Colorimetric Detection Of Trace Metal Ions In Water Based On Functional Silver Nanoparticles

Silver nanoparticles?AgNPs?have unique catalytic,optical and other excellent properties,and have been widely used as a functional material in the fields of catalysis,sensing,electrochemistry,and energy.In view of the excellent optical performance above,in this dissertation,we selected AgNPs as signal probe and modified different ligands on the surface to improve their water solubility and increase their analytical applicability for detection of trace analytes.On this basis,new methods for the visual detection of Cd²⁺,Al³⁺,Cr?VI?and Hg²⁺were established,respectively.The major contents are as follows:1.A facile and effective colorimetric assay for determination of Cd²⁺and Al³⁺under different pH conditions based on sodium dodecyl sulfate?SDS?decorated silver nanoparticles?SDS-AgNPs?was introduced.It was found that in the aqueous solution SDS-AgNPs were uniformly dispersed and the solution was bright yellow.When Cd²⁺was added,the SDS-Ag NPs changed from dispersion to aggregation based on the coordination of SDS and Cd²⁺,and the color of the solution changed from bright yellow to purple red.When the pH of the solution was adjusted to 5.5 with Tris-HAc buffer,SDS-Ag NPs could selectively coordinate with Al³⁺(Cd²⁺without interference),which caused aggregation of AgNPs,resulting in the color of solution change from bright yellow to reddish-brown.Therefor we could establish a new colorimetric method for simultaneous detection of Cd²⁺and Al³⁺by regulating pH values.Under the optimized conditions,there was a good linear relationship between ratio of the A_580nm/A_390nmand the concentretion of Cd²⁺in the range of 4.2×10^-83.0×10^-6mol/L with detection limit of 11.2 nM and the correlation coefficient r=0.998.There was also a good linear relationship between?A_390nm90nm and the concentration of Al³⁺in the range of 3.6×10^-82.0×10^-6mol/L with detection limit was7.20 nM and the correlation coefficient r=0.996.2.Polyvinyl pyrrolidone?PVP?was used as a functional group on the surface of AgNPs to establish a colorimetric method for the detection of Cr?VI?.It was found that when the pH of the solution was adjusted to 5.5with phosphate buffer solution?PBS?,PVP could selectively coordinate with Cr?VI?,shortening the distance between AgNPs,AgNPs changed from dispersion to aggregation,and the color of solution changed from bright yellow to orange red.Characterization by transmission electron microscopy and particle size analyzers also demonstrated that aggregation of PVP-AgNPs after the addition of Cr?VI?.There was a good linear relationship between ratio of the A_530nm/A_390nmand the concentretion of Cr???in the range of 1.0×10^-72.4×10^-66 mol/L with detection limit of34.0 nM and the correlation coefficient r=0.997.3.In NaCl solution,the adenosine triphosphate?ATP?induced aggregation of L-cysteine?L-Cys?modified AgNPs,and the solution turned from bright yellow to brown.When Hg²⁺was present,the binding of Hg²⁺to ATP causes the aggregation of L-Cys-AgNPs to decrease,and the higher the Hg²⁺concentration,the brighter the solution becomes.Based on this,a simple,safe and rapid method for the visual quantitative detection of Hg²⁺was established.The linear relationship between?A_390nmand the concentration of Hg²⁺in the range of 4.00×10^-81.04×10^-66 mol/L with detection limit was 8.00 nM,and correlation coefficient r=0.998.The recoveries of Hg²⁺were from 91.5%to 109.1%,and the method was successfully applied to rapid the actual water in the detection of Hg²⁺.