Dariusz Sternik

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.

Silica with immobilized phosphinic acid-derivative for uranium extraction

A novel adsorbent benzoimidazol-2-yl-phenylphosphinic acid/aminosilica adsorbent (BImPhP(O)(OH)/SiO2NH2) was prepared by carbonyldiimidazole-mediated coupling of aminosilica with 1-carboxymethylbenzoimidazol-2-yl-phenylphosphinic acid. It was obtained through direct phosphorylation of 1-cyanomethylbenzoimidazole by phenylphosphonic dichloride followed by basic hydrolysis of the nitrile. The obtained sorbent was well characterized by physicochemical methods, such as differential scanning calorimetry-mass spectrometry (DSC-MS), surface area and pore distribution analysis (ASAP), scanning electron microscopy (SEM), X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopies. The adsorption behavior of the sorbent and initial silica gel as well as aminosilica gel with respect to uranium(VI) from the aqueous media has been studied under varying operating conditions of pH, concentration of uranium(VI), contact time, and desorption in different media. The synthesized material was found to show an increase in adsorption activity with respect to uranyl ions in comparison with the initial compounds. In particular, the highest adsorption capacity for the obtained modified silica was found at the neutral pH, where one gram of the adsorbent can extract 176mg of uranium. Under the same conditions the aminosilica extracts 166mg/g, and the silica - 144mg/g of uranium. In the acidic medium, which is common for uranium nuclear wastes, the synthesized adsorbent extracts 27mg/g, the aminosilica - 16mg/g, and the silica - 14mg/g of uranium. It was found that 15% of uranium ions leached from the prepared material in acidic solutions, while 4% of uranium can be removed in a phosphate solution.

Adsorption and thermal properties of the bovine serum albumin-silicon dioxide system

The adsorption, electrokinetic, thermal and stability properties of the silicon dioxide (silica, SiO2)/bovine serum albumin (BSA) system were determined. All measurements were carried out as a function of solution pH value. The highest amount of BSA absorbed on the silica surface was observed at pH 4.6 [the value close to the BSA isoelectric point (pI)], which is primarily related to the packed albumin conformation and the lack of adsorbent–adsorbate electrostatic repulsion. At pH 4.6, largest mass decrease was also noticed (thermogravimetric measurements). At pH 3, 7.6 and 9, the adsorption levels were much lower. This phenomenon is associated with the electrostatic repulsion between the BSA macromolecules and the silica particles as well as the expanded BSA structure. During biopolymer adsorption, the whole solid surface is coated with the albumin macromolecules. Then, the properties of the silica particles become similar to those of the BSA macromolecules. In the presence of albumin, the silica pHiep point is identical to the BSA pI value. It should also be noted that the albumin adsorption affects the SiO2 suspension stability. The greatest change was observed at pH 3. Under these conditions, the BSA addition causes electrosteric system stabilization.

Adsorption of citrate ions on hydroxyapatite synthetized by various methods

The specific adsorption of citric acid ions at hydroxyapatite interface was investigated by the means of radioisotope method (14C) as a function of citric acid ions concentration, NaCl concentration and pH. Application of the hydroxyapatite has become wide in the biomaterial field as the Ca10(OH)2(PO4)6 possess biocompatibility with human hard tissue. Hydroxyapatite was synthesized using three different methods. The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical qualities characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of citric acid molecule were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined. Electrical double layer parameters of hydroxyapatite/NaCl interface are influenced by a synthesis method. The points pHpzc and pHIEP for sample 1 are pHpzc 7.5 and pHIEP 3; for sample 2 pHpzc 7.05 and pHIEP 3, for smaple 3 pHpzc 6.7 and pHIEP 3. Temperature has weak influence both on pure substance and with citric acid adsorbed, as derivatographic analysis has shown, and characterization of hydroxyapatite structure may be carried out by this thermal analysis. Two phenomena are responsible for citric acid adsorption: phosphate group’s replacement at hydroxyapatite surface by citric ions parallel to intraspherical complexes formation.

Analysis of the energetic heterogenity of HgBa2Ca2Cu3O8+δ surfaces Q-TG and Q-DTG data

Energetic heterogeneity of adsorbents is conditioned by the differences in topology of adsorption centres, dispersion of pore sizes and other factors. This paper describes theoretical and experimental studies that demonstrate a method for estimation of the energetic heterogeneity of adsorbents by making use of the results from single thermogravimetry Q-TG and Q-DTG curves, recorded under quasi-equilibrium conditions, for preadsorbed liquid on a porous solid surface.

Determination of total heterogeneity and fractal dimensions of high-temperature superconductors

Using thermo-analytical and sorptometric methods physicochemical properties and especially surface heterogeneity of HgBa2Ca2Cu3O8+δ, (Hg-1223) was investigated. The desorption energy distribution was derived from mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption in quasi-isothermal conditions of pre-adsorbed n-octane and water vapour. It is shown that the superconducting Hg-1223 phase is highly sensitive to water vapours. The mechanism of water adsorption depends largely on the activation time. By water vapour saturation in a period of 90 min, physisorption takes place. Prolonged periods result in a chemical decomposition. From nitrogen ad- and desorption isotherms the fractal dimension of superconductors were calculated. A new approach is proposed to calculate fractal dimension from Q-TG curves.

Preparation and properties of organomineral adsorbent obtained by sol–gel technology

Organomineral nanocomposite material has been obtained by sol–gel method through in situ formation of inorganic network in the presence of organic polymer. The most common silica precursor tetraethoxysilane (TEOS) and polysaccharide chitosan solution were used for the sol–gel transformations. The obtained chitosan–silica nanocomposite has been characterized by the physicochemical methods such as differential scanning calorimetry–thermogravimetry–mass spectrometry, Fourier transform infrared spectroscopy–thermogravimetry, elemental analysis, nitrogen adsorption/desorption isotherms, scanning electron microscopy, Fourier transform infrared spectroscopy to determine possible interactions between silica and chitosan macromolecules. Thermal destruction and products from gaseous phase in atmosphere of air and nitrogen were studied. It was found that introducing chitosan in silica network drastically change behavior of polymer during heat treatment in inert atmosphere. Adsorption of microquantities of Zn(II), Cu(II), Fe(III), Cd(II) and Pb(II) cations from the aqueous solutions by the obtained composite has been studied in comparison with the chitosan beads, previously cross-linked with glutaraldehyde. The adsorption capacity and kinetic sorption characteristics of the composite material were estimated. The obtained data were analyzed using the Langmuir and Freundlich isotherms, and the characteristic parameters for each isotherm were determined.

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.

Thermogravimetric and Microgravimetric Studies of the Surface Properties of a High-temperature Superconductor

This paper presents possible applications of thermal analysis, sorptomatic and microgravimetric methods for the study of surface adsorption and porosity properties via the programmed thermodesorption of liquid from the sample. The thermodesorption of liquids under quasi-isothermal conditions demonstrates that the adsorption layers on a high superconductor surface possess non-continuous properties. The degradation of the superconducting properties of an YBa2Cu3O7–δsuperconductor sintered in a CO2-containing atmosphere has been revealed. It is known that atmospheric contaminants such as CO2 and H2O can strongly influence the transition temperature, the critical current density, and the width of the superconducting transition of the YBCO superconductor. Similarly to other liquids adsorbed on solid samples, water induces changes in the physicochemical properties at the interface. A good correlation was obtained between the adsorption and porosimetric, thermal analysis and sorptometric findings. The results prove the applicability of these findings for determination of the adsorption capacity.

Imidazole-2yl-Phosphonic Acid Derivative Grafted onto Mesoporous Silica Surface as a Novel Highly Effective Sorbent for Uranium(VI) Ion Extraction

A new imidazol-2yl-phosphonic acid/mesoporous silica sorbent (ImP(O)(OH)2/SiO2) was developed and applied for uranium(VI) ion removal from aqueous solutions. The synthesized material was characterized by fast kinetics and an extra-high adsorption capacity with respect to uranium. The highest adsorption efficiency of U(VI) ions was obtained for the reaction system at pH 4 and exceeded 618 mg/g. The uranium(VI) sorption proceeds quickly in the first step within 60 min of the adsorbent sites and ion interactions. Moreover, the equilibrium time was determined to be 120 min. The equilibrium and kinetic characteristics of the uranium(VI) ions uptake by synthesized sorbent was found to follow the Langmuir-Freundlich isotherm model and pseudo-second-order kinetics rather than the Langmuir, Dubinin-Radushkevich, and Temkin models and pseudo-first-order or intraparticle diffusion sorption kinetics. The adsorption mechanism for uranium on the sorbent was clarified basing on the X-ray photoelectron spectroscopy (XPS) analysis. The model of UO22+ binding to surface of the sorbent was proposed according to the results of XPS, i.e., a 1:1 U-to-P ratio in the sorbed complex was established. The regeneration study confirms the ImP(O)(OH)2/SiO2 sorbent can be reused. A total of 45% of uranium ions was determined as originating from the sorbent leaching in the acidic solutions, whereas when the basic solutions were used, the removal efficiency was 12%.