Surface interaction and desorption of trimethyl phosphate from ozonized activated carbon fabric

Trimethyl phosphate (TMP) is a typical simulant of the CWA nerve agents and its adsorption on pristine and ozonized ACF has been studied by FT-IR and ESR spectroscopy. The FT-IR analysis is effective in putting in evidence the strong interaction of TMP with the ACF surfaces through the P = O stretching band shift toward lower frequencies after adsorption. Ozonized ACF ensures a stronger interaction with the adsorbate through the hydrogen bond formation between the adsorbed TMP and the oxygenated functional groups present on carbon surface. At room temperature the ozonized ACF is able to adsorb larger amounts of TMP than the pristine ACF and shows also a better retention of the adsorbate at room temperature. The TGA-FTIR analysis of TMP desorption from both ozonized and pristine ACF has shown that TMP undergoes a partial thermal decomposition into methanol and phosphoric acid above 175°C. The maximum methanol production rate was observed at 250°C in the TMP desorption process from ozonized ACF and at 280°C from TMP desorption from pristine ACF.     

Surface modification of activated carbon fabric with ozone. Part 3: Thermochemical aspects and electron spin resonance

It is shown that the differential scanning calorimetry (DSC) analysis of water desorption from activated carbon fabric (ACF) surfaces having different degrees of oxidation, is a valid alternative to immersion calorimetry in determining the desorption/adsorption energy of an adsorbate on the oxidized ACF surfaces. Processing the DSC endotherm relative to water desorption through the Clausius-Clapeyron equation it is possible to calculate either the water desorption energy from the oxidized ACF surfaces and also the hydrogen bond energy through which the water molecules are bound to the oxidized ACF surface. The DSC analysis of the ozonized ACF has revealed that secondary ozonides and peroxides are formed together with other oxygenated groups on the ACF surface, and were detected through an exothermal transition with two peaks at 118°C and 142°C with the measured decomposition enthalpy directly proportional to the degree of oxidation of the ACF surface. The ESR analysis on pristine ACF has revealed the presence of clustered paramagnetic centers. The reaction of the ACF with ozone greatly enhances the ESR signal since more free radicals are formed on the surface mainly in the form of oxygen-centered peroxide-type.     

A new route to graphene starting from heavily ozonized fullerenes: Part 1—thermal reduction under inert atmosphere

It is shown that heavily ozonized C₆₀ or C₇₀ fullerenes (known also as “fullerene ozopolymers”) are suitable substrates for the preparation of graphene or nanographene in place of graphite oxide (GO) by thermal reduction in inert atmosphere. TGA-FTIR study shows that the release profile of CO₂ and CO from fullerene ozopolymers in the temperature range between 25°C and 900°C is comparable to that shown by GO. Furthermore, the FT-IR spectral evolution of fullerene ozopolymers from room temperature to 630°C under inert atmosphere is once again strikingly comparable to that observed on GO under the same conditions.     

A new route to graphene starting from heavily ozonized fullerenes: Part 2—oxidation in air

Graphite oxide (GO) and heavily ozonized C₆₀ and C₇₀ fullerenes known as “fullerene ozopolymers” were studied by TGA-FTIR (Thermogravimetry coupled with FT-IR spectroscopy), DTG (Differential Thermogravimetry) and DTA (Differential Thermal Analysis) in air flow. It was found that GO burns at 70°C higher temperature than the fullerene ozopolymers. This different behavior toward the thermal oxidation of GO is due to the size of the oxidized and staked graphene layers which are expected to be significantly larger than those of the fullerene ozopolymers. Furthermore, the latter should necessarily have a buckybowl shaped structure which should favor their reactivity with oxygen.     

Surface modification of activated carbon fabric with ozone,part 1: Kinetics and oxidation degree

Two samples of activated carbon fabrics (ACF) with very high surface area (>1300 to >1800 m²/g) were reacted with ozone inside a closed flask under static conditions. The kinetics of ozone decomposition and reaction with the ACF surface was measured in the gas phase using Fourier transform infrared analysis (FT-IR) spectroscopy. The ozone consumption under these conditions was following the pseudofirst-order kinetics law and was accompanied by the production of CO₂ and CO. The ozone-oxidized ACF were studied by FT-IR spectroscopy following the growth of key oxidized functional groups, i.e. phenolic OH, ketone groups intended as carboxyl, lactone, and anhydride, as well as quinone groups as a function of the amount of ozone reacted. The weight uptake of the ACF reacted with ozone was followed gravimetrically. The ACF having >1800 m²/g was able to reach a weight increase of 25% of its original weight due to the formation of oxygenated surface functional groups. Raman spectroscopy was used for the evaluation of defective structures formed in ACF because of ozonization reaction.     

Growth of whiskered ZrO2 crystals by hydrothermal decomposition of zirconium oxide sulphate pseudo-crystals

Several kinds of metastable compounds, pseudo zirconium oxide sulphates (PZOS) with a chemical composition of Zr₃O₅SO₄·nH₂O, were previously synthesized by the thermal hydrolysis of solutions containing zirconium sulphate at 200 or 240°C. The obtained PZOS samples were again hydrothermally treated in different sulphuric acid solutions (<1.0 mol l^-1) at 240°C, and their hydrothermal decomposition behaviour was investigated by TEM observation. The PZOS samples mostly crystallized to plate-like zirconium oxide sulphate (ZOS) in the concentrated sulphuric acid solution (>0.5 mol l^-1), but long-whiskered monoclinic ZrO₂ crystals grew with decomposition of the PZOS samples obtained from the starting mixtures with added Zr(OH)₄ when rapidly heated to the hydrothermal treatment temperatures. It was found that many ultrafine monoclinic ZrO2 crystals were simultaneously formed during the hydrothermal preparation of the PZOS samples, and during the following hydrothermal decomposition of the PZOS samples, the whiskered crystals of monoclinic ZrO2 grew with the consumption of PZOS from the coexisting ultrafine monoclinic ZrO2 particles which act as seed crystals. This revised version was published online in November 2006 with corrections to the Cover Date.     

Thermal decomposition behavior of praseodymium oxides,hydroxides, and carbonates

Thermal decomposition behavior was studied for Pr₆O₁₁, Pr₂O₃, Pr(OH₃), and Pr₂(CO₃)₃ · xH₂O. In the course of transformation, the intermediate species were different for each starting material, as well as the surface area and morphology of the final thermal decomposition products. During thermal decomposition in the temperature range of 200°C up to 1400°C, mass losses for each species were attributed to the removal of hydroxide and carbonate species based on changes in the infrared bands for each powder for hydroxide groups at ≃3600 cm⁻¹ and carbonate groups at ≃1300–1500 cm⁻¹. X-ray diffraction analysis identified the final decomposition product at 1400°C for each species as Pr₆O₁₁ regardless of the starting material. A decrease in surface area and increase in equivalent particle radius for each final Pr₆O₁₁ product is attributed to sintering. The presence of hydroxyl and carbonate groups in the Pr₆O₁₁, Pr₂O₃, Pr(OH₃), and Pr₂ (CO₃)₃ · xH₂O precursor dictate the morphology of thermally decomposed Pr₆O₁₁.     

Thermal decomposition of natural dolomite

Thermal decomposition behaviour of dolomite sample has been studied by thermogravimetric (TG) measurements. Differential thermal analysis (DTA) curve of dolomite shows two peaks at 777·8°C and 834°C. The two endothermic peaks observed in dolomite are essentially due to decarbonation of dolomite and calcite, respectively. The TG data of the decomposition steps have also been analysed using various differential, difference-differential and integral methods, viz. Freeman-Carroll, Horowitz-Metzger, Coats-Redfern methods. Values of activation entropy, Arrhenius factor, and order of reaction have been approximated and compared. Measured activation energies vary between 97 and 147 kJ mol⁻¹. The large fluctuation in activation energy is attributed to the presence of impurities such as SiO₂, Al₂O₃, Fe₂O₃, Cl⁻ etc in the samples. FTIR and XRD analyses confirm the decomposition reaction. SEM observation of the heat-treated samples at 950°C shows cluster of grains, indicating the structural transformation.     

Thermal stability and nonisothermal kinetics of Folnak® degradation process

Aim: The purpose of this article is to investigate the thermal stability and nonisothermal kinetics of Folnak® drug degradation process using different thermoanalytical techniques. Methods: The nonisothermal degradation of Folnak® powder samples was investigated by simultaneous thermogravimetry–differential thermal analysis, in the temperature range from ambient to 810°C. Results: It was found that the degradation proceeds through five reaction stages, which include the dehydration, the melting process of excipients, the decomposition of folic acid, corn starch, and saccharose. The presence of compounds such as excipients increases the thermal stability of the drug and some kind of solid–solid and/or solid–gas interaction occurs. Conclusion: It was concluded that the main degradation stage of Folnak® sample represents the decomposition of folic acid. It was established that the folic acid decomposition cannot be explained by simple reaction order model (n = 1) but with the complex reaction mechanism that includes higher reaction orders (n > 1). The isothermal predictions of the folic acid decomposition at four different temperatures (T_iso = 180°C, 200°C, 220°C, and 260°C) were established. It was concluded that the shapes of conversion curves at lower temperatures (180–200°C) were similar, whereas they became more complex with further temperature increase because of the complexity of the decomposition reaction.     

Sorption of uranium from underground leaching solutions with highly basic anion exchangers

Sorption of U on strongly basic anion exchangers AMP, AM-p, Lewatit K6267, Lewatit MonoPlus MP600XL, Purolite A500u, and Purolite A600u was studied at various temperatures in batch and dynamic experiments. The dynamic exchange capacities, (g U) dm^?3, of the anion exchangers to a breakthrough of 0.5 (mg U) dm^?3 at 6–8°C were determined: AMP (9.56) > Purolite A600u (9.26) > Lewatit K6267 (9.13) > Purolite A500u, Lewatit MonoPlus MP600XL (8.87) > AM-p (5.88). Also, the total dynamic exchange capacities, (g U) dm^?3, of the anion exchangers at 6–8°C were determined: AMP (37.13) > Purolite A500u (31.79) > Lewatit MonoPlus MP600XL (28.88) > Lewatit K6267 (27.74) > AM-p (27.58) > Purolite A600u (25.24). The concentration equilibrium distribution coefficients (K _d) of U on these resins were determined in batch experiments. The highest value of K _d = 2869 at 6°C and initial uranium concentration in solution of 65 mg dm^?3 was attained with AMP of commercial grain-size distribution. At 24°C and the same uranium concentration, the highest value of K _d = 5195 was obtained with separated 0.8–1.0-mm fraction of AMP. The kinetic experiments were performed, and the internal diffusion step was found to be the limiting step of the U sorption with all the resins under consideration. The internal diffusion coefficients in ion exchanger grains were calculated to compare the resins with each other.     

(TiZrHf)P2O7: An equimolar multicomponent or high entropy ceramic with good thermal stability and low thermal conductivity

ZrP₂O₇ is a promising material for high temperature insulating applications. However, decomposition above 1400 °C is the bottleneck that limiting its application at high temperatures. To improve the thermal stability, a novel multicomponent equimolar solid solution (TiZrHf)P₂O₇ was designed and successfully synthesized in this work inspired by high-entropy ceramic (HEC) concept. The as-synthesized (TiZrHf)P₂O₇ exhibits good thermal stability, which is not decomposed after heating at 1550 °C for 3 h. It also shows lower thermal conductivity (0.78 W m⁻¹ K⁻¹) compared to the constituting metal pyrophosphates TiP₂O₇, ZrP₂O₇ and HfP₂O₇. The combination of high thermal stability and low thermal conductivity renders (TiZrHf)P₂O₇ promising for high temperature thermal insulating applications.     

Preparation and characterization of silicon nitride-silicon carbide composites

Silicon nitride-silicon carbide (Si₃N₄-SiC) composites were prepared by varying the percentage of silicon nitride at temperatures of 1350 to 1450°C. The mechanical and thermal properties of these composites were determined. The modulus of rupture of the composites increases with increase of temperature whereas the thermal expansion decreases. Composites with 10% and 50% Si₃N₄ have modulus of rupture of 49 and 86 MPa at 1400°C and thermal expansion coefficients (25°–1000°C) of 4·4 × 10⁻⁶ and 3·2 × 10⁻⁶°C⁻¹ respectively.     

High Amplification of the Antiviral Activity of Curcumin through Transformation into Carbon Quantum Dots

It is demonstrated that carbon quantum dots derived from curcumin (Cur‐CQDs) through one‐step dry heating are effective antiviral agents against enterovirus 71 (EV71). The surface properties of Cur‐CQDs, as well as their antiviral activity, are highly dependent on the heating temperature during synthesis. The one‐step heating of curcumin at 180 °C preserves many of the moieties of polymeric curcumin on the surfaces of the as‐synthesized Cur‐CQDs, resulting in superior antiviral characteristics. It is proposed that curcumin undergoes a series of structural changes through dehydration, polymerization, and carbonization to form core–shell CQDs whose surfaces remain a pyrolytic curcumin‐like polymer, boosting the antiviral activity. The results reveal that curcumin possesses insignificant inhibitory activity against EV71 infection in RD cells [half‐maximal effective concentration (EC₅₀) >200 µg mL^?1] but exhibits high cytotoxicity toward RD cells (half‐maximal cytotoxic concentration (CC₅₀) <13 µg mL^?1). The EC₅₀ (0.2 µg mL^?1) and CC₅₀ (452.2 µg mL^?1) of Cur‐CQDs are >1000‐fold lower and >34‐fold higher, respectively, than those of curcumin, demonstrating their far superior antiviral capabilities and high biocompatibility. In vivo, intraperitoneal administration of Cur‐CQDs significantly decreases mortality and provides protection against virus‐induced hind‐limb paralysis in new‐born mice challenged with a lethal dose of EV71.     

The effect of LaFeO3@MnO2 on the thermal behavior of energetic compounds: An efficient catalyst with core-shell structure

Large particle size and low specific surface area are two major factors of restricting metal oxides as combustion catalyst with high performance. The construction of three-dimensional (3D) heterojunction materials with synergistic effect is conducive to enhancing the catalytic activity. In this work, LaFeO₃ were prepared by a facile solvo-thermal method and post-heat treament. However, the LaFeO₃ with a large particle size shows poor specific surface area, resulting in a low catalytic activity. In order to improve its catalytic activity, a 3D core/shell heterostructured LaFeO₃@MnO₂ composite was constructed by coupling LaFeO₃ with MnO₂. The core-shell structured LaFeO₃@MnO₂ provides a larger specific surface area and high catalytic effect on the thermal decomposition of ammonium perchlorate (AP) with a reduced decomposition temperature from 403.73 °C to 281.38 °C, an enhanced energy release from 649.6 J·g⁻¹ to 966.5 J·g⁻¹, and a decreased apparent activation energy from 139.05 kJ·mol⁻¹ to 110.88 kJ·mol⁻¹. Additionally, LaFeO₃@MnO₂ also shows efficient catalytic effects on the thermal decomposition of hexanitrohexaazaisowurzitane (CL-20) and cyclotetramethylenetetranitramine (HMX)_.     

Low temperature preparation of stabilized zirconia

The preparation of stabilized zirconia by thermal decomposition of metal alkoxides is reported. Formation of stabilized zirconia takes place at 400° C. The a.c. conductivity of the samples has been measured from 400 to 1000°C. The best conductivity is found in ZrO₂doped with 15 per cent CaO, which at 400° C is 2.37×10⁻⁶ Ω⁻¹ cm⁻¹ and at 1000°C is 1.26×10⁻² Ω⁻¹ cm⁻¹, with an activation energy of 1.16eV. Transport number measurements show that stabilized zirconia prepared by this method is purely an oxygen ion conductor.     

Chemical vapour deposition of epitaxial Ni-Zn ferrite films by thermal decomposition of acetylacetonato complexes

Epitaxial (Ni, Zn)Fe₂O₄ films were prepared on (100) MgO single crystal substrate by lowpressure chemical vapour deposition using a thermal decomposition of acetylacetonatocomplexes, Ni(acac)₂, Zn(acac)₂ and Fe(acac)₃. These complexes were evaporated at 157, 79 and 146° C, respectively, and transported with nitrogen carrier gas (flow rate 100 ml min⁻¹) to the deposition furnace. Polycrystalline and epitaxial films were grown at 500 to 600 and 600 to 650° C, respectively, under a pressure of 12 torr. The epitaxial film of Ni_1−xZn_xFe₂O₄ (x⋍0.4) treated at 600° C for 60 min, showed the saturation magnetization of 67 e.m.u. g⁻¹ and the coercive force of 20 to 30 Oe.     

Experimental investigation on properties of composite sorbents for three-phase sorption-water working pairs

LiCl/H₂O and CaCl₂/H₂O show a great potential for sorption air-to-water and thermal energy storage (TES) with their large water sorption capacity. A concept of three-phase composite solid-liquid/gas sorption is proposed by using activated carbon fiber (ACF) felt as a porous host matrix to combine with LiCl and CaCl₂. Samples with different proportions of salts and varied mass ratios between LiCl and CaCl₂ are developed, and thermal conductivity, sorption kinetics and simultaneous thermal analysis (STA) are experimentally investigated. Results reveal that ACF is a better choice of matrix because water uptake and energy storage density of aforementioned samples are greatly increased. It appears that the composite sorbent of ALiCa30(3:1) is a promising material for sorption air-to-water and TES, with water uptake of 2.98 g g⁻¹ at 25 °C and 90% relative humidity, mass energy storage density of 0.41 kWh kg⁻¹ and volume energy storage density of 223 kWh m⁻³.     

Thermal oxidation of InAs and characterization of the oxide film

The thermal oxidation of InAs and the properties of the resultant oxide films were studied. Uniform InAs oxide films with a resistivity of 10¹² Ω cm were obtained on InAs substrates by low temperature oxidation at around 400°C. The thermal oxide films are mainly composed of polycrystalline In₂O₃ and As₂O₃. Increasing oxidation temperature causes thermal decomposition of the As₂O₃ and the accumulation of elemental arsenic in the oxide film. The oxide resistivity decreases with increasing oxidation temperature, mainly as a result of the thermal decomposition of the As₂O₃. The interface state densities near the midgap of InAs are (2–5) × 10¹¹ cm^-2 eV^-1. A metamorphic layer is formed beneath the thermal oxide of InAs by high temperature oxidation above 500°C.     

Synthesis and thermal behaviour of potassium sialate geopolymers

The geopolymers potassium polysialate (K-PS) and potassium sialate disiloxo (K-PSDS) have been found to possess extremely good thermal stability. K-PS shows little sign of melting up to 1400 °C, its amorphous structure being replaced by the crystalline feldspars leucite and kalsilite at 1000 °C. ²⁷Al and ²⁹Si MAS NMR confirm the ease of this thermal reaction which involves only slight changes to the tetrahedral Al environment. Silica-rich K-PSDS becomes friable and porous at >1200 °C, with less complete crystallisation of K-feldspar, the formation of some cristobalite and the retention of a degree of amorphous geopolymer. ³⁹K NMR suggests that the charge-balancing alkali ions in the K-PS and K-PSDS geopolymer networks behave similarly to those of Na geopolymers, dehydrating on heating and moving into the feldspar lattice >1000 °C.     

Thermal degradation behavior and kinetic analysis of poly(L-lactide) in nitrogen and air atmosphere

The non-isothermal and isothermal degradation behaviors and kinetics of poly(L-lactide) (PLLA) were studied by using thermogravimetry analysis (TGA) in nitrogen and air atmosphere, respectively. At lower heating rate ((5–10)°C/min), PLLA starts to decompose in air at lower temperature than those in nitrogen atmosphere; however, at higher heating rate ((20–40)°C/min), the starting decomposition temperature in air are similar to those in nitrogen atmosphere, not only showing that PLLA has better thermal stability in nitrogen than in air atmosphere, but also suggesting that the faster heating rate will decrease the decomposition of PLLA in thermal processing. Whether in air or in nitrogen atmosphere, the decomposition of PLLA has only one-stage degradation with a first-order decomposed reaction, suggesting that the molecular chains of PLLA have the similar decomposed kinetics. The average apparent activation energy of nonisothermal thermal degradation (Ē _non) calculated by Ozawa theory are 231.7 kJ·mol⁻¹ in air and 181.6 kJ·mol⁻¹ in nitrogen; while the average apparent activation energy of isothermal degradation (Ē _iso) calculated by Flynn method are 144.0 kJ·mol⁻¹ in air and 129.2 kJ·mol⁻¹ in nitrogen, also suggesting that PLLA is easier to decompose in air than in nitrogen. Moreover, the decomposed products of PLLA are also investigated by using thermogravimetry-differential scanning calorimetry-mass spectrometry (TGDSC-MS). In air atmosphere the volatilization products are more complex than those in nitrogen because the oxidation reaction occurring produces some oxides groups.