Adsorption of acid dyes using polyelectrolyte impregnated mesoporous silica

Cationic polyelectrolyte, PDDA (Poly(diallyldimethylammonium chloride)), was impregnated on mesoporous silica SBA-15 (PDDA/SBA-15) and amorphous conventional silica (PDDA/CS) supports. Acid dye adsorption characteristics, such as adsorption kinetics, adsorption isotherms, maximum adsorption capacity, and breakthrough curves of the prepared PDDA/SBA-15 and PDDA/CS adsorbents, were examined by batch and column adsorption techniques where the Acid Violet 17, Acid Red 44, and Acid Blue 45 were used as target adsorbates. PDDA/SBA-15 adsorbent showed fast adsorption kinetics of less than 10 min and much higher adsorption capacities compared to PDDA/CS due to large pore sizes, ordered cylindrical pore structures, and high amount of impregnated PDDA. Results from batch and column experiments showed that practical use of PDDA/SBA-15 adsorbent for effective removal of acid dyes from aqueous solution would be possible. Polyelectrolyte impregnation method was suggested as a simple method for the development of adsorbent with large pore diameters and efficient adsorption characteristics.     

Adsorption equilibria of benzoic acid on silica gel from supercritical carbon dioxide

Supercritical fluids, especially carbon dioxide, are increasingly used as carriers for adsorption-desorption processes, particularly in the pharmaceutical industry. Nevertheless, equilibria data for such processes are rather limited. Therefore, in this work, the adsorption equilibria of benzoic acid onto non-modified silica gel from scCO₂ were evaluated by Supercritical Fluid Chromatography applying the Peak Maxima method. Solubility of benzoic acid in scCO₂ was enhanced by addition of 2-propanol.The effects of modifier content, temperature and pressure on the solute loading were investigated. Experimental data were best described by the cubic Hill isotherm model, which accounted for the change of curvature of the elution profiles observed as concentrations in the mobile phase increased. For the concentration range reached in this study (up to 6 mg/mL), adsorption of benzoic acid was favoured at low modifier contents, high temperatures and low pressures, conditions at which the solvating power of the modified scCO₂ decreased.     

Adsorption of Cd(II), Hg(II) and Zn(II) from aqueous solution using mesoporous activated carbon produced from Bambusa vulgaris striata

Mesoporous activated carbon (surface area of 608 m²/g) has achieved high efficiency in removal of cadmium, mercury and zinc ions from water solution. The proposed low-cost adsorbent was physically activated with water steam from the bamboo species Bambusa vulgaris striata. The batch studies suggested an activated carbon dose of 0.6 g/L, solution pH of 9 and an equilibrium time of 16 h in static conditions. The pseudo-second order equations represented the adsorption kinetics with high correlation. Fitting of the experimental results to the Langmuir, Freundlich, Redlich–Peterson and Toth isotherm models showed an almost homogeneous surface coverage and presence of physical adsorption. The highest adsorption capacities, calculated from the Langmuir model, are 239.45, 248.05 and 254.39 mg/g of cadmium, mercury and zinc, respectively.     

Effect of Br− on the Adsorption Rate of Palladium(II) Ions onto Condensed-Tannin Gel in Chloride Media

Abstract

In chloride media, chloropalladium(II) species are adsorbed onto tannin gel particles through an inner-sphere redox reaction mechanism containing the intermediate step, formation of a ligand-substituted Pd(II)-tannin complex. In this Pd(II) adsorption process, it was observed that the adsorption rate can be increased by introducing Br^?, a softer ligand than Cl^?, into the aqueous chloride solution. The formation of mixed-ligand palladium(II) complexes accelerates the rate of ligand-substitution reactions with the hydroxyl groups of tannin gel by the trans effect. The adsorption condition can be optimized by controlling the [Br_tot]/[Cl_tot] ratio, in which the predominant Pd(II) species are bromo-chloro palladium(II) complexes, the favorable species for the trans effect.     

Adsorption of Norfloxacin from Aqueous Solution onto Modified Coal Fly Ash

Batch adsorption experiments were carried out for the removal of norfloxacin from aqueous solution using modified coal fly ash as adsorbent. The effects of various parameters such as contact time, initial solution concentration and temperature on the adsorption system were investigated. The optimum contact time was found to be 100 min. The equilibrium experimental data can be well fitted by the Freundlich model. Thermodynamic parameters such as ΔG, ΔH and ΔS were also calculated. The negative Gibbs free energy change and enthalpy change indicated the spontaneous and exothermic nature of the adsorption, and the negative entropy change indicated that the adsorption process was aided by decreased randomness.     

Adsorption and surface properties of silica with transformer insulating oils

The presence of polar species in transformer insulating oil may cause degradation and electric discharges in the power transformer. Such oil polar fraction can originate either from the neat oil and/or from its oxidative degradation in the power transformer. The aim of this study is to examine the relation between the insulating oil and the electrical properties of its polar fraction in order to predict eventual failure in the power transformer.We investigate at ambient temperature the adsorption of the polar fractions of various transformers insulating oils (a new and two used oils) from the neat oils onto silica particles. The adsorbed amount was higher for the used oils as compared to the new one. Infrared spectra of the polar fraction indicate the presence of hydroxyl, aromatic and carboxyl functional groups that are found in the asphaltenes compounds. Microelectrophoresis study of the oil polar fraction covered silica particles gives negatively charged oil polar fraction. Such oil surface charge depends on the pH and results from the ionisation of the oil acidic surface groups. Finally, we obtain a good correlation between the amount of the oil polar fraction and the magnitude of the zeta potential at the water/oil-silica interface.     

Adsorption isotherm of ibuprofen on molecular imprinted polymer

A molecular imprinted polymer (MIP) using (+)-(S)-2-(4-isobutylphenyl) propionic acid ((+)-(S)-ibuprofen) as the template and 4-vinylpyridine (4-VPY) as the functional monomer was prepared. Chloroform and acetonitrile were used as the porogen with ethylene glycol dimethacrylate (EGDMA) as the crosslinker and 2,2′-azobis(isobutyronitrile) (AIBN) as the initiator. Comparison of ibuprofen adsorption isotherm on molecular imprinted and blank polymers was made by the static method. The adsorption equilibrium data were correlated into the Freundlich, Langmuir, Sips (Langmuir-Freundlich) and Radke-Prausnitz isotherm models, respectively. By a nonlinear regression analysis, the experimental parameters in the equilibrium isotherms were estimated and compared. The calculated data is well fitted with the experimented data. Through the analysis, the ibuprofen imprinted polymer showed higher adsorption ability than blank polymer.     

Adsorption characteristics of Cr(III) ionic imprinting polyamine on silica gel surface

In this paper, a kind of ionic imprinting polyamine (IIP) was prepared through an advanced approach. Firstly, functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles, and the PEI/SiO₂ was formed. Secondly, the ionic imprinting process was carried out using Cr³⁺ ion as a template, and epichlorohydrin (ECH) as a crosslinking agent, and Cr³⁺ ionic imprinting polyamine IIP-PEI/SiO₂ was prepared. The adsorption properties of IIP-PEI/SiO₂ for Cr³⁺ ion were studied in details by adopting both static and dynamic methods, and the effects of main imprinting conditions, such as the concentrations of Cr(III) ion and the amount of ECH, on the adsorption property of the imprinted material IIP-PEI/SiO₂ were examined. The experimental results show that the IIP-PEI/SiO₂ has high affinity and excellent selectivity for the template ion. Its adsorption amounts for template ion enhances nearly two times compared to PEI/SiO₂, and its relative selectivity coefficients relative to Zn²⁺ and Pb²⁺ are 24.63 and 59.32 respectively. Besides, the IIP-PEI/SiO₂ has a fine elution property using HCl solution as eluent.     

Adsorption isotherms of caffeine on molecular imprinted polymer

A molecular imprinted polymer (MIP) using caffeine as the template and methacrylic acid (MAA) as the functional monomer was prepared. Acetonitrile was used as the porogen with ethylene glycol dimethacrylate (EGDMA) as the crosslinker and 2,2′-azobis(isobutyronitrile) (AIBN) as the initiator. By a linear and nonlinear regression analysis, the experimental parameters in the equilibrium isotherms were estimated. Then, the linear and quadratic equations for concentration and sorbents to adsorption amounts were expressed, and the adsorption equilibrium data were also correlated into the Freundlich isotherm model. Comparisons of caffeine adsorption isotherm on C₁₈ particles as well as the molecular imprinted polymer were made. The results showed that the caffeine-imprinted polymer showed extraordinarily higher adsorption ability than C₁₈ particles.     

Amine-modified silica surface applied as adsorbent in the phenol adsorption assisted by ultrasound

Abstract

Phenolic compounds are toxic pollutants that are harmful to the human body and aquatic environments, with carcinogenic potential and frequently found in industrial effluents at high levels. Adsorption processes are often employed for the removal of these compounds. Mesoporous materials based on modified silica with amine have been used as adsorbents and can be considered promising for this job due to its high selectivity and better adsorption capacity when compared to materials without any modifications. In addition, adsorption studies can be performed using ultrasound as a mixing mechanism, improving mass transfer through cavitation and acoustic current. In this context, the goal of this study is to modify the surface of mesoporous silica with 3-aminopropyltriethoxysilane (APTES) and to evaluate its efficiency in the adsorption of phenol in an ultrasonic bath. In the phenol adsorption experiments, the Si-APTES showed higher adsorption capacity (12?mg g^?1) than the SiO₂ (2?mg g^?1). The kinetic models of pseudo second-order have shown to be good fits to the experimental data. The adsorption equilibrium data of the phenol on the materials studied were best described in the Langmuir isotherm.     

Adsorption behaviour of Cu and Cd onto natural bentonite

The adsorption behaviour of Cu²⁺ and Cd²⁺ onto bentonite was studied as a function of temperature under optimized conditions of amount of adsorbent, particle size, pH, concentration of metals, and shaking time. The adsorption patterns of metal ions onto followed the Langmuir, Freundlich and Dubinin-Radushkevich isotherms. This included adsorption isotherms of single-metal solutions at 298-333 K by batch experiments. The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK_o vs. 1 / T plots. The adsorptions were endothermic reactions. The results suggested that natural bentonite was suitable as sorbent material for the recovery and adsorption of metal ions from aqueous solutions.     

Kinetics of water sorption on SWS-1L (calcium chloride confined to mesoporous silica gel): Influence of grain size and temperature

Kinetics of water sorption on loose grains of composite sorbent CaCl₂ confined to mesoporous silica (SWS-1L) was measured at and over water uptake range 0-0.47 g/g for various particle sizes R_p (between 0.355 and 1.4 mm). The measurements were performed in a constant pressure unit based on a CAHN microbalance under isothermal external conditions.The results obtained evidence an enhancement of the sorption rate and apparent diffusion constant with the decrease in the particle size (approximately as at ). Contribution of thermal effects was found for water sorption on smaller SWS particles (0.355-0.425 mm), which decreases the sorption rate.The apparent water diffusivity was found to depend on the local slope of the SWS water sorption isotherm. The pore diffusivity of water in the temperature range 33-69 °C was calculated from experimental data that is approximately 10 times lower than the Knudsen pore diffusivity estimated for pores of silica KSK. The possible reasons of the diffusivity reduction are discussed.     

Adsorption equilibrium for Z-ligustilide on C18-bonded silica from supercritical carbon dioxide

Adsorption equilibrium is of great importance for the preparative supercritical fluid chromatography(pre-SFC) in defining supercritical adsorption behavior and the industrial amplification.This paper presents adsorption isotherms of Z-ligustilide from supercritical carbon dioxide(SC-CO_2) on C18-bonded silica.Adsorption behavior was studied at 305.15 K,313.15 K and 323.15 K with SC-CO_2 density varying from 0.687 g·cm~(-3) to0.863 g·cm~(-3) with the elution by characteristic points(ECP) method.The adsorption amount of Z-ligustilide from SC-CO_2 on C18-bonded silica decreased with the increasing density of the mobile phase as well as the increasing temperature.Adsorption equilibrium data were fitted by Langmuir and Freundlich isotherm models,and the Langmuir isotherm model performed better for describing the whole adsorption process on the column.The monolayer saturation adsorption capacity of Z-ligustilide is in the range of 3.0 × 10~(-4) mg·cm~(-3) to5.5 × 10~(-4) mg·cm~(-3) with an average value of 4.0 × 10~(-4) mg·cm~(-3).     

Adsorption properties of composite materials (LiCl + LiBr)/silica

This paper presents experimental data on synthesis and the phase composition of novel composites “(LiCl + LiBr) confined to the silica gel pores” as well as their sorption equilibrium with water and methanol vapour. Phase transformation of the composites during methanol sorption was characterized in situ by an X-ray diffraction analysis. The isobars of sorption on the composites were measured in the temperature range T = 303–383 K at the methanol and water pressure P = 107 and 13 mbar, respectively, using a thermo-gravimetric technique. It was shown that the formation of solid solutions of LiCl and LiBr took place in limited ranges of LiBr (C_Br = 0–11 mol.%) and LiCl (C_Cl = 0–36 mol.%) content. These solutions absorbed water (methanol) at temperature that was intermediate between the individual solvation temperatures for confined LiCl and LiBr. In the composites with LiCl/LiBr molar ratio between the ranges of solubility a mixture of two solid solutions was formed. Each solution absorbed water (methanol) independently at a certain temperature. The use of the binary LiCl–LiBr system confined to the silica pores can be an effective tool for designing innovative materials with predetermined sorption properties.     

Batch and Column Adsorption of Cu(II) on Unmodified and Oxidized Coir

Abstract

The potential of coir, a low cost lignocellulosic material, was assessed for the removal of Cu(II) ion from aqueous solutions of copper sulphate. The coir fiber was also modified by an oxidative treatment, whereby the maximum uptake of Cu(II) increased to 6.99 mg/g as compared to 2.54 mg/g for the unmodified coir. A Langmuir type of adsorption was followed by oxidized coir fiber. A second order rate equation was observed for the Cu(II) uptake. The lowering of pH adversely affects adsorption on both the materials. Almost complete desorption of the loaded Cu(II) was possible using 0.25 N hydrochloric acid. The materials retained the adsorptive capacity up to three cycles when an intermediate regeneration step was given with dilute sodium hydroxide solution. In a fixed column packed with oxidized coir fibers, it was observed that the breakthrough time decreased with an increase in inlet Cu(II) concentration. The desorption level in the fixed bed column was around 90% and the column was regenerated and used up to eight cycles. The fixed bed column packed with oxidized coir was used to remove Cu(II) from an electrochemical industrial effluent. An ion exchange mechanism has been proposed for uptake of Cu(II) on the oxidized coir fiber.     

Adsorption of aqueous cadmium (II) onto modified multi-walled carbon nanotubes following microwave/chemical treatment

This study evaluates the aqueous cadmium (II) adsorption efficiency of as-grown carbon nanotubes (CNTs) and of those modified by microwave (MW)/H₂SO₄ and MW/H₂SO₄/KMnO₄ processes. The surface area, pH_iep, and FTIR spectra of CNTs were, before and after modification, compared. Aromatic groups, carbonyl groups and hydroxyl groups were herein detected on the surfaces of MW/H₂SO₄ and MW/H₂SO₄/KMnO₄-modified CNTs. At a particular pH, the adsorption capacity of Cd²⁺ of the MW/H₂SO₄/KMnO₄-modified CNTs exceeded that of MW/H₂SO₄-modified CNTs and as-grown CNTs. The kinetic analyses of adsorption were performed and a pseudo second-order model accurately captured the adsorption kinetics. This study suggests that MW/H₂SO₄ and MW/H₂SO₄/KMnO₄ modification not only increased the area of active adsorption sites of CNTs but also reduced the modification period by microwave heating.     

Arsenic adsorption using copper (II) oxide nanoparticles

Arsenic poisoning is a major problem in today's life. To reduce its concentration in drinking water, different metal based compounds were explored as arsenic adsorbents. In the present study, copper (II) oxide nanoparticles were prepared by thermal refluxing technique and used as an adsorbent for arsenic removal from water. Characterization of the adsorbent using TEM, BET, XRD and FTIR implied that the prepared adsorbent was in nano size and had excellent adsorption behavior with surface area of 52.11 m²/g. Systematic adsorption experiments were carried out with different process parameters such as contact time, adsorbent mass, pH, temperature and stirring speed and found that copper (II) oxide had very good efficiency towards arsenic adsorption. Thermodynamic parameters and adsorption kinetics were studied in detailed to know the nature and mechanism of adsorption. Results showed that the adsorption process followed pseudo second order kinetic and endothermic behavior. Adsorption equilibrium was studied with Langmuir and Freundlich isotherm models. The adsorption process followed Langmuir isotherm with an adsorption capacity of 1086.2 μg/g. A regeneration study was proposed in order to reuse the adsorbent for better economy of the process. Finally, a process design calculation is reported to know the amount of adsorbent required for efficient removal of arsenic from aqueous medium.     

Adsorption of Cr (VI) Oxyanions onto Modified Wood Pulp

A new adsorbent was prepared from wood pulp (WP) after reaction with epichlorohydrin and dimethylamine in the presence of pyridine and N,N-dimethylformamide (DMF). The adsorption of Cr (VI) from aqueous solutions by the so-prepared wood pulp adsorbent (WP-A) was investigated. Various factors affecting adsorption, such as pH, adsorbent concentration (1–5 g/L), agitation time (5–60 min), and Cr (VI) concentration (50–700), were taken into consideration. The adsorption of Cr (VI) onto (WP-A) was found to be pH-dependent and maximum adsorption was obtained at pH 3. The adsorption data obeyed Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption capacity (Q_max) was found to be 588.24 mg/g. Freundlich constants, K_F and n, were found to be 55.03 and 2.835, respectively.     

Adsorption kinetics and thermodynamics of azo-dye Orange II onto highly porous titania aerogel

We report herein a kinetic and thermodynamic study of the adsorption of azo-dye Orange II from aqueous solutions onto titania aerogels. Aerogels structure was confirmed by FTIR and N₂ adsorption revealed their specific surface area (500 m²/g), pore volume (2.86 cm³/g) and pore size (mean 13.9 nm). Adsorption tests were conducted in batch reactors under various conditions where the effect of pH, temperature, contact time, dye concentration, and adsorbent dose were studied. Experiments performed at pH 2 show the optimal adsorption due to the best surface charge interactions. The temperature shows a weak influence with a decrease in the adsorption uptake as the temperature increases. Adsorption kinetics is shown to be very fast and follows a pseudo second-order indicating the coexistence of chemisorption and physisorption with the intra-particle diffusion being the rate controlling step. The experimental data fit perfectly with Sips isotherms and reveal the ability of titania aerogel to adsorb 420 mg of Orange II per gram of adsorbent at the optimal conditions. The thermodynamic study reveals the activation energy (42.1 kJ mol⁻¹) and the changes in Gibbs free energy (1.2 kJ mol⁻¹), enthalpy (−16.4 kJ mol⁻¹), and entropy (−58 J mol⁻¹ K⁻¹). The entire regeneration of the titania aerogel adsorption sites at pH 11 and 30 °C shows a total recovery of the dye and the efficient reusability and the economic interest of these adsorbing materials for environmental purposes.