Rafal M. Grudzien

Effective method for removal of polymeric template from SBA-16 silica combining extraction and temperature-controlled calcination

An effective method for the removal of polymeric template, which combines extraction and temperature-controlled calcination, is proposed to obtain high pore volume and large pore size ordered mesoporous silicas, SBA-16 (Im3m symmetry group), synthesized in the presence of sodium chloride at low acid concentrations using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic F127) as a structure directing agent and tetraethylorthosilicate as a silica source. The aforementioned materials were characterized by small angle X-ray powder diffraction, nitrogen adsorption, high resolution thermogravimetry and elemental analysis.

Effect of polymer-to-silica ratio on the formation of large three-dimensional cage-like mesostructures

This work shows the influence of polymer-to-silica ratio on the formation of cage-like ordered mesoporous silica, FDU1, having a three-dimensional face-centered cubic symmetry. The FDU1 samples studied were synthesized from tetraethyl orthosilicate (TEOS) under acidic conditions in the presence of poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) (EO39BO47EO39) triblock copolymer. The molar ratio of triblock copolymer to TEOS in the reaction mixture was varied from 0.0037 to 0.0148. Small angle X-ray scattering, argon adsorption–desorption and high resolution thermogravimetry studies indicate that an optimal EO39BO47EO39/TEOS ratio, which led to a high-quality FDU1 material with uniform cage openings, narrow pore size distribution and high specific surface area, was about 0.0074. The FDU1 silicas obtained for lower and higher ratios than the aforementioned value possessed non-uniform cage entrances, broader pore size distributions, lower BET specific surface areas and smaller mesopore diameters.

Cage-like mesoporous organosilicas with isocyanurate bridging groups synthesized by soft templating with poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) block copolymer

Ordered large-pore organosilicas with isocyanurate bridging groups were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS) in the presence of poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) (EO(39)BO(47)EO(39)) B50-6600 template under acidic conditions. It was shown that the extraction of the B60-5500 triblock copolymer with acidified ethanol solution was insufficient to remove completely the template; however, calcination of as-synthesized and extracted samples under air atmosphere at 200 degrees C, 250 degrees C and 300 degrees C caused not only the removal of the polymer but also a substantial decomposition of the ICS groups. In contrast, the heat treatment of extracted organosilicas at 360 degrees C in flowing nitrogen was able to fully remove the residual template without degradation of the ICS bridging groups. Characterization of the resulting materials by small angle X-ray scattering (SAXS) and X-ray powder diffraction (XRD) revealed that isocyanurate-containing organosilicas have a body-centered cubic symmetry (Im3m). Argon adsorption-desorption isotherms of these organosilicas revealed cage-like mesopores, high surface areas and large pore volumes. The diameters of spherical cages were found to be very uniform in the range of 12-14 nm. A complete removal of triblock copolymer was confirmed by high-resolution thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR) and CHNS elemental analysis (EA). The latter showed that the isocyanurate rings are intact in the framework and their loading is up to 1 mmol g(-1). Moreover, these organosilicas were also synthesized using low acid concentration, double amount of polymer and sodium chloride; in this case the template was completely extracted and there was no need for additional heat treatment.

Influence of synthesis time on adsorption properties of FDU1 materials

FDU1 ordered mesoporous silicas with cage-like structure were synthesized using a triblock copolymer template EO 39 BO 47 EO 39 from tetraethyl orthosilicate under acidic conditions. It was reported previously that the structure of FDU1 is a face-centered cubic (Fm3m) with 3-dimensional hexagonal intergrowths. Recent studies of FDU1 have been focused on its thermal and hydrothermal stability, exploration of microwave-assisted synthesis, improvement of the mesopore uniformity by salt addition, and tailoring the size of cage-like mesopores and pore entrances by controlling temperature and time of the hydrothermal treatment. In this work a series of the FDU1 samples synthesized at room temperature by varying time of the self-assembly process was studied by gas adsorption, small angle X-ray scattering and high resolution thermogravimetry. A special emphasis was given on the adsorption study of the FDU1 samples to examine the effect of the synthesis time on their adsorption and structural properties.

Effects of Hydrothermal Treatment and Template Removal on the Adsorption and Structural Properties of SBA-16 Mesoporous Silica

The evolution of the adsorption and structural properties of large-pore SBA-16 silica samples was studied in relation to hydrothermal treatment and template removal procedures. These samples were synthesized using the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer Pluronic F127 as the structure-directing agent and tetraethyl orthosilicate as the silica source in the presence of hydrochloric acid (low concentration) and sodium chloride under various hydrothermal treatment conditions. The concomitant use of the recently reported two-step template removal procedure, which combines solvent extraction and low-temperature calcination, afforded the SBA-16 samples with large pore volumes, high surface areas, uniform cages and uniform cage openings as demonstrated by nitrogen and argon adsorption isotherms measured at −196°C. Small-angle X-ray diffraction spectra confirmed the existence of the Im3m symmetry group (body-centred cubic pore structure) for the samples studied. The efficiency of the aforementioned template removal method was confirmed via thermogravimetric analysis.