Adsorption of 2,4-D on magnetic graphene and mechanism study

Efficient adsorptive removal of 2,4-dichlorophenoxyacetic acid (2,4-D) using biomass derived magnetic activated carbon nanocomposite in synthetic and simulated agricultural runoff water

This study focused on evaluating the efficacy of a magnetic activated carbon material (CPAC@Fe3O4) derived from pods of copper pod tree in adsorbing the toxic herbicide, 2,4- (2,4-D) from aqueous solutions. The synthesized CPAC@Fe3O4 adsorbent, underwent various characterization techniques. FESEM images indicated a rough surface, incorporating iron oxide nanoparticles, while EDS analysis confirmed the presence of elements like Fe, O, and C. Notably, the CPAC@Fe3O4 exhibited high surface area (749.10 m2/g) and pore volume (0.5351 cm³/g), confirming its mesoporous nature. XRD investigations identified distinct signals associated with graphitic carbon and magnetite nanoparticles, while VSM analysis verified its magnetic properties with a high magnetic saturation value (2.72 emu/g). The adsorption process was exothermic, with a decrease in adsorption capacity at higher temperatures. Freundlich isotherm provided the best fit for the adsorption, and the pseudo-second-order equation effectively described the kinetics. Remarkably, the maximum adsorption capacity ranged from 246.43 to 261.03 mg/g, surpassing previously reported values. The ΔH° value (-8.67 kJ/mol) suggested a physisorption mechanism, and the negative ΔG° values established the spontaneous nature. Furthermore, the synthesized adsorbent demonstrated exceptional reusability, allowing for up to five cycles of adsorption-desorption operations. When applied to simulated agricultural runoff, CPAC@Fe3O4 showcased a significant adsorption capacity of 160.71 mg/g for 50 mg/L 2,4-D, using a 0.2 g/L dosage at pH 2. This study showcased the transformation of copper pod biomass into a valuable magnetic nanoadsorbent capable of efficiently eliminating the noxious 2,4-D pollutant from aqueous environments.

Magnetic graphene derivates for efficient herbicide removal from aqueous solution through adsorption

2,4-Dichlorophenoxyacetic acid (2,4-D) is an herbicide and is among the most widely distributed pollutant in the environment and wastewater. Herein is presented a complete comparison of adsorption performance between two different magnetic carbon nanomaterials: graphene oxide (GO) and its reduced form (rGO). Magnetic functionalization was performed employing a coprecipitation method, using only one source of Fe2+, requiring low energy, and potentially allowing the control of the amount of incorporated magnetite. For the first time in literature, a green reduction approach for GO with and without Fe3O4, maintaining the magnetic behavior after the reaction, and an adsorption performance comparison between both carbon nanomaterials are demonstrated. The nanoadsorbents were characterized by FTIR, XRD, Raman, VSM, XPS, and SEM analyses, which demonstrates the successful synthesis of graphene derivate, with different amounts of incorporate magnetite, resulting in distinct magnetization values. The reduction was confirmed by XPS and FTIR techniques. The type of adsorbent reveals that the amount of magnetite on nanomaterial surfaces has significant influence on adsorption capacity and removal efficiency. The procedure demonstrated that the best performance, for magnetic nanocomposites, was obtained by GO∙Fe3O4 1:1 and rGO∙Fe3O4 1:1, presenting values of removal percentage of 70.49 and 91.19%, respectively. The highest adsorption capacity was reached at pH 2.0 for GO∙Fe3O4 1:1 (69.98 mg g-1) and rGO∙Fe3O4 1:1 (89.27 mg g-1), through different interactions: π-π, cation-π, and hydrogen bonds. The adsorption phenomenon exhibited a high dependence on pH, initial concentration of adsorbate, and coexisting ions. Sips and PSO models demonstrate the best adjustment for experimental data, suggesting a heterogeneous surface and different energy sites, respectively. The thermodynamic parameters showed that the process was spontaneous and exothermic. Finally, the nanoadsorbents demonstrated a high efficiency in 2,4-D adsorption even after five adsorption/desorption cycles.

A novel magnetic adsorbent from activated carbon fiber and iron oxide nanoparticles for 2,4-D removal from aqueous medium

Carbonaceous materials have been widely applied as adsorbents, but there are some factors that affect their efficiency. In this context, advances in nanotechnology provide new and more efficient methodologies for water treatment. This study evaluated the efficiency of a novel carbon-based adsorbent developed from Brazilian polyacrylonitrile textile fiber and functionalized with iron oxide magnetic nanoparticles for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from the aqueous medium. The synthesized adsorbent (ACF-Fe3O4) was characterized by FTIR, XRD, VSM, Zeta potential, SEM, EDX, and TEM. The characterization techniques showed that the adsorbent has peaks characteristic of its precursors and superparamagnetic characteristics, confirming the efficiency of the synthesis method. The adsorption tests evaluated the influence of adsorbent dosage, pH of the contaminant solution, contact time and temperature on the removal of 2,4-D. The experimental data were better adjusted by the pseudo-second order kinetic model and by the Langmuir isothermal model. The thermodynamic parameters revealed that the process is exothermic, spontaneous and thermodynamically favorable. Under the best experimental conditions, the maximum adsorption capacity obtained was 51.10 mg g-1 with an adsorbent concentration of 0.33 g L-1, natural pH of the solution, temperature of 288 K at the equilibrium time of six hours. Adsorbent reusage was studied in four desorption cycles. The adsorption mechanism can be explained through π-π bonds, hydrogen bonds and electrostatic interactions. The prepared material presented high-efficiency adsorption capacity of 2,4-D compared to other carbonaceous materials present in the literature, demonstrating its viability for the removal of this contaminant from the aqueous medium.

Adsorption Ability of Graphene Aerogel and Reduced Graphene Aerogel toward 2,4-D Herbicide and Salicylic Acid

Within this work, new aerogels based on graphene oxide are proposed to adsorb salicylic acid (SA) and herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous media. Graphene oxide aerogel (GOA) and reduced graphene oxide aerogel (rGOA) were obtained by freeze-drying processes and then studied by Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and Brunauer-Emmett-Teller (BET) analysis. The influence of contact time and the concentration of the adsorbates were also assessed. It was found that equilibrium for high adsorption is reached in 150 min. In a single system, the pseudo-first-order, pseudo-second-order kinetic models, Intraparticle diffusion, and Elovich models were used to discuss the detail of the aerogel adsorbing pollutant. Moreover, the Langmuir, Freundlich, and Temkin adsorption models were applied to describe the equilibrium isotherms and calculate the isotherm constants.

Adsorption of Phenoxyacetic Herbicides from Water on Carbonaceous and Non-Carbonaceous Adsorbents

The increasing consumption of phenoxyacetic acid-derived herbicides is becoming a major public health and environmental concern, posing a serious challenge to existing conventional water treatment systems. Among the various physicochemical and biological purification processes, adsorption is considered one of the most efficient and popular techniques due to its high removal efficiency, ease of operation, and cost effectiveness. This review article provides extensive literature information on the adsorption of phenoxyacetic herbicides by various adsorbents. The purpose of this article is to organize the scattered information on the currently used adsorbents for herbicide removal from the water, such as activated carbons, carbon and silica adsorbents, metal oxides, and numerous natural and industrial waste materials known as low-cost adsorbents. The adsorption capacity of these adsorbents was compared for the two most popular phenoxyacetic herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA). The application of various kinetic models and adsorption isotherms in describing the removal of these herbicides by the adsorbents was also presented and discussed. At the beginning of this review paper, the most important information on phenoxyacetic herbicides has been collected, including their classification, physicochemical properties, and occurrence in the environment.

Adsorptive behavior of multi-walled carbon nanotubes immobilized magnetic nanoparticles for removing selected pesticides from aqueous matrices

The present work synthesized two new materials of functionalized multi-walled carbon nanotubes (MWCNT-OH and MWCNT-COOH) impregnated with magnetite (Fe₃O₄) using solution precipitation methodology. The resulting MWCNT-OH-Mag and MWCNT-COOH-Mag materials were characterized by scanning electron microscopy coupled with energy dispersion X-ray spectroscopy, Fourier transform infrared, X-ray diffraction, atomic force microscopy, and electrical force microscopy. The characterization results indicate that the -OH functional groups in the MWCNT interact effectively with magnetite iron favoring impregnation and indicating the regular distribution of nanoparticles on the surface of the synthesized materials. The adsorption efficiency of the MWCNT-OH-Mag and MWCNT-COOH-Mag materials was tested using the pollutants 2,4-D and Atrazine. Over batch studies carried out under different pH ranges, it was found that the optimal condition for 2,4-D adsorption was at pH 2, while for Atrazine, it was found at pH 6. The rapid adsorption kinetics of 2,4-D and Atrazine reaches equilibrium within 30 min. The pseudo-first-order model described 2,4-D adsorption well. The General-order model described better atrazine adsorption. The magnetically doped adsorbent functionalized with -OH surface groups (MWCNT-OH-Mag) demonstrated superior adsorption performance and increased Fe-doped sites. The Sips model described the adsorption isotherms accurately. MWCNT-OH-Mag presented the greatest adsorption capacity at 51.4 and 47.7 mg g^-1 for 2,4-D and Atrazine, respectively. Besides, electrostatic forces and complexation rule the molecular interactions between metals and pesticides. The leaching and regeneration tests of the synthesized materials indicate high stability in an aqueous solution. Furthermore, experiments with wastewater samples contaminated with the model pollutants indicate that the novel adsorbents are highly promising for enhancing water purification by adsorptive separation.

Adsorption of 2,4-dichlorophenoxyacetic acid and glyphosate from water by Fe3O4-UiO-66-NH2 obtained in a simple green way

In this study, a green adsorbent (Fe₃O₄-UiO-66-NH₂) with the ability of addressing the issues of separation and recovery of UiO-66-NH₂ is obtained using a simple co-precipitation method under environmentally benign conditions. Various characterization techniques are utilized for evaluating the properties of the developed adsorbent. The capability of Fe₃O₄-UiO-66-NH₂ towards 2,4-dichlorophenoxyacetic acid (2,4-D) and glyphosate (GP) from solution is explored. The results revealed that the magnetization process did not destroy the crystal structure of UiO-66-NH₂, which ensured that Fe₃O₄-UiO-66-NH₂ had good adsorption performance for 2,4-D and GP. The adsorption processes showed a wide pH application range, high salt tolerance, and regeneration performance as well as an excellent adsorption rate. Results from thermodynamic study showed that both processes were spontaneous and endothermic. The unit uptake ability of Fe₃O₄-UiO-66-NH₂ for 2,4-D and GP reached up to 249 mg·g^-1 and 183 mg·g^-1 from Langmuir model at 303 K, respectively. When solid-liquid ratio was 2 g·L^-1, Fe₃O₄-UiO-66-NH₂ can reduce the content of 2,4-D or GP with the initial density of 100 mg·L^-1 below the drinking water requirement limit. In addition, the reusability efficiency of Fe₃O₄-UiO-66-NH₂ towards 2,4-D and GP was found to be 86% and 80% using 5 mmol·L^-1 NaOH as eluent. Analysis of simulated water samples indicated that Fe₃O₄-UiO-66-NH₂ could achieve the single or simultaneous removal of 2,4-D and GP from wastewater. Summarily, Fe₃O₄-UiO-66-NH₂ as a green adsorbent can serve as an alternative for removing 2,4-D and GP from water body.

2,4-Dichlorophenoxyacetic acid (2,4-D) adsorptive removal by algal magnetic activated carbon nanocomposite

In the present study, ferric oxide nanoparticles impregnated with activated carbon from Ulva prolifera biomass (UPAC-Fe₂O₃) were prepared and employed to remove 2,4-Dichlorophenoxyacetic acid (2,4-D) by adsorption. The UPAC-Fe₂O₃ nanocomposite was characterized for its structural and functional properties by a variety of techniques. The nanocomposite had a jagged, irregular surface with pores due to uneven scattering of Fe₂O₃ nanoparticles, whereas elemental analysis portrayed the incidence of carbon, oxygen, and iron. XRD analysis established the crystalline and amorphous planes corresponding to the iron oxide and carbon phase respectively. FT-IR analyzed the functional groups that confirmed the integration of Fe₂O₃ nanoparticles onto nanocomposite surfaces. VSM and XPS studies uncovered the superparamagnetic nature and presence of carbon and Fe₂O_3, respectively, in the UPAC-Fe₂O₃ nanocomposite. While the surface area was 292.51 m²/g, the size and volume of the pores were at 2.61 nm and 0.1906 cm³/g, respectively, indicating the mesoporous nature and suitability of the nanocomposites that could be used as adsorbents. Adsorptive removal of 2,4-D by nanocomposite for variations in process parameters like pH, dosage, agitation speed, adsorption time, and 2,4-D concentration was studied. The adsorption of 2,4-D by UPAC-Fe₂O₃ nanocomposite was monolayer chemisorption owing to Langmuir isotherm behavior along with a pseudo-second-order kinetic model. The maximum adsorption capacity and second order rate constant values were 60.61 mg/g and 0.0405 g/mg min respectively. Thermodynamic analysis revealed the spontaneous and feasible endothermic adsorption process. These findings confirm the suitability of the synthesized UPAC-Fe₂O₃ nanocomposite to be used as an adsorbent for toxic herbicide waste streams.

Valorization of date palm leaves for adsorptive remediation of 2,4-dichlorophenoxyacetic acid herbicide polluted agricultural runoff

Alarming rates of water contamination by toxic herbicides have prompted the need and attention for easy, efficient, and affordable treatment options with a touch of circular economy aspects. This study valorized date palm leaf (DPL) wastes into a valuable adsorbent for remediating agricultural wastewater polluted with 2,4-Dichlorophenoxyacetic acid (2,4-DPA) herbicide. The DPL precursor was modified with H₂SO₄ treatment and both biomass samples were characterized by various analytical techniques. Acid treatment modified the morphology, thermal, and textural properties of the final product (TDPL) while maintaining the structure and surface chemistry intact. Simulated wastewaters containing 2,4-DPA were subsequently treated using TDPL as an adsorbent. Optimum adsorption conditions of pH 2, dosage 0.95 g/L, shaking speed 200 rpm, time 120 min, and temperature 30 °C showed a good herbicide removal efficiency in the range of 55.1-72.6% for different initial feed concentrations (50-250 mg/L). Experimental kinetic data were better represented by the pseudo-second-order model, while the Freundlich isotherm was reliable in describing the equilibrium behavior of the adsorption system. Further, the thermodynamic analysis revealed that the adsorption occurred spontaneously, favorably, and exothermically. Plausible sorption mechanism involved electrostatic interactions, weak van der Waals forces, hydrogen bonds, and π-π interactions between the participating phases. Conspicuously, TDPL application to real-world situations of treating actual herbicide-polluted agricultural runoff resulted in a 69.4% remediation efficiency. Thus, the study demonstrated the valorization of date palm leaves into a valuable and industry-ready adsorbent that can sequester toxic 2,4-DPA herbicide contaminant from aqueous streams.

Adsorption of 2,4-dichlorophenoxyacetic acid by UiO-66-NH2 obtained in a green way

In this study, a zirconium elemental organic framework (UiO-66-NH₂) was prepared by a green synthesis method and showed a good adsorption performance for removing 2,4-dichlorophenoxyacetic acid (2,4-D) from water. UiO-66-NH₂ was analyzed by a variety of characterization methods and the adsorption properties of 2,4-D on UiO-66-NH₂ were investigated by static adsorption experiments. The results showed that the adsorption of 2,4-D had a wide pH range (2-10) and good salt tolerance with the adsorption equilibrium time about 2 h. The maximum adsorption capacity from Langmuir was up to 652 mg g^-1 at 303 K. The isotherms can be described by Langmuir model and the adsorption kinetics was consistent with pseudo-second-order kinetic model and Elovich model. The regeneration efficiency was still 95% after 5 cycles with 0.01 mol L^-1 NaOH as desorption solution. The feasibility of practical application of UiO-66-NH₂ was explored by simulating actual wastewater at different pH. UiO-66-NH₂ is promising to remove 2,4-D from water.

Transformation of Residual Açai Fruit (Euterpe oleracea) Seeds into Porous Adsorbent for Efficient Removal of 2,4-Dichlorophenoxyacetic Acid Herbicide from Waters

Brazil's production and consumption of açai pulp (Euterpe oleracea) occur on a large scale. Most of the fruit is formed by the pit, which generates countless tons of residual biomass. A new purpose for this biomass, making its consumption highly sustainable, was presented in this study, where activated carbon (AC) was produced with zinc chloride for later use as an adsorbent. AC carbon formed by carbon and with a yield of 28 % was satisfactorily used as an adsorbent in removing the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Removal efficiency was due to the highly porous surface (Vp = 0.467 cm³ g^-1; Dp = 1.126 nm) and good surface área (SBET = 920.56 m² g^-1). The equilibrium data fit the Sips heterogeneous and homogeneous surface model better. It was observed that the increase in temperature favored adsorption, reaching a maximum experimental capacity of 218 mg g^-1 at 328 K. The thermodynamic behavior indicated a spontaneous, favorable, and endothermic behavior. The magnitude of the enthalpy of adsorption was in agreement with the physical adsorption. Regardless of the herbicide concentration, the adsorbent displayed fast kinetics, reaching equilibrium within 120 min. The linear driving force (LDF) model provided a strong statistical match to the kinetic curves. AC with zinc chloride (ZnCl₂), created from leftover açai biomass, is a potential alternative as an adsorbent for treating effluents containing 2,4-D.

Efficient removal of 2,4-D from solution using a novel antibacterial adsorbent based on tiger nut residues: adsorption and antibacterial study

We engineered a tiger nut residue (TNR, a low-cost agricultural waste material) through a facile and simple process to take advantage of the introduced functional groups (cetylpyridinium chloride, CPC) in the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) in batch mode and further investigated its impingement on bacterial growth in a yeast-dextrose broth. The surface characterizations of the adsorbent were achieved through Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller method (BET), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The batch adsorption studies revealed that solution pH, adsorbent dose, temperature, and salt affected the adsorptive capacity of TNR-CPC. The equilibrium data were best fitted by Langmuir isotherm model with a maximum monolayer adsorption capacity of 90.2 mg g^-1 at 318 K and pH 3. Pseudo-second-order model best fitted the kinetics data for the adsorption process. Physisorption largely mediated the adsorption system with spontaneity and a shift in entropy of the aqueous solid-solute interface reflecting decreased randomness with an exothermic character. TNR-CPC demonstrated a good reusability potential making it highly economical and compares well with other adsorbents for decontamination of 2,4-D. The adsorption of 2,4-D proceeded through a probable trio-mechanism; electrostatic attraction between the carboxylate anion of 2,4-D and the pyridinium cation of TNR-CPC, hydrogen bonding between the hydroxyl (-OH) group inherent in the TNR and the carboxyl groups in 2,4-D and a triggered π-π stacking between the benzene structures in the adsorbate and the adsorbent. TNR-CPC reported about 99% inhibition rate against both gram-positive S. aureus and gram-negative E. coli. It would be appropriate to investigate the potential of TNR-CPC as a potential replacement to the metal oxides used in wastewater treatment for antibacterial capabilities, and its effects against airborne bacteria could also be of interest.

Graphene oxide/MIL 101(Cr) (GO/MOF) nano-composite for adsorptive removal of 2,4-dichlorophenoxyacetic acid (2,4 D) from aqueous media: synthesis, characterization, kinetic and isotherm studies

Contamination of water resources with various pollutants and therefore lack of clean water resources are major problems that threaten many human societies. The need to develop efficient methods and materials to decontaminate water resource is an undeniable fact. Metal-organic frameworks (MOFs), as new class of highly crystalline porous solids, have attracted a great deal of attention in different research fields, especially in adsorptive removal and purification. In this study, MIL 101(Cr) MOF decorated with graphene oxide nano-layers (GO/MOF) was synthesized by a simple one-pot hydrothermal method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electron dispersion energy (EDS) were utilized to approve the growing of Cr-MOF on graphene oxide nano-layer. The synthesized nano-composite was used as a potential adsorbent for the removal of a pesticide, 2, 4-dichlorophenoxyacetic acid (2,4 D). The adsorption performance, kinetic and mechanism of 2,4 D adsorption onto GO/MOF were studied. The highest adsorption capacities of 476.9 mg g^-1 was obtained at room temperature, pH 6.0 using 0.6 gL^-1 of GO/MOF which was 34% higher than that of pristine Cr-MOF. The kinetics and isotherm data fitted well with pseudo-second kinetic and Langmuir isotherm model, respectively. The reusability and stability analyses showed that the synthesized GO/MOF nanocomposite kept 89% of sorption capacities for 2,4 D after four adsorption-desorption cycles. GO/MOF nano-composite was successfully applied to remove 2,4 D from agricultural waste. The results approved that the synthesized nano-composite could introduce as a stable and high performance adsorbent for adsorptive removal of selected pesticide.

Advances in Amine-Surface Functionalization of Inorganic Adsorbents for Water Treatment and Antimicrobial Activities: A Review

In the last decade, adsorption has exhibited promising and effective outcomes as a treatment technique for wastewater contaminated with many types of pollutants such as heavy metals, dyes, pharmaceuticals, and bacteria. To achieve such effectiveness, a number of potential adsorbents have been synthesized and applied for water remediation and antimicrobial activities. Among these inorganic adsorbents (INAD), activated carbon, silica, metal oxide, metal nanoparticles, metal–organic fibers, and graphene oxide have been evaluated. In recent years, significant efforts have been made in the development of highly efficient adsorbent materials for gas and liquid phases. For gas capture and water decontamination, the most popular and known functionalization strategy is the chemical grafting of amine, due to its low cost, ecofriendliness, and effectiveness. In this context, various amines such as 3-aminopropyltriethoxysilane (APTES), diethanolamine (DEA), dendrimer-based polyamidoamine (PAMAM), branched polyethyleneimine (PEI), and others are employed for the surface modification of INADs to constitute a large panel of resource and low-cost materials usable as an alternative to conventional treatments aimed at removing organic and inorganic pollutants and pathogenic bacteria. Amine-grafted INAD has long been considered as a promising approach for the adsorption of both inorganic and organic pollutants. The goal of this review is to provide an overview of surface modifications through amine grafting and their adsorption behavior under diverse conditions. Amine grafting strategies are investigated in terms of the effects of the solvent, temperature, and the concentration precursor. The literature survey presented in this work provides evidence of the significant potential of amine-grafted INAD to remove not only various contaminants separately from polluted water, but also to remove pollutant mixtures and bacteria.

Magnetic activated charcoal/Fe2O3 nanocomposite for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions: Synthesis, characterization, optimization, kinetic and isotherm studies

Magnetic activated charcoal/Fe₂O₃ nanocomposite (AC/Fe₂O₃NC) was fabricated using Spondias dulcis leaf extract by a facile method and used for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions for the first time. The nanocomposite was characterized by methods such as FE-SEM, EDS, XRD, FTIR, TGA, VSM, and BET to identify and confirm the surface morphology, elemental composition, crystalline nature, functional groups, thermal stability, magnetic behavior, and surface area respectively. Box-Behnken Design (BBD) - an optimization method, which belongs to the Response surface methodology (RSM) and a modeling tool - Artificial Neural Network (ANN) were employed to design, optimize and predict the relationship between the input parameters (pH, initial concentration of 2,4-D, time and agitation speed) versus the output parameter (adsorption efficiency of 2,4-D). Adsorption efficiency of 98.12% was obtained at optimum conditions (pH: 2.05, initial concentration: 32 ppm, contact time: 100 min, agitation speed: 130 rpm, temperature: 30 °C, and dosage: 0.2 g/L). The predictive ability of the ANN was superior (R² = 0.99) than the quadratic model, given by the RSM (R² = 0.93). The equilibrium data were best-fitted to Langmuir isotherm (R² = 0.9944) and the kinetics obeyed pseudo-second-order model (R² = 0.9993) satisfactorily. Thermodynamic studies revealed the spontaneity and exothermic nature of adsorption. The maximum adsorption capacity, q_m was found to be 255.10 mg/g, substantially larger than the reported values for 2,4-D adsorption by other magnetic nanoadsorbents. Therefore, this nanoadsorbent may be utilized as an excellent alternative for the elimination of 2,4-D from the waterbodies.

One step acid modification of the residual bark from Campomanesia guazumifolia using H2SO4 and application in the removal of 2,4-dichlorophenoxyacetic from aqueous solution

The residual bark of the tree species Campomanesia guazumifolia was successfully modified with H₂SO₄ and applied to remove the toxic herbicide 2.4-dichlorophenoxyacetic (2.4-D) from aqueous solutions. The characterization techniques made it possible to observe that the material maintained its amorphous structure; however, a new FTIR band emerged, indicating the interaction of the lignocellulosic matrix with sulfuric acid. Micrographs showed that the material maintained its irregular shape; however, new spaces and cavities appeared after the acidic modification. Regardless of the herbicide concentration, the system tended to equilibrium after 120 min. Using the best statistical coefficients, the Elovich model was the one that best fitted the kinetic data. The temperature increase in the system negatively influenced the adsorption of 2.4-D, reaching a maximum capacity of 312.81 mg g^-1 at 298 K. The equilibrium curves showed a better fit to the Tóth model. Thermodynamic parameters confirmed the exothermic nature of the system (ΔH⁰ = -59.86 kJ mol^-1). As a residue obtained from urban pruning, the bark of Campomanesia guazumifolia treated with sulfuric acid is a promising and highly efficient alternative for removing the widely used and toxic 2.4-D herbicide from aqueous solutions.

Nano-activated carbon derived from date palm coir waste for efficient sequestration of noxious 2,4-dichlorophenoxyacetic acid herbicide

Alarming water contamination rates by toxic herbicides have drawn attention to treat these pollutants using efficient, easy, and economic techniques. In this work, date-palm coir (DPC) waste-based nano-activated carbon (DPC-AC) was successfully prepared and examined for adsorptive removal of toxic 2,4-dichlorophenoxyacetic acid (2,4-DPA) herbicide from synthetic wastewater. The DPC-AC was synthesized via a single-step carbonization-KOH activation approach. The nanosorbent displayed a flaky morphology with graphitic structure and oxygen-rich surface functionalities. The nanocarbon with a mean particle size of 163 nm possessed a high specific surface area of 947 m²/g with an average pore size of 2.28 nm. High 2,4-DPA removal efficiency of 98.6% was obtained for the optimal adsorption conditions of pH 2, dosage 0.15 g, rotational speed 100 rpm, time 90 min, and initial 2,4-DPA concentration of 100 mg/L. Langmuir isotherm best described the equilibrium behavior with a theoretical maximum of 50.25 mg/g adsorption capacity for the system. Pseudo-second order model was more appropriate in quantifying the kinetics for all initial feed concentrations. Thermodynamically, the adsorption process was spontaneous, endothermic, and involved low activation energy. A plausible mechanism for the adsorption-desorption of 2,4-DPA onto DPC-AC is also discussed. Cost analysis and regenerability studies proved the economic value ($3/kg) and reusable nature of DPC-AC without any significant loss in its performance. Overall, this study highlights the advantages of DPC waste valorization into efficient nanoadsorbent and the sequestration of noxious 2,4-DPA herbicide from its aqueous streams using this nanosorbent.

Highly efficient adsorption and mechanism of alkylphenols on magnetic reduced graphene oxide

The influence of alkylphenols to environment cannot be ignored, as they are common product from chemical industries and potential threat to human health. Some alkylphenols are listed as persistent toxic substances (PTS) by the United Nations Environment Programme (UNEP). In this study, the optimized magnetic reduced graphene oxide (MrGO) was synthesized by a facile solvothermal method, and investigated for adsorption of three typical alkylphenols. In neutral condition, MrGO showed extremely high adsorption capacity of three typical alkylphenols, 4-heptylphenol (4-HP), 4-tert-octylphenol (4-OP), and 4-nonylphenol (4-NP), which could reach 938.9 mg g^-1 (40 °C), 987.8 mg g^-1 (40 °C), and 989.7 mg g^-1 (20 °C), respectively. This study revealed that the adsorption process was a heterogeneous multi-layer physical adsorption, and the adsorption rates were related to the number of unoccupied vacancies on the adsorbent surface. From batch experiments and density functional theory (DFT) calculations, the main adsorption interactions between MrGO and alkylphenols were deduced to be π-π, hydrogen-bond, and hydrophobic interactions. What's more, the different affinities of MrGO towards different targets were further distinguished and explained in detail. The wonderful stability and recyclability of MrGO made it a promising cost-effective remediation candidate.

Adsorption investigation of 2,4-D herbicide on acid-treated peanut (Arachis hypogaea) skins

In this work, peanut (Arachis hypogaea) skin, a by-product generated by the agricultural production of its seeds, was employed as a precursor in the preparation of an adsorbent for the 2,4-D removal in water. The skins were treated with sulfuric acid and characterized by different techniques. The adsorption was favored at acid pH = 2 with pH_pzc = 6. The dosage of 0.9 g L^-1 was considered ideal, obtaining satisfactory indications of removal and capacity. The kinetic curves were well represented by the general order model, with the equilibrium reached quickly in the first 30 min for all concentrations. Adsorption isotherm studies showed that the increase in temperature negatively affected the herbicide adsorption, obtaining a maximum capacity of 246.72 mg g^-1, by the Langmuir isotherm at 298 K. The remarkable adsorption efficiency presented by the adsorbent can be associated with the presence of new functional groups on the adsorbent surface generated after the acid treatment. Thermodynamic parameters confirmed the exothermic nature of the adsorptive system. In the treatment of synthetic wastewater consisting of a mixture of herbicides and salts, a high removal efficiency (72%) of herbicides was obtained. Therefore, the development of an adsorbent derived from peanut (Arachis hypogaea) skin treated with sulfuric acid is an excellent alternative, generating remarkable removal results towards 2,4-D herbicide.

Prospective application of diethylaminoethyl cellulose (DEAE-cellulose) with a high adsorption capacity toward the detoxification of 2,4-dichlorophenoxyacetic acid (2,4-D) from water

Detoxification of pesticide residues requires effective methods. In this regard, the adsorption efficiency of diethylaminoethyl cellulose (DEAE-cellulose) as an adsorbent material for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from water at different concentrations, times, pH and temperature was evaluated comprehensively. The obtained results showed that DEAE-cellulose has greater efficacy to eliminate 2,4-D from water with a high Langmuir maximum adsorption capacity of 429.18 mg g^-1 at pH 7.0. Kinetic models and thermodynamics were investigated at length. The adsorption mechanism was understood by way of electrostatic, hydrogen bonding, and Lewis acid-base type interactions. Extensive analytical characterization of the DEAE-cellulose adsorbent before and after 2,4-D adsorption was performed and liquid chromatography with a tandem mass spectrometer (LC-MS/MS) was used for the quantification of 2,4-D. The regeneration of DEAE-cellulose was achievable using dilute formic acid and the DEAE-cellulose adsorbent showed high ability in the removal of 2,4-D from the agriculture run-off water.

Ultrasound-acid modified Merremia vitifolia biomass for the biosorption of herbicide 2,4-D from aqueous solution

In this work, a biosorbent was prepared by the ultrasound-acid treatment of Merremia vitifolia plant and tested for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D), a phenoxy herbicide. Optimal values of five batch biosorption parameters namely stirring speed, contact time, biosorbent dosage, initial pH and initial adsorbate concentration were experimentally obtained in sequential manner for an enhanced biosorption capacity. The kinetics of the biosorption of 2,4-D were best described by the pseudo first order kinetic model (R² = 0.99) and the biosorption equilibrium data were successfully fitted to the Langmuir adsorption isotherm (R² = 0.99) with a maximum biosorption capacity of 66.93 mg g^-1. The mechanism of biosorption was investigated using two intraparticle diffusion models (Weber and Boyd), Dubinin-Radushkevich isotherm model and electrostatic interactions. The presence of intraparticle and film diffusion limitations for the biosorption was confirmed along with the physical and chemical nature of the biosorption. The thermodynamic parameters of the biosorption were calculated using the equilibrium data obtained at four different temperatures. The entropy change for biosorption was found to be negative indicating the decreased randomness at the interface. Desorption studies were carried out using different solvents and the percentages of desorption were compared.

Cationic metal-organic frameworks as an efficient adsorbent for the removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions

Metal-organic frameworks (MOFs) material with high surface area, good chemical stability and multi-functionality, has become an emerging adsorbent for water treatment. A novel kind of quaternary amine anionic-exchange MOFs UiO-66 namely UiO-66-NMe₃⁺ was firstly synthesized for adsorptive removal of a widely used toxic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solutions. The well-prepared UiO-66-NMe₃⁺ MOFs were fully characterized, and then the main parameters affecting the adsorption process including solution pH, adsorbent dosage and coexisting anions were systematically investigated. The maximum adsorption capacity of UiO-66-NMe₃⁺ toward 2,4-D reached as high as 279 mg g^-1, much higher than that of pristine UiO-66 and aminated UiO-66. The adsorption mechanism could be attributed to the electrostatic interactions efficiently enhanced by the functionalization of quaternary amine groups, combining with the π-π conjugations between the linkers in MOFs and 2,4-D molecules, leading to the better adsorption performance of UiO-66-NMe₃⁺. Additionally, the UiO-66-NMe₃⁺ could be well regenerated by simple solvent washing and exhibited a slight decline of adsorption capacity after seven successive recycle. Furthermore, satisfactory adsorption capacity and reusability of the MOFs in environmental water samples were attained. Comparing with reported activated carbon and resin materials, the UiO-66-NMe₃⁺ MOFs possessed higher adsorption capacity and shorter equilibrium time, as well as good reusability and practicality. The developed ion-exchange functionalized MOFs provided an ideal alternative for efficient adsorptive-removal of 2,4-D from complicated aqueous environment.

High-performance of activated biocarbon based on agricultural biomass waste applied for 2,4-D herbicide removing from water: adsorption, kinetic and thermodynamic assessments

Activated biocarbons were prepared using biomass wastes: sugarcane bagasse, coconut shell and endocarp of babassu coconut; as a renewable source of low-cost raw materials and without prior treatments. These activated biocarbons were characterized by textural analysis, solid-state ¹³C nuclear magnetic resonance spectroscopy, X-ray diffraction and scanning electronic microscopy. Textural analysis results revealed that those activated biocarbons were microporous, with specific surface area values of 547, 991 and 1,068 m² g^-1 from sugarcane bagasse, coconut shell and endocarp of babassu coconut, respectively. The innovation of this work was to evaluate which biomass residue was able to offer the best performance in removing 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) from water by adsorption. Adsorption process of 2,4-D was investigated and the Langmuir and Redlich-Peterson models described best the adsorption process, with R² values within 0.96-0.99. The 2,4-D removal performance were 97% and 99% for the coconut and babassu biocarbons, respectively. q_M parameter values obtained from Langmuir model were 153.9, 233.0 and 235.5 mg g^-1 using sugarcane bagasse, coconut shell and endocarp of babassu, respectively. In addition, the adsorption kinetics were described nicely by the second-order model and the Gibbs free energy parameter values were negative, pointing to a spontaneous adsorption, as well.

Development of Porous Titania Structure with Improved Photocatalytic Activity: Response Surface Modeling and Multi-Objective Optimization

Porous titania was successfully synthesized by an ultrasound-assisted sol-gel route. The synthesis process was empirically modeled and optimized using the response surface methodology (RSM). Input variables adopted for optimization dealt with the weight ratio of precursors (r) and the sonication time (t), representing the used factors in the synthesis procedure. With regard to application, the synthesized TiO₂ samples were tested for the photodegradation of two water-soluble organic pollutants under UV-Vis irradiation. Optimal conditions for the efficient pollutants' photodegradation were found to involve a precursors ratio of 3 and a sonication time of 60 min. Thus, the M5 sample prepared under the founded optimal conditions yielded the maximal removal efficiencies of 98.4% and 46.3% for the photodegradation of CR dye and 2,4-D herbicide, respectively. In addition, the photodegradation kinetics revealed the pseudo first-order rate constants, showing the photodegradation of CR (k₁ = 8.86 × 10^-2 min^-1) by M5 sample is about 1.3-fold faster than the photodegradation of 2,4-D pesticide (k₂ = 6.84 × 10^-2 min^-1).

2,4-dichlorophenoxyacetic acid (2,4-D) micropollutant herbicide removing from water using granular and powdered activated carbons: a comparison applied for water treatment and health safety

Activated carbons are well-known porous materials as an effective adsorbent used for the removal of emerging contaminants, such as herbicides, which are increasingly present in water bodies. Most water treatment plants, specially in Brazil, are unable to completely remove such contaminants by the conventional process and advanced treatment using activated carbons is required. The aim of this paper was to verify the influence of the activated carbons granulometry and specific surface area on the 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide removal efficiency using distilled-deionized water and filtered water collected from a conventional Water Treatment Plant. Commercial activated carbons samples used in this work were obtained from two different manufacturers. Activated carbons were analyzed by the specific surface area, pore size and volume distribution, nuclear magnetic resonance, infrared and x-ray spectroscopy, moisture, volatile matter and ash contents. Batch adsorption isotherms experiments were used and performed by Langmuir and Freundlich models. Granular and powdered activated carbons removed over 99% of 2,4-D in distilled water and near to 99% using filtered water. The activated carbons evaluated in this work presented high performance and played a key role in water treatment by removing 2,4-D herbicide, ensuring the protection of human health and the ecosystem.

Adsorption of herbicide 2,4-D from aqueous solution using organo-modified bentonite clay

This study analyzed the performance of organophilic clays obtained from the chemical modification of sodium bentonite clay when applied to the adsorption of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Kinetic curves and equilibrium isotherms were obtained in order to determine time and adsorption capacity of the material, as well as understand the mechanisms involved in this phenomenon. The results showed that the most predictive kinetic model for experimental data was of pseudo-second order (R² > 0.98), and that external mass transfer is the dominant factor in the time of operation. Isotherms were obtained at temperatures of 298, 308, and 318 K, under which the Dubinin-Radushkevich model was shown to have a good fit to data (R² > 0.96), according to mathematical adjustments. The maximum adsorption capacity obtained experimentally was 50.36 mg g^-1, found at a temperature of 298 K, being higher or compatible with other materials reported in the literature. With help of the thermodynamic studies on the process, it was observed that the adsorption of 2,4-D in organophilic clays refers to a spontaneous (ΔG°_ads < 0), exothermal (ΔH°_ads = - 9.99 kJ mol^-1) process of physical nature. Lastly, it was observed that the adsorbent can be easily regenerated when subjected to eluents such as mixtures containing fractions of ethanol/water (desorption = 95%).

Iron-loaded amine/thiol functionalized polyester fibers with high catalytic activities: a comparative study

Dispersion of iron nanoparticles (Fe-NPs) was achieved on polyester fabrics (PET) by diverse stabilizing agents.

Characterization and evaluation of surface modified materials based on porous biochar and its adsorption properties for 2,4-dichlorophenoxyacetic acid

In this study, the effect of surface modification on the properties of porous biochar was studied, and these modification techniques were synthetically evaluated by principal component analysis. The results showed that surface modification significantly affected the surface and adsorption properties of porous biochar. Potassium carbonate activated porous biochar (KBC) was modified by surface oxidation, surface amination, loading nano-zero valent iron (nZVI) and loading nano-iron oxyhydroxide (nHIO). The surface modification affected the pore structure, especially the micropores. Surface modification influenced the oxygen-containing functional groups, amino, and metal-O significantly. It also changed the diffusion of 2,4-dichlorophenoxyacetic acid (2,4-D) on the biochar surface. The specific surface area was not the only factor determining the adsorption capacity. Surfaces rich in oxygen-containing functional groups would favor the adsorption of 2,4-D by biochar. The adsorption of biochars on 2,4-D were determined by π-π interaction, chemisorption and hydrogen bonding. The synthetic properties of modified biochar were evaluated by principal component analysis, and the comprehensive performance was in order of NKBC > OKBC > KBC > BC > nHIO@KBC > nZVI@KBC. Structural activation, surface amination and surface oxidation can improve the comprehensive properties of biochar.

Adsorption of 2,4-dichlorophenoxyacetic acid and 4-chloro-2-metylphenoxyacetic acid onto activated carbons derived from various lignocellulosic materials

Adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-metylphenoxyacetic acid (MCPA) from aqueous solution onto activated carbons derived from various lignocellulosic materials including willow, miscanthus, flax, and hemp shives was investigated. The adsorption kinetic data were analyzed using two kinetic models: the pseudo-first order and pseudo-second order equations. The adsorption kinetics of both herbicides was better represented by the pseudo-second order model. The adsorption isotherms of 2,4-D and MCPA on the activated carbons were analyzed using the Freundlich and Langmuir isotherm models. The equilibrium data followed the Langmuir isotherm. The effect of pH on the adsorption was also studied. The results showed that the activated carbons prepared from the lignocellulosic materials are efficient adsorbents for the removal of 2,4-D and MCPA from aqueous solutions.

Interaction of pesticides with natural and synthetic solids. Evaluation in dynamic and equilibrium conditions

Interactions between pesticides (paraquat, glyphosate, 2,4-D, atrazine, and metsulfuron methyl) and soil organic and inorganic components have been studied in batch experiments by performing adsorption, dissolution, and chemical and photochemical degradation under different conditions. The obtained results confirm that the affinity of a pesticide to the solid surface depends on the nature of both and shows that each reactant strongly affects the mobility of the other one, e.g., anionic pesticides promote the dissolution of the solid humic acid but if this last is retained into the inorganic matrix enhances the adsorption of a cationic pesticide. Adsorption also seems to protect the bonded specie to be chemical degraded, such as shown in two pesticide/clay systems at constant pH. The use of mesoporous silicas could result in a good alternative for pesticide remediation. In fact, the solid shows high adsorption capacity towards paraquat and its modification with TiO₂ nanoparticles increases not only the pesticide adsorption but also seems to catalyze its degradation under UV light to less-toxic metabolites. UV-VIS spectroscopy was relevant and novel in such sense. Electrostatic interactions, hydrogen and coordinative bonds formations, surface complexations and hydrophobic associations play a key role in the fate of mentioned pesticides on soil and ground/surface water environments.