Study of Sorption of 2,4‐D on Outer Peristaltic Part of Waste Tire Rubber Granules

From this study it was evident that outer peristaltic parts of waste tire granules gave the highest removal. Film and pore diffusions are the major factors controlling rates of sorption from solution by porous adsorbents. For sorption of 2,4‐D on waste tire rubber granules, the sorption rate coefficient of second‐order kinetic equation was utilized indirectly to determine the rate‐limiting step. The diffusion coefficient lies in the scale of 10^?8 cm²/s, and the pore diffusion coefficient is in the range of 10^?9–10^?10 cm²/s. So both film and pore diffusion are rate limiting. Considering external mass transfer from fluid to particle, using the effect of initial concentration, and using the effect of adsorbent size, no conclusion was reached regarding rate‐controlling steps. It is apparent from the study that external mass transfer (film diffusion) as well as intra‐particle diffusion (pore diffusion) play significant roles in the sorption process for 2,4‐D removal from water onto rubber granules.     

Adsorption rate of Reactive Black 5 on chitosan based materials: geometry and swelling effects

The overall adsorption rate of Reactive Black 5 dye (RB5) on chitosan based materials was elucidated using diffusional models. Fundamental aspects, such as, geometry of the adsorbents and swelling effects were considered. Chitosan based materials (powder and film) were prepared from shrimp wastes and characterized regarding to the fundamental features for adsorption. Experimental decay curves were obtained under different conditions of stirring rate and initial dye concentration. The data were modeled according to the external mass transfer and diffusional models. The k_L (external mass transfer coefficient), D_ep (effective pore diffusion coefficient) and D_s (surface diffusion coefficient) values were estimated. For both adsorbents, it was found that the surface diffusion was the intraparticle diffusion mechanism governing the adsorption rate of RB5, since its contribution was higher than 92 % regardless the position and time. The D_s values ranged from 2.85 × 10^?11 to 5.78 × 10^?11 for chitosan powder and from 4.15 × 10^?11 to 12.12 × 10^?11 cm² s^?1 for chitosan films. The RB5 adsorption was faster when chitosan powder was used, mainly at higher stirring rates and initial dye concentrations. The swelling effect was most pronounced for the chitosan films, where, provided an increase of about 65 times in the D_s value.     

Synthesis of mesoporous Stöber silica nanoparticles: the effect of secondary and tertiary alkanolamines

The effect of secondary (diethanolamine) and tertiary (triethanolamine) alkanolamines as catalysts on the formation of mesoporous Stöber silica nanoparticles by sol–gel method was studied. The particles were characterized by thermogravimetry and differential thermal analysis, Fourier transform infrared spectroscopy, N₂ physisorption measurements, and field emission scanning electron microscopy. By using ammonia and different alkanolamines as catalysts, the Brunauer–Emmet–Teller (BET) surface area and pore volume increased in the order of ammonia < diethanolamine < triethanolamine. A maximum BET surface area of 140.1 m² g^?1 and pore volume of 0.66 cm³ g^?1 were obtained from triethanolamine catalyzed silica particles. The average particle size of silica prepared by ammonia and different alkanolamines as catalysts decreased in the order of ammonia > diethanolamine > triethanolamine. The role of different alkanolamines on the textural properties and particle size of silica is explained in terms of their relative steric hindrance and basicity.     

Physical and Bioengineering Properties of Polyvinyl Alcohol Lens-Shaped Particles Versus Spherical Polyelectrolyte Complex Microcapsules as Immobilisation Matrices for a Whole-Cell Baeyer–Villiger Monooxygenase

Direct comparison of key physical and chemical-engineering properties of two representative matrices for multipurpose immobilisations was performed for the first time. Polyvinyl alcohol lens-shaped particles LentiKats® and polyelectrolyte complex microcapsules were characterised by advanced techniques with respect to the size distribution of the particles, their inner morphology as revealed by fluorescent probe staining, mechanical resistance, size-exclusion properties, determination of effective diffusion coefficient and environmental scanning electron microscope imaging. While spherical polyelectrolyte complex microcapsules composed of a rigid semipermeable membrane and a liquid core are almost uniform in shape and size (diameter of 0.82 mm; RSD?=?5.6 %), lens-shaped LentiKats® are characterised by wider size distribution (diameter of 3.65 mm; RSD?=?10.3 % and height of 0.341 mm; RSD?=?32.3 %) and showed the same porous structure throughout their whole volume at the mesoscopic (micrometre) level. Despite differences in their inner structure and surface properties, the pore diameter of?～?2.75 nm for regular polyelectrolyte complex microcapsules and?～?1.89 nm for LentiKats® were similar. These results were used for mathematical modelling, which provided the estimates of the effective diffusion coefficient of sucrose. This value was 1.67?×?10^?10 m² s^?1 for polyelectrolyte complex microcapsules and 0.36?×?10^?10 m² s^?1 for LentiKats®. Recombinant cells Escherichia coli-overexpressing enzyme cyclopentanone monooxygenase were immobilised in polyelectrolyte complex microcapsules and LentiKats® for comparison of their operational stability using model Baeyer–Villiger oxidation of (±)-cis-bicyclo [3.2.0] hept-2-en-6-one to regioisomeric lactones as important chiral synthons for potential pharmaceuticals. Both immobilisation matrices rendered high operational stability for whole-cell biocatalyst with no reduction in the biooxidation rate over 18 repeated reaction cycles.     

Preparation and electrochemical characterization of a new NiMoO4 catalyst for electrochemical O2 evolution

The NiMoO₄ catalyst has been obtained by a precipitation method under a controlled pH condition and characterized ex situ by infrared, X-ray diffraction, Brunauer–Emmett–Teller (BET), and particle size, and in situ by cyclic voltammetry, impedance and steady-state anodic Tafel polarization techniques. Results show that NiMoO₄ has pure crystalline monoclinic phase with the crystallite size ~50 nm and the lattice constants, a?=?9.597 Å, b?=?8.765 Å, c?=?7.667 Å, and β?=?114.22°. Values of the average particle size and BET surface area of the oxide powders are found to be 730 nm and 11.75 m²/g, respectively. The oxygen evolution reaction follows the first-order kinetics with respect to OH^? concentration, the Tafel slope being ~70 mV.     

Effect of pore size on the performance of composite adsorbent

Three kinds of commercial silica gels with pore size of 2–3, 4–7 and 8–10 nm respectively are used for preparing composite adsorbents by soaking them into the aqueous solution of calcium chloride. The test result indicates that both the water uptake and adsorption rate of composite adsorbents prepared from 4–7 and 8–10 nm silica gels improve greatly compared to pure silica gels, but they do not for 2–3 nm silica gels. The silica gel with pore size of 2–3 nm is not suitable for preparing the composite adsorbent by impregnation method due to the pore blockage because of the small pore size. The SCP and COP of the adsorption chiller with sample SA50 are 128.3 Wkg^?1 and 0.27 respectively at the hot source temperature of 90 °C, which are largely superior to that of SA0. Hence using the composite adsorbent instead of the pure silica gel can reduce the size of the adsorption chiller.     

Influence of annealing temperature on microstructural and electrochemical properties of rf-sputtered LiMn2O4 film cathodes

The microstructural and electrochemical properties of rf-sputtered LiMn₂O₄ films were investigated as a function of post-deposition process. The degree of crystallization in the films gradually increased with the increase of annealing temperature (T _a). The films annealed at T _a?=?973 K exhibited characteristic peaks with predominant (111) orientation representing the cubic spinel structure of Fd3m symmetry. The estimated Mn–Mn and Mn–O distances obtained from the X-ray diffraction data were observed to be increased slightly with T _a. Characteristic changes in surface morphological features were observed as a function of T _a as evidenced from scanning electron microscopy. The estimated root mean square (RMS) roughness of the films increased from 97 to 161 nm with augmentation of T _a. The electrochemical studies, viz. cyclic voltammetry (CV), specific discharge capacity and Li ion diffusion coefficient were carried out for annealed LiMn₂O₄ films in saturated aqueous electrolyte (Li₂SO₄) in the potential window of 0–1.2 V and correlated with surface morphology and grain size. The LiMn₂O₄ films annealed at T _a?=?973 K exhibited better electrochemical performance and demonstrated a discharge capacity of about 53.5 μA h cm^?2 μm^?1 with diffusion coefficient of 1.2?×?10^?13 cm² s^?1.     

Preparation and microstructure of sol-gel derived silver-doped silica

Silver-doped silica was prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) in the presence of a silver nitrate (AgNO₃) solution by two different synthesis methods. In the first synthesis route, sol-gel mixtures were prepared using an acid catalyst. In the second synthesis route, silver-doped silica gels were formed by two-step acid/base catalysis. For the same concentration of silver dopant [AgNO₃]/[TEOS] = 0.015 acid-catalyzed sol-gel formed a microporous silica with an average pore size of <25 Å whereas the two-step catalyzed silica had an average pore size of 250 Å and exhibited a mesoporous structure when fully dried. The differences in the pore size affected the silver particle formation mechanism and post-calcination silver particle size. After calcination at 800 °C for 2 h the acid-catalyzed silica contained metallic silver particles size with an average particle size of 24 ± 2 nm whereas two-step catalyzed silica with the same concentration of [AgNO₃]/[TEOS] = 0.015 contained silver nanoparticles with an average size of approximately 32 ± 2 nm. Mechanisms for silver particle formation and for silica matrix crystallization with respect to the processing route and calcination temperature are discussed.     

Dynamics of water vapor sorption in a CaCl2/Silica Gel/Binder bed: The effect of the bed pore structure

The dynamics of water vapor sorption in a compact, binder-containing bed of a CaCl₂-in-silica-gelpores sorbent has been investigated by NMR microscopy. The procedure suggested for the preparation of this bed allows the porous structure of the bed to be modified in a wide range. The bed pore structure and water transfer in the bed have been studied in relation to the particle size of the initial silica gel, the size of mesopores in the sorbent particles, and the binder content. By varying these parameters, it is possible to optimize the ratio of the diffusion resistance of the interparticle macropores to that of the internal mesopores of the particles. If sorption is controlled by water diffusion in the macropores, a sorption front forms in the sample to move inside the bed. The distance traveled by the front is proportional to the sorption time to the power 1/2. The effective diffusion coefficient of water in the macropores is estimated from the front motion dynamics to be between 0.8 × 10^?9 and 3.0 × 10^?9 m²/s, depending on the porous structure of the bed.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.     

High-Pressure Solubility of l-Methionine in Water

The solubility (m _S) of l-methionine in water was measured at 298.2 K and pressures up to 200 MPa. The data were fitted to the equation ln(m _S/mol·kg^?1) = ?4.62 × 10^?6 (p/MPa)² + 2.65 × 10^?3 (p/MPa) ? 0.970 with a standard deviation of σ(ln m _S) = 0.002. The pressure coefficient of the logarithm of solubility (?ln m _S/?p) _T was thermodynamically estimated to be (2.62 ± 0.34) × 10^?3 MPa^?1 at 0.10 MPa using several parameters such as partial molar volume and activity coefficient of l-methionine in water and molar volume of solid l-methionine. The resulting value agrees well with the second term on the right-hand side of the fitted equation above, indicating the reliability of the high-pressure solubility measurements. The value of (?ln m _S/?p) _T also was compared with those of other amino acids.     

The electrochemical performance of sodium-ion-modified spinel LiMn2O4 used for lithium-ion batteries

The spinel LiMn₂O₄ cathode material has been considered as one of the most potential cathode active materials for rechargeable lithium ion batteries. The sodium-doped LiMn₂O₄ is synthesized by solid-state reaction. The X-ray diffraction analysis reveals that the Li_1?x Na _x Mn₂O₄ (0?≤?x?≤?0.01) exhibits a single phase with cubic spinel structure. The particles of the doped samples exhibit better crystallinity and uniform distribution. The diffusion coefficient of the Li_0.99Na_0.01Mn₂O₄ sample is 2.45?×?10^?10 cm^?2 s^?1 and 3.74?×?10^?10 cm^?2 s^?1, which is much higher than that of the undoped spinel LiMn₂O₄ sample, indicating the Na⁺-ion doping is favorable to lithium ion migration in the spinel structure. The galvanostatic charge–discharge results show that the Na⁺-ion doping could improve cycling performance and rate capability, which is mainly due to the higher ion diffusion coefficient and more stable spinel structure.     

Study on Dynamic Interfacial Tension of 3‐Dodecyloxy‐2‐hydroxypropyl Trimethyl Ammonium Chloride at n‐Decane/Water Interface

Dynamic interfacial tension (DIT) and interface adsorption kinetics at the n‐decane/water interface of 3‐dodecyloxy‐2‐hydroxypropyl trimethyl ammonium chloride (R₁₂TAC) were measured using spinning drop method. The effects of R_nTAC concentration and temperature on DIT have been investigated, the reason of the change of DIT with time has been discussed. The effective diffusion coefficient, D _a, and the adsorption barrier, ?_a, have been obtained with extended Word‐Tordai equation. The results show that the higher the concentration of surfactants is, and the smaller will be the DIT and the lower will be the curve of the DIT, and the R₁₂TAC solutions follow a mixed diffusion‐activation adsorption mechanism in this investigation. With increase of concentration in bulk solution of R₁₂TAC from 8×10^?4 mol · dm^?3 to 4×10^?3 mol · dm^?3, D _a decreases from 2.02×10^?10 m^?2 · s^?1 to 1.4×10^?11 m^?2 · s^?1 and ? _a increases from 2.60 kJ · mol^?1 to 9.32 kJ · mol^?1, while with increase of temperature from 30°C to 50°C, D _a increases from 2.02×10^?10 m^?2 · s^?1 to 5.86×10^?10 m^?2 · s^?1 and ε_a decreases from 2.60 kJ · mol^?1 to 0.73 kJ · mol^?1. This indicates that the diffusion tendency becomes weak with increase strength of the interaction between surfactant molecules and that the thermo‐motion of molecules favors interface adsorption.     

Simultaneous Determination of Paracetamol and Caffeine in Human Plasma by LC–ESI–MS

A rapid, selective and convenient liquid chromatography–mass spectrometric method for the simultaneous determination of paracetamol and caffeine in human plasma was developed and validated. Analytes and theophylline [internal standard (I.S.)] were extracted from plasma samples with diethyl ether-dichloromethane (3:2, v/v) and separated on a C₁₈ column (150 × 4.6 mm ID, 5 μm particle size, 100 Å pore size). The mobile phase consisted of 0.2% formic acid–methanol (60:40, v/v). The assay was linear in the concentration range between 0.05 and 25 μg mL^?1 for paracetamol and 10–5,000 ng mL^?1 for caffeine, with the lower limit of quantification of 0.05 μg mL^?1 and 10 ng mL^?1, respectively. The intra- and inter-day precision for both drugs was less than 8.1%, and the accuracy was within ±6.5%. The single chromatographic analysis of plasma samples was achieved within 4.5 min. This validated method was successfully applied to study the pharmacokinetics of paracetamol and caffeine in human plasma.     

Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides

Novel complex oxides Sr₂Ga_1+x In_1?x O₅, x?=?0.0–0.2 with brownmillerite-type structure were prepared in air at T?=?1,273 K, 24 h. Study of the crystal structure of Sr₂Ga_1.1In_0.9O₅ refined using X-ray powder diffraction data (S.G. Icmm, a?=?5.9694(1) Å, b?=?15.2091(3) Å, c?=?5.7122(1) Å, χ ²?=?2.48, R _F ²? ₌?0.0504, R _p?=?0.0458) revealed ordering of Ga³⁺ and In³⁺ cations over tetrahedral and octahedral positions, respectively. A partial replacement of Sr²⁺ by La³⁺ according to formula Sr_1?y La _y Ga_0.5In_0.5O_2.5+y/2, leads to the formation of a cubic perovskite (a?=?4.0291(5) Å) for y?=?0.3. No ordering of oxygen vacancies or cations was observed in Sr_0.7La_0.3Ga_0.5In_0.5O_2.65 as revealed by electron diffraction study. The trace diffusion coefficient (D _T) of oxygen for cubic perovskite Sr_0.7La_0.3Ga_0.5In_0.5O_2.65 is in the range 2.0?×?10^?9–6.3?×?10^?8 cm²/s with activation energy 1.4(1)?eV as determined by isotopic exchange depth profile technique using secondary ion mass spectrometry at 973–1,223 K. These values are close to those reported for Ca-doped ZrO₂. High-temperature electrical conductivity of Sr_0.7La_0.3Ga_0.5In_0.5O_2.65 studied by AC impedance was found to be nearly independent on oxygen partial pressure. Calculated values of activation energy at T?<?1,073 K for hole and oxide-ion conductivities are 0.96 and 1.10 eV, respectively.     

The effect of ionic strength on the diffusion of 125I in Gaomiaozi bentonite

The diffusion of ¹²⁵I^? in compacted Gaomiaozi (GMZ) bentonite was investigated by capillary in-diffusion method. Apparent and effective diffusion coefficients and accessible porosity of iodide in GMZ bentonite were obtained, and the effect of ionic strength on diffusion parameters was studied. The apparent diffusion coefficients of iodide in compacted GMZ bentonite are in the range of 1.0–6.0 × 10^?10 m² s^?1 under the conditions of dry bulk density 1,500 kg m^?3 and temperature 298 K, and increase with increasing ionic strength. This effect was explained through the analysis of microscopic structure of compacted bentonite. The iodide can only diffuse in unbound interparticle pore solution of compacted bentonite. The apparent diffusion coefficient is a function of accessible porosity which is decided by the thickness of diffusion double layer, and the thickness is in turn controlled by ionic strength.     

Comparative study on retardation behavior of Cs in crushed and intact rocks: two potential repository host rocks in the Taiwan area

This study investigates sorption and diffusion of Cs in two potential host rocks (granite from Kinmen Island and basalt from Penghu Island) by using batch and through-diffusion methods in order to establish a reliable safety assessment methodology. These methods were applied to crushed and intact rock samples to investigate the actual geological environment. According to solid-phase analysis, including X-ray diffraction, elemental analysis, auto radiography, and polar microscopy, the sorption component primarily contained iron?Cmagnesium (Fe?CMg) minerals in basalt and granite. Moreover, the distribution coefficient (K _d) of Cs in various concentrations (~10^?2?C10^?7?M) obtained from batch tests indicated a higher sorption capacity in basalt than that in granite because of the 10% Fe?CMg mineral content. The diffusion of Cs in both crushed granite and basalt reached steady state after 110?days, and the apparent diffusion coefficients (D _a) were 2.86?×?10^?11 and 1.82?×?10^?12?m²/s, respectively. However, the value of D _a for Cs in intact rocks was estimated to be 1.45?×?10^?12?m²/s in granite and 0.56?×?10^?12?m²/s in basalt, lower than the values obtained using crushed rocks. In addition to the microporous structure (major sorption minerals), it showed that the major retardation of Cs depended on the porosity (??) of compacted media, according to through-diffusion tests. In fact, the solid/liquid (S/L) ratio decreased as is the case when switching from batch to column experiments and the sorption effect on minerals became even more negligible in retardation of radionuclide migration.     

Adsorption equilibrium and kinetics of cesium onto insoluble Prussian blue synthesized by an immediate precipitation reaction between Fe3+ and [Fe(CN)6]4−

The adsorption equilibrium and kinetics of cesium ion (Cs⁺) onto insoluble Prussian blue (PB) prepared by an immediate precipitation reaction between Fe³⁺ and [Fe(CN)₆]^4? was investigated under initial Cs⁺ concentration of under 0.15 mmol/L. Synthesis conditions in this method were almost insensitive to the adsorption ability of insoluble PB, and this method provided one of the smallest PB crystallites among synthesis methods. Even when molar concentration of H₃O⁺ was more than 200 times higher or molar concentration of K⁺ was more than 50,000 times higher than that of Cs⁺ in the aqueous solution, the equilibrium adsorption amount was reduced by only approximately one-half to two-third of that in the pure system; that is, the insoluble PB synthesized possessed a considerably high adsorption selectivity for Cs⁺. In contrast to the excellent adsorption ability under adsorption equilibrium, adsorption rate was quite slow. It took at least 2 weeks at 25 °C to completely attain the adsorption equilibrium, even though the primary particle size (crystallite size) and secondary particle size (aggregate size of the crystallites) were sufficiently small at approximately 14 nm and 53–106 μm, respectively. This slow adsorption is primarily due to the large resistance of intracrystalline diffusion; the intracrystalline diffusion coefficient was extremely small at less than 3.3 × 10^?22 m²/s. We also found that increase in temperature could significantly decrease this diffusion resistance, resulting in much quicker elimination of Cs⁺ from the aqueous solution.     

Template-free sol–gel synthesis of microporous NiO–SiO2 composite with high surface area and narrow pore size distribution

Microporous NiO–SiO₂ composites were synthesized by a new sol–gel chemistry strategy using propylene oxide as gelation agent. Simple procedure, using of cheap precursor and high quality of the synthesized target materials were recognized as the advantages of the process. The obtained maximum pore surface area of the composites is about 718 m² g^?1 with narrow pore size distribution around 9 Å and micropore volume of 0.31 cm³ g^?1. It was found that the surface area of the samples decreases with the increase of Ni/Si molar ratio. However, the micropore size distributions of the samples were not altered with the increase of Ni/Si molar ratio. The unique chemistry of this sol–gel route assures the effectivity, simplicity and low cost of the whole process, showing the characteristics for the potential large scale preparation of microporous mixed oxide composites with very high pore area and very narrow pore size distribution.