Synthesis Of Monodispersed Amino-functionalized Mesoporous Silica Nanoparticles With Large Pores

Mesoporous silica nanoparticles (MSNs) have been attached considerableattentions during the last decades, and have been widely utilized in the fields ofadsorption, separation and catalyst, especially biological application, such asbiomedical imaging, biocatalysis, biosensing, gene and drug delivery. The mostwidely used type of MSNs is MCM-41, with a pore size less than5nm. In some cases,such as catalysis or biomolecule (enzyme, protein, and DNA) immobilization, thepore size is a vital factor. MCM-41typed MSNs are not suitable in those areas due tosmall pores tending to limit the diffusion of large guest molecule. Thus large pore sizeis crucially needed, and it is critical to find a facile method to synthesize MSNs withlarge pores. In this dissertation, by finely tuning the reaction parameters, wesuccessfully synthesized two kinds of monodispersed amino-functionalized MSNswith large pores and diverse porous structures.The synthesis of large pore MSNs was realized by using Pluronic P-123as atemplate,(3-aminopropyl) triethoxysilane (APTES) and tetramethoxysilane (TMOS)were both as precursors, and the reaction was carried out at room temperature. Theobtained nanoparticles are uniform with an average particle size about200nm，whichis presented from TEM image and consistent with the hydrodynamic particle size of220nm determined by dynamic light scattering (DLS). The acid-extracted particles inwater shows a strong positive zeta potential (approximately30mV), which is due tothe amino-functionalized derived from the APTES. The size of nanoparticles can beeasily tuned from50nm to200nm by the addition of different amount of APTES.With a higher concentration of TMOS, nanofibers with large pores could also be prepared. BET surface areas were determined as274m~2/g for acid-extracted samplesand475m2/g for calcined samples. The BJH pore sizes were about11and9nm foracid-extracted and calcined samples, respectively, which agreed well with the size ofthe mesopores detected by TEM (about10nm). Finally, we discussed the formationmechanism of the large pore MSNs.TMB is widely used as a swelling agent and can enlarge the pore size ofmesoporous materials. However, by employing TMB into our reaction system,nanoparticles with hierarchically porous structure can be clearly observed from SEMand TEM images. The nanoparticles have a relative uniform particle size, rangingfrom100-150nm, and a strong positive zeta potential. The hierarchically porousstructure is consist of10-15nm uniform mesopores,30-50nm foam-like pores, and50-100nm macropores composed of concave surfaces and hollow particles. Thehierarchically porous structure is attributed to the P-123micelle and microemulsionformed by the additional TMB, corresponding to the mesopores and macropores，respectively. Due to the structure lose of nanoparticles by the expansion of pore size,concave surface and hollow structure, the BET surface area has a large decreasecompared with uniform large pore MSNs synthesized in the absence of TMB.It’s worth noting that both the uniform and hierarchically MSNs with large poresare amino-functionalized, which can be easily modified, and these large pore MSNswill be good candidates for the loading of polymer and biomolecule, thus have highpotential in the applications involved macromolecule.