Construction And Optoelectronic Applications Of Multifunctional MOF-based Noble Metal Porous Composites

As the economy grows,food safety issues and environmental pollution have become two major problems in the world today.Firstly,there is a lack of effective means to detect illegal or excessive addition of chemicals in the field of food safety,and surface-enhanced Raman spectroscopy（SERS）,which is characterized by fast,sensitive and accurate,can effectively accomplish the detection of such analytes,but the traditional noble metal SERS substrates are costly,single material and complicated to prepare.In this work,metal-organic framework（MOF）materials are introduced to prepare new SERS substrates for the detection of different kinds of chemicals.Secondly,the environmental field urgently needs the emergence of new clean energy to replace the highly polluting traditional energy（fossil fuel）.Traditional clean energy sources such as solar and wind energy have problems of high equipment costs,high power transportation losses,and significant geographical differences.As a new clean energy source,hydrogen is non-polluting to the environment,highly efficient and easy to produce,especially hydrogen production by electrolysis of water under the action of electrocatalyst is the most ideal way to produce hydrogen.However,the cost of conventional electrocatalysts is high,so this thesis introduces MOF materials with modified treatment as electrocatalysts to assist electrolysis of water for hydrogen production.To solve the above problems,this thesis addresses the construction of multifunctional MOF-based-noble metal porous composites and their applications in the field of SERS and electrocatalysis,as follows:（1）Preparation and SERS performance of three-dimensional porous ZIF-noble metal plasmonic composites.The rhombic dodecahedral ZIF-67 nanomaterial with regular porous structure was efficiently prepared and its morphology was optimized and controlled by a simple hard template method,and the flexible porous ZIF-67 thin film SERS substrate was constructed by uniformly dispersing it on the surface of aluminum foil.The SERS enhancement effect of ZIF-67 itself was verified by using two probe molecules,Rhodamine 6G（R6G）and Methylene blue（MB）,and the selective enhancement ability of ZIF-67 was verified by changing the probe molecule and the laser wavelength.The mechanism of selective chemical enhancement of surface probe molecules by ZIF-67 dominated by charge transfer transition resonance.Then,the particle size and pore size of porous ZIF-67 were regulated,and the optimal porous ZIF-67substrate with a pore size of 200 nm and a particle size of 1.2μm was screened by SERS performance.In order to improve the detection capability of the substrate,a new three-dimensional porous composite substrate Au@ZIF-67 was constructed by physical dispersion deposition of an Au layer with a thickness of 180 nm on the surface of the porous ZIF-67 film.The porous Au@ZIF-67 flexible composite substrate can effectively detect the gas-liquid two-phase analyte molecules.It can qualitatively detect not only1000 ppm of gaseous benzaldehyde molecules,but also 1 ppm of malachite green and100 ppm of butylated hydroxytoluene antioxidant and 800 ppb of fomesin pesticide molecules below the national standard for pesticide residue limits in food,demonstrating the effectiveness of this substrate for chemical detection in the food safety field.（2）Preparation and electrocatalytic performance of porous Au@Co_xS_y nanoflowers Firstly,C-ZIF-67 with regular porous structure was simply prepared by the hard template method,and then the porous C-Au@ZIF-67 material loaded with Au nanoparticles was prepared by Na HB₄ ice-water bath reduction.On this basis,the C-Au@Co_xS_ynanoflowers with excellent oxygen evolution reaction（OER）performance were obtained by sulfide etching.The subsequent analysis of the material morphology,OER properties,electrochemical activity area,and Co elemental valence state explored the mechanism of porous structure,adding Au nanoparticles,and sulfide treatment to enhance the catalytic activity of OER.With the combined effect of multiple strategies,the overpotential of C-Au@Co_xS_y material at a current density of 10 m A cm^-2 is as low as 340 m V,which is much lower than 420 m V of commercial Ru O₂.And after chronoamperometry test for28,000 s,C-Au@Co_xS_y can still maintain 92.65%of the initial current with good stability.Not only that,compared with the traditional commercial Ru O₂,the C-Au@Co_xS_y material also showed better electrocatalytic performance and stability in the application of water electrolysis for hydrogen production,proving that the material can be applied in the field of water electrolysis.