Silicon-Based SERS Sensors For In Situ Monitoring Of Photocatalytic Process Of MOFs

Surface-enhanced Raman scattering(SERS)spectroscopy is an advanced analytical tool with the advantages of simple sample preparation,multi-component detection and high sensitivity.Therefore,SERS technique has been widely used in chemistry,biology,medicine,and material science.In recent years,silicon-based SERS substrates have received intensive attentions because of their reliable signal reproducibility and significant Raman signal improvement.Metal-organic framework(MOF)materials,also known as porous coordination polymers,is a class of porous crystals with metal ions/clusters as the connection center and organic ligands as the support structure.Their adjustable metal centers and ligands,diversity of material structures,and strong reusability have prompted a growing number of researchers to investigate their photocatalytic processes.In this thesis,two kinds of silicon-based SERS sensors have been constructed using a "borrowing" strategy and shell isolated nanoparticles structure,which are suitable for in situ monitoring of the photocatalytic processes of zeolitic imidazolate framework-67(ZIF-67),zeolitic imidazolate framework-8(ZIF-8)and zirconium benzenedicarboxylate framework-66(UIO-66).The details are as follows:Chapter 1:We briefly review the development of Raman spectroscopy and the recent research focusing on the catalytical analysis by using SERS technique.Next,we introduce the principles of synthesis of MOFs and their semiconductor-like behaviors.In particular,we highlight the advantages of high porosity and tunability of photofunctional MOFs.Afterwards,we briefly introduce the principles of photocatalysis and the antibacterial applications of photofunctional materials.Finally,the main research content and research significance of this thesis are discussed.Chapter 2:We construct a two-dimensional silicon-based SERS sensor and use it to monitor the ·O2-content generated by ZIF-8 during the photocatalytic process.The gold nanoparticles are synthesized homogeneously onto silicon wafers by electrochemical reaction principle,followed by in situ growth of ZIF-8 shell layer using zinc nitrate hexahydrate and 2-methylimidazole as precursors,finally yielding the zeolitic imidazolate framework-8@gold nanoparticles@silicon(ZIF-8@AuNPs@Si)substrate.When ZIF-8 generates superoxide radicals(·O2-)under photocatalytic conditions,superoxide dismutase(SOD)catalyzes the disproportionation reaction of ·O2-to produce hydrogen peroxide(H2O2).H2O2 converts the non-Raman-active leucomalachite green(LMG)into Raman-active malachite green(MG)through an oxidation reaction,capable of SERS detection.The constructed SERS sensor has a suitable linear detection range(0.1 μM-1 mM),good signal reproducibility(relative standard deviation of 16.83%),as well as high sensitivity(detection limit of 103 nM).The ZIF-8@AuNPs@Si substrate is further applied to in situ monitor the photocatalytic reaction of ZIF-8,with the concentration of ·O2-being 6.3 μM at 120 min.Chapter 3:A type of three-dimensional silicon-based shell layer isolated nanoparticle-enhanced Raman sensor(3D-SHINERS)is firstly fabricated,with reliable signal reproducibility(relative standard deviation:12.55%)and suitable linear detection range(0.1 μM-1 mM).Then ZIF-67,ZIF-8,and UIO-66 are modified on the 3D-SHINERS sensor to construct ZIF-67@3D-SHINERS,ZIF-8@3D-SHINERS,and UIO-66@3D-SHINERS sensors,respectively.In the photocatalytic experiment,the resultant MOF@3D-SHINERS substrates are capable of capturing the characteristic 1616 cm-1 peak of MG molecules in real-time manner,and the linear relationship transformation yields the concentration of ·O2-at 120 min as 10.26 μM(ZIF-67@3D-SHINERS),6.64 μM(ZIF-8@3D-SHINERS),and 0.24 μM(UIO-66@3D-SHINERS),respectively.Mechanism investigation indicates that the electrons of ZIF-67 are most readily excited to the conduction band,thus being ready to produce the ·O2-.We further explore the resultant MOF@3D-SHINERS sensor to reveal the best photocatalytic ability of ZIF-67,with antibacterial efficiency of 95%for Staphylococcus aureus(S.aureus)and 99%for Escherichia coli(E.coli),respectively.Chapter 4:Firstly,we summarize the main research contents of the thesis,and then we present the innovation points of this thesis in combining silicon-based SERS technology and photocatalysis research,as well as the shortage of monitoring MOF species and propose the corresponding improvement plans.In summary,two kinds of silicon-based SERS sensors,i.e.,ZIF-8@AuNPs@Si and MOF@3D-SHINERS,are constructed in this thesis.The first class of substrate combines AuNPs@Si with ZIF-8 and employs MG as the probe molecule,which is suitable for in situ quantitative investigation of ZIF-8 photocatalytic production.The second type of substrate combines 3D-SHINERS sensor with MOF,which is able to achieve in situ quantitative studies of photocatalytic production and predict antibacterial properties of ZIF-67,ZIF-8,and UIO-66.