Preparation And Performance Of Novel Functional Mesoporous Metal Oxides

Ordered mesoporous materials with high surface and numerous nanoscale pore channels are attracting much attention because of their unique applications in catalysis, optics,electrics,magnetism,nanotechnology,and sensors et al.Many efforts have been devoted to study the synthesis and applications of these materials since 1992.A great numbers of mesoporous materials with the different composition,structure,pore size and morphology have been obtained through the different methods.The composition of pore-walls changed from silica to different metal oxide,metal sulfide, and further many mesostuctures with pure organic or inorganic-organic framework. The mesoporous composite materials with several functional actions are attracting the increasing attention.Varsities of synthetic techniques,i.e.Sol-Gel,Hydrothermal, Ultrasonic,Nanocasting,Coating,Grafting et al,have been used to prepare ordered mesoporous materials by soft-template or hard template route.However,many challenges and difficulty need to be overcame in the large-scale production and application of ordered mesoporous materials.The general synthetic methods with simple,fast,inexpensive and environmental-friendly properties must be developed to obtain the ordered mesoporous materials with high quality,i.e high thermal and hydrothermal stability.The new potential function of the different mesoporous materials should be study in detail for their more widely application in new fields.Ordered mesoporous metal oxides with high surface have already attracted much attention because of their numerous potential applications.In contrast to mesoporous silica materials,metal oxides mesostructure often show their special properties such as the different composition,structure,and these metal oxides reveal a large amount of potential applications in catalysis,optics,electrics,magnetism et al.Wide efforts have been made over the past decade to develop new methods for the preparation of these mesoporous materials.However,owing to their complexity of reactive properties and chemical stability intrinsic in the desired constituents,as well as the difficult control of hydrolysis,polymerization,cross-linkage,and inorganic-organic assembly,most oxides are disordered or hybrid-mesostructured by soft-template route, that is,more distinct for multicomponent mesoporous solids.It is not general although several methods have been applied into controlling the hydrolysis of inorganic precursors,for example,relying on metal chlorides and coordination.Recently,the nanocasting technique using mesoporous silica and carbon as hard template represents the other important opportunity for synthesis of ordered nonsiliceous mesoporous metal oxides materials.The most fascinating success is the replication of mesoporous carbon materials.Unfortunatly,other inorganic replicas are not as successful that normally consist of disordered nanowires or nanoparticles without long-range periodicity owing to the partial loadings of precursors inside the mesopores and the fast growth of guest molecules outside the mesopores.How to promote the filling of guest into the hard host is therefore an urgent task,especially for metal oxide precursors.In general,it is still a focus to develop the effective synthetic methods for mesoporous metal oxides with novel properties.Here we developed a novel and generalized one-step wetness impregnation nanocasting pathway that can drive concentrated inorgnic precusors into the channels of hard template in one time.A series of ordered cubic mesoporous rare earth oxides with high surface and amorphous structure have been firstly prepared,and this method can also be successfully extended to obtain ordered crystalline mesoporous metal oxides with high surface such as Co₃o₄,Cr₂O₃,NiO et al..Unlike the traditional nanocasting process,we attempt to produce the high negative pressure in the internal-pores of hard template,which not only results in the more available space of host template and but also provides guest precursors incorporation with a powerful directional,transportation force from the large difference of pressure between internal-pores and external-pores.In the second section,a novel general route has been developed to introduce high copper species into the block copolymer templated mesoporous materials such as silica or polymer.The general key is that a large amount of copper oxalate can be in-situ produced by the oxidation of block copolymer in a special solution containing copper ions.Based on it,the one-step direct method has been applied to obtain CuO loaded(～37.5wt%)large-pore mesoporous SBA-15 with well-dispersed properties in ethanol-water solution.Cubic mesoporous silica with even higher CuO loading (-45.3wt%)also was directly prepared by the simple adjustment of copper precursor amount in the same system.Two kinds of CuO modified mesoporous silica show the enhanced catalytic properties,in comparison to mesoporous CuO/silica obtained by the traditional impregnation method.Besides,we successfully obtain copper oxalate nanowires inside the nanoscale channels of mesoporous silica when the hybrid mesoporous silica composites obtained was treated in this special solution.Especially, as we known,it is the first 1D organic coordination compound nanowires inside the mesoporous channels.Furthermore,we have testified that large-scale and high intensity copper oxide nanowires embedded in the mesoproous channels can be also easily given by calcinations of mesoporous CuC₂O₄/SBA-15 composites.This special method easily overcomes the remarkable difficulty to introduce two absolutely different species of organicmetallic salt into the mesoporous channels.It can also be widely applied to create copper species nanostructures inside block polymer-templated mesoporous channels and obtain useful copper species-modified mesoporous functional materials.Mesoporousγ-Fe₂O₃ with nanocrystalline walls and high surface area has already been synthesized using mesoporous CMK-3 carbon as hard template.TEM images show the worm-like mesostructure of as-prepared sample. Brunauer-Emmett-Teller analysis shows that it has high surface area(187m²g^-1)and large mesopore size(5.0nm).To the best of our knowledge,so far it is superparamagnetic mesoporousγ-Fe₂O₃ samples with the highest surface area,which maybe enhances its properties such as magnetic storage,catalysts,and potential electrodes et al.At the same time,Magnetic properties of iron oxide have also been characterized by Mo"ssbauer spectra and magnetization curve measurements.We developed a new low-cost synthetic procedure to obtain worm-like mesoporous silica using environmental friendly and industrial grade cation alkyl polyglycoside as structure-directing agents.What is more,mesoporous carbon materials can be obtained through the direct pyrolysis in N₂ of silica/ cation alkyl polyglycoside composites with trace mount H₂SO₄ as catalyst,which is the first sample prepared by the direct pyrolysis of structure-directing agents in worm-like mesoporous silica channels.Furthermore,mesoporous carbon synthesized shows more effective absorption performance for fuchsine dyes in aqueous solution than commercial active carbon.In the final section,with a short synthetic period,highly ordered mesoporous titania with crystalline anatase walls has been synthesized through modified sol-gel method in a nonaqueous solution.Trace mount Ce³⁺addition did not affect the synthetic period,and remarkably enhanced the thermal stability of mesoporous titania resulting in the formation of mesoporous titania with crystalline framework. Crystalline mesoporous titania exhibits excellent properties in photo oxidation ofα-methystyreme to acetophenone.