Removal of Reactive Orange 12 from aqueous solutions by adsorption on tin sulfide nanoparticle loaded on activated carbon

In the present study, tin sulfide nanoparticle loaded on activated carbon simply was synthesized and characterized using different techniques such as SEM, XRD and UV-analysis. Then, this new efficient adsorbent was used for Reactive Orange 12 (RO-12) adsorption. To improve the efficiency of adsorption effect of variables viz. pH, mass of SnS-NP-AC, initial dye concentration, contact time and temperature were examined and optimized. The adsorption mechanism and rate of processes was investigated by analyzing time dependency data to various conventional kinetic models such as pseudo-first-order and second order, Elovich and intra-particle diffusion models. Among them it was found that adsorption followed the pseudo-second-order kinetic model with good agreement between the equilibrium experimental and expected adsorption data. High fitting with the Langmuir models shows heterogeneous surface and mono-layer nature adsorption of Reactive Orange 12 on the SnS-NP-AC. Thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), activation energy (E_a), of sticking probability (S^*) and Gibb's free energy changes (ΔG) were also calculated. It was seen that the proposed adsorbent has high tendency and adsorption capacity for RO-12 adsorption in a feasible, spontaneous and endothermic fashion.     

Removal of methylene blue from aqueous solutions by adsorption onto chemically activated halloysite nanotubes

This study examines the adsorption behavior of methylene blue (MB) from aqueous solutions onto chemically activated halloysite nanotubes. Adsorption of MB depends greatly on the adsorbent dose, pH, initial concentration, temperature and contact time. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms and the Langmuir model agrees very well with experimental data. The maximum adsorption capacities for MB ranged from 91.32 to 103.63 mg·g⁻¹ between 298 and 318 K. A comparison of kinetic models applied to the adsorption data was evaluated for pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion equation. The results showed the adsorption process was well described by the pseudo-second-order and intra-particle diffusion mode. Thermodynamic parameters suggest that the adsorption is spontaneous and endothermic. The obtained results indicated that the product had the potential to be utilized as low-cost and effective alternative for dye removal in wastewater.     

Removal of arsenic from aqueous solution using polyaniline/rice husk nanocomposite

The present study deals with the adsorption of arsenic ions from aqueous solution on polyaniline/rice husk (PAn/RH) nanocomposite. Batch studies were performed to evaluate the influence of various experimental parameters like pH, adsorbent dosage, contact time and the effect of temperature. Optimum conditions for arsenic removal were found to be pH 10, adsorbent dosage of 10 g/L and equilibrium time 30 minutes. Adsorption of arsenic followed pseudo-second-order kinetics. The equilibrium adsorption isotherm was better described by Freundlich adsorption isotherm model. The adsorption capacity (q _max ) of PAn/RH for arsenic ions in terms of monolayer adsorption was 34.48 mg/g. The change of entropy (ΔS⁰) and enthalpy (ΔH⁰) was estimated at −0.066 kJ/(mol K) and −22.49 kJ/mol, respectively. The negative value of the Gibbs free energy (ΔG⁰) indicates feasible and spontaneous adsorption of arsenic on PAn/RH.     

Adsorption characteristics of methylene blue on poplar leaf in batch mode: Equilibrium,kinetics and thermodynamics

Adsorption characteristics of methylene blue (MB) from aqueous solution on natural poplar leaf were investigated. Batch experiments were carried out to study the effects of initial pH, contact time, adsorbent dosage, and initial MB concentration, salt concentration (Ca²⁺ and Na⁺) as well as temperature on MB adsorption. The optimum condition for adsorption was found at pH 6–9 and adsorbent dosage of 2 g L⁻¹. The equilibration time was 240 min. The salt concentration had a negative effect on MB removal. The equilibrium data were analyzed with Langmuir, Freundlich and Koble-Corrigan isotherm models using nonlinear regression method. The adsorption process was more effectively described by Langmuir isotherm based on the values of the correlation coefficient R² and chi-square statistic x². The maximum monolayer adsorption capacity of poplar leaf from the Langmuir model was 135.35 mg g⁻¹ at 293 K. The pseudo second order equation provided a better fit to experimental data in the kinetic studies. Intraparticle diffusion was involved in adsorption process, but it was not the only rate-controlling step. Thermodynamic quantities such as ΔG, ΔH and ΔS were calculated, indicating that the adsorption process was spontaneous and endothermic. Dye-adsorbent interactions were examined by FTIR and SEM analysis. The FTIR results suggested that there were hydroxyl and carboxyl groups on the surface of poplar leaf, which would make MB adsorption possible. The SEM images showed effective adsorption of MB molecules on the adsorbent surface.     

Adsorption kinetics of 3-hydroxybenzaldehyde on native and activated bentonite

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

Removal of cationic dyes from aqueous solutions by kaolin: Kinetic and equilibrium studies

Experimental investigations were carried out using commercially available kaolin to adsorb two different toxic cationic dyes namely crystal violet and brilliant green from aqueous medium. Kaolin was characterized by performing particle size distribution, BET surface area measurement and XRD analysis. The effects of initial dye concentration, contact time, adsorbent dose, stirring speed, pH, salt concentration and temperature were studied in batch mode. The extent of adsorption was strongly dependent on pH of solution. Free energy of adsorption (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) changes were calculated. Adsorption kinetic was verified by pseudo-first-order, pseudo-second-order and intra-particle-diffusion models. The rate of adsorption of both crystal violet and brilliant green followed the pseudo-second-order model for the dye concentrations studied in the present case. The dye adsorption process was found to be external mass transfer controlled at earlier stage and intra-particle diffusion controlled at later stage. Calculated external mass transfer coefficient showed that crystal violet dye adsorbed faster than brilliant green on kaolin. Adsorption of crystal violet and brilliant green on kaolin followed the Langmuir adsorption isotherm.     

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.     

Cadmium removal from aqueous solutions using biosorbent <Emphasis Type="Italic">Syzygium cumini</Emphasis> leaf powder: Kinetic and equilibrium studies

Syzygium cumini L. leaf powder and Cd(II) loaded samples were characterized using FTIR and SEM techniques. The biosorption of cadmium ions from aqueous solution was studied in a batch adsorption system as a function of pH, contact time, adsorbate, adsorbent, anion and cation concentrations. The biosorption capacities and rates of transfer of cadmium ions onto S. cumini L. were evaluated. The kinetics could be best described by both linear and nonlinear pseudo-second order models. The isothermic data fitted to various models in the order Freundlich>Redlich-Peterson>Langmuir>Temkin. The maximum adsorption capacity of S. cumini L. leaves at room temperature was estimated to be 34.54 mg g⁻¹. The negative values of ΔG⁰ indicated the feasibility of the adsorption process. The endothermic nature was confirmed by the positive value of the enthalpy change (ΔH⁰=3.7 kJ mol⁻¹). The positive value of entropy change (ΔS⁰=16.87 J mol⁻¹ K⁻¹) depicted internal structural changes during the adsorption process.     

Equilibrium and Kinetic Studies on Lithium Adsorption from Geothermal Water by λ-MnO2

The adsorption equilibria of lithium from geothermal water were investigated by using both powdery and granulated forms of λ-MnO₂ derived from spinel-type lithium manganese dioxide. Optimum amounts of adsorbents were 1.0 g adsorbent/L-geothermal water for powdery λ-MnO₂ and 6.0 g adsorbent/L-geothermal water for granulated λ-MnO₂. The adsorbents exhibited the promising adsorption capacities and their adsorption equilibria of lithium agreed well with the Langmuir adsorption isotherm model. The kinetic data of lithium adsorption have been evaluated using pseudo-first-order, pseudo-second-order kinetics models, as well as Elovich kinetic model. In addition, intra-particle diffusion model has been used for evaluating the kinetic data to evaluate the adsorption mechanism. The adsorption kinetic process was attributed to the gradual adsorption stage where intra-particle diffusion was found as the rate-controlling step.     

ADSORPTION OF TOLUENE ON BENTONITES MODIFIED BY DODECYLTRIMETHYLAMMONIUM BROMIDE

The adsorption of toluene was studied by using various types of adsorbents (Na⁺- and Al³⁺-bentonite) modified by dodecyltrimethylammonium bromide (DTAB). The characterization of these new sorbing matrices by XRD and IR indicates that DTAB tallow interacted with bentonite and increased the interlayer spacing of the clay with double-layered formation. Adsorption of toluene on modified bentonites was characterized by linear isotherms with no limitation of adsorption within the concentration range studied, thus indicating a mechanism of adsorption due to partition. Adsorption was fast and favored by a slightly acid medium. Pseudo-first-order, pseudo-second-order, the Elovich equation, and intra-particle diffusion models were used to fit the experimental data. The adsorption kinetic of toluene was described by the pseudo-first order onto DTAB-Na-bent, and pseudo-second order onto DTAB-Al-bent. The intra-particle diffusion process was identified as the main mechanism controlling the rate of toluene adsorption. Thermodynamic parameters such as standard free energy change (ΔG ⁰), the standard enthalpy change (ΔH ⁰), and the standard entropy (ΔS ⁰) were also evaluated. The variation of adsorption energy versus the types of adsorbent suggested a physical adsorption mechanism.     

Kinetics and thermodynamics of water adsorption onto rice husks ash filled polypropene composites during soaking

The kinetics and thermodynamics of water adsorption onto rice husks ash filled polypropene composites during soaking were studied at different temperatures, quantities and nature of fillers. Raw rice husk, “white” and “black” rice husks ash and Aerosil were used as fillers of polypropene. The increase of fillers contents in the polymer matrix was found to result in non-linear increase of the amount of adsorbed water. The highest adsorption capacity showed the samples filled with raw rice husks, while the lowest—those filled with black rice husks ash. The adsorption kinetics was limited by intra-particle diffusion in plane sheet particles. The values of the diffusion coefficients D, diffusion constants D ^o, activation energy of the diffusion process Е _а, changes of free energy ΔG ^≠, enthalpy ΔH ^≠ and entropy ΔS ^≠ for the formation of the activated complex from the reagent were calculated. A compensation effect between D ^o and Е _а was observed. Based on the Van’t Hoff equation, the values of the changes of standard free energy ΔG ^o, enthalpy ΔH ^o and entropy ΔS ^o of water adsorption were calculated. The sorption process is exothermal in nature and accompanied with decrease of the entropy. The values of the sorption coefficient S and permeability coefficient P were calculated at 25 and 90 °C.     

Kinetic and thermodynamic studies of adsorption of Cu2+ and Pb2+ onto amidoximated bacterial cellulose

Removal of Cu²⁺ and Pb²⁺ from aqueous solutions by adsorption onto amidoximated bacterial cellulose (Am-BC) was investigated. The effects of pH, initial concentration, contact time and temperature were studied in batch experiments. The pseudo-first and pseudo-second orders and intraparticle diffusion equation were used to evaluate the kinetic data and the constants were determined. The experimental data fits well to the pseudo-second order kinetic model, which indicates that the chemical adsorption is the rate-determining step, instead of mass transfer. The equilibrium adsorption data were described by the Langmuir, Freundlich, and Temkin isotherms. The Am-BC showed a better fit to the Langmuir isotherm. The separation factor (R _L ) revealed the favorable nature of the isotherm. The thermodynamic parameters (ΔH _ads⁰, ΔS _ads⁰, ΔG _ads⁰) for Cu²⁺ and Pb²⁺ adsorption onto Am-BC were also determined from the temperature dependence. The values of enthalpy and entropy indicated that this process was spontaneous and exothermic. The experimental studies indicate that Am-BC would be a potential effective adsorbent to remove the metal ions from wastewater.     

Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite

The use of low-cost and ecofriendly adsorbents was investigated as an ideal alternative to the current expensive methods of removing dyes from wastewater. Sepiolite was used as an adsorbent for the removal of methyl violet (MV) and methylene blue (MB) from aqueous solutions. The rate of adsorption was investigated under various parameters such as contact time, stirring speed, ionic strength, pH and temperature for the removal of these dyes. Kinetic study showed that the adsorption of dyes on sepiolite was a gradual process. Quasi-equilibrium reached within 3 h. Adsorption rate increased with the increase in ionic strength, pH and temperature. Pseudo-first-order, the Elvoich equation, pseudo-second-order, mass transfer and intra-particle diffusion models were used to fit the experimental data. The sorption kinetics of MV and MB onto sepiolite was described by the pseudo-second-order kinetic equation. Intra-particle diffusion process was identified as the main mechanism controlling the rate of the dye sorption. The diffusion coefficient, D, was found to increase when the ionic strength, pH and temperature were raised. Thermodynamic activation parameters such as ΔG¹, ΔS¹ and ΔH¹ were also calculated.     

Adsorption and desorption of phenylalanine and tryptophane on a nonionic polymeric sorbent

Adsorption equilibrium of two amino acids — Phenylalanine (Phe) and Tryptophane (Trp) — onto nonionic polymeric sorbent, SP850 was studied under various pH values and temperatures. Adsorption equilibrium data of two amino acids on SP850 were fitted well with the Langmuir and Freundlich equations. Thermodynamic parameters such as Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) were evaluated by applying the Van’t Hoff equation. Besides, adsorption kinetic of Phe was also investigated. Adsorption kinetic data were analyzed using the models of pseudo-first-order, pseudo-second-order and intraparticle diffusion. The results indicated that the pseudo-second-order model was more successful in simulating the adsorption kinetic data and the adsorption rate was mainly controlled by the diffusion rate in adsorption process. On the other hand, desorption studies were conducted by employing different organic solvents such as isopropyl alcohol (IPA), ethanol, and methanol. It was found that IPA was the best material for desorbing amino acid on the polymeric sorbent.     

Adsorption behaviors of mercury from aqueous solution using sulfur-impregnated adsorbent developed from coal

Adsorption of mercury from aqueous solution on sulfur-impregnated adsorbent has been studied. Raw coal was mixed with K₂S powder, and then heated at 800-1000 °C for 30 min in nitrogen to produce sulfur-impregnated adsorbent. The sulfur content and specific surface area of the adsorbent were determined, and the ability of the adsorbent to adsorb mercury in aqueous solution was examined. With increasing temperature of sulfur-impregnation, specific surface area of the adsorbent increases, while sulfur content of the adsorbent is almost constant. The adsorbent obtained at 900 °C shows the highest and fastest adsorption of mercury from aqueous solution at 25 °C, and the elution extents of adsorbed mercury are negligible in distilled water and 10% in 0.1 M HCl solution, respectively. Adsorption kinetics was tested for pseudo-first order and pseudo-second order reactions, and the rate constants of adsorption for these kinetic models were calculated. Adsorption experiments demonstrate that the adsorption process corresponds to pseudo-second-order kinetic model than pseudo-first-order model. With increasing temperature of aqueous solution, the kinetics of adsorption becomes faster and the amount of mercury adsorbed on the adsorbent increases. The thermodynamic values, ΔG⁰, ΔH⁰ and ΔS⁰, indicated that adsorption was an endothermic and spontaneous process.     

Alpha-Cypermethrin Pesticide Adsorption on Carbon Aerogel and Xerogel

Carbon aerogel (CA) and xerogel (CX) are proposed for pesticide adsorption as new carbon adsorbent materials. These materials are prepared by polycondensation of resorcinol and formaldehyde in Na₂CO₃ catalysis, followed by a drying step, in CO₂ supercritical or normal conditions to obtain organic aerogel or xerogel, and a pyrolytic step to obtain CA or CX. Adsorption experiments were carried out in batch conditions under magnetic stirring. Adsorbent quantity and grain size, pH, and temperature, and alpha-cypermethrin concentration influence on the adsorption efficiency were considered. The optimum parameters were established to be as follows: 0.01 g adsorbent, d < 0.025 mm, and 318 K. In all cases, CA proved to be more efficient than CX for alpha-cypermethrin removal from water samples. Equilibrium (Langmuir and Freundlich isotherms), kinetics (pseudo-first- and pseudo-second-order, intra-particle diffusion, and liquid film diffusion models) and thermodynamics of the considered adsorption process were discussed in detail. Equilibrium was best described by the Langmuir isotherm, while the kinetic of the process was best described by the pseudo-second-order model. Thermodynamic parameters showed that alpha-cypermethrin adsorption is an endothermic process.     

Equilibria,Kinetics, and Mechanisms for the Adsorption of Four Classes of Phenolic Compounds onto Synthetic Resins

The adsorption of five phenolic compounds of four different classes from aqueous batch solutions onto four styrene-divinylbenzene and acrylic resins (EXA 90, EXA 118, XAD 7, and XAD 16) was investigated regarding their equilibria, kinetics and surface-energy heterogeneity, and mechanisms of adsorption. The experimental equilibrium data were very well fitted to Langmuir and Freundlich models (R ² > 0.900). Three kinetic models (pseudo-first-order, pseudo-second-order, and an intra-particle diffusion model) were suitable for describing the experimental data, the pseudo-second-order kinetic model being the best one (p < 0.001). The adsorption energy values were low (<19.00 kJ/mol), suggesting a physical adsorption process. Driving forces involved in the adsorption of the phenolic compounds onto the resins were hydrogen bonding, π ? π stacking and hydrophobic interactions.     

Polyamine Functionalized Magnetite Nanoparticles as Novel Adsorbents for Cu(II) Removal from Aqueous Solutions

Three novel magnetic adsorbents were synthesized through the immobilization of di-, tri-, and tetraamine onto the surface of silica coated magnetite nanoparticles. The adsorbents were characterized by XRD patterns, FTIR spectroscopy, elemental and thermogravimetric analysis, magnetic measurements, SEM/TEM, EDX spectroscopy, and N₂ adsorption/desorption isotherms. Their capacity to remove copper ions from aqueous solutions was investigated and discussed comparatively. The equilibrium data were analyzed using Langmuir and Freundlich isotherms. The kinetics was evaluated using the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The best interpretation for the equilibrium data was given by the Langmuir isotherm for the tri- and tetraamine functionalized adsorbents, while for the diamine functionalized adsorbent the Freundlich model seemed to be better. The kinetic data were well fitted to the pseudo-second-order model. The overall rate of adsorption was significantly influenced by external mass transfer and intraparticle diffusion. It was observed that the adsorption capacity at room temperature decreased as the length of polyamine chain immobilized on the adsorbent surface increased, the maximum adsorption capacities being 52.3 mg g^?1 for 1,3-diaminopropan functionalized adsorbent, 44.2 mg g^?1 for diethylenetriamine functionalized adsorbent, and 39.2 mg g^?1 for triethylenetetramine functionalized adsorbent. The sorption process proved to be highly dependent of pH. The results of the present work recommend these materials as potential candidates for copper removal from aqueous solutions.     

Hydrothermal Synthesis of Hierarchical Copper Oxide Nanoparticles and its Potential Application as Adsorbent for Pb(II) with High Removal Capacity

In this study, copper oxide nanoparticles with hierarchical morphologies (CuO) have been synthesized via a hydrothermal route. The morphology and microstructure of the as prepared samples were characterized by XRD, SEM, TEM, and SAED. CuO exhibited excellent performance for the removal of Pb(II) from aqueous solution. The effects of initial Pb(II) concentration and contact time on CuO were investigated from batch tests. The results indicate that the equilibrium adsorption data were best fitted by the Langmuir isothermal model, with the maximum adsorption capacity of 1428.5 mgg^?1 which is found to be one of the highest values reported elsewhere in the literature; adsorption kinetics follows the pseudo-second-order kinetic equation and intra-particle diffusion model. A possible adsorption mechanism was predicted by using FTIR, EDX techniques. Large adsorption capacity for heavy metal ion and effective regeneration ability suggesting CuO is a very promising adsorbent for metal ion removal and wastewater cleanup.