Mesoporous activated carbon from <Emphasis Type="Italic">Pentace</Emphasis> species sawdust via microwave-induced KOH activation: optimization and methylene blue adsorption

This work studied the optimization of preparation conditions of Pentace species sawdust activated carbon (PSAC) via microwave-induced KOH activation for the adsorption of methylene blue (MB) dye from aqueous solutions. The produced activated carbon was characterised through Brunauer–Emmett–Teller (BET) surface area and pore structural analysis, proximate and ultimate, scanning electron microscopy, and Fourier transform infrared spectroscopy. Response surface methodology technique was used to optimize the radiation power, radiation time and impregnation ratio for MB removal and PSAC yield through central composite design. The optimum preparation conditions for PSAC were obtained at a radiation power of 418 W, radiation time of 6.4 min, and an impregnation ratio of 0.5, which resulted in 27% PSAC yield and 93.74% MB removal. A mesoporous structure of PSAC was formed, with a BET surface area, total pore volume and average pore diameter of 914.15 m²/g, 0.52 cm³/g, and 3.19 nm, respectively. The experimental kinetic data were well described by a pseudo-second-order model and intraparticle diffusion. Adsorption data fitted the Redlich–Peterson equation better than the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich and Sips equations. However, the exponential value of Redlich–Peterson approached unity, hence, resulting in the original Langmuir equation, with adsorption capacity of 357.14 mg/g. The adsorption performance was effectively preserved even after four consecutive cycles, demonstrating good regeneration ability.     

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.     

Conversion of teak wood waste into microwave-irradiated activated carbon for cationic methylene blue dye removal: Optimization and batch studies

The objective of this study is to find optimum preparation conditions in converting teak wood waste into activated carbon (TWAC) and to evaluate its performance in adsorbing cationic dye of methylene blue (MB). TWAC was produced via physiochemical activation (potassium hydroxide, KOH chemical treatment, and carbon dioxide, CO₂ gasification) and heated through microwave irradiation technique. With the aid of response surface methodology (RSM), optimized TWAC was successfully synthesized at radiation power, radiation time, and impregnation ratio (IR) of 366 W, 5.30 min, and 1.15 g/g, respectively. These preparation conditions produced TWAC with MB adsorption uptakes of 66.69 mg/g and a yield of 38.23%. Characteristics of TWAC in terms of BET surface area, mesopores surface area, total pore volume, and average pore diameter were determined to be 1345.25 m²/g, 878.63 m²/g, 0.6140 cm³/g, and 2.85 nm, respectively. Isotherm studies divulged that the MB-TWAC adsorption system followed the Langmuir model with a maximum monolayer adsorption capacity of 567.52 mg/g. In terms of kinetic studies, this adsorption system fit pseudo-second order model the best whereas Boyd plot confirmed that the adsorption process was controlled by the film diffusion mechanism. Thermodynamic parameters of enthalpy change, ΔH°, entropy change, ΔS°, Gibbs free energy, ΔG° and Arrhenius activation energy, E_a were calculated to be ?4.06 kJ/mol, 0.06 kJ/mol.K, –22.69 kJ/mol and 16.03 kJ/mol, respectively. The activation and microwave heating methods employed succeeded to produce TWAC with excellent adsorption performance in removing MB dye. TWAC was also successfully regenerated for 5 cycles via microwave heating technique.     

Uranium extraction from aqueous solution using dried and pyrolyzed tea and coffee wastes

The adsorption of U(VI) onto dried and pyrolyzed tea and coffee wastes was investigated. The adsorption properties of the materials were characterized by measuring uranium uptake as a function of solution pH, kinetics and adsorption isotherms. pH profile of uranium adsorption where UO₂ ²⁺ is expected to be the predominant species was measured between pH 0 and 4. Both Langmuir and Freundlich adsorption models were used to describe adsorption equilibria, and corresponding constants evaluated. Using the Langmuir model, the maximum adsorption capacity of uranium by dried tea and coffee wastes was 59.5 and 34.8 mg/g, respectively at 291 K. Adsorption thermodynamic constants, ΔH° ΔS° and ΔG° were also calculated from adsorption data obtained at three different temperatures. Adsorption thermodynamics of uranyl ions on dried tea and coffee systems indicated spontaneous and endothermic processes. Additionally, a Lagergren pseudo-second-order kinetic model was used to fit the kinetic experimental data for both adsorbents and the constants evaluated. Dried tea and coffee wastes proved to be effective adsorbents with high capacities and significant advantage of a very low cost.     

Chemically activated Ipomoea carnea as an adsorbent for the copper sorption from synthetic solutions

An indigenously prepared zinc chloride activated Ipomoea carnea (morning glory), a low-cost and abundant adsorbent, was used for removal of Cu(II) ions from aqueous solutions in a batch adsorption system. The chemical activating agent ZnCl₂ was dissolved in deionised water and then added to the adsorbent in two different ratios 1:1 and 1:0.5 adsorbent to activating agent ratio by weight. Studies were conducted as a function of contact time, initial metal concentration, dose of adsorbent, and pH. Activated Ipomoea carnea (AIC) were characterised using scanning electron microscopy (SEM), iodine number and methylene blue number. High iodine numbers indicates development of micro pores with zinc chloride activation. Maximum adsorption was noted within pH range 6.0(±0.05). Adsorption process is fast initially and reaches equilibrium after about 4 hours. The kinetic data were analysed using pseudo-first-order and pseudo-second-order models. The pseudo-second-order kinetic model was found to agree well with the experimental data. Adsorption equilibrium data were analyzed using Langmuir and Freundlich isotherm models. The Langmuir model represented the sorption process better than the Freundlich model. Based on the Langmuir isotherm, the monolayer adsorption capacity of Cu(II) ions was 7.855 mg?g^?1 for AIC (1:1) and 6.934 mg?g^?1 for AIC (1:0.5).     

N-Octyl Quaternized P4VP Interaction With Orange Telon

The removal of orange Telon from aqueous solutions by poly(N-octyl-4-vinylpyridiniumbromide) copolymer was investigated. Batch adsorption experiments were carried out to study the effect of experimental parameters on the orange Telon adsorption equilibrium. The adsorption characteristics of copolymer to ward orange Telon in dilute aqueous solution were followed using UV-Vis spectrophotometry. Adsorption equilibrium was reached within 60 min for 0.03 g of poly(4-vinylpyridine quaternized at 58%. The kinetic of adsorption is best described by a pseudo-second-order model. Results also showed that the equilibrium modeling of orange Telon removal process was described by Langmuir isotherms. The maximum adsorption capacity determined from the Langmuir isotherm was 76.4 mg g^{? 1}. The study of the thermodynamic parameters showed that the adsorption of orange Telon on copolymer is an exothermic process and the randomness decreases at the solid-solution interface during the adsorption of dye on the copolymer.     

Preparation of Fe3O4/chitosan/poly(acrylic acid) composite particles and its application in adsorbing copper ion (II)

Fe₃O₄/chitosan/poly(acrylic acid) (Fe₃O₄/CS/PAA) composite particles, which are reusable, biodegradable and of high adsorption capacity, have been prepared through polymerizing acrylic acid in chitosan and Fe₃O₄ nanoparticles aqueous solution. By varying in-feed mole ratio of carboxyl to amino group (n^c/n^a) and reactant concentration, the average diameter of Fe₃O₄/CS/PAA composite particles can be controlled to vary from 100 to 300 nm. FT-IR, XRD and TEM were used to characterize Fe₃O₄/CS/PAA composite particles. Results showed that Fe₃O₄ was indeed incorporated into CS/PAA particles. The composite particles showed high efficient to remove copper ions (II) in aqueous solution. Adsorption kinetic studies showed that the adsorption process followed a pseudo-second-order kinetic model and the equilibrium data agreed well with the Langmuir model. The saturated adsorption capacity obtained from the experimental was 193 mg/g in close to proximity to the data 200 mg/g calculated from Langmuir model. The saturated adsorption capacity still retained 100 mg/g after three cycles of adsorption–desorption of copper ions (II).     

Gold Nanoparticles Loaded on Activated Carbon as Novel Adsorbent for Kinetic and Isotherm Studies of Methyl Orange and Sunset Yellow Adsorption

In this research, a novel adsorbent gold nanoparticle loaded on activated carbon (Au-NP-AC) was synthesized by a low cost in a routine protocol. Subsequently, this novel material characterization and identification are followed by different techniques such as th eBruner–Emmet–Teller (BET) theory, scanning electron microcopy, and transmission electron microscopy analysis. Unique properties such as high BET surface area (>1229.55 m²/g) and low pore size (<22.46 Å) and average particle size lower than 48.798 Å in addition to high reactive atom and presence of various functional groups make it possible for efficient removal of sunset yellow (SY) and methyl orange (MO). Generally, the influence of variables including amount of adsorbent, initial dyes concentration, contact time, temperature on dyes removal percentage has great effect on removal percentage that their influence was optimized. The kinetic of proposed adsorption processes efficiently followed, pseudo-second-order and intra-particle diffusion approach. The equilibrium data of the removal strongly follow the Langmuir monolayer adsorption with high adsorption capacity in a short amount of time. This novel adsorbent by small amount (0.01 g) really is applicable for removal of high amount of both dyes (MO and SY) in short time (<18 minutes). Equilibrium data fitted well with the Langmuir model at all amount of adsorbent, while maximum adsorption capacity for MO 161.29 mg g^?1 and for SY 227.27 for 0.005 g of Au-NP-AC.     

Sorption of trifluoromethane in activated carbon

Sorption isotherms for trifluoromethane (R-23) in activated carbon have been measured at ca. 298 and 323 K using a gravimetric microbalance. High-resolution TEM images of the activated carbon show a very uniform microstructure with no evidence of any contaminants. The adsorption in the activated carbon reaches about 22.8 mol kg^?1 at 2.0 MPa and 298 K or 17.6 mol kg^?1 at 2.0 MPa and 323 K. Three different adsorption models (Langmuir, multi-site Langmuir, and BET equations) have been used to analyze the activated carbon sorption data, with a particular interest in the heat of adsorption (?ΔH). The heat of adsorption for R-23 in the activated carbon was about 29.78 ± 0.04 kJ mol^?1 based on the multi-site Langmuir model and is within the range of typical physical adsorption. According to the IUPAC classification, the activated carbon exhibits Type I adsorption behavior and was completely reversible. Compared with our previous work for the sorption of R-23 in zeolites (5A (Ca,Na-A), 13X (Na-X), Na,K-LSX, Na-Y, K,H-Y, Rb,Na-Y) and ionic liquids ([omim][TFES] and [emim][Tf₂N]) the activated carbon had the highest adsorption capacity. The adsorption process in the activated carbon also took less time than in the zeolites or the ionic liquids to reach thermodynamic equilibrium.     

Organoclay modified with lignin as a new adsorbent for removal of Pb2+ and UO2 2+

This study investigated a new adsorbent prepared from lignin modified organoclay for the removal of Pb²⁺ and UO₂ ²⁺ from aqueous solutions. The characterization of new adsorbent was performed by FT-IR and XRD. Adsorption of Pb²⁺ and UO₂ ²⁺ species in aqueous solution as a function of ion concentration, pH, temperature and time of adsorption was investigated in detail. The adsorption data were analyzed by using the Langmuir, Freundlich and Dubinin-Radushkevich models. The monolayer adsorption capacities of organoclay–lignin were 0.12 mol kg^?1 and 0.42 mol kg^?1 for Pb²⁺ and UO₂ ²⁺, respectively. The experimental kinetic data were analyzed by using pseudo-second-order kinetic and intra-particle diffusion models. The proposed adsorption mechanism follows a pseudo-second-order kinetic and endothermic because of increasing disorderliness at adsorbate/adsorbent interface.     

Adsorption characteristics of Titan yellow and Congo red on CoFe2O4 magnetic nanoparticles

This paper assesses the adsorption characteristics of Titan yellow and Congo red on CoFe₂O₄ magnetic nanoparticles. The adsorption behavior of Titan yellow and Congo red from aqueous solution onto CoFe₂O₄ magnetic nanoparticles has been determined by investigating the effects of pH, concentration of the dye, amount of adsorbent, contact time, ionic strength and temperature. Experimental results indicated that CoFe₂O₄ nanoparticles can remove more than 98 % of each dye under optimum operational conditions of a dosage of 15.0 mg CoFe₂O₄, pH 3.0, initial dye concentration of 22–140 mg L^?1, and contact times of 2.0 and 15.0 min for Congo red and Titan yellow, respectively. Langmuir and Freundlich isotherm models have been used to evaluate the ongoing adsorption kinetic equations. Regeneration of the saturated adsorbent was possible by NaCl/acetone solution as eluent. The maximum adsorption capacities were 200.0 and 212.8 mg dye per gram adsorbent for Congo red and Titan yellow, respectively. With the help of adsorption isotherm, thermodynamic parameters such as free energy, enthalpy and entropy have been calculated. On the basis of pseudo-first-order and pseudo-second-order kinetic equations, different kinetic parameters have been obtained.     

Environmental remediation by hydroxyapatite: Solid state synthesis utilizing waste chicken eggshell and adsorption experiment with Congo red dye

This study reports the adsorption efficacy of hydroxyapatite (HAp) for removing Congo Red (CR) dye from aqueous solution. HAp was synthesized utilizing chicken eggshell as a precursor of Ca source. Solid state synthesis method was implemented which comprised calcination at 950 °C (E-HAp950). XRD analysis confirmed the formation of bi-phasic HAp with 15.5% of β-TCP. Elemental composition was evaluated by XPS and EDX analysis. FESEM analysis revealed the particles are of plate and spherical shaped also confirmed by the TEM images. DLS particle size, zeta potential, BET surface area and point of zero charge were also evaluated. Adsorption efficacy of E-HAp950 for removing CR was evaluated by batch adsorption experiment. Maximum adsorption capacity (q_max) was found to be 9.64 mgg⁻¹ which was best explained by the non-linear fitting (R² = 0.98) of Langmuir isotherm. Adsorption kinetics profusely followed pseudo second order kinetic model (R² = 0.999) with q_{e (experimental)} being very much closer to q_{e (calculative)} for this model. Thus, hydroxyapatite prepared by utilizing eggshell waste through solid state method has the potential to remove toxic dyes.     

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.     

Adsorption of phenols from contaminated water through titania-silica mixed imidazolium based ionic liquid: Equilibrium,kinetic and thermodynamic modeling studies

The present study describes the synthesis and characterization of titania-silica mixed imidazolium based ionic liquid (Ti-Si-IL) as well as evaluation of its adsorption behavior towards the 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trichlorophenol (2,4,6-TCP). Synthesized Ti-Si-IL adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), BET surface area Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA) and elemental analysis (CHN). The adsorption of 2,4-DNP and 2,4,6-TCP on Ti-Si-IL was investigated systematically by evaluating the effects of adsorbent dosage, initial pH, contact time and temperature. Satisfactory adsorption 95% and 65% for 2,4-DNP and 2,4,6-TCP was observed at pH 4 and 6, respectively. The kinetic results for 2,4-DNP and 2,4,6-TCP on Ti-Si-IL indicated that the kinetic data follows pseudo-second-order model (R² = 0.9985 and 0.9750, respectively). Adsorption isotherms were fitted well by the Langmuir model for 2,4-DNP (q_m = 44.64 mg g^?1 at 318 K) and Freundlich model for 2,4,6-TCP (K_F = 0.63 mg g^?1 at 318 K). The +ΔH° and -ΔG° values demonstrated that the adsorption of 2,4-DNP was endothermic and spontaneous in nature. While the -ΔH° and +ΔG° values for 2,4,6-TCP adsorption demonstrated exothermic and comparatively nonspontaneous. During the removal process, the role of different functional groups, cyclic structure was monitored and found that the ionic property as well as π-π interactions of host molecules played important role in the extent of adsorption.     

Effect of acid and alkali treatments of a forest waste,Pinus brutia cones,on adsorption efficiency of methyl green

The removal of methyl green (MG) dye from aqueous solutions using acid- or alkali-treated Pinus brutia cones (PBH and PBN) waste was investigated in this work. Adsorption removal of MG was conducted at natural pH, namely, 4.5 ± 0.10 for PBH and near 4.8 ± 0.10 for PBN. The pseudo-second-order model appeared to be the most appropriate to describe the adsorption process of MG on both PBN and PBH with a correlation coefficient R² > 0.999. Among the tested isotherm models, the Langmuir isotherm was found to be the most relevant to describe MG sorption onto modified P. brutia cones with a correlation factor R² > 0.999. The ionic strength (presence of other ions: Cl^?, Na⁺, and SO₄^2?) also influences the adsorption due to the change in the surface properties; it had a negative impact on the adsorption of MG on these two supports. A reduction of 68.5% of the adsorption capacity for an equilibrium dye concentration Ce of 30 mg/L was found for the PBH; while with PBN no significant influence of the ionic strength on adsorption was observed, especially in the presence of NaCl for dye concentrations superior to 120 mg L^?1.     

Carbon dioxide sequestration and methane removal from exhaust gases using resorcinol–formaldehyde activated carbon xerogel

The world is faced with intrinsic environmental issues. Among these issues, the minimization of greenhouse gas emission to acceptable levels presents a high priority. This study seeks to help to reduce the greenhouse effect in sustainable manner. A resorcinol–formaldehyde xerogel was synthesized at specific conditions and used to prepare an activated carbon xerogel (RF-ACX). RF-ACX exhibited micropores in range of 1.2–1.4 nm, a surface area of 496 m²/g and a cumulative pore volume of 0.81 cm³/g. Scanning electron microscopy showed that it is made of microspherical particles with an almost uniform particle size of 1.3 ± 0.2 μm. Equilibrium and kinetic studies for the adsorption of CO₂, CH₄ and N₂ on RF-ACX were conducted at five temperatures (293, 303, 313, 323, and 333 K) and pressures of up to 1 MPa. The adsorption capacity on RF-ACX was highest for CO₂, followed by CH₄ and then N₂. Isosteric heats of adsorption and adsorption rates were investigated. The measured adsorption equilibria were fitted with the extended multisite Langmuir adsorption model and further used to predict adsorption equilibria of their corresponding binary systems.     

Amorphous titanium dioxide as an adsorbent for dye polluted water and its recyclability

Amorphous TiO₂, synthesized from TiCl₄ and diluted NH₃ solution, was characterized by X-ray diffraction spectrometry, UV–Vis diffused reflectance spectroscopy, Fourier-transformed infrared spectroscopy, and scanning electron microscopy. The powder exhibited high specific surface area at 508 m²/g as measured by the Brunauer-Emmett-Teller method. The pH at point of zero charge of the as-prepared amorphous TiO₂ was determined by the pH drift method to be 6.8. The product was studied for its sorption efficiency using two dyes—crystal violet (CV) and malachite green (MG). Studies on the effects of various sorption parameters (contact time, TiO₂ dosage, pH of solution, and initial concentration of dye) were carried out in order to find the optimum adsorption conditions for which the results were: contact time ~30 min, TiO₂ dosage ~0.05–0.1 g, pH 7–9, and initial concentration <1 × 10^?4 M. The adsorption data were analyzed and fitted better with the Langmuir model than the Freundlich model. The maximum adsorption capacities obtained from the Langmuir model were 0.4979 and 0.4075 mmol dye/g TiO₂ for CV and MG dye, respectively. In addition, the regeneration and the recyclability of the prepared amorphous TiO₂ were also studied. The used adsorbent should be regenerated 10–12 h before reuse in the next cycle for the best result.     

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.     

Sorption study of uranium from aqueous solution on ordered mesoporous carbon CMK-3

The ability of ordered mesoporous carbon CMK-3 has been explored for the removal and recovery of uraium from aqueous solutions. The textural properties of CMK-3 were characterized using small-angle X-ray diffraction and N₂ adsorption–desorption, and the BET specific surface area, pore volume and the pore size were 1143.7 m²/g, 1.10 cm³/g and 3.4 nm. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CMK-3 showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 35 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir and Freundlich isotherm. The thermodynamic parameters, ?G°(298 K), ?H° and ?S° were determined to be ?7.7, 21.5 k J mol^?1 and 98.2 J mol^?1 K^?1, respectively, which demonstrated the sorption process of CMK-3 towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed CMK-3 could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 2.0 g CMK-3.