Removal of Orange II from Aqueous Solutions Using N-Vinyl Imidazole-based Hydrogels as Adsorbents

Poly(N-vinyl imidazole) hydrogel (p-VIm) and its partially quaternized analogue (p-VIm-Ar) were prepared and used for the removal of Orange II (OII). A fourier transform infrared spectrophotometer, scanning electron microscope with an energy dispersive X-ray spectrometer attached, thermogravimetric analyzer, zeta potential analyzer, and a drop shape analyzer were used for the characterization of the hydrogels. The influence of some experimental parameters, such as pH of the OII solution, contact time, and initial OII concentration on the adsorption process, was examined, and the obtained data were used to calculate the isotherm and kinetic parameters. Adsorption processes of OII onto adsorbents were coherent with the Langmuir isotherm and pseudo-second-order kinetic models. The quaternized analogue exhibited remarkable adsorption performance in the pH range of 2–12, while the effective adsorption with p-VIm occurred only at pH 2.0. The maximum adsorption capacity values of adsorbents were determined as 2331 (for p-VIm) and 1327 mg g^?1 (for p-VIm-Ar) at pH 2.0 and 132 (for p-VIm) and 1357 mg g^?1 (for p-VIm-Ar) at pH 6.0.     

Fast and efficient adsorption of azure (II) on nanoporous MCM-41 for its removal,preconcentration and determination in biological matrices

The objective of the present study was to investigate the potential of nanoporous MCM-41 silicate for the azure (II) adsorption from the aqueous solutions. The method is based on the adsorption of azure (II) after passing on MCM-41 in a column. The adsorption with respect to contact time, pH, flow rate of sample, eluent kind and volume was investigated to provide more information about the adsorption characteristics of MCM-41. After elution of the adsorbed dye, the concentrations of dye were determined by UV–Vis spectrophotometer. The method showed good linearity for the determination of azure (II) in the range of 1–200 ng mL^?1 with a regression coefficient of 0.9997. The limit of detection was 0.5 ng mL^?1 and the relative standard deviation for 50 ng mL^?1 of azure (II) was 1.26 %. The adsorption properties of the MCM-41 were investigated using batch method. In order to investigate the efficiency of adsorption, pseudo-first-order, pseudo-second-order and intra particle diffusion kinetic models were studied. It was observed that the pseudo-second-order kinetic model fits better than other kinetic models with good correlation coefficient. Equilibrium data were fitted to the Langmuir model. Adsorption equilibrium reach within 5 min of contact time and adsorption capacity was found to be 66.0 mg g^?1. The method was applied to the determination of azure (II) in river water, broth culture medium and DNA samples.     

Adsorptive removal of cationic dye from aqueous solutions by ZnO/ZnMn2O4 nanocomposite

The ZnO/ZnMn₂O₄ nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scanning electron microscope, TEM, Fourier transform infrared ray, BET, particle size distribution and zeta potential measurements. The adsorption parameters, such as temperature, pH and initial dye concentration, were studied. Kinetic adsorption data were analyzed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The Langmuir and Freundlich isotherm models were applied to fit the equilibrium data. The maximum adsorption capacity of BY28 was 48.8 mg g^?1. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated.     

ADSORPTION OF A LEATHER DYE ON MESOPOROUS STRUVITE OBTAINED FROM SWINE WASTEWATER

Struvite powder obtained from swine wastewater was used as adsorbent to remove an azo leather dye from aqueous solution. The material was characterized by X-ray diffraction, surface area, and atomic force microscopy. The sample presented a single phase having a mesoporous structure and surface area of 35.63 m² g^?1. Langmuir and Freundlich isotherm models were fitted to the adsorption data and both satisfactorily represented the process. The maximum adsorption capacity was 38.14 mg g^?1. From the analysis of thermodynamic parameters such as free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) it was verified that the adsorption process is very fast, spontaneous, and exothermic in nature, with weak forces acting.     

Removal of Copper(II) and Zinc(II) from Aqueous Solutions Using a Lignocellulosic-Based Polymeric Adsorbent Containing Amidoxime Chelating Functional Groups

In this study, the adsorption of Cu(II) and Zn(II) ions from aqueous solutions onto amidoximated polymerized banana stem (APBS) has been investigated. Infrared spectroscopy was used to confirm graft copolymer formation and amidoxime functionalization. The different variables affecting the sorption capacity such as pH of the solution, adsorption time, initial metal ion concentration, and temperature have been investigated. The optimum pH for maximum adsorption was 10.5 (99.99%) for Zn²⁺ and 6.0 (99.0%) for Cu²⁺ at an initial concentration of 10 mg L^?1. Equilibrium was achieved approximately within 3 h. The experimental kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models and are well fitted with pseudo- second-order kinetics. The thermodynamic activation parameters such as ΔG^o, ΔH^o, and ΔS^o were determined to predict the nature of adsorption. The temperature dependence indicates an exothermic process. The experimental isotherm data were well fitted to the Langmuir model with maximum adsorption capacities of 42.32 and 85.89 mg g^?1 for Cu(II) and Zn(II), respectively, at 20°C. The adsorption efficiency was tested using industrial effluents. Repeated adsorption/regeneration cycles show the feasibility of the APBS for the removal of Cu(II) and Zn(II) ions from water and industrial effluents.     

Starch/rice husk ash based superabsorbent composite: high methylene blue removal efficiency

Superabsorbent hydrogels composites based on the biopolymer starch (ST) and rice husk ash (RHA) were successfully developed and tested towards the removal of methylene blue (MB), a cationic dye. RHA content hit the morphology, mechanical and water uptake properties of the composite. Batch adsorption experiments, carried out under pH 5 at 33 °C and with 2000 mg L^?1 as the initial concentration of MB, showed that at 5 wt% RHA the composite exhibited a remarkable adsorption capacity reaching up to 1906.3 mg g^?1 within 60 min. The adsorption kinetics followed the pseudo-second-order model and intraparticle diffusion was involved in this process. The Langmuir adsorption isotherm suggested a monolayer formation and spontaneous process. Thermodynamic parameters confirmed the spontaneity of the adsorption and suggested electrostatic interaction among the cationic dye molecules and the anionic adsorption sites on the adsorbent surface. FTIR analysis confirmed the adsorption process occurs via electrostatic mechanism associated with hydrophobic interactions. The adsorbents showed reusability with slight loss of adsorption capacity in five consecutive adsorption/desorption cycles. These results demonstrate ST/RHA superabsorbent composite as a low-cost, eco-friendly, robust and powerful adsorbent material for wastewater remediation.     

Factors Affecting Lanthanum and Cerium Biosorption on Pinus brutia Leaf Powder

The biosorption behavior of lanthanum and cerium ions from aqueous solution by leaf powder of Pinus brutia was separately studied in a batch system as a function of initial pH, contact time, initial metal ion concentration, temperature, and adsorbent amount. The uptake of lanthanum and cerium was increased when the initial pH of the solution was increased. Thermodynamic parameters such as standard enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were calculated and the results indicated that biosorption was endothermic and spontaneous in nature. The biosorption of lanthanum and cerium on powdered leaf of Pinus brutia was investigated by the Freundlich, Langmuir, and D-R isotherms. The results show that lanthanum and cerium adsorption can be explained by the Langmuir isotherm model and monolayer capacity was found as 22.94 mg g^?1 for lanthanum and 17.24 mg g^?1 for cerium. Desorption of lanthanum and cerium was studied using 0.5 M HNO₃ solution. The results suggested that powdered leaf of Pinus brutia may find promising applications for the recovery of lanthanum and cerium from aqueous effluents.     

EFFECT OF TEMPERATURE ON THE ADSORPTION OF METHYLENE BLUE DYE ONTO SULFURIC ACID–TREATED ORANGE PEEL

The present study explains the preparation and application of sulfuric acid–treated orange peel (STOP) as a new low-cost adsorbent in the removal of methylene blue (MB) dye from its aqueous solution. The effects of temperature on the operating parameters such as solution pH, adsorbent dose, initial MB dye concentration, and contact time were investigated for the removal of MB dye using STOP. The maximum adsorption of MB dye onto STOP took place in the following experimental conditions: pH of 8.0, adsorbent dose of 0.4 g, contact time of 45 min, and temperature of 30°C. The adsorption equilibrium data were tested by applying both the Langmuir and Freundlich isotherm models. It is observed that the Freundlich isotherm model fitted better than the Langmuir isotherm model, indicating multilayer adsorption, at all studied temperatures. The adsorption kinetic results showed that the pseudo-second-order model was more suitable to explain the adsorption of MB dye onto STOP. The adsorption mechanism results showed that the adsorption process was controlled by both the internal and external diffusion of MB dye molecules. The values of free energy change (ΔG ^o) and enthalpy change (ΔH ^o) indicated the spontaneous, feasible, and exothermic nature of the adsorption process. The maximum monolayer adsorption capacity of STOP was also compared with other low-cost adsorbents, and it was found that STOP was a better adsorbent for MB dye removal.     

Kinetic and Equilibrium Study for the Fluoride Adsorption using Pyrophyllite

Batch adsorption study was carried out to remove excess fluoride from water using pyrophyllite. Result showed that adsorption of fluoride was rapid in first 20 min and thereafter increased slowly to reach the equilibrium in about 2 hrs. About 85% removal efficiency was obtained within 2 hrs at an adsorbent dose of 4 g/L for initial fluoride concentration of 10 mg/L. Maximum fluoride adsorption takes place at pH 4.9. Thermodynamic parameters such as Gibb's free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were determined for the adsorption process. Negative ΔH° value signified that the adsorption process was exothermic in nature. From the kinetic study it was found that fluoride adsorption by pyrophyllite followed pseudo-second-order kinetics with an average rate constant of 0.92 g/mg · min. Intraparticle diffusion model was studied to determine the rate limiting step of the adsorption process. The system followed the Langmuir isotherm with maximum adsorption capacity of 2.2 mg/g of fluoride.     

Application of Full Factorial Design for Removal of Polycyclic Aromatic Dye from Aqueous Solution Using 4A Zeolite: Adsorption Isotherms,Thermodynamic and Kinetic Studies

In this study, removal of the cationic dye acridine orange (AO) from aqueous solution using 4A zeolite was studied. The adsorption experiments were performed using batch system, and full factorial design was employed for investigating the condition of removal efficiency of dye. The four most important operating variables were the initial pH of the solution, the concentration of dye, the contact time, and the temperature. The 18 experiments were required to investigate the effect of variables on removal of the dye. The results were statistically analyzed to define important experimental variables and their levels using the analysis of variance (ANOVA). A regression model that considers the significant main and interaction effects was suggested and fitted the experimental data very well. Model predictions were found to be in good agreement (R² = 99.99%, adjusted R² = 99.86%) with experimental data. The optimized conditions for dye removal were at initial pH 3.0, 20.0 mg L^?1 dye, temperature 298.0 K and 80.0 min adsorption time. The experimental data were analyzed by the Langmuir, Freundlich, Temkin and Sips adsorption models. The maximum predicted adsorption capacities for AO was obtained as 29.851 mg g^?1. The adsorption thermodynamic parameters, namely ΔH°_ads, ΔG°_ads and ΔS°_ads, were determined. Furthermore, the kinetic of AO adsorption on the 4A zeolite was analyzed using pseudo-first- and second-order kinetic models and the results showed that the removal was mainly a pseudo-second-order process.     

Application of mesoporous magnetic nanosorbent developed from macadamia nut shell residues for the removal of recalcitrant melanoidin and its fractions

ABSTRACT

A novel mesoporous magnetic nanosorbent developed from macadamia nut shell residues was applied as an adsorbent for the removal of dissolved organic carbon (DOC) associated with melanoidin and its fractions in a batch system. The most favored molecular fraction of the melanoidin for adsorption onto the nanosorbent was 1–5 kDa with adsorption capacity of 10.26 mg DOC g^?1 achieving 68.4% removal efficiency. The sorption behaviors were all well fitted to a pseudo-second-order kinetic model and Langmuir isotherm. Optimum operating conditions needed for the maximum uptake of 14.7 mg DOC g^?1 were found to be pH of 6.3, temperature of 41.7°C at the dosage of the magnetic nanosorbent of 877.7 ppm.     

Investigation of equilibrium and kinetic parameters of methylene blue adsorption onto MCM-41

Mesoporous MCM-41 was synthesized at room temperature using tetraethoxysilane (TEOS) with cetyltrimethylammonium bromide (CTAB) and employed as an effective adsorbent for the adsorption of methylene blue dye from aqueous solution. The as-synthesized MCM-41 was calcined at 250 and 550°C to study the relation between the surface area and pore volume with surfactant removal. The synthesized MCM-41 was characterized using thermo gravimetric analysis (TGA), X-ray diffraction (XRD) patterns, nitrogen adsorption/desorption isotherms and Fourier transform infrared (FT-IR) spectroscopy. The MCM-41 calcined at 550°C showed higher surface area (1,059 m² g^?1) with pore volume of 0.89 ml g^?1 and was used for the investigation of adsorption isotherms and kinetics. The experimental results indicated that the Freundlich and Redlich-Peterson models expressed the adsorption isotherm better than the Langmuir model. In addition, the influence of temperature and pH on adsorption was also investigated. The decrease in temperature or the increase in pH enhanced the adsorption of dye onto MCM-41. A maximum adsorption capacity of 1.5×10^?4 mol g^?1 was obtained at 30°C. The kinetic studies showed that the adsorption of dye on MCM-41 follows the pseudo-second-order kinetics.     

SYNTHESIS OF ACTIVATED CARBON FROM JATROPHA SEED COAT AND APPLICATION TO ADSORPTION OF IODINE AND METHYLENE BLUE

This article provides evidence that jatropha seed coat residues can be used as a carbon source for preparing activated carbons that have good adsorption properties for iodine and methylene blue. Activated carbons were prepared using three different methods of activation, physical, chemical, and physico-chemical, for a range of activation temperatures (600°, 700°, 800°, and 900°C) and activation hold times (1, 2, and 3 h). The highest BET surface area (1479 m² g^?1) and the highest iodine adsorption (1511 mg g^?1) were obtained with physico-chemical activation at a temperature of 900°C and a hold time of 2 h. This activated carbon gave higher BET surface area and iodine adsorption than commercial activated carbon (1169.1 m² g^?1 and 1076 mg g^?1). The activated carbons prepared by physico-chemical activation at 900°C and 2 h were then tested for adsorption of methylene blue at a range of concentrations of methylene blue (100, 200, 300, 400, and 500 mg L^?1). It was found that a Langmuir isotherm gave a better fit (R ² = 0.999) to the observed adsorptions than a Freundlich isotherm (R ² = 0.884). For the adsorption kinetics, a pseudo-second-order model gave a better fit (R ² > 0.998, Δq _e  = 3.7%) than a pseudo-first-order model (R ² ≈ 0.95, Δq _e  = 85.6%). These results suggest that chemisorption is the rate-controlling step for the adsorption of methylene blue. The experimental results show that jatropha seed coat is a lignocellulosic waste precursor for preparation of activated carbon that is an alternative source for preparation of commercial-grade activated carbons.     

Adsorption of Rhodamine B onto O-Carboxymethylchitosan-N-Lauryl

The adsorption of a cationic dye (rhodamine B; RB) on O-carboximethyl-N-acetylated (L-CMCh) in aqueous solution was investigated. The effect of the process parameters such as the contact time, pH, and temperature are reported. Both temperature and pH influence dye adsorption. To determine the adsorption capacity, the equilibrium adsorption data were analyzed by the Langmuir, Langmuir-Freundlich, and Redlich-Peterson isotherm models. The results showed better agreement with the Langmuir-Freundlich model than the other models. The maximum adsorption capacity of RB for L-CMCh was determined as 38.5 mg g^?1 at pH 8.5 and 25°C. The kinetic results follow a pseudo-second-order rate equation. The activation energy value for adsorption of RB on L-CMCh was found to be 52.0 kJ mol^?1. The negative values of Gibbs free energy and enthalpy show the adsorption to be spontaneous and exothermic. The negative value of the enthalpy for adsorption of RB onto L-CMCh shows the adsorption to be exothermic.     

Performance of Unmodified Paper Solid Waste for Cadmium Removal From Aqueous Phase: Equilibrium and Kinetic Studies

The reuse of paper solid waste (PSW) as a low-cost sorbent for Cd removal from aqueous phase was investigated. Batch experiments were conducted to study the effects of pH (3.5, 5.5, 7.5), contact time (10–360 min), PSW dose (2.5–20 g L^?1), and Cd concentration (5–50 mg L^?1) at an ionic strength of 0.01 M NaNO₃ on adsorption efficiency and capacity. Cd removal of ～96% occurred in 20 mg L^?1 Cd solution at pH 5.5 containing 20 g L^?1 PSW. Equilibrium was attained after 120 min and the equilibrium adsorption capacity of PSW increased with increasing Cd concentration from 5 to 50 mg L^?1. The kinetic process of Cd adsorption obeyed the pseudo-second-order kinetic model. Langmuir and Freundlich models described equally well the experimental data and the maximum adsorption capacity was 4.89 mg g^?1. PSW can be used for reducing Cd concentration in Cd-contaminated water systems.     

Methylene Blue Adsorption on Natural and Modified Clays

Toxic methylene blue dye is removed from water by accumulating it on the surface of clay minerals. Clay adsorbents are obtained from kaolinite, montmorillonite, and their acid activated forms. The adsorption experiments are carried out in a batch process in environments of different pH, initial dye concentration, amount of clay, interaction time, and temperature. Adsorption of dye is best described by second order kinetics. In the temperature range of 303 to 333 K, the Langmuir monolayer capacity for three kaolinite species increased from 45.5 to 56.5 mg g^?1, 45.9 to 57.8 mg g^?1, 46.3 to 58.8 mg g^?1, and for three montmorillonites species from 163.9 to 181.8 mg g^?1, 166.7 to 188.8 mg g^?1, and 172.4 to 192.3 mg g^?1. The interaction is an endothermic process driven by entropy increase and spontaneous adsorptive accumulation is ensured by favorable Gibbs energy decrease. It is found that acid activation enhances the adsorption capacity of kaolinite and montmorillonite.     

Mechanistic,Kinetic, and Thermodynamic Evaluation of Adsorption of Hazardous Malachite Green onto Conch Shell Powder

The present study explores the ability of a new adsorbent—conch shell powder (CSP) in removing Malachite Green from aqueous solutions. The effect of various process parameters, namely initial solution pH, temperature, initial dye concentration, adsorbent dose, and contact time was investigated. Adsorption equilibrium data were well described by the Langmuir isotherm with maximum adsorption capacity of 92.25 mg g^?1 at 303 K. The kinetic data conformed to the pseudo-second-order kinetic model. A thermodynamic study showed the spontaneous nature and feasibility of the adsorption process. The results provide strong evidence to support the hypothesis of adsorption mechanism.     

Adsorption Thermodynamic and Kinetic Studies of Fluoride Aqueous Solution Treated with Waste Iron Oxide

This study uses a waste iron oxide material (BT3), which is a by-product of the fluidized-bed Fenton reaction (FBR–Fenton), for the treatment of a fluoride (F^?) solution. The purpose of this study is to investigate a low-cost sorbent as a replacement for the current costly methods of removing fluoride from wastewater. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the BT3. Contact time, F^? concentration (from 0.75 to 6 mmol L^?1), and temperature (from 303 to 323 K) are used as operation parameters to treat the fluoride. The highest F^? adsorption capacity of the BT3 adsorbent was determined to be 1.17 mmol g^?1 (22.2 mg g^?1) for a 6 mmol L^?1 initial F^? concentration at pH 3.9 ± 0.2 and 303 ± 1 K. Adsorption data were well described by the Langmuir model, and the thermodynamic constants of the adsorption process, ΔG°, ΔH°, and ΔS°, were evaluated as ?1.63 kJ mol^?1 (at 303 K), ?1.75 kJ mol^?1, and ?52.4 J mol^?1 K^?1, respectively. Additionally, a pseudo-second-order rate model was adopted to describe the kinetics of adsorption. BT3 could be regenerated with NaOH, and the regeneration efficiency reached 95.1% when the concentration of NaOH was 0.05 mol L^?1.     

Competitive Separation of Lead,Cadmium, and Nickel from Aqueous Solutions Using Activated Carbon: Response Surface Modeling,Equilibrium, and Thermodynamic Studies

In this study, the competitive separation of lead, cadmium, and nickel ions from aqueous solutions using a commercial activated carbon (AC) has been investigated and optimized using response surface methodology (RSM). The optimal conditions to reach the highest adsorption capacity for these metals were found as follows: initial pH = 6.3, temperature = 56.8°C, and shaking speed = 308 rpm. Under these conditions, the sequence of adsorption capacity toward the metal ions was as follows: Pb (II): 9.44 mg g^?1 > Cd (II): 9.37 mg g^?1 > Ni (II): 4.52 mg g^?1. The effect of shaking speed on the adsorption capacity of AC was higher than the effects of the initial pH and temperature, indicating the more important role of physisorption than chemisorption in the adsorption of these metal ions. This was confirmed by the results of thermodynamic studies. The equilibrium adsorption data were fitted to the Freundlich, Langmuir adsorption isotherm models and the Dubinin–Radushkevich model parameters were evaluated. All the models were tested and all were shown to represent the experimental data satisfactorily. The thermodynamic parameters such as ΔH, ΔS, and ΔG were computed from the experimental data. These values show that the adsorption is endothermic and spontaneous. The positive value of ΔS° indicates increasing of randomness at the solid/liquid interface during the adsorption of metal ions on AC.     

Removal of Crystal Violet Dye from Aqueous Solution Using Calcined and Uncalcined Mixed Clay Adsorbents

In this work, calcined and uncalcined mixed clays containing kaolin, ball clay, feldspar, pyrophyllite, and quartz are examined as a potential adsorbent for the removal of crystal violet dye from aqueous solution. These clays are characterized by nitrogen adsorption/desorption isotherms, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermo gravimetric analysis (TGA). The kinetics and thermodynamic parameters as well as the effects of the pH, the temperature, and the adsorbent dosage have also been investigated. The experimental results indicate that the Langmuir model expresses the adsorption isotherm better than the Freundlich model. The obtained result showed a tremendous increase in the crystal violet adsorption capacity (1.9 × 10^?3 mol g^?1) after calcination, which is one order greater than that of the uncalcined mixed clay. The mechanism of the adsorption process is elucidated on the basis of experimental data. The percentage removal of crystal violet dye increases with increasing the pH, the temperature, and the adsorbent dosage. The investigation of kinetic studies indicates that the adsorption of crystal violet on calcined and uncalcined mixed clays could be described by the pseudo-second-order model. The negative Δ G ⁰ values obtained from the thermodynamic investigation confirm that the adsorption is spontaneous in nature. The adsorption results suggest that the calcined and uncalcined mixed clays can also be used as low cost alternatives to the expensive activated carbon for the removal of dyes from aqueous solution.