Synthesis And Properties Of Functional Micro-Nanometer Silica Materials

The synthesis and properties of functional silicon dioxide micro-nanometer materials were studied.These studies on Phytoliths,super-microporous silica and heterodimers of SiO₂-Ag nanoparticles are helpful to synthesis and application of silica materisals,and can provide a potential application for zea mays and others.1.Phytoliths and silica in zea maysPhytoliths,opal phytoliths,or plant opal,are minute biogenic structures of silica that's deposited,depending on the species of plant,between the cells,within the cell walls,or even sometimes completely infilling the cells themselves.It is known that there are lots of silica in gramineous plants,in this paper phytoliths in its stalk,leaf and root of zea mays were focused on.The morphology of phytoliths were studied in different conditions such as under the combustion,in acid(hydrochioride,sulfate,nitric acid)soulution,through acid and alkali method,and using the enzyme(mixture).Firstly,the combustion in 500℃can give the morphology of phytoliths in the micro-meter level;then silica nanoparticles in the nano-meter level were obtained in different acid solution.We found that the best process is in the nitric acid solution,and the nano-silica obtained have the diameter of 200nm.When the enzyme was used to treat the plant,the phytoliths is not affected,but the cellulose,hemicellulose,hemicellulose,lignin in zea mays can be decomposed,and their morphology were destroyed.At last,these silica materials formed in different experiments were characterized by microscope,TEM, SEM,FTIR,XRD,EDS etc.2.Synthesis of super-microporous silica materialsAccording to the definition,porous materials can be divided into three types depending on their pore size(diameter,d),micro-(d＜2nm),meso-(2nm＜d＜50nm), and macroporous materials(d＞50nm).In this section,super-microporous materials with smaller pores of 1.0-2.0nm were discussed.Mesoporous materials are usually synthesized templated by self-assembly of surfactants through sol-gol chemistry process,but in recent years,small biological molecules as a new falmily of template have been reported more and more.Several small-molecular hydrogels(Fmoc-D-Ala-D-Ala-OH,Fmoc-D-Ala-L-Tyr-OH, Fmoc-D-Ala-L-Thr-OH)are considered as the templates to synthesize the super-microporous silica,and they were characterized by different techniques such as Ultraviolet spectrophotometry(UV),fourier transform IntraRed(FTIR),X-ray diffraction(XRD),TEM,HRTEM,Nitrogen adsorption-desorption technique.The results showed that the pore diameter was between 1.0-2.0nm,which is in the range of super-micropores materials.And the maximum of BET specific surface area above 880.353m²/g.3.Modification of SiO₂ and synthesis of heterodimers of SiO₂-Ag nanoparticlesIn this section,nano-silica were synthesized by TEOS and silane coupling agent(A-151 and KH570)have good hydrophobic property.The surface morpholgy of nano-silica before and after modification was studied.It is verified that modification of nano-silica can be carried out through this method.The analysis of FTIR proved that the A-151 and KH570 has been successfully grafted on the surface of nano-silica. Analysis of XRD proved that nano-silica have the amorphous structure.TEM showed that the modified nano-silica can be dispersed in organic reagent such as ethylalcohol etc.In addition,the heterodimers of SiO₂-Ag nanoparticles were synthesized on hydrophilic and hydrophobic surface of nano-silica.On hydrophilic surface,the smaller nanoparticle can form the heterodimers easily,however,the bigger particles normally form multimers.On hydrophobic surface,the dimers can be formed in the low temperature.The innovations in the thesis are as follows:1.This paper focued on the phytoliths in zea mays,and the morphology of phytoliths were studied after combustion,in acid(hydrochloride,sulfate,nitric acid) soulution,through acid and alkali method,and using the enzyme(mixture).Finally, the silica nanoparticles were investigated through the phytoliths.2.Some small-molecular hydrogels(incloud Fmoc-D-Ala-D-Ala-OH,Fmoc-D-Ala -L-Tyr-OH,Fmoc-D-Ala-L-Thr-OH)were used as the new templates to synthesize the super-microporous silica materials.3.Through the simply method,silica nanoparticles were synthesized directly by TEOS and silane coupling agents.The heterodimers of SiO₂-Ag nanoparticles were synthesized on the hydrophilic and hydrophobic SiO₂ nanoparticles.