Biosorption of Pb(II) ions from aqueous solution by pine bark (Pinus brutia Ten.)

The biosorption potential of pine (Pinus brutia Ten.) bark in a batch system for the removal of Pb(II) ions from aqueous solutions was investigated. The biosorption characteristics of Pb(II) ions on the pine bark was investigated with respect to well-established effective parameters including the effects of solution pH, initial Pb(II) concentration, mass of bark, temperature, and interfering ions present, reusability, and desorption. Initial solution pH and contact time were optimized to 4.0 and 4 h, respectively. The Langmuir and Freundlich equilibrium adsorption models were studied and observed to fit well. The maximum adsorption capacity of the bark for Pb(II) was found to be 76.8 mg g⁻¹ by Langmuir isotherms (mass of bark: 1.0 g L⁻¹). The kinetic data fitted the pseudo-second-order model with correlation coefficient greater than 0.99. The thermodynamic parameters Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were also calculated, and the values indicated that the biosorption process was spontaneous. Reutilization of the biosorbent was feasible with a 90.7% desorption efficiency using 0.5 M HCl. It was concluded that pine bark can be used as an effective, low cost, and environmentally friendly biosorbent for the removal of Pb(II) ions from aqueous solution.     

Kinetic and isothermal studies of lead ion adsorption onto bentonite

The use of bentonite for the removal of Pb(II) from aqueous solutions for different contact times, pH of suspension, and initial concentration of Pb and particle sizes of absorbent was investigated. Batch adsorption kinetic experiments revealed that the adsorption of Pb(II) onto bentonite involved fast and slow processes. The adsorption mechanisms in the lead/bentonite system followed pseudo-second-order kinetics with a significant contribution of film diffusion. The adsorption isotherms were described by means of the Langmuir and Freundlich isotherms and the Langmuir model represented the adsorption process better than the Freundlich model. The maximum adsorption capacity of Pb(II) onto natural bentonite was 78.82 mg g^− 1.     

Enhanced fluoride removal from drinking water by magnesia-amended activated alumina granules

This paper describes the fluoride removal potential of a novel sorbent, magnesia-amended activated alumina (MAAA) from drinking water. MAAA, prepared by calcining magnesium hydroxide impregnated alumina at 450 °C has shown high fluoride sorption potential than activated alumina from drinking water. Batch sorption studies were performed as a function of contact time, pH, initial fluoride concentration, and adsorbent dose. Studies were also performed to understand the effect of various other co-existing ions present in real ground water samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDAX) and a gas adsorption porosimetry analyses were used to characterize the physicochemical properties of MAAA. More than 95% removal of fluoride (10 mg l⁻¹) was achieved within 3 h of contact time at neutral pH. Sorption of fluoride onto MAAA was found to be pH dependant and a decrease in sorption was observed at higher pHs. Among the kinetic models tested, pseudo-second-order model fitted the kinetic data well, suggesting the chemisorption mechanism. Among the various isotherm model tested, Sips model predicted the data well. The maximum sorption capacity of fluoride deduced from Sips equation was 10.12 mg g⁻¹. Most of the co-existing ions studied have negligible effect on fluoride sorption by MAAA. However, higher concentrations of bicarbonate and sulfate have reduced the fluoride sorption capacity.     

Adsorption kinetics of 3-hydroxybenzaldehyde on native and activated bentonite

In this study, the adsorption kinetics of 3-hydroxybenzaldehyde dissolved in ethanol on native and activated (acid/heat activation) bentonites were examined. The specific surface areas, pore size and pore-size distributions of the samples were fully characterized. The cation exchange capacities (CEC) of the native and activated bentonites were found as 65 and 97 meq/100 g, respectively. The adsorption efficiency of 3-hydroxybenzaldehyde onto the native and activated bentonites was increased with increasing initial bentonite amount and temperature. Also, it was found that the adsorption efficiency with activated bentonite was greater than native bentonite. The kinetics of adsorption of 3-hydroxybenzaldehyde was discussed using three kinetic models, the pseudo-first-order, the pseudo-second-order and the intra-particle diffusion model. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intra-particle diffusion model up to 20 min. The rate constants of pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics and the amount of the solute sorbed at equilibrium were determined. The initial sorption rate and the activation energy were also calculated. The activation energy of the sorption was calculated using the pseudo-second-order rate constant, and it was found to be 53.36 kJ mol^− 1 and 14.03 kJ mol^− 1 for native and activated bentonites, respectively.     

Investigations on the kinetics and mechanisms of sorptive removal of fluoride from water using alumina cement granules

This paper examines the kinetics of fluoride removal from water by the adsorbent alumina cement granules (ALC), exploring the mechanisms involved. ALC exhibited a biphasic kinetic profile of sorption with an initial rapid uptake phase followed by a slow and gradual phase. The kinetic profile has been modeled using pseudo-first-order model, pseudo-second-order model, intraparticle diffusion model and Elovich model. The kinetic sorption profiles offered excellent fit with pseudo-second-order model with a high R² value of 0.9987. The value of activation energy of the system (17.67 kJ mol⁻¹) indicates the significance of diffusion in the sorption process. The rate-limiting step of sorption was evaluated by analyzing the response of the system to pH, inert electrolyte concentration, and desorption pattern of the adsorbent, instead of assigning it to a single kinetic model. Accordingly, the surface reactions involving the heterogeneity of the surface site bonding energy or other reactions occurring on the surface of ALC were found predominant in defining the rate-limiting step. The dominant mechanism of fluoride removal appeared to be a chemisorptive ligand exchange reaction involving the formation of inner-sphere complexation of fluoride with ALC.     

Preparation and characterization of aluminum pillared K10 and KSF for adsorption of trimethoprim

Montmorillonite KSF and K10 were used as precursor materials for synthesis of aluminum pillared K10 and KSF (Al-K10 and Al-KSF) which characterized by TGA, XRD, SEM and FT-IR spectroscopic analysis. The sorption of trimethoprim (TMP) which is commonly employed as an antibiotic onto Al-K10 and Al-KSF was also investigated as a function of adsorbent dosage, solution pH, contact time and temperature. The adsorption kinetics was interpreted using pseudo-first-order, pseudo-second-order kinetic models and intraparticle diffusion model. The pseudo-second-order model provided the best correlation. Adsorption isotherm parameters were obtained from Freundlich, Langmuir and Dubinin–Radushkevich (DR) isotherm models. Adsorption of TMP onto Al-K10 and Al-KSF was physical in nature and ion-exchange mechanism for DR equation, respectively. Al-K10 exhibits higher removal capacity at lower adsorbent dosages in comparison with Al-KSF. The removal capacity was increased by increasing pH. ΔH⁰, ΔS⁰ and ΔG⁰ showed that adsorption of trimethoprim was endothermic, increasing randomness and not spontaneous in nature.     

A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

In situ STM studies of Ga electrodeposition from GaCl3 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide

In the present paper the electrodeposition of Ga on Au(1 1 1) from 0.5 mol L⁻¹ GaCl₃ in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, has been investigated by in situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The CV shows two redox processes: the one at −0.3 V vs. Pt is attributed to a Ga deposition on a Ga layer formed during an electroless deposition process at OCP and/or to the formation of a Au–Ga alloy; the other one at −0.9 V is due to the bulk deposition of Ga. The XPS measurement reveals that there is an oxide layer on the top of the gallium electrodeposit due to exposure to air. In situ STM measurements show that the first layer of the Ga deposit consists of islands of 10–30 nm in width and several nanometers in height surprisingly the result of an electroless deposition at the OCP. If the electrode potential is further reduced the bulk deposition of Ga sets in.     

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.     

Recovery of entomotoxicity components from Bacillus thuringiensis fermented wastewater and sludge: Ultrafiltration scale-up approach

This study reports results on the possibility of scale-up of ultrafiltration system for recovery of entomotoxicity components from Bacillus thuringiensis fermented wastewater/wastewater sludge broths. The wastewater/wastewater sludge comprised starch industry wastewater and hydrolyzed sludge. The study demonstrated that the optimal operational parameters, namely transmembrane pressure and feed flux for starch industry wastewater were 90 kPa and 550 L h⁻¹ m⁻², respectively. Likewise, the respective values for hydrolyzed sludge were 110 kPa and 720 L h⁻¹ m⁻². The loss in biological activity reported in terms of viable spores and soluble proteins was higher for hydrolyzed sludge due to higher viscosity and lower particle size. In the context of scale-up, dynamic resistance can serve as a key parameter which was reported to be higher for hydrolyzed sludge when compared to starch industry wastewater. Thus, starch industry wastewater will impose relatively less power input requirements and can be easily scaled-up.     

Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3−xTixO4 (0 ≤ x ≤ 0.78) at neutral pH values

In this work, a series of Fe_3−xTi_xO₄ (0 ≤ x ≤ 0.78) was synthesized using a new soft chemical method. The synthetic Fe_3−xTi_xO₄ were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, thermogravimetric and differential scanning calorimetry (TG–DSC) analyses. The results showed that they were spinel structures and Ti was introduced into their structures.Then, decolorization of methylene blue (MB) by Fe_3−xTi_xO₄ in the presence of H₂O₂ at neutral pH values was studied using UV–vis spectra, dissolved organic carbon (DOC) and element C analyses. Furthermore, the degradation products remained in reaction solution after the decolorization were identified using ionic chromatography (IC), ¹³C nuclear magnetic resonance spectra (NMR), liquid chromatography and mass spectrometry (LC–MS). Although small amounts of MB were mineralized, the aromatic rings in MB were destroyed completely after the decolorization. Decolorization of MB by Fe_3−xTi_xO₄ in the presence of H₂O₂ was promoted remarkably with the increase of Ti content in Fe_3−xTi_xO₄ due to the enhancement of both adsorption and degradation of MB on Fe_3−xTi_xO₄.     

Pt recovery using Cyphos IL-101 immobilized in biopolymer capsules

Cyphos^® IL-101, a tetraalkylphosphonium chloride salt (ionic liquid, IL) has been immobilized in capsules prepared by ionotropic gelation in calcium chloride solutions. The IL content was varied in the resin between 0.29 and 1.28 mmol IL g⁻¹. These resins have been tested for Pt recovery from HCl solutions. The equilibrium was very slightly affected by the concentration of HCl and chloride ions. The sorption isotherms were modeled using the Langmuir equation: the maximum sorption capacity was influenced by the drying of the resin but remained close to 177 mg Pt g⁻¹ for wet resin (i.e. 0.9 mmol Pt g⁻¹, dry weight basis, or 0.7 mol Pt mol⁻¹ Cyphos) and 142 mg Pt g⁻¹ for dry resin (i.e. 0.73 mmol Pt g⁻¹, or 0.57 mol Pt mol⁻¹ Cyphos). The presence of nitrates, nickel or copper ions (added under the form of chloride salts) did not significantly decrease sorption capacity even at concentrations as high as 5 g L⁻¹. Conversely, zinc at the concentration of 5 g L⁻¹, significantly decreased Pt sorption, probably due to the competition effect of chloro-anionic Zn species. This is another evidence of the ion exchange mechanism involved in the binding of hexachloroplatinate species. The kinetics are weakly affected by the agitation speed (in the range 150–350 rpm) indicating that the resistance to film diffusion is not the limiting step. The kinetics are affected by the IL content, metal concentration and more specifically the drying of the resin: intraparticle diffusion sounds to be the controlling kinetic step: the intraparticle diffusion coefficient varied between 2 × 10⁻¹² and 18 × 10⁻¹¹ m² min⁻¹, depending on experimental conditions. Platinum can be desorbed from loaded resin using either nitric acid (5 M) or thiourea (0.1 M in 0.1 M HCl acid solution). The resin was efficiently used for three sorption/desorption cycles using nitric acid: a decrease in sorption capacity and desorption efficiency was observed beginning with the third cycle, probably due to a progressive degradation of the resin.     

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.     

Kinetics and irreversibility of cesium and uranium sorption onto bentonite colloids in a deep granitic environment

Sorption of radionuclides onto a stable colloidal phase may significantly enhance their transport in groundwater. A key point, to be analysed to assess the relevance of colloids in the safety of a deep geological radioactive waste repository, is the irreversibility of the colloid/radionuclide bond.In this work, sorption and desorption kinetics of cesium and uranium(VI) onto bentonite colloids in a granitic reduced environment was studied by means of batch experiments, carried out in anoxic conditions under N₂ atmosphere. Sorption kinetics was followed during 18 weeks, and sorption isotherms were also carried out to get additional information on sorption mechanisms. The water used in all the experiments was an alkaline, low ionic strength (pH=9.5 and I=1×10⁻³M) granitic groundwater from the NAGRA's Grimsel Test Site (GTS), Switzerland, which also presents reduced Eh (−200 mV). In this water, bentonite colloids were shown to be stable during several months.Both cesium and uranium presented a nonlinear sorption behaviour in the range of concentration investigated. In kinetic experiments, the measured log Kd for Cs ([Cs]=1×10⁻⁷ M) was 3.94±0.15, and this value did not show significant variations with time. However, the adsorption of cesium on bentonite colloids involves two reactions, a rapid exchange on planar sites (hours) and a slower component (days) in which cesium diffuses to less available but highly selective sites. This slow process, that can be evidenced only when very low tracer concentrations are used (<1×10⁻⁹ M), is most probably responsible for the fixation of a fraction of the sorbed cesium, and for the partial sorption irreversibility shown in desorption tests. Kd values measured after several desorption experiments increased significantly with the age of the sorption complex. For example, for the sample with 1-day contact time, the second desorption Kd was 8600 ml/g whereas the 5 and 8 weeks contact time samples showed second desorption Kd 15 000 and 30 000 ml/g, respectively.The measured log Kd for U ([U(VI)]=4×10⁻⁷ M) varied from 2.91 to 3.21 (±0.15) during 18 weeks of the kinetic experiment. The main variation of Kd values took place in the first 4 weeks, and then a very slow increasing trend was observed, which could be probably attributed to a partial reduction of U(VI) to U(IV).In desorption tests with uranium, desorption K_ds were independent on the initial contact time. Nevertheless, a certain sorption/desorption hysteresis was observed, which is most probably due to the contribution of surface complexation reactions, at the edge sites of clay colloids, to uranium sorption. Hence, U sorption is not completely reversible.     

Study of IrxRu1−xO2 oxides as anodic electrocatalysts for solid polymer electrolyte water electrolysis

Electrocatalysts of the general formula Ir_xRu_1−xO₂ were prepared using Adams’ fusion method. The crystallite characterization was examined via XRD, and the electrochemical properties were examined via cyclic voltammetry (CV) in, linear sweep voltammetry (LSV) and chronopotentiometry measurements in 0.5 M H₂SO₄. The electrocatalysts were applied to a membrane electrode assembly (MEA) and studied in situ in an electrolysis cell through electrochemical impedance spectroscopy (EIS) and stationary current density–potential relations were investigated. The Ir_xRu_1−xO₂ (x = 0.2, 0.4, 0.6) compounds were found to be more active than pure IrO₂ and more stable than pure RuO₂. The most active electrocatalyst obtained had a composition of Ir_0.2Ru_0.8O₂. With an Ir_0.2Ru_0.8O₂ anode, a 28.4% Pt/C cathode and the total noble metal loading of 1.7 mg cm⁻², the potential of water electrolysis was 1.622 V at 1 A cm⁻² and 80 °C.     

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.     

Supercritical CO2 extraction of glycosides from Stevia rebaudiana leaves: Identification and optimization

The aim of this work was to optimize the glycoside composition of Stevia rebaudiana leaves using supercritical fluid extraction (SFE). A Box-Behnken statistical design was used to evaluate the effect of various values of pressure (150–350 bar), temperature (40–80 °C) and concentration of ethanol-water mixture (70:30) as co-solvent (0–20%) by CO₂ flow rate of 15 g min⁻¹ for 60 min. The most effective variables were co-solvent concentration (P < 0.005) and temperature (P ≤ 0.005). Evaluative criteria for both dependent variables (stevioside and rebaudioside A yields) in the model was assigned maximum. Optimum extraction conditions were elicited as 211 bar, 80 °C and 17.4% which yielded 36.66 mg/g stevioside and 17.79 mg/g rebaudioside A. Total glycosides composition were close to those obtained using conventional water extraction (64.49 mg/g) and a little higher than ethanol extraction (48.60 mg/g) demonstrating challenges for industrial scale application of SFE.     

Kinetics and isotherm studies for the adsorption of boron from water using titanium dioxide

Boron is a necessary element for plants that are generally found in the ground and seawater, but it can also be poisonous in large doses. Contamination of water with boric acid or borate ions is a global concern. Due to the absence of the chemical charge that boron possesses, its removal is often difficult. To investigate boron's adsorption characteristics, kinetic, isotherm, and isothermal studies were performed. The adsorption of boron was shown to be a pH-dependent mechanism, with the best results at around pH 9.0. About 47% of the boron from a solution of 50 mg L⁻¹ was removed using 5 g titanium dioxide in 30 min. It was also demonstrated that boron adsorption kinetics increased with temperature, which is best described by the pseudo-second-order kinetic model (R² > 0.98) and also fits well with Elovich and pseudo-first-order models (R² > 0.94) at pH 9.0. Equilibrium was reached in about 40 min for all the samples. The film boundary layer diffusion step limits the rate. Experimental results correspond well to the Freundlich isotherm (R² = 0.95–0.99). Langmuir and Temkin's isotherms also fitted reasonably well (R² = 0.94–0.98). The Freundlich and Langmuir constants indicate favourable adsorption. The Gibbs free energy (ΔG) values increased negatively (from −11.47 to −15.63 kJ mol⁻¹) with increasing temperature, signifying a feasible and spontaneous process. The enthalpy change (ΔH) value of about 30.35 kJ mol⁻¹ indicated endothermic physical adsorption. The results indicate that titanium dioxide is an excellent and safe adsorbent for the removal of boron from water.     

Amidoximation of Cyano Group for Chelating Ion Exchange of Some Heavy Metal Ions from Wastewater

Ion exchange behavior of some heavy metal ions, Pb²⁺, Ni²⁺, and Cd²⁺, onto amidoximated polyacrylonitrile based Ce(IV) phosphate was investigated. Polyacrylonitrile based Ce(IV) phosphate was prepared and followed by functionalization of the cyano group to amidoxime group with hydroxylamine. The amidoximated resin was characterized using FT-IR and SEM. Removal of Pb²⁺, Ni²⁺, and Cd²⁺ ions from aqueous solution was examined by studying some factors using the batch technique such as effect of pH, contact time, initial metal ion concentration, and temperature. Some kinetic and isotherm models had been applied. The calculated amount of the sorbed values in case of the pseudo-second-order model are closer to the experimental data than that of the pseudo-first-order model, and with a correlation coefficients R² > 0.99. Therefore, the sorption of the three metal ions can be approximated more favorably by the pseudo-second-order model. The sorption process obeys the Freundlich isotherm model. The sorption has an endothermic nature which is indicated by the positive value of the enthalpy change, ΔH, the high positive values of the entropy change, and ΔS show the increased randomness at the solid/solution interface. The obtained negative values of free energy change, ΔG, indicate the feasibility and the spontaneous nature of the sorption process.