Viktor Hronský

The effect of acid treatment on the structure and surface acidity of tetraalkylammonium-montmorillonites.

The effect of tetrabutylammonium (Bu4N+) and tetrapentylammonium (Pe4N+) cations on the modification of the organo-montmorillonite structure upon acid-treatment was investigated. Samples were treated with HCl for various times (2-12 h). Structural changes were followed by MAS NMR spectroscopy. The 29Si MAS NMR spectra of initial Na-saturated form (Na-SAz) showed gradual decrease of the intensity of the resonance assigned to SiO4 cross-linked in the tetrahedral sheets Q3(0Al) while signals arising from the reaction product Q31OH and Q4(0Al) became more pronounced upon acid treatment. The Q3(0Al) signal almost completely disappeared for Na-SAz treated for 8 h on contrary to Bu4N-SAz and Pe4N-SAz showing signal of relatively high intensity even after 12 h. The 27Al MAS NMR measurement proved that more than one half of Al remained in the reaction product of Bu4N-SAz and Pe4N-SAz after 8 h treatment, while Al content dropped below 5% for Na-SAz. Formation of acid sites was investigated via pyridine adsorption. Only physically adsorbed and H-bonded pyridine was detected for acid-untreated samples. In contrast, the IR spectra of the samples partially decomposed in HCl revealed bands of pyridine adsorbed on Brønsted acid sites. Strongly bonded pyridine was able to bear up heating even at 230°C.

Spectroscopic study of water adsorption on Li+, TMA+ and HDTMA+ exchanged montmorillonite

The potential of IR and NMR spectroscopy in characterization the interaction of water with natural and organically modified montmorillonites was introduced. Organoclays were prepared from Li-saturated montmorillonite (Li-S) and tetramethylammonium (TMA) or hexadecyltrimethylammonium (HDTMA) salts. The influence of organic cation size on the water vapour uptake was examined and a comparative study with natural clay mineral was provided. The near-IR spectra confirmed the reduced water content in TMA-S and HDTMA-S. After exposure of the samples to water vapour under various relative humidities (RH) the H2O content was determined. According to the adsorption isotherms the amount of water decreased in order Li-S>TMA-S>HDTMA-S. The intensities of the 2νOH and [Formula: see text] bands, corresponding to the vibrations of H2O, gradually increased in hydrated samples. The (13)C MAS NMR and near-IR of hydrated organoclays confirmed the presence of H2O close to the cations headgroup. NMR signals of inner -CH2- groups in HDTMA-S were also affected by hydration: the intensity of disordered gauche conformers (31.1 ppm) overtook the intensity of ordered all-trans conformers (33.0 ppm).

Characterisation of crumb rubber modifier using solid-state nuclear magnetic resonance spectroscopy

Crumb rubber (CR) can be used for binder modification or aggregate replacement in asphalt mixtures for road construction, when it is usually referred to as CR modifier (CRM). CRM elastic properties depend on the quality of parent material and storage conditions of final material. They deteriorate in time due to degradation processes and among other things they can influence CRM swelling capacity during asphalt rubber preparation. The presented paper demonstrates the sensitivity of basic nuclear magnetic resonance (NMR) parameters (proton spin-lattice relaxation time T1, proton spin–spin relaxation time T2 and the line broadening in 13C NMR and 1H NMR spectra) for detecting changes in CRM degradation. These NMR parameters are proposed to be used to assess CRM degradation before application in asphalt mixtures. In laboratory conditions, CRMs with different degrees of degradation were prepared by thermal ageing at 85°C for 0–36 days.

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse 13C NMR spectra and spin-lattice relaxation times T1(1H), detected indirectly via 13C carbons, and T1(13C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the 13C NMR lines and proton spin-lattice relaxation times T1(1H). The spin-lattice relaxation times T1(13C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.

β-Cyclodextrin-epichlorohydrin polymer/graphene oxide nanocomposite: preparation and characterization

In this study, we report a novel and simple technique to synthesize water-insoluble nanocomposite macromolecule composed of graphene oxide (GO) nanosheets and β-cyclodextrin (β-CD) polymer. These nanocomposites were synthesized by the one-pot precipitation polymerization process via polycondensation of β-CD with epichlorohydrin (ECH) in an aqueous suspension of GO under alkaline condition. The obtained β-CD polymer/GO (CDP-ECH/GO) were characterized by thermal gravimetry, differential scanning calorimetry, infrared and Raman spectroscopies, high-resolution solid state 13C NMR, X-ray diffraction, electron microscopy (both SEM and TEM), and energy dispersive spectroscopy. Furthermore, the mechanism of CDP-ECH/GO nanocomposites formation is also discussed depending on the type of mixing device that has been used during polymerization. The swelling ratio of the nanocomposites as well as their absorption properties toward methylene blue (MB), phenol (PN), 1-naphtol (1-NPH) and 2-naphtol (2-NPH) have been determined. Increasing the GO content in the nanocomposites results in an increase of the adsorption capacity of the materials.

Photo-switchable nanoporous silica supports for controlled drug delivery

A photo-responsive ligand 7-[(3-triethoxysilyl)propoxy]coumarin (C) was grafted on the surface of a mesoporous silica SBA-12 material. The obtained functionalized support SBA-12_C was used as an effective light-controlled storage/release system of the anti-inflammatory drug naproxen. Irradiation with UV light at 365 nm induces the photo-dimerization of the coumarin on the surface, giving a dimer connected by a cyclobutane ring, leading to pore closure. However, irradiation with UV light of a shorter wavelength, 254 nm, leads to the cleavage of the dimers, opening of the pores, and the guest drug molecules can be released from the pores. The release of the drug was studied in two types of media, a simulated body fluid at pH = 7 and a simulated gastric fluid at pH = 2. The prepared materials were characterized by high resolution transmission electron microscopy (HR-TEM), nitrogen adsorption/desorption, infrared spectroscopy (FT-IR), thermoanalytical methods (TG/DTA) and liquid and solid-state NMR spectroscopy. The amount of released drug was monitored by HPLC chromatography at defined time intervals. The samples with pores closed by coumarin dimers were tight enough to show premature release of the drug from the sample. After light-driven pore opening, the amounts of released naproxen from coumarin modified mesoporous silica were different, depending on the pH conditions of the release media.

Problems with Solidification of Fly Ashes from the Municipal Solid Waste Incineration

One of the negative aspects of MSW (municipal solid waste) incineration is production of hazardous fly ashes. MSW fly ash usually contains heavy metals like for example chromium, lead, cadmium and organic substances (dioxins, furans), soluble compounds (salts) and other harmful substances. According to environmental legislative and with respect to the environment fly ash as a hazardous waste should be stabilized before landfilling. This work deals with certain problems occurring at solidification process of MSW fly ash by cementation. This work also describes efficiency of stabilization by two different binders (slag cement and waste containing alumina and silica). Leachability tests by TCLP (toxicity characteristic leaching procedure) and compressive strength of original and solidified samples by use of uniaxial pressing were studied in order to find suitable parameters for effective stabilization.