Stanisław Pikus

Tailoring properties of SBA-15 materials by controlling conditions of hydrothermal synthesis

The influence of synthesis time and temperature on the properties of SBA-15 is investigated for the samples prepared by using two different silica sources, tetraethylorthosilicate (TEOS) and sodium metasilicate. The samples studied were obtained via two-step synthesis, which involved an initial self-assembly of polymer and silica species at 40 °C for 2 hours followed by longer hydrothermal treatment at higher temperatures. The SBA-15 samples obtained from both silica sources were highly ordered as evidenced by SAXS spectra showing up to seven reflection peaks characteristic of the P6mm symmetry group. While for the samples studied the specific surface area decreased with increasing time and temperature of the hydrothermal treatment, their mesopore size distributions became narrower and their mesopore widths and mesopore volumes showed a tendency to increase. In contrast, a slight decrease in the mesopore wall thickness and micropore volume was observed with increasing time of this treatment. Also, the samples obtained from sodium metasilicate exhibited thicker mesopore walls than those prepared from TEOS. It was shown that the adsorption properties of SBA-15 can be tailored by adjusting the time and temperature of the hydrothermal treatment and simultaneously reducing the time of the initial self-assembly process from 24 h to 2 h.

Bifunctional periodic mesoporous organosilica with large heterocyclic bridging groups and mercaptopropyl ligands

Bifunctional periodic mesoporous organosilicas with large heterocyclic bridging groups and mercaptopropyl surface ligands located on the pore walls are reported. These materials were synthesized by co-condensation of tris[3-(trimethoxysilyl)propyl]isocyanurate, 3-mercaptopropyltrimethoxysilane and tetraethyl orthosilicate in the presence of a block copolymer. They exhibit ordered and uniform mesopores with multifunctional groups of high adsorption affinity towards heavy metal ions such as mercury.

Equilibrium study of selected divalent d-electron metals adsorption on A-type zeolite

The objective of the presented study was to investigate the adsorption of Cu, Co, Mn, Zn, Cd and Mn on A-type zeolite. The isotherms for adsorption of metals from their nitrates were registered. The following adsorption constants K of metals were found: 162,890, 124,260, 69,025, 16,035, 10,254, and 151 [M(-1)] for Cu, Co, Mn, Zn, Cd, and Ni, respectively, for the concentration range 10(-4)-10(-3) M. On the other hand, the investigation of pH influence on the distribution constants of metals showed that the adsorption of metals proceeds essentially through an ion-exchange process, surface hydrolysis, and surface complexation. The supplementary results from DRIFT, scanning electron microscopy, and X-ray diffraction methods confirmed the presumption about the possible connection between the electronic structure of divalent ions and their adsorption behavior, showing that ions with d5 and d10 configurations such as Mn2+, Zn2+, Cd2+, with much weaker hydrolytic properties than Cu2+ and Ni2+, strongly interact with the zeolite framework and therefore their affinity to the zeolite phase is much stronger when compared with that of the Ni2+ ion, but at the same time not as strong as the affinity of the Cu2+ ion, the latter forming a new phase during the interaction with zeolite framework. For Zn2+, during inspection of the correlation between the proton concentration H/Al and zinc concentration Zn/Al on the zeolite surface, the formation of the surface complex [triple bond]S-OZn(OH) was proposed. A correlation between the heterogeneity of proton concentrations H/Al on Me-zeolite surfaces and the hydrolysis constants pKh of Me2+ ions was found.

Uranium sorption on bentonite modified by octadecyltrimethylammonium bromide.

The sorption of U(VI) on octadecyltrimethyl-bentonite was investigated at the pH values of the aqueous phase ranging from 3 to 10 and the concentrations of U(VI): 0.1-1 mmol/dm(3). The concentrations of alkylammonium cation in bentonite were increased from 21% to 150% of CEC (cation exchange capacity). It was determined that the sorption of U(VI) on modified bentonite, i.e. the distribution constant -K(d) decreases with the percent of mineral modification until it attains a minimum at 76% of CEC and then increases again. The effective sorption of U(VI) was found to be in the pH range: 6-10 for the modified bentonite and was explained as the consequence of U(VI) anionic hydroxy complexes sorption. Both FT-IR and XRD spectra of the modified bentonite were analyzed and provided arguments for the existence of surfactant cations in the form of monolayer and bilayer in the interlamellar space of bentonite. In turn the luminescence spectra of bentonite suspensions, i.e. their character at different values of pH, proved the existence of hydroxide-like planar polymeric U(VI) species in the bentonite phase at pH 9.

Application of the SAXS method and viscometry for determination of the thickness of adsorbed polymer layers at the ZrO2-polymer solution interface.

The authors studied the influence of the molecular weight of polyacrylic acid (PAA) and polyacrylamide (PAM), solution pH and ionic strength, and the background electrolyte type on adsorption and the thickness of polyelectrolyte adsorption layers formed on ZrO(2) surface. Carboxyl groups distributed along PAA and PAM chains were shown to be responsible for their interface conformation, which directly influences the thickness of the adsorbed polyelectrolyte layers. Bonding of macromolecules with solid surface occurs through the hydrogen bridges of these groups. Two methods were applied to determine the PAA and PAM adsorption layer thickness on ZrO(2), i.e., SAXS (small angle X-ray scattering) and viscometry. Despite some limitations of the SAXS method resulting from the relationship between the size of solid pores, polymer molecular weight, and conformation of the adsorbed macromolecule, all obtained SAXS results were very close to those calculated from viscometry data.

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.

Factors affecting inulin crystallization after its complete dissolution

In this study, we analyzed inulin crystallization during one year after its complete dissolution and an effect of inulin crystal seeds concentration on rheological and textural properties of inulin gels. 20% and 25% solutions of three different inulins, one native and two high performance (crystal and amorphous), were prepared by heating at 100°C for 5 min. During one year of storage at 20°C, inulin did not form a gel structure, but only precipitates and a crystal layer on the walls of the containers. Addition of crystal seeds (0.02-2%) caused formation of gel structure. Minimal concentration of the crystal seeds necessary to form a strong inulin gel was 0.4%. Crystallographic structure of inulin powder did not have an influence on the formed gels. The obtained results allow inulin gelation to control which can be crucial in novel foods, the structure of which is based on inulin.

Unexpected difference in phenol sorption on PTMA- and BTMA-bentonite

The comparison of phenol sorption on phenyltrimethylammonium (PTMA)- and benzyltrimethylammonium (BTMA)-bentonite shows a clear difference as far as phenol sorption isotherms are concerned. For PTMA-bentonite the sorption isotherm is of a straight-line character which results from simple partitioning of phenol between the aqueous and organic phases sorbed on the bentonite surface. For BTMA-bentonite the isotherm has a convex shape, characteristic of physicochemical sorption. For the first time a three-parametric model, including the dissociation constant of phenol pK(a), distribution constant of phenol Kd(phen) and phenolate anion Kd(phen)(-) between the aqueous phase and the bentonite phases is used for the evaluation of phenol sorption on organoclays with pH change. The model shows that the values of Kd(phen) are higher than those of Kd(phen)(-) for all investigated initial phenol concentrations. The inspection of the FTIR spectrum of BTMA-bentonite loaded with phenol in the regions 1300-1600 and 1620-1680 cm(-1) shows the features of pi-pi electron interaction between the benzene rings of phenol and the BTMA cation together with the phenol-water hydrogen bond strengthened by this interaction.

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.

Adsorption of light lanthanides on the zeolite A surface

Abstract Adsorption studies of light lanthanides on the powdered zeolite type A are presented. It results from the mathematical description of the adsorption isotherms and from complementary scanning electron microscopy (SEM) studies of the adsorbent surface, that heterogeneity of the A type zeolite is most pronounced in the case of lanthanum and cerium, which fact correlates very well with the ability of these lanthanides to hydroxide complexes formation. It was found from the observation of the distribution constants Kd of lanthanides on pH values of the aqueous phase, that lanthanide adsorption proceeds through ion-exchange pathway up to pH 4.9, 4.8, 5.2, 4.0, 4.5 for La, Ce, Pr, Nd and Sm, respectively. For higher pH values surface hydrolysis with evolution of LnpZe3p(OH)q−q seems to be dominant component in the overall adsorption process. The separation of Nd from La, Ce and Pr via adsorption process is recommended.