Effect of reagents mixing on the thermal behavior of sol-gel precursors for silica-based nanocomposite thin films

The paper presents, based on TG-DTG-DSC data, some results of the thermal decomposition of some complex sol-gel precursors used for the deposition of mesoporous ZnO/SiO₂ nanocomposite thin films for gas sensing applications. The effect chemical composition of the sol and reagents mixing during the sol preparation is discussed. The chemical nature of ZnO source (zinc acetate solid salt, zinc acetate alcoholic solution or ZnO nanopowder) used for the sol preparation significantly affects the thermal decomposition of complex precursor and the microstructure and properties of the nanocomposite thin films.     

Short-range structure and in vitro behavior of ZnO–CaO–P2O5 bioglasses

Ternary zinc–calcium-phosphate glasses prepared by classical melting method were characterized through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) along with energy dispersive X-ray analysis (EDAX), Fourier Transform InfraRed (FTIR) and Raman spectroscopy. The study of these glasses was done in order to supply information regarding their structural particularities since the zinc role in biological environment, especially in the bone, is still under debate.XRD analysis confirmed the vitreous character of the as-prepared samples, while SEM and EDAX measurements indicated the presence of some non-homogeneous domains on their surfaces with approximately similar elemental composition. According to FTIR and Raman spectroscopy, the local structure of glasses up to 10 mol% ZnO is mainly built by Q² tetrahedrons connected by P–O–P linkages. For 50 mol% ZnO, the modifier role of zinc ions is strongly reflected on the local structure dominated in this case by Q¹ pyrophosphate units.The surface reactivity of the samples has been analyzed in vitro by immersion in simulated body fluid (SBF) at 37 °C. XRD, SEM–EDAX, FTIR and Raman methods were employed to characterize the structural changes that occurred on the surface of ZnO–CaO–P₂O₅ samples reacting with SBF. The X-ray diffraction patterns demonstrated the formation of a hydroxyapatite layer on the samples surface while the other used methods didn't reveal concisely that phenomenon. Based on X-ray measurements, the influence of zinc concentration on the hydroxyapatite layer development was followed.     

Pulsed Corona Discharge for Degradation of Methylene Blue in Water

A pulsed corona discharge in multiwire-plate geometry, generated above water was studied for the removal of organic compounds in liquids. The degradation of methylene blue (MB) and the formation of hydrogen peroxide (H₂O₂) were investigated. The MB solution was rapidly decolorized, evidencing the degradation of the dye after approximately 10 min plasma treatment. Nitrate, formate, sulphate and chlorine ions have been detected in the treated solution, explaining partly the change in the solution properties with plasma exposure, i.e. increase of electrical conductivity and decrease of pH. It was found that the concentration of H₂O₂ generated in water increased with plasma exposure time, reaching 200 mg/L after 30 min treatment. In the MB solution less hydrogen peroxide was detected, suggesting reactions with the dye and its degradation products. The addition of FeCl₂ catalyst had a slight favorable effect on methylene blue degradation due to Fenton’s reaction. It was observed that MB and H₂O₂ concentrations continue to decrease after the plasma treatment was stopped, suggesting that active species which accumulate in the solution may react post-plasma with methylene blue and its degradation products.     

Photoluminescence response of terbium-exchanged MFI-type materials to Si/Al ratio, texture, and hydration state

Terbium-exchanged MFI zeolite type materials, i.e., microporous-mesoporous Zeotile-1 with the Si/Al ratio in the range 33-200, Zeogrid with the Si/Al ratio of 75, and nanocrystalline MFI with the Si/Al ratio of 75, were prepared via an ion exchange procedure. All of these zeolites were investigated by means of time-resolved photoluminescence techniques in various hydration states: as-synthesized (hydrated), calcined (heated at 450 degrees C in air), and rehydrated (after a six-month exposure to the atmospheric moisture). The photoluminescence decays and spectra were analyzed by discrete exponential fitting, distribution lifetimes analysis, and area-normalized time-resolved photoluminescence spectra. The results sustained a single average terbium species coordinated to both water molecules and framework oxygens in the hydrated zeolites. The framework contribution increased with the Si/Al ratio in Zeotile-1 and was greatest for the nanocrystalline MFI zeolite. For the calcined Zeotile-1 and Zeogrid, two main terbium species of different environments were found. For the nanocrystalline Tb3+-MFI, a distinct number of species could not be inferred, indicating a more heterogeneous distribution. Rehydration further differentiated among the Tb3+-exchanged zeolites. Photoluminescence line shape and decay of Tb3+-Zeotile-1 were between those of the hydrated and calcined states indicating a slow rehydration rate in contrast with the photoluminescence properties of Tb3+-MFI, which fully recovered the values of the hydrated state. Tb3+-Zeogrid presented an intermediate case: while the PL line shape was fully restored to that measured for the hydrated sample, the decay was still longer than that measured with the hydrated sample. Terbium photoluminescence response related to zeolite texture, Si/Al ratio, and hydration state suggest different sitting and location of terbium in Zeotile-1, Zeogrid, and nanocrystalline MFI materials. In mesoporous Zeotile-1 and Zeogrid, the results sustained two types of terbium sites: one on the internal surface of mesopores, the other inside the pores, while for the nanocrystalline MFI, terbium sites inside the pores predominate.     

Silver sorption on acrylic copolymers functionalized with amines. Equilibrium and kinetic studies

The sorption capacity of three weak base ion exchangers based on acrylic copolymers functionalized with ethylenediamine, triethylenetetramine and N, N- dimethylamino propylamine for Ag(I) ions was evaluated. Adsorption experiments were carried out by batch method. The effect of pH, crosslinking degree of copolymers, amount of sorbent, initial ion concentration, contact time and temperature was studied. The parameters which characterize the retention process were estimated using Langmuir and Freundlich isotherm models, the best fitting being for the first model. Kinetic data were fitted to pseudo-first order, pseudo-second order and intraparticle diffusion models. Experimental data were in good agreement with the pseudo second order.      

Internal conversion in inner shells of atomic ions and relativistic ionic potentials

Internal conversion coefficients for inner shells of atomic ions of Sn are calculated for various degrees of ionization and compared with neutral atom predictions. The relativistic version of an analytic perturbation theory is used to include screening effects.     

Rayleigh scattering fromn=3 states of hydrogenlike atoms

An exact analytic evaluation of the Kramers-Heisenberg matrix elements for Rayleigh scattering fromn=3 states of hydrogenlike atoms is performed in the nonrelativistic dipole approximation, using the Green's function method. The results are given separately for each subshell. The possibility of 3s?3d transitions is also considered. The dependence on the photon energy is contained in six invariant amplitudes. The formulas needed for the evaluation of the various cross sections are presented. The numerical results are contained in tables from which partial and total cross sections can be easily built, covering the energy range from zero up to 20 times theK threshold energy. In the vicinity of Balmerα frequency the cross section is large and comparable with that for excitedn=2 states, confirming an earlier hypothesis of Röhr. At other energies the cross sections forn=2 andn=3 states are comparable, too. The results should be useful in plasma diagnostics.     

One‐Step Pyrolysis Preparation of 1.1.1 Oriented Gold Nanoplatelets Supported on Graphene and Six Orders of Magnitude Enhancement of the Resulting Catalytic Activity

Pyrolysis of chitosan films containing Au³⁺ renders 1.1.1 oriented Au nanoplatelets (20 nm lateral size, 3–4 nm height) on a few layers of N‐doped graphene ( /fl‐G), while the lateral sides were 0.0.1 oriented. Comparison of the catalytic activity of /fl‐G films with powders of unoriented Au NPs supported on graphene showed that /fl‐G films exhibit six orders of magnitude enhancement for three gold‐catalyzed reactions, namely, Ullmann‐like homocoupling, C? N cross coupling, and the oxidative coupling of benzene to benzoic acid. This enhancement is the result of the defined morphology, facet orientation of Au nanocrystals, and strong gold‐graphene interaction.     

Separation of haloacetic acids in water by capillary zone electrophoresis with direct UV detection and contactless conductivity detection

The separation of haloacetic acids (HAAs) in water by capillary zone electrophoresis with direct UV and contactless conductivity detection was investigated using phosphate, citrate, and borate buffers, and the experimental data were compared to simulation data predicted by a computational program known as PeakMaster. Good agreement between the experimental data and simulation data predicted by PeakMaster was found. Using the phosphate buffer or the citrate buffer and electrokinetic injection it was possible to quantitate HAAs at 0.1 ppm levels in water.