Ionic Liquid Modified Resin for the Adsorptive Removal of Dibutyl Phthalate: Equilibrium,Kinetic, and Thermodynamic Studies

This study evaluated the adsorptive properties of dibutyl phthalate (DBP) on room temperature ionic liquid (RTIL) modified XAD‐4 resin. The modified RTIL‐XAD 4 sorbent was characterized by FTIR. Effect of varying experimental conditions such as pH, contact time, temperature, shaking speed, concentrations, and interfering species were investigated by batch adsorption experiments. Adsorption was found to be most favorable at pH 6 within 30 min. Experimental data were evaluated in terms of kinetic, equilibrium, and thermodynamic modeling. Kinetics of the sorption was found to follow pseudo second order rate equation whereas Freundlich and D–R isotherms were the most suitable models to explain sorption phenomenon. Thermodynamically sorption was endothermic, irreversible, and spontaneous in nature.     

Copper Biosorption by Spent Coffee Ground: Equilibrium,Kinetics, and Mechanism

The potential use of spent coffee ground (SCG) for the removal of copper has been investigated as a low‐cost adsorbent for the biosorption of heavy metals. Adsorption batch experiments were conducted to determine isotherms and kinetics. The biosorption equilibrium data were found to fit well the Freundlich model and an experimental maximum biosorption capacity of copper ions 0.214 mmol/g was achieved. The biosorption kinetics of SCG was studied at different adsorbate concentrations (0.1–1.0 mM) and stirring speeds (100–400/min). The results showed an increase in the copper ion uptake with raising the initial metal concentration and the kinetic data followed the pseudo‐second order rate expression. The effect of stirring speed was a significant factor for the external mass transfer resistance at 100/min and coefficients were estimated by the Mathews and Weber model. Biosorption of copper ions onto SCG was observed to be related mainly with the release of calcium and hydrogen ions suggesting that biosorption performance by SCG can be attributed to ion‐exchange mechanism with calcium and hydrogen ions neutralizing the carboxyl and hydroxyl groups of the biomass.     

Adsorption of Metal Ions onto the Chemically Modified Agricultural Waste

This paper discusses about the adsorption of metal ions such as Cu(II), Cd(II), Zn(II), and Ni(II) from aqueous solution by sulfuric acid treated cashew nut shell (STCNS). The adsorption process depends on the solution pH, adsorbent dose, contact time, initial metal ions concentration, and temperature. The adsorption kinetics was relatively fast and equilibrium was reached at 30 min. The adsorption equilibrium follows Langmuir adsorption isotherm model. The maximum adsorption capacity values of the modified cashew nut shell (CNS) for metal ions were 406.6 mg/g for Cu(II), 436.7 mg/g for Cd(II), 455.7 mg/g for Zn(II), and 456.3 mg/g for Ni(II). The thermodynamic study shows the adsorption of metal ions onto the STCNS was spontaneous and exothermic in nature. The kinetics of metal ions adsorption onto the STCNS followed a pseudo‐second‐order kinetic model. The external mass transfer controlled metal ions removal at the earlier stages and intraparticle diffusion at the later stages of adsorption. A Boyd kinetic plot confirms that the external mass transfer was the slowest step involved in the adsorption of metal ions onto the STCNS. A single‐stage batch adsorber was designed using the Langmuir adsorption isotherm equation.     

Removal of COD from Industrial Effluent Containing Indigo Dye Using Adsorption Method by Activated Carbon Cloth: Optimization,Kinetic, and Isotherm Studies

The pollution of underground and surface water streams is a tremendous environmental problem. Adsorption, in which activated carbon (AC) is used as an adsorbent, is one of efficient procedures to remove organic and inorganic pollutants from industrial wastewaters. Activated carbon fiber (ACF), a newly developed form of AC, has high adsorption rate and surface area and can be used for the treatment of industrial wastewaters. In this work, ACF was prepared by physicochemical activation method from kenaf and we studied its ability in the treatment of indigo‐containing wastewater produced from a dying factory. The filtered wastewater was treated via adsorption by ACF, and response surface experimental design method was used to study the effect of ACF dosage, contact time, temperature, and pH of the wastewater on the removal process. ACF dosage of 0.256 g, temperature of 12.5°C, pH 8.5, and contact time of 125 min were optimum treatment conditions. The adsorption process obeys pseudo‐second‐order kinetic and Freundlich isotherm models.     

Malachite Green Removal from Aqueous Solution by the Peel of Cucumis sativa Fruit

This study investigates the potential use of activated carbon prepared from the peel of Cucumis sativa fruit for the removal of malachite green (MG) dye from simulated wastewater. The effects of different system variables, adsorbent dosage, initial dye concentration, pH, and contact time were investigated and optimal experimental conditions were ascertained. The results showed that when the amount of the adsorbent increased, the percentage of dye removal increased accordingly. Optimum pH value for dye adsorption was 6.0. Maximum dye was sequestered within 50 min of the start of every experiment. The adsorption of MG followed the pseudo‐second‐order rate equation and fits the Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Tempkin equations well. The maximum removal of MG was obtained at pH 6 as 99.86% for adsorbent dose of 1 g/50 mL and 25 mg L^?1 initial dye concentration at room temperature. Activated carbon developed from the peel of C. sativa fruit can be an attractive option for dye removal from diluted industrial effluents since test reaction made on simulated dyeing wastewater showed better removal percentage of MG.     

Adsorption Characteristics of Reactive Black 5 from Aqueous Solution onto Chitosan

Adsorption of reactive black 5 (RB5) from aqueous solution onto chitosan was investigated in a batch system. The effects of solution pH, initial dye concentration, and temperature were studied. Adsorption data obtained from different batch experiments were modeled using both pseudo first‐ and second‐order kinetic equations. The equilibrium adsorption data were fitted to the Freundlich, Tempkin, and Langmuir isotherms over a dye concentration range of 45–100 µmol/L. The best results were achieved with the pseudo second‐order kinetic and Langmuir isotherm equilibrium models, respectively. The equilibrium adsorption capacity (q_e) was increased with increasing the initial dye concentration and solution temperature, and decreasing solution pH. The chitosan flakes for the adsorption of the dye was regenerated efficiently through the alkaline solution and was then reused for dye removal. The activation energy (E_a) of sorption kinetics was estimated to be 13.88 kJ/mol. Thermodynamic parameters such as changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) were evaluated by applying the van't Hoff equation. The thermodynamics of reactive dye adsorption by chitosan indicates its spontaneous and endothermic nature.     

Removal of EDTA from Aqueous Solutions Using Activated Carbon Prepared from Rubber Wood Sawdust: Kinetic and Equilibrium Modeling

Adsorptive removal of EDTA (ethylenediaminetetraacetic acid) from aqueous solution was studied using steam pyrolyzed activated carbon. Rubber wood sawdust, obtained from a local timber facility at Kodangavila, Trivandrum, Kerala, India was used as the precursor for the production of the activated carbon. Batch adsorption experiments were employed to monitor and optimize the removal process. The experimental parameters, i. e., solution pH, agitation time, initial EDTA concentration and adsorbent dosage, affecting the adsorption of EDTA onto sawdust activated carbon (SDAC) were optimized. The inner core mechanism for the interaction between EDTA and SDAC, which resulted in the adsorption process, was also discussed. The change in amount of EDTA adsorbed onto SDAC and CAC (commercial activated carbon) was compared over a wide range of pH (2.0–8.0). The maximum removal of EDTA took place in the pH range of 4.0–6.0 for SDAC and 5.0–5.5 for CAC, which demonstrates the effectiveness of the former adsorbent. Kinetic as well as equilibrium studies were performed to determine the rate constant and adsorption capacity, respectively. The adsorption kinetic data was fitted with pseudo‐first‐order kinetics and the equilibrium data was shown to follow the Langmuir isotherm model. These observations explain the formation of a monolayer of EDTA on the surface of SDAC as confirmed by the slow approach to equilibrium after 4 h of contact time. The adsorption capacity of SDAC for the removal of EDTA was 0.526 mmol/g and is seen to be greater than that of CAC and other reported adsorbents (0.193–0.439 mmol/g). Finally, it is clear that the production of steam pyrolyzed activated carbon in the presence of K₂CO₃ greatly enhanced EDTA removal and resulted in a product with possible commercial value for wastewater treatment strategies.     

Adsorption Kinetics of Chloroform from Aqueous Solutions onto Activated Lignite

The lignite coal researched by this study was subjected to a two‐stage activation process performed in the scope of obtaining active carbon from domestic resources. “Activation” and “carbonization” stages were used in the experiments. The modified lignite was produced by impregnating lignite with KOH and washing the activation product with 15% HCl solution after thermal treatment. Increasing KOH dosage also increased the removal efficiency. The variables investigated in adsorption experiments were contact time, initial concentration, pH, and sorbent dosage. Adsorption kinetics was fitted by using the pseudo‐first‐order equation, pseudo‐second‐order equation, and intra‐particle diffusion. Isotherm modeling was carried out using Langmuir, Freundlich, and Dubinin–Radushkevich equations. Selected target compound in this work is common environmental pollutant in waters. A commonly known effect of chloroform is its carcinogenic effect. Therefore, removal of these compounds from water is considerably important. Chloroform removal of 97% for was achieved by the use of Konya region activated lignite.     

Adsorptive Removal of Acid Blue 15: Equilibrium and Kinetic Study

Activated carbons prepared from sunflower seed hull have been used as adsorbents for the removal of acid blue 15 (AB‐15) from aqueous solution. Batch adsorption techniques were performed to evaluate the influences of various experimental parameters, e. g., temperature, adsorbent dosage, pH, initial dye concentration and contact time on the adsorption process. The optimum conditions for AB‐15 removal were found to be pH = 3, adsorbent dosage = 3 g/L and equilibrium time = 4 h at 30°C. The adsorption of AB‐15 onto the adsorbent was found to increase with increasing dosage. It was found from experimental results that the Langmuir isotherm fits the data better than the Freundlich and Temkin isotherms. The maximum adsorption capacity, Q_m (at 30°C) was calculated for SF1, SF2, and SF3 as 75, 125 and 110 mg g^–1 of adsorbent, respectively. It was found that the adsorption follows pseudo‐second order kinetics. The thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were also evaluated. The activated carbons prepared were characterized by FT‐IR, SEM and BET analysis.     

Preparation of Nano‐Lepidocrocite and an Investigation of Its Ability to Remove a Metal Complex Dye

Lepidocrocite (γ‐FeOOH) nanoparticles were synthesized from iron(II) sulfate solution and characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform‐IR (FT‐IR), nitrogen adsorption, and point of zero charge pH (pH_PZC) analyses. TEM, XRD, and FT‐IR analyses proved the synthesis of nano‐lepidocrocite. Surface area and pH_PZC of the synthesized lepidocrocite were 68.1 m² g^?1 and 4.8, respectively. Utilization of the synthesized lepidocrocite in the adsorption of Lanacron brown S‐GL (LBS‐GL) from aqueous solutions was investigated, and the effect of lepidocrocite dosage, pH, temperature, and contact time on this process were optimized and modeled using response surface methodology approach. The lepidocrocite dosage of 0.015 g, pH 3.5, temperature of 38°C, and contact time of 100 min were determined as optimum adsorption conditions. Isotherm and kinetics of the adsorption process were analyzed at the optimum conditions. The equilibrium data were fitted well to the Langmuir isotherm model. The maximum monolayer adsorption capacity was 528.21 mg g^?1. The adsorption process was described by the pseudo‐second‐order kinetic model. Furthermore, the effect of pH on the desorption of LBS‐GL was investigated. High LBS‐GL desorption efficiency was achieved at a high pH value.     

Biosorption of Methylene Blue from Aqueous Solution Using a Bioenergy Forest Waste: Xanthoceras sorbifolia Seed Coat

Xanthoceras sorbifolia seed coat (XSSC), a bioenergy forest waste, was used for the adsorption of methylene blue (MB) from aqueous solutions. The effects of adsorbent dosage, pH, adsorbate concentration and contact time on MB biosorption were studied. The equilibrium adsorption data was analyzed by Langmuir and Freundlich isotherm models. The results indicated that the Langmuir model provided the best correlation with the experimental data. The adsorption capacity of XSSC for MB was determined with the Langmuir model and was found to be 178.6 mg/g at 298 K. The adsorption kinetic data was modeled using the pseudo‐first order, pseudo‐second order, and intraparticle diffusion kinetic equations. It was seen that the pseudo‐second order equation could describe the adsorption kinetics, and intraparticle diffusion was not the sole rate controlling factor. Thermodynamic parameters were also evaluated. Standard Gibbs free energy was spontaneous for all interactions, and the biosorption process exhibited exothermic standard enthalpy values. The results indicated that XSSC is an attractive alternative for removing cationic dyes from wastewater.     

Adsorption of Selenium Using Bagasse Fly Ash

The present work involves the study of Se(IV) adsorption onto bagasse fly ash. The adsorbents were coated with a ferric chloride solution for the effective removal of selenium. The physico‐chemical characterization of the adsorbent was carried out using standard methods, e. g., proximate analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, thermo‐gravimetric analysis and differential thermal analysis. Batch experiments were carried out to determine the effect of various parameters such as adsorbent dose, initial pH, contact time, and temperature on the adsorption process. Results obtained from these studies were analyzed using various kinetic models and isotherms. Se(IV) adsorption onto adsorbent was high at low pH values, and decreased with an increase in initial pH. A temperature study showed that the uptake of Se(IV) was greatest at 293 K, within the temperature range studied. The parameters of pseudo first order, pseudo second order, and Weber‐Morris intra‐particle kinetic models were determined. Equilibrium isotherms were analyzed using Langmuir, Freundlich, and Temkin isotherms. Error analyses were also carried out using hybrid fractional error function and Marquardt's percent standard deviation.     

Removal of Organic Dyes in Environmental Water onto Magnetic‐Sulfonic Graphene Nanocomposite

A magnetic‐sulfonic graphene nanocomposite (G‐SO₃H/Fe₃O₄) was synthesized and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. It was used for removal of three cationic dyes: safranine T (ST), neutral red (NR), victoria blue (VB), and three anionic dyes: methyl orange, brilliant yellow, and alizarin red, from environmental water. The experimental conditions were optimized, including pH, amount of adsorbent, adsorption kinetics, adsorption isotherms, ionic strength, etc. The results show that G‐SO₃H/Fe₃O₄ can adsorb cationic dyes more efficiently and selectively than anionic dyes at pH 6.0. In the first 10 min of adsorption time, more than 93% of the cationic dyes were removed by the sorbent. Adsorption kinetics follow the pseudo‐second‐order kinetic model well. The adsorption isotherm coincided with Langmuir and Freundlich adsorption models. The maximum adsorption capacities of G‐SO₃H/Fe₃O₄ for ST, NR, and VB dyes were 199.3, 216.8, and 200.6 mg g^?1. The adsorbed cationic dyes were eluted by using different pH values of ethanol as the solvent. The established method was simple, sensitive, and rapid, and was suitable for the adsorption of cationic dyes in environmental water.     

Adsorption of Two Taste and Odor Compounds IPMP and IBMP by Granular Activated Carbon in Water

Granular activated carbon (GAC) adsorption of two representative taste and odor (T & O) compounds, 2‐isopropyl‐3‐methoxy pyrazine (IPMP), and 2‐isobutyl‐3‐methoxy pyrazine (IBMP), in drinking water was investigated. Results show that the modified Freundlich equation best fit the experimental data during the adsorption isotherm tests, and the pseudo first‐order kinetics and intra‐particle diffusion kinetics well described the adsorption kinetics pattern. The calculated thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) indicated a spontaneous and endothermic adsorption process. Factors affecting the treatment efficiency were carefully evaluated. Acidic and alkaline conditions both favored GAC adsorption of IPMP and IBMP, especially the former. With the GAC dosage increasing, the first order adsorption rates increased, while the intra‐particle adsorption rates decreased. Within 12 h, 200 mg/L GAC could remove >90% of 150 µg/L IPMP and IBMP via adsorption at pH 3–11. Therefore, GAC is a promising treatment technology to control the T & O compounds associated water pollution.     

Studies on the Removal of Iron from Drinking Water by Electrocoagulation – A Clean Process

The present study describes an electrocoagulation process for the removal of iron from drinking water using magnesium as the anode and galvanized iron as the cathode. Experiments were carried out as a function of pH, temperature and current density. The adsorption capacity was evaluated using both the Langmuir and the Freundlich isotherm models. The results show that the maximum removal efficiency of 98.4% was achieved at a current density of 0.06 A dm^–2, at a pH of 6.0. The adsorption of iron was better explained by fitting the Langmuir adsorption isotherm, which suggests a monolayer coverage of adsorbed molecules. The adsorption process followed a second‐order kinetics model. Temperature studies showed that adsorption was endothermic and spontaneous in nature.     

Adsorption of Basic Dyes from Aqueous Solutions by Depolymerization Products of Post‐Consumer PET Bottles

The purpose of this work is the removal of basic dyes (Safranine T and Brilliant Green) from aqueous media by depolymerization products (DP) obtained from aminoglycolysis of waste poly(ethylene terephthalate) (PET). The surface morphology and physical properties of depolymerization product were also determined. Adsorption behaviors (adsorption capacities, adsorption kinetics and adsorption isotherms) of these samples were realized at room temperature. Then, the amounts of residual dye concentrations were measured using Visible Spectrophotometer at 530 and 618 nm for Safranine T (ST) and Brilliant Green (BG), respectively. All adsorption experiments were carried out for different depolymerization products (DP1, DP2, DP3, and DP4). Adsorption capacities of depolymerization products for both of dyes decrease with following order: DP2 > DP4 > DP1 > DP3. The maximum adsorption capacities for ST and BG onto DP2 sample were found to be 29 and 33 mg g^?1, respectively. In addition, the adsorption kinetic results show that the pseudo‐second‐order kinetic model is more suitable than pseudo‐first‐order model for the adsorption of basic dyes onto DP samples. Adsorption data were evaluated using Langmuir and Freundlich adsorption isotherm models. The results revealed that the adsorption of basic dyes onto DP sample fit very well Langmuir isotherm model. In conclusion, the depolymerization products of post‐consumer PET bottles can be used as low cost adsorbent for the removal of basic dyes from wastewaters.     

Electrocoagulation/Electroflotation Process for Removal of Organics and Microplastics in Laundry Wastewater

In the present research, laundry wastewater treatment is studied using the electrocoagulation/electroflotation process. For the optimization of treatment conditions such as electrode type (Al–Al, Al–Fe, Fe–Fe, and Fe–Al), initial pH (5–9), current (0.54–2.16 A), and application time (15–60 min), response surface methodology is used. Removal efficiencies of chemical oxygen demand (COD), color, anionic surfactant, microplastic, and phosphate are studied. It is determined that the most effective removal is obtained with 2.16 A current, pH 9, and 60 min reaction time using Fe–Al electrode. Here, 91%, 94%, 100%, and 98% removal efficiencies are achieved for COD, surfactant, color, and microplastic, respectively. The operating cost of the combined process is calculated as $1.32 m^?3 for the optimum removal parameters. The adsorption kinetics study shows that the removal follows second‐order kinetics. The laboratory‐scale test results indicate that the electrocoagulation/electroflotation process is feasible for the treatment of laundry wastewater.     

Adsorption Kinetic Modeling of Safranin onto Rice Husk Biomatrix Using Pseudo‐first‐ and Pseudo‐second‐order Kinetic Models: Comparison of Linear and Non‐linear Methods

Batch kinetic studies were carried out for the removal of safranin from aqueous solution using a biomatrix prepared from rice husk. The adsorption kinetic data were modeled using the pseudo‐first‐order and pseudo‐second‐order kinetic equations. The linear and non‐linear forms of these two widely used kinetic models were compared in this study. In order to determine the best‐fitting equation, the coefficient of determination (r²), the sum of the squares of the errors (SSE), sum of the absolute errors (SAE), average relative error (ARE), hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), and the Chi‐squared test (χ²) were used as error analysis methods. Results showed that the non‐linear forms of pseudo‐first‐order and pseudo‐second‐order models were more suitable than the linear forms for fitting the experimental data. Non‐linear method is thus more appropriate for estimating the kinetic parameters and should primarily be used to describe adsorption kinetics.