Mechanism Research And Performance Evaluation Of Different Materials Induced Nanoparticle Aggregation Enhanced Laserinduced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy?LIBS?,as an emerging method of atomic spectroscopy,has gradually developed into a cutting-edge analysis method in the field of spectral analysis.LIBS is widely used in many fields such as geological exploration,metallurgical analysis,cultural heritage,jewelry identification,industrial analysis and environmental monitoring due to its advantages of rapid analysis,no complex sample pretreatment,in-situ detection and remote online monitoring.In recent years,the water pollution problems caused by toxic metals such as nickel,chromium and lead have aroused people's eager attention.LIBS technology has great potential in liquid sample detection because of its unique advantages.However,compared with other mature elemental analysis techniques,the problem of low sensitivity caused by plasma quenching restricts the development of LIBS technology in practical applications.Under this background,we have studied different materials induced nanoparticle aggregation enhanced laser-induced breakdown spectroscopy technique,and evaluated the analytical performance of the technique applied to liquid samples.The main research results and innovations obtained are as follows:?1?Designed and built LIBS experimental optical platform.The laser pulse energy,delay time,optical path transmission system,signal receiving system and sample position were optimally adjusted to avoid minor changes in the optical path system affecting the repeatability of the experimental results.The Au nanoparticles?Au NPs?with the best size were screened according to the spectral information of LIBS,which laid the foundation for the mechanism research and performance evaluation of different materials induced nanoparticle aggregation enhanced laser-induced breakdown spectroscopy.?2?Considering the low sensitivity of LIBS technology caused by plasma quenching,the combination of liquid-solid matrix conversion technology and metal chelate induced Au nanoparticle aggregation technology were used to study the mechanism of LIBS signal enhancement.In addition,the analytical performance of the above techniques applied to heavy metals?Cd,Cu,Ag,Pb and Cr?in water was evaluated.In the experiment,sodium diethyldithiocarbamate?DDTC?as a low-cost universal chelating agent achieved the pre-enrichment of target elements at first;Then,the metal chelate solution reacted with the Au NPs solution and induced the aggregation of Au nanoparticles.Finally,microporous filter membrane as the sample carrier achieved the morphological transformation of the liquid-solid phase.As a result,the proposed method overcomed the problem of plasma quenching in liquid samples,significantly improved the signal intensity of target elements,and obtained lower detection limits in a shorter time(the LODs of Cd,Cu,Ag,Pb,and Cr were 4.6,1.5,3.4,3.5,and 3.5 ng·m L^-1,respectively).The LODs of target elements were notably 7?10times lower than those of chelating reagent enrichment alone and 3?4 orders of magnitude lower compared to traditional LIBS methods,which proves the sensitivity of the LIBS technology was greatly improved.?3?Based on the basic starting point of nanoparticle enhanced LIBS technology and solid-liquid conversion,in this paper,metal organic frameworks?MOFs?,Au NPs and portable LIBS instrument were combined for the first time to achieve the sensitive detection of target elements?Pb,Cr?in liquid samples.The LODs of Pb,and Cr were 8.0 and 4.2ng·m L^-1,respectively.The LODs of target elements were notably 8?10 times lower than those of the MOFs enrichment alone and 4 orders of magnitude lower compared to traditional LIBS methods,which realizes another new breakthrough in the traditional liquid analysis methods.The great improvement in seneitivity can be attributed to the following aspects:First,the synthesized MOFs have a special structure like"flowers"and the gap between"petals"and"petals"can accommodate a larger volume of liquid samples,which increases the contact area between the MOFs material and the target elements.In addition,the exposed metal binding sites?N-H?further increased the enrichment efficiency of target elements;Second,Au NPs as an auxiliary reagent for pretreatment of liquid samples increased the spatial range of the plasma light during the interaction between laser and matter,thus improving the efficiency of laser ablation.