Preparation And Properties Of Materials Based On Fluorescent Carbon Dots For Detection And Adsorption Of Metal Ions

Fluorescent carbon dots（CDs）is a new type of zero-dimensional carbon nanomaterials with an average particle size of less than 10 nm.It has the advantages of stable fluorescence performance,low toxicity and good biocompatibility.CDs can detect metal ions through fluorescence quenching,and can also adsorb metal ions through surface amino functional groups.In this paper,CDs with good fluorescence performance was first prepared.Then PVDF and aminated silica（NSiO₂）were prepared into the membrane by blending.The surface of NSiO₂was rich in-NH₂,and the blending of NSiO₂in the membrane could increase the adsorption performance of the membrane.The CDs modified by silanization was grafted on the surface of PVDF/NSiO₂membrane to prepare a dual-functional membrane material capable of detecting and adsorbing metal ions.Next,SA@PEI gel microsphere with higher adsorption performance was prepared,and CDs was grafted on the surface to obtain dual functional materials with higher fluorescence sensitivity and better adsorption performance.Firstly,using citric acid and polyethyleneimine as the carbon source and nitrogen source,CDs with better dispersibility and uniform particle size was prepared by hydrothermal method,and its structure and fluorescence properties were characterized.The results show that the prepared CDs had abundant hydrophilic functional groups such as-NH₂,-COOH and-OH.Its average particle size was about 6.65 nm,and its fluorescence quantum yield was as high as 32.86%.CDs was excitation wavelength dependent.CDs had specific detection for Hg²⁺and Fe³⁺,with detection limits of 1.1nM and 1.5μM,which had strong practical application value.The CDs modified by silanization was grafted onto the surface of PVDF/NSiO₂membrane to prepare PVDF/NSiO₂-g-CDs membrane,and its structure,fluorescence properties and adsorption properties were studied.The research results show that the properties of NSiO₂and CDs were retained,and the hydrophilicity and permeability of the membrane had also been improved to a certain extent.PVDF/NSiO₂-g-CDs membrane could specifically detect Hg²⁺and Fe³⁺,with detection limits of 1.6 nM and 2.1μM,respectively.The adsorption capacity of Fe³⁺by PVDF/NSiO₂-g-CDs membrane reached 47.04 mg·g^-1,and chemical adsorption was dominant in the adsorption process,and it was a monolayer adsorption.In addition,glutaraldehyde was used to cross-link the-NH₂of CDs with-NH₂on the surface of SA@PEI gel microsphere,and the SA@PEI-g-CDs gel microsphere with three-dimensional cross-linked network structure was prepared.Studies had shown that SA@PEI-g-CDs gel microsphere had good thermal stability and excitation wavelength dependence,and it could be specifically detected for Hg²⁺and Fe³⁺,with detection limits of 1.3 nM and 1.6μM,respectively.The pore volume and specific surface area of SA@PEI-g-CDs gel microsphere had been greatly improved,and the adsorption capacity for Fe³⁺was as high as 70.87 mg·g^-1.Chemical adsorption was dominant,and the adsorption process belonged to the surface non-uniform adsorption.Compared with PVDF/NSiO₂-g-CDs membrane,the fluorescence detection sensitivity and adsorption performance of SA@PEI-g-CDs gel microsphere had been greatly improved.