Adsorption of nitrogen from natural gas by clinoptilolite

Much of world’s natural gas reserves are impure, one of the principal contaminants being nitrogen which makes it unsuitable for application and, hence, its separation is important. In this research, clinoptilolite, the most abundant natural zeolite with an open aluminosilicate framework structure and high internal surface area, was modified by ion exchange process to highly exchanged forms of cations of Na⁺, K⁺ and H⁺. The adsorption of N₂, CH₄ and C₂H₆ on natural clinoptilolite (Cp) and on its cation-exchanged forms (Na-Cp, K-Cp and H-Cp) was studied at 25 °C. The influence of cation exchange on equilibrium adsorption of N₂ showed that selectivity decreased in the order of Cp > Na-Cp > K-Cp and H-Cp has no affinity to nitrogen.     

Differences in coating mechanism of structurally different aluminosilicates observed through the thermal analysis

Systematic modification of three structurally different minerals (zeolite, mica, and vermiculite) was carried out with the aim of determining the modification mechanism and exposing the hydrophobic surface that can be used as a sorbent for many organic compounds. Mechanism of modification with cationic surfactant depends strongly on the mineral type. In order to identify the influence of aluminosilicates structural differences on the modification process, adsorption experiments with organic matter and water vapor, supplemented with the DTA/TG analysis, were performed. The cation exchange capacity (CEC) value was 1454?>?560?>?28 meq kg^?1 for zeolite (clinoptilolite), vermiculite, and mica (muscovite), respectively. Despite its CEC value, vermiculite adsorbed three times the amount of organic matter than did clinoptilolite due to the porous structure of zeolite, which acted to limit the adsorption only on the external exchangeable cations. If the loading amount is equal to the CEC or the external cation exchange capacity for clinoptilolite (ECEC?≈?10% CEC), the monolayer will form while mineral surface will have hydrophobic character. Only one active center exists at the surface of the clinoptilolite that was identified by DTA curves with a sharp and defined peak around 300 °C and by the mass loss at the TG diagrams. Two significant and equal active centers were observed in vermiculite, one for the exchange of the surface cations and the other for the interlayer cations and H₂O molecules. Muscovite CEC is negligible, and due to the absence of any other functional groups, the modification of this mineral was impossible.     

Investigation of clinoptilolite rich natural zeolites from Turkey: a combined XRF,TG/DTG,DTA and DSC study

Turkey clinoptilolite-rich tuffs from Gördes and Bigadiç regions of western of Anatolia and their exchanged forms (K⁺, Na⁺, Mg²⁺ and Ca²⁺) were characterized by TG/DTG-DTA, DSC and XRF methods and the surface areas were also determined for both tuffs. TG-DTG and DTA curves of all clinoptilolite samples were measured in the temperature range 30–1000 °C. All clinoptilolite samples had major, rapid mass losses between 30 and 200 °C, with slower and less significant mass losses at higher temperatures. The mass loss of the Natural-G is 9.54% while that of the Natural-B sample is 10.50%. Water content increases in the order of K < Na < Ca < Mg for Bigadiç clinoptilolite samples and in the following sequence K < Na < Mg < Ca for Gördes clinoptilolite samples. One mass loss step for all clinoptilolite samples was observed using differential scanning calorimeter (DSC) in the range of 30–550 °C.     

Thermal decomposition kinetics of diethyl dithiocarbamate complexes of copper(II) and nickel(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and NiL₂ (L^?=diethyl dithiocarbamate anion) in air are studied. The main decomposition temperature ranges are: For CuL₂, DTG 250–350°, DTA 300–320° and for NiL₂, DTG 290–390°, DTA 360–400°. Mass loss considerations at the main decomposition stages indicate conversion of the complex to sulphides. Mathematical analysis of TG data shows that first order kinetics are applicable in both cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.

     

The thermal decomposition of doped ammonium perchlorate

The thermal decomposition of ammonium perchlorate doped with Cu²⁺, Mn²⁺, Co²⁺ and Fe³⁺ (with and without H⁺) was studied using DTA and TG. Small concentrations of these ions inhibit the decomposition by eliminating the first exothermic peak. At higher concentrations, a catalyzed decomposition is observed. Either the influence of the doping ions on the mechanism of the thermal decomposition is different from that of added oxides or a modification of the electron transfer mechanism is needed.     

Influence of Basic Red 1 dye adsorption on thermal stability of Na-clinoptilolite and Na-bentonite

Influence of physically adsorbed basic red 1 (BR1) dye on the physicochemical properties of natural zeolite (clinoptilolite) and clay (bentonite) was compared using adsorption, FTIR, and TG/DTA methods. A larger adsorption of the dye was observed for bentonite (0.143 mmol/g) than for clinoptilolite (0.0614 mmol/g) per gram of an adsorbent. However, the adsorption values are the same per surface unit (1.8 μmol/m²). The result (per gram) is due to location of dye molecules in interlayer and interparticle space of bentonite with much larger specific surface area than that of clinoptilolite. The dye adsorption leads to a decrease in the specific surface area and the pore volume of both minerals. The adsorption changes also a character of active sites and thermal stability. A TG study shows that the dye adsorption on bentonite changes adsorbed water amounts, weight loss, and decomposition temperature. In the case of zeolite, the dye adsorption insignificantly influences the thermal stability. The dehydration energy distributions calculated from the Q-TG and Q-DTG data demonstrate a complex mechanism of water thermodesorption and the influence of adsorbed dye on this process.     

Study of adsorption phenomena ongoing onto clinoptilolite with the immobilized interfaces

The development of innovative clean-up technologies remains a challenge as current procedures have many limitations, such as being expensive, concentration or pollutant specific, and many others. Natural zeolite of clinoptilolite type was beneficiated with surfactant octadecylammonium and alginate biopolymers using the sol-gel method. Carbonization process in pyrolysis chamber combusted organic waste materials and reaching the maximum temperature of 700°C was used for the surface carbonization, respectively. Resulted zeolite based products were analyzed by FTIR, TG, DTA and examined on the selected aqueous pollutants removal using the conventional laboratory adsorption experiments. The ability of ODA and alginate linked zeolite of clinoptilolite type to form complexes with anions (such as nitrate, sulphate, chloride and phosphate) and to remove them from contaminated waters was validated. Carbon deposition onto clinoptilolite surface originated from the pyrolytic carbon-rich waste combustion simulated the new zeolite based hybrid to active coke, adsorption efficiency of which towards phenol was approved. Thermogravimetric analyses of the advanced zeolite-based adsorbents were accomplished to find out how temperature resistant are the novel zeolite based materials in respect to the original, untreated one. While the native clinoptilolite indicated according to DTA analysis one broad endothermic response around 100–130°C, resulted from the loss of adsorbed water, by the ODA-modified clinoptilolite was except this DTA peak, the broad exothermic response started from 370 up to 560°C observed. This DTA profile is assumed to record a slowly breakdown of attached ODA surfactant and sequential loss of mass due to continual heating of sample under elevated temperature.     

Thermal characterization of new complexes of Zn(II) and Cd(II) with some bipyridine isomers and propionates

New mixed ligand complexes of the following stoichiometric formulae: M(2-bpy)₂(RCOO)₂·nH₂O, M(4-bpy)(RCOO)₂·H₂O and M(2,4’-bpy)₂(RCOO)₂·H₂O (where M(II)=Zn, Cd; 2-bpy=2,2’-bipyridine, 4-bpy=4,4′-bipyridine, 2,4′-bpy=2,4′-bipyridine; R=C₂H₅; n=2 or 4) were prepared in pure solid-state. These complexes were characterized by chemical and elemental analysis, IR and conductivity studies. Thermal behaviour of compounds was studied by means of DTA, DTG, TG techniques under static conditions in air. The final products of pyrolysis of Cd(II) and Zn(II) compounds were metal oxides MO. A coupled TG/MS system was used to analyse of principal volatile products of thermal decomposition or fragmentation of Zn(4-bpy)(RCOO)2·H2O under dynamic air and argon atmosphere. The principal species correspond to: C⁺, CH⁺, CH₃ ⁺, C₂H₂ ⁺, HCN⁺, C₂H₅ ⁺ or CHO⁺, CH₂O⁺ or NO⁺, CO₂ ⁺, ¹³C¹⁶O₂ ⁺ and ¹²C¹⁶O¹⁸O⁺ and others; additionally CO⁺ in argon atmosphere.     

Thermal decomposition of barium(II) tetraphenylborate

Barium(II) tetraphenylborate, Ba(Bph₄))₂·4H₂O was prepared, and its decomposition mechanism was studied by means of TG and DTA. The products of thermal decomposition were examined by means of gas chromatography and chemical methods. A kinetic analysis of the first stage of thermal decomposition was made on the basis of TG and DTG curves and kinetic parameters were obtained from an analysis of the TG and DTG curves using integral and differential methods. The most probable kinetic function was suggested by comparison of kinetic parameters. A mathematical expression was derived for the kinetic compensation effect.     

Iodide adsorption on the surface of chemically pretreated clinoptilolite

The possibility to use the monoionic Ag⁺-form (eventually Hg⁺- and Hg²⁺- forms) of clinoptilolite of domestic origin for radioactive iodide elimination from waters has been studied. The capacity of the monoforms of clinoptilolite towards iodide exceeds many times that of the capacity of clinoptilolite in natural form. Due to the low solubility product of AgI, Hg₂I₂ and HgI₂ iodides generate precipitates on the zeolite surface. Rtg analyses of the silver form of clinoptilolite after sorption of iodide demonstrate the formation of new crystals on the zeolite surface. The influence of interfering anions on the adsorption capacity of silver clinoptilolite towards iodide was investigated, too. Kinetic curves of iodide desorption from the surface of silver and mercury clinoptilolite were compared. Simultaneously, adsorption isotherms for the systems aqueous iodide solution/Ag^–, Hg-clinoptilolite were determined.     

Study on the first-step adsorption of dodecyltrimethylammonium bromide solutions on silica wafer surfaces by ultramicroelectrode voltammetry

Ultramicroelectrode (UME) voltammetry is introduced to study the first-step adsorption of dodecyltrimethylammonium bromide (DTAB) solutions on silica wafer surfaces. This method is based on the exchange reaction of the surfactant molecules with hydrogen ions (H⁺) on the surfaces. In the first-step adsorption process, when a surfactant molecule is adsorbed to the hydroxylated silica surfaces, a H⁺ will be displaced. Therefore, H⁺ concentration will change with the adsorption process until it reaches saturation of the first-step adsorption. The molar adsorption amount of DTAB (mol m⁻²) before critical micelle concentration (CMC) can be calculated from the change in H⁺ concentration. The following adsorption process at higher surfactant concentrations is dominated by hydrophobic forces. Consequently, the H⁺ concentrations do not change with the adsorption process any more, which makes the measurement uninfluenced by the following hydrophobic adsorption process. The adsorption isotherms of DTAB on silica wafer surfaces under different pH are measured with this method. It is found that all the adsorption isotherms exhibit asymptote (L) shape and the equilibrium molar adsorption amounts increase with increasing the pH of the solution. These results indicate that H⁺ not only change the surface charge but also compete with surfactant for adsorption at higher proton concentrations.     

Crystallization of single phase (K,Na)-clinoptilolite

A single phase (K, Na)-clinoptilolite was hydrothermally crystallized without seed crystals from a reactant mixture of (K, Na)-aluminosilicate gel slurry through homogeneous mixing at 150 °C for 144 h. Compositions of the reactant mixtures and reaction temperatures to obtain the clinoptilolite were restricted within narrow limits in the case of syntheses without seed crystals, while the compositions and temperatures were expanded into wide ranges in the case of syntheses with 1 wt.-% of seed crystals. Coexistence of Na⁺- and K⁺-ions with appropriate ratios in the reactant mixture, and homogeneous mixing of this mixture, were indispensable for the crystallization of clinoptilolite. The crystals obtained were characterized by X-ray diffraction, chemical analysis, thermal analysis (DTA/TG), electron microscopy, and electron diffraction. The crystals were assigned as clinoptilolite, not heulandite, based on their chemical compositions and thermal stability.     

<Emphasis Type="Italic">In situ</Emphasis> analysis of the formation steps of gold nanoparticles by oleylamine reduction

A colloidal solution of gold nanoparticles is synthesized with the use of sodium tetrachloroaurate(III) as a precursor, oleylamine as a reducer and surfactant, and 1-octadecene as a solvent. Reaction stages are analyzed in situ by optical (UV-vis) absorption spectroscopy with a simultaneous analysis of particle sizes by dynamic light scattering and X-ray absorption near edge spectroscopy for the analysis of the gold oxidation state. After the synthesis the size of obtained nanoparticles is determined by transmission electron microscopy. The analysis of the obtained experimental data reveals the presence of three main steps in the reduction reaction mechanism, corresponding to Au³⁺, Au⁺, Au⁰, which enables the construction of the reaction model. The reaction mechanism involves the formation of gold(I) complexes with oleylamine, followed by polymerization and the formation of gold nanoclusters coated with oleylamine.     

Influence of the exchangeable cations on SO<Subscript>2</Subscript> adsorption capacities of clinoptilolite-rich natural zeolite

The sulfur dioxide adsorption on clinoptilolite-rich tuff from Bigadiç region of Western of Turkey and its modified forms (Na⁺, K⁺, Ca²⁺ and Mg²⁺) have been studied at 273 K and 293 K up to 100 kPa. The structural properties of clinoptilolites were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). The quantitative XRD analysis demonstrated that the Natural-B sample is mainly constituted by clinoptilolite (80–85%) with minor contents of quartz (7–8%), feldspar (5–6%) and mica-illit (4–5%). It was found out that the adsorption capacity and the affinity of SO₂ with clinoptilolite samples depended mainly on the type of exchanged cations and decreased as Na-B > K-B > Mg-B > Natural-B > Ca-B for both temperature. These results show that clinoptilolite-rich zeolites are considered potentially good adsorbents for SO₂ removal.     

Thermal stability of Ag-exchanged clinoptilolite rich mineral

Thermal stability of clinoptilolite rich mineral from Western Anatolia, Turkey and its Ag-exchange forms was investigated. Parent mineral of different sizes were heated up to 1000°C with heating rate of 2 and 10°C min^-1 using differential thermal analyzer (DTA) and thermogravimetric analyzer (TG). Ag exchange was conducted both in conventional constant temperature waterbath and microwave at 40, 60 and 80°C. The exchanged minerals were then characteized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), DTA and TG. The particle size and heating rate do not have significant effect on the thermal behavior of the parent mineral and no structural changes were observed with Ag exchange, only decomposition temperature was lowered. It was finally concluded that, Ag-exchanged clinoptilolite rich minerals were less thermally stable compared to parent mineral that does not affect their use for possible applications.     

Thermal analytic study of the adsorption of crystal violet by laponite

The adsorption of crystal violet on laponite was investigated by X-ray diffraction and thermal analysis. DTA, TG and DTG curves were recorded in air. The evolved H₂O, CO₂, NO₂, H₂ and C₂H₆ were simultaneously determined by mass spectrometry. The thermal analysis curves were compared on one hand with the thermal analysis curves of laponite and on the other hand with thermal analysis curves of non-adsorbed crystal violet and of crystal violet adsorbed on montmorillonite. The thermal analysis curves of crystal violet adsorbed on laponite show similarities to the curves of the non-adsorbed crystal violet, but differ from the curves of crystal violet adsorbed on montmorillonite. The differences in the thermal behaviour were attributed toπ interactions which do not occur between crystal violet and laponite but do occur between this dye and montmorillonite.     

Solid phase extraction�Cinductively coupled plasma spectrometry for adsorption of Co(II) and Ni(II) from radioactive wastewaters by natural and modified zeolites

Natural and modified clinoptilolite as low-cost adsorbents have been used for adsorption of Co(II) and Ni(II) from nuclear wastewaters both in batch and continuous experiments. Zeolite X was also synthesized and its ability towards the selected cations was examined. Kinetic and thermodynamic behaviors for the process were investigated and adsorption equilibrium was interpreted in term of Langmuir and Freundlich equations. The effect of various parameters including the initial concentration, temperature, ionic strength and pH of solution were examined to achieve the optimized conditions. The clinoptilolite was shown good sorption potential for Co(II) and Ni(II) ions at pH values 4?C6. Based on desorption studies, nearly 74 and 85% of adsorbed Co(II) and Ni(II) were removed from clinoptilolite by HCl. The Na⁺ and NH₄ ⁺ forms of clinoptilolite were the best modified forms for the removal of investigated cations. It is concluded that the selectivity of clinoptilolite is higher for Co(II) than Ni(II). The synthesized zeolite showed more ability to remove cobalt and nickel ions from aqueous solution than the natural clinoptilolite. The microwave irradiation was found to be more rapid and effective for ion exchange compared to conventional ion exchange process.     

Zeolitic properties of mixed hexacyanoferrates/II/: Adsorption isotherms and differential heats of adsorption of water vapour

The series of mixed hexacyanoferrates M₂Zn₃[Fe/CN/₆]₂.xH₂O (M=K⁺, Na⁺, Cs⁺) present zeolitic properties. The adsorption water vapour isotherms were determined by TG at 303 K. The differential heats of adsorption of water vapour were measured by microcalorimetry; the molar integral entropy of the sorbed phase was calculated. The data obtained show that (i) the H₂O-sorbent interactions are very weak at the beginning of cavity filling, whereas the sorbed molecules exhibit the same mobility as in the vapour phase; (ii) during the filling, the H₂O-H₂O interactions increase up to a maximum; (iii) close to total filling, the adsorption phenomenon is comparable to a vapour-liquid transition and the sorbed phase has the same molar entropy as that of the liquid phase.     

Interaction between tetracycline and smectite in aqueous solution

The fate and transport of commonly used antibiotics in soil and groundwater have attracted renewed studies due to increased sensitivities of analytical instruments and thus frequent detections of these compounds even in treated wastewater. Smectite, an important soil component, has large surface area and high cation exchange capacity, while tetracycline (TC) can exist in different forms and charges under different pH conditions. Thus, the interaction between smectite and TC in aqueous systems is of great importance. This research focused on elucidating the mechanisms of TC uptake by smectite, in terms of TC adsorption, cation desorption, and pH changes associated with TC adsorption by smectite and intercalation in smectite. TC adsorption onto smectite was a relatively fast process even though most of the adsorption sites were in the interlayer position involved in intercalation as confirmed by the expansion of d₀₀₁ spacing. The TC adsorption capacity was equivalent to 0.74–1.11 times the cation exchange capacity for three of the four smectite minerals studied. Accompanying TC adsorption was simultaneous adsorption of H⁺, resulting in protonation of TC on the dimethylamine group. At higher TC input concentrations further adsorption of H⁺ resulted in the ratio of H⁺ adsorbed to TC adsorbed greater than one, suggesting that additionally adsorbed H⁺ could serve as counterions to partially offset the negative charges on the tricarbonyl or phenolic diketone functional groups. The positive correlations between cations desorbed and TC adsorbed, as well as TC adsorbed and H⁺ adsorbed, provided a first time evidence to confirm cation exchange as the main mechanism of TC uptake, even under neutral pH conditions.     

Thermal Decomposition and Dehydration Kinetics of Tetra(piperidinium) Octamolybdate Tetrahydrate in Air

Thermal decomposition of tetra(piperidinium) octamolybdate tetrahydrate, [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O, was investigated in air by means of TG‐DTG/DTA, DSC, TG‐IR and SEM. TG‐DTG/DTA curves showed that the decomposition proceeded through three well‐defined steps with DTA peaks closely corresponding to mass loss obtained. Kinetics analysis of its dehydration step was performed under non‐isothermal conditions. The dehydration activation energy was calculated through Friedman and Flynn‐Wall‐Ozawa (FWO) methods, and the best‐fit dehydration kinetic model function was estimated through the multiple linear regression method. The activation energy for the dehydration step of [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O was 139.7 kJ/mol. The solid particles became smaller accompanied by the thermal decomposition of the title compound.