECL stablity of MQDs in aqueous solution(7 days)or solid powders(3 months)were also tested,which showed that MQDs possessed promising application in ECL biosensor or chemical sensors.3.Although electrochemiluminescence(ECL)has been developed significantly in the past few decades,ECL efficiency in aqueous solution remains quite low.Finding out the energy losses and developing new ECL enhancing strategies are still of great value.In this work,we discovered a detrimental non-radiation relaxation pathway by concurrent oxygen evolution reaction(OER)process in well-known Ruthenium(?)Tris(2,2'-bipyridyl)(Ru(bpy)3)2+)aqueous ECL system due to similar surface sensitive characteristics,and for the first time a chemical strategy was developed that carbon nitride quantum dots(CNQDs)could inhibit surface OER process,alleviated the energy losses by non-radiation relaxation and enhance the anodic ECL of Ru(bpy)32+.In Ru(bpy)32+/CNQDs system,CNQDs could enhance the anodic ECL of Ru(bpy)32+in nitrogen stream(10-fold)and ambient air(161-fold).The luminous and nitrogen-rich CNQDs was also confirmed not to serve as ECL luminophore,anodic coreactant,or donor/acceptor in ECL.The coreactant-free Ru(bpy)32+/CNQDs system possesses several advantages over common coreactant ECL system,such as low dosage(100?g/mL CNQDs),favorable regeneration capacity,etc.As an example,ECL on-off detection of dopamine utilizing Ru(bpy)32+/CNQDs system was also developed to show prospects in ECL sensing.Besides,CNQDs was introduced into classical Ru(bpy)32+/C2O42-coreactant ECL system endowing suppressed OER and improved ECL signal.Overall,the proposed new ECL enhancing strategy is promising for applicable ECL sensing,could extend to other ECL luminophore with high oxidation potential,and helps in-depth understanding of ECL process and mechanism.