Functionalization And Catalytic Application Of Mesoporous Organosilica Nanotubes

Organosilica nanotubes is a new type of organic-inorganic hybrid material,which could be easily functionalized through variety methods and perform an important role in heterogeneous catalysis due to its high specific area/mechanical stability,tunable surface hydrophilic/hydrophobic property derived from variety organic components and nanotube confinement effects.This thesis is focused on catalytic performance of catalysts including Palladium nanoparticles loaded on organosilica nanotubes as well as sulfonic acid functionalized organosilica nanotubes on oxidation of benzyl alcohol and hydrolysis of cellobiose,respectively.Furthermore,silica nanotubes doped with carbon quantum dots obtained from high temperature treatment of organosilica nanotubes.We first investigated the effect of morphology and composition of catalysts on the selective oxidation of benzyl alcohol to benzaldehyde.Through a self-assembly process and high temperature treatment,organosilica nanotubes bridged with ethylene and phenylene as well as corresponding carbon doped silica nanotubes were prepared.After that,an impregnation-reduction method was applied to encapsulate Pd nanoparticles into nanotube while pure silica nanotubes and SBA-15 were used as control experiments.The results showed that,organosilica nanotubes catalysts could give higher conversions and yields.Compared to SBA-15 with 2D hexagonal structure,nanotube structure could expose more active sites which makes the reactants more accessible to active sites.On the other hand,the introduction of organic groups enhanced hydrophobility of surface,beneficial to reactants diffusion.Besides,owing to carbon doped in silica nanotubes,99%conversion and 94%selectivity could be obtained maybe because of the increasing of electron transfer rate.Functionalized organosilica nanotubes could be synthesized through the co-condensation of different organosilane precursors under hydrothermal reaction.In the second part of this thesis,sulfonic acid functionalized nanotubes with variety surface acid contents per unit area?acid density?,which are controlled by the amount of mercaptopropyl silane added in precursor,were evaluated in hydrolysis of cellobiose.From the results,catalysts with nanotube morphology possess higher catalytic activity and along with the increase of surface acid density,catalytic effect increases gradually.When the surface acid density rose to 3.35?mol·m^-2,conversion of cellobiose and selectivity of glucose were 92%and 96%at two hours,respectively,while TOF was12.1 h^-1.In addition,compared with sulfonic acid functionalized pure silica nanotubes,organic groups embedded in framework also have a positive effect on this reaction.Carbon-doped silica nanotubes derived from phenylene-bridged nanotubes was etched by hydrofluoric acid and the residue was proved as carbon quantum dots.Clear lattice fringes could be observed in TEM images while Raman scatter spectra indicated a high degree of crystallinity.More importantly,the obtained carbon quantum dots possess obviously UV-vis absorptive and fluorescent properties.