Detection Of Heavy Metals In Water With Fluorescent Paper Strip Based On Carbon Dots

The pollution of heavy metals in the water environment extremely harmful to the ecological environment and human health.The current methods for heavy metals detection need expensive equipments,complicated operation processes,and complex sample preparation,which limit the applications of these methods for heavy metals detection in real samples.Thus,it is still a great challenge to develop a sensitive,rapid,simple and cost-effective method for trace heavy metals detection in aqueous solutions.Test paper method is a rapid detection method which transfers the chemical reactions from the glass instruments to test paper.Inspired by the test paper method and fluorescence characteristics of carbon quantum dots,a method for the detection of heavy metals by carbon quantum dots fluorescence test paper is established.The carbon quantum dots fluorescence test paper can realize rapid detection of Hg???and other heavy metals in water.The thesis consists of the following three parts:The first part of this thesis,a nitrogen doped carbon quantum dot test paper was prepared to detect Hg???in water.The NCD is synthesized by hydrothermal method using anhydrous citric acid and urea.The TEM results shows that the average particle size of the NCD is 2.2 nm.Under the optimized detection conditions of HAc-NaAc buffer solution at pH7,the NCD concentration is 102 ?g·mL^-1,the detection of Hg???can be completed within 5 minutes.And the F/F₀ were linearly corresponded to Hg???at the concentrations ranging from 0 to 5 ?mol·L^-1,detection limit is 0.076 ?mol·L^-1?n=9?based on three standard deviations.The adding standard recoveries of Hg???detection in tap water and lake water ranged from 84.8%-101.9% and 109.2%-118.6%,respectively.The NCD test paper was prepared by a simple soaking method of NCD under optimal conditions.Upon the addition of different concentrations of Hg???,the NCD test paper changed from light to dark under a UV lamp?365 nm?.The second part,a two-color fluorescent test paper for Hg???detection in water was constructed based NCD and Rhodamine B?Rh B?ratio fluorescent probe.Zeta potential indicates that NCD and Rh B are combined by electrostatic attraction.At the same time,NCD and RHB retain their respective fluorescence properties,and the fluorescence intensity of Rh B does not change with the change of the mercury concentration.Therefore,the NCD@Rh B ratio fluorescent probe can be used for Hg???detection in water.Under the optimized detection conditions of 1 mmol·L^-1 HAc-Na Ac buffer solution at pH7,the ratios of F₄₄₀/F₅₈₀ were linearly corresponded to Hg???at the concentrations ranging from 0 to 3 ?mol·L^-1,the detection limitwas 2.7 nmol·L^-1?n=9?based on three standard deviations.The adding standard recoveries of Hg???detection in lake water and tap water ranged from 91.9% to 117.9% and 91.89% to108.1%,respectively.A visualized two-color fluorescent test strip was prepared by a simple soaking method of NCD and Rh B under optimal conditions.Upon the addition of different concentrations of Hg???,the color of test paper changed from light purple to orange accordingly under a UV lamp?365 nm?,in which each of the detection time took only 3 minutes,and Hg???could be detected as low as 10 nmol·L^-1 by naked eyes.The third part,a carbon dot quantum dots test paper was prepared for the simultaneous detection of Cr???,Cu???,Fe???and Hg???.The four kinds of carbon quantum dots that constitute the test paper have specific detection for Cr???,Cu???,Fe???and Hg???respectively.Under 20 mmol·L^-1PBS buffer?pH=7?,the linear range of Cr???is 0 to 70?mol·L^-1.The detection limit was 0.5 ?mol·L^-1?n=9?based on three standard deviations.The blue-green fluorescence of test paper changes from light to dark.The linear range of Fe???is 0to100 ?mol·L^-1.The detection limit was 1.2 ?mol·L^-1?n=9?based on three standard deviations.Blue fluorescence of test paper changes from light to dark.Under 20 mmol·L^-1HAc-NaAc buffer?pH=4?,the linear range of Cu???is 0 to 50 ?mol·L^-1.The detection limit was 0.1?mol·L^-1?n=9?based on three standard deviations.The fluorescence of test paper changed from light blue-purple to dark purple.The linear range of Hg???is 0 to 3 ?mol·L^-1.The detection limit was 2.7 nmol·L^-1?n=9?based on three standard deviations.Fluorescence of test paper changed from blue-purple to orange.Therefore,the contents of Cr???,Cu???,Fe???and Hg???in water can be simultaneously determined by the fluorescence test paper of carbon quantum dots.It provides a new method for rapid detection of heavy metal ions in water environment.