Biosorption of mercury(II) ions from aqueous solution by garlic (<Emphasis Type="Italic">Allium sativum</Emphasis> L.) powder

A biosorbent was prepared by drying garlic (Allium sativum L.) under vacuum and tested in its powder form for its mercury adsorption capability in aqueous solution. Results show that garlic powder has a good adsorption capacity for mercury and that the mercury concentration of the solution has a significant impact on the adsorption capacity of the biosorbent. The Langmuir and Freundlich adsorption isotherms were also constructed. The adsorption capacity, q _max , adsorption efficiency, b, and correclation confficient, r² for the Langmuir model were 0.6497, 0.4903, and 0.9980, respectively. For the Freundlich model, the model parameters, K _F , 1/n, and r² for mercury were 4.1879, 0.3467, and 0.9518, respectively. Langmuir adsorption isotherm was better suited for the adsorption of mercury onto garlic powder, and that the maximum amount of mercury adsorbed (q _max ) was 0.6497 mg/g.     

Equilibrium Modeling of Ternary Adsorption of Phenols onto Modified Activated Carbon

The prediction of adsorption equilibria in multicomponent systems is of prime importance. Therefore, the equilibrium adsorption data for the following multicomponent systems have been studied. The present paper deals with the simultaneous removal phenol (P), 4-chlorophenol (CP), 4-nitrophenol (NP) and catechol (C), resorcinol (R), hydroquinone (HQ) onto modified activated carbon (MAC) from ternary mixtures. The BET surface area of SC was found to be 934 m²/g, whereas BJH adsorption/desorption surface area of pores is 53.03/58.15 m²/g. The equilibrium adsorption data were obtained at different initial concentrations (C₀ = 50–1000 mg/L), 12 h contact time, 30°C temperature, MAC dosage of 10 mg/L at solution pH. Equilibrium isotherms for the ternary adsorption of P–CP–NP and C–R–HQ onto MAC have been analyzed by using non-modified Langmuir, modified Langmuir, extended Langmuir, extended Freundlich and Sheindorf–Rebuhn–Sheintuch (SRS) models. The competitive Sheindorf–Rebuhn–Sheintuch (SRS) model fits for both ternary adsorption equilibrium data satisfactorily and adequately.     

Adsorption characteristics of sericite for cesium ions from an aqueous solution

To efficiently remove cesium ions from aqueous solution, sericite was used as a novel adsorbent. The silanol (SiO₂) and aluminol (Al₂O₃) groups in sericite are likely to play an important role in adsorption process. The maximum adsorption capacity (q_m) and adsorption constant (K_L) for cesium ions obtained from the Langmuir isotherm model were 6.68 mg/g and 0.227 L/mg, respectively and regression curve fit well with the experimental data as the 0.965 of correlation coefficients (r²). However, when the Freundlich isotherm model was used correlation coefficient (r²) was 0.973. Therefore, it was concluded that Freundlich model fits equilibrium data better than Langmuir model. When the 6.0 g/L of sericie concentration was added to aqueous solution, cesium ions were removed by about 80% and the increase was not happened above 6.0 g/L of sericite concentration any more. The process was determined as exothermic reaction because the removal efficiency of cesium ions decreased as temperature increased. Furthermore, all adsorption was completed in 120 min and comparing the pseudo first and second-order kinetic models indicates that the adsorption of cesium ions using sericite follows well the pseudo-second-order kinetics.     

A new model for water adsorption in porous ceramics

This research proposes a new isotherm model that is derived for adsorption of clustering and condensable vapors on mesoporous ceramics. The adsorption characteristics of water vapor on both experimental data and isotherm model were investigated over the relative pressure ranging from 0 to 0.95. The applicability of the model was evaluated by significance of fitting parameters. For each adsorption isotherm there are five parameters (m, q _f , K _f , q _m and K _m ). The comparison of modeling fit with experimental data was used as the methodology for selecting the most informative and the best-fitting model. The experimental testing results showed that this model is able to describe all possible behaviors of the water adsorption isotherm displaying type IV classification. The model is based on the forming and growth of the water molecule clusters and capillary condensation mechanism in mesopore. The findings suggest a significant tool for understanding the behavior of water adsorption in humidity-control porous ceramics.     

Adsorption kinetics and mechanism of acid dye onto montmorillonite from aqueous solutions: Stopped-flow measurements

The adsorption of acid dye, namely, acid fuchsin (AF), onto sodium montmorillonite (Na⁺-Mt) from aqueous solutions was investigated. The adsorption process was very fast and attained equilibrium within 1 h, which was an economically favorable requisite. The Freundlich and Langmuir adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were calculated. The experimental data fit well with Freundlich model rather than the Langmuir model. The equilibrium adsorption constant, K_c, was determined and used to calculate the enthalpy and entropy of the adsorption process. The adsorption kinetics was followed up using a stopped-flow spectrophotometer under pseudo-first-order conditions. The influence of initial dye concentrations, amount of sodium montmorillonite, and temperature on the rate of adsorption were studied. The activation energy of adsorption was calculated and indicated a chemical adsorption process. The enthalpy of adsorption confirmed an exothermic process. A proper mechanism for adsorption supported by X-ray and atomic absorption data was proposed.     

Preparation of a Cu(II)-PVA/PA6 Composite Nanofibrous Membrane for Enzyme Immobilization

PVA/PA6 composite nanofibers were formed by electrospinning. Cu(II)-PVA/PA6 metal chelated nanofibers, prepared by the reaction between PVA/PA6 composite nanofibers and Cu²⁺ solution, were used as the support for catalase immobilization. The result of the experiments showed that PVA/PA6 composite nanofibers had an excellent chelation capacity for Cu²⁺ ions, and the structures of nanofibers were stable during the reaction with Cu²⁺ solution. The adsorption of Cu(II) onto PVA/PA6 composite nanofibers was studied by the Langmuir isothermal adsorption model. The maximum amount of coordinated Cu(II) (q_m) was 3.731 mmol/g (dry fiber), and the binding constant (K_l) was 0.0593 L/mmol. Kinetic parameters were analyzed for both immobilized and free catalases. The value of V_max (3774 μmol/mg·min) for the immobilized catalases was smaller than that of the free catalases (4878 μmol/mg·min), while the K_m for the immobilized catalases was larger. The immobilized catalases showed better resistance to pH and temperature than that of free form, and the storage stabilities, reusability of immobilized catalases were significantly improved. The half-lives of free and immobilized catalases were 8 days and 24 days, respectively.     

Batch adsorption of trichlorotrifluoroethane (freon-113) onto activated carbon — surface diffusivity and pore diffusivity

Activated carbon was found more active than molécular sieve 13X and silica gel in adsorbing 1,1,2 trichloro-1,2,2 trifluoroethane (CFE). Batch adsorption experiments were carried out with activated carbon to adsorb CFE at 15, 25 and 30°C. The adsorption isotherms of CFE on activated carbon were of the Langmuir type: q(C) = q_m KC / (1 + KC) where q^m and K were evaluated for the three temperatures. The measured bulk concentration-time data were interpreted equally well with the surface diffusion model and the pore diffusion model; for the former model the surface diffusivity increased with increasing initial CFE concentration, and for the latter the pore diffusivity was independent upon the initial CFE concentration.     

Acid Black 172 dye adsorption from aqueous solution by hydroxyapatite as low-cost adsorbent

The Acid Black 172 dye adsorption on the uncalcined hydroxyapatite nanopowder was investigated. The hydroxyapatite prepared by wet coprecipitation method has high specific surface area of 325 m²/g and crystal sizes smaller than 70 nm. The batch adsorption experiments revealed that under the optimum adsorption conditions (pH 3, hydroxyapatite dosage 2 g/L, initial dye concentration 400 mg/L and temperature 20 °C) the dye removal efficiency was 95.78% after 1 h of adsorption. The adsorption kinetics was best described by the pseudo-second order kinetic model. The intraparticle diffusion model shows that intraparticle diffusion is not the sole rate-limiting step; the mass transfer also influences the adsorption process in its initial period. The Langmuir isotherm model best represented the equilibrium experimental data, and the maximum adsorption capacity (q _m ) was 312.5 mg/g.     

Contact time optimization of two-stage batch adsorber systems using the modified film-pore diffusion model

In this paper, a contact time optimization methodology of a two-stage batch adsorber system taking minimum contact time as the objective function has been developed. The initial concentration of the second stage unit and adsorbent weight have been designated as variables and these have been studied under two conditions of the equilibrium solid-phase concentration, q_e, namely, when q_e is a variable and when q_e is a constant. Contact time optimization of a two-stage batch adsorber system has been demonstrated at three different conditions/cases for the adsorption of phenol on activated carbon and the adsorption of Astrazone Blue dye (Basic Blue 69) onto silica. A new concept of “pinch point” for the optimum design of batch adsorber system has been proposed. The optimization solutions show that there is a significant difference for minimum contact time at different process conditions.The diffusion mass transport model used to predict the concentration-time decay curve is a film-pore diffusion model. An analytical solution has been used for simplicity which assumes a constant capacity pseudo-irreversible isotherm.     

Adsorption ability of oxidized multiwalled carbon nanotubes towards aqueous Ce(III) and Sm(III)

The aim of the present work was to investigate the adsorption of Ce(III) and Sm(III) onto multiwalled carbon nanotubes (MWCNTs) oxidized with concentrate nitric acid. The effects of solution pH, adsorbent dosage, and contact time were studied by batch technique. Langmuir, Freundlich and D-R isotherms were used to describe the adsorption behavior of Ce(III) and Sm(III) by oxidized MWCNTs, and the experimental results fitted Freundlich model well. The maximum uptake capacities (q _m ) calculated by applying the Langmuir equation for samarium and cerium ions were found to be 89.28 and 92.59 (mg/g), respectively. A comparison of the kinetic models and the overall experimental data was best fitted by the pseudo second-order kinetic model. The calculated thermodynamic parameters (ΔG^o, ΔH^o, and ΔS^o) showed that the adsorption for Ce(III) and Sm(III) is feasible, spontaneous and exothermic at 30–60 °C. Moreover, more than 70% of Ce(III) and Sm(III) adsorbed onto Oxidized MWCNTs could be desorbed with HNO₃.     

Production and characterization of activated carbon derived from brewer’s yeast

Activated carbon (AC) was produced from brewer’s yeast with K₂CO₃ activation. The effects of K₂CO₃/yeast ratio and activation temperature on the yield and adsorption properties of the AC were investigated. The results indicate that the optimum conditions were as follows: ratio of K₂CO₃/yeast=2 and activation temperature 800 °C. The AC produced under the optimum conditions has BET surface area of 1,603 m²/g, pore volume of 1.43 cm²/g and average pore diameter of 3.5 nm. Adsorption of phenol onto the AC was determined by batch test at solution pH of 7. The effects of contact time and initial phenol concentration were investigated. The adsorption process was found to follow pseudo-second-order kinetics. The rate of phenol adsorption onto the AC produced was rapid with the adsorption equilibrium reached within 5 min. The experimental data fitted well with the Langmuir isotherm model. The maximum phenol uptake by the AC was estimated to be 513.5 mg/g.     

Adsorption behavior of methylene blue onto titanate nanotubes

Calcined titanate nanotubes were synthesized with hydrothermal treatment of the commercial TiO₂ (Degussa P25) followed by calcination. The morphology and structures of as-prepared samples were investigated by transmission electron microscopy, X-ray diffraction and N₂ adsorption/desorption. The samples exhibited a tubular structure and a high surface area of 157.9 m²/g. The adsorption of methylene blue onto calcined titanate nanotubes was studied. The adsorption kinetics was evaluated by the pseudo-first-order, pseudo-second-order and Weber's intraparticle diffusion model. The pseudo-second-order model was the best to describe the adsorption kinetics, and intraparticle diffusion was not the rate-limiting step. The equilibrium adsorption data were analyzed with three isotherm models (Langmuir model, Freundlich model and Temkin model). The best agreement was achieved by the Langmuir isotherm with correlation coefficient of 0.993, corresponding to maximum adsorption capacity of 133.33 mg/g. The adsorption mechanism was primarily attributed to chemical sorption involving the formation of methylene blue-calcined titanate nanotubes nanocomposite, associated with electrostatic attraction in the initial bulk diffusion.     

Adsorption Behaviors of Platinum Group Metals in Simulated High Level Liquid Waste Using Macroporous (MOTDGA-TOA)/SiO2-P Silica-based Absorbent

As fundamental research for separation of platinum group metals (PGMs) from high level liquid waste (HLLW) by macroporous silica-based adsorbent, (MOTDGA-TOA)/SiO₂-P adsorbent was prepared by impregnation of N,N′-dimethyl-N,N′-di-n-octyl-thiodiglycolamide (MOTDGA) and Tri-n-octylamine (TOA) into silica/polymer composite support (SiO₂-P). The adsorption behavior of Ru(III), Rh(III), and Pd(II) in simulated HLLW onto the adsorbent were investigated by the batch method to obtain their corresponding equilibrium and kinetic data. The adsorbent showed strong adsorption for Pd(II) and the adsorption reached equilibrium within 2 hr. High distribution coefficient (K _d) values for Pd(II) were obtained in 0.1–1 M HNO₃ concentration. In addition, the use of both MOTDGA and TOA improved adsorption of Ru(III) and Rh(III) better than individual use of them. Especially, the K _d value for Ru(III) towards (MOTDGA-TOA)/SiO₂-P adsorbent was three times larger than that in the adsorption using only with MOTDGA or TOA as extractant. The adsorptions of Ru(III), Rh(III), and Pd(II) followed the Langmuir adsorption model, and were found to be controlled by the chemisorption mechanism.     

Study on adsorption characteristic of macroporous resin to phenol in wastewater

The removal of phenol from solution was investigated using macroporous resin. The effects of initial concentration, pH, and temperature on phenol removal were studied. The experimental results indicated that the adsorption capacity reached equilibrium state within 20 min and adsorption followed pseudo‐second‐order kinetic model. Langmuir isotherm model could be better to describe the isothermal adsorption of phenol, the maximum adsorption capacity (Q_m) and Langmuir constant (K_L) were 103.64 mg/g and 0.2719. Macroporous resin after reached to saturation has a high desorption percentage, indicating that H‐103 is an excellent reusing adsorption material. It provided theoretical references for practical application in phenolic wastewater treatment.     

Sorption/release of diclofenac sodium in/from free‐standing poly(acrylic acid)/poly(ethyleneimine) multilayer films

Polyelectrolyte multilayer films deposited onto various substrates have been used extensively as drug delivery systems. However, little attention has been paid to the release of drugs from free‐standing polymeric films. Herein, we report the construction of thermal crosslinked free‐standing poly(acrylic acid) (PAA)/branched poly(ethyleneimine) (PEI) multilayer films composed of 25 double layers [(PAA/PEI)₂₅] and their use in sorption/release of diclofenac sodium (DS). The (PAA/PEI)₂₅ multilayer films were characterized by scanning electron microscopy, potentiometric titrations and Fourier transform infrared spectroscopy, while the sorption/release of DS was monitored by UV – Vis spectroscopy. The DS sorption equilibrium data were fitted with five isotherm models (Langmuir, Freundlich, Sips, Dubinin–Radushkevich, and Temkin). The maximum equilibrium sorption capacity, q_m, given by the Langmuir model was 32.42 mg DS/g. The Korsmeyer–Peppas semiempirical equation showed that the release of DS from the free‐standing (PAA/PEI)₂₅ films proceeded by pseudo‐Fickian diffusion, irrespective of the releasing media. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43752.     

Kinetic and equilibrium studies of Pb(II) and Cd(II) removal from aqueous solution onto colemanite ore waste

The adsorption characteristics of Pb(II) and Cd(II) onto colemanite ore waste (CW) from aqueous solution were investigated as a function of pH, adsorbent dosage, contact time, and temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were applied to describe the adsorption isotherms. Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The adsorption capacity of CW was found to be 33.6 mg/g and 29.7 mg/g for Pb(II) and Cd(II) ions, respectively. Analyte ions were desorbed from CW using both 1 M HCl and 1 M HNO₃. The recovery for both metal ions was found to be higher than 95%. The mean adsorption energies evaluated using the D-R model indicated that the adsorption of Pb(II) and Cd(II) onto CW were taken place by chemisorption. The thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) showed that the adsorption of both metal ions was feasible, spontaneous and exothermic at 20-50 °C. Adsorption mechanisms were also investigated using the pseudo-first-order and pseudo-second-order kinetic models. The kinetic results showed that the adsorption of Pb(II) and Cd(II) onto CW followed well pseudo-second order kinetics.     

Random forest model for removal of bromophenol blue using activated carbon obtained from Astragalus bisulcatus tree

In this research, activated carbon (AC) simply was prepared from a local, abundant tree in south of Iran. The AC with low cost and toxicity is a good candidate for bromophenol blue (BPB) removal from aqueous media. The AC with nano scale pore diameter is applicable for this dye removal following optimization of the influence of various parameters including contact time, pH, initial dye concentration and amount of adsorbent. Subsequently, experimental data was analyzed by four kinetic models including pseudo first and second-order, Elovich and the intraparticle diffusion equations and subsequently their respective parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients was investigated and based on well known criterion their applicability was judged. The result shows that adsorption of BPB onto proposed adsorbent at all conditions such as versatile adsorbent dosages and initial BPB concentrations sufficiently described by the combination of the pseudo second-order equation and interparticle diffusion model. It was found that equilibrium rate of the BPB adsorption at various adsorbent dosage well fitted by Langmuir. Investigation of experimental result by two approaches (multiple linear regressions (MLR) and random forest (RF)) models show that RF is a powerful tool for prediction of BPB adsorption by activated carbon obtained from Astragalus bisulcatus tree. The optimal tuning parameters for RF model are obtained based on the n_tree = 100, m_try = 2. For the training data set, the MSE values of 0.0006 and the coefficient of determination (R²) values of 0.9895 for RF model and the MSE value of 0.0104 and the R² value of 0.823 for MLR model are obtained.     

Use of a selective extractant-impregnated resin for removal of Pb(II) ion from waters and wastewaters: Kinetics,equilibrium and thermodynamic study

Adsorption of Pb(II) ion by a novel extractant-impregnated resin, EIR, was studied as a function of various experimental parameters using batch adsorption experiments. The new EIR was prepared by impregnating gallocyanine (GCN) onto Amberlite XAD-16 resin beads. The EIR was characterized by nitrogen analysis and SEM micrographs. The new EIR showed excellent selectivity factor values (α) for Pb(II) adsorption respect to other metal ions. The effects of some chemical and physical variables were evaluated and the optimum conditions were found for Pb(II) removal from aqueous solutions. The equilibrium adsorption isotherm was fitted with the Langmuir adsorption model. The maximum adsorption capacity (q_max) of EIR for Pb(II) ions was found to be 367.92 mg g⁻¹. The kinetic studies showed that the intra-particle diffusion is the rate-controlling step. Also, the intra-particle diffusion coefficients, D_ip values, were of the order of 10⁻¹² m² s⁻¹. The values of enthalpy (ΔH°) were positive, which confirms the endothermic nature of adsorption process. Also, the positive entropy changes (ΔS°) were showed that the randomness increased along with the adsorption process. In addition, the obtained negative values of Gibbs free energy (ΔG°) indicated feasible and spontaneous nature of the adsorption process at different temperatures. The new adsorbent was very stable so that it can be successfully used for many consecutive cycles without significant loss in its adsorption capacity.