Phosphorus-containing oligoamides obtained by a novel one-pot degradation of polyamide-6

This paper describes a novel strategy for the recycling of polyamide materials and their transformation into functional reactive oligomers with new properties. The method is illustrated by the heating of polyamide-6 (20,000 Da) in the presence of diesters of the phosphonic acid, (RO)₂P(O)H, where R could be -CH₃, -C₂H₅ or -C₆H₅. It is found that the reaction proceeds in several parallel processes: (i) phosphorylation of the amide group by the alkyl esters of the phosphonic acids and (ii) degradation of the main chain through an exchange reaction between the amide and phosphonic acid ester groups. Alternatively the depolymerization could be induced via a radical reaction with the participation of the polyamide moieties and the P-H group. The proceeding of the abovementioned reactions and the structure of the phosphorus-containing oligoamides are confirmed by ³¹P, ¹H and ¹³C NMR spectroscopy. Their molecular weights are determined by size exclusion chromatography.     

Restructuring and break-up of two-dimensional aggregates in shear flow

We consider single two-dimensional aggregates, containing glass particles, placed at a water/air interface. We have investigated the critical shear rate for break-up of aggregates with different sizes in a simple shear flow. All aggregates break-up nearly at the same shear rate (1.8 +/- 0.2 s(-)(1)) independent of their size. The evolution of the aggregate structure before break-up was also investigated. With increasing shear rate, the aggregates adopt a more circular shape, and the particles order in a more dense, hexagonal structure. A simple theoretical model was developed to explain the experimentally observed break-up. In the model, the aggregate is considered as a solid circular disk that will break near its diameter. The capillary and drag force on the two parts of the aggregate were calculated, and from this force balance, the critical shear rate was found. The model shows a weak size dependence of the critical shear rate for the considered aggregates. This is consistent with the experimental observations.     

Electrolytic nucleation of silver on a glassy carbon electrode: Part II. Steady-state nucleation rate

The dependence of the number of nuclei on time is investigated in a wide overvoltage interval using different glassy carbon electrodes. The data for the steady-state nucleation rate are interpreted on the basis of both classical and atomistic theoretical concepts. Conclusions are drawn for the applicability of the two models of nucleation.     

On the Mixed Crystals Formation in the Fe(Zn) (HCOO)2–Cd(HCOO)2–H2O System

The solubility in the Fe(HCOO)₂–Cd(HCOO)₂–H₂O and Zn(HCOO)₂–Cd(HCOO)₂–H₂O systems have been studied by the method of physico-chemical analysis at 25 °C and mixed crystals of the type Fe_1-xCd_x(HCOO)₂.2 H₂O and Zn_1-xCd_x (HCOO)₂. 2 H₂O have been obtained. The lattice parameters of the mixed crystals have been calculated. It has been established that the isostructural Fe(HCOO)₂. 2 H₂O and Cd(HCOO)₂. 2 H₂O form isomorphous mixed crystals, whereas the isostructural Zn(HCOO)₂. 2 H₂O and Cd(HCOO)₂. 2 H₂O yield isodimorphous mixed crystals. The difference in the behaviour of the two pairs of formate salts has been attributed to the difference in the Me–O_m, bond lengths in the coordination octahedra, forming the crystal structures.     

Advantages of the iridium permanent modifier in fast programs applied to trace-element analysis of plant samples by electrothermal atomic absorption spectrometry

The application of a fast program combined with the advantages of the iridium permanent modifier is proposed for trace element analysis of plant samples by electrothermal atomic absorption spectrometry (ETAAS). For two volatile elements (Cd, Pb) and two mid-refractory elements (Cr, Ni) it was demonstrated that coating of the platform or of the tube atomization area with Ir is an efficient means of improving the accuracy and precision of results. A detailed study of interference from individual main matrix components and from composite plant matrices has confirmed the usefulness of the whole approach. The validity of the method has been confirmed by analysis of eight reference plant materials.     

Characterization of the distribution of the sintering activator boron in powder metallurgical steels with SIMS

Powder metallurgy is a well-established method for manufacturing ferrous precision parts. A very important step is sintering, which can be strongly enhanced by the formation of a liquid phase during the sintering process. Boron activates this process by forming such a liquid phase at about 1200 °C. In this work, the sintering of Fe–B was performed under the protective atmospheres of hydrogen, argon or nitrogen. Using different grain sizes of the added ferroboron leads to different formations of pores and to the formation of secondary pores. The effect of boron was investigated by means of Secondary Ion Mass Spectrometry (SIMS) supported by Scanning Electron Microscopy (SEM) and Light Microscopy (LM). To verify the influence of the process parameters on the mechanical properties, the microstructure (pore shape) was examined and impact energy measurements were performed.The concentrations of B in different samples were varied from 0.03–0.6 weight percent (wt%). Higher boron concentrations are detectable by EPMA, whereas the distributions of boron in the samples with interesting overall concentration in the low wt% range are only detectable by means of SIMS.This work shows that the distribution of boron strongly depends on its concentration and the sintering atmosphere used. At low concentration (up to 0.1 wt%) there are boride precipitations; at higher concentration there is a eutectic iron–boron grain boundary network. There is a decrease of the impact energy observed that correlates with the amount of eutectic phase.     

Synthesis,characterization and adsorption properties of nanostructured hybrid materials modified by boron and zirconium

The adsorption properties of two new nanostructured hybrid materials containing B₂O₃ and ZrO₂ were studied. The new organic-inorganic materials were synthesized via a sol-gel method. As a modifying agent, a quantity of 10 wt.% Zr(OPr)₄ or B(OCH₃)₃ was added. The structure of the hybrid materials was investigated by means of (Fourier transform infrared spectroscopy (FTIR), x-ray diffractometry (XRD), scanning electron microscopy (SEM), (atomic force microscopy (AFM) and nuclear magnetic resonance spectroscopy (NMR). Based on the obtained data, the most probable cross-linking mechanism for the derived gels was proposed. The characterization of texture parameters of both materials was carried out with the use of low-temperature adsorption of nitrogen. Adsorption of Cu(II), Fe(III), Cr(III), Cd(II) and Pb(II) ions on both materials was investigated using multi-component solutions with different concentrations and acidity by means of the batch method. Kinetics of adsorption was also investigated. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze kinetic data. The adsorption was significantly affected by the pH value. Equilibrium data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models and maximum adsorption capacities were calculated.      

Characterization of Two Bulgarian Herbs for Use as Biosorbents for Copper(II)

Abstract

Two biomaterials based on the abundant Bulgarian medicinal plants Mentha spicata L. (denoted as MS) and Ruta graveolens L. (denoted as RG) were investigated as environmentally friendly biosorbents for Cu(II) removal from aqueous solutions. Grain size distribution, slurry pH, texture parameters, thermal behavior and mineralogical composition of MS and RG were determined. Instrumental methods such as scanning electron microscopy (SEM), X-ray-diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) analysis, differential thermal analysis (DTA), and thermogravimetric analysis (TGA) were used for their characterization. It was demonstrated that the surface morphology of both materials is rough and contains pores that could entrap different pollutants, as well as functional groups that can attach metal ions. In order to examine the feasibility of these materials for use as biosorbents for heavy metals, adsorption experiments were performed. The results for the removal of Cu(II) ions from aqueous solution reveal capabilities suggesting that both materials have potential to be used as promising, efficient and low-cost biosorbents.