Synthesis And Magnetic Properties Of Rodlike Mesoporous Oxides By Hard Template

Mesoporous materials possess highly ordered pore structures and the porediameter can be adjusted in a wide range from1.3to30nm. Comparing with theconventional mesoporous molecular sieve, mesoporous materials have a higherspecific surface and porosity. Mesoporous materials have been widely used not onlyin the field of adsorption separation, but also have certain application in spacematerials, optoelectronic devices, biological chemistry and assembly nanostructures.Hard template method is one of the most important methods to preparenanomaterials with the uniform and controllable structure and morphology, which isimportant for the discussion of properties. In this paper, we used orderedmesoporous silica material （SBA-15） as hard template to synthesize a series ofrodlike mesoporous oxide nanowire array. And then morphology and pore size ofmesoporous template were adjusted by controlling the sol-gel and hydrothermalconditions. Different series of rodlike mesoporous metal oxide nanowires weresynthesized by hard template, and the magnetic properties were investigated indetail.Firstly, SBA-15hard templates were synthesized with three block copolymer（P123） were used as soft template and TEOS as silicon source in acidic solution bysol-gel and hydrothermal method. The influence of pH value, solution temperature,and hydrothermal temperature on the morphology and microstructure of SBA-15were revealed. All results showed that the pore sizes and morphology of SBA-15could be adjusted by chemical conditions. Rodlike mesoporous SBA-15hardtemplate was successfully obtained with the length of0.9¹.2μm, the diameter of0.3⁰.6μm, And the average pore diameter of the SBA-15nanochannels could beajusted from4to7.5nm.Secondly, mesoporous Co₃O₄nanowires with the different diameter weresynthesized with the above rodlike SBA-15hard templates by nanocasting technique.It was found that the Co₃O₄nanowire arrays presented the similar ordered structures to SBA-15, and the diameter of the nanowires could be controlled with the different SBA-15hard templates. The rodlike CO3O4nanowires have the diameters of3.8nm,4.8nm and7.2nm, respectively, which accorded to the pore size of SBA-15hard templates. The magnetic results show that three kinds of CO3O4nanowires arrays are paramagnetic and saturation magnetization and remanent magnetization hardly changed. Due to the shape anisotropy and finite-size effect, the coercive force decreases gradually with the increase of diameter of CO3O4naowores.Finally, the different series of metal oxide nanowires with4.8nm diameter were synthesized in this way, such as rodlike mesoporous CO3O4, Fe2O3and NiO nanowires arrays. Furthermore, NiO and CO3O4nanowires arrays were paramagnetic while the Fe2O3nanowires presented ferromagnetic properties. These magnetic properties were totally different from those of the bulk samples, in which finite-size effect greatly affected the magnetic performance of three different metal oxides.