Fabrication and optimization calix[8]arene-PbS nanoadsorbents for the adsorption of methylene blue: Isotherms,kinetics and thermodynamics studies

The present study aims to determine the adsorption behaviour of methylene blue (MB) dye based on calix[8]arene-modified lead sulphide (PbS) nanoadsorbents under optimal conditions. Response surface methodology (RSM) was executed to evaluate the interactive effect of three factors (adsorbent dosage, contact time, and pH) on the adsorption of MB dye using a central composite design (CCD). The optimised values for adsorbent dosage, contact time, and pH solution were found to be 45.00 mg of calix[8]arene-modified PbS, contact time of 180 min, and pH 6. This study reports the results of batch adsorption experiments, which include the adsorption capacity, kinetics, and isotherm of the MB adsorption process. Pseudo-first order and pseudo-second order were demonstrated for their quality to fit the data. Pseudo-second order was the best in fitting the adsorption data with the higher R² values (R² > 0.928), indicating chemisorption to be the mechanism of adsorption. The Langmuir and Freundlich equilibrium models were employed to determine the isotherm parameters. The equilibrium assessment illustrated that the Langmuir isotherm model fitted well with the adsorption data, and a maximum MB adsorption capacity of 11.90 mg/g was achieved. The characterisation studies with EDX, FESEM, and FTIR indicated a successful synthesis of calix[8]arene-modified PbS.     

Synthesis of NiO coated chitosan-cenosphere buoyant composite for enhanced adsorptive removal of methylene blue

The objective of the present study is to utilize fly ash cenosphere to remove methylene blue (MB) from the water streams. Nickel oxide is a typical semiconductor used as proficient adsorbent material for degradation of dye with environment friendly applications due to its excellent chemical stability and high catalytic activity. The chitosan cenosphere buoyant composite coated with NiO was synthesized with hydrothermal grafting reaction using silane coupling agent and epichlorohydrin as a cross-linking reagent. The batch adsorption experiments were carried out with a cationic dye, methylene blue as a representative organic pollutant to investigate the adsorptive capabilities of the composite as adsorbent. The influence of pH (2-12), initial concentration of dye (50–200 mg/L), temperature (37–47 °C) and contact time (0–24 h) were taken as parameters in the study. On the relative elimination of MB, the effect of time and temperature were investigated. The adsorption kinetics for MB was correlated and found to observe the pseudo-second order kinetic model, whereas the equilibrium adsorption isotherm follows the Langmuir model (R² > 0.99). The results indicate that the floating fly ash cenosphere coated with NiO proved to be more responsive for enhanced degradation of methylene blue.     

Quartzite an efficient adsorbent for the removal of anionic and cationic dyes from aqueous solutions

Quartzite obtained from local source was investigated for the removal of anionic dye congo red (CR) and cationic dye malachite green (MG) as an adsorbent from aqueous solution in batch experiment. The adsorption process was studied as a function of dye concentration, contact time, pH and temperature. Adsorption process was described well by Langmuir and Freundlich isotherms. The adsorption capacity remained 666.7 mg/g for CR dye and 348.125 mg/g for MG dye. Data was analyzed thermodynamically, ΔH⁰ and ΔG⁰ values proved that adsorption of CR and MG is an endothermic and spontaneous process. Adsorption data fitted best in the pseudo-first order kinetic model. The adsorption data proved that quartzite exhibits the best adsorption capacity and can be utilized for the removal of anionic and cationic dyes.     

Highly efficient removal of diazinon pesticide from aqueous solutions by using coconut shell-modified biochar

This study evaluates the adsorption of diazinon from aqueous solutions onto coconut shell-modified biochar using a batch system. The amount of dosage and initial pH are the main parameters being studied to obtain maximum adsorption capacity of the probe molecules. The carbonized coconut shell biochar (BC1), activated coconut shell biochar (BC2), chemically modified phosphoric acid (BC3) and sodium hydroxide coconut shell biochar (BC4) were prepared and tested as variables in the adsorption experiment. The characteristic of biochar via SEM, EDX and BET analysis revealed the large porous of surface morphology and slight changes in the composition with high surface area (405.97 – 508.07 m²/g) by following the sequence of BC3 > BC2 > BC4. Diazinon removal percentage as high as 98.96% was achieved at pH 7 with BC3 as adsorbent dosing at 5.0 g/L. The high coefficient of determination, R² with a small value of ERRSQ and χ² error analysis present the BC1 (0.9971) and BC2 (0.9999) are best fitted with Freundlich isotherm indicates multilayer sorption onto heterogeneous surface whereby the Langmuir isotherm model is the best fitting is described of monolayer adsorption process onto the homogenous surface of BC3 and BC4. The results indicated the maximum adsorption capacity (q_m) was achieved by BC3 with 10.33 mg/g, followed by BC2 (9.65 mg/g) in accordance to the Langmuir isotherm while Freundlich isotherm showed the highest adsorption capacity (k_F) with 1.73 mg/g (L/mg)^1/n followed by BC4 with 0.63 mg/g (L/mg)^1/n at favorable adsorption isotherm (1 ≤ n ≤ 10). Thus, the results obtained depicted that BC2 and BC3 are highly efficient adsorbents and both exhibit great potential in removing diazinon from aqueous solutions.     

Activated carbon blended with grape stalks powder: Properties modification and its application in a dye adsorption

In this study, activated carbon was blended with grape stalks powder to adsorb methylene blue (MB) dye with various concentrations from a wastewater. For this purpose, five independent variables involving pH (2–13), contact time (5–270 min), grape stalks powder dosage (0.1–10 g/l), methylene blue initial concentration (20–300 mg/l), and activated carbon dosage (0.1–10 g/l) for methylene blue adsorption were studied. The Central Composite Design (CCD) under Response Surface Methodology (RSM) was applied to estimate the independent variables effects on the methylene blue adsorption. The pseudo- first order, pseudo-second order, Elovich and intraparticle diffusion models were employed to study the adsorption kinetics and isotherm. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models were applied to investigate the adsorption isotherm. It was concluded that the intraparticle diffusion isotherm and pseudo-second order kinetic models could show the best results. Furthermore, some data such as physical adsorption (by analyzing FTR and applying some standard equations) and mean free energy (E) were discovered in this research. Finally, activated carbon blended with grape stalks powder as an effective bio-adsorbent for the methylene blue reduction from a wastewater was introduced.     

Liquid phase adsorption of Congo red dye on functionalized corn cobs

This study investigates the adsorption of Congo red (CR) dye onto corn cob based activated carbon (CCAC) in the batch process. The activated carbon was characterized using FTIR, SEM, and EDX techniques, respectively. The effect of operational parameters such as the initial dye concentration (10–50?mg/L), contact time (5–160 minutes), and solution temperature (30–50°C) were studied. The amount of the CR dye adsorbed was found to increase as these operational parameters increased. Kinetic data for CR dye adsorption onto CCAC were best represented by the pseudo second-order kinetic model. Four different isotherms namely Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models were used to test the adsorption data. It fitted the Langmuir isotherm model most. Thermodynamic parameters such as ΔH⁰, ΔS⁰, and ΔG⁰ were evaluated. The adsorption process was found to be exothermic and spontaneous. The study shows that CCAC is an effective adsorbent for the adsorption of CR dye from aqueous solution.     

Cellulose nanocrystals as promising adsorbents for the removal of cationic dyes

Cellulose nanocrystals (CNCs) prepared from cellulose fibre via sulfuric acid hydrolysis was used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of pH, adsorbent dosage, temperature, ionic strength, initial dye concentration were studied to optimize the conditions for the maximum adsorption of dye. Adsorption equilibrium data was fitted to both Langmuir and Freundlich isotherm models, where the Langmuir model better described the adsorption process. The maximum adsorption capacity was 118 mg dye/g CNC at 25 °C and pH 9. Calculated thermodynamic parameters, such as free energy change (ΔG = ?20.8 kJ/mol), enthalpy change (ΔH = ?3.45 kJ/mol), and entropy change (ΔS = 0.58 kJ/mol K) indicates that MB adsorption on CNCs is a spontaneous exothermic process. Tunability of the adsorption capacity by surface modification of CNCs was shown by oxidizing the primary hydroxyl groups on the CNC surface with TEMPO reagent and the adsorption capacity was increased from 118 to 769 mg dye/g CNC.     

Adsorption of methyl orange on nanoparticles of a synthetic zeolite NaA/CuO

CuO supported on an NaA zeolite (CuO/NaA) was prepared with an NaA zeolite through the ion-exchange (CuO/NaA) method. The morphology and the physicochemical properties of the prepared samples were investigated by XRD, MEB, and EDS. The various parameters, such as contact time, catalyst dose, initial dye concentration, initial pH, and temperature, influencing the adsorption of methyl orange (MO) were optimized. The MO adsorption equilibrium was reached after 240 min of contact time. Removal of MO is better at neutral pH than in acidic and alkaline solutions. Among the tested models, the equilibrium adsorption data are well fitted by the Langmuir isotherm. The adsorption kinetics is best described by the pseudo-second-order model. The evaluation of the thermodynamic parameters, i.e. ΔG^o, ΔH^o, and ΔS^o, revealed that MO adsorption was spontaneous, while the activation energy (20.98 kJ/mol) indicates a physical adsorption. The photodegradation of MO decreased from 100 mg/L down to 2 mg/L when the solution is exposed to visible light.     

Application of artificial neural network for comparison and modeling of the ultrasonic and stirrer assisted removal of anionic dye using activated carbon supported with nanostructure material

In this study, a green approach has been described for the synthesis of copper sulfide nanoparticles loaded on activated carbon (CuS‐NP‐AC) and usability of it for the removal of sunset yellow (SY) dye by ultrasound‐assisted and stirrer has been compared. In addition, the artificial neural network (ANN) model has been employed for a forecasting removal percentage of SY dye using the results obtained. This material was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The impact of variables, including initial dye concentration (mg/L), pH, adsorbent dosage (g), sonication time (min) and temperature (°C) on SY removal was studied. Fitting the experimental equilibrium data of different isotherm models such as Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models display the suitability and applicability of the Langmuir model. Analysis of experimental adsorption data of different kinetic models including pseudo‐first and second order, Elovich and intraparticle diffusion models indicate the applicability of the second‐order equation model. The adsorbent (0.005 g) is applicable for successful removal of SY dye (> 98%) in short time (9 min) under ultrasound condition. A three layer ANN models with 8 and 6 neurons at hidden layer was selected as optimal models using stirrer and ultrasonic, respectively. These models displayed a good agreement between forecasted data and experimental data with the determination coefficient (R²) of 0.9948 and 0.9907 and mean squared error (MSE) of 0.0001 and 0.0002 for training set using stirrer and ultrasonic, respectively.     

Optimization of methylene blue removal from aqueous solutions using activated carbon derived from coffee ground pyrolysis: A response surface methodology (RSM) approach for natural and cost-effective adsorption

This study aimed to examine the impact of operational factors on the adsorption capacity of methylene blue (MB) using a natural and cost-effective adsorbent, activated carbon from coffee grounds (CAP). The three-factor Box-Behnken design of the response surface methodology (RSM) was employed to optimize this economically viable process with maximum efficiency. Through extensive experiments, the factors influencing the adsorption process were identified, their interactions were measured, and a mathematical model was developed. The experiment evaluated the quantity of MB adsorbed by CAP based on pH (2.5–10), initial MB concentration (10–100 mg/L), and CAP adsorbent amount (0.05–0.1 g/L). The results revealed that both concentration and mass significantly influenced the decoloration enhancement. Optimal conditions for achieving a 91 % degradation efficiency were determined as 0.05 g/L adsorbent weight, 100 mg/L dye concentration, and pH 2.5, with a desirability score of approximately 0.986, aligning closely with the predictions of the BBD model. In conclusion, this research addresses a research gap by demonstrating the high effectiveness of the CAP adsorbent in removing dyes from textiles.     

Effective sequestration of Congo red dye with ZnO/cotton stalks biochar nanocomposite: MODELING,reusability and stability

Widespread application of dyes and disposal of their untreated effluents into water bodies adversely affect the ecosystem due to their complex aromatic structures and persistent nature. The present study aims to utilize the cotton stalks biochar (CSB) and its composite with zinc oxide nanoparticles (CSB/ZnONPs) to evaluate for the decontamination their batch scale potential of Congo red dye from wastewater. The characterization of CSB and CSB/ZnONPs was performed with Fourier-transform infra-red (FTIR) spectroscopy, scanning electron microscopy, energy-dispersive X-ray (EDX) and point of zero charge (PZC) to get insight of their potential for the decontamination of CR. The effects of initial CR concentration (25–500 mg/L), dosage of CSB and CSB/ZnONPs (0.5–2 g/L), solution pH (2–10) and contact time (0–180 min) were evaluated on CR removal at temperature (25 ± 1.5 °C). The results disclosed that CSB/ZnONPs showed excellent adsorption potential (556.6 mg/g) in comparison with CSB (250 mg/g) and most of the other adsorbents previously studies in the literature. The equilibrium experimental data were equally explained with Freundlich and Langmuir isotherm models (R² > 0.98) while kinetic data demonstrated the best fit with pseudo second order model. The CSB/ZnONPs composite exhibited excellent reusability (89.65%) after five adsorption/desorption cycles for the sequestration of CR from contaminated systems. The present study demonstrated that metallic nanocomposite of CSB (CSB/ZnONPs) is an excellent candidate for the cost effective and environment friendly decontamination of CR from industrial wastewater and is suggested to be considered for the decontamination of other pollutants from the wastewater.     

Adsorption of organochlorine pesticides on modified porous Al30/bentonite: Kinetic and thermodynamic studies

Adsorption of pesticides (heptachlor epoxide, dieldrin and endrin) onto modified bentonite by Keggin cation [Al₃₀O₈(OH)₅₆(H₂O)₂₄]¹⁸⁺ denoted Al₃₀ cation to form composite (Al₃₀/B), has been investigated as a possible alternative method for their removal from aqueous solutions. The study was aimed to use a low-cost material as a step towards cleaner environment. Interestingly, these chemical modifications altered the physicochemical characteristics of bentonite in term of morphology, surface area and functionality which has been confirmed by using nitrogen adsorption–desorption isotherm, scanning electronic microscopy (SEM) and X-ray diffraction (XRD). Gas chromatography coupled to mass spectrometry (GC–MS) was used to identify and analyze the pesticides. Different physicochemical parameters were analyzed: contact time, adsorbent dose, pH, and temperature. The results showed that the removal percentage of pesticides on Al₃₀/B was the highest at contact time of 5 h, adsorbent dosage of 25 mg, at pH 7.5, and at optimum temperature of 45 °C. Furthermore, the Kinetic study indicated that the adsorption of pesticides on Al₃₀/B was well adapted to the pseudo-first order kinetic with a correlation coefficient near unity. The results of adsorption were fitted to the Langmuir and Freundlich isotherms. The Freundlich model represented the adsorption process better than Langmuir model, with correlation coefficients (R²) values range from 0.986 to 0.989. The Thermodynamic study suggested that the adsorption of pesticides was chemisorption, spontaneous and endothermic process. Therefore, Al₃₀/B composite can be utilized effectively for removal of pesticides with efficiency up to 98%.     

Adsorption of cationic methylene blue dye using microwave-assisted activated carbon derived from acacia wood: Optimization and batch studies

This study assesses the performance of optimized acacia wood-based activated carbon (AWAC) as an adsorbent for methylene blue (MB) dye removal in aqueous solution. AWAC was prepared via a physicochemical activation process that consists of potassium hydroxide (KOH) treatment, followed by carbon dioxide (CO₂) gasification under microwave heating. By using response surface methodology (RSM), the optimum preparation conditions of radiation power, radiation time, and KOH-impregnation ratio (IR) were determined to be 360 W, 4.50 min, and 0.90 g/g respectively, which resulted in 81.20 mg/g of MB dye removal and 27.96% of AWAC’s yield. Radiation power and IR had a major effect on MB dye removal while radiation power and radiation time caused the greatest impact on AWAC’s yield. BET surface area, mesopore surface area, and pore volume of optimized AWAC were found to be 1045.56 m²/g, 689.77 m²/g, and 0.54 cm³/g, respectively. Adsorption of MB onto AWAC followed Langmuir and pseudo-second order for isotherm and kinetic studies respectively, with a Langmuir monolayer adsorption capacity of 338.29 mg/g. Mechanism studies revealed that the adsorption process was controlled by film diffusion mechanism and indicated to be thermodynamically exothermic in nature.     

Yolk–shell microspheres assembled from Preyssler‐type NaP5W30O11014− polyoxometalate and MIL‐101(Cr) metal–organic framework: A new inorganic–organic nanohybrid for fast and selective removal of cationic organic dyes from aqueous media

Novel inorganic–organic yolk–shell microspheres based on Preyssler‐type NaP₅W₃₀O₁₁₀^14? polyoxometalate and MIL‐101(Cr) metal–organic framework (P₅W₃₀/MIL‐101(Cr)) were synthesized by reaction of K_12.5Na_1.5[NaP₅W₃₀O₁₁₀], Cr(NO₃)₃·9H₂O and terephthalic acid under hydrothermal conditions at 200°C for 24 h. The as‐prepared yolk–shell microspheres were fully characterized using various techniques. All analyses confirmed the incorporation of the Preyssler‐type NaP₅W₃₀O₁₁₀^14? polyoxometalate into the three‐dimensional porous MIL‐101(Cr) metal–organic framework. The results revealed that P₅W₃₀/MIL‐101(Cr) demonstrated rapid adsorption of cationic methylene blue (MB) and rhodamine B (RhB) with ultrahigh efficiency and capacity, as well as achieving rapid and highly selective adsorption of MB from MB/MO (MO = methyl orange), MB/RhB and MB/RhB/MO mixtures. The P₅W₃₀/MIL‐101(Cr) adsorbent not only exhibited a high adsorption capacity of 212 mg g^?1, but also could quickly remove 100% of MB from a dye solution of 50 mg l^?1 within 8 min. The effects of some key parameters such as adsorbent dosage, initial dye concentration and initial pH on dye adsorption were investigated in detail. The equilibrium adsorption data were better fitted by the Langmuir isotherm. The adsorption kinetics was well modelled using a pseudo‐second‐order model. Also, the inorganic–organic hybrid yolk–shell microspheres could be easily separated from the reaction system and reused up to four times without any change in structure or adsorption ability. The stability and robustness of the adsorbent were confirmed using various techniques.     

Xanthan or esterified xanthan/cobalt ferrite-lignin hybrid materials for methyl blue and basic fuchsine dyes removal: equilibrium,kinetic and thermodynamic studies

In this study, new adsorbents based on xanthan (XG) or esterified xanthan (XGAC) and ferrite-lignin hybrids were obtained and characterized by using the dynamic vapor sorption (DVS) method, infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The porosity, swelling ratio and point of zero charge (PZC) of the adsorbents were also evaluated. Batch adsorption experiments have been performed to determine the adsorption capacity of the adsorbents for Methyl Blue (MB) and Basic Fuchsine (BF). Ferrite-Lignoboost® lignin and ferrite-organosolv lignin hybrid materials (CFLB and CFLO) presented the highest adsorption capacity for MB dye (44.73 and 37.54 mg/g), while the adsorbents based on xanthan and ferrite-lignin hybrids (XG/CFLO and XG/CFLB) retained the highest quantities of BF dye (36.23 and 33.33 mg/g). The chemical nature of the adsorption process was determined, the analyzed data being better fitted to the pseudo second order (PSO) kinetic model. The data analysis showed that the adsorption process followed Langmuir, Dubinin-Radushkevich and Jovanovi? isotherm models. All the studied adsorption processes were endothermic (ΔH^o > 0) and the positive values of the entropy (ΔS^o > 0) indicated disorder at the interface between the adsorbent and the dye solutions.     

Removal of Cr (VI) from aqueous solution using magnetic biochar synthesized by a single step method

Magnetic biochar, as an adsorbent, was synthesized by a single step method, where iron salt was directly mixed with pinewood sawdust by chemical co-precipitation and subsequently pyrolyzed at 700°C for Cr (VI) removal from aqueous solution. The effects of some important parameters including adsorbent dosage (0.4–2.8?g/L), pH (1–10) of the solution, contact time (0–1440 minutes), initial concentration (30–120?mg/L), and temperature (20–40°C) were investigated in batch experiments. Both pre- and post-adsorbents were characterized by SEM-EDX and XPS to investigate the adsorption mechanism. The maximum adsorption capacity of the tested magnetic biochar under the certain experimental conditions determined as optimal was 42.7?mg/g for Cr (VI). The adsorption data were proved to be suitable for the pseudo-second order model for kinetics and the Langmuir model for isotherms with correlation R²?=?0.9996 andR²?>?0.9980, respectively, after fitting with four kinetic models (pseudo-first order, pseudo-second order, W-M model, and Elovich) and three isotherm models (Langmuir, Freundlich, and Temkin). The characteristic analyses further verified that the efficient particle was a mixture of iron oxides in essence, and it had a strong effect on the spontaneous and endothermic adsorption process.     

Adsorptive scavenging of cationic dyes from aquatic phase by H3PO4 activated Indian jujube (Ziziphus mauritiana) seeds based activated carbon: Isotherm,kinetics, and thermodynamic study

In the present work, a cost-effective Indian jujube seeds derived activated carbon (IJSAC) prepared via o-phosphoric acid chemical activation, is studied for the sequestration of acriflavine (AF) and Victoria blue B (VB) from the aquatic environment. The activated carbon is characterized by Fourier transform infrared spectroscopy, N₂-adsorption/desorption isotherm, scanning electron microscopy techniques and point of zero-charge measurement. The specific surface area (S_BET) of 571 m²/g with a pore radius of 22.45 Å specifies mesoporous nature of the IJSAC. The implication of operational conditions on the adsorption of both dyes onto IJSAC assessed by batch methodology, establish the optimal conditions as dosage (1.5 and 2.5 g/L), contact time (60 min), pH (8 and 10), and initial concentration (130 and 140 mg/L) for AF and VB uptake, respectively. The Freundlich adsorption isotherm model (R² = 0.99) appropriates the equilibrium data suggesting multilayer adsorption onto heterogeneous surface sites, while pseudo-second order (R² = 0.95–0.99) is the best fit kinetic model. The liquid film and intraparticle diffusion modelling demonstrate that the adsorption process of these dyes is governed by both the steps. Maximum Langmuir adsorption capacity is 113.6 mg/g for acriflavine and 92.78 mg/g for Victoria blue B. Thermodynamic studies indicate endothermic and spontaneous adsorption of dyes. The adsorption mechanism for the uptake of AF and VB by IJSAC most probably involves hydrogen bonding, electrostatic and π-π interactions. Based on its high adsorption capacity, relatively faster kinetics, and reusability, IJSAC can be perceived as a proficient and effective adsorbent for cationic dyes removal from the liquid waste.