Preparation And Application Of Novel Functionalized Non-metallic Element Doped Carbon Dots

Carbon dots（CDs）,as one of the important members of carbon family,shows excellent optical properties,low cytotoxity and so on.Element doping,as a commonly used strategy for regulating the fluorescence performance of CDs,has received widespread attention,but its mechanism of action needs further in-depth explanation and summary.In this thesis,four kinds of non metallic element doped CDs was synthesized use non-metallic element and Malic Acid（MA）as raw materials,focused on developing CDs with different doped element and explore the microstructure,PL mechanism and their applications.The thesis has been divided into the following sections:A novel nitrogen doped CDs was developed with microwave-assisted approach using MA and ethylenediamine（EDA）as raw meterials.The developed NCDs have been further used for the detection of Ce⁴⁺in real water samples,for which the PL of NCDs was quenched through dynamic quenching effect（DQE）,static quenching effect（SQE）and inner filter effect（IFE）.A linear relationship between the quenching ratio,F/F₀and concentration of Ce⁴⁺was developed for Ce⁴⁺concentration varying between 20 and 80μM,where the limit of detection（LOD）determined as 1.5μM.Furthermore,the formed NCDs-Ce⁴⁺complex without PL were used as fluorescent sensor for S-mandelic acid（S-MA）based on“Off-On”mode.S-MA molecule might be highly interacted with Ce⁴⁺in NCDs-Ce⁴⁺complex,where the PL of NCDs were recoverd after the addition of S-MA.And thus a new emissive peak at 355 nm was formed with increased intensity.The increased intensity was found to be linear to the concentration of S-MA ranging from 0 to300μM,where the LOD was estimated as 1.0μM.The recovery rate for both Ce⁴⁺and S-MA are quite reasonable.Moreover,the as-sythesized NCDs showed low cell toxity,approving its potential application for detection of Ce⁴⁺and S-MA in real samples.In order to improve the PL properties of NCDs,a novel nitrogen and sulfur co-doped carbon dots（NS-CDs）were prepared though microwave assisted approach using MA and allyl thiourea（ATU）for the first time.The sensitivity study of NS-CDs against metal ions and organic molecules has approved that the fluorescence could be further quenched by Ce⁴⁺and Fe³⁺ions,with the same linear detection ranges varying from 10 to 90μM.The LOD were determined as low as 0.75μM and 0.67μM for Ce⁴⁺and Fe³⁺ions,respectively.The possible quenching mechanism is explained by inner filter effect and static quenching mechanism for Ce⁴⁺,while the quenching effect caused by Fe³⁺is attributed to the inner filter effect,static and dynamic quenching mechanisms.Additionally,the developed sensor was used for the detection of Ce⁴⁺and Fe³⁺ions in tap water with satisfactory recoveries.Finally,the designed NS-CDs sensor possesses good biocompatibility against MA104 cells,suggesting the sensor can be potentially applied to detect Ce⁴⁺and Fe³⁺ions in environment and biological systems.For investigateing the influence of doped elements on CDs,a facile one-step strategy for the preparation of solid-state carbon dots phosphors with high yield has been developed via microwave-assistant reaction between ratio of MA and Levofloxacin（Lev）as 1:1,5 min.Its aqueous solution emits bright blue-green fluorescence under UV lamp irradiation,with an PL emission wavelength of 490 nm and shows non-excitation dependence.Thus,solid-state carbon dots with fluorine and nitrogen as heteratomic dopants were successfully synthesized with bright blue fluorescence under UV light,the emission peak at the excitation wavelength of 280 nm is located at 470 nm,with a quantum yield of 18.9%.Through the optical analysis,the fluorescence of obtained fluorine,nitrogen-doped carbon dots（FNCDs）in both solution and solid state were observed as excitation-independent.In order to investigate the solid state emission mechanism,additional structural analysis was conducted.The skeleton of levofloxacin was retained in solid state CDs together with the carbon-containing and oxygen-containing functional groups,which have suppressed theπ-πinteractions,thus resulting in self-quenching resistant carbon dots powder.Moreover,the phosphors were further used for fingerprint identification and anti-counterfeiting,approving their potential applications in practical areas.Finally,a novel nitrogen and fluorine co-doped CDs（FNCDs-2）were synthesized with mass ratio of MA and Lev as 9:1,5 min.Unfortunitely,the formed FNCDs-2suffered from ACQ in solid-state.In order to prepare CDs based solid phosphors,the as-prepared FNCDs-2 was embedded into inorganic salt crystals through three different approaches.The results showed that the FNCDs-2@Na Cl,FNCDs-2@KCl,FNCDs-2@Sr Cl₂complex was successfully designed through cooling crystallization of the correspongding salts.It can be found that as thesize and Z number of the cation ions in inorganic salts increases,the emission spectra have changed and a red-shift was observed.Thus,it is possible to tune the optical properties of FNCDs-2@inorganic salts complex through changing the inorganic salt.Moreover,the FNCDs-2@KCl was chosen to prepare the color conversion layer for LED chips.With different fraction of FNCDs-2@KCl solids and resins in the layer,the color of LED has changed accordingly.Thus,this approach has approved the FNCDs-2 particles can be embedded into the matrix of inorganic salt crystals through cooling crysatllization process,and thus resulting solid state phosphors used for LED fields.