Preparation Of N,P-doped Carbon Quantum Dots And Their Application In The Detection Of Iron And Mercury Ions

Fluorescent carbon quantum dots(CQDs),a new zero-dimensional nanomaterial,are mainly composed of C,H,and O elements,and the particle size is generally below 10 nm.Compared with traditional semiconductor quantum dots,carbon quantum dots have the advantages of excellent optical properties,great biocompatibility,good water solubility,low cost,and simple-green synthesis.Heteroatom(N,P,B,S,etc.)doping could improve the fluorescence quantum yield(QY)of carbon quantum dots,giving them special luminescent properties.In recent years,more and more researches had focused on the synthesis and application of heteroatom-doped carbon dots.The presence of even trace amounts of iron and mercury ions would cause certain health risks,so monitoring the concentration of iron and mercury ions in water is critical.Most of the traditional ion detection methods are time-consuming,labor-intensive and expensive,so it is necessary to establish a more rapid,low-cost and sensitive detection method.Due to the characteristics of wide fluorescence emission range,green,low cost and surface functionalization,doped fluorescent carbon quantum could be used to construct fluorescent sensors for metal ions.In this experiment,two common water treatment agents were used as synthetic precursors to prepare two kinds of doped carbon quantum dots,nitrogen and phosphorus co-doped N,PCQDs and nitrogen-doped N-CQDs,respectively.And the characterization information and chemical sensing applications of the two carbon dots were studied:(1)N,P-CQDs with a quantum yield of 17.74%were prepared by an optimized one-step hydrothermal method using Amino trimethylene phosphonic acid(ATMP)and sodium citrate as precursors.The N,P-CQDs emit blue fluorescence(λex=320 nm,λem=425 nm)under UV light irradiation,the morphology is approximately spherical.The average particle size is 1.18 nm.And they have good water solubility and optical stability.The fluorescence of N,P-CQDs could be selectively quenched by Fe2+and Fe3+.Based on this,we established a fluorescence sensing system capable of detecting the two kinds of iron ions,whichfilled the research gap of carbon quantum dot fluorescent probes for simultaneous detection of the two kinds of iron ions.The detection ranges are Fe2+:0-600 μmol/L and Fe3+:0-250 μmol/L,the detection limit was less than 1 μmol/L.The detection system was applied to real water samples.The recovery rates of Fe2+and Fe3+ were both between 96%and 106%.In addition,the Ca2+scale inhibition effect of N,P-CQDs was also been studied,the scale inhibition efficiency reached 90%at 80℃.(2)Using L-Glutamic acid,N,N-bis(carboxymethyl)-,tetrasodium salt(GLDA)and mphenylenediamine as precursors,N-CQDs were synthesized hydrothermally under acidic conditions.And the quantum yield of the final product was as high as 85.75%after optimizing the experimental scheme,which are better than most research-synthesized carbon quantum dots.N-CQDs have green fluorescence(λex=440 nm,λem=510 nm),approximate spherical shape.Their particle size is between 2-7 nm.And they have good water dispersibility and stability.The fluorescence of N-CQDs can be selectively quenched by Hg2+,and completely recovered by halogen ions(Cl-,Br-,I-),which shows special fluorescence application performance.Based on this feature,a fluorescence off-on sensing system for Hg2+and halogen ions was established.The detection range of Hg2+is 0-40 μmol/L,and the detection range of Cl-,Br-,I-is 0-160 μmol/L,0-140 μmol/L,0-100 μmol/L,respectively.The detection limit reaches the nmol level.In actual water samples,the recovery rate of Hg2+by N-CQDs was between 93%and 110%.