Environmental mineralization of caffeine micro-pollutant by Fe-MFI zeolites.

Environmentally emerging micro-pollutant, caffeine, was mineralized (i.e., full degradation) by the isomorphic incorporation of Fe into silicalite-1 (mordenite framework inverted (MFI) structure zeolite) through a microwave synthesis method. The Fe incorporation conferred mesopore formation that facilitated caffeine access and transport to the MFI zeolite structure. Increasing the Fe content favored the formation of Fe(O)4 sites within the MFI structure. The catalytic activity for the degradation of caffeine increased as a function of Fe(O)4 sites via a Fenton-like heterogeneous reaction, otherwise not attainable using Fe-free pure MFI zeolites. Caffeine degradation reached 96% (TOC based) for zeolites containing 2.33% of Fe.

Hydrothermal stability investigation of micro- and mesoporous silica containing long-range ordered cobalt oxide clusters by XAS.

This work investigates the hydrothermal stability of cobalt doped silica materials with different Co/Si molar ratios (0, 0.05, 0.10, and 0.25). The resultant materials were characterized by N2 sorption and chemical structures by Raman and X-ray absorption spectroscopy before and after a harsh hydrothermal exposure (550 °C, 75 mol% vapour and 40 h). The cobalt silica materials showed a lower surface area loss from 48% to 12% with increasing Co/Si molar ratio from 0.05 to 0.25 and relatively maintaining their pore size distribution, while pure silica exhibited significant surface area reduction (80%) and pore size broadening. For low cobalt loading sample (Co/Si = 0.05), the cobalt was highly dispersed in the silica network in a tetrahedral coordination with oxygen and a small proportion of Co-Co interaction in the second shell. Long range order Co3O4 was observed when Co/Si molar ratio increased to 0.10 and 0.25. The hydrothermal exposure did not affect the local cobalt environments and no cobalt-silicon interaction was observed by X-ray absorption spectroscopy. The hydrothermal stability of the silica matrix was attributed to the physical barrier of cobalt oxide in opposing densification and silica mobility under harsh hydrothermal conditions.

Modulation of microporous/mesoporous structures in self-templated cobalt-silica.

Finite control of pore size distributions is a highly desired attribute when producing porous materials. While many methodologies strive to produce such materials through one-pot strategies, oftentimes the pore structure requires post-treatment modification. In this study, modulation of pore size in cobalt-silica systems was investigated by a novel, non-destructive, self-templated method. These systems were produced from two cobalt-containing silica starting materials which differed by extent of condensation. These starting materials, sol (SG') and xerogel (XG'), were mixed with pure silica sol to produce materials containing 5-40 mol% Co. The resultant SG-series materials exhibited typical attributes for cobalt-silica systems: mesoporous characteristics developed at high cobalt concentrations, coinciding with Co3O4 formation; whereas, in the XG-series materials, these mesoporous characteristics were extensively suppressed. Based on an examination of the resultant materials a mechanism describing the pore size formation and modulation of the two systems was proposed. Pore size modulation in the XG-series was caused, in part, by the cobalt source acting as an autogenous template for the condensation of the silica network. These domains could be modified when wetted, allowing for the infiltration and subsequent condensation of silica oligomers into the pre-formed, mesoporous cages, leading to a reduction in the mesoporous content of the final product.