Preparation And Applications Of Functionalized Fluorescent Carbon Dots

Carbon dots（CDs）as a zero-dimensional carbon nano-material,are generally spherical fluorescent particles with a particle size of less than 10 nm,which are composed of carbon cores and surface functional groups.CDs have become a rising star of the carbon material family because of their excellent biocompatibility,photoluminescence characteristics,and potential market application value.At present,CDs still have some disadvantages,such as uncontrollable fluorescence emission wavelength and single function.This dissertation focuses on the simple synthesis and multifunctional application of CDs,and the specific contents are as follows.（1）The nitrogen-doped multicolor CDs（M-CDs）including green,chartreuse,and pink emissive CDs（G-CDs,C-CDs,and P-CDs）are successfully synthesized by ultrasonic treatment of kiwifruit juice with different additive reagents such as ethanol,ethylenediamine,and acetone.Owing to their strong fluorescence upon irradiation with 365 nm UV light,the highly water-soluble M-CDs present great potential in the anticounterfeit field as fluorescent inks.Particularly,the resulting green emission CDs（G-CDs）with excellent fluorescence and stability are applied as a label-free probe model for“on-off”detection of Fe³⁺.The fluorescence of G-CDs is significantly quenched by Fe³⁺through static quenching.The nanoprobe demonstrates good selectivity and sensitivity toward Fe³⁺with a detection limit of～0.11μM.Besides,compared with most"turn-off"sensors,these biomass CDs are further constructed as an"on-off-on"sensor.The quenched fluorescence of G-CDs by Fe³⁺can be recovered by the addition of PO₄^3-or ascorbic acid（AA）into the CDs/Fe³⁺system to realize the“off-on”fluorescent process.Furthermore,NOT and IMPLICATION logic gates are constructed based on the selection of Fe³⁺and PO₄^3-or AA as the inputs,which makes the G-CD-based sensors utilized as various logic gates at the molecular level.（2）Boron,nitrogen co-doped CDs（BN-CDs）with water-solubility were solvothermally synthesized with aromatic small molecule p-phenylenediamine as carbon source and nitrogen source,boric acid as boron source,and ethanol as reaction solvent towards dual ion detection.The BN-CDs emit bright tangerine fluorescence,and demonstrate a fluorescent quantum yield of 17%.Besides,the obtained BN-CDs show a good linear relationship with Cu²⁺/Co²⁺in a wide dynamic range of 1–8μM,along with detection limits of 16 n M(Cu²⁺)and 24 n M(Co²⁺).The joint effect of dynamic and static quenching mechanisms is proposed as well for fluorescence quenching by Cu²⁺/Co²⁺.Furthermore,two BN-CDs-based solid sensors including test strips and hydrogel beads are fabricated to sensitively monitor both Cu²⁺and Co²⁺.The paper-based sensors exhibit selective and sensitive response towards Cu²⁺and Co²⁺in a low-cost manner.The fluorescence hydrogel integrates comprehensive advantages of hydrogel and BN-CDs,which makes it not only conduct as efficient fluorescent sensors to detect Cu²⁺and Co²⁺but act as the absorbent towards removal of the ions.The simple yet reliable sensing technique developed here favor efficiently detecting and recognizing dual metal ions in environmental samples.（3）Dual-emission carbon dots（BN-CDs,N-CDs,and T-CDs）were synthesized by using triammonium citrate,urea,boric acid,and formamide as reaction materials via a one-step solvothermal method.The static and dynamic characterizations of the prepared CDs were studied,and the effects of doping and environment on the structure and optical properties of CDs were obtained.It is further shown that BN-CDs have more suitable dual-emission performance and higher quantum yield（QY）.Therefore,a novel type of sustainable light conversion composite films（BN-CDs/PSC films）were fabricated by using polyvinyl alcohol（PVA）and starch solutions as matrix and BN-CDs as both light conversion agents and nano reinforcements.The results demonstrate that the prepared films possess excellent optical properties,environmental compatibility,mechanical properties,and water resistance.The composite films can efficiently convert ultraviolet light to blue and red light in order to improve the utilization rate of sunlight.The effects of the obtained films on the growth of plants are investigated.It is found that the growth and the chlorophyll content of the plants are promoted to a certain extent.Hence,rationally designed BN-CDs/PSC films are expected to extensively apply in the field of agricultural planting for sunlight conversion.