Adsorption study for removal of Congo red anionic dye using organo-attapulgite

The organo-attapulgite was prepared using hexadecyltrimethylammonium bromide (HTMAB) with equation equivalent ratio of HTMAB to CEC of attapulgite added and then used as adsorbent for the removal of Congo red (CR) anionic dye from aqueous solution. Adsorbent characterizations were investigated using infrared spectroscopy and X-ray diffraction. The effects of contact time, temperature, pH and initial dye concentration on organo-attapulgite adsorption for CR were investigated. The results show that the amount adsorbed of CR on the organo-attapulgite increase with increasing dye concentration, temperature, and by decreasing pH. The adsorption kinetics was studied with the pseudo-first-order, pseudo-second-order and intraparticle diffusion models, and the rate constants were evaluated. It was found that the adsorption mechanisms in the dye/organo-attapulgite system follow pseudo-second-order kinetics with a significant contribution of film diffusion. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model, and the maximum adsorption capacity was 189.39 mg g⁻¹ for the adsorbent. Kinetic and desorption studies both suggest that chemisorption should be the major mode of CR removal by the organo-attapulgite. The results indicate that HTMAB-modified attapulgite could be employed as low-cost material for the removal of Congo red anionic dye from wastewater.     

Kinetics and adsorption equilibrium in the system aqueous solution of copper ions—granulated activated carbon

The feasibility of using granulated activated carbon for adsorption removal of copper from aqueous solution was studied. The influence of pH, amount of the adsorbent, contact time, and copper concentration on adsorption of copper was investigated. The single-component equilibrium data on copper adsorption were analyzed using the Langmuir, Freundlich, Redlich—Peterson, Temkin, and Toth adsorption isotherms. The adsorption process was followed by two simplified kinetic models including pseudo-first- and pseudo-second-order equations. Kinetic parameters, rate constants, equilibrium sorption capacities, and the corresponding correlation coefficients were calculated and examined for each kinetic model. It was shown that copper adsorption can be described by the pseudo-second-order equation.     

Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks

The mesoporous carbon CMK-3 adsorbent was prepared, characterized, and used for the removal of anionic methyl orange dye from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH, initial dye concentration, and salt concentration. The dye adsorption equilibrium was rapidly attained after 60 min of contact time. Removal of dye in acidic solutions was better than in basic solutions. The adsorption of dye increased with increasing initial dye concentration and salt concentration. The equilibrium data were analyzed by the Langmuir and Freundlich models, which revealed that Langmuir model was more suitable to describe the methyl orange adsorption than Freundlich model. Experimental data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was found that kinetics followed a pseudo-second-order equation. Thermodynamic study showed that the adsorption was a spontaneous and exothermic process.     

Comparative Adsorption of Crystal Violet and Congo Red onto ZnCl2 Activated Carbon

In this study, the adsorption characteristics of crystal violet (CV) and Congo red (CR) dyes from the aqueous solution onto prepared activated carbon were examined. The activated carbon was prepared from wood apple shell by chemical activation with ZnCl₂. The parameters studied were the effect of contact time, initial dyes concentration, and pH of solution. The experimental equilibrium data were analyzed and fitted to Langmuir, Freundlich, and Temkin isotherms. The maximum monolayer adsorption capacities of CV and CR dyes were found to be 142.85 and 83.33 mg per gram of prepared activated carbon at 298 K. The kinetic data obtained at different concentrations were analyzed using pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. Batch adsorption kinetic studies showed that the adsorption of dyes followed pseudo-second-order kinetics and at four different concentrations of both dyes, indicating that chemisorption is the rate-limiting step. Thermodynamic studies reveal that the removal of dyes from aqueous solution onto activated carbon was a spontaneous, feasible, and endothermic process at a temperature greater than standard equilibrium temperature.     

Study of congo red adsorption on the polyaniline and polypyrrole

Polyaniline (PANI) and polypyrrole (PPY) were synthesized via in situ chemical oxidative polymerization and are used as adsorbents for removal of Congo Red (CR) dye from aqueous solution. The effects of various experimental parameters including pH of the solution, contact time, initial concentration, adsorbent dosage, and temperature on adsorption of CR by PANI and PPY were systematically investigated. The experimental results showed that the adsorption efficiency was increased with contact time and adsorbent dosage. The maximum removal efficiency was found after 45 minutes of solid/liquid contact with adsorbent doses of 0.4 and 1.73?g/L for PANI and PPY, respectively. The kinetic data were best fitted by the pseudo-second-order model. The adsorption equilibrium results were well fitted by the Langmuir isotherm model. These results suggest that the PANI and PPY can be used as alternative adsorbents for the treatment of wastewaters containing dyes.     

Adsorption of Pb(II) on a composite material prepared from polystyrene-alumina and activated carbon: Kinetic and thermodynamic studies

The ability of polystyrene-alumina-activated carbon composite as a synthetic adsorbent was investigated for the removal of Pb(II) ions from aqueous solutions. Various physico-chemical parameters such as pH, initial metal ion concentration, adsorbent dosage and contact time were studied. The optimum solution pH for the maximum adsorption of Pb(II) was found to be 4. Kinetic data were best described by pseudo-second-order model. The adsorption process followed both Langmuir and Freundlich adsorption isotherms at 30 °C. Thermodynamic studies indicated that the adsorption was spontaneous and endothermic in nature. Desorption studies were carried out by batch and column operations and it was found that 97% Pb(II) could be recovered by the column process using 0.1 M HCl as eluent.     

Hydroxyapatite-coated carboxymethyl chitosan scaffolds for promoting osteoblast and stem cell differentiation

This study investigated the potential of MIEX resin as the adsorbent for the removal of phosphate from aqueous solutions. In our batch experiments, we studied the effect of some parameters on the removal of phosphate. It was observed that uptake of phosphate was mainly affected by initial phosphate concentration, adsorbent dosage, initial pH of solution, and coexistent anions. The adsorption equilibrium data at 288 K fitted well to Freundlich and Koble-Corrigan isotherm models. The kinetics studies displayed that the adsorption process followed the pseudo-second-order model. The diffusion studies showed that the intra-particle diffusion was not the only rate-controlling step and, the diffusion process of phosphate from solution to MIEX resin was controlled by film diffusion. The thermodynamics parameters were evaluated. The results showed that the adsorption process was spontaneous thermodynamically, endothermic, and entropy driven. These results have established a good potentiality for MIEX resin to be used as an adsorbent for the removal of phosphate from aqueous solutions. This work will deepen our understanding of the adsorptive characteristics of phosphate by MIEX resin and provide a better way to remove phosphate from wastewater.     

Application of polyaniline as an efficient and novel adsorbent for azo dyes removal from textile wastewaters

In this work, application of polyaniline coated onto wood sawdust (PAni/SD) for the removal of methyl orange (MO) as a typical azo dye from aqueous solutions is introduced. The effects of some important parameters such as pH, initial concentration, sorbent dosage, and contact time on the uptake of MO solution were also investigated. In order to get a better comparison, adsorption experiments were also carried out using commercial grade of granulated activated carbon (GAC) and sawdust without coating (SD) at the same time. It was found that PAni/SD can be used to remove azo dyes such as MO from aqueous solutions very efficiently. Experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Kinetic parameters for the adsorption of MO dyes for the selected adsorbents are also reported. In order to study the possibility of desorption for frequent application, chemical regeneration of the used adsorbents was also investigated. Desorption or recovery of dye and regeneration of adsorbent (PAni/SD) was found to be quite possible and of high performance. Application of modified sawdust with polyaniline for the removal of azo dye is very promising for textile wastewater treatment.     

Adsorption of uranium(VI) from aqueous solution by diethylenetriamine-functionalized magnetic chitosan

In this paper, the modified magnetic chitosan resin containing diethylenetriamine functional groups (DETA-MCS) was used for the adsorption of uranium ions from aqueous solutions. The influence of experimental conditions such as contact time, pH value and initial uranium(VI) concentration was studied. The Langmuir, Freundlich, Sips and Dubinin–Radushkevich equations were used to check the fitting of adsorption data to the equilibrium isotherm. The best fit for U(VI) was obtained with the Sips model. Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed the pseudo-second-order kinetic model, indicating that the chemical adsorption was the rate-limiting step. The present results suggest that DETA-MCS is an adsorbent for the efficient removal of uranium(VI) from aqueous solution.     

Removal of nickel ions by adsorption on nano-bentonite: Equilibrium,kinetics, and thermodynamics

Nano-bentonite was used as an adsorbent to remove nickel ions from aqueous solutions. Experimental investigation was carried out to identify the effect of pH, contact time, initial concentration, and adsorbent dose of Ni(II). Equilibrium data were described by and fitted to Langmuir, Freundlich, and Dubinin–Radushkevich models. Results showed that the optimum conditions for the removal of the Ni(II) are initial concentration 100 mg/L, adsorbent dose 0.5 g, and pH 6. Surface morphology and functionality of nano-bentonite were characterized by SEM and FTIR. The kinetics data were more accurately described by pseudo-second-order model. The intra-particle diffusion model gave multi-linear curves, so more than one step controlled the adsorption process. Nano-bentonite removed nickel with maximum adsorption capacity of 39.06 mg/g (30°C, pH) and thermodynamic data indicated that adsorption reaction is spontaneous and of an endothermic nature.     

Biosorption of lead from aqueous solution by seed powder of Strychnos potatorum L.

In the present study, Pb(II) removal efficiency of Strychnos potatorum seed powder (SPSP) from aqueous solution has been investigated. Batch mode adsorption experiments have been conducted by varying pH, contact time, adsorbent dose and Pb(II) concentration. Pb(II) removal was pH dependent and found to be maximum at pH 5.0. The maximum removal of Pb(II) was achieved within 360 min. The Lagergren first-order model was less applicable than pseudo-second-order reaction model. The equilibrium adsorption data was fitted to Langmuir and Freundlich adsorption isotherm models to evaluate the model parameters. Both models represented the experimental data satisfactorily. The monolayer adsorption capacities of SPSP as obtained from Langmuir isotherm was found to be 16.420 mg/g. The FTIR study revealed the presence of various functional groups which are responsible for the adsorption process.     

Adsorption of U(VI) from aqueous solution by cross-linked rice straw

Adsorption of U(VI) from aqueous solution by cross-linked rice straw(CRS) was studied with batch experiments. The adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR). The effect of contact time, initial pH, temperature, adsorbent amount and initial U(VI) concentration was investigated. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) adsorption isotherms and two kinetic models of pseudo-first-order and pseudo-second-order were used to describe the adsorption process. The result showed that the adsorption process was highly pH dependent and the favorable initial pH was 5.0. The adsorption process was rapid within first 60 min and equilibrium reached at 100 min. The adsorption process could be well defined by the Langmuir isotherm and pseudo-second-order equation, which indicated that the chemical adsorption was the rate-limiting step. The thermodynamic parameters (?H°, ?S°, ?G°) of the adsorption system were also calculated. The negative value of ?H° and ?G° indicated that the reaction was endothermic and spontaneous in nature. All the above suggested that CRS has considerable potential for the removal of U(VI) from aqueous solution.     

Adsorption of Copper (II) onto Different Adsorbents

Removal of copper (II) from aqueous solution of CuCl₂·2H₂O by different adsorbents, namely, sissoo sawdust, activated carbon, and fly ash were investigated. Adsorption of copper (II) on sissoo sawdust, activated carbon, and fly ash has been studied using batch techniques. Kinetic and isotherm studies were determined as a function of the solution pH, temperature, contact time, adsorbent dosage, and initial adsorbate concentration. Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The maximum adsorption capacities for copper (II) on sissoo sawdust, activated carbon, and fly ash adsorbents at 30, 40, and 50°C temperatures were found to be 263.2, 166.6, and 142.8; 125.0, 88.49, and 72.46; 69.93, 181.8, and 111.1 mg/g, respectively. The thermodynamics of copper (II) adsorption on sissoo sawdust, activated carbon, and fly ash indicates its spontaneous and endothermic nature. Kinetic studies showed that the adsorption followed a pseudo-second-order kinetic model.     

Adsorptive performance of MWCNTs for simultaneous cationic and anionic dyes removal; kinetics,thermodynamics, and isotherm study

Disposal of contaminated wastewater causes many serious problems especially when it gets mixed with the ground and seawater. It is, therefore, important to apply any remedial action to eradicate dangerous pollutants from the aqueous effluents and to avoid exposure of this wastewater to aquatic life. The research results discussed herein deal with the removal of Rhodamine B (RhB) and Congo Red (CR) dye from wastewater by using multi-walled carbon nanotubes (MWCNTs) as an adsorbent. Different factors like solid dosage, initial pH and concentration, time, and temperature were studied to understand the behavior and mechanism of adsorption. The maximum adsorption capacity in case of a single component system was found to be 302 mg/g and 300 mg/g for Congo Red and Rhodamine B, respectively. Moreover, the mechanism of adsorption was best described by a pseudo-second-order kinetic model. Thermodynamic parameters showed that adsorption of CR and RhB was exothermic when these were removed from a single dye system. However, the overall process became endothermic for concurrent removal of both dyes from the solution. The research results showed that the MWCNTs could successfully be utilized to remove the dye from the industrial wastewater.     

Removal of uranium from aqueous solution by using activated palm kernel shell carbon: adsorption equilibrium and kinetics

Activated palm kernel shell carbon (APKSC) was used to remove U(VI) from aqueous solutions in a batch system. The adsorption kinetics, isotherms, and effects of various parameters, such as temperature, contact time, solution pH, adsorbent dosage, and initial U(VI) concentration on the U(VI) adsorption process were studied. Equilibrium was reached after 120 min in the range of studied U(VI) concentrations and temperatures. U(VI) uptake was insignificantly affected by temperature, but was highly pH dependent, and the optimum pH for removal was 5.5. U(VI) removal efficiency increased with the increasing adsorbent dosage. U(VI) sorption capacity increased with increasing initial U(VI) concentration; any further increases in initial U(VI) concentration above a certain point caused insignificant changes in U(VI) sorption capacity. Isotherm data could be described by the Langmuir isotherm model with a maximum U(VI) adsorption capacity of 51.81 mg/g. Kinetic data were fitted to pseudo-first-order and pseudo-second-order equations, which suggested that the U(VI) adsorption onto APKSC was better reproduced by the pseudo-second-order model rather than pseudo-first-order model. Our results indicated that APKSC might be used as a cheap adsorbent in the treatment of uranium-containing wastewater.     

Synthesis, characterization, thermodynamic and kinetic investigations on uranium (VI) adsorption using organic-inorganic composites: Zirconyl-molybdopyrophosphate-tributyl phosphate

Zirconyl-molybdopyrophosphate-tributyl phosphate (ZMPP-TBP) was a novel organic-inorganic composite adsorbent prepared by co-precipitation method and used in the adsorption of uranium from aqueous solution in batch adsorption experiments. The as-obtained product was characterized using SEM, energy dispersive X-ray spectroscopy (EDX), XRD and BET-N₂ adsorption measurements. The study had been conducted to investigate the effects of solution pH, temperature, contact time, initial concentration and coexisting ions. A maximum removal of 99.31% was observed for an initial concentration 5 mg/L, at pH 6.0 and an adsorbent dose of 1.0 g/L. The isothermal data were fitted with both Langmuir and Freundlich equations, but the data fitted the former better than the latter. According to the evaluation using the Langmuir equation, the maximum adsorption capacity of uranium (VI) was 196.08 mg/g at 293 K and pH 6.0. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the kinetic data, and the pseudo-second-order kinetic model was better. The thermodynamic parameter ΔG was calculated, the negative ΔG values of uranium (VI) at different temperature showed that the adsorption process was spontaneous. The good reusability of ZMPP-TBP also indicated that the ZMPP-TBP was a very promising adsorbent for uranium adsorption from aqueous solution.     

Enhanced Removal of Cu(II) Ions from Aqueous Solution by Poorly Crystalline Hydroxyapatite Nanoparticles

Poorly crystalline and well-dispersed hydroxyapatite (HAP) nanoparticles were synthesized and used as novel adsorbents for the removal of Cu(II) from aqueous solution. Various factors affecting the adsorption such as adsorbent crystallinity, pH, adsorbent dosage, contact time, temperature, competing cations, and the presence of humic acid were investigated in detail. Results showed that the HAP calcined at lower temperature was poorly crystalline and had better adsorption capacity for Cu(II) than those calcined at higher temperature. Cu(II) removal was increased with increases of pH, adsorbent dosage, temperature, and the presence of humic acid, but decreased as the existence of competing divalent cations. Kinetic studies showed that pseudo-second-order kinetic model better described the adsorption process. Equilibrium data were best described by Langmuir model, and the estimated maximum adsorption capacity of poorly crystalline HAP was 41.80 mg/g at 313 K, displaying higher efficiency for Cu(II) removal than many previously reported adsorbents. Thermodynamics studied revealed that the adsorption of Cu(II) by poorly crystalline HAP was spontaneous, endothermic, and entropy-increasing in nature. This study showed that poorly crystalline HAP could be used as an efficient adsorbent material for the removal of Cu(II) from aqueous solution.     

Adsorption of Pb(II) and Ni(II) From Aqueous Solution by a High-Capacity Industrial Sewage Sludge-Based Adsorbent

In the present study, adsorption of Ni(II) and Pb(II) from aqueous solution was investigated using activated carbon synthesized with industrial wastewater sludge. The synthesized adsorbent was analyzed using nitrogen adsorption–desorption and Fourier transfer infrared (FTIR) techniques. Batch adsorption mode was used to evaluate the effect of solution pH, contact time, adsorbent dose, initial metal ion concentration, and temperature on the adsorption capacity of the synthesized adsorbent. The kinetic data were analyzed using different kinetic models. The pseudo-second-order equation gave the best fit to the experimental data for both metal ions. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm models. The results showed that the data obtained for the Ni(II) and Pb(II) adsorption are in good agreement with the Langmuir model. The Langmuir mono-layer maximum adsorption capacities for Ni(II) and Pb(II) ions were estimated to be 74.06 and 88.76 mg g^?1 at 25°C, respectively. In addition, the thermodynamic studies proved that the adsorption process of both metals could be considered endothermic.     

Environment-friendly bio-materials based on cotton-carbon aerogel for strontium removal from aqueous solution

Cotton carbon aerogel was prepared and used as a new water-insoluble adsorbent to remove strontium from aqueous solution. A comprehensive study on adsorption of strontium by cotton carbon aerogel was conducted regarding the effects of initial pH, temperature, initial strontium concentration, and contact time. The adsorbent was characterized by SEM. The results of regression analysis indicated that the adsorption process largely depends on the pH and temperature. The optimum pH range for adsorption process is 5–7. The maximum removal efficiency of strontium from aqueous solution was 60.16%. Moreover, cotton carbon aerogel adsorbent has good reusability before the fifth reuse.