The effect of mechanical activation on the thermal reactions of P2O5–Al2O3–Fe2O3–Na2O phosphate glasses

The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were activated by grinding in a planetary mill. Mechanical activation causes a decrease of the T _g temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain the observed regularities governing the crystallization of the activated glasses.     

Studies on fibrillar form of trimolybdate Rb2O · 3MoO3 · H2O

The fibrillar rubidium trimolybdate was investigated. Its structure has been discussed on the basis of X-ray, thermogravimetric, IR and NMR measurements.     

In-situ growth hierarchical and superhydrophobic flower-like Cu3(PO4)2·2H2O nanosheets based on copper mesh for efficient oil–water separation

Superhydrophobic porous membranes with interconnected open structures for effective treatment oily wastewater have gradually drawn researchers’ attentions owing to frequent occurrence of organics leakage accidents. In this paper, we successfully fabricated superhydrophobic flower-like Cu₃(PO₄)₂·2H₂O nanosheets on copper mesh surface via in-situ growth strategy and silane coupling agent (A151) hydrophobic modification. Specifically speaking, commercial copper mesh served as substrate and Cu could react with (NH₄)₂S₂O₈ and Na₂HPO₄, forming flower-like micro-nanostructure. As-synthesized materials were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). In addition, chemical, mechanical stability and durability of as-prepared materials were also investigated under different condition. The relevant experiment results demonstrated that flower-like Cu₃(PO₄)₂·2H₂O nanosheets successfully grew on copper mesh surface, resulting in the formation of rough structure. Modified copper mesh showed superhydrophobic and superoleophilic properties simultaneously with water contact angle (CA) of 151.24° and oil contact angle of 0°, respectively. The as-prepared materials could be used to separate oily wastewater with high separation efficiency (above 95.0%). The mechanism of oil–water separation was investigated in detail based on positive and negative capillary effect. High separation efficiency, excellent stability and durability of superhydrophobic copper mesh make it one of best promising separation candidates for wastewater treatment.     

Influence of redox behavior of copper ions on dielectric and spectroscopic properties of Li2O–MoO3–B2O3: CuO glass system

Li₂O–MoO₃–B₂O₃ glasses mixed with different concentrations of CuO (ranging from 0 to 1.2 mol%) were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Optical absorption, luminescence, ESR, IR and dielectric properties (viz., dielectric constant ?′, loss tan δ and a.c. conductivity σ_ac, over a wide range of frequency and temperature) of these glass materials have been investigated. The results of differential scanning calorimetric studies suggest that the glass forming ability is higher for the glasses containing CuO beyond 0.6 mol%. The analysis of results of the dielectric properties has revealed that the glasses possess high insulating strength when the concentration of CuO is >0.6 mol%. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 0.6 mol%. In the high-temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction. The optical absorption spectra of these glasses exhibited bands due to Cu⁺ ions in the UV region in addition to the conventional band due to Cu²⁺ ions in the visible region. The ESR spectral studies have indicated that there is a gradual adoption of Cu²⁺ ions from ionic environment to covalent environment as the concentration of CuO increases beyond 0.6 mol% in the glass matrix. The luminescence spectra excited at 271 nm have exhibited an intense yellow emission band centered at about 550 nm and a relatively broad blue emission band at about 450 nm; these bands have been attributed to the ³D₁ → ¹S₀ transition of isolated Cu⁺ ions and ³D₁ → ¹S₀ transition of (Cu⁺)₂ pairs, respectively. The quantitative analysis of the results of all these studies has indicated that as the concentration of CuO is increased beyond 0.6 mol% in the glass matrix, a part of Cu²⁺ ions have been reduced to Cu⁺ ions that have influenced the physical properties of these glasses to a substantial extent.     

Thermal properties and crystallization of BaO–MoO3–P2O5 glasses

Journal of Thermal Analysis and Calorimetry - The thermal behavior and crystallization of barium molybdate-phosphate glasses were studied in two compositional series, namely A:...     

Physical–chemical and catalytic properties of deposited MoO3 and V2O5

The deposition of molybdenum and vanadium oxides onto fumed silica, titania, and alumina as supports through dry milling has been carried out. The structure of prepared compositions has been investigated by means of XRD, DTA?CTG, FTIR, and UV?CVis spectroscopy, nitrogen adsorption. The deposited crystal phases are sufficiently uniformly distributed on support surface. The supported oxides are subjected to dispersion in process of milling to the state of oligomeric or isolated species. Milled bulk and deposited MoO₃ (first of all, on alumina) possesses improved catalytic performance in process of epoxidation of 1-octene. Vanadium pentoxide also has higher activity in this process.     

Synthesis,Structure and Characterization of Three Metal Molybdate Hydrates: Fe(H2O)2(MoO4)2·H3O,NaCo2(MoO4)2(H3O2)and Mn2(MoO4)3·2H3O

Three metal molybdate hydrates,Fe(H2O)2(MoO4)2·H3O(FeMo),NaCo2(MoO4)2(H3O2)(CoMo)and Mn2(MoO4)3·2H3O(MnMo),were synthesized by the mixed-solvent-thermal methods and characterized by singlecrystal X-ray...     

The thermal dehydration and decomposition of Ba[Cu(C2O4)2(H2O)]·5H2O

The thermal behaviour of Ba[Cu(C₂O₄)₂(H₂O)]·5H₂O in N₂ and in O₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol^–1 (or 52±5 kJ (mol of H₂O)^–1). The overall enthalpy change for the decomposition of Ba[Cu(C₂O₄)₂] in N₂ was estimated from the combined area of the peaks of the DSC curve as –347 kJ mol^–1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the -time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol^–1 and (1.38±0.08)×10¹⁵ min^–1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.The values ofE _a andA were 206±23 kJ mol^–1 and (2.2±0.5)×10¹⁹ min^–1, respectively, for the fast process, and 259±37 kJ mol^–1 and (6.3±1.8)×10²³ min^–1, respectively, for the slow process.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Trisaminomethane–cobalt complex supported on Fe3O4 magnetic nanoparticles as an efficient recoverable nanocatalyst for oxidation of sulfides and C–S coupling reactions

In this work, trisaminomethane–cobalt complex immobilized onto the surface of Fe₃O₄ magnetic nanoparticles was successfully prepared via a simple and inexpensive procedure. The prepared nanocatalyst was considered a robust and clean nanoreactor catalyst for the oxidation and synthesis of sulfides under green conditions. This ecofriendly heterogeneous catalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, inductively coupled plasma-atomic emission spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, X-ray mapping, scanning electron microscopy, and transmission electron microscopy techniques. Use of green medium, easy separation and workup, excellent reusability of the nanocatalyst, and short reaction time are some outstanding advantages of this method.     

A combined experimental and model analysis on the effect of pH and O2(aq) on γ-radiolytically produced H2 and H2O2

The effects of pH and dissolved O₂ on the γ-radiolysis of water were studied at an absorbed dose rate of 2.5 Gy s⁻¹. Argon- or air-saturated water with no headspace was irradiated and the aqueous samples were analyzed for molecular radiolysis products (H₂ and H₂O₂) as a function of irradiation time. The experimental results were compared with computer simulation results using a comprehensive water-radiolysis kinetic model, consisting of the primary radiolysis production, subsequent reactions and related acid–base equilibria. Both the experimental and computer model results were discussed based on the steady-state kinetic analysis of smaller reaction sets consisting of key production and removal reactions. While the main production path for a water decomposition product is the primary radiolysis, the main removal path varies. For H₂O₂ the main removal path is the reactions with e_aq⁻ and OH, whereas for H₂ it is the reaction with OH. As a result, the presence of a dissolved species, or a change in chemical environment, affects the concentrations of H₂O₂ and H₂ through interaction with radicals e_aq⁻ and OH. Over a wide range of conditions, there exist quantitative but simple relationships between the radical and the molecular product concentrations. The experimental and model analyses show that dissolved oxygen increases the steady-state concentrations of H₂O₂ and H₂ by reacting with OH and e_aq^–, and the impact of oxygen is more noticeable at pH below 8. The steady-state concentrations of water decomposition products are nearly independent of pH in the range 5–8. However, raising pH above the pKa value of the acid–base equilibrium of H (⇆e_aq⁻+H⁺) significantly increases [H₂O₂] and [H₂] at the expenses of [OH] and [e_aq^–]. At pH >10, the radiolytical production of O₂ becomes significant, but at a finite rate. This considerably increases the time for the irradiated system to reach a steady state, and is responsible for different impacts on [H₂O₂] and [H₂] due to radically produced O₂, compared to impacts due to initially dissolved O₂. Model sensitivity analysis has shown that at higher pHs (pH >10) transient species such as O₂⁻ and O₃⁻ play a major role in determining the steady-state concentration of molecular products H₂ and H₂O₂. Further validation of the water radiolysis model, particularly at higher pHs, is also discussed.     

Thermal decomposition study of HAuCl4·3H2O and AgNO3 as precursors for plasmonic metal nanoparticles

Thermal decomposition of HAuCl₄·3H₂O and AgNO₃, as precursors for Au and Ag nanoparticles, respectively, was monitored by coupled TG–DTA with TG/EGA–FTIR and EGA–MS techniques in a flowing 80 %Ar + 20 %O₂ and Ar atmospheres in the temperature range of 30–600 °C. The intermediate and final products of thermal decomposition were analysed by ex situ XRD and FTIR techniques. The thermal degradation of HAuCl₄·3H₂O starts immediately after melting at 75 °C and takes place in three steps in the temperature range of 75–320 °C with total mass loss of 49.4 and 49.7 % in artificial air and Ar atmospheres, respectively. EGA by MS and FTIR revealed a simultaneous release of H₂O and HCl in the temperature range of 75–235 °C. EGA by MS revealed a release of Cl₂ at around 225 °C and in the interval of 250–320 °C. According to the XRD analysis, the main solid product in the end of the first decomposition step at 190 °C is AuCl₃; in the end of the second decomposition step at 240 °C is AuCl and the final product at 320 °C is Au. The thermal decomposition of AgNO₃ takes place in a single step in the temperature range of 360–515 °C with a total mass loss of 39.0 and 37.8 % in flowing artificial air and Ar atmospheres, respectively. According to EGA–MS and EGA–FTIR the main evolved gases are NO₂, NO and O₂. The final product of the thermal decomposition at 600 °C is Ag irrespective of the atmosphere.     

Thermal stability of In2(MoO4)3 and phase equilibria in the MoO3–In2O3 system

Thermal stability of a compound forming in a binary system MoO₃?CIn₂O₃ was investigated by DTA/TG, XRD and SEM methods in this study. For the first time, the diagram of phase equilibria established in the whole range of concentrations of this system's components has been constructed. The temperature and concentration ranges of the components of MoO₃?CIn₂O₃ system in which the compound In₂(MoO₄)₃ co-exists in solid state with MoO₃ or In₂O₃ or with the liquid were determined. The composition and melting point of the eutectic mixture consisting of In₂(MoO₄)₃ and MoO₃ were found.     

Kinetics of thermal decomposition of a synthetic K–H3O jarosite analog

The thermal decomposition kinetics of a synthetic K–H₃O jarosite analog was determined from thermogravimetric analysis at various heating rates in air. A thermal decomposition mechanism was proposed based on X-ray analysis of partially decomposed material and distinct features observed during thermal decomposition analysis. The decomposition path is complex. The material was treated as a composite of K-jarosite, H₃O-jarosite, and a “vacancy component”. The evolution of (OH)^? and SO₃ from these individual components was modeled. The decomposition is broken into subreactions according to distinct features in the thermoanalytical measurements. The subreactions are arranged sequentially and in parallel according to the evolution of the participating phases. A set of associated apparent activation energies was determined using isoconversion analysis. Kinetic triplets were assigned to each subreaction. A reasonable match with the observed decomposition was achieved by varying pre-exponential factors.     

Preparation and electrocatalytic performance of Fe–N–C for electroreduction of H2O2

Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen source, and calcination temperature on the catalytic performance of the Fe–N–C for H₂O₂ electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed good performance and stability for electroreduction of H₂O₂ in alkaline solution. An Al–H₂O₂ semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V and its power density reached 51.4 mW cm⁻² at 65 mA cm⁻².     

Surface reactions of dimethyl ether on γ-Al2O3

The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al₂O₃) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°С were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm^–1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm^–1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450–500°С; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.     

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)][Cu(NO3)4]· H2O

The thermal decomposition process of the complex [Cu(NBOCTB)][Cu(NO₃)₄] H₂O has been studied by TG and DTG technique, and possible intermediates of the thermal decomposition have also been conjectured from the TG and DTG curves. The results suggest that the decomposition of the complex involves five steps: The non-isothermal kinetics of steps 1, 2 and 3 have been studied by means of the Achar and Coats-Redfern method based on TG and DTG curves. Step 1 is a Coring and Growth mechanism (n= 1), its kinetic equation may be expressed as: d/dt=Ae^–E/RT(1–). Steps 2 and 3 are both two order chemical reaction mechanisms, their kinetic equations can be expressed as: d/dt=Ae^–E/RT(1–)².This project was supported by the National Natural Science Youth Fundation of China.     

Phase Diagrams of Fullerenol-d–LaCl3–H2O and Fullerenol-d–GdCl3–H2O Systems at 25°С

Russian Journal of Physical Chemistry A - Isothermal phase diagrams of ternary systems fullerenol-d–LaCl3–H2O and fullerenol-d–GdCl3–H2O at 25°C are studied via...