Metal-organic Framework (MOFs) Derived Nanocomposites: Synthesis and Applications in Photocatalysis

Abstract

Metal-organic frameworks (MOFs) are exceptionally porous coordination polymers forming highly crystalline reticular networks via the coordination bonds between organic ligands and inorganic metal clusters. In the past 10 years, MOFs have been proved to be excellent rationally designed precursors and sacrificial templates to derive metal compounds, metal compounds/carbon composites, porous carbons and related nanostructures. The inherited morphologies, adjustable structural and textural properties, in-situ modifiable physicochemical and semiconducting properties make MOFs derived composites excellent nanomaterials for a wide variety of applications in chemistry, physics, electronics and medical sciences. This thesis demonstrates the synthesis of selected Zn-MOFs and Ti-MOFs and their derived functionalised nanocomposites for applications in environment and energy. Briefly, this thesis systematically presents the following research findings: The role of pyrolysis temperature and gaseous atmosphere in Zn-MOF derived composites was studied. Homogeneously dispersed crystalline ZnO nanoparticles embedded in a porous carbon matrix were synthesised via simple one-step carbonisation of MOF-5 at 800 °C and 1000 °C in air, argon and water vapour atmospheres. The resulting carbon doped ZnO, ZnO/C or porous carbon, decorated with hydrophilic functional groups retains the inherited cubic morphology of the precursor MOF-5. Built on the finding of the optimal synthesis conditions for best performing ZnO/C composites, a comparative study of 3 different Zn-MOFs including MOF-5, MOF-74 and ZIF-8 derived ZnO/C nanocomposites was carried out to further understand the structure-property-application relationships. The photocatalytic performance of these derived composites was also evaluated for photodegradation of organic dye pollutants and photocatalytic H2 evolution reaction. Moreover, an in-depth in-situ study was carried out to understand the pyrolytic conversion mechanism of Ti-MOF precursors into the desired TiO2/C nanocomposites. The ¬in-situ TGA-MS and in-situ STEM/EDX combined with other characterisation techniques were employed to investigate the evolution of the structural, physicochemical, textural and morphological properties of the NH2-MIL-125(Ti) derived nanocomposites. Based on the understanding of the thermal decomposition mechanism of NH2-MIL-125(Ti), Cu species were loaded into NH2-MIL-125(Ti) via the post-synthetic method to obtain bimetallic NH2-MIL-125(Ti/Cu). The effect of pyrolysis temperature on the thermal decomposition of NH2-MIL-125(Ti/Cu) under water vapour atmosphere and the subsequent in-situ formation of the p-n heterojunction between TiO2 and CuxO nanoparticles were investigated, and their performance in photocatalytic H2 evolution from water splitting was evaluated.