Preparation Of Doped Biomass Carbon Quantum Dots And Its Application In The Detection Of Heavy Metal Ions

Carbon quantum dots（carbon quantum dots,CQDs）are friendly environmental fluorescent nanomaterials,that have attracted wide attention in the detection of metal ions and biological imaging because their excellent photostability,low toxicity and good water solubility.Biomass raw materials are high-quality carbon quantum dot precursors,which have a wide range of sources,rich in amounts of carbon,hydrogen,oxygen,nitrogen and other elements so its easy to synthesize hydroxyl,carboxyl and other functional groups.Therefore,it is of great significance to study the materials synthesis processes and mechanism in order to reduce the cost and turn waste into treasure.This paper selects potatoes which the first major crop in Yulin,and food processing waste bean residue,as biomass carbon source,and prepares biomass carbon quantum dots by water heat synthesis.The optical properties are changed by surface modification and element doping,and the structure and characteristics of carbon quantum dots are applied in the study of heavy metal ion detection.The specific work is as follows:（1）With potatoes as the carbon source and ammonium sulfate as the nitrogen and sulfur source,nitrogen-sulfur doped carbon quantum dots（NSCQDs）with blue fluorescence were synthesized by one step hydrothermal method.The structures of NSCQDs were characterizated by TEM,XRD,FTIR,XPS,UV-vis,fluorescence spectrum.NSCQDs is in a spherical shape,its particle size is mainly distributed between 0.46 and 4.85 nm,the average particle size was 2.03 nm.The surface of NSCQDs has hydrophilic groups such as hydroxyl,carboxyl and amine groups,so NSCQDs is very water soluble.The experimental results showed that NSCQDs has good fluorescence stability and excellent selectivity and antiinterference for detection of Fe³⁺concentrations,the response concentrations range from 3to 500μmol/L,with a detection limit of 0.28μmol/L.NSCQDs As a probe for Fe³⁺detection in tap wate and mineral water,the recovery rate was 99.57%-104.03%.（2）With waste bean residue as carbon source and urea as nitrogen dopant,nitrogen-doped carbon QDs（NCQDs）were synthesized by one-step water-thermal synthesis.According to the characterization results of TEM,XRD,FTIR and XPS,UV-vis,fluorescence spectrum,NCQDs have good dispersion and no agglomeration,with an average particle size around1.50 nm after Gaussian fitting and NCQDs have hydrophilic functional groups such as-OH.The results showed that NCQDs had good fluorescence stability and NCQDs had excellent selectivity and anti-interference against Cr⁶⁺,with detection range of 0.5 to 1000μmol/L and detection limit of 0.2μmol/L.The recovery rate of Cr⁶⁺spike in laboratory tap water and off-campus river water was 97.56%-101.92%,proving that NCQDs can be used for the detection of Cr⁶⁺in natural water samples.（3）A ratiometric fluorescent probe was established using bean residue carbon spots combined with rhodamine B.At a single excitation wavelength of 365 nm,this ratiometric-type probe has two emission peaks at 445 nm and 592 nm,The formation of carbon complex and rhodamine B（NCQDs-Rh B）was demonstrated by fluorescence characteristics and UV visible characteristics.At the 445 nm emission peak,the blue fluorescence was gradually quenched with the concentration increasing of Cu²⁺,The Cu²⁺concentration between 20 and300μmol/L showed a good linear relationship with the relative fluorescence intensity than I/I_{0（445/592）},with a detection limit of 0.64μmol/L.This proportional fluorescent probe was successfully applied to determine Cu²⁺content in tap water and mineral water,with a recovery rate of 97.92%-104.36%.