Sol–gel derived ion imprinted thiocyanato-functionalized silica gel as selective adsorbent of cadmium(II)

A Cd(II)-imprinted thiocyanato-functionalized silica gel adsorbent with high adsorption capacity was prepared by surface imprinting technique combined with sol–gel process for the selective adsorption of Cd(II) ion in aqueous solution, and was characterized by Fourier-transform infrared spectroscopy, nitrogen gas sorption and thermogravimetric analysis. The influences of different conditions (such as the pH of solutions, the contact time and the initial concentrations of Cd(II) ions) on the adsorption capacity of Cd(II) were investigated. The optimum pH of adsorption was in the range of 4–8.5. The adsorption equilibrium could be reached in 20 min. The relatively selectivity coefficients of the imprinted silica were higher than those of the non-imprinted adsorbents. Ho’s pseudo-second-order model well described the kinetics of the adsorption reaction. The adsorption process of metals followed Redlich–Peterson isotherm model, and the experimental value of maximum adsorption capacity for Cd(II) was 72.8 mg·g^?1. The positive value of ΔH ^o suggested endothermic nature of Cd(II) adsorption on the imprinted silica adsorbent. Increase in entropy of adsorption reaction was shown by the positive value of ΔS ^o and the negative value of ΔG ^o indicating that the adsorption was spontaneous in nature.     

Methylene blue removal from aqueous solution by magnetic clinoptilolite/chitosan/EDTA nanocomposite

In this study, clinoptilolite as a natural zeolite which was magnetized using precipitation of maghemite nanoparticles was coated by chitosan and then modified by thylenediamine tetra-acetic acid to add functional groups and its performance in the removal of toxic methylene blue from aqueous solution was investigated. Synthesized magnetic nanocomposite was characterized by VSM, XRD, SEM, and FTIR analyses. The saturation magnetization of the final nanocomposite was obtained as 22.2 emu/g. In addition, the factors affecting adsorption process and its optimization were investigated using response surface methodology and central composite design. Data obtained by different isotherm, adsorption kinetic and thermodynamic models were also studied. The results showed good agreement of these data with the Freundlich isotherm model (R ² = 0.99), and it was found that adsorption follows the second-order kinetics model (R ² = 1). Negative values of ΔG and positive values of ΔH obtained from this adsorption thermodynamic study revealed that the methylene blue adsorption process is exothermic and spontaneous. The optimum conditions to ensure maximum adsorption efficiency were determined, and included pH = 5.54, adsorbent amount of 0.03 g, temperature of 31.18 °C, and initial solution concentration of 16.21 mg/l which resulted in a removal efficiency of 99.44%. The results indicated that this nanocomposite can be used as a proper adsorbent for adsorbing methylene blue and other dye contaminants.     

Saw-sedge <Emphasis Type="Italic">Cladium mariscus</Emphasis> as a functional low-cost adsorbent for effective removal of 2,4-dichlorophenoxyacetic acid from aqueous systems

For the first time in the published literature, a study is described concerning the use of the saw-sedge Cladium mariscus (C. mariscus) for adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous systems. Among the experiments carried out, the elemental composition of C. mariscus was determined (C = 48.0 %, H = 7.1 %, N = 0.95 %, S = 0.4 %), FTIR spectroscopic analysis was performed to confirm the chemical structure of the adsorbent, and porous structure parameters were measured: BET surface area (A _BET  = 0.6 m²/g), total pore volume (V _p  = 0.001 cm³/g) and average pore size (S _p  = 6.6 nm). It was shown that the effectiveness of removal of 2,4-D from aqueous systems using C. mariscus depends on parameters of the process: contact time, system pH, mass of sorbent, and temperature. Maximum adsorption was attained for a solution at pH = 3. Further increase in the alkalinity of the tested systems led to a reduction in the effectiveness of the process. The kinetic of adsorption of 2,4-D by C. mariscus was also determined, and thermodynamic aspects were investigated. The experimental data obtained correspond to a pseudo-second-order kinetic model of type 1. Additionally the negative values obtained for ΔHº indicate that the process is exothermic, and the negative values of ΔGº show it to be spontaneous. As the temperature of the system increases the spontaneity of adsorption is reduced, in accordance with the exothermic nature of the process.     

Assessment of <Emphasis Type="Italic">Urtica</Emphasis> as a low-cost adsorbent for methylene blue removal: kinetic,equilibrium, and thermodynamic studies

Methylene blue (MB) removal using eco-friendly, cost-effective, and freely available Urtica was investigated. The morphology of the adsorbent surface and the nature of the possible Urtica and MB interactions were examined using SEM analysis and the FTIR technique, respectively. Various factors affecting MB adsorption such as adsorption time, initial MB concentration, temperature, and solution pH were investigated. The adsorption process was analysed using different kinetic models and isotherms. The results showed that the MB adsorption kinetic follows a pseudo-second-order kinetic model and the isotherm data fit the Langmuir isotherm well. Thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were also evaluated, and the results indicated that the adsorption process is endothermic and spontaneous in nature. The MB adsorption capacity of Urtica was found to be as high as 101.01 mg g^?1, higher than those of many other adsorbents studied in the literature. This superior adsorption capacity, along with the ready availability of Urtica, render this adsorbent potentially suitable for practical applications.     

Removal of Th(IV), Ni(II)and Fe(II) from aqueous solutions by a novel PAN–TiO<Subscript>2</Subscript> nanofiber adsorbent modified with aminopropyltriethoxysilane

A novel polyacrylonitrile (PAN)–titanium oxide (TiO₂) nanofiber adsorbent functionalized with aminopropyltriethoxysilane (APTES) was fabricated by electrospinning. The adsorbent was characterized by SEM, FTIR, TEG and BET analyses. The pore diameter and surface area of the adsorbent were 3.1 nm and 10.8 m² g^?1, respectively. The effects of several variables, such as TiO₂ and amine contents, pH, interaction time, initial concentration of metal ions, ionic strength and temperature, were studied in batch experiments. The kinetic data were analyzed by pseudo-first-order, pseudo-second-order and double-exponential models. Two isotherm models, namely Freundlich and Langmuir, were used for analysis of equilibrium data. The maximum adsorption capacities of Th(IV), Ni(II) and Fe(II) by Langmuir isotherm were found to be 250, 147 and 80 mg g^?1 at 45 °C with pH of 5, 6 and 5, respectively, and greater adsorption of Th(IV) could be justified with the concept of covalent index and free energy of hydration. Calculation of ΔG°, ΔH° and ΔS° demonstrated that the nature of the Th(IV), Ni(II) and Fe(II) metal ions adsorption onto the PAN–TiO₂–APTES nanofiber was endothermic and favorable at a higher temperature. The negative values of ΔG° for Th(IV) showed that the adsorption process was spontaneous, but these values for Ni(II)and Fe(II) were positive and so the adsorption process was unspontaneous. Increasing of ionic strength improved the adsorption of Ni(II) and Fe(II) on nanofiber adsorbent but decreased the adsorption capacity of Th(IV). The adsorption capacity was reduced slightly after six cycles of adsorption–desorption, so the nanofiber adsorbent could be used on an industrial scale. The inhibitory effect of Ni(II) and Fe(II) on the adsorption of Th(IV) was increased with an increase in the concentration of inhibitor metal ions.     

Cadmium removal from aqueous solution by biochar obtained by co-pyrolysis of sewage sludge with tea waste

Resource utilization is a critical pathway for sustainable solid waste treatment. Biochar was prepared from the co-pyrolysis of sewage sludge and tea waste. Brunauer–Emmett–Teller measurement, scanning electron microscopy and Fourier transform infrared analysis were employed to characterize the biochar. Then, the interface behavior between biochar and Cd from aqueous solution was investigated. The effect of adsorbent dose and pH on Cd adsorption was evaluated. Adsorption kinetics and the adsorption isotherm were studied, and the adsorption mechanism was explored. The results showed that the suitable adsorbent dose was 4 g L^?1 and the optimal pH of the Cd solution remained at 6.0. Cadmium sorption on the biochar could be well described by the pseudo-second order kinetic model (R ² > 0.98). The adsorption process was described using the Langmuir (R ² > 0.86), Freundlich (R ² > 0.86), Temkin (R ² > 0.84) and Dubinin–Radushkevich (R ² > 0.86) isotherm models. The proportion of organic constituents in biochar was 69.2–72.4%. Minerals that originated in biochar played an important role during the Cd adsorption process, and the contribution of minerals accounted for 27.6–30.8% of the total adsorption. The main mechanism of the Cd adsorption process by biochar involved ion exchange, surface complexation, electrostatic interaction, surface co-precipitation, and other mechanisms. Therefore, biochar created by the co-pyrolysis of sewage sludge and tea waste could be used as an adsorbent for the removal of metal ions from contaminated water.     

Modeling of fixed-bed column studies for removal of cobalt ions from aqueous solution using <Emphasis Type="Italic">Chrysanthemum indicum</Emphasis>

The present study investigates the adsorption capability of raw and biochar forms of Chrysanthemum indicum flowers biomass to remove cobalt ions from aqueous solution in a fixed-bed column. Column adsorption experiments were conducted by varying the bed height (1.0, 2.0, 3.0 cm), flow rate (1.0, 2.5, 5.0 mL min^?1) and initial cobalt ion concentration (25, 50, 75 mg L^?1) to obtain the experimental breakthrough curves. The adsorption capacity of the raw and biochar forms of C. indicum flowers were found to be 14.84 and 28.34 mg g^?1, respectively, for an initial ion concentration of 50 mg L^?1 at 1.0 cm bed height and 1.0 mL min^?1 flow rate for Co (II) ion adsorption. Adam–Bohart, Thomas and Yoon–Nelson models were applied to the experimental column data to analyze the column performance. The Thomas model was found to best represent the column data with the predicted and experimental uptake capacity values correlating well and with higher R ² values for all the varying process parameters. Desorption studies revealed the suitability of the adsorbents for repeated use up to four adsorption–desorption cycles without significant loss in its efficiency. It can thus be inferred from the fixed-bed column studies that C. indicum flowers can suitably be used as an effective adsorbent for Co (II) ion removal from aqueous solution on a higher scale.     

Binding interaction and conformational changes of human serum albumin with ranitidine studied by spectroscopic and time-resolved fluorescence methods

This study was designed to examine the interaction of histamine H₂-receptor antagonist drug ranitidine (RTN) with human serum albumin by multi-spectroscopic methods. The experimental results showed the involvement of dynamic quenching mechanism which was further confirmed by lifetime spectral studies. The binding constants (K _a) at three temperatures (288, 298, and 308 K) were 2.058 ± 0.020, 4.160 ± 0.010 and 6.801 ± 0.011 × 10⁴ dm³ mol^?1, respectively, and the number of binding sites (m) were 1.169, respectively; thermodynamic parameters ΔH ⁰ (44.152 ± 0.047 kJ mol^?1), ΔG ⁰ (?26.214 ± 0.040 kJ mol^?1), and ΔS ⁰ (236.130 ± 0.025 J K^?1 mol^?1) were calculated. The distance r between donor and acceptor was obtained (r = 3.40 nm) according to the Förster theory of non-radiative energy transfer. Synchronous fluorescence, CD, AFM and 3D fluorescence spectral results revealed the changes in secondary structure of the protein upon interaction with RTN. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.     

Removal of uranium(VI) from aqueous solutions using nanoporous ZnO prepared with microwave-assisted combustion synthesis

The adsorption of the uranyl ions from aqueous solutions on the nanoporous ZnO powders has been investigated under different experimental conditions. The adsorption of uranyl on nanoporous ZnO powders were examined as a function of the contact times, pH of the solution, concentration of uranium(VI) and temperature. The ability of this material to remove U(VI) from aqueous solution was followed by a series of Langmuir and Freunlinch adsorption isotherms. The adsorption percent and distribution coefficient for nanoporous ZnO powders were 98.65 % ± 1.05 and 7,304 mL g^?1, respectively. The optimum conditions were found as at pH 5.0, contact time 1 h, at 1/5 Zn²⁺/urea ratio, 50 ppm U(VI) concentration and 303 K. The monomolecular adsorption capacity of nanoporous ZnO powders for U(VI) was found to be 1,111 mg g^?1 at 303 K. Using the thermodynamic equilibrium constants obtained at different temperatures, various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, have been calculated. Thermodynamic parameters (ΔH° = 28.1 kJ mol ^?1, ΔS° = 160.30 J mol^?1 K^?1, ΔG° = ?48.54 kJ mol^?1) showed the endothermic and spontaneous of the process. The results suggested that nanoporous ZnO powders was suitable as sorbent material for recovery and adsorption of U(VI) ions from aqueous solutions.     

Adsorptive removal of uranyl ions in aqueous solution using hydrothermal carbon spheres functionalized with 4-aminoacetophenone oxime group

Hydrothermal carbon spheres (HCSs) functionalized with 4-aminoacetophenone oxime group (HCSs-oxime) were prepared by a grafting method and explored to adsorption of uranyl ions from aqueous solution. The results of FT-IR, elemental analysis and zeta potential indicate a successfully modification with oxime group. The adsorbent shows an excellent adsorption capacity (Langmuir, q _m  = 588.2 mg g^?1) and quick adsorption kinetic (equilibrium time of approximately 60 min) at optimal pH of 6.0. The adsorptive selectivity for uranyl ions has been also great improved in present with various co-existing ions. Overall, HCSs-oxime is a potentially promising material for selective removal of uranium in the contaminated solution.     

Dye removal using 4A-zeolite/polyvinyl alcohol mixed matrix membrane adsorbents: preparation,characterization, adsorption,kinetics, and thermodynamics

In pursuit of improving performance of the methylene blue adsorption process, the potential of a novel 4A-zeolite/polyvinyl alcohol (PVA) membrane adsorbent was investigated. Adding 4A-zeolite particles to the PVA membrane adsorbent provided an effective structure for the adsorptive membrane in dye removal processes. Effect of zeolite content was also studied via synthesis of different mixed matrix membrane adsorbents (MMMAs) with 5, 10, 15, and 20 wt% 4A-zeolite content. Morphology of MMMAs was analyzed by scanning electron microscope and the intermolecular interactions were determined by Fourier transform infrared spectroscopy. X-ray diffraction was performed to determine the crystal structure of MMMAs. For the sake of finding optimum condition, the adsorption capacity was examined at various operating parameters, such as contact time, temperature, pH, and initial concentration. The maximum value of the adsorption capacity (q _e) of 41.08 mg g^?1 and the highest removal efficiency of 87.41 % were obtained by applying 20 wt% loading of 4A-zeolite. The experimental data were fitted well with the Freundlich adsorption isotherm model (R ² = 0.9917) compared with the Langmuir (R ² = 0.9489) and the Tempkin (R ² = 0.8886) adsorption isotherm models, and the adsorption kinetic data verified the best fitting with the pseudo-second-order model (R ² = 0.9999). The estimated data for Gibb’s free energy (ΔG°) showed that the adsorption process is spontaneous at lower temperature values and non-spontaneous at higher temperature values. Other evaluated thermodynamic parameters such as changing in enthalpy (ΔH°) and entropy (ΔS°) revealed that the adsorption process is exothermic with an increase in orderliness at the solid/solution interface.     

Treatment of chromium effluent by adsorption on chitosan activated with ionic liquids

This study proposes, verifies, and refines the use of biopolymers treated with two new ionic liquids (ILs) (sec-butylammonium acetate and n-octylammonium acetate), as a platform for chromium adsorption. The ILs were synthesized, characterized, and applied to chitosan treatment. Analyzing the size distribution of microparticles of chitosan and chitosan activated with ILs (sec-butylammonium acetate and n-octylammonium acetate), we observed that a little decrease in the particle size occurred with the activation of chitosan (176 ± 0.02 μm to 167 ± 0.054 and 168.5 ± 0.05 μm, respectively), as well as changes in the X-ray diffraction FTIR_ATR spectra. Further studies were performed using the best adsorbent – chitosan treated with sec-butylammonium acetate. In this case, the chromium VI concentration in the sample was reduced by more than 99% when using chitosan treated with IL sec-butylammonium acetate. The best reaction time was determined as 1 h, which allowed a chromium adsorption of 99.1% and the adsorption kinetic data were best represented by the second-order model (k₂ = 11.7258 g mg^?1 min^?1). The maximum adsorption capacity was obtained using the Langmuir isotherm model (20.833 mg g^?1 at pH 4 during 1 h, using 1.0 g of chitosan), and the adsorption efficiency was enhanced at 25 °C by the Freundlich isotherm model, in which the constants KF and n were determined as 0.875 mg L^?1 and 1.610, respectively.     

Modelling of proton and metal exchange in the alginate biopolymer

Acid–base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l^?1≤1.0) and in different supporting electrolytes (Et₄NI, NaCl, KCl, LiCl, NaCl+MgCl₂), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H⁺]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at α=0.5, are log K ^H=3.686±0.005, ΔG ⁰=?21.04±0.03 kJ mol^?1, ΔH ⁰=4.8±0.2 kJ mol^?1 and TΔS ⁰=35.7±0.3 kJ mol^?1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=?9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.     

Polyvinyl alcohol fibers with functional phosphonic acid group: synthesis and adsorption of uranyl (VI) ions in aqueous solutions

PVA functionalized with vinylphosphonic acid was prepared as a new adsorbent for uranyl (VI) adsorption from aqueous solutions. The vinylphosphonic acid was cografted onto PVA fibers by preirradiation grafting technique. The adsorbent were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The adsorbent was observed to possess a fibrous structure and was bonded with phosphonic acid groups successfully. The adsorbent was used for the adsorption of low levels uranyl (VI) ions from aqueous solutions. The influence of analytical parameters including pH, adsorption time, amount of adsorbent, metal ion concentration, and temperature were investigated on the recovery of uranyl (VI) ion in aqueous solution. The maximum adsorption capacity (32.1 mg g^?1) and fast equilibrium time (30 min) were achieved at pH of 4.5 at room temperature. Thermodynamic parameters (ΔH° = 2.695 kJ mol^?1; ΔS° = 31.15 J mol^?1 K^?1; ΔG° = ?6.748 kJ mol^?1) show the adsorption of an exothermic process and spontaneous nature, respectively. The possible coordination mechanism was illustrated. Adsorption and desorption coexist in aqueous solutions and then the system becomes equilibrium.     

Removal of thorium from aqueous solution by ordered mesoporous carbon CMK-3

The ability of ordered mesoporous carbon CMK-3 has been explored for the removal and recovery of thorium from aqueous solutions. The textural properties of CMK-3 were characterized using small-angle X-ray diffraction and N₂ adsorption–desorption, and the BET specific surface area, pore volume and the pore size were 1143.7 m²/g, 1.10 cm³/g and 3.4 nm. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CMK-3 showed the highest thorium sorption capacity at initial pH of 3.0 and contact time of 175 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G°(298 K), △H° and △S° were determined to be -0.74 kJ·mol^?1, 9.17 kJ·mol^?1 and 33.24 J·mol^?1·K^?1, respectively, which demonstrated the sorption process of CMK-3 towards Th(IV) was feasible, spontaneous and endothermic in nature. The adsorbed CMK-3 could be effectively regenerated by 0.02 mol/L HCl solution for the removal and recovery of Th(IV).     

Adsorptive recovery of geniposidic acid from gardenia yellow pigment extraction wastewater by anion exchange: equilibrium,thermodynamics and mechanism modeling and simulation

For many years, the traditional process of gardenia yellow pigment extraction has produced wastewater containing significant quantities of Geniposidic acid (GSA), a substance that could be put to pharmacological uses if it could be effectively recovered. This study aimed to provide an efficient adsorption material, D08, for recycling GSA. Batch experiments showed that adsorption capacity depends on initial concentration and temperature. The maximal adsorption capacity of GSA onto an anionic exchanger reached 310 mg/g. The pK _a value of GSA was determined to be 4.21. Pore diffusion coefficients (D _p) of GSA for 283, 298 and 313 K were 3.274 × 10^?10, 5.069 × 10^?10 and 7.356 × 10^?10 m²/s, respectively. Recovery efficiency of GSA was achieved to 99.81 %. In comparison with pseudo first-order and pseudo second-order equations, the PDM model demonstrated the best fit to the kinetics data of GSA adsorption. Adsorption/desorption experiments proved that D08 offers great adsorption capacity, high adsorption rate and good repeatability. In order to help us to accurately comprehend the mass transfer process, numerical simulation and post-processing to variables c(r, t) and q(r, t) were performed to clarify the adsorption process.     

Thermodynamics of Viscous Flow of <Emphasis Type="Italic">tert</Emphasis>-Butanol with Butylamines: UNIFAC–VISCO,Grunberg–Nissan and McAllister Three Body Interaction Models for Viscosity Prediction and Quantum Chemical (DFT) Calculations

Thermodynamic activation parameters, enthalpies (ΔH ^?), entropies (ΔS ^?) and Gibbs energies (ΔG ^?) for viscous flow of the systems tert-butanol (TB)+n-butylamine (NBA), TB+di-n-butylamine (DBA) and TB+tri-n-butylamine (TBA) have been calculated from measured density and viscosity data at temperatures ranging from 303.l5 to 323.15 K over the composition range 0 ≤ x ₂ ≤ 1, where x ₂ is the mole fraction of TB. For all systems, the corresponding excess properties ΔH ^?E, ΔS ^?E and ΔG ^?E have been determined, which are negative in the whole range of composition. The observed negative excess activation properties have been accounted for in terms of dispersive forces and H-bonding. The derived properties are well represented by fourth degree polynomial equations whereas the excess properties could be fitted to third degree Redlich–Kister polynomial equations. Furthermore, the viscosities have been predicted by using the UNIFAC–VISCO model, Grunberg–Nissan model and McAllister three-body interaction model. The UNIFAC–VISCO model and Grunberg–Nissan model do not show good agreement with the experimental data, whereas the McAllister three-body interaction model shows excellent agreement for all three systems, with small average absolute percent deviations (AAD% = 0.6–2.3). The DFT-B3LYP method with the 6-311 G (d, p) basis set has been employed for the optimization of the geometry and calculation of the total energies of the pure compounds and their binary complexes.     

Facile synthesis of 5A zeolite from attapulgite clay for adsorption of <Emphasis Type="Italic">n</Emphasis>-paraffins

5A zeolites were facilely synthesized from attapulgite clay and sodium aluminate precursors. The optimum synthesis condition for 4A zeolite (Na-form) were H₂O/attapulgite ratio of 40:1 volume/mass, NaOH/attapulgite mass ratio of 2.35:1, the crystallization time was 4 h at 80–85 °C. The 4A zeolite was converted to related 5A zeolite (Ca-form) through ionic exchanges using calcium chloride solution with the Si/Al mole ratio of 1.3. SEM images demonstrated that as-synthesized 5A zeolites are ordered cubic crystals, average crystals length dimension is 1–2 μm. And the zeolites product had a specific surface area of 482 m² g^?1 and total pore volume of 0.274 cm³ g^?1. The static adsorption experiments showed that the equilibrium adsorption capacities of n-decane and n-pentadecane on produced 5A zeolite were 0.253 and 0.510 g g^?1, respectively. And the adsorption equilibrium time of n-decane and n-pentadecane on 5A zeolite were 45 and 60 min, respectively. The experimental adsorption data of n-decane and n-pentadecane on three zeolites could be properly fitted by the Langmuir–Freundlich isotherm model.     

Adsorption of thorium (IV) by amorphous silica; response surface modelling and optimization

The amorphous SiO₂ (200–300 nm) was synthesized as an absorbent and thorium adsorption of SiO₂ was investigated using experimental and RSM method. The SiO₂ particles were made for the adsorption of thorium from aqueous solutions, and characterized by particle size measurement, XRD and SEM. The adsorption of thorium process was optimized with RSM method. The correlation between four variables was modeled and studied. Under optimum conditions, the adsorption capacity of SiO₂ particles was found to be 134.4 mg/g, the correlation coefficient (R²) and the F value was obtained 0.96 and 1.98?×?10^?6, respectively. In addition, the adsorption isotherms were examined.     

Electrochemical sensing of <Emphasis Type="SmallCaps">D</Emphasis>-penicillamine on modified glassy carbon electrode by using a nanocomposite of gold nanoparticles and reduced graphene oxide

A new electrochemical sensor was developed for determination of D-penicillamine using glassy carbon electrode which had been modified by gold nanoparticles–reduced graphene oxide nanocomposite (AuNPs/RGO/GCE) in aqueous solution. Cyclic voltammetry, transmission electron microscopy and electrochemical impedance spectroscopy were used for characterization of the modified electrode. The results indicated that the kinetic of oxidation reaction of D-penicillamine at the surface of the electrode was controlled by both diffusion and adsorption processes. In 0.1 mol L^?1 phosphate buffer (pH 2.0), the oxidation current increased linearly with concentration of D-penicillamine with a linear range of 5.0 × 10^?6 to 1.1 × 10^?4 mol L^?1 and regression coefficient of R ² = 0.9972. Theoretical detection limit, defined based on 3σ of the blank signal (n = 9) divided by the slope of the linear regression equation, was 3.9 × 10^?6 mol L^?1 D-penicillamine using differential pulse voltammetry. The developed method was successfully applied to the determination of D-penicillamine in pharmaceutical formulation and blood serum samples.