Nanostructured Porous Functional Materials:Design, Synthesis And Applications In Sorption And Catalysis

Over the past several decades, porous materials have gained unprecedentedly practical apllications in the field of sorption, catalysis, biomedicine and electrochemistry, and have also been widely applied in our daily life, owing to their outstanding structural properties including high surface area, high pore volume, controllable nanopore structure and various chemical compositions. However, with the fast development of our society and economy, the problems about energy crisis and environment pollutions have been more and more challenging. Unfortunately, the conventional porous materials such as zeolites and mesoporous silica can only make a little contribution. So developing multifunctional porous materials is being highly desirable. Recently, numbers of publications reveal that engineering the structure of porous materials on the nano level is an efficient and advanced method to introduce various multifunctionalities into porous materials. Porous functional materials with different structures, kinds, functionalities and applications can be obtained via designing the nanostructures or integrating various functional nanoparticles with porous materials. Although there are all kinds of porous materials, engineering the nanostructures of materials is almost limited to mesoporous silica. Therefore, in order to expand the functionalities and applications of porous materials, designing and constructing the nanostructures of other porous materials is more and more important.This thesis is based on the perspective of the functionality of porous materials, and further engineers the nanostructures of periodic mesoporous silica(PMO) materials and porous noble metal materials. The goal of this thesis is to develop new strategy for preparing nanostructured porous functional materials, invent novel nanostructured porous functional materials and further explore the practical applications of these materials in the field of sorption and catalysis.In the chapter Ⅱ, we develop a new strategy of growth-induced etching for preparing hollow structured PMO materials. This simple, efficent and highly controllable strategy is a one-step route. Hollow structured PMO nanospheres with different shell thicknesses, particle diameters and bridged organic groups could be obtained via adjusting the reaction conditions. Moreover, this strategy can be extended as a general method for fabricating yolk-shell structured PMO nanomaterials. Becase of the co-existence of a hydrophobic-O1.5Si-Ph-SiO1.5- unit and a hydrophilic-SiO2- unit in the framework, these marterials show unique amphiphilicity and even could be used as good particle emulsifiers for O/W or W/O emulsions in various systems. Most importantly, owing to the hollow nanostructures, the amphiphilic frameworks and highly ordered radial mesochannels, these nanostructured PMO materials exhibit excellent performances in the field of sorption of contaminants in water and catalytic reactions proceeding in green solvent water. Moreover, we believe that this efficient strategy would offer a platform for designing various nanostructured functional materials for the applications in sorption, drug delivery, bio-imaging, sensing and heterogeneous catalysis.In the chapter Ⅲ, we report one new class of one-dimentinal(1D) PMO helical nanotubes and demonstrate their applications in the removal of contaminants from water. The chiral mesoporous silica helical nanorods are used as the hard templates for preparing 1D PMO helical nanotube with perpendicular mesochannels in walls via a growth-induced etching strategy and simple chiral transfer. This approach is simple, efficient and highly controllable. PMO helical nanotube with different wall thicknesses, aspect ratios, curvatures and bridged organic groups could be obtained via adjusting the reaction conditions. Similar with the PMO hillow spheres, these PMO helical nanotubes show unique amphiphilicity and even can be used as superior particle emulsifiers for fabricating O/W or W/O emulsions with different morphologies in various systems. Most importantly, owing to the interstitial 1D hollow cavities, amphiphilic frameworks and highly accessable mesochannels, these PMO helical nanotubes exhibit excellent performances in the removal of contaminants from water with an ultrahigh sorption capacity(1800–3000 mg/g), which was much higher than those of mesosilica nanotubes and conventional MCM-41, and even comparable to those of some sponges. We believe that these amphiphilic 1D hollow porous nanostructured materials will have great potentials in various applications such as water treatments, templated synthesis, bio-medicine and Pickering interfacial catalysis.In the chapter Ⅳ, we report a series of amphiphilic nanoreactors and demonstrate their applications in the catalytic reactions proceeding in green solvent water. Firstly, one new kind of amphiphilic nanoreactor is constructed through encapsulating bimetal Au@Pd nanoparticles with an amphiphilic porou hollow shell. Owing to the unique yolk–shell nanostructure, the high hydrothermal stability and the enrichment effect for hydrophobic organics in water, this amphiphilic nanoreactor shows excellent catalytic activity and stability in aerobic oxidation of alcohols in water using air as an oxidizing agent under atmospheric pressure, which is much higher than that of hydrophilic SiO2 nanoreactors and hydrophobic C nanoreactors. Secondly, we design and prepare a series of amphiphilic nanoreactors with high laoding of metal species, high catalytic activity and high catalytic stability through incorporating porous noble metal nanoparticles into an amphiphilic porou hollow shell. Owing to the ultrathin subunit and highly open structure of porous noble metal nanoparticles and the unique structural properties of amphiphilic porou hollow shell, this nanoreactor shows unexceptionable catalytic activity and stability in aerobic oxidation of alcohols in water. Finnaly, these amphiphilic nanoreactors are successfully applied in the one pot aerobic oxidation-aldol condensation cascade reaction and show superior catalytic performances, which means that one-step synthesis of α,β-unsaturated ketones from alcohols has been achieved. Obviously, this will provide an efficient and green method for preparing relevant fine chemicals. We believe that these amphiphilic nanoreactors will have great potentials in the catalytic reactions proceeding in water and interfacial catalysis.In the chapter Ⅴ, we report one new class of porous noble metal Rh nanostructures and demonstrate their excellent catalytic performances. Using cetyltrimethylammonium bromide(CTAB) and I- as the structure-directing agent, water as the solvent, RhCl3 as the metal precursor, ascorbic acid(AA) as the reducing agent, respectively, we prepare highly porous Rh nanospheres(HPRhS) with uniform morphology and particle size under hydrothermal conditions. The formation process involves in a typical seeding/overgrowth mechanism. The surfactant CTAB and I- play the critical role in the formation of HPRhS, in which the CTAB is responsible for the highly porous feature and the I- regulates the uniform spherical morphology and particle size. Moreover, when increasing the concentration of Rh precursor, the particle size increases from 28 nm to 55 nm, and the worm-like mesochannels transform to an ordered oriented radially mesopore array. Furthermore, core-shell structured Pd@Rh porous bimetal nanostructures can be fabricated under similar conditions for HPRhS. Most importantly, owing to the ultrathin subunit, the highly open structure, the ultrahigh surface areas and the most exposed active atoms on the surface, HPRhS exhibits excellent catalytic activity for the hydrolytic dehydrogenation of ammonia borane, whose turnover frequency(TOF) value is much higher than those of pure noble metal catalysts and even higher than those of noble metal-based multimetal catalysts. HPRhS also shows excellent catalytic activity, selectivity and stability for the selective hydrogenation of phenol, which is much higher than those of commercial Rh/C catalyst and conventional Rh nanoparticles. We believe that these highly active Rh catalysts will have great potentials in the various catalytic reactions.