Characterization of clay intercalated cobalt-salen catalysts for the oxidation of p-cresol

The intercalation of cobalt-salen complexes into the interlamelar spaces of montmorillonite clay was investigated by various characterization studies. The “neat” cobalt-salen complex showed a weight loss at 368 °C while the weight loss for the corresponding intercalated complex was observed at much higher temperature of 492 °C due to decomposition of the complex. The thermal stabilization observed was due to the host–guest interaction of clay and metal complex and thus confirmed the intercalation. The XANES spectrum of Co(salen)-mont sample revealed the change of symmetry from the tetrahedral in plane to the octahedral structure having an axial bonding of oxygen to the cobalt, indicating that cobalt atoms in Co(salen)-mont were coordinated axially with the lattice oxygen of montmorillonite. Both XANES and EXAFS results indicated that cobalt atoms in Co(salen)-mont form two additional Co–O bonds with a bond length of 0.199 nm by the intercalation while retaining the Co-salen structure. Co-salen intercalated into the montmorillonite clay showed the highest activity for the air oxidation of p-cresol, giving 88% selectivity to the oxidation products. Effects of NaOH concentration and various solvents on the conversion and selectivity patterns also have been studied.     

Temperature effects on iodine adsorption on organo-clay minerals: II. Structural effects

Smectites and vermiculites modified with hexadecylpyridinium (HDPy⁺), hexadecyltrimethylammonium (HDTMA⁺), benzethonium (BE⁺) and dipyridinododecane (DPyDD²⁺) cations exhibit high adsorption capabilities for the anionic radionuclide ¹²⁵I⁻ (Part I of this article). In some cases, exposure to higher temperature decreased the anion adsorption. To clarify the mechanisms of temperature dependence of the investigated organo-clay minerals, structural properties and thermal stabilities were examined by in situ powder X-ray diffraction (XRD), thermogravimetry (TG), thermocalorimetry (DTA) and FTIR spectral analyses.The organic cations HDPy, HDTMA and BE form bilayers, pseudotrimolecular layers and paraffin-type structures. The basal spacings of DPyDD-smectite and DPyDD-vermiculite were more or less unchanged in comparison to the original clay minerals (1.4 nm). It is assumed that the anion adsorption is due to the uptake of organic cations in an excess of the CEC, predominantly in the interlayer spaces as ion pairs.The decreasing iodide adsorption with increasing temperature is probably due to conformational changes of the alkyl chains, which are most pronounced for DPyDD-vermiculite at 60 °C (1.48→1.20 nm). Additionally, dehydration reactions, which occur at distinct temperatures for the organo-vermiculites (HDPy, 71; HDTMA, 57, 72; BE, 61; DPyDD, 41 °C), may be another reason for a decrease in iodide adsorption. The thermal decomposition of the organic cation starts at 200 °C. The HDPy, HDTMA and DPyDD-smectites and the HDTMA and BE-vermiculites show a high thermal stability with the basal spacing remaining constant up to 150 °C, which recommends the use for anion retention in engineered barriers for heat-producing waste.     

Thermal transformations of sonicated pyrophyllite

The differences on the thermal behaviour (DTG–DTA) of three pyrophyllite samples measured before and after sonication have been studied. Sonication treatment produces substantial textural modifications but negligible changes in the structure of the material. These modifications produce important changes in the thermal behaviour of pyrophyllite samples. Thus, it produces a decrease of more than 100 °C in the dehydroxylation temperature as measured by DTG and DTA effects. In addition, the exothermic effect of mullite formation shifts to lower temperature (about 30 °C) in sonicated pyrophyllite. These modification in the thermal behaviour are related to the pronounced decrease in particle size. The dehydroxylation effect of kaolinite that accompanies two of the studied samples, overlaps with that of sonicated pyrophyllite; however, the exothermic effect at 975 °C of kaolinite remain unchanged with the treatment.     

Thermal characteristics of nongraphitizable carbon negative electrodes with electrolyte in Li-ion batteries

Two kinds of nongraphitizable carbon were applied as active materials of negative electrodes in Li-ion batteries. The thermal properties of cycled electrodes mixed with or without commercial 1 M LiPF₆/EC–DMC electrolyte were investigated by TG–DSC from room temperature to 400 °C at a heating rate of 5 °C/min. Both kinds of lithiated electrodes showed exothermic peaks at about 310 °C due to decomposition of SEI by lithiated carbon powder. For the mixture of delithiated electrodes and electrolytes, the heat generation was attributed mainly to thermal decomposition of the electrolyte at about 280 °C. But for the mixture of lithiated electrodes and electrolytes, thermal risk mainly came from the reaction between original/secondary SEI and intercalated Li ions, which caused drastic heat generation at about 285 °C. Moreover, the thermal behavior of the mixture of cycled electrodes and electrolytes was directly related to the ratio between electrodes and coexisting electrolytes. When the ratio between electrodes and electrolytes was suitable, an endothermic reaction between SEI and electrolytes became dominant and depressed other exothermic heat, which reduced the thermal risk of the mixture of electrodes and electrolytes at elevated temperature.     

Burnout behavior of ceramic coated open cell polyurethane (PU) sponges

Open cell rigid foams made from polyurethane (PU) are frequently used in ceramic processing for preparation of porous ceramics by the so-called replica technique. This work presents data regarding the PU burnout, shrinkage characteristics as well as the morphology of the ceramic coated PU sponges during heating up. Shrinkage of the ceramic coated PU sponges closely follows the mass loss due to PU decomposition. Two temperatures (i) 267 °C and (ii) 380 °C were identified at which PU decomposition reaches local maxima. Shrinkage measurements on ceramic coated PU sponges reveal that both PU decomposition stages lead to similar extends of shrinkage in the ceramic coated PU sponge. Differential thermal analysis (DTA) showed that the two decomposition related temperatures (267 and 380 °C) differ concerning the energy release. While the low-temperature signal is endothermic, an exothermic signal was detected at 380 °C. The morphology of the ceramic coated PU sponges was investigated with scanning electron microscopy (SEM) which gave insight into the formation of hollow ceramic struts—a well known feature of ceramics being prepared by the replica technique.     

Fluridone adsorption–desorption on organo-clays

The adsorption–desorption of the herbicide fluridone on Na-montmorillonite and several organo-montmorillonite complexes was studied at a variety of loadings of the organic cation and pH levels. The aim was to find the organo-clay complex, which would be an optimal adsorbent for the hydrophobic fluridone. The organic cations studied were hexadecyltrimethylammonium (HDTMA), benzyltriethylammonium (BTEA), benzyltrimethylammonium (BTMA) and methylene blue (MB) at loadings equal to 25%, 50% and 100% of the cation exchange capacity (CEC) of the clay-mineral. The adsorbed amount of fluridone increased several-fold when montmorillonite was preadsorbed by the organic cation HDTMA up to its CEC and with BTMA at a loading of 5/8 of the CEC. BTEA and MB did not improve the adsorption capacity of the clay for fluridone. The results suggest that interactions between the phenyl rings of the herbicide and that of a small organic cation are geometrically easier to establish than with a larger organic cation. A reduced interaction between the phenyl rings of MB and those of fluridone may account for the low affinity of fluridone adsorption on montmorillonite-MB. In all cases, fluridone adsorption increased with decreasing pH and reached 100% for pH 2.7. Protonation of fluridone molecules with decreasing pH would result in increased adsorption through cation exchange. Thus, by regulating the pH, complete fluridone adsorption can be achieved. Desorption isotherms demonstrate high degree of irreversibility of the adsorption–desorption process and suggest that strong binding mechanisms dominate the fluridone-clay and organo-clay interactions. The results for fluridone adsorption–desorption demonstrate that, for similar molecules, a clay-based slow release formulation can be designed by first lowering the pH.     

Thermal Decomposition of Potassium Titanium Hexacyanoferrate（Ⅱ） Loaded with Cesium in a Fixed Bed Calciner

The thermal decomposition of potassium titanium hexacyanoferrate（ Ⅱ ） （KTiFC） loaded with cesium （referred to as Used Exchanger,or UE） was-studied at different flow rate of air in a fixed bed calciner. The calcina t ign processconsisted of four stages：ambient temperature- 180℃ （stageⅠ ）, 180-250℃（stage Ⅱ）, 250-400℃ （stage Ⅲ）, and constant 400℃ （stage Ⅳ）.The most intense reaction occurred in stage .Ⅱ. The rate of thermal decomposition was controlled, depending on the O2 flux, by O2 or CN concentration in ditterent stages. Results from differential thermal analysis （DTA） showed that the calcination reaction of the anhydrous UE was exothermic, with an approximate heat output of 4.6kJ·g^-1, which was so large to cause the possible agglomeration of calcined residues. The agglomeration could be avoided by enhancing heat transfer and controlling the O2 flux. It was found that there was no cyanides in the calcined residues and no CN-bearing gases such as HCN and （CN）2 in the off-gas. It seemed that the catalytic oxidation furnace behind the fixed bed calciner could be cancelled.     

The mechanism of β- Carotene adsorption on activated montmorillonite

The variations in the structure of mineral during adsorption have been examined comparing the results of X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetry (TG) and infrared (IR) spectroscopy of the acid activated montmorillonite clay mineral before and after adsorption of β-carotene. Based on the results, it was concluded that β-carotene attaches to the clay surface in the form of carbonium ions either by forming hydrogen bonds with Br?nsted sites or by forming coordination bonds with Lewis sites of the activated clay mineral.     

Changes in potassium exchangeability in heated lepidomelane

Changes in the K behavior of lepidomelane were induced by heating samples of the mica. These changes were related to concurrent alterations in the heated mineral to obtain information about the role of mineral properties in the exchangeability of interlayer K. The masking effects of small particles and fixable cations in the extractant were minimized by using 5–10 μm samples and NaCl---NaBPh₄ extracting solutions, respectively. The mica samples were heated in a muffle furnace for different periods at several temperatures between 300° and 950°C before they were characterized in terms of their K release to the NaCl---NaBPh₄ solutions. The effects of these thermal treatments on the Fe²⁺ content, d-spacing and weight of the mica samples were also recorded.The thermal treatments reduced the rate and degree of interlayer K exchange in the lepidomelane. Heat treatments at 300°C had relatively little effect, but the extraction of interlayer K required progressively longer periods when the temperature was increased incrementally to 950°C or the heating period at these higher temperatures was increased. Using the amounts of K extracted in 3 days as an index of the average rate of K release, a close relationship between the K release rate and Fe²⁺ oxidation in the heated mica was shown to exist. At the same time, however, reductions in the sample weight and basal spacing of the mineral occurred and were attributed to dehydroxylation in the heated mica. These changes in basal spacing probably had some effect on the rate with which all the K was released but had a more pronounced effect on the last 30% of interlayer K and finally made this part of the K nonexchangeable. The reduction in maximum extractable K indicates that a portion of the mica layers have a higher charge density. The processes of dehydroxylation and Fe²⁺ oxidation occurred independently in the heated mica and are reflected in the combined effects of basal spacing, layer charge and OH status of the mineral on interlayer K exchange.     

Experimental study of uranium carbide pyrophoricity

Mixed plutonium and uranium monocarbide (UPuC) is considered as a possible fuel material for future nuclear gas fast reactors. Its safe handling is currently a major concern, because inflammation of this material under the shape of fine powders is easy and highly exothermic (pyrophoricity) even under ambient temperature and partial pressure of oxygen inferior to 0.2 bar. CEA Marcoule is implied in both experimental and numerical studies on the UC powder oxidation exothermic reaction. Experimental tests consist in determining the influence of various parameters (gas composition, heating ramp, specific surface of powders) on the sample inflammation temperature. Two kinds of analytical apparatus are used: The differential thermal analysis (DTA) and the differential scanning calorimetry (DSC) coupled to the thermo gravimetric analysis (TGA). These apparatus are also linked to a gas mass spectrometer to follow the composition of combustion chamber gases. Results obtained with small quantities revealed that UC powder is highly reactive in air in the temperature range of 150-250 °C and showed a strong dependence between powder height in crucibles and inflammation temperature.     

Thermal evolution and crystallization kinetics of potassium-based geopolymer

In this paper crystallization kinetics of potassium-based geopolymer (Si/Al = 2.5, denoted as KG2.5) upon heating are investigated by differential thermal analysis (DTA) under non-isothermal conditions at various heating rates. From 35 to 700 °C KG2.5 shows a significant weight loss due to both evaporation of free water and condensation of hydroxyl groups. Crystallization of KG2.5 starts at a low temperature of ∼960 °C according to XRD and DTA analysis. KG2.5 also exhibits a low onset temperature of viscous sintering stage and on heating to 950 °C the sintering is completed. In the DTA graphs, the exothermic peaks which are caused by leucite crystallization shift to higher temperatures with increasing heating rate. The activation energy value of crystallization for leucite is found to be 455.9 kJ/mol and the corresponding Avarami constant is 3.89 indicating the three-dimensional crystal growth mechanism.     

Kinetics of the thermo-oxidative and thermal cracking reactions of Athabasca bitumen

The thermo-oxidative and thermal cracking reactions of Athabasca bitumen were examined qualitatively and quantitatively using differential thermal analysis (DTA). Reaction kinetics of low temperature oxidation (LTO) and high temperature cracking (HTC) were determined. The rate of the LTO reaction was found to be first order with respect to oxygen concentration. The activation energy and the Arrhenius pre-exponential factor were 64 MJ kg^?1 mol^?1 and 10^5.4 s^?1, respectively. The effects of atmosphere, pressure, heating rate and support material on the thermal reactions of bitumen were studied. In general, it was found that partial pressures of oxygen > 10% O₂ favoured exothermic oxidation reactions. High pressure increased the rates of LTO and HTC as well as the exothermicity of these reactions. A major contribution of this study to thermal in-situ processes is that heating rate can be used effectively to control the extent of low temperature oxidation and hence fuel availability during in-situ combustion. Low linear heating rates (2.8 °C min^?1) favoured low temperature oxidative addition and fission reactions. The reaction products readily formed coke and combusted upon heating. High linear heating rates (24.5 °C min ^?1) led to rapid oxidation reactions in the high temperature zone; the high temperature and the energy released during oxidation appeared to promote combustion. Finally, when sand was used as the support material there appeared to be a catalytic effect in both LTO and HTC reactions.     

Synthesis of hectorite–TiO2 and kaolinite–TiO2 nanocomposites with photocatalytic activity for the degradation of model air pollutants

We studied the synthesis and photocatalytic activity of small-sized TiO₂ supported on hectorite and kaolinite. Deposition of TiO₂ on the clay mineral surface was conducted by using a sol–gel method with titanium isopropoxide as precursor. Anatase TiO₂ particles formation was achieved by hydrothermal treatment at 180 °C. Material characterization was conducted using XRD, SEM, XPS, ICP-OES, BET and porosimetry analysis. fficiency in synthesizing clay–TiO₂ composites depended strongly on the clay mineral structure. Incorporation of anatase in hectorite, an expandable clay mineral, was found to be very significant (> 36 wt.% Ti) and to be followed by important structural changes at the clay mineral surface. Instead, no major structural modifications of the clay were observed for kaolinite–TiO₂, as compared with the untreated material. Photocatalytic performance of clay–TiO₂ composites was evaluated with ATR-FTIR following the oxidation of adsorbed toluene and d-limonene, two model air pollutants. In either case, the photocatalytic removal efficiency of these hydrophobic substrates by the synthesized clay–TiO₂ composites was comparable to that observed using pure commercial TiO₂ (Degussa P25).     

HES-HEMA nanocomposite polymer hydrogels: swelling behavior and characterization

Organophilic sodium montmorillonite (Na-MMT) and Laponite-RD clays were incorporated into photopolymerizable hydroxyethyl starch (HES) modified with 2-hydroxyethyl methacrylate (HEMA). Swelling, mechanical properties and thermal stability of obtained crosslinked nanocomposite polymers were evaluated. A camphorquinone-amine system was used as photoinitiating system in visible light. The interaction between nano-sized filler particles and polymer hydrogel was evaluated by FT-IR spectroscopy and the platelet distribution was investigated by SEM. An increased thermal stability of nanocomposite polymers upon addition of clay was observed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicating interaction between the clay platelets and the polymer chains. The crosslinking density for HES-HEMA/MMT nanocomposite hydrogels as investigated by swelling measurements increases with increasing the organo-clay content. The mechanical properties of virgin hydrogels were improved by the introduction of organo-clay as evidenced by oscillation rheology measurements. Whereas, the increase in crosslink density and storage modulus with clay content for laponite was found to be increasing for all concentrations investigated, for MMT there is an optimum content of ca. 1.5 wt%.     

Surfactant-modified bentonite as adsorbent for the removal of humic acid from wastewaters

The effectiveness of surfactant-modified bentonite (SMB) in removing humic acid (HA) from wastewaters was evaluated. Hexadecyl trimethylammonium (HDTMA) chloride was used to modify the surface of the clay mineral. The SMB exhibits very high adsorption potential for HA and at pH 3.0 more than 99% removal was achieved from an initial concentration of 25 μmol/L. The experimental kinetic data were analyzed using the pseudo-first-order kinetic model. Adsorption occurs through film diffusion at low as well as at higher concentrations and temperatures. The adsorption of HA using SMB was an exothermic process. HA adsorption was found to decrease with increase of ionic strength due to the formation of outer-sphere surface complexes on SMB. The equilibrium isotherms were determined and data were analysed using the Langmuir isotherm model. The maximum adsorption capacity, Q° was 73.52 μmol/g with binding constant, b = 0.155 L/μmol at 30 °C and pH 3.0. The adsorbent was suitable for repeated use (more than 3 cycles) without any noticeable loss of capacity.     

Organo-clay formulations of pesticides: reduced leaching and photodegradation

Adsorption of organic cations on several clay minerals is reviewed with an emphasis on the effect of ionic strength and modeling. The clay exchanged with suitable organic cations forms a basis for ecologically acceptable formulations of herbicides with reduced leaching, ground water contamination and enhanced weed control efficacy. Incomplete neutralization of the clay surface charge by an organic cation may be advantageous in achieving maximal adsorption of hydrophobic herbicides. One conclusion from these studies is that optimization of clay-based herbicide formulations requires a selection of structurally compatible organic cations preadsorbed on the clay at optimal coverage. New experimental results are presented for alachlor formulations, which significantly reduce herbicide leaching under conditions of heavy irrigation. We were able to demonstrate that organo-clay formulations of alachlor and metolachlor can increase crop yields in a 1-year field experiment. The photostabilization of pesticides is reviewed and improved organo-clay formulations of the herbicides trifluralin and norflurazon are described. A pillared clay, nanocomposite micro- and/or meso porous material, was effective in reducing leaching and in conferring photostabilization, without added organic cations.     

Study of the thermooxidative behavior of edible oils by thermal analysis

The complex thermoanalytical investigation of oil stability has been made by means of the Derivato-graph using dynamic and static programs. TG, DTG and DTA curves have been registered simultaneously. The aim of the experiments was to determine the optimum conditions for examination of oxidative stability and oxidation state of edible oils. Results show that the study of thermal decomposition under dynamic conditions allows the detection of thermal and oxidative degradation. Storability can be investigated under static (isothermal) conditions by modeling the oxidation processes. Oxidative changes can be followed quantitatively with thermogravi-metry (TG) and derivative thermogravimetry (DTG) curves, while differential thermal analysis (DTA) measurements show exothermic enthalpy changes. A novel method has been developed for rapid indication of the oxidative stability using isothermal conditions. Presented in part at the International Society for Fat Research meeting in Marseille, September 1976     

Preparation and characterization of novel organo-clay minerals for Hg(II) ions adsorption from aqueous solution

Novel organo-clay minerals for adsorption of Hg(II) ions were prepared. The clay minerals were grafted with 2-(3-(2-aminoethylthio)propylthio)ethanamine (AEPE). AEPE-montmorillonite and AEPE-hectorite were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), CHN element analysis (EA) and surface area analysis. The XRD patterns indicated that the chelating agents (AEPE) were mainly grafted on the external surface of montmorillonite while AEPE was grafted on both the external and interlayer surfaces of hectorite. The results from IR, TGA and EA showed a difference in chemical composition of the unmodified and modified clay minerals. The results confirmed that montmorillonite and hectorite were modified with the desired organic groups. The extent of ligand loading depended on the nature of the clay mineral. The AEPE-modified clay minerals were good chelating materials for Hg(II) ions, compared to the unmodified clay minerals. The adsorption capacity for Hg(II) of AEPE-montmorillonite and AEPE-hectorite was 46.1 and 54.7 mg g^− 1, respectively, for solution containing 140 mg L^− 1 Hg(II) ions (pH 4).     

Temperature dependence of processes during oxidation of PAN fibres

The 3000-PAN-filament tows have been stretched by a constant axial load during heating in air at a constant rate of . The extension of the tow begins about the glass-transition temperature (70°C). Temperature dependence of the fibre diameter, width of X-ray reflection of the PAN, and endothermic effect occurring at low temperature (below 240°C), suggest that at 130°C begins a molecular rearrangement. IR spectra of the oxidized fibres and gas evolution suggest that near this temperature (at about 145°C) begins cyclization, but the cyclized fraction of the fibres remains very low up to over 220°C, unless a prolonged oxidation at this temperature is carried out. TGA and DTA results suggest that at about 240°C begins rapid cyclization, which is at about 320°C followed by partial degradation of the fibres. In these processes the fibres lose about 26% of their original weight. Final degradation of the fibres begins at about 400°C.     

Permeability to water of sintered clay ceramics

The microstructural characteristics of sintered clay ceramics depend mainly on the clay type and thermal transformations. Different pore morphology and connectivity change the liquid water flow process through the material, as in the case of roof tiles which are progressively saturated with water during rain. In this study, 2 clays mined in Burkina Faso are used for manufacturing roof tiles. The major phases detected by X-ray diffraction in the two clays are kaolinite, illite, smectite, quartz and feldspar.The thermal behavior of clays by DTA and TG between 25 °C and 1100 °C is mainly related to individual roles of clay minerals. During sintering, dilatometry curves show successive densification stages in variable temperature ranges, as a function of clay mineral fractions in compositions. It explains differences in microstrutural characteristics and pore structure.The simulation of the capillary absorption of water uses the Sharp Front model. The interesting feature of this approach is that measurement of the data for the model requires no complex equipment. Only the Darcy permeability of the material and the steady state capillary pressure are necessary. Results evidence the strong difference of water absorption rates in the 2 clay ceramics, whereas they present similar porosity. It confirms the importance of pore morphology and connectivity in ceramics, induced mostly by the clay type and the sintering process.