Construction And Properties Of Titania/Silver Nanocom-posites Mediated By Metal-Organic Frameworks

Water pollution caused by pesticides and organic dyes have been a serious threat to human health.Therefore,efficient detection and removal of the above pollutants in water are of great significance for the protection of human health.Precious metal-semiconductor composites combine the advantages of precious metals and semiconductors,and are prone to produce synergistic effects in precious metals and semiconductors,which have attracted researchers’attention in the fields of surface enhanced Raman spectroscopy（SERS）detection and photocatalytic degradation.It is known that the Raman signals of the target analytes can be enhanced by precious metal Ag due to the local surface plasmon resonance（LSPR）effect.Furthermore,the Fermi energy level of Ag is lower than the conduction band of TiO₂semiconductor,which is conducive to the transfer of TiO₂ electrons and the separation of electron/hole pairs.Therefore,TiO₂/Ag nanocomposites are often used in SERS detection and photocatalytic degradation of pollutants.However,some key problems in the TiO₂/Ag nanocomposite systems restricted its development and further application,such as high loading of silver,easy aggregation of silver particles,and low detection and degradation performances of pollutants.Metal organic frameworks（MOFs）exhibit excellent adsorption capacity due to their large specific surface area and adjustable pore size.Moreover,the distribution of metal nanoparticles can be regulated,and thus more“hot spots”will be generated.Subsequently,pollutants can be effectively enriched,which is conducive to improving the detection and degradation performance of materials.Based on this,three metal-organic framework-mediated titanium oxide/silver nanocomposite systems were constructed and used for SERS detection and photocatalytic degradation of organic pollutants in wastewater.The main contents are as follows:1.Aimed at obtaining a new type of bi-functional materials for highly efficient SERS detection and photocatalytic degradation of organic pollutants,a low content of Ag nanoparticles（0.5 wt.%Ag）anchored flower-like 2-methylimidazole zinc metal organic frameworks（ZIF-8）induced by TiO₂/Zn sheet was facilely constructed without adding any reductants or UV-light reduction.With p-aminothiophenol（PATP,a typical pesticide）as an analyte,SERS and photocatalytic degradation performances of the resulting Zn/TiO₂/ZIF-8/Ag（Zn-TZA）sheet were evaluated.The cost-effective Zn-TZA sheet exhibited high SERS activity and excellent stability towards PATP detection,and its detection limit can reach 1×10^-11 mol·L^-1.In addition,the Zn-TZA sheet showed high and stable photocatalytic performance for PATP degradation.In particularly,by means of the plug and play Zn-TZA,the detection and degradation of PATP in real samples can also be effectively achieved.The strong coupling and electron transfer among Ag NPs,TiO₂/Zn,and ZIF-8 in the Zn-TZA sheet were very advantageous to enhancing the bi-functionality.Additionally,the increased enrichment of PATP on the special sheet was also an important factor for the enhanced bi-functionality.It will provide new ideas for designing competitive bi-functional materials that are used to detect and degrade organic poisons in waste water.2.By hydrothermal method,MIL-53（Fe）was in-situ induced by means of TiO₂,and further the growth and distribution of Ag were controlled by the mediation of the MIL-53（Fe）.Subsequently,a low cost（only 0.5 wt.%Ag）TiO₂/MIL-53（Fe）/Ag nanocomposite（TMAg）with tight heterojunction was constructed.The composition,morphology and structure of TMAg were characterized by X-ray diffraction（XRD）,transmission electron microscope（TEM）and X-ray photoelectronic spectroscopy（XPS）in detail.The SERS activity and photocatalytic degradation of crystal violet（CV）by TMAg were studied,and its stability was also evaluated.The results showed that the detection limit of CV on the TMAg can be as low as 8×10^-11 mol·L^-1,and the high SERS activity can be maintained within 40 days.In addition,CV can be completely degraded in the presence of the TMAg within 21 minutes of illumination,and the high activity can still be maintained after five degradation cycles.Additionally,the SERS detection and photocatalytic degradation performance of the TMAg for CV in actual water samples were further studied,and the possible mechanisms of SERS detection and photocatalytic degradation of the TMAg for CV were discussed.3.By hydrothermal method,MIL-53（Fe）was in-situ induced by means of TiO₂,and further the growth and distribution of Ag-Cu were controlled by the mediation of the MIL-53（Fe）.Subsequently,the TiO₂/MIL-53（Fe）/Ag-Cu nanocomposites（TMAgCu）with low cost（only0.5 wt.%Ag-Cu）and tight heterojunction were assembled.The composition,morphology and structure of TMAgCu nanocomposites were characterized by various means.The SERS detection and photocatalytic degradation performances of the TMAgCu nanocomposite for CV were studied,and its stability was also evaluated.The results showed that the detection limit of CV on the TMAgCu can be as low as 1×10^-11 mol·L^-1,and high SERS activity can be maintained within 40 days.Furthermore,CV can be completely degraded by the TMAgCu within 15 minutes of illumination.Importantly,the TMAgCu possessed higher activity and lower cost than TMAg.It was also found that,after five degradation cycles,high degradation activity of the TMAgCu for CV can still be maintained.In addition,the SERS detection and degradation performance of the TMAgCu for the CV in actual water samples were studied,and the possible mechanisms of SERS detection and photocatalytic degradation of CV were discussed.This work will provide a theoretical and experimental basis for the construction of low-cost multifunctional materials for the detection and treatment of organic dye pollutants in water.In this thesis,by introducing two kinds of MOFs into TiO₂/Ag or TiO₂/Ag-Cu systems,respectively,three kinds of MOFs medited TiO₂/Ag-related nanocomposites were constructed.It provides new ideas in the assembly,performance and mechanism of those nanocomposites used in SERS detection and photocatalytic degradation of pesticides and organic dyes in waste water.