Preparation Of Carbon/Silicon Composite Quantum Dots And Its Application In Rapid Detection Of Formaldehyde In Indoor Air

Formaldehyde is a common indoor pollutant.When people are in an environment with a higher concentration of formaldehyde for a long time,it can easily induce various diseases such as respiratory diseases,leukemia,heart disease and cancer.Therefore,the monitoring technology of formaldehyde pollution in indoor air has always attracted people’s attention,and it is of great significance to develop simple,sensitive and rapid formaldehyde detection methods.Traditional methods for detecting formaldehyde（such as UV-visible spectrophotometry,high-performance liquid chromatography,and mass spectrometry）have disadvantages such as complicated operation and expensive equipment.Fluorescent probe method has been developed as an important detection method due to its advantages such as simple operation,high sensitivity,and fast analysis speed.Many fluorescent probes have been developed for the detection of formaldehyde,but most of them are based on fluorescent dyes.They still have the disadvantages of complex preparation and high toxicity.In contrast,quantum dots（QD）have the characteristics of simple preparation method,high fluorescence intensity,excellent light stability,and good biocompatibility.It is a high-quality fluorescent material as a fluorescent probe.Therefore,a silicon quantum dot（Si QDs）is designed and synthesized as a fluorescent probe for selective recognition of formaldehyde.By incorporating carbon dots（CDs）,carbon/silicon composite quantum dots（CDs@Si QDs）with high detection sensitivity and good stability are obtained;Based on the addition of gold nanoparticles（AuNP）to the mixed solution of composite quantum dots and formaldehyde,the resonance Rayleigh scattering intensity and the color of the solution changed significantly.Resonance Rayleigh scattering spectroscopy and visual detection of formaldehyde were separately constructed to achieve rapid detection of formaldehyde.The specific research content and main results are as follows:（1）Using 3-ureapropyltriethoxysilane and trisodium citrate as raw materials,a one-step hydrothermal method was used to synthesize water-soluble fluorescent Si QDs.Based on the fact that formaldehyde can quench the fluorescence of Si QDs,it is used as a formaldehyde fluorescent probe and applied to the detection of formaldehyde in indoor air.Single-factor experiments were used to select the best detection conditions:Si QDs concentration 15 mg·L^-1,Tris-HCl buffer solution concentration 10 m M,buffer solution p H=6.0.The results show that the fluorescence intensity of Si QDs decreases with the increase of formaldehyde concentration,and the detection linear range is 0.05～0.80 mg·L^-1（R²=0.9989）,and the detection limit is 0.045 mg·L^-1.This fluorescent probe was used for the detection of formaldehyde in indoor air.There was no significant difference between the detection result and the phenol reagent spectrophotometric detection result.The spiked recovery of the sample was between 87.47%and 130.18%.The relative standard deviation RSD≤9.47%（n=5）.The method is simple to operate,highly sensitive,and is not affected by similar substances such as acetone and acetaldehyde,and has high potential application value in the detection of formaldehyde in indoor air.（2）In the process of preparing Si QDs,CDs were incorporated to obtain carbon/silicon composite quantum dots（CDs@Si QDs）.Using CDs@Si QDs as a fluorescent probe for formaldehyde detection,a fluorescence spectrometry method for the determination of formaldehyde was established and applied to the detection of formaldehyde in indoor air.Add 40 mg·L^-1 CDs@Si QDs solution and 0.02 mol·L^-1Tris-HCl buffer solution（p H=6.0）to formaldehyde solution of different mass concentration,with 350 nm as the excitation wavelength,the fluorescence intensity F at 442 nm was measured.The results show that F₀/F（F₀ is the fluorescence intensity of the system without formaldehyde）and formaldehyde have a linear relationship within a certain concentration range,the linear range is 0.02～0.60 mg·L^-1（R²=0.992）,and the detection limit is 0.018 mg·L^-1.CDs@Si QDs was used as a fluorescent probe for the detection of formaldehyde in indoor air.There was no significant difference between the test results and those of phenol reagent spectrophotometry.The spiked recovery of the samples was between 92.06%and114.10%,The relative standard deviation RSD≤9.63%（n=5）.The method is simple to operate,highly sensitive,and not affected by similar substances and common VOCs in indoor air,and has a good application prospect in the detection of formaldehyde in indoor air.（3）Based on the addition of AuNP to the mixed solution of CDs@Si QDs and formaldehyde,the resonance Rayleigh scattering intensity was changed,and the sensitive and rapid detection of formaldehyde was achieved by the resonance Rayleigh scattering spectroscopy.The prepared CDs@Si QDs and AuNP were characterized accordingly,and their detection mechanisms were analyzed.The results show that CDs@Si QDs can induce AuNP aggregation,and formaldehyde can occupy the sites where CDs@Si QDs interacts with AuNP,resulting in a decrease in the degree of AuNP aggregation and a decrease in resonance Rayleigh scattering intensity.The amount of CDs@Si QDs and AuNP,p H value,reaction time,and reagent addition order were optimized by single factor experiments.Under optimized conditions,this system was used for the determination of formaldehyde content.The results show that the resonance Rayleigh scattering intensity of the system decreases with increasing formaldehyde concentration,and the linear range of detection is 0.1～8.0 mg·L^-1（R²=0.9984）,The detection limit is 0.04 mg·L^-1.The method is simple in operation,high in sensitivity,fast in detection,and not affected by ions and common VOCs in the air,and has a good application prospect in the rapid detection of formaldehyde in indoor air.（4）Based on the addition of AuNP to the mixed solution of CDs@Si QDs and formaldehyde,resulting in a significant change in solution color,visual detection of formaldehyde by using CDs@Si QDs and AuNP.The amount of CDs@Si QDs and AuNP and the order of reagents were optimized by single factor experiments.Under optimized conditions,this system was used for the visual determination of formaldehyde.The results show that the formaldehyde concentration in the solution can be determined according to the color of the solution.The formaldehyde concentration ranges from 0 to 10.0 mg·L^-1,and the color of the solution changes from blue to purple and then to red.This method is simple and fast,and has high potential application value in the visual detection of formaldehyde.