Microfluidic Chip-Based Synthesis Of （AuNR@Ag）-PANI Janus Nanoparticles And Their Application As A SERS Substrate For Hg²⁺Detection

As a conductive polymer,polyaniline(PANI)possesses not only good stability in the air and excellent conductivity,but also unique electrochemical properties and chemical sensing properties.Making composites of PANI with inorganic nanoparticles,especially with noble metal particles is a conventional method to improve the physical and chemical properties of PANI.Compared with pure PANI,the activities of PANI composite with noble metal have been dramatically improved in chemical sensing,electrocatalysis and other aspects.In the present thesis,(AuNR@Ag)-PANI Janus nanoparticles with good dispersity and uniform morphology were prepared on the basis of microfluidic droplet technique.The particles were used as active substrates of surface-enhanced Raman scattering(SERS),rapid and sensitive detection of mercury ions was realized.In chapter one,the preparation methods of Janus particles and the applications of Janus particles in sensing and analysis were summarized.The preparation methods of noble metal-polyaniline nanocomposite particles and their applications in electrochemistry and sensors were reviewed.The concept of microfluidic technology and the advantages of microfluidic droplet platform in preparing nanoparticles were introduced.Finally,the purpose and design of this thesis were proposed.In chapter two,Au nanorods(NRs)and(AuNR@Ag)-PANI Janus nanoparticles were prepared based on microfluidic droplets,and the products were characterized.Firstly,AuNRs were prepared by using seed growth method in microfluidic droplets,and the effect of three-phase flow velocity on the aspect ratio of AuNRs was investigated.Thereafter,with the same microfluidic chip,the gold nanorods were used as precursors for preparing Janus nanoparticles in the microfluidic droplets.Due to the high efficiency of mixing in the microenvironment,Ag+ could be reduced on the surface of gold nanorods,which induced the oxidation and polymerization of aniline monomers on one side of gold nanorods,and thus(AuNR@Ag)-PANI Janus nanoparticles were formed.The reaction time was shortened from 24 h to 6 h,and the batch difference of Janus nanoparticles produced using the conventional methods was avoided.The as-prepared particles were evenly distributed and had uniform size and special asymmetrical morphology.In chapter three,the Raman spectra of(AuNR@Ag)-PANI nanoparticles were studied.Under the electromagnetic coupling effect of gold and silver nanostructures,the Raman characteristic peak signal of polyaniline was enhanced.Based on the positive correlation between Raman signal intensity of PANI and the concentration of Hg2+ within a certain range,a rapid and sensitive sensing method for Hg2+ was established.The method showed good selectivity and sensitivity,and had a linear range of 1.0×10-9-1.5×10-7molL-1 and a detection limit of 9.7×10-10 mol L-1.Hg2+ in the river water and tap water was analyzed and spiked using the SERS sensing strategy,and the method was proved to be applicable.In chapter four,the preparation method of(AuNR@Ag)-PANI Janus nanoparticles and the detection method using the particles as SERS active substrates were summarized and forecasted.