Optimizing Adsorption of 17α-Ethinylestradiol from Water by Magnetic MXene Using Response Surface Methodology and Adsorption Kinetics,Isotherm, and Thermodynamics Studies

Magnetic MXene composite Fe₃O₄@Ti₃C₂ was successfully prepared and employed as 17α-ethinylestradiol (EE2) adsorbent from water solution. The response surface methodology was employed to investigate the interactive effects of adsorption parameters (adsorption time, pH of the solution, initial concentration, and the adsorbent dose) and optimize these parameters for obtaining maximum adsorption efficiency of EE2. The significance of independent variables and their interactions were tested by the analysis of variance (ANOVA) and t-test statistics. Optimization of the process variables for maximum adsorption of EE2 by Fe₃O₄@Ti₃C₂ was performed using the quadratic model. The model predicted maximum adsorption of 97.08% under the optimum conditions of the independent variables (adsorption time 6.7 h, pH of the solution 6.4, initial EE2 concentration 0.98 mg L⁻¹, and the adsorbent dose 88.9 mg L⁻¹) was very close to the experimental value (95.34%). pH showed the highest level of significance with the percent contribution (63.86%) as compared to other factors. The interactive influences of pH and initial concentration on EE2 adsorption efficiency were significant (p < 0.05). The goodness of fit of the model was checked by the coefficient of determination (R²) between the experimental and predicted values of the response variable. The response surface methodology successfully reflects the impact of various factors and optimized the process variables for EE2 adsorption. The kinetic adsorption data for EE2 fitted well with a pseudo-second-order model, while the equilibrium data followed Langmuir isotherms. Thermodynamic analysis indicated that the adsorption was a spontaneous and endothermic process. Therefore, Fe₃O₄@Ti₃C₂ composite present the outstanding capacity to be employed in the remediation of EE2 contaminated wastewaters.     

Optimization of cadmium adsorption from aqueous solutions by functionalized graphene and the reversible magnetic recovery of the adsorbent using response surface methodology

Novel functionalized graphene adsorbent was prepared and characterized using different techniques. The prepared adsorbent was applied for the removal of cadmium ions from aqueous solution. A response surface methodology was used to evaluate the simple and combined effects of the various parameters, including adsorbent dosage, pH, and initial concentration. Under the optimal conditions, the cadmium removal performance of 70% was achieved. A good agreement between experimental and predicted data in this study was observed. The experimental results revealed of cadmium adsorption with high linearity follow Langmuir isotherm model with maximum adsorption capacity of 502 mg g^?1, and the adsorption data fitted well into pseudo‐second order model. Thermodynamic studies showed that adsorption process has exothermic and spontaneous nature. The recommended optimum conditions are: cadmium concentration of 970 mg L^?1, adsorbent dosage of 1 g L^?1, pH of 6.18, and T = 25 °C. The magnetic recovery of the adsorbent was performed using a magnetic surfactant to form a noncovalent magnetic functionalized graphene. After magnetic recovery of the adsorbent both components (adsorbent and magnetic surfactant) were recycled by tuning the surface charges through changing the pH of the solution. Desorption behavior studied using HNO₃ solution indicated that the adsorbent had the potential for reusability.     

Enhanced Adsorption of Sulfonamides by Attapulgite-Doped Biochar Prepared with Calcination

The extensive use of sulfonamides seriously threatens the safety and stability of the ecological environment. Developing green inexpensive and effective adsorbents is critically needed for the elimination of sulfonamides from wastewater. The non-modified biochar exhibited limited adsorption capacity for sulfonamides. In this study, the attapulgite-doped biochar adsorbent (ATP/BC) was produced from attapulgite and rice straw by calcination. Compared with non-modified biochar, the specific surface area of ATP/BC increased by 73.53–131.26%, and the average pore width of ATP/BC decreased 1.77–3.60 nm. The removal rates of sulfadiazine and sulfamethazine by ATP/BC were 98.63% and 98.24%, respectively, at the mass ratio of ATP to rice straw = 1:10, time = 4 h, dosage = 2 g∙L⁻¹, pH = 5, initial concentration = 1 mg∙L⁻¹, and temperature = 20 °C. A pseudo-second-order kinetic model (R² = 0.99) and the Freundlich isothermal model (R² = 0.99) well described the process of sulfonamide adsorption on ATP/BC. Thermodynamic calculations showed that the adsorption behavior of sulfonamides on the ATP/BC was an endothermic (ΔH > 0), random (ΔS > 0), spontaneous reaction (ΔG < 0) that was dominated by chemisorption (−20 kJ∙mol⁻¹ > ΔG). The potential adsorption mechanisms include electrostatic interaction, hydrogen bonding, π–π interaction, and Lewis acid–base interactions. This study provides an optional material to treat sulfonamides in wastewater and groundwater.     

Highly efficient elimination of thorium(IV) from aqueous solution using poly(cyclotriphosphazene-co-melamine) microspheres

Highly crosslinked organic–inorganic hybrid polymer poly(cyclotriphosphazene-co-melamine) microspheres (PZM) were synthesized by a simple method. The microspheres was characterized by FTIR, SEM and EDX. It was applied to eliminate thorium(IV) from aqueous solution under various conditions, i.e., pH, initial concentration, dosage and contact time. The experimental data were well-imitated via the pseudo-second-order kinetic model and its adsorption processes comply with the Langmuir isotherm model. Adsorption thermodynamic studies demonstrated that the adsorption process, in essence, was spontaneous and endothermic. Furthermore, the maximum experimental adsorption capacity was 98.6 mg g^?1 for initial thorium(IV) concentration 50 mg L^?1. When pH?=?0.0, the thorium(IV) removal efficiency reached at 76.9%, which indicates that the adsorbent can also was used in a peracid environment. Adsorption behavior of thorium(IV) onto the microspheres were weakly affected via temperature, implying that adsorption would be done at room temperature.

     

Synthesis of calcium alginate nanoparticles for removal of lead ions from aqueous solutions

Calcium alginate nanoparticles (CANPs) were synthesized to remove lead ion [Pb(??)] as pollutant of environment from aqueous solutions. The produced CANPs were characterized by Fourier transform infrared spectroscopy (FTIR), particle size analysis (PSA) and scanning electron microscope (SEM). Various factors, which affected adsorption efficiency of lead ions by CANPs, such as pH (pH from 1 to 8), initial ions concentration (in the range of 25 to 125 mg L^–1), contact time (varying from 5 to 120 min), and adsorbent dose (50 to 500 mg L^–1), were investigated for determination of optimum experimental conditions. The result of tests showed that the investigated factors had significant effects on adsorption of Pb(??) ions and the maximum adsorption percentage of lead at pH = 6~7, 25 mg L^–1 initial ions concentration, contact time of more than 140 min. and for adsorbent dose at 500 mg L^–1. Also these results demonstrated the effective adsorption of Pb²⁺ ions by synthesized CANPs that occurred due to a high surface area of CANPs and the presence of anionic carboxylate functional groups and allowed effective absorbing and removing Pb(??) ions from aqueous solutions. Thus, these nanoparticles were able to remove over 99% of lead ions from solution.     

Beta-Cyclodextrin-Decorated Magnetic Activated Carbon as a Sorbent for Extraction and Enrichment of Steroid Hormones (Estrone, β-Estradiol,Hydrocortisone and Progesterone) for Liquid Chromatographic Analysis

A β-cyclodextrin-decorated magnetic activated carbon adsorbent was prepared and characterized using various analytical techniques (X-ray diffraction (XRD), scanning electron microscopy–electron diffraction spectroscopy (SEM-EDS) and transmission electron microscopy (TEM)), and the adsorbent was used in the development of a magnetic solid-phase microextraction (MSPE) method for the preconcentration of estrone, β-estradiol, hydrocortisone and progesterone in wastewater and river water samples. This method was optimized using the central composite design in order to determine the experimental parameters affecting the extraction procedure. The quantification of hormones was achieved using high-performance liquid chromatography equipped with a photodiode array detector (HPLC-DAD). Under optimum conditions, the linearity ranged from 0.04 to 300 µg L⁻¹ with a correlation of determinations of 0.9969–0.9991. The limits of detection and quantification were between 0.01–0.03 and 0.033–0.1 µg L⁻¹, with intraday and interday precisions at 1.1–3.4 and 3.2–4.2. The equilibrium data were best described by the Langmuir isotherm model, and high adsorption capacities (217–294 mg g⁻¹) were obtained. The developed procedure demonstrated high potential as an effective technique for use in wastewater samples without significant interferences, and the adsorbent could be reused up to eight times.     

Removal of zinc metal ion (Zn) from its aqueous solution by kaolin clay mineral: A kinetic and equilibrium study

A laboratory batch study has been performed to study the effect of various physic-chemical factors such as initial metal ion concentration, solution pH, and amount of adsorbent, contact time and temperature on the adsorption characteristics of zinc (Zn²⁺) metal ions onto kaolin. It has been found that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn²⁺) on kaolin is a two steps process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intra-particle diffusion in the interior of the adsorbent which has also been confirmed by intra-particle diffusion model. The equilibrium time is found to be in the order of 60 min. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetics among pseudo-first-order and intra-particle diffusion model. The different kinetic parameters including rate constant are determined at different initial metal ion concentration, solution pH, amount of adsorbent and temperature respectively. The equilibrium adsorption results are analyzed by both Langmuir and Freundlich models to determine the mechanistic parameters associated with the adsorption process. The value of separation factor, R_L from Langmuir equation also gives an indication of favorable adsorption. Finally thermodynamic parameters are determined at three different temperatures and it has been found that the adsorption process is exothermic due to negative ΔH° accompanied by decrease in entropy change and Gibbs free energy change (ΔG°).     

Dynamic Adsorption of H2S onto a Goethite-Based Material

The use of adsorption technology to remove H₂S from synthetic gas (H₂S and N₂) using a goethite-based adsorbent was investigated. The influence of the H₂S feed concentration (150–600 mg), the adsorbent dosage (1–4 g), and the gas flow rate (210–540 cm³/min) on the breakthrough curves and H₂S adsorption on the adsorbent at the breakthrough point was investigated. Dynamic column experiments were performed to provide data for the theoretical models and to verify the performance of the system in the adsorption process. The theoretical models used in the present work were found to predict the adsorption breakthrough performance reasonably well.     

Adsorption of Cr(VI) using activated neem leaves: kinetic studies

In the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, R _L, signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0<R _L<1). The adsorption process follows second order kinetics and the corresponding rate constant is found to be 0.00137 g/(mg) (min).     

Phragmites australis (Reed) as an Efficient,Eco-Friendly Adsorbent for Brackish Water Pre-Treatment in Reverse Osmosis: A Kinetic Study

A cost-effective adsorbent was prepared by carbonization of pre-treated Phragmites australis reed at 500 °C. Phragmites australis was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface analyses. XRD of the as-prepared adsorbent exhibited a partially crystalline structure with a specific surface area of 211.6 m²/g and an average pore diameter of 4.2 nm. The biosorption potential of novel biosorbent Phragmites australis reed was investigated with a batch scale and continuous flow study. The study was conducted at different constraints to obtain optimum pH conditions, adsorbent dose, contact time, agitation speed, and initial TDS concentration. In order to analyze the properties of the procedure and determine the amount of sodium removal, Langmuir, Freundlich, and Dubinin–Radushkevich isotherms were tested. The optimal values of contact time, pH, and adsorbent dose were found to be 150 min, 4, and 10 g/L, respectively, with an agitation speed of 300 rpm at room temperature (27 °C). The three tested isotherms show that the adsorption of Na⁺ onto the prepared adsorbent is a hybrid process from physi- and chemisorption. For industrial application, the adsorbent was tested using the adsorbent column technique. Pseudo-first-order, pseudo-second-order, and diffusion models were connected, and it was discovered that the information fit best to the pseudo-second-arrange active model. According to the intraparticle diffusion model, the mechanism goes through four stages before reaching equilibrium. The periodicity test shows that the adsorption ability of Phragmites australis can be recovered by washing with 0.1 M HCl.     

Response surface methodology for optimization of heavy metal removal by magnetic biosorbent made from anaerobic sludge

In this study, optimum conditions for adsorption of heavy metals such as Cu²⁺, Cd²⁺ and Pb²⁺ onto a low-cost, magnetically modified-alkali conditioned anaerobically digested sludge (MADS) adsorbent were obtained. Response Surface Methodology (RSM) incorporating Central Composite Design (CCD) of experiments was applied to optimize four independent process variables. Statistical analysis was executed by ANOVA and the quadratic model developed had regression coefficients of 0.959, 0.957 and 0.95 for Cu²⁺, Cd²⁺ and Pb²⁺, respectively. The independent variables such as pH, time and initial concentration positively influenced adsorption capacity, q_e, whereas the value of q_e decreased with an increase in MADS dosage. Model validation experiments for optimization of adsorption process showed comparable results with predicted values. The adsorption capacity of MADS adsorbent at optimum conditions found through RSM analysis was 29.721 mg L^?1, 28.551 mg L^?1 and 28.601 mg L^?1 for Cu²⁺, Cd²⁺ and Pb²⁺ respectively.     

Solid phase extraction of hexavalent chromium by Mannich base polymer wrapped flower-like layered double hydroxide

In the present work, synthesis of polymer wrapped flower-like MgAl layered double hydroxide was done through condensation of 1,4 phenylenediamine and resorcinol by p-formaldehyde. The nanocomposite was characterised with X-ray diffraction analysis, fourier transform infrared spectroscopy, thermogravimetric analysis and field emission scanning electron microscopy techniques and employed for effective adsorption of Cr(VI) from aqueous solution prior to flame atomic absorption spectrometer determination. Optimum level of effective parameters (pH, reaction time and adsorbent dosage) and their interaction was determined by response surface methodology. To investigate applicability of method for trace heavy metal adsorption, the method was employed for preconcentration of Cr(VI) in water samples. At the optimum conditions, pH = 4.5, shaking time of 15 min and adsorbent dosage of 20 mg, analytical performance of the method was evaluated and results showed that calibration curve is linear in the concentration range of 2–100 μg L^?1. Moreover, limit of detection was 0.22 µg L^?1 and relative standard deviation of six replicate experiments at initial concentration of 0.1 mg L^?1 was 3.3%. Isotherm study showed that Freundlich model can better describe adsorption behaviour as well as the sorbent showed the adsorption capacity of 62.5 mg g^?1. Moreover, thermodynamic study revealed that chromate adsorption was spontaneous and followed the endothermic path. Regeneration of sorbent was performed using 1.0 mol L^?1 of NaOH solution. The sorbent was employed for Cr(VI) determination from food additives and seawater samples.     

Amoxicillin removal from aqueous matrices by sorption with almond shell ashes

The adsorption of the antibiotic amoxicillin at low concentration levels (µg?L^?1 order) from aqueous solution on almond shell ashes has been investigated, either by kinetic or equilibrium assays. The effect of the adsorbent amount, initial concentration of the antibiotic, particle diameter (d_p) and temperature were considered to evaluate the adsorption capacity of the adsorbent. The results showed that amoxicillin sorption is dependent on these four factors. The adsorption process was relatively fast and equilibrium was established in about 12 hours. The optimum parameters for an initial concentration of 450?µg?L^?1 were 50?mg of adsorbent, 303?K and d_p?<?600?µm. A comparison of kinetic models showed that pseudo-second order kinetics provides the best correlation of the experimental data. Isotherm data adjusted better to Langmuir equation, with an adsorption capacity of 2.5?±?0.1?mg?g^?1 at 303?K. The desorption process was also evaluated (maximum efficiency of 5%). Thermodynamic parameters were calculated and the negative value of ΔH⁰ and ΔG⁰ showed that adsorption was exothermic and a spontaneous process.     

Evaluating the Removal of the Antibiotic Cephalexin from Aqueous Solutions Using an Adsorbent Obtained from Palm Oil Fiber

This study aimed to understand the adsorption process of cephalexin (CPX) from aqueous solution by a biochar produced from the fiber residue of palm oil. Scanning electron microscopy, Fourier transform infrared spectroscopy, Boehm titration, and the point of zero charge were used to characterize the morphology and surface functional groups of the adsorbent. Batch tests were carried out to evaluate the effects of the solution pH, temperature, and antibiotic structure. The adsorption behavior followed the Langmuir model and pseudo-second-order model with a maximum CPX adsorption capacity of 57.47 mg g⁻¹. Tests on the thermodynamic behavior suggested that chemisorption occurs with an activation energy of 91.6 kJ mol⁻¹ through a spontaneous endothermic process. Electrostatic interactions and hydrogen bonding represent the most likely adsorption mechanisms, although π–π interactions also appear to contribute. Finally, the CPX removal efficiency of the adsorbent was evaluated for synthetic matrices of municipal wastewater and urine. Promising results were obtained, indicating that this adsorbent can potentially be applied to purifying wastewater that contains trace antibiotics.     

Adsorption of uranium (VI) from aqueous solution by tetraphenylimidodiphosphinate

The adsorption of uranium (VI) using tetraphenylimidodiphosphinate (Htpip) was studied. Factors of affecting sorption efficiency have been investigated and results showed the adsorption of uranium (VI) was equilibrium at pH 4.5, time 20 min, adsorbent dosage 0.005 g and initial concentration 50 mg L^?1 reaching 99.86 mg g^?1 of adsorption capacity and 99.86% of removal efficiency. Additionally, the interfering ions studies showed that the adsorbent possessed excellent adsorption selectivity of uranium (VI). The surface morphology of Htpip was investigated by SEM. The adsorption process of uranium (VI) onto Htpip fit the pseudo-second-order kinetic model and the Freundlich isotherm model very well.     

Removal of Reactive Yellow 84 from aqueous solutions by adsorption onto hydroxyapatite

The adsorption of a reactive dye, Reactive Yellow 84, from aqueous solution onto synthesized hydroxyapatite was investigated. The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, absorbent dosage, initial dye concentration, temperature and pH of dye solution. The experimental results show that the amount of dye adsorbed increases with an increase in the amount of hydroxyapatite. The maximum adsorption occurred at the pH value of 5. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. The experimental isotherm data were analyzed using Langmuir isotherm equation. The maximum monolayer adsorption capacity was 50.25 mg/g. The adsorption has a low temperature dependency and was endothermic in nature with an enthalpy of adsorption of 2.17 kJ mol⁻¹.     

Multi‐responses optimization of simultaneous adsorption of methylene blue and malachite green dyes in binary aqueous system onto Ni:FeO(OH)‐NWs‐AC using experimental design: derivative spectrophotometry method

In this research, response surface methodology (RSM) approach using Central Composite Design (CCD) coupled by derivative spectrophotometry method was applied to develop mathematical model and optimize process parameters for simultaneous adsorption of methylene blue (MB) and malachite green (MG) from aqueous solution using Ni:FeO(OH) ‐ NWs‐AC. The optimal conditions to adsorption of MB and MG in binary mixture solution from aqueous solution were found at pH 8.0, MB concentration 20 mg L^‐1, MG concentration 20 mg L^‐1, adsorbent dosage 0.033 g and contact time 40 min. At these conditions, high adsorption efficiency (99.39% and 100.0% for MB and MG, respectively) was achieved. Among experimental equilibrium, Langmuir isotherm model fitted well with maximum monolayer adsorption capacity of 28.6 and 29.8 mg g^‐1 for MB and MG, respectively. The adsorption kinetic data followed pseudo second‐order kinetics for MB and MG dyes.     

Bio-adsorption of dyes from aqueous solution by powdered excess sludge (PES): Kinetic,isotherm, and thermodynamic study

Over 30 million tons of excess sludge is discharged from rural municipal sewage plants annually in China and it is predicted that this figure will keep increasing. However, most of the excess sludge is dumped in landfills except for minor applications. In this study, based on low-cost and recycling waste, the excess sludge was used to adsorb organic dyes from aqueous solution after being directly dewatered. The powdered excess sludge (PES) presents selective adsorption property to cationic dyes. Statics batch adsorption experiments of malachite green (MG) on PES were performed to evaluate the effects of pH, adsorbent dosage, and initial MG concentration. Results revealed that the bio-adsorption equilibrium of MG on the PES can be quickly achieved at 30 min with maximum percentage adsorption of 84% at pH 7, initial dye concentration of 20 mg L^?1, and adsorbent dosage of 1.5 g L^?1. Moreover, the adsorption kinetics follows a pseudo-second-order pathway, and the equilibrium adsorption data could be described well by the Langmuir isotherm equation. Intra-particle diffusion is not the only rate-controlling step in the entire adsorption process. The adsorption process is endothermic, spontaneous, and random. PES can be used as a low-cost adsorbent for refractory cationic organic dye in effluent.     

Biosorption behaviors of uranium (VI) from aqueous solution by sunflower straw and insights of binding mechanism

Uranium (VI)-containing water has been recognized as a potential longer-term radiological health hazard. In this work, the sorptive potential of sunflower straw for U (VI) from aqueous solution was investigated in detail, including the effect of initial solution pH, adsorbent dosage, temperature, contact time and initial U (VI) concentration. A dose of 2.0 g L^?1 of sunflower straw in an initial U (VI) concentration of 20 mg L^?1 with an initial pH of 5.0 and a contact time of 10 h resulted in the maximum U (VI) uptake (about 6.96 mg g^?1) at 298 K. The isotherm adsorption data was modeled best by the nonlinear Langmuir–Freundlich equation. The equilibrium sorption capacity of sunflower straw was observed to be approximately seven times higher than that of coconut-shell activated carbon as 251.52 and 32.37 mg g^?1 under optimal conditions, respectively. The positive enthalpy and negative free energy suggested the endothermic and spontaneous nature of sorption, respectively. The kinetic data conformed successfully to the pseudo-second-order equation. Furthermore, energy dispersive X-ray, fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that U (VI) adsorption onto sunflower straw was predominantly controlled by ion exchange as well as complexation mechanism. The study revealed that sunflower straw could be exploited for uranium remediation of aqueous streams as a promising adsorbent.     

Synthesis and Properties of Surface Molecular Imprinting Adsorbent for Removal of Pb<Superscript>2+</Superscript>

A new chitosan imprinting adsorbent using diatomite as core material was prepared by using the surface molecular imprinting technology with the Pb²⁺ as imprinted ion. The preparation process conditions of the surface molecular imprinting adsorbent were studied. The adsorbent was characterized by using Fourier transform infrared (FTIR) spectrum. FTIR spectrum indicated that it was cross-linked by epichlorohydrin. The new imprinting adsorbent could provide a higher adsorption capacity for Pb²⁺, which reached 139.6 mg/g increasing 32.3% compared with cross-linking chitosan adsorbent (the initial Pb²⁺ concentration of 600 mg/L). The adsorption velocity was quick and the equilibration time of the imprinting adsorbent for Pb²⁺ was 3 h that shortened about 40% compared with cross-linking chitosan adsorbent. It had a more wide pH range of 5–7 than that of cross-linking chitosan adsorbent. The new imprinting adsorbent can be reused for up to ten cycles without loss of adsorption capacity. In the kinetics and isotherm study, the pseudosecond order model and Langmuir model could represent the adsorption process.