Equilibrium and kinetic studies for removal of malachite green from aqueous solution by a low cost activated carbon

A low cost activated carbon was synthesized from coconut coir and was applied for the removal of malachite green (MG) from its aqueous solutions. Characterization of the adsorbent was carried out and BET surface area of the adsorbent was found to be 205.27 m²/g. The process of removal of MG was better governed by second order kinetics with a rate constant of 0.21 g mg^?1 min^?1 at 323 K. The coefficient of mass transfer was found to be 3.70 × 10^?5 cm s^?1. The value of ΔG° was found to be negative indicating feasibility and spontaneity of the adsorption process.     

Study of competitive adsorption of malachite green and sunset yellow dyes on cadmium hydroxide nanowires loaded on activated carbon

Cadmium hydroxide nanowires loaded on activated carbon (Cd(OH)₂-NW-AC) was applied for removal of malachite green (MG) and sunset yellow (SY) in single and binary component systems. This novel material was characterized and identified by different techniques such as Brunauer, Emmett and Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis. Unique properties such as high surface area (>1271 m² g⁻¹) and low pore size (<35 Å) and average particle size lower than 50 Å in addition to high reactive atom and presence of various functional groups make it possible for efficient removal of these two dyes. In the single component system in this study, maximum adsorption capacity of 80.6 for SY and 19.0 mg g⁻¹ for MG at 25 °C was reported. The Langmuir model had very well fit with the experimental data (R² > 0.996). A better agreement between the adsorption equilibrium data and mono-component Langmuir isotherm model was found. The kinetics of adsorption for single and binary mixture solutions at different initial dye concentrations were evaluated by the nonlinear first-order and second-order models. The second-order kinetic model had very well fit with the dynamical adsorption behavior of a single dye for lower and higher initial dye concentrations. SY and MG without spectra overlapping were chosen and analyzed with high accuracy in binary solutions. The effect of multi-solute systems on the adsorption capacity was investigated. The isotherm constants for SY and MG were also calculated in binary component systems at concentrations within moderate ranges, the Langmuir isotherm model satisfactorily predicted multi-component adsorption equilibrium data. The competitive adsorption favored the SY in the A mixture solution (both SY and MG concentration at 10 mg L⁻¹) and B mixture solution (25 mg L⁻¹ of SY and 10 mg L⁻¹ of MG). Also, in both cases, kinetic data was fairly described by two-step diffusion model. An endothermic and spontaneous nature for the adsorption of the dyes studied were shown from thermodynamic parameters in single and binary component systems.     

Artificial neural network – Imperialist competitive algorithm based optimization for removal of sunset yellow using Zn(OH)2 nanoparticles-activated carbon

The effects of variables were modeled using multiple linear regressions (MLR) and artificial neural network (ANN) and the variables were optimized by imperialist competitive algorithm (ICA). Comparison of the results obtained using introduced models indicated the ANN model is better than the MLR model for the prediction of sunset yellow removal using zinc oxide nanoparticles-activated carbon. The coefficient of determination (R²) and mean squared error (MSE) for the optimal ANN model with 9 neurons at hidden layer were obtained to be 0.9782 and 0.0013, respectively. A nano-scale adsorbents namely as Zn(OH)₂ was synthesized and subsequently loaded with AC. Then, this new material efficiently applied for sunset yellow (SY) removal, from aqueous solutions in batch process. Firstly the adsorbent were characterized and identified by XRD, FESEM and BET. Unique properties such as high surface area (>1308 m²/g) and low pore size (<20 Å) and average particle size lower than 45.8 Å in addition to intrinsic properties of nano-scale material high surface reactive atom and the presence of various functional groups make it possible for efficient removal of (SY). The effects of adsorbent dose, pH, initial SY concentration and contact time were optimized. Fitting the experimental data of adsorption over time in the range of 30 min to various models show the suitability of second-order and intraparticle diffusion models for the prediction of removal rate and their parameters (R² > 0.999). The factors controlling adsorption process were also calculated and discussed. Equilibrium data fitted well with the Langmuir model at all amount of adsorbent with maximum adsorption capacity of 158.7 mg g⁻¹.     

Chitosan-modified palygorskite: Preparation,characterization and reactive dye removal

Chitosan-modified palygorskite (CTS-modified PA) was prepared by surface grafting of PA with chitosan, and the CTS-modified PA was used as an effective adsorbent for the removal of reactive dye. The effects of various experimental parameters such as initial pH, adsorbent dosage, contact time and initial dye concentration on adsorption were investigated. The adsorption behavior of CTS-modified PA showed that the adsorption kinetics and isotherms were in good agreement with the pseudo-second-order equation and the Langmuir equation, and the maximum adsorption capacity of CTS-modified PA calculated by the Langmuir model was 71.38 mg g^− 1, which was much higher than that of the unmodified PA (6.3 mg g^− 1).     

Palladium,silver, and zinc oxide nanoparticles loaded on activated carbon as adsorbent for removal of bromophenol red from aqueous solution

The adsorption of bromophenol red (BPR) onto three adsorbents including palladium, silver and zinc oxide nanoparticles loaded on activated carbon (Pd-NP-AC, Ag-NP-AC and ZnO-NP-AC) in a batch system has been studied and the influence of various parameters has been optimized. The influence of time on removal of BPR on all adsorbent was investigated and experimental data were analyzed by four kinetic models including pseudo first and second-order, Elovich and the intraparticle diffusion equations. Following fitting the experimental data to these models, the respective parameters of each model such as rate constants, equilibrium adsorption capacities and correlation coefficients for each model were investigated and based on well known criterion their applicability was judged. It was seen that the adsorption of BPR onto all adsorbents sufficiently described by the pseudo second-order equation in addition to interparticle diffusion model. The adsorption of BPR on all adsorbent was investigated at various concentration of dye and the experimental equilibrium data were analyzed and fitted to the Langmuir, Freundlich, Tempkin, Dubinin, and Radushkevich equations. A single stage in batch process was efficient and suitable for all adsorbents using the Langmuir isotherm with maximum adsorption of 143 mg g^?1 for Pd-NP-AC, 250 mg g^?1 for Ag-NP-AC and 200 mg g^?1 for ZnO-NR-AC. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° for Pd-NP-AC adsorbent were calculated.     

Artificial neural network optimization for removal of hazardous dye Eosin Y from aqueous solution using Co2O3-NP-AC: Isotherm and kinetics study

The present research is focused on the synthesis and characterization of cobalt (III) oxide (Co₂O₃) nanoparticle loaded on activated carbon to prepare an outstanding sorbent for the removal of eosin Y (EY) as hazardous dye from aqueous solution. The sorbent was identified by SEM and XRD analysis. The effect of solution pH, adsorbent dosage (0.005–0.02 g), contact time (0.5–30 min) and initial eosin Y concentration (30–80 mg L⁻¹) on the adsorption process was investigated and modeled by artificial neural network. Following optimization of variables, the experimental equilibrium data was analysis by Langmuir, Freundlich, Tempkin and D–R isothermal models and explored that the data well presented by Langmuir model with a maximum adsorption capacity of 555.56 mg g⁻¹ at 25 °C. Kinetic studies at various adsorbent dosage and initial EY concentrations show that high removal percentage (>90%) was achieved within 15 min of the start of every experiment at most conditions. The adsorption of EY follows the pseudo-second-order rate equation in addition to intraparticle diffusion model. The experimental data were applied to train the multilayer feed forward neural network with three inputs and one output with different algorithms and different numbers of neurons in the hidden layer. The minimum mean squared error (MSE) of 1.49e − 04 and determination coefficient of (R²) 0.9991.     

Optimised activation of bentonite for toluene adsorption

Acid-activation of bentonite was optimised to prepare an effective adsorbent of toluene. The activated bentonite was obtained with a specific surface area of 195 m²/g, a pore volume of about 0.46 cm³/g and a most frequent pore size of 62 Å. Compared to the raw bentonite, the adsorption of toluene onto acid-activated bentonite was increased from 66 mg/g to 197 mg/g. Vapor–solid adsorption isotherms of toluene were measured at 120 °C, 140 °C, 160 °C and 182 °C using an inverse gas chromatography. The experimental data were correlated with different adsorption isotherm models such as Langmuir, Freundlich, Langmuir–Freundlich and Toth models. Only the Langmuir–Freundlich equation provided good fit to the experimental data.     

Ionic liquid based periodic mesoporous organosilica: An efficient support for removal of sunset yellow from aqueous solutions under ultrasonic conditions

The efficiency of an ionic liquid based periodic mesoporous organosilica (PMO-IL) in the removal of sunset yellow from aqueous solutions using ultrasonic assisted adsorption method was investigated. The PMO-IL was first characterized by nitrogen sorption and TEM techniques. The optimized conditions (0.013 g of adsorbent, 32 mg L⁻¹ of sunset yellow at 2 min of sonication time and pH 7) were obtained by central composite design (CCD). Fitting the equilibrium data show the suitability of the Langmuir model with second-order equation to control the kinetic of the adsorption process and good reusability (5 cycles) of PMO-IL for adsorption of dye.     

Optimizing adsorption of arsenic(III) by NH2-MCM-41 using response surface methodology

Response surface methodology (RSM) was used to optimize process parameters for arsenic (As(III)) removal from aqueous solution using amine-functionalized MCM-41 (NH₂-MCM-41). Four independent variables such as pH, initial metal concentration, temperature and adsorbent dosage were investigated. The optimal conditions to remove As(III) by NH₂-MCM-41 was found to be pH 5.62, initial As(III) concentration 5.00 mg/L, temperature 20 °C and NH₂-MCM-41 dosage 5.00 g/L. XRD, FTIR and SEM analyses testified to the obvious change of the surface morphology and the presence of metal on the sorbent after adsorption.     

Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

In this study, bio-chars were evaluated as a potential adsorbent for the removal of Cr (VI) ions from aqueous solutions. The effects of some important parameters including initial pH (1.5–7), adsorbent dose (0.2–5 g/L), contact time (5–900 min) and initial Cr (VI) ion concentration (5–75 mg/L) were tested on the removal of Cr (VI) ions from aqueous solution in batch experiments. Maximum adsorption capacities of the tested bio-chars under the certain experimental conditions determined as optimal were 3.53 mg/g for NCBC, 3.97 mg/g for NZCBC and 6.08 mg/g for ACBC, respectively. Results of the kinetic and isotherm modeling studies revealed that the adsorption data fitted well with a pseudo-second order and Langmuir model. In among the tested bio-chars, the bio-char (ACBC) was largely equivalent to activated carbon: AC (9.97 mg/g) in terms of adsorption capacity. All results indicated that the bio-chars had higher adsorption capacity than some chars and activated carbons reported previously, and also that these bio-chars could be used successfully as low-cost adsorbents for the removal of chromium ions from aqueous solutions under the tested experimental conditions.     

Activated carbon/CoFe2O4 composites: Facile synthesis,magnetic performance and their potential application for the removal of malachite green from water

Activated carbon/CoFe₂O₄ composite (AC/CFO) was synthesized by a simple one-step refluxing route and was used as adsorbent for the removal of malachite green (MG) dye from water. The structure, morphology and magnetic properties of as-prepared composite were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The results indicated that CoFe₂O₄ particles deposited on the surface of activated carbon in the composite were uniform with the particle size in the range of 14–20 nm. The composite adsorbents exhibited a clearly hysteretic behavior under applied magnetic field, which allowed their magnetic separation from water. Batch experiments were carried out to investigate adsorption isotherms and kinetics of MG onto the composite. The experimental data fitted well with the Langmuir model with a monolayer adsorption capacity of 89.29 mg g^?1. The adsorption kinetics was found to follow pseudo-second-order kinetic model. It was indicated that the as-prepared composite could be used as a promising and effective adsorbent for the removal of MG from water.     

Principal component analysis-artificial neural network and genetic algorithm optimization for removal of reactive orange 12 by copper sulfide nanoparticles-activated carbon

In this study a green approach described for the synthesis of copper sulfide nanoparticles loaded on activated carbon (CuS-NP-AC) and usability of it for the removal of reactive orange 12 (RO-12). This material was characterized using instruments such as scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of variables were optimized using Principal component analysis-artificial neural network (PCA-ANN). Fitting the experimental equilibrium data shows the suitability of the Langmuir isotherm. The small amount of proposed adsorbent (0.017 g) is applicable for successful removal of RO-12 (RE > 95%) in short time (31.09 min) with high adsorption capacity (96.9 mg g⁻¹)     

Kinetic,isotherm and thermodynamic study of nitrate adsorption from aqueous solution using modified rice husk

In this article, we prepared anionic sorbent using rice husk (RC). Anionic rice husk (ARC) structural characteristics and adsorption properties for nitrate removal from aqueous solution were investigated. The sorption of NO₃^? by batch method is carried out. The optimum conditions of sorption were found to be: a sorbent dose of 0.4 g in 100 mL of NO₃^? solution, contact time of 90 min, pH = 7. In optimum condition, removal efficiency was 94.3% for the NO₃^?. The nitrate adsorption process was well described by the pseudo-second-order kinetic model, and the experimental isotherm data fitted well with the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters such as Gibbs free energy change, enthalpy change and entropy change were calculated and the results showed that the adsorption of nitrate on ARC was spontaneous and exothermic in nature. The effect of other anions were also studied and was found that the anions reduced the nitrate adsorption in the order of carbonate > chloride > phosphate > sulphate. ARC was used for the removal of NO₃^? from real wastewater (urban wastewater) that high performance of adsorbent was considerable.     

Synthesis of an affinity adsorbent based on silica gel and its application in endotoxin removal

An affinity media for endotoxin removal based on silica gel was prepared by activation with silane coupling agent and subsequent conjugation with histidine (His) as a ligand. The influence of pore size and particle dimension of the silica gel and the grafting conditions such as reaction temperature and concentration of His in solution on the grafting yield of His were studied by means of IR, thermogravimetric analysis and elemental analysis. The results show that the silica gel with a particle size of 200 μm and a pore size of about 12 nm was a good carrier material for the preparation of the affinity adsorbent. Under the optimal conditions, histidine was covalently immobilized on silica gel at about 20 mg/g, with a corresponding maximum endotoxin adsorption capacity q_m in contaminated water of about 1.2 mg/g and an apparent dissociation constant K_d of about 1350 μg/L. The adsorbent had little nonspecific adsorption from a protein-containing solution.     

Random forest model for removal of bromophenol blue using activated carbon obtained from Astragalus bisulcatus tree

In this research, activated carbon (AC) simply was prepared from a local, abundant tree in south of Iran. The AC with low cost and toxicity is a good candidate for bromophenol blue (BPB) removal from aqueous media. The AC with nano scale pore diameter is applicable for this dye removal following optimization of the influence of various parameters including contact time, pH, initial dye concentration and amount of adsorbent. Subsequently, experimental data was analyzed by four kinetic models including pseudo first and second-order, Elovich and the intraparticle diffusion equations and subsequently their respective parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients was investigated and based on well known criterion their applicability was judged. The result shows that adsorption of BPB onto proposed adsorbent at all conditions such as versatile adsorbent dosages and initial BPB concentrations sufficiently described by the combination of the pseudo second-order equation and interparticle diffusion model. It was found that equilibrium rate of the BPB adsorption at various adsorbent dosage well fitted by Langmuir. Investigation of experimental result by two approaches (multiple linear regressions (MLR) and random forest (RF)) models show that RF is a powerful tool for prediction of BPB adsorption by activated carbon obtained from Astragalus bisulcatus tree. The optimal tuning parameters for RF model are obtained based on the n_tree = 100, m_try = 2. For the training data set, the MSE values of 0.0006 and the coefficient of determination (R²) values of 0.9895 for RF model and the MSE value of 0.0104 and the R² value of 0.823 for MLR model are obtained.     

Highly ordered macroporous γ-alumina prepared by a modified sol-gel method with a PMMA microsphere template for enhanced Pb2+, Ni2+ and Cd2+ removal

The adsorption performance of three-dimensionally ordered macroporous (3DOM) γ-alumina was investigated for enhanced Pb²⁺, Ni²⁺ and Cd²⁺ removal. The synthesis was based on a modified sol-gel method using a colloidal crystal template (CCT) method based on PMMA microspheres. The structure was characterized by means of FTIR spectroscopy and XRD analysis. The three-dimensional structure was examined by scanning electron microscopy, which enabled image analysis that showed significantly low shrinkage (8.77%) after calcination at 800 °C. The influential parameters, including contact time and adsorbent dosage, were investigated in a batch adsorption study. The adsorption equilibrium and kinetic data were found to be in agreement with the Freundlich isotherm for Pb²⁺ removal and the Dubinin-Radushkevich isotherm for Ni²⁺ and Cd²⁺ removal. The time-dependent adsorption was best described by a pseudo-second-order kinetic model and the Weber-Morris model. High adsorption capacities: 95.39, 23.32 and 25.39 mg/g were obtained for Pb²⁺, Cd²⁺ and Ni²⁺ removal at 45 °C, respectively. The existence of interconnected macroporous and mesoporous structures of highly ordered γ-alumina enabled a higher adsorption capacity in comparison with literature data for others alumina-based adsorbents.     

Comparison of removal of bromothymol blue from aqueous solution by multiwalled carbon nanotube and Zn(OH)2 nanoparticles loaded on activated carbon: A thermodynamic study

In this research Zn(OH)₂ nanoparticles loaded on activated carbon (Zn(OH)₂-NPs-AC) as novel adsorbent and raw multiwalled carbon nanotube (MWCNT) were applied for efficient removal of bromothymol blue (BTB). Both adsorbent has been characterized with different techniques such and SEM, XRD and UV–vis spectrometry. Their size was less than 100 nm. In the removal process the variables are pH, temperature, concentration of BTB, amount of adsorbent and contact time that their influence on removal of BTB was optimized using one at a time approach in batch procedure. Adsorptions of BTB on bath adsorbent depend highly on pH. Following the investigation of temperature effect, the thermodynamic parameters including change in entropy, enthalpy and free Gibbs energy were calculated. For both adsorbents, positive value of enthalpy and negative value of ΔG⁰ show routine feasibility of adsorption using energy. At optimum value of variables, the removal processes onto both adsorbent have high adsorption capacity for best fitting model Langmuir, i.e. for Zn(OH)2-NP-AC and 150 mg/g for PAC. The adsorption rates were well explained with pseudo second order and interparticle diffusion model. It is expected that there could an increase in the number of reactive sites due to their expected high volume, pore size and high surface area.     

Heavy metals uptake from aqueous solutions and industrial wastewaters by humic acid-immobilized polymer/bentonite composite: Kinetics and equilibrium modeling

This study explored the feasibility of utilizing a novel adsorbent, humic acid-immobilized-amine-modified polyacrylamide/bentonite composite (HA-Am-PAA-B) for the adsorption of Cu(II), Zn(II) and Co(II) ions from aqueous solutions. The FTIR and XRD analyses were done to characterize the adsorbent material. The effects of pH, contact time, initial adsorbate concentration, ionic strength and adsorbent dose on adsorption of metal ions were investigated using batch adsorption experiments. The optimum pH for Cu(II), Zn(II) and Co(II) adsorption was observed at 5.0, 9.0 and 8.0, respectively. The mechanism for the removal of metal ions by HA-Am-PAA-B was based on ion exchange and complexation reactions. Metal removal by HA-Am-PAA-B followed a pseudo-second-order kinetics and equilibrium was achieved within 120 min. The suitability of Langmuir, Freundlich and Dubinin-Radushkevich adsorption models to the equilibrium data was investigated. The adsorption was well described by the Langmuir isotherm model. The maximum monolayer adsorption capacity was 106.2, 96.1 and 52.9 mg g^?1 for Cu(II), Zn(II) and Co(II) ions, respectively, at 30 °C. The efficiency of HA-Am-PAA-B in removing metal ions from different industry wastewaters was tested. Adsorbed metal ions were desorbed effectively (97.7 for Cu(II), 98.5 for Zn(II) and 99.2% for Co(II)) by 0.1 M HCl. The reusability of the HA-Am-PAA-B for several cycles was also demonstrated.     

Copper oxide nanoblades as novel adsorbent material for cadmium removal

A wide variety of new materials and their hybrids have emerged as novel adsorbents to help resolve contamination of heavy metals in water resources. In this research, copper oxide (CuO) nanoblades were synthesized in high yield using a facile chemical method. These synthesized CuO nanoblades were characterized for their topological, morphological, structural, optical, and chemical behavior using a variety of techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infra red (FTIR) spectrometry, Raman spectroscopy, and UV–Visible spectroscopy. The in-depth investigation confirmed that the blade-shaped synthesized nanomaterial was in pure CuO form. The synthesized nanoblades were 3–4 nm thick and 70–200 nm in length with consistent dots of 3 nm at one side on every blade. The performance of these nanoblades was further evaluated and optimized for cadmium (Cd) removal in relation to the parameters solution pH, contact time, and adsorbent/adsorbate dose. Their cytotoxicity was also assessed for probable utilization at the industrial/commercial level. CuO nanoblades showed a maximum adsorption capacity of 192.30 mg/g for Cd (adsorbent dose: 0.5 mg/ml) and exhibited a best fit for Langmuir isotherm with R² value of 0.99 and b =0.007. This is the first report for chemical synthesis of copper oxide nanoblades followed by their utilization for removal of cadmium ions with such high adsorption capacity.     

Nano-TiO2 modified with 2-mercaptobenzimidazole as an efficient adsorbent for removal of Ag(I) from aqueous solutions

Nano-TiO₂ was modified with 2-mercaptobenzimidazole via surfactant activation and used as an adsorbent for the removal of Ag(I) under optimum conditions. The adsorbent was characterized using powder X-ray diffraction and FT-IR spectroscopy. The equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherm models. Langmuir isotherm describes the adsorption data better than Freundlich isotherm and Temkin. Kinetic studies showed that the pseudo second order kinetic model fits the adsorption kinetic processes well. Maximum adsorption capacity for Ag(I) was 128.2 mg g⁻¹ of nano-TiO₂. The method was successfully applied to the removal of silver from radiology film processing wastewater samples.