To analyze the influence of silica surface modification and confined space effects on specific interactions of divalent and trivalent metal cations with surface functionalities, three different high surface area silicas with different pore size distributions were modified with the following organosilanes: 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-(trimethoxysilylpropyl)diethylenetriamine, N-(triethoxysilylpropyl)ethylenediaminetriacetic acid (EDTrA), and 3-(2,4-dinitrophenylamino)propyltriethoxysilane. The silicas were characterized by N(2) adsorption and reflectance FTIR spectroscopy before and after surface modification. N(2) adsorption and pore size distributions showed an increase in the pore width for all EDTrA-modified silicas, opposite to what occurred with the other organosilanes. Adsorption isotherms of Cd(II), Cr(III), Cu(II), and Sr(II) obtained from aqueous solutions were compared and analyzed by silica type, organosilane functional group, and metal adsorbed. Reflectance FTIR spectroscopy was used to probe the acetate functionality in EDTrA as a function of adsorbed metal content. A band shift to higher energy for Cr(III) on the wide pore silica studied indicated that the interaction with the acetate groups can be probed in this manner. In general, the wider pore distribution silica provided larger adsorption maxima, whereas the narrower pore distribution silica provided more favorable ΔG because of stronger binding of the cations. Cr(III) and Cu(II) exhibited larger adsorption maxima compared to Cd(II) and Sr(II), with the grafted organosilanes studied since the first cations have a greater charge/radius ratio than the second ones that provide a greater binding energy.

Ordered mesoporous silicas (OMSs) were prepared at different temperatures by using tetraethyl orthosilicate (TEOS) as a silica source, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (Pluronic F127) as a structure directing agent and sodium chloride as an additive under acidic conditions and microwave irradiation. The small angle X-ray diffraction patterns of these samples indicate the presence of ordered mesopores, while adsorption studies show that they possess high volumes of pores, bimodal pore size distributions and large pore sizes. There is an interesting change in the hysteresis loop of nitrogen adsorption isotherms with increasing temperature of hydrothermal treatment; a delayed desorption characteristic for cage-like mesostructures is observed for the OMS samples treated at 100 and 120 °C, while the hydrothermal treatment at 140 and 160 °C leads to the samples having hysteresis loops characteristic for channel-like materials.

Ethane and disulfide-bridged periodic mesoporous organosilicas have been synthesized under microwave conditions. These materials were obtained by co-condensation of 1,2-bis(triethoxysilyl)ethane and bis(triethoxysilylpropyl) disulfide organosilica precursors and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer template under weakly acidic conditions. Incorporation of bridging groups into the framework and the presence of ordered mesopores were confirmed by nitrogen adsorption at −196°C, transmission electron microscopy (TEM), elemental analysis, and powder X-ray diffraction. The resulting organosilica samples have the specific surface area, single-point pore volume and pore width in the ranges of 960–1220m2/g, 1.14–1.56cm3/g, and 7.1–8.4nm, respectively. TEM images show domains of hexagonally ordered mesopores in these samples, although this ordering is much less pronounced as in the case of purely siliceous SBA-15.

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 degrees 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.

Monofunctional and bifunctional cubic silicas with cage-like structure (FDU-1) containing surface and bridging groups were prepared by one-pot synthesis route using various organosilanes such as tetraethyl orthosilicate (TEOS) along with ureidopropyltrimethoxysilane (UP), 3-mercaptopropylsilane (MP) and bis(triethoxysilylpropyl) disulfide (DS). The aforementioned mesostructures were characterized by X-ray diffraction, N-2 adsorption and elemental analysis.

Two series of ordered mesoporous organosilica (OMO) SBA-15 materials with surface and bridging groups were fabricated by varying the organic precursor addition at different synthesis stages. The consequence of the delayed introduction of organic precursor on the structural and adsorption properties of the resulting OMOs was investigated. The OMOs studied were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and ureidopropyltrimethoxysilane (UPS) as well as TEOS and bis(triethoxysilylpropyl) disulfide (BTDS) in the presence of poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) triblock copolymer Pluronic P123 (EO20PO70EO20). The aforementioned OMOs were characterized by nitrogen adsorption-desorption isotherms at −196 °C and powder X-ray diffraction (XRD). Nitrogen adsorption isotherms were used to estimate the pore volume, mesopore diameter and the BET specific surface area, whereas the XRD data provided information about structural ordering and unit cell of the samples studied.

Channel-like and cage-like mesoporous silicas, SBA-15 ( P6mm symmetry group) and SBA-16 ( Im3m symmetry group), were modified by introducing single ureidopropyl surface groups, mixed ureidopropyl and mercaptopropyl surface groups, and single bis(propyl)disulfide bridging groups. These hexagonal and cubic organosilicas were prepared under acidic conditions via co-condensation of tetraethyl orthosilicate (TEOS) and proper organosilanes using poly(ethylene oxide)- block -poly(propylene oxide)- block -poly(ethylene oxide) amphiphilic block copolymer templates, P123 (EO 20 PO 70 EO 20 ) and F127 (EO 106 PO 70 EO 106 ). The modified SBA-15 and SBA-16 materials were synthesized by varying the molar ratio of organosilane to TEOS in the initial synthesis gel. The removal of polymeric templates, P123 and F127, was performed with ethanol/hydrochloric acid solution. In the case of SBA-15 the P123 template was fully extracted, whereas this extraction process was less efficient for the removal of F127 template from the SBA-16-type organosilicas; in the latter case a small residue of F127 was retained. The adsorption and structural properties of the resulting materials were studied by nitrogen adsorption-desorption isotherms at −196 ∘ C (surface area, pore size distribution, pore volumes), powder X-Ray diffraction, CHNS elemental analysis and high-resolution thermogravimetry. The structural ordering, the BET specific surface area, pore volume and pore size decreased for both channel-like and cage-like mesoporous organosilicas with increasing concentration of incorporated organic groups.

Two cubic cage-like mesoporous silicas, SBA-16 (Im3m) and FDU-1 (Fm3m), with different concentrations of imidazole groups were synthesized by co-condensation of tetraethyl orthosilicate and N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole in the presence of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (EO106PO70EO106) and poly(ethylene oxide)-block-poly(butylene oxide)-block-poly(ethylene oxide) (EO39BO47EO39) triblock copolymers, respectively, under low acidic conditions and with addition of sodium chloride. The polymeric templates used were removed via extraction with acidified ethanolic solution. The organosilicas studied were characterized by nitrogen adsorption, powder X-Ray diffraction, thermogravimetry and elemental analysis. The amount of incorporated imidazole groups gradually increased with increasing concentration of N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole in the synthesis gel. This incorporation was slightly better for FDU-1, which has larger mesopores and mesopore entrances than those in SBA-16. The interplanar d-spacing, total pore volume, pore diameter and specific surface area tended to systematically decrease with increasing loadings of organic ligands. This work reveals that an enlargement of pore openings in the cage-like organosilicas studied can be achieved by controlling time of their hydrothermal treatment. In addition, it was shown that their calcination in air at 550°C caused a complete removal of organic species but this process did not lead to the disappearance of structural ordering in the resulting silica.

Remarkable achievements in the area of pure siliceous mesoporous molecular sieves such as MCM-41, SBA-15, SBA-16 and FDU-1 paved the way for the discovery of periodic mesoporous organosilicas (PMOs). This work reports the effect of organosilane/polymer ratio on the synthesis of PMO with ethane bridging groups inside the SBA-15-type framework. This ethane-silica was obtained by self-assembly of 1,2-bis(triethoxysilyl)ethane (BTESE) precursor and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer Pluronic P123 (EO20PO70EO20) as structure directing agent under low acidic conditions. The amount of triblock copolymer P123 was increased progressively from 0.5 and 3g, while the mass of BTESE in the synthesis gel mixture was kept constant. The polymeric template was removed via extraction with acidified ethanolic solution. The resulting PMO materials were characterized by powder X-ray diffraction, thermogravimetry and nitrogen adsorption at −196°C. The latter was used to evaluate the specific surface area, mesopore width, total pore volume and the volume of complementary pores. The polymer/BTESE weight ratios of 0.73 and 1.46 favoured the formation of additional amorphous silica inside channel-like mesopores, which resulted in plugged hexagonal templated silicas (PHTS) with low mesopore volume, small mesopore size, wide pore size distribution (PSD), thick pore walls and low mesostructural ordering. A further increase in the polymer/BTESE ratio (2.2) led to a material with large pore diameter, narrow PSD, uniform pore openings and high structural ordering. On the other hand, high polymer/BTESE ratios (from 2.93 to 4.39) afforded PMOs with very broad PSD and high non-uniformity of pore entrances as well as low ordering. Furthermore, a complete removal of ethane bridging groups at elevated temperatures in air did not lead to the disappearance of mesostructural ordering in the OMS studied.

Bifunctional periodic mesoporous organosilica was synthesized by co-condensation of tri[3-(trimethoxysilyl)propyl]isocyanurate and 1,2-bis(triethoxysilyl)ethane in the presence of a triblock copolymer template at low acid conentrations. This PMO features high surface area, large pore volume, and channel-like ordered mesopores, the walls of which contain two types of bridging groups, ethane and isocyanurate.

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.

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.