Preparation Of Several Carbon-based Materials And Their Application In The Fluorescence Sensing And Photocatalytical Field

Carbon-based materials have a wide range of potential applications in environment,energy,biochemical sensing,bioimaging and photocatalysis due to their advantages including low cost,non-toxicity,harmlessness and chemical stability,and play an important role in human life and economic development.Among the carbon-based materials,carbon quantum dots?C-dots?and graphite carbon nitride quantum dots?g-C₃N₄-dots?have the advantages of stable FL performance and good biocompatibility.Bulk carbon nitride?CN?has the advantages of stable structure and adjustable energy band gap.They have great potential in the fields of FL sensing,bioimaging and photocatalysis.At present,there are still many shortcomings in the preparation and controling performance of these three materials.Therefore,it is of great significance to develop new and simple methods for the preparation of these three materials and solve some shortcomings,such as low fluorescence quantum yield?FLQY?,complex functionalization,long synthesis process,harsh synthesis conditions and low photocatalytic efficiency.Based on a brief summary of the preparation,properties and applications of C-dots,g-C₃N₄-dots and CN,a series of simple,green,low-cost and efficient methods for the preparation of C-dots,g-C₃N₄-dots and g-C₃N₅ were developed.Due to the excellent FL properties of quantum dots,several highly sensitive,multi-functional and multi-signal chemical/biological sensors were constructed.Sensors were used for the detection of small biological molecules and several metal ions.Meanwhile,g-C₃N₅ with excellent photocatalytic performance was prepared for photocatalytic degradation of organic pollutants.The main research contents are as follows:1)A novel colorimetric and ratiometric FL method for the detection of iodide ions?I^-?was developed.In the presence of I^-,the color of N-doped C-dots/H₂O₂/OPD system aqueous solution varied from colorless to yellow due to 2,3-diaminophenazine?OPDox?produced from I^--catalyzed H₂O₂-o-phenylenediamine?OPD?reaction.At the same time,the OPDox had an excellent FL property.Under the excitation wavelength at 390 nm,a novel FL emission ascribed to OPDox was clearly observed at 565 nm.In addition,the FL at 565 nm gradually increased,while the FL of emission peak at 450 nm attributed to N-doped C-dots gradually decreased with the increasing concentration of I^-due to the FL resonance energy transfer?FRET?between N-doped C-dots and OPDox.Therefore,a dual-signal optical sensor was developed for detection of I^-.Under the optimized conditions,the linear response to I^-was in the range of 0.09?M-50?M and the limit of detection was 0.06?M.Moreover,this proposed assay was successfully applied for the detection of I^-in urine.These results indicate that the colorimetric and ratiometric FL dual-readout assay method has great potential for applications in physiological and pathological diagnosis.2)The sulfur,nitrogen co-doped carbon dots?SN co-doped C-dots?as highly selective fluorescent probe were designed.The SN co-doped C-dots with high quantum yield of 73.1%were prepared by hydrothermal method.It was found that the FL of SN co-doped C-dots was quenched apparently by hydroxyl radicals from Fenton reaction between H₂O₂ and Fe²⁺.The production of H₂O₂ originated from the oxidization of UA by uricase.Therefore,an optical biosensor was developed for the detection of UA based on Fenton reaction and enzymatic reaction.Under the optimized conditions,two linear relationships between the ratio of FL quenching of the C-dots and UA concentration were found in the range of 0.08?M-10?M and 10?M-50?M,respectively.The detection limit was down to 0.07?M.Moreover,the proposed biosensor was successfully applied to the detection of uric acid in human serum samples.3)The oxygen and sulfur co-doped graphitic carbon nitride quantum dots?OS-g-C₃N₄-dots?with high FLQY of 33.9%were firstly synthesized by a simple electrochemical“tailoring”process.It was found that OS-g-C₃N₄-dots could specifically bind copper ions(Cu²⁺)and silver ions?Ag⁺?due to their electron transfer,accompanied with a dramatic“turn-off”FL response.With the help of different masking agents,OS-g-C₃N₄-dots are able to selectively detect Cu²⁺and Ag⁺.Furthermore,the generated OS-g-C₃N₄-dots/Ag⁺displayed a“turn-on”fluorescent response specific to biothiols?HCy,Cys and GSH?.Therefore,the multiple functional sensing platforms based on“ON–OFF–ON”FL response of OS-g-C₃N₄-dots for the detection of Cu²⁺,Ag⁺and biothiols were constructed.Under the optimal conditions,the detection limits of Cu²⁺,Ag⁺,HCy,Cys and GSH were as low as 7.0×10^-1010 M,2.0×10^-99 M,1.0×10^-88 M,1.0×10^-88 M and8.4×10^-99 M,respectively.Moreover,the prepared platforms could be successfully applied to the determination of Cu²⁺,Ag⁺and biothiols in practical samples and exhibited excellent sensitivity and selectivity.4)A novel triazole ring-based graphite carbon nitride?g-C₃N₅?is developed by one step pathway of NaOH-assisted thermal polymerization for the first time.The obtained band structures of the prepared g-C₃N_x-M can be controlled by tuning the mass ratio of precursor and NaOH.Those unique band structures offer a slightly narrowed band gap of 1.69-2.00 eV,which is significantly smaller than the traditional melamine derived g-C₃N₄?ca 2.7 eV?.More interesting,the prepared g-C₃N_x exhibits lower recombination rates of electron-hole pairs.Therefore,the g-C₃N_x shows significantly the enhanced photocatalytical and photoelectrochemical performance.We believe that this work will provide a new enlightenment to synthesize g-C₃N₅ with high photocatalytic activity in the photocatalytic and photoelectrochemical field application,which is a highly potential to produce renewable fuels and remove pollutants.The prepared g-C₃N_x also makes up the deficiency of the application of C-dots in the field of photocatalysis.5)A new type of graphite nitride?RN-g-C₃N₅?with rod-like structure and rich nitrogen was synthesized by a simple salt template method using3-amino-1,2,4-triazole as precursor through recrystallization,thermal shrinkage polymerization and salt template removal.The proposed synthesis method not only avoids the use of dangerous etching reagents?HF?,but also does not require complex and toxic template removal process.The salt template?KBr?we used can remove the template by water washing and recycle the template.This special rod-like structure with mesoporous enhances the specific surface area,visible light utilization and lower band gap of g-C₃N₅,which greatly improves the photocatalytic activity of g-C₃N₅,and has broad application prospects in photocatalysis.