The study of adsorption characteristics Cu and Pb ions onto PHEMA and P(MMA-HEMA) surfaces from aqueous single solution

The adsorption characteristics of Cu²⁺ and Pb²⁺ ions onto poly2-hydroxyethyl methacrylate (PHEMA) and copolymer 2-hydroxyethyl methacrylate with monomer methyl methacrylate P(MMA-HEMA) adsorbent surfaces from aqueous single solution were investigated with respect to the changes in the pH of solution, adsorbent composition (changes in the weight percentage of MMA copolymerized with HEMA monomer), contact time and the temperature in the individual aqueous solutions. The linear correlation coefficients of Langmuir and Freundlich isotherms were obtained. The results revealed that the Langmuir isotherm fitted the experimental results better than the Freundlich isotherm. Using the Langmuir model equation, the monolayer adsorption capacity of PHEMA surface was found to be 0.840 and 3.037 mg/g for Cu²⁺ and Pb²⁺ ions and adsorption capacity of (PMMA-HEMA) was found to be 31.153 and 31.447 mg/g for Cu²⁺ and Pb²⁺ ions, respectively. Changes in the standard Gibbs free energy (ΔG⁰), standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) show that the adsorption of mentioned ions onto PHEMA and P(MMA-HEMA) are spontaneous and exothermic at 293–323 K.     

Removal of phenol from aqueous solutions by adsorption onto organomodified Tirebolu bentonite: Equilibrium, kinetic and thermodynamic study

A natural bentonite modified with a cationic surfactant, cetyl trimethylammonium bromide (CTAB), was used as an adsorbent for removal of phenol from aqueous solutions. The natural and modified bentonites (organobentonite) were characterized with some instrumental techniques (FTIR, XRD and SEM). Adsorption studies were performed in a batch system, and the effects of various experimental parameters such as solution pH, contact time, initial phenol concentration, organobentonite concentration, and temperature, etc. were evaluated upon the phenol adsorption onto organobentonite. Maximum phenol removal was observed at pH 9.0. Equilibrium was attained after contact of 1 h only. The adsorption isotherms were described by Langmuir and Freundlich isotherm models, and both model fitted well. The monolayer adsorption capacity of organobentonite was found to be 333 mg g⁻¹. Desorption of phenol from the loaded adsorbent was achieved by using 20% acetone solution. The kinetic studies indicated that the adsorption process was best described by the pseudo-second-order kinetics (R² > 0.99). Thermodynamic parameters including the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also calculated. These parameters indicated that adsorption of phenol onto organobentonite was feasible, spontaneous and exothermic in the temperature range of 0–40 °C.     

Application of natural and modified hectorite clays as adsorbents to removal of Cr(VI) from aqueous solution–Thermodynamic and equilibrium study

A hectorite (H) clay sample has been modified with 2-mercaptobenzimidazole (MBI) using homogeneous and heterogeneous routes. Both modification methodologies resulted in similar products, named H_HOM and H_HET, respectively. These materials were characterized by CO₂ gas adsorption, elemental analysis, nuclear magnetic nuclei of carbon-13 and silicon-29. The effect of two variables (contact time and metal concentration) has been studied using batch technique at room temperature and pH 2.0. After achieving the best conditions for Cr(VI) adsorption, isotherms of this adsorbate on using the chosen adsorbents were obtained, which were fitted to non-linear Sips isotherm model. The maximum number of moles adsorbed was determined to be 11.63, 12.85 and 14.01 mmol g⁻¹ for H, H_HOM and H_HET, respectively, reflecting the maximum adsorption order of H_HET > H_HOM > H. The energetic effects (Δ_intH°, Δ_intG° and Δ_intS°) caused by chromium ion adsorption were determined through calorimetric titrations.     

Sorption behavior of nano-TiO2 for the removal of selenium ions from aqueous solution

Titanium dioxide nanoparticles were employed for the sorption of selenium ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, and temperature. The sorption was found to be fast, and to reach equilibrium basically within 5.0 min. The sorption has been optimized with respect to the pH, maximum sorption has been achieved from solution of pH 2–6. Sorbed Se(IV) and Se(VI) were desorbed with 2.0 mL 0.1 mol L⁻¹ NaOH. The kinetics and thermodynamics of the sorption of Se(IV) onto Nano-TiO₂ have been studied. The kinetic experimental data properly correlate with the second-order kinetic model (k₂ = 0.69 g mg⁻¹ min⁻¹, 293 K). The overall rate process appears to be influenced by both boundary layer diffusion and intraparticle diffusion. The sorption data could be well interpreted by the Langmuir sorption isotherm. The mean energy of adsorption (14.46 kJ mol⁻¹) was calculated from the Dubinin–Radushkevich (D–R) adsorption isotherm at room temperature. The thermodynamic parameters for the sorption were also determined, and the ΔH⁰ and ΔG⁰ values indicate exothermic behavior.     

The removal of an anionic red dye from aqueous solutions using chitosan beads-the role of experimental factors on adsorption using a full factorial design

A factorial design was employed to evaluate the quantitative removal of an anionic red dye from aqueous solutions on epichlorohydrin-cross-linked chitosan. The experimental factors and their respective levels studied were the initial dye concentration in solution (25 or 600 mg L⁻¹), the absence or the presence of the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the adsorption temperature (25 or 55 °C). The adsorption parameters were analyzed statistically using modeling polynomial equations. The results indicated that increasing the dye concentration from 25 to 600 mg L⁻¹ increases the dye adsorption whereas the presence of DBS increases it. The principal effect of temperature did not show a high statistical significance. The factorial results also demonstrate the existence of statistically significant binary interactions of the experimental factors. The adsorption thermodynamic parameters, namely Δ_adsH, Δ_adsG and Δ_adsS, were determined for all the factorial design results. Exothermic and endothermic values were found in relation to the Δ_adsH. The positive Δ_adsS values indicate that entropy is a driving force for adsorption. The Δ_adsG values are significantly affected by an important synergistic effect of the factors and not by the temperature changes alone.     

Removal of disperse dye from aqueous solution by novel adsorbent prepared from biomass plant material

The adsorption of Disperse Orange 25 (3-[N-ethyl-4-(4-nitrophenylazo) phenylamino] propionitrile) onto activated carbon was investigated in a batch system with respect to contact time, carbon dosage, pH and temperature from aqueous solutions. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Langmuir isotherm model agrees with the experimental data well. Maximum adsorption capacity (q_max) of Disperse Orange 25 onto adsorbent was 118.93 mg g⁻¹ at 20 °C. The first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated as well. The experimental data fitted very well to pseudo-second-order kinetic model. The results show that activated carbon prepared from Euphorbia rigida by sulfuric acid chemical activation could be employed as low-cost material to compare with commercial activated carbon for the removal of disperse dyes from effluents.     

Cr(VI) sorption behavior from aqueous solutions onto polymeric microcapsules containing a long-chain quaternary ammonium salt: Kinetics and thermodynamics analysis

This work studies the adsorption of Cr(VI) ions from an aqueous acid solution on hydrophobic polymeric microcapsules containing a long-chain quaternary ammonium salt-type extractant immobilized in their pore structure. The microcapsules were synthesized by adding the extractant Aliquat 336 during the in situ radical copolymerization of the monomers styrene (ST) and ethylene glycol dimethacrylate (EGDMA). The microcapsules, which had a spherical shape with a rough surface, behaved as efficient adsorbents for Cr(VI) at the tested temperatures. The results of kinetics experiments carried out at different temperatures showed that the adsorption process fits well to a pseudo-second-order with an activation energy of 82.7 kJ mol⁻¹, confirming that the sorption process is controlled by a chemisorption mechanism. Langmuir's isotherms were found to represent well the experimentally observed sorption data. Thermodynamics parameters, namely, changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰), are also calculated. The results indicate that the chemisorption process is spontaneous and exothermic. The entropy change value measured in this study shows that metal adsorbed on microcapsules leads to a less chaotic system than a liquid–liquid extraction system.     

Biosorption of cadmium(II), zinc(II) and lead(II) by Penicillium simplicissimum: Isotherms, kinetics and thermodynamics

The isotherms, kinetics and thermodynamics of Cd(II), Zn(II) and Pb(II) biosorption by Penicillium simplicissimum were investigated in a batch system. The effects of pH, initial metal ions concentration, biomass dose, contact time, temperature and co-ions on the biosorption were studied. Adsorption data were well described by both the Redlich–Peterson and Langmuir model. Chemical ion-exchange was found to be an important process based on free energy value from Dubini–Radushkevich isotherm for all metal ions. The results of the kinetic studies of all metal ions at different temperature showed that the rate of adsorption followed the pseudo second-order kinetics well. The thermodynamics constants ΔG°, ΔH° and ΔS° of the adsorption process showed that biosorption of Cd(II), Zn(II) and Pb(II) ions on Penicillium simplicissimum were endothermic and spontaneous.     

Sorption of uranium(VI) from aqueous solutions by akaganeite

Removal of U(VI) ions from aqueous solutions was investigated using synthetic akaganeite-type nanocrystals. Nanocrystals of iron oxyhydroxides were synthesized with two different methods and then compared their adsorption capacities. Akaganeite (β-FeOOH) was synthesized in the laboratory by precipitation from aqueous solution of Fe(III) chloride and different precipitating agents. The relative importance of test parameters like solution pH, contact time, temperature and concentration of adsorbate on adsorption performance of akaganeite for U(VI) ion were studied. Typical adsorption isotherms (Langmuir, Freundlich, Dubinin-Raduskevich) were determined for the mechanism of sorption process. Also the thermodynamic constants (ΔH°, ΔS° and ΔG°) were calculated. The product materials were examined by powder X-ray diffraction for crystalline phase identification and scanning electron microscope (SEM).     

Adsorption of p-chlorophenol from aqueous solutions on bentonite and perlite

The adsorption of p-chlorophenol (p-CP) from aqueous solutions on bentonite and perlite was studied. These materials are available in large quantities in Bulgaria. Model solutions of various concentrations (1–50 mg dm⁻³) were shaken with certain amounts of adsorbent to determine the adsorption capacity of p-CP on bentonite and perlite as well. The influence of several individual variables (initial adsorbate concentration, adsorbent mass) on the rate of uptake of the studied compound on the adsorbent was determined by carrying out experiments at different contact times using the batch adsorber vessel designed according to the standard tank configuration. Rapid adsorption was observed 20–30 min after the beginning for every experiment. After that, the concentration of p-CP in the liquid phase remained constant. The adsorption equilibrium of p-CP on bentonite and perlite was described by the Langmuir and the Freundlich models. A higher adsorption capacity was observed for bentonite (10.63 mg g⁻¹) compared to that for perlite (5.84 mg g⁻¹).     

Adsorption of Cr(VI) on 1,2-ethylenediamine-aminated macroporous polystyrene particles

An adsorbent, 1,2-ethylenediamine-aminated macroporous polystyrene (EDA-PSt) particles was used to adsorb Cr(VI) from aqueous solution. Effect of pH value, contact time, temperature, adsorbent dosage and initial Cr(VI) concentration on adsorption amount of Cr(VI) on EDA-PSt were investigated. The results showed that the adsorption isotherm can be well described by the Langmuir equation and the adsorption kinetics fitted to the pseudo-second-order model. According to Langmuir equation, Q_m was calculated to be 175.75 mg g⁻¹. The breakthrough curve experiment showed that the dynamic adsorption capacity for Cr(VI) on EDA-PSt was 100.06 mg g⁻¹. The adsorbed Cr(VI) could be desorbed by 0.1 mol L⁻¹ NaOH and the desorption ratio was 67.28%.     

Interactive behavior of caffeine at a platinum electrode surface

Interactive behavior of caffeine at a charged platinum/solution interface was investigated in a wide temperature range, from 295 to 333 K, in a phosphate buffer solution pH 7.0. It was shown that the amount of adsorbed caffeine (surface concentration) is directly proportional to the measured adsorption surface charge density resulting from caffeine oxidation to theophilline. At low temperatures, a monolayer of caffeine molecules laying in a flat orientation on the Pt surface is adsorbed, while at higher temperatures, conformational changes occur, resulting in tilting of the adsorbed molecules to allow for higher surface concentrations to be achieved. A highly negative Gibbs energy of adsorption, ranging from −51.1 kJ mol⁻¹ at 295 K to −60.6 kJ mol⁻¹ at 333 K, demonstrated a high affinity of caffeine for the Pt surface. Although the adsorption process was found to be endothermic (ΔH_ADS = 20 kJ mol⁻¹), it was determined that a large positive change in the adsorption entropy (TΔS_ADS = 75 ± 3 kJ mol⁻¹) represents the driving force for the strong interaction of caffeine with Pt.     

Adsorptive removal of phenols by Fe(III)/Cr(III) hydroxide,an industrial solid waste

Phenolics have recently been of great concern because of the extreme toxicity and persistency in the environment. Laboratory investigations of the potential use of Fe(III)/Cr(III) hydroxide as an adsorbent for the removal of bisphenol A and 2-aminophenol from aqueous solution were conducted. The operating variables studied are agitation time, initial concentration, adsorbent dose, pH and temperature. Equilibrium data follow Langmuir, Freundlich and Dubinin–Radushkevich isotherms. The Langmuir adsorption capacity of untreated and pretreated adsorbent was found to be 3.47 and 3.67 mg g⁻¹, respectively, for bisphenol A; and 2.94 and 6.03 mg g⁻¹ for 2-aminophenol. Adsorption was analyzed using first order, second order and Elovich kinetic models and the data were found to follow second order and Elovich kinetic models for the adsorption of bisphenol A by untreated adsorbent and first order and Elovich kinetic models for the adsorption of 2-aminophenol by untreated adsorbent. Thermodynamic parameters such as ΔG ⁰, ΔH ⁰ and ΔS ⁰ for the adsorption were evaluated.     

Removal of chromium (VI) ions from aqueous solution by adsorption onto two marine isolates of Yarrowia lipolytica

The removal of chromium (VI) ions from aqueous solutions by the biomass of two marine strains of Yarrowia lipolytica (NCIM 3589 and 3590) was studied with respect to pH, temperature, biomass, sea salt concentration, agitation speed, contact time and initial concentration of chromium (VI) ions. Maximum biosorption was observed at pH 1.0 and at a temperature of 35 °C. Increase in biomass and sea salts resulted in a decreased metal uptake. With an agitation speed of 130 rpm, equilibrium was attained within 2 h. Under optimum conditions, biosorption was enhanced with increasing concentrations of Cr (VI) ions. NCIM 3589 and 3590 displayed a specific uptake of Cr (VI) ions of 63.73 ± 1.3 mg g⁻¹ at a concentration of 950 ppm and 46.09 ± 0.23 mg g⁻¹ at 955 ppm, respectively. Scatchard plot analysis revealed a straight line allowing the data to be fitted in the Langmuir model. The adsorption data obtained also fitted well to the Freundlich isotherm. The surface sequestration of Cr (VI) by Y. lipolytica was investigated with a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS) as well as with ED-X-ray fluorescence (ED-XRF). Fourier transform infrared (FTIR) spectroscopy revealed the involvement of carboxyl, hydroxyl and amide groups on the cell surfaces in chromium binding.     

Biosorption of total chromium from aqueous solution by red algae (Ceramium virgatum): equilibrium, kinetic and thermodynamic studies

This study focused on the biosorption of total chromium onto red algae (Ceramium virgatum) biomass from aqueous solution. Experimental parameters affecting biosorption process such as pH, contact time, biomass dosage and temperature were studied. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were applied to describe the biosorption isotherms. Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The biosorption capacity of C. virgatum biomass for total chromium was found to be 26.5 mg/g at pH 1.5 and 10 g/L biomass dosage, 90 min equilibrium time and 20 °C. From the D–R isotherm model, the mean free energy was calculated as 9.7 kJ/mol, indicating that the biosorption of total chromium was taken place by chemisorption. The calculated thermodynamic parameters (ΔG°, ΔH°and ΔS°) showed that the biosorption of total chromium onto C. virgatum biomass was feasible, spontaneous and exothermic at 20–50 °C. Kinetic evaluation of experimental data showed that the biosorption processes of total chromium followed well pseudo-second-order kinetics.     

Transient flow behaviour in a near alpha titanium alloy Timetal 834 in the dynamic strain aging regime

The transient flow behaviour in Timetal 834 titanium alloy was studied in the temperature range between 400 °C and 475 °C by means of stress relaxation and reloading during tensile testing at a strain rate of 6.67 × 10⁻⁴ s⁻¹. The increment in flow stress during reloading (Δσ_f) and the decrement in flow stress during stress relaxation (Δσ_r) were measured at different strains at each temperature. The observation of maximum value of Δσ_f and Δσ_r, normalized with respect to the Young's modulus at the corresponding temperature, confirmed that the maximum dynamic strain aging (DSA) effect in this alloy occurs at 450 °C.     

Effect of the adsorbate (Bromacil) equilibrium concentration in water on its adsorption on powdered activated carbon. Part 1. Equilibrium parameters

This study was carried out to investigate the adsorption equilibrium and kinetics of a pesticide of the uracil group on powdered activated carbon (PAC). The experiments were conducted at a wide range of initial pesticide concentrations (5 μg L⁻¹ to 500 μg L⁻¹ at pH 7.8), corresponding to equilibrium concentrations of less than 0.1 μg L⁻¹ for the weakest, which is compatible with the tolerance limits of drinking water. Such a very broad range of initial solute concentrations resulting powdered activated carbon (PAC) concentrations (0.1–5 mg L⁻¹) is the main particularity of our study. The application of several monosolute equilibrium models (two, three or more parameters) has generally shown that Bromacil adsorption is probably effective on two types of sites. High reactivity sites (K_L  10³ L mg⁻¹) which are 10–20 less present in a carbon surface than lower reactivity sites (K_L  10 L mg⁻¹), according to the q_m values calculated by two- or three-parameter models. The maximum capacity of the studied powdered activated carbon (PAC), corresponding to monolayer adsorption, compared to the Bromacil molecule surface, would be between 170 mg g⁻¹ and 190 mg g⁻¹. This theoretical value is very close to the experimental q_m values obtained when using linearized forms of Langmuir, Tóth and Fritz–Schluender models.     

Bromate removal from water by granular ferric hydroxide (GFH)

The feasibility of granular ferric hydroxide (GFH) for bromate removal from water has been studied. Batch experiments were performed to study the influence of various experimental parameters such as effect of contact time, initial bromate concentration, temperature, pH and effect of competing anions on bromate removal by GFH. The adsorption kinetics indicates that uptake rate of bromate was rapid at the beginning and 75% adsorption was completed in 5 min and equilibrium was achieved within 20 min. The sorption process was well described by pseudo-second-order kinetics. The maximum adsorption potential of GFH for bromate removal was 16.5 mg g⁻¹ at 25 °C. The adsorption data fitted well to the Langmuir model. The increase in OH peak and absence of Br–O bonding in FTIR spectra indicate that ion-exchange was the main mechanism during bromate sorption on GFH. The effects of competing anions and solution pHs (3–9) were negligible. Results of the present study suggest that GFH can be effectively utilized for bromate removal from drinking water.     

Application of statistical design of experiment with desirability function for the removal of organophosphorus pesticide from aqueous solution by low-cost material

This paper deals with the multiple response optimization for the removal of organophosphorus pesticide quinalphos [QP: O,O-diethyl O-2-quinoxalinyl phosphorothioate] from the aqueous solution onto low-cost material and tried to overcome the drawbacks of univariate optimization. Used tea leaves were used as low-cost adsorbent and batch equilibration method was followed for this study. A Box–Behnken design was used to develop response model and desirability function was then used for simultaneous optimization of all affecting parameters in order to achieve the highest removal% of quinalphos. The optimum conditions of factors predicted for quinalphos removal% were found to be: pH 8.83, concentration 7 mg L⁻¹ and dose 0.40 g. Under these conditions, maximum removal% of quinalphos was obtained 96.31%. Considering the above optimum conditions, the adsorption isotherms were developed and provided adsorption capacity of 196.07 μg g⁻¹ by using Langmuir equation, indicating that used tea leaves may be applied as a low-cost material for pesticides removal from aqueous matrices.     

Adsorption of copper (II), chromium (III), nickel (II) and lead (II) ions from aqueous solutions by meranti sawdust

The present study proposed the use of meranti sawdust in the removal of Cu(II), Cr(III), Ni(II) and Pb(II) ions from synthetic aqueous solutions. Batch adsorption studies showed that meranti sawdust was able to adsorb Cu(II), Cr(III), Ni(II) and Pb(II) ions from aqueous solutions in the concentration range 1–200 mg/L. The adsorption was favoured with maximum adsorption at pH 6, whereas the adsorption starts at pH 1 for all metal ions. The effects of contact time, initial concentration of metal ions, adsorbent dosage and temperature have been reported. The applicability of Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm was tried for the system to completely understand the adsorption isotherm processes. The adsorption kinetics tested with pseudo-first-order and pseudo-second-order models yielded high R² values from 0.850 to 0.932 and from 0.991 to 0.999, respectively. The meranti sawdust was found to be cost effective and has good efficiency to remove these toxic metal ions from aqueous solution.