The Green Synthesis And Applications Of Fluorescent Silver Nanoclusters In The Detection Of Copper And Mercury Ions

At present,the common methods to detect heavy metals in sewage often use harmful reagents,and there are some shortcomings such as interference.It is urgent to develop some new detection methods with more green environmental protection,fast and convenient detection,low cost and higher accuracy.In recent years,some new fluorescent nanomaterials are expected to be used in this field.Silver nanoclusters have been widely used in ion detection,reaction catalysis,biological imaging and other research due to the advantages of excellent fluorescence properties,high catalytic performance and good biological safety.In this thesis,glutathione was used as the ligand to prepare silver nanoclusters with blue fluorescence by three green synthesis methods,namely,ultrasonic method,ultraviolet method and natural aging method.The effects of temperature,pH value and metal ions in solution on the fluorescence stability of silver nanoclusters were studied.The qualitative and semi quantitative detection of trace copper ions and mercury ions in solution was achieved by using the fluorescence quenching effect of silver nanoclusters under specific conditions.Among the three green preparation methods,the ultrasonic method is the fastest to synthesize fluorescent silver nanoclusters.The 60 W ultrasonic reaction takes only 6min to8 min.The size of the synthesized silver nanocluster is small,about 2nm,and the fluorescence intensity is higher.When the molar ratio of glutathione to silver is 1:1～1:8,the temperature is within 4℃～25℃,and the pH value is within the range of 4.5～5.2,the fluorescent silver nanoclusters can be synthesized by this method,and the best fluorescent performance can be obtained when the molar ratio of glutathione to silver is 1:1,25℃ and pH value is 5.0.It takes about 40min-50 minutes to synthesize the silver nanoclusters by ultraviolet method.Some of the silver nanoclusters grow up and their fluorescence intensity is lower than that by ultrasonic method.The size and fluorescence properties of silver nanoclusters synthesized by natural aging method are similar to those synthesized by ultrasonic method,but the reaction time is 30h～40h,and the reaction rate is slow.It is found that the storage temperature,pH value and different metal ions in the solution may affect the fluorescence stability of the silver nanoclusters.The synthesized silver nanoclusters have almost the same fluorescence performance when stored at 4℃ for several months,but a significant decrease will occur quickly during heat preservation at 40℃.However,we found that adding ascorbic acid as a stabilizer can improve the temperature stability of the silver nanoclusters.The fluorescence intensity of silver cluster is the highest when it is used in the environment of pH 4.2.Both copper ions and mercury ions can quench the fluorescence of silver nanoclusters,but their UV spectra have different characteristics.Copper ions will blue shift the absorption peak of silver nanoclusters from 350 nm to 343 nm,while mercury ions will make the absorption peak of silver nanoclusters weaken and disappear.Based on the spectral response of silver nanoclusters to different concentrations of copper ions and mercury ions,the semi quantitative detection of trace copper ions and mercury ions in solution can be realized.