Adsorption Of Paraquat Research Articles

Kinetic study of paraquat adsorption on alginate beads loaded with montmorillonite using shrinking core model

Water contamination by pesticides threatens clean water availability, highlighting the need for advanced sustainable sanitation systems. Adsorption using biopolymers and minerals is prominent. Understanding process kinetics and influencing parameters is crucial for optimizing contaminant-adsorbent contact time for safe water disposal. The adsorption kinetics of Paraquat (PQ) at three initial concentrations (C0 = 19, 38, and 50 ppm) were studied using alginate-montmorillonite (Alg-Mt) beads with varying clay contents and a 30-min gelation time. The beads were characterized by elemental analysis, TG/DTG, FTIR, XRD, SEM, and EDX. The Shrinking Core Model (SCM) was applied to the experimental data to determine if the diffusion of PQ within the beads depended on clay content. The effective diffusion coefficient (Dp) in the adsorbent increased from 7 × 10−12 to 1 × 10−10 m2 s−1 with increasing clay content, suggesting that diffusion into the interior depended on interaction with the mineral.This investigation also demonstrated that the synthesis of beads at different gelation times does not impact either the adsorption capacity or the adsorption rate of the herbicide on the materials. These results indicate that diffusion depends solely on the interaction of the cationic herbicide with the clay encapsulated within the bead hydrogel.

Adsorption and removal of herbicide paraquat from aqueous solutions via novel bimetal organic framework: Kinetics, equilibrium and statistical surface modeling

This study examines the adsorption and removal of the herbicide paraquat in relation to a bimetal organic framework known as the Terbium/Palladium Metal-Organic Framework (Tb/Pd-MOF). Analysis of N2 adsorption/desorption isotherms, which were used to assess the properties of the Tb/Pd-MOF, revealed that the absorption of paraquat on Tb/Pd-MOF resulted in a reduction in pore volume, pore size, and surface area. Specifically, the pore volume decreased from 8.25 to 5.68 cm3/g, the pore size decreased from 11.34 nm to 8.92 nm, and the surface area decreased from 1456.61 to 1262.82 m2/g. The pore radius also decreased from 0.96 nm to 0.58 nm. Tb/Pd-MOF’s functional groups were identified through FT-IR, and the structure of the compound was confirmed using XPS. Various adsorption parameters including temperature, adsorbent dosage, pH, paraquat concentration, and contact time were studied. Density functional theory (DFT) was used to understand the electrical properties, reactivity, and morphology of paraquat. Results from the DFT analysis revealed that the electrophilic and nucleophilic attack sites aligned with the molecular orbitals (HOMO and LUMO) and MEP outcomes. The study found that Tb/Pd-MOF demonstrated a significant absorption capacity for paraquat, with adsorption data consistent with the Langmuir isotherm and pseudo-second-order kinetic models. The paraquat adsorption capability of Tb/Pd-MOF was determined to be 574.8 mg/g. Furthermore, chemisorption was identified as the primary form of adsorption, as indicated by the adsorption energy of 26.98 kJ·mol−1. The optimal conditions for achieving a high adsorption capacity were identified as pH 8 and 0.02 g of Tb/Pd-MOF. The temperature-dependent changes in the thermodynamic parameters ΔG°, ΔH°, and ΔS° indicated that the paraquat absorption onto Tb/Pd-MOF occurred spontaneously, was endothermic, and involved random processes. To optimize the absorption process, Response Surface Methodology and Box-Behnken design (RSM, BBD) were employed. These techniques enabled effective removal of paraquat from the Tb/Pd-MOF material. During chemisorption, the adsorbate and adsorbent form chemical bonds, while aromatic rings are involved in π-π bonding. Additionally, pore-filling occurs when the adsorbate fills the pores of the adsorbent, and electrostatic interactions result from the attraction or repulsion of charges between the adsorbate and adsorbent. As a means of eliminating paraquat from wastewater, Tb/Pd-MOF demonstrates significant potential due to its diverse absorption processes and high capacity for adsorption.

Spectrophotometric adsorption isotherms of paraquat and methylene blue on montmorillonite: Unveiling adsorption modes without filtration or centrifugation

Measuring adsorption isotherms in a single experimental run is important for designing environmentally friendly adsorption experiments, reducing resources usage and contamination risks. In this study, one-pot adsorption isotherms of the divalent cation paraquat (PQ) and the monovalent cation methylene blue (MB) on montmorillonite were directly measured by UV-Vis spectrophotometry, with no need for separation of the solid phase from the aqueous phase by filtration or centrifugation. PQ adsorption resulted in a bathochromic shift (red shift) in the absorption band position, moving from 258 nm to 277 nm, and only one adsorbed species was detected. MB adsorption induced a hypsochromic shift (blue shift) from 664 nm to lower wavelengths, and at least three different adsorbed species were identified. In the case of PQ, the spectrophotometric isotherm coincided with a regular isotherm, saturating at the cation exchange capacity (CEC) of the solid, 9.1×10−4 Eq/g. In the case of MB, the spectrophotometric isotherm also saturated at the CEC, but the regular isotherm saturated at a higher adsorption extent, 1.2×10−3 Eq/g. In both cases, the presence of negative structural charges of the clay and the planar environment of the interlayer space were crucial for inducing the observed spectral changes. PQ neutralizes the charges of montmorillonite adsorbing as a monomer and undergoing rigidification and planarization in the clay interlayer. On the contrary, MB is forced to form dimers to accomplish the same charge neutralization.

Selective sensing of paraquat by simple off-the-shelf compounds: Applications using composite hydrogel beads and smartphone

The massive use of paraquat (PQ) in agricultural practices has posed serious threats to food safety and human health. Real-time monitoring of PQ remains an obstacle. Herein, a fluorometric as well as smartphone-based very cheap sensing assay is discussed for the detection of this non-selective contact herbicide PQ based on simple off-the-shelf commercially available dyes PTSA (1), HPTS (2) and Eosin Y (3) in pure aqueous media. Owing to their sensitivity towards PQ through electrostatic interactions, these dyes undergo a fluorescence quenching process. Dyes (2) and (3) show a rapid colorimetric change in the presence of PQ as shown by UV-Vis absorption spectral studies. 1 exhibits high sensitivity for PQ in comparison to 2 and 3 with the detection limit as low as 182 nM. All three probes exhibit high sensitivity, high selectivity for PQ over other analytes and excellent anti-interference properties. The Stern-Volmer plots and fluorescence lifetime studies confirm the static quenching process of the probes in the presence of PQ. Furthermore, sensor-coated paper-based test strips were successfully used for the ultrafast detection and quantification of PQ in spiked real water, fruit and vegetable samples. For the first time, silica-sodium alginate (SA) polymer hybrid hydrogel beads incorporated with probes 1, 2 and 3 were used for the detection and adsorption of PQ from water samples. For assessing the reliability of the proposed sensing system for the on-site detection of PQ, an easy-to-use portable test cassette kit integrated with a smartphone was used. The signal outputs were captured and analysed via RGB color value to use the probes for the practical application by using a smartphone as a portable analytical device for the rapid point-of-care monitoring of PQ.

Adsorption of atrazine and paraquat on montmorillonite loaded with layered double hydroxide and active site energy distribution analysis

Abstract Clay minerals are effective adsorbents for the remediation of pesticides in wastewater due to their large superficial areas and excellent cation-exchange capabilities. However, this adsorption effect can be reduced by the accumulation of adsorbents on clay minerals, amongst other problems. Therefore, in this study, montmorillonite (Mnt) modified by layered double hydroxide (LDH) with different loading amounts was successfully prepared using an in situ method. The results from X-ray diffraction, Fourier-transform infrared spectrometry, Brunauer–Emmet–Teller (BET) and scanning electron microscopy analyses revealed that LDH structures were successfully combined with the Mnt layer and formed a porous structure. However, excess LDH still caused the aggregation and accumulation of layers. The adsorption performance of LDH@Mnt for atrazine (ATZ) and paraquat (PQ) was investigated, and the removal efficiency of the LDH@Mnt composite was higher than those of Mnt and LDH alone. The kinetic study revealed that the adsorption process fitted the pseudo-second-order model and internal diffusion model, and 3-LDH@Mnt had the greatest absorbability efficiency for both ATZ and PQ, indicating the adsorption process was controlled by the number of active sites of the adsorbent. The generalized Langmuir model accurately characterized the adsorption process of ATZ and PQ elimination in the adsorption isotherm investigation, indicating that the adsorption energies of the active sites on the adsorbents were different. 3-LDH@Mnt had better absorbability performance for ATZ/PQ, and the sorption capacities were 7.03 and 91.9 mg g–1, respectively. According to site energy distribution theory, the amount of sorption sites of the composite adsorbent was large and the average adsorption energy was high, both of which being beneficial for the adsorption of ATZ and PQ. The effects of pH, coexisting anions and reuse experiments were also tested, indicating that the LDH@Mnt composite possessed high adsorption stability. This excellent removal performance represents a promising strategy for the remediation and elimination of pesticide contaminations from the environment.

Low-cost iron nanoparticles for remediation of agricultural pollution: adsorption of herbicides bromoxynil and paraquat

Green synthesis of 10 nm zero-valent iron nanoparticles (ZVI-NPs) and incorporation into a polymer membrane offers a promising solution for removal of herbicides, bromoxynil and paraquat. 100% removal was achieved in 18–25 mins with 0.1 mg ZVI-NPs.

Cyclodextrin-silica hybrid materials: synthesis, characterization, and application in pesticide aqueous removal.

Overusing and misusing pesticides, including paraquat (PQ), have led to numerous environmental contamination complications. PQ is an emerging bio-accumulative contaminant that is present in environmental aqueous matrices. Adsorption techniques are part of a set of technologies applied in ecological remediation, known for their high effectiveness in removing aqueous PQ. A study of the PQ adsorption capacity of three cyclodextrin-silica nanocomposites (α-CDSi, β-CDSi, and γ-CDSi) from contaminated waters is presented in this paper. The cyclodextrin-silica nanocomposites were synthesized via an esterification reaction between the inorganic matrix and cyclodextrins (CDs) (α, β, and γ) and were characterized physicochemically by spectroscopic, thermal, and surface methods. Their PQ removal performance from contaminated aqueous media was studied under different experimental conditions. The results showed a fast adsorptive response in removal treatment studies over time. Adsorption capacities of 87.22, 57.17, and 77.27mg.g-1 were found for α-CDSi, β-CDSi, and γ-CDSi, respectively, at only 30min of treatment. Thermodynamic studies indicated spontaneous and exothermic adsorption processes. The removal assays responded mainly to physisorption mechanisms with contributions from chemisorption mechanisms. Spectroscopic assays showed a strong interaction of PQ with the adsorbents used. Innovative CDSi nanocomposites have proven to be highly efficient in applying aqueous PQ remediation, thus proving to be sustainable adsorbents of contaminants of emerging importance worldwide.

A highly sensitive electrochemical sensor based on poly(3-aminobenzoic acid)/graphene oxide-gold nanoparticles modified screen printed carbon electrode for paraquat detection

Herein, a modified screen printed carbon electrode (SPCE) based on a composite material, graphene oxide-gold nanoparticles (GO-AuNPs), and poly(3-aminobenzoic acid)(P3ABA) for the detection of paraquat (PQ) is introduced. The modified electrode was fabricated by drop casting of the GO-AuNPs, followed by electropolymerization of 3-aminobenzoic acid to achieve SPCE/GO-AuNPs/P3ABA. The morphology and microstructural characteristics of the modified electrodes were revealed by scanning electron microscopy (SEM) for each step of modification. The composite GO-AuNPs can provide high surface area and enhance electroconductivity of the electrode. In addition, the presence of negatively charged P3ABA notably improved PQ adsorption and electron transfer rate, which stimulate redox reaction on the modified electrode, thus improving the sensitivity of PQ analysis. The SPCE/GO-AuNPs/P3ABA offered a wide linear range of PQ determination (10−9–10−4 mol/L) and low limit of detection (LOD) of 0.45 × 10−9 mol/L or 0.116 µg/L, which is far below international safety regulations. The modified electrode showed minimum interference effect with percent recovery ranging from 96.5% to 116.1% after addition of other herbicides, pesticides, metal ions, and additives. The stability of the SPCE/GO-AuNPs/P3ABA was evaluated, and the results indicated negligible changes in the detection signal over 9 weeks. Moreover, this modified electrode was successfully implemented for PQ analysis in both natural and tapped water with high accuracy.

Synthesis of thermoresponsive PNIPAm nanogel adsorbent by microwave-assisted polymerization for wastewater treatment application

This research demonstrated the fast synthesis technique using microwave-assisted polymerization for the preparation of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) nanogel which was to be used for paraquat pesticide adsorption. PNIPAm nanogel was synthesized by free-radical polymerization in an aqueous solution using water-soluble ammonium peroxodisulfate (APS) and N,Ń-methylenebisacrylamide (BIS) as initiators and cross-linker, respectively. Microwave irradiation was used as an alternative heating technique and its efficiency was compared to that of the conventional heating method. The results showed that reaction time could be greatly shortened from several hours to only 20 min with the yield of PNIPAm nanogel of approximately 65 % using microwave heating method. The FTIR analysis confirmed that microwave irradiation did not alter the chemical structure of PNIPAm nanogel. The cross-linker concentrations and the sequence of cross-linker addition affected the hydrodynamic diameter of PNIPAm nanogel. The hydrodynamic diameter of swollen PNIPAm nanogels at 25 °C decreased as increasing the cross-linker concentrations and then further decreased when the cross-linker was added after 10 min of the irradiation time. Besides, all PNIPAm nanogel showed well thermoresponsive reversibility over 5 cycles, across the volume phase transition temperature (VPTT) at around 32 °C. The adsorption and release mechanisms of the paraquat took advantage of the phase transition change (swelling-collapse) in response to temperature stimuli, respectively. The PNIPAm nanogel synthesized from the microwave heating method had a profound effect on paraquat adsorption, having 60 – 70 % adsorption with a paraquat release of around 35 – 45 %. These results demonstrated that PNIPAm nanogels could be used as an alternative adsorbent material for industrial wastewater treatment.

Nanocomposite hydrogels 3D printed for application in water remediation

Three-dimensional (3D) printing of bioinks for the development of nanocomposite hybrid adsorbent hydrogels was performed. Sodium alginate (SA) matrix hydrogels and bentonite clay (SA-B) nanocomposite hydrogels were synthesized for this purpose. The bioinks used were characterized rheologically and the devices obtained were characterized physicochemically and morphologically. The efficiency of the hydrogels in the adsorption of the pesticide paraquat (PQ) was also studied. The results revealed the efficient formation of hybrid hydrogels and that the presence of clay in the biopolymer matrix improved the rheological, mechanical, thermal, and porous properties of the SA-B hydrogels. Both the SA-B30 bioink and corresponding 3D-printed device were found to be the best systems for use. PQ adsorption tests showed equilibrium adsorption capacities of 1.16, 1.33, 1.45, 2.10, 2.29, and 1.64 mg/g for SA, SA-B5, SA-B10, SA-B20, SA-B30, and SA-B50, respectively. Adsorption was exothermic and spontaneous in nature, involving physisorption processes. In addition, it exhibited a correlation mainly with the Freundlich isotherm model and the pseudo-first-order kinetic model used for nanocomposite devices. The SA-B30 hydrogel exhibited the best PQ adsorption performance. Recovery and reusability of the devices were achieved at least six times. This indicates that the synthesized eco-friendly, biodegradable, and low-cost materials can contribute to the circular economy. Thus, the developed adsorbent materials significantly contribute to ensuring that water is safe for human consumption.

Utilization of agricultural waste to herbicide removal: Magnetic BEA zeolite adsorbents prepared by dry-gel conversion using rice husk ash–derived SiO2 for paraquat removal

This study presents a method that will allow for the sustainable utilization of rice husk ash-SiO2 (RHAS), an agricultural-waste–derived material, as a bulky solid SiO2 source in the zeolite beta (BEA)/Fe3O4 composite (magnetic RHAS-BEA) synthesis via a dry-gel conversion method for the removal of paraquat, a typical herbicide, from aqueous solutions. Ultrasonic waves were used to facilitate the formation of uniform Fe3O4-contained dry precursor gel before converting to the magnetic BEA zeolite composite for the first time. Magnetic RHAS-BEA was then characterized and compared with a non-magnetic sample (RHAS-BEA) using X-ray diffraction and field-emission scanning electron microscopy. In terms of adsorption, we found that paraquat had a high adsorption rate on the samples and conformed to a pseudo-second-order kinetic model. The adsorption behavior of paraquat on the synthesized RHAS-BEA and magnetic RHAS-BEA obeyed the Langmuir adsorption isotherm model. The synthesized adsorbents were reusable for at least four cycles, via thermal regeneration at 450 °C. The inclusion of Fe3O4 particles in magnetic RHAS-BEA disrupted neither the crystallization of the BEA zeolite nor the adsorption of paraquat and enabled easy collection via an external magnet.

Efficient Removal of Paraquat Pollutants Using Magnetic Biochar Derived from Corn Husk Waste: A Sustainable Approach for Water Remediation

Due to the widespread production of maize, the waste created by this crop has become a serious concern. This study applied the concept of waste circulation to the production of magnetic biochar from corn husk waste to remediate paraquat-contaminated water. Magnetic biochar (MB) was produced by impregnating maize husks with iron and carbonizing the residue in a nitrogen environment. Carbonized MB at the temperature of 850°C (MB-01-850) exhibited a combination of microporous and mesoporous structures ([Formula: see text], [Formula: see text]), while biochar created only a microporous structure ([Formula: see text]). According to the findings, Fe(NO3)3 significantly affected the increase in mesopore formation after carbonization. In addition, biochar exhibits excellent magnetic responsiveness. MB-01-850 reached equilibrium within approximately 20 min in synthetic water. Batch adsorption studies showed that MB-01-850 had maximum adsorption capacities ([Formula: see text]) of 34.97 mg/g and 31.63 mg/g for synthetic and natural water, respectively. The unmodified biochar (without mesopores) had a [Formula: see text] of 4.08 mg/g. This indicates that the presence of mesopores improves the effectiveness of paraquat adsorption. Additionally, the adsorption performance of magnetic biochar exhibited no statistically significant variance when tested under natural water conditions. Furthermore, magnetic biochar demonstrates impressive regeneration capacity, allowing it to be regenerated almost entirely for a minimum of four cycles using a sodium hydroxide (NaOH) solution with a concentration equal to or greater than 0.5 M.

Mutual influence of copper and paraquat on their adsorption in soil

Paraquat and copper (Cu) have been commonly used and detected in soils. Therefore, it is important to understand their mobility in the environment. This study investigated the competitive effects of paraquat and Cu on their adsorption in five representative Chinese soils by performing batch adsorption equilibrium experiments and spectroscopic analysis. The adsorption of paraquat in soils varied with soil types and was positively correlated with both cationic exchange capacity and soil organic matter content. Paraquat exerted a more remarkable suppression effect on the adsorption of Cu than Cu on the adsorption of paraquat. In the presence of 0.12 and 0.19 mmol L−1 paraquat, Cu adsorption decreased by 16% and 22% in Heilongjiang soil and by 24% and 37% in Jiangxi soil, respectively. While in the presence of 0.1 and 0.2 mmol L−1 Cu, paraquat adsorption decreased by 4% and 8% in Heilongjiang soil and by 15% and 19% in Jiangxi soil. Exchange selectivity involving symmetric (Paraquat2+, Cu2+) cation exchange is the probable basis for the suppression effect. An ultraviolet-visible absorption study suggested that formation of Cu–paraquat complexes was unlikely in solution or on the soil surface. Cu K-edge X-ray absorption spectroscopy indicated that Cu in soils may have some water hydration layers as the nearest neighbors, and each Cu was coordinated with five oxygen atoms. The results greatly improve our knowledge about the molecular-scale adsorption mechanisms of paraquat and Cu in soils and will be useful to predict the behavior, transport, and fate of paraquat and Cu in agricultural soils.

Cotton Cord Coated with Cyclodextrin Polymers for Paraquat Removal from Water.

The contamination of hazardous agrochemical substances in water caused essential trouble for humans and the environment. The functional textile was used as an effective adsorbent for paraquat removal from an aqueous solution. The coating of anionic cyclodextrin polymer, issued from the cross-linking between 1,2,3,4-butanetetracarboxylic acid and β−cyclodextrin in the presence of poly (vinyl alcohol), on the cotton cord, was firstly investigated. Their physicochemical characteristics were also characterized by gravimetry, acid–base titration, ATR-FTIR, 13C NMR, TGA, and stereo-microscopy. The BDP5 system revealed 107.3% coating yield, 1.13 mmol/g COOH groups, and 95.1% paraquat removal for 25 mg/L of initial concentration. The pseudo-second-order model was appropriate for kinetics using 6 h of contact time. Langmuir isotherm was suitable with the maximum adsorption of 30.3 mg/g for paraquat adsorption. The weight loss was 10.7% and 7.8%, respectively, for water and 5% v/v of HCI in ethanol after 120 h of contact time. Finally, the reusability efficiency stayed at 88.9% after five regeneration.

Design and synthesis of amphiphilic carboxyl-functionalized magnetic polymer microspheres for fast determination of paraquat and its four metabolites in human urine samples prior to ultra-high performance liquid chromatography-high resolution mass spectrometry

In cases of low concentration paraquat (PQ) poisoning, as the disease progresses over a long period of time, the prototype PQ may not be detected in the urine, which has a significant negative impact on the precise treatment of the poisoning. But PQ poisoning can also be confirmed by the detection of specific metabolites of PQ in the urine samples. In the present study, core-shell amphiphilic carboxyl-functionalized magnetic polymer microsphere (Amphiphilic-MPs-COOH) was prepared, and the as-prepared Amphiphilic-MPs-COOH was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetry and differential thermogravimetry analyses (TG-DTG). Then, the Amphiphilic-MPs-COOH was employed as a magnetic solid-phase extraction (MSPE) adsorbent for pretreatment and rapid determination of PQ and its four metabolites from urine samples prior to ultra-high performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS). The extraction-elution conditions of Amphiphilic-MPs-COOH towards PQ and its metabolites were optimized in spiking urine samples to obtain the best MSPE efficiency. The adsorption mechanism of PQ and its metabolites by Amphiphilic-MPs-COOH involves electrostatic attraction and π-π stacking interactions. Moreover, the effect of different ratios of hydrophilic monomer NVP and functional monomer 4-VBA on the extraction and purification performance of PQ and its metabolites in urine samples. And the results revealed that both hydrophilic monomer and functional monomer were important for the adsorption of PQ and its metabolites, and the addition of the appropriate amount of the hydrophilic monomer NVP can improve the compatibility of the adsorbent with the urine substrate. In addition, this study compared the matrix effect of the Amphiphilic-MPs-COOH based MSPE method and the commercial Waters Oasis WCX SPE method. The results showed that the Amphiphilic-MPs-COOH based MSPE method developed in this paper had better resistance to matrix interference. Under optimal conditions, the recoveries of PQ and its metabolites were ranging from 84.5 to 103%, with relative standard deviations (RSDs) of 1.1–6.3%. While the limits of detection (LODs, S/N ≥ 3) and limits of quantification (LOQs, S/N ≥ 9) of the method were in range of 0.1–1.6 μg/L and 0.3–4.8 μg/L, respectively. Finally, the established MSPE-UPLC-HRMS method in this study was used to confirm PQ poisoning not only based on detecting PQ prototype, but also on its four metabolites, providing strong technical support for clinical precision treatment.

Core-shells of magnetite nanoparticles decorated by SBA-3-SO3H mesoporous silica for magnetic solid phase adsorption of paraquat herbicide from aqueous solutions

Paraquat, the most well-known herbicides of toxicological class I, is widely used as an effective herbicide despite its high toxicity for humans and animals. In the current research, a simple synthesis approach was utilized to prepare Fe3O4 @SiO2 @SBA-3-SO3H core-shell mesoporous magnetic nanoparticles (MMNPs) as effective adsorbent for paraquat removal from the aqueous solutions. The characterization of nanoparticles was examined by XRD, BET, FT-IR, FESEM, VSM, mapping and TEM. To optimize the various experimental variables affecting the removal efficiency of paraquat, the effects of four experimental parameters at four levels including solution pH, adsorbent amount, contact time and ionic strength were evaluated by Taguchi fractional factorial design method (OA16). Based on the ANOVA results, ionic strength (80.69%) was recognized as the most significant factor contributing to the paraquat removal efficiency followed by the adsorbent mass (12.67%), pH of the solution (3.52%), and stirring time (0.141%). At the optimum conditions (sample volume = 50 mL, adsorbent dose = 2.4 g L−1, solution pH = 7 and ionic strength = without salt addition), the four kinetic models for the paraquat adsorption on the Fe3O4 @SiO2 @SBA-3-SO3H MMNPs were studied at two concentrations of 25 and 75 mg L−1 in the time range of 0.5–120 min. According to the results, the pseudo-second order kinetic model is the best model (R2 > 0.99, qe, cal =80.0 mg g−1), confirming diffusion plays a key role in determining the rate of adsorption process. Adsorption equilibrium data were investigated by four known isotherm models and the results demonstrated the best fitting with the Langmuir model. From the thermodynamic studies, ΔH°, ΔS°, ΔG°, and Ea of adsorption process were obtained as − 4697.08 J mol−1, − 3.938 J mol−1 K−1, − 3523.45 J mol−1 and − 4246.46 J mol−1, respectively. The negative ΔH° and ΔG° values indicated the exothermic and spontaneous nature of paraquat sorption on the surface of nanoparticles, respectively. Moreover, the obtained values of ΔH°, ΔG° and Ea confirmed the physisorption nature of interaction. The negative ΔS° and Ea shows a decrease in the randomness at the interface of solution-adsorbent with the progress of the sorption process and exothermic nature of adsorption, respectively. The calculated sticking probability (S*) showed the high probability of sticking to the surface. The proposed adsorbent showed very good adsorption behavior and showed reusability more than six cycles without significant reduction in its performance that makes it as a proper adsorbent for paraquat removal.

Bentonite-based sodium alginate/ dextrin cross-linked poly (acrylic acid) hydrogel nanohybrids for facile removal of paraquat herbicide from aqueous solutions

Removal of hazardous herbicides from the aqueous solution is critical for overcoming health-related issues across the wider population. In the current work, we have prepared sodium alginate (SAlg), dextrin, and acrylic acid (AA) based cross-linked hydrogels, composed of bentonite incorporated in the biocompatible hydrogel matrix. This hydrogel composite can remove highly toxic herbicide paraquat (PQ). As-synthesised hydrogel (SAlg/dextrin-cl-PAA) and hydrogel composite (SAlg/dextrin-cl-PAA/bentonite) were further analysed by infra-red spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA/DSC). For the first time, PQ adsorption onto sodium and dextrin-based hydrogel was also evaluated. The measured highest removal capacities were 76.923 and 90.909 mg g−1 for the SAlg/dextrin-cl-PAA and SAlg/dextrin-cl-PAA/bentonite, respectively. Pseudo-second-order (PSO) and Langmuir isotherm models have shown to be best suited for accurately describing the adsorption mechanism. A thermodynamics study verified that the adsorption of PQ on adsorbents is spontaneous, favourable and exothermic. Moreover, reusability analysis shows that the adsorbents possess good reproducibility even after six successive cycles. The adsorption results demonstrate that the synthesised adsorbents are very efficient for removing herbicides (PQ) from wastewater.

Experimental design for the optimization of paraquat removal from aqueous media using a fixed-bed column packed with Pinus Eldarica stalks activated carbon

In this study, a fixed-bed column packed with an activated carbon (Pinus eldarica stalks (PES-AC)) was used to evaluate the performance of paraquat removal from wastewater. The effect of bed height, initial paraquat concentration, contact time, flow rate on the removal of paraquat was investigated using response surface methodology (RSM) based on central composite design (CCD). From the RSM model, the optimum experimental conditions to achieve 94.65% removal of paraquat were solution pH of 8.0, 6 mg L−1 of paraquat, 4 mL min−1 of flow rate, 0.8 cm of the bed height, and 40 min of contact time. The breakthrough data were significantly fitted with Thomas, bed depth services time (BDST), and Yoon–Nelson models. The high values of NBD (14.33, 32.29, and 54.46 mg L−1) and critical bed depth (0.396, 0.370, and 0.330 cm) obtained from BDST model revealed the high efficiency and suitability of the adsorbent. Adsorption of paraquat on PES-AC was strongly dependent on solution pH, indicating an electrostatic attraction mechanism.

Facile Method by Bentonite Treated with Heat and Acid to Enhance Pesticide Adsorption

In this work, simple conditions were applied to modify bentonite for the removal of pesticides from aqueous solution. Bentonite was modified in a single step as BA0.5 (with HCl 0.5 M) and BC500 (calcined at 500 °C) and combined steps with different sequences (BA0.5C500 and BC500A0.5). These adsorbents were characterised by XRD, XRF, FT-IR, 27Al MAS NMR, BET, NH3-TPD, TGA, HPLC, particle size analysis and zeta potential. Single-component adsorption with atrazine, diuron, 2,4-D and paraquat was used in aqueous solution at various pesticide concentrations, contact times and pH levels. It was found that the sequence of the treatment significantly affected atrazine adsorption. BC500A0.5 exhibited the highest efficiency for atrazine adsorption in a broad pH range of 3.0–9.0. Its adsorption at pH 6.0 was about 12 times greater than that of other adsorbents with an initial atrazine concentration of 50 mg L−1, which indicates BC500A0.5 specifically for the adsorption of atrazine. In addition, for the simultaneous adsorption of all four pesticides, BC500A0.5 was found to remove the maximum total amount of the pesticides, indicating that it could be used as a good multifunctional adsorbent. All modified bentonites showed similar diuron adsorption better than that of unmodified bentonite. The greatest adsorption of 2,4-D prefers BA0.5C500, occurring at pH 2–4. In the case of paraquat adsorption, all adsorbents are good at absorbing paraquat, but bentonite had the highest rate of paraquat removal, whereas BA0.5C500 was found to have the lowest, and the adsorption increased with increasing pH. Furthermore, the adsorption process on the adsorbents fits well with the Langmuir isotherm and pseudo-second-order kinetics models, as the thermodynamic parameters showed a spontaneous and endothermic process.

Adsorption and electrosorption of paraquat, diquat and difenzoquat from aqueous solutions onto activated carbon cloth as monitored by in-situ uv–visible spectroscopy

Removal of high polarity herbicides, paraquat (PQ), diquat (DQ) and difenzoquat (DFQ) from their aqueous solutions was investigated by adsorption and electrosorption onto activated carbon cloth (ACC). Adsorption and electrosorption processes were followed on-line by in- situ uv–visible spectroscopy. Kinetics of adsorption and electrosorption was found to follow pseudo-second order model in a better way than pseudo-first order model. Excellent open circuit (OC) adsorption efficiency (99.9%) was achieved for DFQ. Lower OC adsorption efficiencies of PQ (47.1%) and DQ (45.9%) were increased by the application of electrosorption (over 98%). Adsorption and electrosorption behaviors of the herbicides under study were explained based on herbicide-ACC surface interactions. Adsorption isotherms were derived and examined according to Langmuir and Freundlich models. Adsorption isotherm data fitted to Freundlich isotherm model better than Langmuir isotherm model. Parameters of these models were determined. Application of electrodesorption caused the removal of mainly electrosorbed herbicides.