Shih-Yuan Chen

Synthesis and catalytic activity of amino-functionalized SBA-15 materials with controllable channel lengths and amino loadings

Aminopropyl-functionalized SBA-15 mesoporous materials (NH2-SBA-15) with different lengths of channeling pores and aminopropyl loadings up to 2.6 mmol g−1 were synthesized by one-pot co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyltrimethoxysilane (APTMS) with the aid of appropriate amounts of Zr(IV) ions and NaCl. The morphologies and pore lengths of the resultant materials were tuned by varying the Zr/TEOS and NaCl/TEOS molar ratios in the synthesis gels. The assembly processes were examined by in situsmall-angle X-ray scattering (SAXS) and conventional characterization techniques. Accordingly, TEOS prehydrolysis for around 2 h in the synthesis solution before the addition of APTMS was essential for preparing platelet NH2-SBA-15 materials with well-ordered p6mmpore structure and narrowly distributed pore size distribution, due to the strong interference from APTMS. When applying these materials as solid base catalysts in solvent-free flavanone synthesis, the platelet material with short-channeling poresca. 200–300 nm was superior to the rod-like and fiber-like counterparts with lengthy channels in the micrometre scale due to better molecular diffusion and less possibility of pore blockage. Furthermore, the platelet materials with high surface areas (∼450 m2 g−1) and amino loadings around 1.4–1.8 mmol N g−1 were the most efficient catalysts for flavanone synthesis, and the high activity was retained by a simple regeneration method.

Tuning pore diameter of platelet SBA-15 materials with short mesochannels for enzyme adsorption

A novel route for preparing highly ordered platelet SBA-15 materials with short mesochannels (ca. 200 nm) and large pore diameters up to 12 nm is reported for the first time. Appropriate quantities of Zr(IV) ions and trimethylbenzene (TMB) were added to the conventional SBA-15 synthesis solution to obtain platelet SBA-15 (SBA-15-p) materials with expanded pores. Based on the results of conventional characterization techniques and in situsmall-angle X-ray scattering experiments, the key step to obtain a well-ordered 2D hexagonal pore structure without vesicle contamination was the pre-hydrolysis of tetraethyl orthosilicate (TEOS) in the Zr(IV) containing synthesis solution for about 25 min before adding TMB as the pore swelling agent. The resultant SBA-15-p materials had high surface areas (∼800 m2 g−1), large pore volumes (∼1.2 cm3 g−1) and short mesochannels (∼200 nm). More importantly, the mesopore diameters Φa_BdB, analyzed by a modified Broekhoff-de Boer method with the Frenkel-Halsey-Hill equation (BdB-FHH) on the nitrogen adsorption isotherms, could be finely tuned to 7–12 nm by varying the amount of swelling agent and the hydrothermal temperature. When adsorbing cytochrome c enzyme at pH 4–10, the short-channel SBA-15-p materials demonstrated higher adsorption capacities and adsorption rates compared to conventional fiber-like SBA-15 materials (SBA-15-f). Furthermore, the uptakes of cytochrome c enzyme per surface area increased significantly on the large pore materials.

Effect of calcination on the structure and catalytic activities of titanium incorporated SBA-15

Well-ordered Ti-incorporated SBA-15 materials (shortly termed Ti–SBA-15) with Ti loading up to 10 mol% of Si were prepared by a one pot co-condensation method using tetraethyl orthosilicate (TEOS) as the silica source and titanium oxychloride as the Ti source in an acidic environment close to the isoelectric point of silanol groups (pH = 1.27–2.37). The Ti–SBA-15 materials with Ti/Si ratios smaller than 0.05 were curved solid tubes, while those with the Ti/Si ratios between 0.05–0.1 possessed platelet morphology and short mesochannels (ca. 150–500 nm). Titanium was homogeneously distributed in the silica framework of the as-made Ti–SBA-15 materials as isolated Ti species when the Ti/Si ratios were lower than 0.03. It formed small TiO2 nanocrystallites when the Ti loading was further increased or after the materials were calcined at temperatures higher than 500 °C. It is noteworthy that tetrahedrally coordinated Ti(IV) species were generated on the superficial areas of SBA-15 silica framework upon calcination at 600–1000 °C. These tetrahedrally coordinated Ti(IV) species not only stabilized the mesopore ordering up to 950–1000 °C, but also acted as effective catalytic sites in cyclohexene epoxidation.

Effect of combination sequence of precursors on the structural and catalytic properties of Ti–SBA-15

The combination sequence of Ti and Si precursors (TTIP and TEOS) in the synthesis solution of Ti-incorporated SBA-15 mesoporous silica (shortly termed Ti–SBA-15) was found for the first time to be critical for the distribution of tetrahedrally (Td) coordinated Ti(IV) sites in the resultant Ti–SBA-15. It was found that TTIP pre-assembled with P123 in the synthesis solution for 3 h before the addition of TEOS gave Td-coordinated Ti(IV) sites predominately incorporated near the superficial regions of the framework and were highly accessible to the reactants in catalytic reactions.

Acid-Free synthesis of mesostructured silica materials in a triblock copolymer-based system

Mesostructured silica materials with tunable pore structure including mesoporous cellular foam and worm pore structure have been synthesized in the acid-free condition by using P123 triblock copolymer as the pore directing agent in the presence of salt and co-solvent.