Isotherm Constants Research Articles

Metal oxide enhanced microfiltration for the selective removal of Co and Sr ions from nuclear laundry wastewater

The present study investigated the potential use of a hybridized adsorption/microfiltration system for the selective removal of hazardous cobalt and strontium ions from nuclear power plant laundry wastewater, which is essential for managing low-level radioactive wastes. A crystalline silicotitanate (CST) and four different iron oxides were fabricated and used as adsorbents, which had different crystal structures and adsorptive mechanisms, such as ion exchange and surface coordination. CST showed the greatest affinity for Co and Sr ions (e.g., the Freundlich isotherm constant, KF=23.5mg/g and 33.9mg/g, respectively, at pH 7) and its adsorption capacity was independent of solution pH (pH 5–9), whereas the iron oxides removed substantive amounts of Co ions at neutral and alkaline pH levels, but only marginal amounts of strontium. Background species (e.g., K+, Na+, Ca2+, and Mg2+) had no significant impact on the affinities of the adsorbents for Co and Sr ions. The selectivity coefficients of CST for both Co and Sr ions ranged from 3 to 130. CST and ferrihydrite adsorbents were successfully regenerated using NaCl and HCl solutions, respectively, and their post-regeneration adsorption capacities were unchanged without any sign of significant inactivation after multiple adsorption and regeneration cycles. The addition of adsorbents to the microfiltration system enhanced the membrane permeability (>30%), probably because the cobalt species were removed prior to precipitation at the membrane surface. Substantial and stable metal removals (>90% for both Co and Sr) were achieved during 50h of continuous system operations.

Decoration of multi-walled carbon nanotubes (MWCNTs) with different ferrite nanoparticles and its use as an adsorbent

Abstract A simple and inexpensive synthesis route to produce multi-walled carbon nanotubes (MWCNTs) decorated with CoFe2O4 and Co0.5Ni0.5Fe2O4 nanoparticles using a simplified hydrothermal precipitation is reported. Transmission electron microscopy and X-ray diffraction confirm the formation of 14.9 nm CoFe2O4 and 26 nm Co0.5Ni0.5Fe2O4 nanoparticles on MWCNTs surface. The prepared composite was used for methyl green adsorption. The effects of various parameters, such as temperature, initial dye concentration, and composite dosage, were investigated. Experimental results have shown that the amount of adsorbed dye increased with increasing initial dye concentration, composite dosage, and temperature. The adsorption kinetic data were analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. It was found that the pseudo-second-order kinetic model was the most appropriate model in describing the adsorption kinetics. The adsorption isotherms of methyl green onto MWCNTs decorated with CoFe2O4 and Co0.5Ni0.5Fe2O4 nanoparticles were determined at 298, 313, and 323 K. Equilibrium data were fitted to the Langmuir and the Freundlich isotherm models, then the isotherm constants were determined. The equilibrium data were best represented by the Langmuir isotherm model. Thermodynamic parameters such as changes in the free energy of adsorption, enthalpy, entropy, and activation energy were calculated.

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 (>1271m2g−1) and low pore size (<35Å) and average particle size lower than 50Å 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 19.0mgg−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 10mgL−1) and B mixture solution (25mgL−1 of SY and 10mgL−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.

ADSORPTIVE TREATMENT OF CYANIDE-BEARING WASTEWATER: A PROSPECT FOR SUGAR INDUSTRY WASTE

The biosorption of cyanide ions from aqueous solution by bagasse was studied in a batch adsorption system with pH, contact time, cyanide ion concentration, metal ion concentration, and adsorbent dosage as variables. XRD, FT-IR spectroscopy, CHN, proximate, ultimate, and TG/DTG thermal analyses were used for the characterization of bagasse. The biosorption capacities and rates of biosorption of cyanide ions onto bagasse were evaluated. The Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Biosorption isothermal data were interpreted by the Langmuir model followed by the Freundlich model with maximum adsorption capacity of 98% of cyanide ion on bagasse. The kinetic experimental data were properly correlated with the first- and second-order kinetic model.

Comparison Study of the Adsorption of Copper Ions By Activated Carbon and A Locally Collected Bentonite

In this study, a locally collected bentonite and activated carbon (AC) synthesized from spent lubricant oils by chemical treatment were used as new non conventional and low cost adsorbents for the copper (Cu+2) ions adsorption in a batch mode at various initial concentrations and different temperatures. Systematic studies on Cu+2 ions adsorption equilibrium and kinetics by both adsorbents were carried out. The investigation were performed at different initial concentrations of Cu+2 ions (10, 20, 30, 40, 50, 60 mg/L), contact time (10-90 min), and temperatures (25-55 °C). Depending on the results of temperature effect, thermodynamic parameters (ΔG°, ΔH and ΔS°) were estimated from two sources. First; from the adsorption distribution constant (Kd) which is represented by the ratio between the adsorbed and remained Cu+2 ions in solution at equilibrium and second, from Freundlich isotherm constant (Kf). Comparable results are obtained. Freundlich and Langmuir isotherm models were applied to the adsorption data of the studied systems. The results obtained indicated that, the clay adsorbs Cu+2 ions more intense than AC, with higher maximum adsorption capacity. Langmuir isotherm is better fitted to the adsorption data of the study system than Freundlich isotherm. The effect of contact time data of Cu+2 ions adsorption onto clay, conducted at various initial concentrations were applied to pseudo first and second order kinetic models. The rate of adsorption was found to conform to pseudo second order kinetic with good correlation (R2>0.99) and consistent values of the experimental (qe(exp)) and calculated (qe(cal)) adsorption capacities. The initial rate of adsorption was found to increase with initial concentration, where as the over all rate constant exhibited opposite variation. The employed adsorbents might be successfully used for the removal of other heavy metal ions from industrial wastewater.

EXPERIMENTAL STUDIES AND DESIGN OF BATCH REACTOR FOR SORPTION OF Cu(II) IONS ONTO POLYMERIZED TAMARIND FRUIT SHELL CATION EXCHANGER

A new cation exchanger (PGTFS-SP-COOH) was prepared from tamarind fruit shell (TFS) and used for the uptake of Cu(II) ions from aqueous solutions by batch mode. Cu(II) adsorption was dependent on the pH of the medium, and maximum adsorption was observed at an initial pH of 6.0. The equilibrium was attained within 2 h. The adsorption kinetics was best described by pseudo-second-order kinetic model. The effect of adsorbent dose, particle size, and ionic strength of the medium on Cu(II) adsorption was studied. The equilibrium data tend to fit the Sips isotherm model, and the model parameters were regressed to yield mathematical relations connecting isotherm constants such as , K s , and m S with the particle size of the adsorbent. PGTFS-SP-COOH was evaluated for its efficiency in Cu(II) recovery from electroplating wastewater. The reusability of the spent adsorbent for several cycles was demonstrated using 0.2 M HCl solution. The results prove that PGTFS-SP-COOH can be used as a potential environmentally benign adsorbent for Cu(II) removal from aqueous solutions.

Synthesis, characterization and application of goethite mineral as an adsorbent

In the present work goethite mineral synthesized using chemical precipitation method was evaluated for Cu(II) and Cd(II) uptake. The mineral was characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy for their morphological and structural features. Using this goethite, the adsorption of Cu(II) and Cd(II) was studied in synthetic waste water in a batch system by varying pH in the range 3–5, varying the initial concentration (5–25mgL−1), varying the adsorbent dose (0.2–1.0g) and effect of temperature (293–313K). The adsorption percentage of the Cu(II) and Cd(II) were found to be 98.00% and 87.50% respectively. The adsorption kinetic data were analyzed using pseudo-first-order and pseudo-second-order models. It was found that the pseudo-second-order kinetic model was the most appropriate model, describing the adsorption kinetics. Adsorption isotherms of Cu(II) and Cd(II) onto goethite were determined at 293K, 303K and 313K with 10mgL−1 as initial concentration of Cu(II) and Cd(II) respectively. The equilibrium isotherm data were analyzed using Freundlich, Langmuir and Temkin isotherm models and isotherm constants were determined. The linear transformed model provided the highest R2 regression coefficient with the Freundlich isotherm than other isotherms. Thermodynamic parameters such as change in the Gibb's free energy of adsorption (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated. The negative values of ΔG° indicate that the adsorption process was spontaneous in nature and the positive value of ΔH° indicates the endothermic nature of Cu(II) and Cd(II) adsorption onto goethite.

Competitive adsorption of Direct Yellow 12 and Reactive Orange 12 on ZnS:Mn nanoparticles loaded on activated carbon as novel adsorbent

A novel adsorbent (ZnS:Mn nanoparticles loaded on activated carbon) was made. The competitive adsorption of Direct Yellow 12 (DY12) and Reactive Orange 12 (RO12) dyes in binary mixture onto this adsorbent was studied. DY12 and RO12 with severe spectra overlapping were chosen and analyzed simultaneously with high accuracy by first order derivative spectrophotometric method in binary solutions. The effect of multi-solute systems on the adsorption capacity was investigated. Because of the specific characteristics of ZnS:Mn-NP-AC was found to be efficient for the removal of the dyes studied. The adsorption capacities were investigated and described by the mono- and multi-component Langmuir and Freundlich isotherm models for both single and binary dye solutions. The isotherm constants for DY12 and RO12 were calculated. For single solution of DY12 and RO12 dyes, the adsorption capacities of the applied adsorbent were found to be 90.05mg/g and 94.52mg/g, respectively. Equilibrium uptake amounts of DY12 and RO12 in binary solution onto the applied adsorbent were found to be considerably decreasing with increasing the concentrations of the other dye. A better agreement between the adsorption equilibrium data and mono-component Langmuir isotherm model was found. However, at concentrations within moderate ranges, the extended Freundlich isotherm model satisfactorily predicted multi-component adsorption equilibrium data. An endothermic and a spontaneous nature for the adsorption of the dyes studied were shown from thermodynamic parameters.

Approaches to increasing the sensitivity of the determination of phenolic compounds using chitosan-based solid-phase optical biosensors

It was shown that the sensitivity of the determination of phenolic compounds using chitosan-based optical biosensors could be increased by varying the sorption conditions of products of enzymatic oxidation of phenolic compounds. Sorption isotherms of oxidation products of phenolic compounds by a chitosan film were studied according to Langmuir and Freundlich models. Quantitative characteristics of the sortpion process, such as maximum sorption capacity, the Langmuir isotherm constants, and the Gibbs free energy were determined.

Removal of malathion from aqueous solution using De-Acidite FF-IP resin and determination by UPLC–MS/MS: Equilibrium, kinetics and thermodynamics studies

In the present study, De-Acidite FF-IP resin was used to remove a highly toxic and persistent organophosphorus pesticide (malathion) from the aqueous solution. Batch experiments were performed as a function of various experimental parameters such as effect of pH (2–10), contact time (10–120min), resin dose (0.05–0.5g), initial malathion concentration (0.5–2.5µgmL−1) and temperature (25–65°C). The concentration of malathion was determined using a sensitive, selective and rapid ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method. The uptake rate of malathion on De-Acidite FF-IP resin was rapid and equilibrium established within 40min. Kinetics studies showed better applicability for pseudo-second-order model. The equilibrium data was fitted to Langmuir and Freundlich isotherm models and the isotherm constants were calculated for malathion. The values of thermodynamic parameters (ΔG0, ΔH0 and ΔS0) were computed from the Van't Hoff plot of lnKC vs. 1/T which showed that the adsorption of malathion was feasible, endothermic and spontaneous. The regeneration studies were carried out which demonstrated a decrease in the recovery of malathion from 95% to 68% after five consecutive cycles. Breakthrough and exhaustive capacities of malathion were found to be 1.25mgg−1 and 3.5mgg−1, respectively.

Removal of nitrate by synthetic organosilicas and organoclay: Kinetic and isotherm studies

In this work, octadecyltrimethylammonium (ODTMA) chloride was used to prepare MCM-41 at room temperature while cetyltrimethylammonium (CTMA) bromide was used to synthesize MCM-48 and layered organosilica material under hydrothermal conditions. These synthetic organosilica materials, in addition to a commercially available organoclay, Cloisite®10A, were characterized by powder X-ray diffraction (XRD) and tested with the occluded surfactant as sorbents for nitrate. The Langmuir and Freundlich models were applied with determination of the equilibrium isotherms and the isotherm constants. Adsorption kinetics data were tested using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The results showed that the highest nitrate uptake capacities were achieved with Cloisite®10A (0.359±0.003meq/g) followed by a layered organosilica (0.287±0.008meq/g). MCM-48and MCM-41 silica adsorbed 0.096±0.002 and 0.157±0.005meq/g of nitrate, respectively. Kinetics studies showed that the adsorption followed pseudo-second-order kinetic model. Layered organosilica gave a good fit to the Langmuir model among all the studied samples with correlation coefficient (R2) close to unity (0.99).

Sorption of Pb2+ from Aqueous Solution unto Modified Rice Husk: Isotherms Studies

Investigation of the sorption potential of rice husk, an agricultural waste, as an adsorbent was carried out. The rice husk was modified with orthophosphoric acid and was used for adsorption of lead (II) ions (Pb2+) from aqueous solution. Physicochemical properties of the modified rice husk were determined. Equilibrium sorption data were confirmed with Langmuir, Freundlich and Temkin adsorption isotherms. On the basis of adsorption isotherm graphs, R2 values were determined to be 0.995, 0.916, and 0.797 for Langmuir, Temkin, and Freundlich isotherms, respectively, indicating that the data fitted well into the adsorption isotherms, but Langmuir isotherm is a better model. The maximum monolayer coverage from Langmuir studies, Qmax=138.89 mg/g, Langmuir isotherm constant, KL=0.699 L/mg, and the separation factor, RL=1.41×10−2 at 100 mg/L of lead(II) ions indicating that the sorption process, was favourable. The suitability of modified rice husk as an adsorbent for the removal of lead ions from aqueous solution and its potential for pollution control is established.

Application of isotherm, kinetic and thermodynamic models for the adsorption of nitrate ions on graphene from aqueous solution

Graphene was prepared by a liquid phase exfoliation and was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy and zeta potential measurements. A systematic study of the adsorption process was performed by varying pH, ionic strength, and temperature. The experimental results showed that graphene is an excellent nitrate (NO3−) adsorbent with an adsorption capacity of up to 89.97mg/g at an initial NO3− concentration of 500mg/L and temperature of 303K. The adsorption kinetics was modeled by first- and second-order rate models. The rate constants for all these kinetic models were calculated, and the results indicate that the second order kinetics model was well suitable to model the kinetic adsorption of NO3−. The Langmuir and Freundlich models were used to describe the equilibrium isotherms and the isotherm constants were determined. Equilibrium data were well described by the typical Langmuir adsorption isotherm. Thermodynamic studies revealed that the adsorption reaction was spontaneous and was an endothermic process.

Chromium Adsorption by Three Yeast Strains Isolated from Sediments in Morocco

Biosorption is an effective method to remove heavy metals from wastewater. In this work, Biosorption of Cr(VI) has been investigated by live and dead cells of three yeasts species: Cyberlindnera fabianii, Wickerhamomyces anomalus and Candida tropicalis. Sorption experiments were conducted in aqueous solutions at various pH conditions. Cr(VI) adsorption was highly pH dependent and the results indicated that the most effective pH range was found to be between 2 and 4 for the three species. Adsorption isotherms were modeled with the Langmuir and Freundlich equations and isotherm constants were calculated. The adsorption capacity calculated from Langmuir isotherm was 18.9 mg, 28.14 mg and 29.1 mg Cr(VI) g−1 Cr(VI) g−1 for C. fabianii, W. anomalus and C. tropicalis, respectively. The results suggest that the three yeasts could be used as effective adsorbents for the removal of Cr(VI) ions from contaminated sites.

Enzyme-based glucose delivery: a possible tool for biosorbent preparation for heavy metal removal from polluted environments

This study was performed to examine the influence of the controlled glucose supply technology, EnBase(®) Flo, on growth and heavy metals uptake capacity of two Bacillus strains isolated from food industry wastewater. Bacillus sp. growth on EnBase Flo (mineral salt complex medium containing starch-derived polymer as substrate) was examined in 24 deep well plates, controlling the glucose amount release by adding two amyloglucosidase concentrations (3 and 6 UL(-1)). Adsorption of the heavy metals Zn(2+), Cd(2+) and Pb(2+) was assessed in a single component system using synthetic metal solutions and as a function of the initial concentration of adsorbate, equilibrium time and removal efficiency. The Langmuir and Freundlich adsorption models were used for the mathematical description of the biosorption equilibrium and isotherm constants. A pseudo second-order model was applied to describe the uptake rate for two isolates. The EnBase(®) Flo technology improved the cells growth over ten times after 24 h of fed-batch cultivation. The EnBase(®) Flo technology improved the Cd(2+) and Pb(2+) uptake capacity of the bacterial strains by approximately 55 and 44 %, respectively. The biosorption of each metal was fairly rapid (within 30 min), which could be an advantage for large scale treatment of contaminated sites. This initial study may be a basis for future developments to apply EnBase Flo for the biomass production used further as biosorbent for heavy metal removal from aqueous solutions.

Removal of acid yellow-17 dye from aqueous solution using eco-friendly biosorbent

Dyes are usually present in trace quantities in the treated effluents of many industries. The effectiveness of adsorption for dye removal from wastewaters has made it an ideal alternative to other expensive treatment methods. Biosorption of acid yellow (AY17), a monoazo acid dye, was investigated using Typha angustata L. as biosorbent in a batch system with respect to initial pH, temperature, initial dye concentration, biosorbent dosage, and contact time. The biomass exhibited the highest dye uptake capacity at 303K, initial pH value of 2, the initial dye concentration of 150mg/L, biosorbent dosage of 0.5g and contact time of 40min. The extent of dye removal increased with increase in time, biosorbent dosage and decreased with increase in temperature. The equilibrium sorption capacity of the biomass increased on increasing the initial dye concentration up to 150mg/L and then started decreasing in the studied concentration up to 600mg/L. The experimental results have shown that the acidic pH favors the biosorption. Langmuir and Freundlich adsorption model is used for the mathematical description of the biosorption equilibrium and isotherm constants are evaluated at different temperatures. Equilibrium data fitted very well to the Freundlich model in the studied concentration (25‐600mg/L) and temperature (303‐323K) ranges. The pseudo-first- and second-order kinetic models were also applied to the experimental data. The results indicated that the dye uptake process followed the pseudosecond-order rate expression and the adsorption rate constants increased with increasing concentration. The adsorption results in this study indicated that all the adsorbents were attractive candidates for removing acidic dyes from dye wastewater.

Adsorptive removal of cadmium (II) using P. oceanica biomass: effect of NaCl concentration on equilibrium and kinetic parameters

In this study, biosorption of cadmium (II) from saline solutions by Posidonia oceanica (L.), a marine biomass, was studied as a function of pH, initial cadmium (II) and NaCl concentrations in a batch system. The sorbent exhibited the maximal cadmium (II) uptake at pH 6 in the absence and in the presence of increasing concentration of NaCl. Equilibrium uptake increased with the cadmium (II) concentration up to 250 mg/L and diminished considerably in the presence of increasing concentrations of salt up to 50 g/L. At 100 mg/L, initial cadmium (II) concentration, P. oceanica biosorbed 15.69 mg/g of cadmium (II) without salt medium. When NaCl concentration was raised to 50 g/L, this value dropped to 6.87 mg/g of cadmium (II) at the same conditions resulting in 56.21% decrease in biosorption capacity. The equilibrium sorption data were analysed by using Freundlich, Langmuir and Redlich–peterson models. Langmuir was the most suitable adsorption model for describing the biosorption equilibrium data of cadmium (II) both individually and in salt-containing medium. Pseudo-second-order kinetic model also fitted well to both systems, viz. cadmium (II) and cadmium (II) + NaCl. Isotherm constants varied due to the level of salt were expressed as a function of initial NaCl concentration.

Preparation and Characterization of Modified Cellulose for Adsorption of Cd(II), Hg(II), and Acid Fuchsin from Aqueous Solutions

A novel absorbent composed of cellulose with thiosemicarbazide was prepared for the sorption of heavy metal ions and organic dyes from aqueous solutions. Cellulose was grafted with the vinyl monomer glycidyl methacrylate using ceric ammonium nitrate as initiator and was further functionalized with thiosemicarbazide to afford chemically modified cellulose (CMC). CMC was characterized with FTIR, SEM, TGA, XPS, and XRD. In this work, CMC was used for the adsorption of Hg(II), Cd(II), and acid fuchsin (AF) from their aqueous solutions. The effects of varying parameters such as pH, contact time, temperature, and initial concentration on the adsorption process were examined. According to the obtained results, the adsorption processes could be described by a pseudo-second-order kinetic model. Langmuir, Freundlich, and Temkin adsorption isotherm models were applied to describe isotherm constants. Cd(II) and AF equilibrium data agreed well with the Langmuir isotherm model, while Hg(II) equilibrium data exhibited a...

Removal of hexavalent chromium from aqueous solution by barium ion cross-linked alginate beads

Barium ion cross-linked alginate beads have shown great affinity to toxic hexavalent chromium ions in aqueous solution, in contrast to the traditionally used cal- cium alginate beads. Our adsorption experiments were carried out by the batch contact method. The optimal pH for removal was found to be pH 4. The equilibrium was established in 4 h, and the removal efficiency of chro- mium(VI) was found to be 95 %. The adsorption data were applied to Langmuir, Freundlich, Dubinin-Redushkevich (D-R), and Temkin isotherm equations. Both Langmuir and Freundlich isotherm constants indicated a favorable adsorption. The value of mean sorption energy calculated from D-R isoterm indicates that the adsorption is essen- tially physical. The high maximum chromium(VI) adsorption capacity was determined from the Langmuir isotherm as 36.5 mg/g dry alginate beads. The chro- mium(VI) adsorption data were analyzed using several kinetic models such as the pseudo-first-order, pseudo-sec- ond-order, intraparticle diffusion, and Elovich models, and the rate constants were quantified. Our study suggests that barium alginate beads can be used as cost-effective and efficient adsorbents for the removal of chromium(VI) from contaminated waters.

Strategically designed porous polysilicate acid/graphene composites with wide pore size for methylene blue removal

Polysilicate acid/graphene composites were synthesized in the oil phase using a facile one-pot method. Si-based groups, Cl, and residual oxygenated functional groups effectively reduced the irreversible aggregation process. Stacking sheets with these groups tend to form wide pores. These pores were not formed in the graphene sheets, but they were formed instead by sheet aggregation. Adsorption data indicated that the porosity of the material had more remarkable influence on the adsorption capacity than high surface area. The adsorption kinetics was modeled using first- and second-order rates and the Elovich and Weber–Morris intraparticle diffusion models. The adsorption process follows the second-order rate and Elovich model. The Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models were applied to describe the equilibrium isotherms and determine the isotherm constants. Methylene blue adsorption preferably fits the Langmuir adsorption isotherm model, which suggests a monolayer coverage of adsorbed molecules.