Kinetic studies on sorption of n-hexane in vanadium substituted MFI type zeolites of various crystal morphologies

The MFI type materials isomorphously substituted with vanadium form crystals of two morphology types. Investigations of sorption kinetics for n-hexane indicated for both morphologies a non-typical increase in the value of corrected transport diffusion coefficient with the crystals dimensions. An increase in the D₀ values with the vanadium content of the crystals has also been found, although it is not so well expressed as that with the dimensions. The increase in the D₀ values is from 1.1 × 10⁻¹¹ to 1.1 × 10⁻¹⁰ m²/s and may be a consequence of an additional system of larger pores, which is not reflected in the adsorption isotherms due to common occurrence of these pores in all crystals. It is also possible that vanadium causes a superior structure ordering and a decrease in/weakening of diffusion barriers.     

Development and applications of quaternary ammonium (QA) membrane electrodes in pharmaceutical preparation and in bioavailability of Prostaglandin E1 and Deoxycholate

The two novel ion-pairs (PB-TPB and NB-TPB) of quaternary ammonium drugs; propantheline bromide (PB), N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]-trimethylazanium have been synthesized, respectively and incorporated in poly (vinyl chloride)-based membrane electrodes for the quantification of propantheline bromide and neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane electrodes have been found to substantially improve the performance characteristics. The best performance was reported with membranes having composition (w/w) of PB-TPB or NB-TPB (6%): PVC (34%): o-NPOE (60%). The proposed electrodes exhibit nernstian response in the concentration ranges of 2.1 × 10⁻⁷ M to 1.0 × 10⁻² M and 4.4 × 10⁻⁷ M to 1.0 × 10⁻² M with detection limit of 1.5 × 10⁻⁷ M and 3.3 × 10⁻⁷ M, respectively. Both the membrane electrodes perform satisfactorily over pH ranges of (3.5–7.5 and 4.0–7.0) with fast response times (11 s and 13 s), respectively. These drugs (PB and NB) were further utilized as different ion-pairs of Prostaglandin E₁ (PGE₁) and Deoxycholate (DOC) in poly (vinyl chloride)-based membrane electrodes for the determination of bioavailability of Prostaglandin E₁ and Deoxycholate in plasma of different patients.     

Evaluation of atrazine degradation in UV/FeZSM-5/H2O2 system using factorial experimental design

Degradation of atrazine in model wastewater by UV/FeZSM-5/H₂O₂ system chosen as optimal for application of advanced oxidation process (AOP) has been studied in a batch photo reactor. The statistical study of the process was performed using two-level full factorial experimental design with the three process parameters. Individual parameters and their interaction effects on atrazine degradation were determined and statistical model of process was developed. The optimal operating conditions were established. This approach has also given a broader insight of the processes that were occurring in the reaction system, and it has finally led to simplification in terms of kinetics. Atrazine degradation was described by pseudo-first-order kinetics with observed rate constant k′ = 2 × 10⁻³ s⁻¹.     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Application of silica gel as an effective modifier for the voltammetric determination of dopamine in the presence of ascorbic acid and uric acid

Amorphous silica gel modified carbon paste electrode (CPE) offers substantial improvements in voltammetric sensitivity and selectivity towards determination of dopamine (DA). Cyclic voltammetry of Fe(CN)₆^3−/4− as a negatively charged probe revealed that the surface of the silica gel modified carbon paste electrode had a high density of negative charge at pH 8.0. Therefore, the modified electrode adsorbed DA (pK_a = 8.9) and enhanced its voltammetric response while repulsed ascorbic acid (AA) (pK_a = 4.2) and uric acid (UA) (pK_a = 5.4) and inhibited their interfering effects. The influence of various experimental parameters including percent of silica gel in the CPE, pH of solution, and accumulation time and potentials, on the voltammetric response of DA was investigated. At the optimum conditions, the analytical curve was linear for dopamine concentrations from 2.0 × 10⁻⁷ to 1.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit (3σ) of 4.8 × 10⁻⁸ mol L⁻¹. The prepared electrode was used for determination of DA spiked into DA injection and human serum samples, and very good recovery results were obtained over a wide concentration range of DA.     

Urea release rate from a scoop of coated pure urea beads: Unified extreme analysis

Urea release from a scoop of coated beads in a given volume of a well stirred liquid has been investigated analytically and experimentally. A method for determining the fractional cumulative release and fractional release rate curves for the scoop without knowing particle number and radii is presented. The representative D/K_b for a scoop of urea beads spray coated with ethyl cellulose is near 3.5 × 10⁻⁸ cm²/s, and that with cellulose acetate phthalate is near 7 × 10⁻⁸ cm²/s.     

The photoelectrochemical reduction of pyrene in acetonitrile solution

The reduction of pyrene (Py) at a mercury channel electrode is studied in acetonitrile solution, both in the dark and under conditions where the pyrene radical anion (Py^−.) is photoexcited, using a wavelength of 501.7 nm. In the dark a reversible one-electron process occurs forming the radical anion. However, upon photoexcitation of the electrogenerated radical anion, photocurrents are observed, and the precise electrode mechanism is shown to be: The photocurrent arising from further reduction of Py, since rapid homogeneous reactions of Py⁻² give electroinactive products. With this scheme an “effective” second order decay of Py^−√ is observed, RATE = −k_eff[Py^−√]^p2 where k_eff is proportional to k₃ I/k_f. k_eff has been evaluated from analysis of the limiting current-flow rate behaviour at the channel electrode at the channel electrode. This was found to be 4.0 ± 0.1 × 10³ mol−1 dm³ s⁻¹ at a light intensity of 0.30 W cm⁻² and a pyrene concentyration of 2.97 mM.     

Magnetic properties of CNX whiskers

Carbon–nitrogen whiskers have been prepared by pyrolysis of 1,2-diaminopropane at 950 °C or of allylamine at 900 °C followed by quenching. They are scrolls of carbon film typically 250 nm thick and up to 1 mm long with about five layers in a structure like a “cigare russe” or “brandy snap”, about 50 μm in diameter. Approximately 8 wt% of nitrogen is incorporated into the carbon films, which are practically amorphous, exhibiting a broad diffraction peak at d = 0.34 nm. The whiskers are on the border of metallic conductivity with a resistivity of about 10⁻⁶ Ωm, and they may show either a positive or a negative temperature coefficient of resistance. The pyrolysis produces either whiskers, soot or both. Magnetization measurements of the whiskers made from 1,2-diaminopropane reveal a large diamagnetic susceptibility of χ = −170 × 10⁻⁹ m³  kg⁻¹ and a small ferromagnetic component of unknown origin with σ_S of up to 0.2 A m² kg⁻¹, whereas the soot shows a purely diamagnetic signal, with χ ≈ −40 × 10⁻⁹ m³ kg⁻¹.     

Nickel inhibition of calcium precipitation by ureolytic mixed microorganisms under batch conditions

The respirometric assessment of the inhibitory impact of Ni(II) on substrate utilization and microbial carbonate precipitation (MCP) by ureolytic mixed microorganisms was investigated with a glucose containing mineral medium under batch conditions over an incubation period of 134 h. The IC₂₅ was determined as 224 mg Ni(II) L⁻¹ from the BOD values of samples. The interpretation of kinetic data showed that the substrate removal rate fitted a zero-order at the beginning of the incubation period and first-order during the last period, for a range of Ni(II) concentrations between 0 and 512 mg L⁻¹. Increasing Ni(II) concentrations from 0 to 512 mg L⁻¹ reduced the substrate degradation rate constant from 10.8 to 5.3 mg L⁻¹ h⁻¹ for zero-order rate constant (k₀), and from 0.015 to 0.002 h⁻¹ for first-order rate constant (k₁). The zero- and first-order reaction rates during incubation period were equalized to the reaction rate of the Monod equation in order to determine the kinetic constants, half saturation concentration (K_S) and maximum substrate removal rate (R_max). BOD removal rate was inhibited accordingly to mixed inhibition model with increasing Ni(II) concentrations during the calcification process. Also, the inhibition of calcium precipitation was observed at a higher Ni(II) concentration because of inhibition of ammonium production in these samples.     

Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

Spontaneous adsorption of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4α-Co^IITAPc) on glassy carbon (GC) electrode leads to the formation of a stable self-assembled monolayer (SAM). Since the SAM of 4α-Co^IITAPc is redox active, its adsorption on GC electrode was followed by cyclic voltammetry. SAM of 4α-Co^IITAPc on GC electrode shows two pairs of well-defined redox peaks corresponding to Co^III/Co^II and Co^IIIPc⁻¹/Co^IIIPc⁻². The surface coverage (Γ) value, calculated by integrating the charge under Co^II oxidation, was used to study the adsorption thermodynamics and kinetics of 4α-Co^IITAPc on GC surface. Cyclic voltammetric studies show that the adsorption of 4α-Co^IITAPc on GC electrode has reached the saturation coverage (Γ_s) within 3 h. The Γ_s value for the SAM of 4α-Co^IITAPc on GC electrode was found to be 2.37 × 10⁻¹⁰ mol cm⁻². Gibbs free energy (ΔG_ads) and adsorption rate constant (k_ad) for the adsorption of 4α-Co^IITAPc on GC surface were found to be −16.76 kJ mol⁻¹ and 7.1 M⁻¹ s⁻¹, respectively. The possible mechanism for the self-assembly of 4α-Co^IITAPc on GC surface is through the addition of nucleophilic amines to the olefinic bond on the GC surface in addition to a meager contribution from π stacking. The contribution of π stacking was confirmed from the adsorption of unsubstituted phthalocyanatocobalt(II) (CoPc) on GC electrode. Raman spectra for the SAM of 4α-Co^IITAPc on carbon surface shows strong stretching and breathing bands of Pc macrocycle, pyrrole ring and isoindole ring. Raman and CV studies suggest that 4α-Co^IITAPc is adopting nearly a flat orientation or little bit tilted orientation.     

Immobilization of horseradish peroxidase on self-assembled (3-mercaptopropyl)trimethoxysilane film: Characterization, direct electrochemistry, redox thermodynamics and biosensing

Highly organized (3-mercaptopropyl)trimethoxysilane (3-MPT) films have been prepared via self-assembled coupled with sol–gel linking technology. Horseradish peroxidase (HRP) is successfully immobilized onto the densely packed three-dimensional (3D) 3-MPT network and the direct electrochemistry of HRP is achieved without any electron mediators or promoters. Redox thermodynamics of HRP on the 3-MPT films, which is obtained from the temperature dependence of the reduction potential, suggests that the positive shift of redox potentials of HRP at the interface of 3-MPT originates from the solvent reorganization effects and conformational change of the polypeptide chain of HRP. Based on the direct electrochemistry and electrocatalytic ability of HRP, a sensitive third-generation amperometric H₂O₂ biosensor is developed with two linear dependence ranges of 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ and 1.0 × 10⁻⁴ to 2.0 × 10⁻² mol L⁻¹.     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Solubilities of actinides in a domestic groundwater and a bentonite porewater calculated by using PHREEQC

This study presents the solubilities and speciations of actinides, calculated by the PHREEQC (V.2) code in a granitic groundwater and a Ca-bentonite porewater under a reducing condition. The respective solubilities for the amorphous U, Am, Th, Np and Pu compounds in the groundwater were 2.2 × 10⁻⁵, 1.2 × 10⁻⁷, 3.1 × 10⁻⁹, 3.4 × 10⁻⁹ and 6.3 × 10⁻¹¹ mole/L, and these values are comparable to the results calculated by the MUGREM and EQ3/6 codes. The major dissolved species for U, Am, Th, Np and Pu were UO₂(OH)₃⁻, Am(OH)₂⁺, Th(OH)₄(aq), Np(OH)₃CO₃⁻ and Pu(OH)₃CO₃⁻, respectively. However, carbonate complex ions were anticipated as the major species in the porewater except for thorium due to an increase of the carbonate concentration and a decrease of the pH.     

Impedance investigation of the mechanism of copper electrodeposition from acidic perchlorate electrolyte

The mechanism of the copper electrodeposition from acidic perchlorate electrolyte has been investigated with polarization and impedance methods. The impedance of the copper electrode in copper perchlorate electrolytes has been measured as a function of frequency for different Edc overpotential values and different copper(II) ion concentrations. The relations between the shape of a complex plane impedance display and the copper electrode potential values as well as the concentration of CuII ion were analysed in terms of the electrode reaction mechanism. It is shown, that the presence of the intermediate cuprous ion and its sinusoidal change of transport rate is one of the main factors determining the depressed shape of the impedance arc. The quantitative relation between the faradaic impedance and the rates of electrode reaction rates was established. The impedance arc was simulated with a set of parameters involving: rate constants, Tafel slopes, diffusion coefficient of cuprous ion and double layer capacitance. The rate constants were calculated with respect to ECu2 + Cu00 as: k10 = 6.50 × 10−5 cm s−1, k20 = 0.139 cm s−1, k−20 = 1.88 × 10−7 mol cm−2 s−1.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.     

Spatial variability of transport parameters in the Boom Clay

Several transport parameters (as hydraulic conductivity K, apparent diffusion coefficient D_p and diffusion accessible porosity η of HTO and iodide) have been intensively measured in the laboratory on high-quality cores taken at the Mol-1 borehole of the Mol site, in Belgium. The borehole was cored in 1997 from about 145 to 325 m depth, including the whole thickness of the Boom Formation, a Tertiary clay situated between 186 and 288 m depth (ground level), and part of the surrounding layers.The hydraulic conductivity measurements confirm the low permeability of the Boom Clay. An upper 90-m-thick clay layer within this formation can be considered as homogeneous with respect to the hydraulic conductivity. The vertical hydraulic conductivity K_v (i.e. K perpendicular to the bedding) is in the order of magnitude of 10⁻¹² m s⁻¹ and the average is 2.3×10⁻¹² m s⁻¹. This layer comprises from top to bottom the “Transition Zone”, the Putte Member, the Terhagen Member and the top of the Belsele-Waas Member of the Boom Formation. The 12 m at the base of the Formation, which corresponds to the lower part of the Belsele-Waas Member is characterised by larger K_v values (ranging between 10⁻¹¹ and 9×10⁻¹¹ m s⁻¹).The same thick clay layer can also be considered as homogeneous, regarding the values of the apparent diffusion coefficient and the diffusion accessible porosity η of tritiated water (HTO) and iodide. The average value of the diffusion accessible porosity is 0.37±0.03 for HTO and 0.16±0.02 for iodide. The apparent diffusion coefficient varies from 1.1×10⁻¹⁰ to 5.5×10⁻¹⁰ m² s⁻¹ for HTO and from 9.1×10⁻¹¹ to 5.2×10⁻¹⁰ m² s⁻¹ for iodide.     

Biological COD reduction and inorganic suspended solids accumulation in a pilot-scale membrane bioreactor for traditional Chinese medicine wastewater treatment

A pilot-scale test was conducted in a membrane bioreactor (MBR) for 452 days to treat high-strength traditional Chinese medicine (TCM) wastewater from two-phase anaerobic digest effluent. This study focuses on the chemical oxygen demand (COD) reduction and inorganic suspended solid (ISS) accumulation. The wastewater was high in COD, varying daily between 259 and 12,776 mg L⁻¹. Almost all the COD was removed by the MBR system, leaving a COD of <50 mg L⁻¹ in the MBR effluent. This indicated a great potential of the MBR in TCM wastewater reuse. ISS produced in the bioreactor by metabolism of microorganism increased from 265 to 4912 g h⁻¹, which showed that there were large numbers of ISS accumulation in the bioreactor. Two models, built on the material balances of COD and ISS, were developed for the simulation of MBR system performance in the biodegradation of TCM wastewater. Consequently, the kinetic constants including the maximum substrate specific biodegradation rate (V_max), the half-saturation coefficient (K_s) and the inorganic suspended solids growth rate (k) were calculated as V_max, 3.64, 3.82, 4.39 d⁻¹, K_s, 56.4, 225, 394 mg L⁻¹ and k, 265, 888, 4912 mg L⁻¹ d⁻¹ using the operational data at different hydraulic retention times (HRTs). The models well fitted the pilot-scale experimental data, and were able to simulate the COD reduction and ISS accumulation.     

Multi-walled carbon nanotubes (MWCNTs) and room temperature ionic liquids (RTILs) carbon paste Er(III) sensor based on a new derivative of dansyl chloride

Solution studies showed the strong interaction of [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (NSP) with Er(III) ions. NSP was used as a sensing material during construction of carbon paste Er(III) sensors. The electrodes were modified with 1-n-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF₄, as room temperature ionic liquid (RTIL) and multi-walled carbon nanotube (MWCNT). Potentiometric sensors constructed with [bmim]BF₄ and MWCNTs show better sensitivity, selectivity, response time, and response stability compared to Er(III) carbon paste sensors. The best performance for the modified sensor was obtained with an electrode composition of 20% [bmim]BF₄, 20% NSP, 45% graphite powder and 15% MWCNT. This particular sensor formulation exhibits a Nernstian response (19.8 ± 0.3 mV decade⁻¹) toward Er(III) ions in the range of 1.0 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. The proposed modified Er(III) sensor can be used over the pH range from 3.5 to 9.0.     

Preparation and electrochemical properties of functionalized ionic liquid self-assembled modified graphite electrode

A modified graphite electrode with functionalized ionic liquid (IL) pyridinium derivative of β-cyclodextrin ([CDbPy]BF₄) was prepared by layer-by-layer self-assembly technique. With ferrocene as probe, the characterization of the (CDIL/PDDA)_n/GE SAMs in the solution of phosphate (PBS, pH 7.0) was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry. The electrochemical behavior of p-chloronitrobenzene (p-CNB) at the modified electrode was studied. It was found that the modified electrode could catalyze the reduction of p-CNB and made the cathode peak move about 100 mV in positive direction in the solution of 0.1 mol/L PBS (pH 7.0). Differential pulse voltammetry (DPV) was applied to the determination of p-CNB in waste water with satisfactory results. The detection limit and the linear range of the concentration of p-CNB to the reduction peak current were 8.0 × 10⁻⁸ mol/L and 3.0 × 10⁻⁷–1.0 × 10⁻⁵ mol/L, respectively.     

Thermal stability of Mesoporous SBA-15 and Sn-SBA-15 Molecular Sieves: An in situ HTXRD study

Highly ordered SBA-15 and Sn-SBA-15 mesoporous molecular sieves with Si/Sn = 80, 60, 40 and 10 have been prepared through direct synthesis route under milder acidic conditions, which were used for the in situ high temperature X-ray diffraction (HTXRD) studies in the temperature range 298–1573 K for the first time in the literature. SBA-15 is found to be thermally stable up to 1473 K and appearance of α-cristobalite was observed at 1573 K also supported by the thermogravimetric (TG) data. A strong negative thermal expansion was observed on heating from 298 to 1573 K (α_a = −4.3 × 10⁻⁶ K⁻¹). Sn containing samples (Si/Sn = 80 and 60) showed a positive thermal expansion (6.75 × 10⁻⁶ K⁻¹ and 9.04 × 10⁻⁶ K⁻¹, respectively). On the other hand, the samples with Si/Sn = 40 and 10 showed a strong negative thermal expansion (−4.12 × 10⁻⁶ K⁻¹ and −7.56 × 10⁻⁶ K⁻¹) similar to SBA-15. The linear thermal expansion coefficient varied in the order: Si/Sn = 60 > 80 > 40 > 0 > 10. Sn⁴⁺ ions exhibit both tetrahedral and octahedral coordination depending upon the location of these ions either on the walls of the silica (Si/Sn = 80 and 60) or in the corona region of the structure (Si/Sn = 40 and 10), respectively. The thermal decomposition of the samples (TG data) is correlated to the thermal expansion behavior (HTXRD data). The decomposition behavior of template ions located within the pores is strongly influenced by the presence of Sn in the framework and a ‘soft’ interaction probably exists between the template ions and the Sn sites.