Synthesis And Properties Of Three-dimensionally Ordered Hierarchical Porous Nanomaterials

Nanostructured materials play an importent role in the recent development of many technological fields, such as catalysis, electronics, optoelectronics, medical diagnostics, environmental science, and energy-related systems. Nanomaterials are different from the microsized and bulk materials not only at their dimension scale, but also in the fact that they could possess special physical and chemical properties and provide great significance in various applications. Appropriately designing nanostructured materials with well controlled size, structure, morphologies, and composition has attracted intense attention because they can effectively optimize the catalytic, electronic, optical, and magnetic properties of the nanomaterials. For example, as for the nanomaterials used in the electrocatalysis, it could be a efficient way to improve the catalytic activity and durability of the eleltrocatalysts by controlling the structure, morphology, and size of the materials.Hierarchical porous nanomaterials, which can synergistically show the advantage of each class of pores, have provided substantial property improvements in numerous important applications, such as energy storage and conversion, catalysis, adsorption, filtration, sensing, and biomedical science. Many technologies have been explored to prepare nanostructured materials wich hierarchical porous structure, templated synthesis is one of the most effective strategies, since it is in favour of acquiring high level of synthetic control, especially is suitable to synthesis nanomaterials with orderd structure.In this paper, we prepared hierarchical porous nanomaterials by using the self-assembled colloidal crystals (silica or PMMA opal) as the template, and then tested their performances. The major works and results are summarized as follows:1) Three dimensionally ordered macro-/mesoporous (3DOM/m) Ni catalysts are fabricated by the chemical reduction deposition method using lyotropic liquid crystals (LLC) to template the mesostructure within the regular voids of the PMMA colloidal crystal (opal). The macropore walls of the prepared 3DOM/m Ni exhibit a well-defined mesoporous structure with a narrow pore size distribution of 3-5 nm. The average size of the Ni particles is approximately 4 nm. The 3DOM/m Ni shows greatly enhanced electrocatalytic performance for the hydrogen reduction reaction (HER) compared to the ordered mesoporous (Om) Ni,3D ordered macroporous (3DOM) Ni and Ni nanoparticles (NPs);2) Ordered mesoporous Ni sphere arrays (3D-OMNiSA) are fabricated by using a poly(methyl methacrylate) (PMMA) inverse opal molded from silica opal (colloidal crystal) as a hard template and the lyotropic liquid crystals (LLC) as the meso-structural template. The prepared 3D-OMNiSA catalyst inherits the spherical shape and ordered close-packed face-centered cubic (fcc) structure of the original silica opal architecture. The diameter of the mesoporous Ni spheres is ～290 nm and the mesopore size is in the range of 3-5 nm. The 3D-OMNiSA shows higher oxygen evolution reaction (OER) activity, more favorable kinetics, and higher durability than Ni nanoparticles and the state-of-the-art RuO2 catalyst;3) Cobalt-nitrogen-doped three-dimensionally (3D) ordered macro-/mesoporous carbons (Co-N-OMMCs) are fabricated through a dual-templating synthesis approach in a one-pot controllable procedure by the use of silica colloidal crystal (opal) as a macroporous mold and triblock copolymer Pluronic F127 as a mesoporous template. By varying the mass of Co(NO3)2·6H2O, a series of samples with different Co content were also synthesized. The as-prepared Co-N-OMMCs exhibit ordered face-centered cubic (fcc) macropores with well-defined mesopores locating in the macropore walls. The optimal Co-N-OMMC with a average pore diameter of 11.8 nm and a high BET surface area of 635 m2 g-1 exhibits comparable catalytic activity but much greater durability and tolerance of methanol than commercial 20 wt% Pt/C catalyst for oxygen reduction reaction (ORR) with four-electron transfer process in alkaline medium;4) Based on the self-assembled SiO2 colloidal crystals (opal), three-dimensionally (3D) ordered mesoporous SiO2/SiO2 opal composite was fabricated by a combination of templating synthesis and sol-gel method. Several 3D ordered macro-/mesoporous (3DOM/m) materials, such as 3DOM/m Pt,3DOM/m Pd, and 3DOM/m C have been sucessufully fabricated by the chemical method applying the mesoporous SiO2/SiO2 opal composite as the hard template to form the macroporous and mesoporous structure. The prepared 3DOM/m materials pocess the well-ordered bicontinuous mesopores with 3D interconnected periodic macropores. The high surface area from the mesopores and efficient mass transport from the macropores could contribute to the excellent performace of the materias with 3DOM/m structure in various areas, such as fuel cells, batteries, catalysis, adsorption, and magnetics.