Microwave-hydrothermal For High Synthesis Yield And Ferric Ions Specific Sensitive Fluorescent Carbon Dots

Iron is one of the essential trace elements in the body,and the available iron in the body is bivalent,so the content of Fe²⁺in body is very important.In addition,the content of Fe²⁺in the environment is also an important indicator for evaluation of water quality.Therefore,detection of Fe²⁺is very necessary and significant.As a new type of fluorescent carbon nanomaterial,fluorescent carbon dots have brilliant luminescent properties and small size characteristics,and also have excellent biocompatibility and fluorescence stability.Hence,it has a good application prospect in the fields of ion detection.At present,the synthesis yield and preparation efficiency of carbon dots are low,the quantum yield is not high,and the function of carbon dots is single.The choice of microwave hydrothermal method instead of hydrothermal method can improve the efficiency of carbon dots preparation.Compared with microwave synthesis,microwave hydrothermal synthesis has the advantage of controllable pressure and temperature,avoiding more side reactions and making the product more pure.The nature of carbon dots is closely related to the source of synthetic carbon dots.In order to obtain fluorescent carbon dots with excellent properties,we should focus on the precursor.At present,doped carbon dots of various elements have emerged.However,the research on changing the nature of carbon dots by controlling carbon-site functional groups needs to be carried out.In this paper,chitosan/unsaturated precursors with different functional groups were used as precursors.The carbon dots containing specific functional groups were synthesized by microwave hydrothermal carbonization.The optical properties were investigated by UV-Vis absorption spectra and fluorescence spectra.The effect of the precursor functional group on the synthesis yield and fluorescence properties of the product was studied.The phase structure,elemental composition and bonding state of carbon dots derived from unsaturated precursors were characterized by transmission electron microscopy,X-ray diffraction,infrared spectroscopy and X-ray photoelectron spectroscopy.The use of CDs-NH₂ as a fluorescent probe for the detection of iron ions was demonstrated.The results showed that four kinds of fluorescent carbon dots were synthesized by microwave hydrothermal carbonization using chitosan/unsaturated amide,carboxylic acid or ester as two-component carbon source.Divided into amino-containing fluorescent carbon dots?CDs-NH₂?,carboxyl-containing fluorescent carbon dots?CDs-COOH?,ester-containing fluorescent carbon dots?CDs-COOR?and amino-/carboxy-containing bifunctional fluorescent carbon dots?CDs-NH₂-COOH?.Among the above four carbon points,the synthetic yield of CDs-NH₂ is also the highest,which is 45.9 wt%.Compared to the carbons?CDs?of chitosan as a single carbon source,the synthesis yield of CDs-NH₂ is increased by 6.8 times.CDs-NH₂ is amorphous carbon with an average particle size of 10.9 nm.The main elements contained C,N,and O,in which the mass ratio of C:N:O was 72.07:7.39:20.54,and active functional groups such as-NH₂,-OH were present in the CDs-NH₂.The maximum absorption wavelength of CDs-NH₂ is 330 nm,and the corresponding maximum emission wavelength is 409 nm.The quantum yield of CDs-NH₂ was 12.17%.Compared to the fluorescent carbon dots?CDs?of chitosan as a single carbon source,the quantum yield of CDs-NH₂ is increased by 103%.This is due to the high N content in the amino group,which increases the quantum yield of fluorescent carbon dots.In the pH range of 4-10,the fluorescence intensity fluctuation of CDs-NH₂ was less than 2.1%,so it has excellent pH fluorescence stability.CDs-NH₂ had a selective quenching effect on Fe²⁺with a linear detection range of 0-50?M and a detection limit of 160 nM.The CDs-NH₂ has excellent anti-interference in the detection of Fe²⁺,and it is of great significance to detect the Fe²⁺in the real water sample for this carbon dots.Furthermore,the determination of metal ion concentrations using fluorescence imaging has been achieved.By comparing with Na₂EDTA,CDs-NH₂ is more strongly chelated with Fe²⁺and has potential as a Fe²⁺chelator.