Influence of selected cation and anion species on the adsorption of mercury (II) by montmorillonite

The influence of Cl⁻, NO₃⁻, ClO₄⁻, Na⁺, and Ca²⁺ on the kinetics of the Hg adsorption by montmorillonite was studied. The data indicate that the Hg adsorption process in different salt solutions obeyed multiple first order kinetics. In the absence of salts, the Hg adsorption in the fast process was 1.6, 2.0, 2.0, 4.6, and 4.6 times faster than that in the presence of NaClO₄, NaNO₃, Ca(NO₃)₂, NaCl, and CaCl₂, respectively. Similarly, after the initial rapid adsorption, the system in the presence of the strong complexing ligand, Cl⁻, had a slower adsorption rate than the systems in the absence of salts or in the presence of weaker ligands, NO₃⁻ and ClO₄⁻. However, the bulk of the Hg adsorption by montmorillonite took place in the initial rapid adsorption process. The magnitude of the reduction in the rate of the Hg adsorption was evidently dependent upon the ability of the ligands to complex with Hg. No significant differences between Na⁺ and Ca²⁺ in their ability to suppress the Hg adsorption were observed. When the Cl/Hg and ClO₄/Hg molar ratios were higher than 50 and 500, respectively, their suppressing effects on the adsorption of Hg by montmorillonite were evident.     

Special features of synthesis of a heat-resistant glass-ceramic coating

In order to protect Ni–Cr alloys from high-temperature corrosion, a new heat-resistant glass-ceramic coating was developed with a glass matrix synthesized on the basis of a composite R _x O–Al₂O₃–SiO₂–TiO₂ (R–Li^–, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺) system. The special features of the formation of crystalline phases in the glasses in heat treatment and the optimum regime for the formation of a glass ceramic structure are described.Translated from Steklo i Keramika, No. 3, pp. 30–32, March, 1996.     

Adsorption and desorption of Ni on Na-montmorillonite: Effect of pH, ionic strength, fulvic acid, humic acid and addition sequences

Humic substances and clay minerals have been studied intensively because of their strong complexation and adsorption capacities. In this work, adsorption of Ni²⁺ on Na-montmorillonite was studied using batch technique under ambient conditions. Effect of pH, ionic strength, solid content, humic acid (HA), fulvic acid (FA) and the addition sequences of fulvic acid/Ni²⁺/montmorillonite on Ni²⁺ adsorption was also investigated. The results indicate that adsorption of Ni²⁺ on montmorillonite are strongly dependent on pH and ionic strength. The adsorption of Ni²⁺ is mainly dominated by surface complexation and ion exchange. The adsorption–desorption hysteresis suggests that the adsorption of Ni²⁺ is irreversible. The thermodynamic parameters (ΔH, ΔS, and ΔG) are calculated from the temperature dependence, and the results suggest that the adsorption reaction is endothermic and spontaneous. The presence of FA and the addition sequences of FA/Ni²⁺/montmorillonite do not influence the adsorption of Ni²⁺ on FA bound montmorillonite hybrids. Montmorillonite is a suitable candidate for pre-concentration and solidification of Ni²⁺ from large volume of solutions.     

Preparation of Berberine-montmorillonite-metolachlor formulations from hydrophobic/hydrophilic mixtures

Metolachlor which is a pre-emergent hydrophobic herbicide with moderate solubility, was detected in several water wells in agricultural and even urban areas. This study aims for the preparation of organoclay platforms which could release metolachlor in a more controlled pattern, thus — reducing the leaching to groundwater. The adsorption of metolachlor to organoclays based on difenzoquat, diquat or berberine added up to neutralizing the original charge of the clay mineral was tested. The adsorption loadings of metolachlor on berberine-montmorillonite were found to be more than 30% of the compound, whereas for difenzoquat- and diquat-montmorillonite the amounts were only 3.8% and 4.9%, respectively. Consequently, further experiments were conducted focusing on berberine-montmorillonite. Loading of preadsorbed berberine was crucial to the hydrophobicity of the platforms and it had also influence on the adsorption of metolachlor in mixed immiscible phases experiments. The exact procedure of preparation was also a key issue on determining final metolachlor amounts on the formulation: Preparation of the formulation from suspended organoclay which was not dried after preadsorbing the berberine, and was mixed with metolachlor dissolved in chloroform gave the highest percentages of adsorbed herbicide. Release from organoclay formulation was at a more controlled fashion than for commercial herbicide, or commercial herbicide mixed with non-modified montmorillonite, leaving a relatively constant concentration of herbicide after several desorption cycles.     

Chitosan intercalated montmorillonite: Preparation, characterization and cationic dye adsorption

Chitosan intercalated montmorillonite (Chi-MMT) was prepared by dispersing sodium montmorillonite (Na⁺-MMT) into chitosan solution at 60 °C for 24 h. The Chi-MMT was characterized by XRD, XRF and FT-IR. The intercalation was accomplished via the ion-exchange of Na⁺ ions with –NH₃⁺ of chitosan, resulting in the expansion of d₀₀₁ from 1.42 nm of Na⁺-MMT to 2.21 nm of Chi-MMT. The chitosan content in the Chi-MMT measured by TGA was about 17 mass%. The adsorption capacity of Chi-MMT was investigated in comparison with the starting Na⁺-MMT and chitosan using three different cationic dyes, i.e. basic blue 9 (BB9), basic blue 66 (BB66) and basic yellow 1 (BY1). The Chi-MMT showed the highest adsorption capacity in the range of 46–49 mg/g when the initial dye concentration was 500 mg/L, being equivalent to 92–99 wt.% of dye removal. The adsorption capacities of Chi-MMT for all basic dyes increased with an increase of initial dye concentration. An increase of adsorption capability of Chi-MMT was attributed to the existence of intercalate-chitosan. It could enlarge the pore structure of Chi-MMT, facilitating the penetration of macromolecular dyes, and also electrostatically interact with the applied dyes. These results indicated the competency of Chi-MMT adsorbent for basic dye adsorption.     

Influence of interlayer cations on the water sorption and swelling–shrinkage of MX80 bentonite

The potential of water sorption and swelling–shrinkage in the expansive clays is practically defined by the nature of interlayer cations. The purpose of this paper is to estimate the effects of the cation saturation (Mg⁺, Ca⁺, Li⁺, Na⁺, and K⁺) on the swelling–shrinkage behaviour of the MX80 bentonite.The MX80 bentonite (a “commercial clay”) was treated with concentrated solutions (1 N) of sodium, calcium, magnesium, potassium, and lithium chlorides. This treatment was made three times with constant agitation for 1 h. Then, the clay was washed three times with distilled water. The scanning transmission electron microscopy (STEM) and inductively coupled plasma atomic emission microscopy (ICP-AES) analyses were used to verify the efficiency of the cation saturation.Finally, two techniques were employed to estimate the effect of the cation saturation on the swelling–shrinkage behaviour of the bentonite: the first one uses an isothermal system of water adsorption, where the water activity is controlled by a supersaturated salt solution. In the second, environmental scanning electron microscopy (ESEM), coupled with a digital image analysis (DIA) program, was used to estimate the swelling–shrinkage potential at different water activities. The swelling–shrinkage isotherms were always estimated on isolated aggregates.The isotherms of water adsorption and swelling–shrinkage of the bentonite MX80 show that the amount of adsorbed water and the swelling–shrinkage potential depend directly on the interlayer cation. For example, the sodium bentonite presents an excellent capacity to swell while the lithium bentonite does not swell significantly at the aggregate scale. In addition, other textural properties may be modified by the cation saturation, such as the specific surface, the particle size, porosity, etc.     

Reversible collapse and Mg release of de- and rehydroxylated homoionic cis-vacant montmorillonites

Homoionic Na⁺, Ca²⁺, Sr²⁺, Li⁺, Cu²⁺ and Zn²⁺ samples of the <2 μm fraction of a cis-vacant montmorillonite from Linden (Bavaria) were steam treated at 200°C (≈1.5 MPa), 240°C (≈3.3 MPa) and 300°C (≈8.0 MPa) after dehydroxylation at temperatures up to 630°C. Cation exchange capacity (CEC) measurements, determination of exchangeable cations and X-ray diffraction (XRD), supplemented by thermoanalytical investigations of the evolved water in a thermobalance linked to a mass spectrometer, infrared (IR) and electron spin resonance (ESR) spectroscopy were employed to obtain information about the state of expandability and structural changes of swellable montmorillonite and the sites of interlayer and octahedral cations after heating and rehydroxylation.The XRD pattern of the initial samples showed a well-defined (001) reflection according to the interlayer cation and its hydration state under laboratory atmosphere. After dehydroxylation the pattern exhibited (001) reflections between 9.6 and 9.8 Å, corresponding to a collapsed structure for all samples. The Na⁺-, Ca²⁺- and Sr²⁺-rich montmorillonites regained partial expandability after rehydroxylation at 200°C and full expandability after rehydroxylation at 300°C if the dehydroxylation temperature was less than 630°C. Rehydroxylation at 300°C of the Cu²⁺- and Zn²⁺-rich montmorillonites did not cause reexpansion, whereas the Li⁺-rich samples recovered a partial swellability after rehydroxylation at 240°C and nearly the full swellability after rehydroxylation at 300°C.The Li⁺-, Cu²⁺- and Zn²⁺-rich samples underwent a strong CEC reduction due to migration of the interlayer cations into the 2:1 layer before dehydroxylation started. After rehydroxylation under water steam Cu²⁺- and Zn²⁺-rich samples released 16–30 meq/100 g of Mg²⁺ from the structure, increasing with the steam temperature. Mg²⁺ release was not observed for the Li⁺-rich montmorillonite.     

Adsorption of difenzoquat on montmorillonite: model calculations and increase in hydrophobicity

The adsorption of difenzoquat (DZ) on montmorillonite was studied at a wide range of concentrations and ionic strengths. Up to difenzoquat loadings of 0.4 mmol/g clay, all the added cation were adsorbed. Maximal adsorbed amounts exceeded slightly the cation exchange capacity (CEC) of the clay (0.8 mol_c/kg). The adsorbed amounts did not change upon increasing the concentration of NaCl in the medium to 500 mM. An adsorption model that combines electrostatic equations with specific binding in a closed system could adequately predict the adsorbed amounts of DZ, even at high ionic strength. Simultaneous adsorption of the divalent cationic herbicide diquat (DQ) and DZ was also determined and the predictions of the model were adequate for total loadings up to the CEC of the clay. At higher loads the model adequately predicts the DZ adsorbed, but underestimates the amounts of DQ adsorbed. The influence of adsorbed DZ on the hydrophobicity of montmorillonite was tested by using the hydrophobic herbicide pendimethalin (PM). The adsorption isotherm of PM on crude montmorillonite is of the S type, indicating very low adsorption at low added amounts, and increasing affinity after part of the surface is covered with the hydrophobic molecules. Adsorption of PM on montmorillonite saturated with DZ up to 80% of the CEC showed a C behavior, indicating a partition mechanism between the solvent and the adsorbent even at low added amounts. The enhanced hydrophobicity of DZ–montmorillonite was also demonstrated in qualitative experiments in a mixed chloroform–water environment: whereas the crude clay mineral stayed in the water phase, DZ–montmorillonite concentrated in the chloroform phase.     

Enhanced pesticide adsorption by thermally modified bentonites

Wyoming bentonite was calcined at 350–550° for 1, 3, and 12 h, dispersed in water and freeze-dried. Calcination at 350–450°C for 12 h decreased the specific surface area strongly. At higher calcination temperatures, the surface area became similar to the value of the uncalcined bentonite (24 m²/g). The micropore (diameter <2 nm) volume of the calcined samples was very small (<0.2 μl). In contrast, the mesopore (diameter 2–50 nm) volume increased sharply when the bentonite was calcined at >450°C. The total specific surface area mainly comprised the mesopore surface area. The Wyoming bentonite used in these experiments adsorbed considerable amounts of metolachlor from aqueous solutions, and the adsorption was enhanced by calcinating the bentonite. The metolachlor molecules, very likely, interact with aluminum ions or oligomeric hydroxoaluminum cations enriched on the edges of the silicate layers as a consequence of the thermal attack to the edges. A pronounced adsorption–desorption hysteresis is advantageous for using these bentonites in slow-release pesticide formulations.     

Brønsted and Lewis acid catalysis with ion- exchanged clays

An acid-treated montmorillonite clay has been ion-exchanged with Al³⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺ and Na⁺. The catalytic activities of these materials have been measured in the Brønsted acid catalysed rearrangement of α-pinene to camphene, and the Lewis acid catalysed rearrangement of camphene hydrochloride to isobornyl chloride, following thermal activation at temperatures from 75 to 350°C. The surface acidities of the ion-exchanged clays have been measured using a microcalorimetric method involving ammonia adsorption, and through the infrared spectra of adsorbed pyridine. The results show that maximum Brønsted acidity is generated on thermal activation at approximately 150°C and maximum Lewis acidity at 250- -300°C. A good correlation has been found between the surface acidities and the catalytic activities of the ion- exchanged clays in both reactions. A significant result is the relatively low surface Lewis acid strength of Al³⁺- exchanged clays, for which a possible explanation is proposed.     

Kinetics and Mechanism of the Interaction of Alkali Calcium Silicate Glasses with Salt Melts in the KNO3–Pb(NO3)2 System

The interaction of alkali calcium silicate glasses with salt melts in the KNO₃–Pb(NO₃)₂ system is investigated at temperatures of 420–520°C. The chemical composition of crystalline coatings formed upon treatment contains both components of the initial glass (SiO₂, 9–12 wt %; CaO, 0.8–1.2 wt %) and components of the salt melt (PbO, 82–89 wt %). The treatment temperature is the main factor affecting the structure of the modified surface layer. The mechanism of the interaction of alkali calcium silicate glasses with salt melts is analyzed. According to this mechanism, the interaction involves the ion exchange (with the participation of Na⁺, K⁺, Ca²⁺, and Pb²⁺ ions), crystallization of modified surface layers, and incorporation of Pb _x O _y nanoparticles (formed in the salt melt) into the coating structure.     

Adsorption of MCPA pesticide by MgAl-layered double hydroxides

In the present study, the adsorption characteristics of the herbicide MCPA (4-chloro-2-methylphenoxyacetic acid) on layered double hydroxides (LDHs) were evaluated under laboratory conditions with particular attention to the effect of layer charge, original interlayer anion and morphology. The final objective is the use of LDHs and modified LDH materials as recyclable adsorbents and heterogeneous catalysts for the treatment of contaminated waste waters.The anionic clays tested were [Mg_1−xAl_x(OH)₂]^x+[X_x/m^m−·nH₂O] materials. The MCPA adsorption capacity was determined from adsorption isotherms and a kinetic study. We looked at the influence of the pH, the Mg²⁺/Al³⁺ ratio, i.e. the anion exchange capacity, the nature of the intercalated anion X (CO₃²⁻, NO₃⁻, Cl⁻) and the morphology of the adsorbent on the extent of adsorption. The adsorption isotherms, described by Freundlich model, are of S-type with tendency to L-type for high MCPA equilibrium concentration. Furthermore, the adsorption capacity increases with the layer charge density. Hence, MCPA adsorption on LDHs occurs by anion exchange in two steps, an external exchange followed by an interlayer exchange, which explain these changes of type within the same isotherm. Besides, the adsorption capacity depends on the nature of the starting anions, following the affinity order (NO₃⁻<Cl⁻<CO₃²⁻) proposed by Miyata and increases with the specific surface area.     

Effective MgO surface doping of Cu/Zn/Al oxides as water–gas shift catalysts

Trace amounts of MgO were doped on Cu/ZnO/Al₂O₃ catalysts with the Cu/Zn/Al molar ratio of 45/45/10 and tested for the water–gas shift (WGS) reaction. A mixture of Zn(Cu)–Al hydrotalcite (HT) and Cu/Zn aurichalcite was prepared by co-precipitation (cp) of the metal nitrates and calcined at 300 °C to form the catalyst precursor. When the precursor was dispersed in an aqueous solution of Mg(II) nitrate, HT was reconstituted by the “memory effect.” During this procedure, the catalyst particle surface was modified by MgO-doping, leading to a high sustainability. Contrarily, cp-Mg/Cu/Zn/Al prepared by Mg²⁺, Cu²⁺, Zn²⁺ and Al³⁺ co-precipitation as a control exhibited high activity but low sustainability. Mg²⁺ ions were enriched in the surface layer of m-Mg–Cu/Zn/Al, whereas Mg²⁺ ions were homogeneously distributed throughout the particles of cp-Mg/Cu/Zn/Al. CuO particles were significantly sintered on the m-catalyst during the dispersion, whereas CuO particles were highly dispersed on the cp-catalyst. However, the m-catalyst was more sustainable against sintering than the cp-catalyst. Judging from TOF, the surface doping of MgO more efficiently enhanced an intrinsic activity of the m-catalyst than the cp-catalyst. Trace amounts of MgO on the catalyst surface were enough to enhance both activity and sustainability of the m-catalyst by accelerating the reduction–oxidation between Cu⁰ and Cu⁺ and by suppressing Cu⁰ (or Cu⁺) oxidation to Cu²⁺.     

Adsorption of β-carotene: II. On cation exchanged bleaching clays

X-ray diffraction patterns of a number of commercial bleaching earths indicate that they consist mainly of montmorillonite mixed with smaller amount of kaolinites as well as mica, quartz and cristobalite. The active sites in these earths for the adsorption of β-carotene are identified through ion exchange and found to be the protonic sites and some metallic ions. The efficiencies of the various cations in imparting activities to the earths are found to be in the order Mg²⁺ > Fe³⁺ > H⁺ > Ca²⁺ > Na⁺. For Fe³⁺ and H⁺ exchanged clays, the activity was found to be linear function of the concentration of these ions. The high activities of Mg²⁺ and Ca²⁺ exchanged clays are discussed. Presented in part as paper T12 in the International Conference on Palm Oil Product Technologies in the Eighties, Kuala Lumpur, May 1981.     

Interactions of Carbaryl with homoionic montmorillonite

Adsorption and catalytic degradation of the insecticide Carbaryl on montmorillonite self-supporting films (Upton, Wyoming) saturated with different cations (Al³⁺, Ca²⁺, Cu²⁺, Na⁺) was studied using thin-layer chromatography, X-ray diffraction, infrared and mass spectroscopy techniques. Carbaryl is adsorbed at room temperature by a coordination bond, through a water bridge, between the C=O group and the exchangeable cation. X-ray diffraction patterns showed that the molecule is always intercalated in the smectite layers except for Na-montmorillonite. On moderate heating (90°C for 30 h) the Carbaryl adsorbed on Cu- and Al-montmorillonite decomposes to CO₂, N-methylammonium cation, and 1-naphthol and polymerization products, di- and tri-condensate of 1-naphthol, are formed. By contrast for Ca- and Na-montmorillonite systems no degradation of Carbaryl was observed on heating at 90°C for 30 h. The Carbaryl decomposition can be ascribed to the concurrent effect, enhanced by dehydration, of the stronger polarizing power of Cu²⁺ and Al³⁺ ions and the acidity of the residual solvation water.     

Foam‐like polymer/clay aerogels which incorporate air bubbles

The structure/property relationships of polymer/clay aerogels interfused with uniformly distributed air bubbles were examined. Through the incorporation of a polyelectrolyte in a montmorillonite(MMT) clay solution, the viscosity was systematically changed by the addition of ions with different charges. The bubbles were achieved via high speed mixing and were stabilized through the use of the surfactant sodium dodecyl sulfate (SDS). As the charge of the ion increased from +1 (Na⁺ ions) to +2 (Ca²⁺ ions) to finally +3 (Al³⁺ ions), the modulus of the resultant aerogels increased. The foamed polymer/clay aerogels showed a reduction in thermal conductivity while retaining similar mechanical properties to unfoamed polymer/clay aerogels. The most promising composition was one which contained 5% MMT clay/5% poly(vinyl alcohol)/0.5% xanthum gum/0.5% SDS/0.2% Al₂(SO₄)₃·6(H₂O) possessing a density of 0.083 g/cm³, an average modulus of 3.0 MPa, and a thermal conductivity of 41 W/m·K. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39546.     

Heavy metal-adsorption on micas and clay minerals studied by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to study the adsorption of Cs-, Ba-, Cu-, Zn-, and Pb-ions on the external surfaces of various, well characterized 2:1 layer silicates (micas and illites).Before studying metal adsorption, it was necessary to determine the charge magnitude of the adsorption surface. This was done for chemically well-characterized micas (margarite, muscovite, sericite). The XPS analyses showed that the depth of analysis is about 15 Å. As a result it was possible to measure the surface- and interlayer ions on both sides of the outermost 2:1 layer. In determining the layer charges, the following strategy was used. The outer surface cations were replaced by Ba²⁺, giving, for ideal margarite an interlayer cation (Ca²⁺)/surface cation (Ba²⁺) ratio of 2:1 and in the case of muscovite a K⁺/Ba²⁺ ratio of 4:1. Deviations from these ratios indicate an asymmetry of layer charge in the outer sheet. Using the margarite, muscovite and sericite as standards, surface charge determination of a number of micas, illites, and I/S clays could be carried out by XPS.The properties of the metal-ions (charge, ionic radius, ionic potential), as well as layer charge characteristics of the clay, including surface charge magnitude and point of origin from tetrahedral or octahedral substitution, are factors which influence adsorption selectivity [Sposito, G., 1989. Surface reactions in natural aqueous colloidal solutions, G. Chimia, 43, 169–176]. The selection of previously well-characterized minerals, margarite, muscovite, celadonite, illite, montmorillonite, and beidellite for XPS study made it possible to relate these factors to heavy metal adsorption by the clay minerals.The results show that Cu²⁺ and Zn²⁺ are adsorbed as monovalent ions, presumably as (CuOH)¹⁺ and (ZnOH)¹⁺ hydroxy surface-complexes, due to their high ionic potential. Saturating the mica series with equimolar pairs of Cu–Zn and Cu–Pb, the ratios of Cu/Zn and Cu/Pb increase systematically with external surface charge. The higher the surface charge, the more selective is the exchange process for Cu with respect to Zn or Pb. Increasing external surface charge parallels increasing tetrahedral charge, which indicates that selectivity takes place at points of tetrahedral negativity on the crystallite surface, whereas octrahedral charge plays little role in the selective adsorption process.     

Property and Stability of Astaxanthin Emulsion Based on Pickering Emulsion Templating with Zein and Sodium Alginate as Stabilizer

Astaxanthin loaded Pickering emulsion with zein/sodium alginate (SA) as a stabilizer (named as APEs) was developed, and its structure and stability were characterized. The encapsulation efficiency of astaxanthin (Asta) in APEs was up to 86.7 ± 3.8%, with a mean particle size of 4.763 μm. Freeze-dried APEs showed particles stacked together under scanning electronic microscope; whereas dispersed spherical nanoparticles were observed in APEs dilution under transmission electron microscope images. Confocal laser scanning microscope images indicated that zein particles loaded with Asta were aggregated with SA coating. X-ray diffraction patterns and Fourier transform infrared spectra results showed that intermolecular hydrogen bonding, electrostatic attraction and hydrophobic effect were involved in APEs formation. APEs demonstrated non-Newtonian shear-thinning behavior and fit well to the Cross model. Compared to bare Asta extract, APEs maintained high Asta retention and antioxidant activity when heated from 50 to 10 °C. APEs showed different stability at pH (3.0–11.0) and Na⁺, K⁺, Ca²⁺, Cu²⁺ and Fe²⁺ conditions by visual, zeta potential and polydispersity index measurements. Additionally, the first order kinetics fit well to describe APEs degradation at pH 3.0 to 9.0, Na⁺, and K⁺ conditions. Our results suggest the potential application of Asta-loaded Pickering emulsion in food systems as a fortified additive.     

A crucial role of O2 and O2 on mayenite structure for biomass tar steam reforming over Ni/Ca12Al14O33

Newly synthesized nickel calcium aluminum catalysts (Ni/Ca₁₂Al₁₄O₃₃) were tested in a fixed bed reactor for biomass tar steam reforming, toluene as tar destruction model compound. Four catalysts (Ni/Ca₁₂Al₁₄O₃₃) were prepared with Ni loading amount from 1, 3, 5 to 7 wt%, even 1% loading catalyst also showed excellent performance. Catalysts aged experiments in the absence (60 h on stream) and presence of H₂S were characterized by BET, X-ray diffraction (XRD), and Raman spectra. It was observed that Ni/Ca₁₂Al₁₄O₃₃ showed excellent sustainability against coke formation due to the “free oxygen” in the catalysts. It also exhibited higher H₂S-poisoning resistance property compared to the commercial catalysts Ni/Al₂O₃ (5%) and Ni/CaO_0.5/MgO_0.5. Raman spectra revealed that “free oxygen O₂⁻ and O₂²⁻” in the structure of the catalysts could be substituted by sulfur then protected Ni poisoning on some degree, but reactivation experiments by O₂ flowing showed that the sulfide Ni/Ca₁₂Al₁₄O₃₃ was difficult to completely restore, incorporation of sulfur in the structure only partly regain by O₂. The kinetic model proposes, as generally accepted, a first-order reaction for toluene with activation energy of 82.06 kJ mol⁻¹ was coincident with the literature data. The Ni/Ca₁₂Al₁₄O₃₃ catalyst was effective and relative cheap, which may be lead to reduction in the cost of hot gas cleaning process.     

Interactions of pendimethalin with organo-montmorillonite complexes

Pendimethalin (PM) is a dinitroaniline herbicide, highly hydrophobic and with a very low solubility in water. It is used for pre-emergence weed control, is usually applied before sowing, and mechanically incorporated into the soil. We tested sorption of PM on montmorillonite and on two different organo-montmorillonites in a mixed water–chloroform environment, to determine the feasibility of developing an environmentally oriented formulation of the herbicide. FTIR measurements show that the interactions of PM with montmorillonite on which difenzoquat (DZ) or mepiquat (MQ) were previously adsorbed are via the nitro and methyl groups of the herbicide. The pre-adsorbed organocations cause a dehydration of the interlayer space, leading to hydrophobicity of the organoclay. Changes in the electrokinetic surface charge of the organoclay, measured using a particle charge detector, confirm these results. The high affinity to PM and the hydrophobic behavior of the used organoclays were also demonstrated in experiments using a mixed chloroform–water environment. The crude clay mineral stayed in the water phase, whereas DZ- and MQ-montmorillonites concentrated in the PM-chloroform phase. Amounts of PM adsorbed to the organoclays using this method were very high (up to 0.65 mol PM kg⁻¹ compound), which suggests a very efficient technology of preparation of herbicide-clay formulations, compared with techniques used in the past for similar herbicide-organoclay compounds. Plant experiments using the organoclay-herbicide formulation with higher amount of active ingredient (based on DZ-clay) demonstrate efficient herbicidal activity with 30% less active ingredient.