Volume 68, Issue 7

Since the 1950s, cellulose pyrolysis has been the subject of intense study, with kinetic analyses forming a major part of these studies. They represent useful tools for a better understanding of the physicochemical process and for the proper design of industrial pyrolysis units. Until recently, the methods most frequently used in these analyses were based on model-fitting, i.e. the fitting of the experimental data to a number of mathematical models. Nowadays, other methods, so-called “model-free” methods, are considered to be more suited. These are based on the principle that, at constant conversion, the reaction rate depends only on temperature. In its first part, this short review presents the particularities and drawbacks of the traditional model-fitting models. Subsequently, several main contributions in this field are listed and discussed. Finally, the more suited “model-free” (isoconversional) methods are explained and several main studies presented, as well as a comparison of this method with the model-fitting ones.

The aim of the study was to design and validate a reversed phase high performance liquid chromatography method for the separation and quantification of two active pharmaceutical ingredients (ciprofloxacin hydrochloride, hydrocortisone) and a preservative (benzyl alcohol) in ear drops. Effective separation of the examined compounds was achieved on a GraceSmart™ RP 18 column (150 mm × 4.6 mm, 5 μm) with gradient elution and a diode array detector. The total assay run time was 25 min. Analytical method validation assays were performed. Validation parameters used for the evaluation were: specificity, linearity, trueness, precision (repeatability and reproducibility), limit of detection and limit of quantitation. Results of the validation procedure (high recoveries, good standard deviations, no interfering peaks at the retention times corresponding to the analytes) confirm that the developed chromatographic method can be applied for routine analysis of ear drops.

The importance of feeding strategy for the long-term selective inhibition of nitrite-oxidising bacteria (NOB) was demonstrated by comparison of laboratory-scale bioreactors: Completely Stirred Tank Reactor (CSTR) and Sequencing Batch Reactor (SBR). Moreover, the effect of the change of reactor operation regime from CSTR to SBR was demonstrated. Sludge liquor containing ammonia nitrogen in a range of 970–1500 mg L−1 was the influent of the reactors. The experiments were performed at (23 ± 2)°C, with high concentration of dissolved oxygen (up to 8 mg L−1) and with unlimited sludge retention time. In the SBR, permanent restriction of NOB activity was achieved for more than 700 days by the strong inhibition effect of fluctuating concentrations of free ammonia and free nitrous acid during the operational cycles of SBR. In contrast, nitrite-oxidising bacteria were able to gradually adapt to the conditions prevailing in CSTR and produce nitrate although the concentration of free ammonia and free nitrous acid significantly exceeded inhibition limits for NOB activity in this system. Transferring the reactor operation regime from CSTR to SBR resulted in immediate and permanent inhibition of NOB activity in the reactor.

Posidonia oceanica (PO) is a marine plant endemic to the Mediterranean basin, forming extensive grasslands. Onshore residues represent a major environmental, economic, social and hygienic problem in all coastal zones of the Mediterranean basin due to the great disturbance they cause to bathers and beachfront populations. This work sought to evaluate the thermo-chemical properties of PO in pyrolysis and thermo-oxidative degradation processes. The investigations were carried out using a thermogravimetric analyser (TGA) coupled to a quadrupole mass spectrometer (MS) and an infrared spectrometer (FTIR). In addition, proximate, ultimate, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and biodegradability analyses were carried out on PO. The biodegradability analysis confirmed that residues of PO were a biodegradable material. Accordingly, the application of PO as a feedstock for combustion/co-combustion or biorefining is recommended.

In the paper, simultaneous removal of Al(III) and Cu(II) from dilute aqueous solutions by ion and precipitate flotation methods is investigated. Influence of the pH of the initial solution, the surface active collector concentration and the gas flow rate on the final removal ratio and the course of ion and precipitate flotations is presented. The results show that simultaneous flotations of Al(OH)3 and Cu(OH)2 insoluble species occur allowing to achieve their almost complete removal in the pH range between 7 and 9. An increase of the surface active agent concentration causes a decrease of the final removal ratio as well as of the flotation rate constant. An increase of the gas flow rate results in an increase of ion and precipitate flotation rates.

The current study presents the results of a numerical simulation of hydrodynamics in an agitated vessel equipped with an eccentric HE 3 impeller. CFD (computational fluid dynamics) simulations were carried out using ANSYS 14.0 software. Time-dependent simulations of turbulent flow were carried out using the SAS-SST (scale adaptive simulation-shear stress transport) method coupled with the SM (sliding mesh) method. The results of the calculations are presented as contours of velocity in different cross-sections of the agitated vessel, as well as profiles of components of velocity vector and turbulence kinetic energy and its dissipation rate. The iso-surface of vorticity, which shows the region of possible vortex existence, is also presented. A numerically obtained data set of impeller power number was used to calculate the averaged impeller power number. This value was compared with the experimental data with good results. The relationship between impeller position and fluctuation of the impeller power number was also analysed.

In this study, the influence of alkaline hydrogen peroxide (H2O2) pretreatment of the three different plant sources: Miscanthus giganteus, Sorghum Moench, and Sida hermaphrodita, for biogas production was investigated. The influence of temperature, reaction time, and H2O2 concentration on the efficiency of biomass degradation and on the further methanogenic fermentation were studied. The results obtained after chemical pretreatment indicate that using H2O2 at alkaline conditions leads to the decomposition of three major structures: lignin, hemicellulose, and cellulose. The best results were achieved for the process performed at 25°C for 24 h with the use of a 5 mass % H2O2 solution. Although the degradation level was very high for all three plant sources, the biogas production from the energy crops pretreated chemically was strongly inhibited by byproducts and the residual oxygen formed after H2O2 decomposition. This fact indicates that alkaline H2O2 pretreatment is a very promising method for plant material degradation for further biogas production, but pretreated biomass must be separated from supernatant before the fermentation process because of the high concentration of inhibitors in the hydrolysates. The best results were obtained for Sida with biogas and methane production of 2.29 Ndm3 and 1.06 Ndm3, respectively.

The template reaction of salicylaldehyde and its substituted derivatives and 2-hydroxy-5-bromobenzylamine or 2-hydroxy-5-chlorobenzylamine with copper(II) acetate in dimethyl sulphoxide (dmso) afforded eight dinuclear Cu(II) complexes, [Cu2(L)2(dmso)2] (H2 L = N-salicylidene-2-hydroxy-5-bromobenzylamine, N-salicylidene-2-hydroxy-5-chlorobenzylamine and their 5-bromo, 5-nitro and 5-methyl-substituted salicylidene derivatives). These Cu(II) complexes were characterised by IR and UV-VIS-NIR spectroscopy, electric conductivity, cyclic voltammetry, and temperature dependence of magnetic susceptibilities (4.5–300 K). In the THF solution, the complexes are nonelectrolytes and exhibit a characteristic CT band due to phenoxido-bridging at 360–384 nm. In the cyclic voltammograms, an irreversible reduction process was observed at −1.18–1.54 V vs Fc/Fc+. Single-crystal X-ray crystallography revealed that two Cu(II) ions were bridged by the two phenoxido-oxygen atoms of the two Schiff-base ligands with axial coordination of dmso molecules forming a square pyramid with a Cu-Cu distance of 3.0628(8)–3.0931(6) °A. In accordance with the crystal structures, the magnetic interaction between the two Cu(II) ions is relatively anti-ferromagnetic with −2J value of 386–575 cm−1. The axial coordination effect of the dmso molecule was discussed in relation to the correlation between the Cu-O-Cu angle and the −2J value.

The ligands 2-(diphenylphosphino)benzyl-(2-thiophene)methylimine (V) and 2-(diphenylphosphino) benzyl-(2-thiophene)ethylimine (VI) were prepared from 2-(diphenylphosphino)benzaldehyde and thiophene amines with very good yields. An equimolar reaction of V and VI with either PdCl2(cod) (cod = cyclooctadiene) or PdClMe(cod) afforded palladium(II) complexes I–IV. The molecular structure of II was confirmed by X-ray crystallography. The coordination geometry around the palladium atom exhibited distorted square planar geometry at the palladium centre. Complexes I, II, and IV were evaluated as catalysts for Heck coupling reactions of iodobenzene with methyl acrylate under mild reaction conditions; 0.1 mole % catalyst, Et3N base, MeCN reflux for 8 h, 80°C; isolated yield on a 10 mmol scale with catalyst I (64 %), II (68 %), and IV (58 %). They all exhibited significant activities.

In the memory of Prof. Ing. Ladislav Valko, DrSc. (1930–2013) A room-temperature synthesis of copper(II) 2-pyridylmethanolate tetrahydrate, [CuL2] · 4H2O, with nearly quantitative yields with its structure redetermined at 213 K is presented. In agreement with the X-ray structure data, the DFT quantum-chemical calculations confirmed the planar structure of CuL2 (C 2h symmetry). The measured IR and Raman spectra were interpreted using the DFT calculations and some erroneous assignments in the previous studies have been corrected.

Clay mineral containing kaolinite, illite and montmorillonite was organofunctionalized with silylating agents: (3-aminopropyl)triethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane and (3-mercaptopropyl)trimethoxy-silane, to yield three hybrids labelled Clay1, Clay2 and Clay3, respectively. These solids were characterized using elemental analysis, thermogravimetry, X-ray diffractometry, infrared spectroscopy, scanning electron micrograph, and 29Si and 27Al solid state NMR. Immobilized quantities of the organic groups were 0.66 mmol g−1, 0.48 mmol g−1 and 0.88 mmol g−1 for Clayx (x = 1–3), respectively. X-ray diffraction patterns confirmed the immobilization of silanes onto the surface without changes in the textural properties of the clay mineral as noted from the SEM images. Spectroscopic measurements were in agreement with the covalent bonding between the silanes and the hydroxyl groups deposited on the surface. The new hybrids were utilized as adsorbents of cobalt in aqueous solution, with retention values of 0.78 mmol g−1, 1.1 mmol g−1 and 0.70 mmol g−1 for Clayx (x = 1–3), respectively.

Nano-titania doped with noble metals (Au/TiO2, Ag/TiO2, Pd/TiO2) has been synthesized by mild hydrolysis of the mixture of metal salts or complexes and titanium isopropoxide ((iPr-O)4Ti). After thermal decomposition of the obtained precursors, nanomaterials were formed. Morphological characterization of the nanomaterials was provided by scanning electron microscopy (SEM) and stereological analysis, determining the BET specific surface area, and BJH nanoporosity (pore volume, pore size). It has been found that the structure of nanomaterials (size of nanoparticles and agglomerates) depended strongly on the method of the (iPr-O)4Ti hydrolysis. A minor dependence on the kind of solvents and precursors of noble metals was observed. The presence of doping metal nanoparticles was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Nanomaterial phases were identified by X-ray diffraction (XRD). According to the XRD patterns, Ag/TiO2 and Pd/TiO2 products with doping metals in their oxidized form contain Ag-Ti and Pd-Ti phases. Peaks of the metal oxides Ag2O and PdO are absent in the XRD patterns. The average size of TiO2 nanoparticles is situated in the region of 20–60 nm, whereas metals are present as about 10–15 nm sized particles and fine nanoparticles.

A series of 6,8-dichloro-quinazoline derivatives bearing a sulfide group was synthesized and characterized via 1H NMR, 13C NMR, IR and elemental analyses. All the compounds were tested for their insecticidal activity against Plutella xylostella in vitro. The results indicate that the synthesized compounds possess good insecticidal activity. Among these compounds, Vc, Vi, Vj, Vk and Vm displayed 75 %, 85 %, 80 %, 70 % and 63 % activities, respectively. These may prove useful as insecticidal agents.

The total content of polyphenols and flavonoids determined in the same plant and their corresponding antioxidant activities may vary widely, depending on the extraction conditions applied. This study was conducted to optimise the extraction conditions of phenolics and flavonoids from the mistletoe plant. Various extraction methods, i.e. ultrasound-assisted extraction technology, maceration, maceration with stirring, accelerated solvent extraction (ASE), and extraction under reflux were evaluated for their percentage extraction of polyphenols (TPC) and flavonoids (TFC) from Viscum album subsp. abietis. In addition, the anti-radical activity of extracts was analysed using the 2,2-diphenyl-1-picrylhydrazyl method. The effects of temperature, solvent type, and concentration on the phenolic extraction efficiency and antioxidant activity were studied using chemometric and statistical methods. The results showed that the extracts of V. album subsp. abietis contained large amounts of polyphenols and flavonoids (up to 57.673 mg g−1 and 9.955 mg g−1 of dry extract, respectively) and exhibited potent antioxidant activity, hence representing promising sources of powerful antioxidants. Due to its high extraction efficiency and considerable saving of time and solvent, ASE was more effective than the other extraction techniques. Extracts prepared with water-polar solvent mixtures displayed the highest TPC, TFC, and antioxidant activity, while organic polar solvents were the least efficient extractants.

Spherical melamine-formaldehyde resin (MFR) particles were synthesised using the condensation reaction of melamine and formaldehyde with PEG-2000 as an additive. After thermal treatment at 200°C and then sulphonation by chlorosulphuric acid, an MFR-supported strong acid catalyst (SMFR) was prepared with an acidity of 3.23 mmol g−1. This new acid catalyst was evaluated in the reactions of esterification and acetalisation, with the results indicating that this novel acid catalyst was highly efficient in the traditional acid-catalysed reaction. Its high activity, stability and reusability give it great potential for “green” chemical processes.

The main aim of this paper was to study the effect of a new tripodal chelating agent on La1−x SrxCo1−y FeyO3−δ perovskite prepared by the complexation method. For this purpose, a phenolic derivative of glycine (L) was synthesized applying the Mannich reaction and characterized by NMR and IR spectroscopies as well as by elemental analysis. To evaluate the complexation capability of L, its formation constants with the perovskite cations were measured. Comparison of these results with those reported for the complexaion with glycine, introduced L as a good candidate for the complexation with Fe(III) and La(III) cations. Furthermore, the powder XRD observations confirmed an improvement in the perovskite formation in the presence of L.