Synthesis and Catalytic Application of Dendritic Fibrous Nanosilica - Nano Metal-Organic Framework Hybrid Nanomaterials

Abstract

This thesis describes the controllable fabrication and catalytic applications of nano metal-organic framework-based hybrid nanomaterials. First, a shape-controllable synthetic protocol for zinc-based coordination polymer nanocubes (Zn-CPNs) is reported. 2,6-bis[(4-carboxyanilino)carbonyl] pyridine ([N3]) ligand is employed as an efficient shape-directing modulator to control the size and shape of Zn-CPNs. The [N3] ligand provides metal binding sites suitable for the decoration of other functional metals such as copper ions. The cooper-modified Zn-CPNs show good activities in a heterogeneous catalytic reaction. Second, the hierarchical design and fabrication of advanced nanohybrids composed of dendritic fibrous nanosilica (DFNS) and DFNS/gold (DFNS/Au) hybrids as the core and zinc-based NMOF (Zn-NMOF) as the shell through a solution-based approach are demonstrated. The combined fibrous morphology of DFNS and micropores of Zn-NMOF can be directly employed for nanospace engineering in the resulting multi-compositional and hierarchical systems in a controllable manner. The DFNS/Au dots@Zn-NMOF nanohybrid shows improved catalytic performance in the Knoevenagel condensation reaction, attributed mainly to the cooperative effect stemming from the suitably organized configurations of each component. Third, the hierarchical preparation of hybrid nanoparticles composed of dendritic fibrous nanosilica (DFNS) and zirconium(IV) -based metal-organic framework (UiO-66-NH2) is investigated. In the synthesis, the formation of DFNS@UiO-66-NH2 nanosystems can be readily controlled by island growth or full coverage of UiO-66-NH2 on the surface of DFNS. Interestingly, the nanospace within DFNS@UiO-66-NH2 structure could be utilized for loading Au/Pd nanoparticles to generate DFNS/Au/Pd@UiO-66-NH2 nanoarchitectures. The obtained DFNS/Au/Pd@UiO-66-NH2 nanohybrids can serve as dual-functional catalysts, performing an enhanced catalytic activity for aerobic alcohol oxidation-Knoevenagel condensation reaction compared to that of individual components. Fourth, a controlled synthesis of gold nanodot assembly within cobalt chalcogenide nanoshell (dots-in-shell Au/CoxSy nanohybrids) is examined. A cobalt-based NMOF (the cobalt-based zeolite imidazole framework, ZIF-67) is used as a versatile sacrificial template to yield dots-in-shell Au/CoxSy nanohybrids. Due to the synergistic effect of the well-dispersed Au nanodots and the thin CoxSy nanoshell, the obtained dots-in-shell Au/CoxSy nanohybrids exhibit enhanced performance for the oxygen evolution reaction (OER) with low overpotential values at a current density of 10 mA cm−2 and a small Tafel slope (343 mV and 62 mV dec–1, respectively).