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.     

Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 [m²/s] and D _p (90 Å) =5.8?10^?10 [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.     

Prominent Study on Surface Properties and Diffusion Coefficient of Urease-Conjugated Magnetite Nanoparticles

Herein, the magnetite nanoparticles (MNs) were prepared by facile solvothermal method and its porous nature was modified using 3-(2-aminoethyl)-3-aminopropyl trimethoxysilane (AEAPS). Magnetite formation, successful amino tagging, and urease conjugation on the surface were confirmed from the presence of certain functional groups in Fourier transform infrared (FT-IR) spectra. Also, nanosize (13.2 nm) and spherical morphology of MNs were evaluated from diffraction patterns and electron micrographs respectively. Lower retentivity and coercivities in magnetization curve revealed the superparamagnetic behavior, and nitrogen adsorption/desorption curves exhibited decrease in its surface porosity. Conductivity measurements showed lower diffusion coefficient (D_e?=?1.9?×?10^?17 cm²/min) and higher diffusion with limited hydrolytic reaction in native urease and improved activity of conjugated urease with higher D_e (12.62?×?10^?16 cm²/min). Hence, this study revealed that the surface porous nature of MNs can be altered effectively by amino tagging in order to overcome diffusional limitations thereby enhancing enzyme activity.     

Structural,electrochemical, and adsorption studies of Ni and Zn benzylimidazole coordination polymers with terephthalate linkers

Two coordination polymers, [Ni(bim)₂(L1)(H₂O)₂] _n (CP-1) and [Zn(bim)(L1)(Cl)] _n (CP-2) (bim = 1-benzylimidazole, L1 = terephthalic acid), were synthesized and characterized by physicochemical and spectroscopic methods. The Ni(II) center in CP-1 is octahedral, while the Zn(II) center in CP-2 is tetrahedral. CP-1 and CP-2 were used to modify carbon paste electrodes to assess their effect on the electrochemical behavior of ferricyanide. The redox reactions of ferricyanide on both electrodes proved to be reversible and diffusion controlled, with ferricyanide diffusion coefficients for CP-1 and CP-2 of 1.88 × 10⁵ and 3.44 × 10⁵ cm² s^?1, respectively. These coordination polymers were also investigated for their adsorption behavior toward two dyes: Chicago sky blue and methylene blue. CP-1 and CP-2 both rapidly adsorbed the anionic Chicago sky blue dye by different intermolecular interactions; in contrast, the cationic methylene blue dye was adsorbed to a lesser extent. The adsorption of these CPs depends on the charge but not the size of the dye. Addition of methanolic potassium nitrate solution caused the release of the adsorbed dyes.     

Electrodeposition of zinc oxide nanoparticles on multiwalled carbon nanotube-modified electrode for determination of caffeine in wastewater effluent

We report on the development of an electrochemical sensor based on electrodepositing zinc oxide on multiwalled carbon nanotube-modified glassy carbon electrode for the detection of caffeine in pharmaceutical wastewater effluents. The measurements were carried out using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and differential pulse voltammetry (DPV). DPV measurements showed a linear relationship between oxidation peak current and concentration of caffeine in 0.1 M HClO₄ (pH 1.0) over the concentration range 0.00388–4.85 mg/L and a detection limit of 0.00194 mg/L. The diffusion coefficient and Langmuir adsorption constant for caffeine were calculated to be 3.25 × 10^?6 cm² s^?1 and 1.10 × 10³ M^?1, respectively. The sensor showed satisfactory results when applied to the detection of caffeine in wastewater effluents.     

The States,Diffusion, and Concentration Distribution of Water in Radiation‐Formed PVA/PVP Hydrogels

Abstract

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1‐vinyl‐2‐ pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma‐rays from ⁶⁰Co sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T₂ relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range ?10 to +10°C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was referred to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with F_VP=0.19 has been estimated to be g_H2O/g_Polymer=0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve‐fit of the early‐stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5×10^?11 m² s^?1 and 4.5×10^?11 m² s^?1, depending on the polymer composition, the cross‐link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was ≈24 kJ mol^?1. Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.     

Electrochemical study of vinylsulphone azo dye Reactive Black 5 and its determination at a glassy carbon electrode

The electrochemical oxidation of vinylsulphone azo dye, Reactive Black 5 (RB5), at a glassy carbon electrode has been carried out in phosphate buffer solutions in the pH range 2.85?C11.79 employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). RB5 showed one well-defined oxidation peak at 0.560 V vs. Ag-AgCl using DPV. The oxidation process was shown to be irreversible over the pH range 2.85?C8.39 and was diffusion controlled. The linear relationship between the peak current height and RB5 concentrations allowed the differential pulse voltammetric determination of the dye over a wide concentration range, from 6.0 × 10^?7 to 1.5 × 10^?6 M with a detection limit of 4.0 × 10^?7 M. The precision and recovery did not exceed 4.9 and 98.2%, respectively. A UV-Vis spectrophotometry method was also proposed for the determination of the RB5 in concentration range from 5.0 × 10^?6 M to 1.0 × 10^?5 M at ??_max = 600 nm with limit of detection of 4.7 × 10^?6 M and RSD of 1.8% for RB5 concentration of 1.0 × 10^?5 M.     

Separation of Ni<Superscript>2+</Superscript> from ammonia solution through a supported liquid membrane impregnated with Acorga M5640

Separation of Ni²⁺ from ammonia/ammonium chloride solution using a flat-sheet supported liquid membrane (SLM) impregnated with Acorga M5640 in kerosene was investigated. The fundamental experimental variables influencing Ni²⁺ transport, such as ammonia concentration, carrier concentration, H₂SO₄ concentration in the stripping solution, stirring speed, and initial Ni²⁺ concentration were studied. Almost all of Ni²⁺ was transported from the feed to the stripping phase after 18 h of operation with a permeability coefficient of 9.28 × 10^?6 m s^?1 under optimum conditions: stirring speed of 1000 rpm in both phases, 20 vol.% Acorga M5640 as the carrier, 1.70 mmol L^?1 Ni²⁺ in the feed phase and 0.10 mol L^?1 H₂SO₄ in the stripping phase. The flux value of Ni²⁺ was 15.82 × 10^?6 mol m^?2 s^?1. Additionally, the influences of temperature and ultrasound on flux were examined, and results indicated that higher temperature and ultrasonic assistance improved transport of Ni²⁺ through the SLM. Selective separation of nickel from cobalt in an ammonia/ammonium chloride solution was also achieved through SLM. The stability of the SLM was examined on a continuous run mode and satisfactory stability of the nickel permeation was observed for 84 h (7 runs).     

Proton NMR studies of lanthanum nickel hydride: Structure and diffusion

The proton magnetic resonance spectrum of lanthanum nickel hydride LaNi_5.3H₆ was measured over the temperature range 118°K < T < 300°K. The second moment of the absorption at 118°K is M₂ = 13.4 ± 0.3 G². Several possible arrangements of the hydrogen atoms are discussed. Narrowing of the line above 140°K is analyzed in terms of proton diffusion and gives an activation enthalpy E = 21 ± 1 kJ mol^?1, NMR correlation time pre-exponential 0.2 ps < τ_c⁰ < 1.6 ps and a self diffusion coefficient at 300°K of 2 × 10^?12 m² s^?1 < D < 2 × 10^?11 m² s^?1.     

Can the Theoretical Fitting of the Proton‐Nuclear‐Magnetic‐Relaxation‐Dispersion (Proton NMRD) Curves of Paramagnetic Complexes Be Improved by Independent Measurement of Their Self‐Diffusion Coefficients?

The self‐diffusion (D_c) coefficients of various lanthanum(III) diamagnetic analogues of open‐chain and macrocyclic complexes of gadolinium used as MRI contrast agents were determined in dilute aqueous solutions (3–31 mM ) by pulsed‐field‐gradient (PFG) high‐resolution ¹H‐NMR spectroscopy. The self‐diffusion coefficient of H₂O (D_w) was obtained for the same samples to derive the relative diffusion constant, a parameter involved in the outersphere paramagnetic‐relaxation mechanism. The results agree with an averaged relative diffusion constant of 2.5 (±0.1)×10^?9 and of 3.3 (±0.1)×10^?9 m² s^?1 at 25 and 37°, respectively, for 'small' contrast agents (M_r 500–750 g/mol), and with the value of bulk H₂O (2.2×10^?9 and 2.9×10^?9 m² s^?1 at 25° and at 37°, respectively) for larger complexes. The use of the measured values of D_c for the theoretical fitting of proton NMRD curves of gadolinium complexes shows that the rotational correlation times (τ_R) are very close to those already reported. However, differences in the electronic relaxation time (τ_SO) at very low field and in the correlation time (τ_V) related to electronic relaxation were found.     

Ozone reduction at Nafion modified Au electrode and the measurement of ozone concentration in highly resistive solutions

The mass transport and charge transfer kinetics of ozone reduction at Nafion coated Au electrodes were studied in 0.5 mol/L H2SO4 and highly resistive solutions such as distilled water and tap water. The diffusion coefficient and partition coefficient of ozone in Nafion coating are 1.78×10-6 cm2·s-1 and 2.75 at 25℃ (based on dry state thickness), respectively. The heterogeneous rate constants and Tafel slopes for ozone reduction at bare Au are 4.1×10-6 cm·s-1, 1.0×10-6 cm·s-1 and 181 mV, 207 mV in 0.5 mol/L H2SO4 and distilled water respectively and the corresponding values for Nafion coated Au are 5.5×10-6 cm·s-1, 1.1×10-6 cm·s-1 and 182 mV, 168 mV respectively. The Au microelectrode with 3 μm Nafion coating shows good linearity over the range 0-10 mmol/L ozone in distilled water with sensitivity 61 μA·ppm-1 ·cm-2, detection limit 10 ppb and 95% response time below 5 s at 25℃. The temperature coefficient in range of 11-30℃ is 1.3%.     

Removal of cationic dyes: basic magenta and methylene blue from aqueous solution by adsorption on modified loofah

Modified loofah was prepared by a simple chemical graft method to improve its adsorption for cationic dyes. Experimental results showed that the maximum amounts of basic magenta and methylene blue loaded on the modified loofah were 83.5 and 85.5 mg g^?1, and that on the unmodified loofah were 22.2 and 33.7 mg g^?1, respectively. The adsorption for both dyes could reach equilibrium after 300 min. A pseudo-second-order model is suitable for describing the adsorption and desorption kinetics of both dyes on the modified sorbent. According to the intra-particle diffusion model, sorption and desorption processes for the two dyes both presented two distinct phases and were mainly controlled by intra-particle diffusion. The dye-loaded modified loofah could be regenerated by using the mixture solution of HCl and ethanol (V_HCl:V_ethanol = 3:2) as eluent. Adsorption in the binary system showed that adsorption of the dyes was depressed by the presence of the other dye, and the two dyes could be removed efficiently when the initial concentrations were lower than 5.0 × 10^?5 mol L^?1. The Langmuir competitive model was suitable to predict the sorption isotherm in the binary system.     

Electrochemical Study on the Interaction of Irinotecan with Calf Thymus Double Stranded DNA

Voltammetric behavior of Irinotecan (CPT‐11) was studied in a phosphate buffer (0.002 mol·L^?1, pH 7.5) solution at the hanging mercury drop electrode (HMDE) using cyclic voltammetry (CV). CPT‐11 showed two irreversible cathodic peaks at ?1.01 V and ?1.09 V which involved two electrons and two protons in each reduction step. In addition, the interaction of Irinotecan with double‐stranded calf thymus DNA (ds‐DNA) was studied by CV at the HMDE employing an irreversible electrochemical equation. As a result of the reaction with ds‐DNA, the reduction peaks related to CPT‐11 were shifted in a negative direction and the peak currents were decreased. The diffusion coefficients of CPT‐11 in the absence (D_f) and presence (D_b) of ds‐DNA were calculated as 2.8×10^?5 cm²·s^?1 and 1.6×10^?5 cm²·s^?1 respectively. The binding constant (K=1.0×10⁴ L·mol^?1), and binding site size (s=0.60) of CPT‐11 interacting with ds‐DNA were obtained simultaneously by non‐linear fit analysis. The results demonstrate that the main interaction mode of CPT‐11 with ds‐DNA is electrostatic.     

Determination of sodium ion diffusion coefficients in sodium vanadium phosphate

Carbon-coated Na₃V₂(PO₄)₃ (NVP) was prepared by a standard sol–gel procedure. The apparent diffusion coefficients of sodium ions in the rhombohedral NVP have been determined by different techniques such as galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). It was found that the apparent diffusion coefficients range from 6?×?10^?13 cm² s^?1 to 2?×?10^?15 cm² s^-1. These sodium ion apparent diffusion coefficients follow a similar trend as observed for lithium ions in the closely related monoclinic modification of Li₃V₂(PO₄)₃, demonstrating a minimum at the potential where the ion extraction/insertion occurs.     

Competitive Adsorption of Methylene Blue and Rhodamine B on Natural Zeolite: Thermodynamic and Kinetic Studies

A batch system was applied to study the adsorption behavior of methylene blue (MB) and rhodamine B (RB) in single and binary component systems on natural zeolite. In the single component systems, the zeolite presents higher adsorption capacity for MB than RB with the maximal adsorption capacity of 7.95×10^?5 and 1.26×10^?5 mol/g at 55°C for MB and RB, respectively. Kinetic studies indicated that the adsorption followed pseudo‐second‐ order kinetics and could be described by a two‐step diffusion process. For the single component systems, the adsorption isotherm could be fitted by the Langmuir model. In the binary component system, MB and RB exhibit competitive adsorption on the zeolite. The adsorption is approximately reduced to 50% and 60% of single component adsorption systems of MB and RB, respectively at an initial concentration of 6×10^?6 mol·L^?1 at 25°C. In the binary component system, kinetic and adsorption isotherm studies demonstrate that the experimental data are following pseudo‐second‐order kinetics and Langmuir isotherm and kinetic data are fairly described by a two‐step diffusion model. Effect of solution pH on adsorption of MB and RB in both single and binary component systems was studied and the results were described by electrostatic interactions.     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of ⁹⁹TcO₄ ^? and ReO₄ ^? in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For ⁹⁹TcO₄ ^? in present of EDTA, the D _e values was (1.2 ± 0.1) × 10^?11 m²/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between ⁹⁹TcO₄ ^? and EDTA might be formed. By contrast, the D _e values of ReO₄ ^? remained unchanged in present or absent of EDTA, indicating that ReO₄ ^? could not complex with EDTA. However, the diffusion of ReO₄ ^? could be increased in present of EDTA, the D _a value was found to be increased from 1.8 × 10^?10 to 5.4 × 10^?10 m²/s. It demonstrated that ReO₄ ^? need more drastic conditions to form the Re(VII)–EDTA complexes than those used for ⁹⁹TcO₄ ^?. For both ReO₄ ^? and ⁹⁹TcO₄ ^?, the rock capacity factor α is less than the total porosity ε _tot, indicating that they has little retention/sorption on the surface of bentonite.     

Biosensor for Hydrogen Peroxide Based on Chitosan and Nanoparticle Complex Film–Modified Glassy-Carbon Electrodes

Abstract

A biosensor for hydrogen peroxide was fabricated by co-immobilizing cadmium telluride (CdTe) nanoparticles, chitosan, and hemoglobin (Hb) matrix. There was a pair of nearly reversible redox peaks around ?0.360 V, and the electrochemical behavior of Hb was a surface-controlled process, with an electron-transfer rate constant of 1.36 s^?1 and surface coverage of 2.62 × 10^?10 mol cm^?2. Fourier transform infrared (FT-IR) spectra and ultraviolet–visible (UV-vis) spectra indicated that Hb sustained its natural conformation. It was demonstrated that Hb in the matrix kept its bioactivity and exhibited catalytic ability toward H₂O₂, with a response ranging from 7.44 × 10^?6 to 6.95 × 10^?4 M and a detection limit of 2.23 × 10^?6 M.