Verónica R. Elías

Drug release profiles of modified MCM-41 with superparamagnetic behavior correlated with the employed synthesis method

Mesoporous materials with superparamagnetic properties were successfully synthesized by two different methods: direct incorporation (DI) and wet impregnation (WI). The synthetized solids were evaluated as host of drugs for delivery systems and their physicochemical properties were characterized by XRD, ICP, N2 adsorption-desorption, spectroscopies of UV-Vis DR, FT-IR and their magnetic properties were measured. Indomethacin (IND) was incorporated into the materials and the kinetic of the release profiles was studied by applying the Pepas and Sahlin model. In this sense, materials modified by DI, particularly that with hydrothermal treatment, showed the higher adsorption capacity and slower release rate. This behavior could be associated to the synthesis method used that allowed a high percentage of silanol groups available in the solids surface, which can interact with the IND molecule. This feature coupled with the superparamagnetic behavior; make these materials very interesting for drug delivery systems.

Advances in the study of nano-structured Co/MCM-41 materials: surface and magnetic characterization

Co-modified mesoporous supports with MCM-41 structure and several metal loadings were successfully synthesized by a fast wet impregnation method. The nature and location of different Co species formed on the solids were inferred by TEM/SEM, XPS, XANES/EXAFS, adsorption of pyridine coupled to FT-IR spectroscopy and temperature dependence of magnetization. The presence of Co oxide species (clusters and Co3O4 nanoparticles) inside the channels of all the samples could be evidenced by TEM, XPS and XANES/EXAFS. In this sense, the surface Co/Si atomic ratios obtained by XPS were notably lower than the corresponding bulk Co/Si ratios obtained by ICP, indicating that the Co atoms are mostly incorporated inside the mesopores channels of the silica matrix. Nevertheless, by TEM, Co3O4 nanoparticles of small size segregated on the external surface of the silicate were also observed for the higher metal loadings. The temperature dependence of the magnetization performed for the Co/M(2.5) sample allowed to assign its superparamagnetic behavior to the presence of clusters and Co3O4 nanoparticles of very small size that grow inside the MCM-41 mesopores. Therefore, the analyses presented in this work indicate that a Co theoretical loading of 2.5 wt% leads to the formation of Co oxide nanospecies in the MCM-41 support with a particular superparamagnetic behavior. This sample with improved structural and magnetic properties result an attractive porous solid for drug hosting, to be applied in the field of the controlled release of medicaments.

COMPARATIVE STUDY OF THE PHYSICOCHEMICAL PROPERTIES AND PHOTOCATALYTIC ACTIVITY OF MODIFIED MCM-41 SYNTHESIZED BY DIRECT (ONE-STEP) INCORPORATION AND IMPREGNATION

MCM-41 structures were synthesized and modified by direct (one-step) incorporation (DI) and wet impregnation (WI) methods. The solids were characterized by XRF, XRD, N2 adsorption and UV-Vis DR, and catalytically evaluated in the Acid Orange 7 (AO7) degradation under visible light. Significant influence of the presence, dispersion and location of the different Cr species on photoactivity was evident. Both synthesis methods allowed greater dispersion of the photoactive Cr species for lower metal content, enhancing efficiency for dye degradation. More specifically, after Ti loading in samples synthesized by DI, a notable AO7 degradation increase was associated with the strong heterojunction between Ti and Cr6+ species, which wereare highly dispersed due to the DI method used.