Mesoporous material systems for catalysis and drug delivery

Resumen

This study evolved to its last form primarily around the development of a hybrid material is the core of the work . This hybrid material is then further explored for two different applications which are catalysis and drug delivery . A nanoassembly was established around a mesoporous silica support. SBA-15 was picked as this support among the other mesoporous silica dueto its well-defined pore structure and accessible pore volume. The silica framework was doped with Zr-atoms and the pores partly infiltrated with Cu nanoparticles resulting in a hybrid material with tunable properties. SBA-15 was synthesized by a sol-gel method where a micellar solution was employed as a template for the silica framework. To achieve the doped version, a Zr precursor was added to the synthesis solution. The effects of different synthesis conditions on the final material were investigated. lt was observed that changes in these synthesis conditions yielded different particle morphology, pore size, and specific surface area. The infiltration method is based on functionalizing the (Zr-) SBA-15 support surfaces before the Cu ion attachment whereas EIWI is based on slow evaporation of the liquid from the (Zr-)SBA-15 - Cu aqueous suspension. Both methods are designed to yield preferential growth of Cu NPs in the pores with a diameter smaller than 1O nm and in oxidized form. However, depending on the infiltration method used different chemical states of the final material is achieved, i.e. Zr content and porous network properties are different. Cu-Zr-SBA-15 nanoassembl ies were used for the catalytic conversion of C02 into valuable fuels such as methanol and dimethyl ether (DME). The effect of different chemical states of the catalyst was investigated. lt was found that the Si precursor had a considerable impact on the overall performance of the catalyst whereas the Cu loading method (lnf or EIWI) changed the catalytic selectivity between DME and methanol. The activity of the catalyst was further investigated in a time-evolution study where the accumulation of each product in the gas phase and the molecular groups attached to the catalyst surface were recorded over time. Accordingly, thermodynamic equilibrium was achieved on the 14th day of the reaction under 250ºC and 33 bar. The resulting total C02 conversion was 24%, which is the thermodynamically highest possible conversion, according to theoretical calculations. lt was also concluded from the experimental results that, DME is formed by a combination of two methoxy surface groups . Additionally, the formation of DME also boosts the total C02 conversion to fuels, which otherwise is limited to 9.5%. The design of Cu-Zr-SBA-15 was also investigated for drug delivery applications, dueto its potential as a biomaterial, e.g. , a filler in dental composites, and the antibacterial properties of Cu. Also, the bioactivity of Si02 and Zr02 was considered to be an advantage . With this aim, Cu infiltrated Zr doped SBA-15 material was prepared by using TEOSas the silica precursor and the lnf-method to grow Cu NPs. The performance of the final material as a drug delivery vehicle was tested by an in-vitro delivery study with chlorhexidine digluconate. The nanoassemblies show a drug loading capacity of 25-40% [mg drug 1 mg (drug+carrier)] . The drug release was determined to be composed of two steps. The presence of Zr and Cu limits the burst release and beneficially slows down the drug release process. The effect of pore properties of SBA-15 was explored in a study where the antibiotic doxycycline hyclate was loaded in SBA-15 materials with different pore sizes. lt was observed that the pore size is directly proportional to the drug loading capacity [mg drug 1 mg (drug+carrier)] and the released drug % (the released drug amounUtotal amount of loaded drug). The release profile was fast, dueto its weak interactions with the SBA-15 and smaller size molecule compared to chlorhexidine digluconate.