Preparation Of Carbon Based 2D Materials And Fine Tuning Over Their Fluorescent Properties

Fluorescent carbon nanomaterials(such as carbon nanotubes,fullerenes,graphene derivatives,nanodiamonds)possess intriguing optical properties owing' to their manifold structure,morphology and functionalization.Especially in recent years,carbon dots(CDs)have drawn tremendous attention for their high aqueous solubility,facile preparation and low toxicity.However,previous studies on nanocarbon fluorescent materials are mainly focused on aqueous or colloid systems;solid-state quantum yield(SSQY)decreases sharply as a result of aggregation-induced PL quenching,which restricts their employment in solid state devices.Therefore,how to attain carbon materials based phosphors with excellent SSQY and stability simultaneously via material design and synthesis exploration is of scientific and technological importance,and remains a challenge.Layered double hydroxides(LDHs)are an important class of 2D inorganic matrix with versatility in chemical composition,structure,and morphology,which have attracted a broad research interest in multi-functional materials and applications.In this dissertation,carbon nanomaterial and LDHs host-guest fluorescent materials have been fabricated via layer-by-layer(LBL)assembly and in situ interlayer reaction,respectively.These composite materials not only maintain fluorescent properties under solid conditions,but also boost the SSQY into an unprecedented level.Meanwhile,the optical properties can be modified by adjusting the composition of host LDH layer.Furthermore,both experimental studies and theoretical calculations reveal that the host-guest interactions between rigid LDH matrix and interlayer carbon species,as well as the confinement effect impose significant influences on their fluorescent properties.The detailed contents are as follows:1.CDs@PSS/LDH UTF has been fabricated by LBL assembly of fluorescent CDs@PSS with the positively-charged LDH nanosheets.The resulting UTF owns long-range ordered architecture and excitation-dependent PL emission property.In particular,CDs@PSS/LDHUTF shows largely improved fluorescence QY and lifetime(57.17%;14.47ns),which are superior to pristine CDs(3.04%,0.813 ns)andCDs@PSSdrop-casted film(20.73%,9.398 ns).The confinement effect imposed by LDH nanosheets inhibits the electron transfer,facilitates the electrons/holes recombination and therefore results in the markedly enhanced fluorescence properties.Moreover,the UTF exhibits stable and reversible temperature-dependent PL and ECL response in the temperature range 20-80 ?,and enhanced anti-photobleaching and anti-heatbleaching properties.This work demonstrates a successful way for the design and fabrication of CDs-based UTF by virtue of 2D LDH ultrathin matrix,whichcan serve as a promising candidate in optical/optoelectronic sensing devices.2.Solid-state N-CDs intercalated LDHs composites have been synthesized through in situ interlayer reaction,which showed bright blue luminescence.The resulting N-CDs/LDH composite materialspossess 2D layered structureand ultrathin N-CDs are produced in the LDHs gallery during thehydrothermal reaction process.The PLQY of N-CDs/LDH materials can be regulated via changing the doping amount of nitrogen and the maximal PLQY reaches 61.63%,which is among the highest level of CDs-based solid-state materials.Moreover,N-CDs/LDHcomposite exhibits temperature-dependent luminescence at low temperatures;the as-prepared N-CDs/LDH@PVA film can be integrated with a commercial UV LED chip,which converts UV light to pure and strong blue-emitting.In addition,this N-CDs/LDH composite material shows high UV-resistance and storage stability,which would guarantee its prospective applications in optical and optoelectronic devices.3.Layered carbon nitride was synthesized in 2D confined region of LDHs by microwave-induced condensation reaction of CA and urea.The resulting CN/LDH composite phosphor emits bright cyan light under UV light with an ultrahigh SSQY of 95.9 ± 2.2%,which is the highest value among carbon dots,graphene quantum dots and carbon nitrides based phosphors.This superior property is due to the inhibition on carbonization process and the formation of carbon nitride structure in the confined reation;furthermore,the promotion toward photoexcited electron-hole recombination based on the host-guest electronic structure gives a predominant contribution.In additon,the CN/LDH phosphor exhibits strong stability against external stimulus(photo,heat,pH),which guarantees its prospective applications in WLED and upconversion cell imaging.