Adsorption Of Glyphosate Research Articles

First Principle Study of the Adsorption of Glyphosate on Illite Clay for Water Depollution

The use of herbicides such as glyphosate in the agricultural sector enables agricultural intensification and thus satisfies the demand for agricultural products on the market. Glyphosate is widely used in agriculture as a herbicide for weeding fields. However, its use has a major drawback that calls into question its many advantages. After use, its toxic residues and metabolites end up in groundwater, which is an important source of drinking water for the population. Adsorption is the most suitable technique for recovering these toxic residues before the water is consumed. Based on Density Functional Theory, implemented in the VASP simulation code, we studied the ability of illite to adsorb glyphosate. The absorbent properties, the abundance of illite throughout the world, particularly in Benin, and the fact that it is free from toxic products were the criteria that guide us in the of illite clay for our work. Our work revealed that the process of adsorption of glyphosate on the illite surface is exothermic. This process does not present any risk of release of toxic by-products on five of the six studied sites. The illite clay can then be used to design water depollution filters to decrease medical as well as financial burden.

Insights into the enhanced adsorption of glyphosate by dissolved organic matter in farmland Mollisol: effects and mechanisms of action.

Dissolved organic matter (DOM) is easy to combine with residual pesticides and affect their morphology and environmental behavior. Given that the binding mechanism between DOM and the typical herbicide glyphosate in soil is not yet clear, this study used adsorption experiments, multispectral techniques, density functional theory, and pot experiments to reveal the interaction mechanism between DOM and glyphosate on Mollisol in farmland and their impact on the environment. The results show that the adsorption of glyphosate by Mollisol is a multilayer heterogeneous chemical adsorption process. After adding DOM, due to the early formation of DOM and glyphosate complex, the adsorption process gradually became dominated by single-layer chemical adsorption, and the adsorption capacity increased by 1.06 times. Glyphosate can quench the endogenous fluorescence of humic substances through a static quenching process dominated by hydrogen bonds and van der Waals forces, and instead enhance the fluorescence intensity of protein substances by affecting the molecular environment of protein molecules. The binding of glyphosate to protein is earlier, of which affinity stronger than that of humic acid. In this process, two main functional groups (C-O in aromatic groups and C-O in alcohols, ethers and esters) exist at the binding sites of glyphosate and DOM. Moreover, the complexation of DOM and glyphosate can effectively alleviate the negative impact of glyphosate on the soil. This study has certain theoretical guidance significance for understanding the environmental behavior of glyphosate and improving the sustainable utilization of Mollisol.

Kinetics and sorption behavior of glyphosate and tricyclazole for their efficient retention in biomixtures

The present investigation aims to study adsorption-desorption behavior of glyphosate and tricyclazole in rice straw-compost biomixtures. To enhance pesticide adsorption and performance of the bio-purification system, rice straw-compost (BM) biomixture was mixed with wheat straw biochar (WBC, 1% and 5%), and adsorption of both pesticides in control (BM) and WBCBM(1%) and WBCBM(5%) biomixtures was compared. The kinetics study suggested that the pseudo-second-order model best explained the time-dependent adsorption of both pesticides and intraparticle adsorption was not the rate-determining step. Tricyclazole was more sorbed than glyphosate in all biomixtures which can be attributed to its lower water solubility. The WBC increased the sorption of both pesticides, but the effect varied with the nature of pesticides and biochar content. The adsorption coefficient values in BM, WBCBM(1%), and WBCBM(5%) biomixtures were 26.74, 38.16, and 51.97 (glyphosate) and 38.07, 59.94, and 84.54 (tricyclazole), respectively. The adsorption data was subjected to the Freundlich, the Langmuir, and the Temkin isotherms, and among them, the Freundlich isotherm best explained pesticide adsorption behavior. Desorption results suggested that the adsorption of glyphosate was more irreversible than tricyclazole and depended upon initial pesticide concentration. This study suggested that biochar mixed rice straw-compost biomixtures can be exploited in bio-purification systems for glyphosate and tricyclazole.

D113 resin in-situ loaded with Fe3+ to develop glyphosate adsorbent with the characteristics of salt-resistance and the remarkable saturated adsorption capacity

There are inorganic salts in glyphosate production liquor and natural water bodies coexisting with glyphosate. It is imperative to develop a salt-tolerant adsorbent for glyphosate in water. Industrial D113 resin undergone two-step transformation to optimize the preparation of D113 in-situ loaded with Fe3+ (D113-Fe3+) as salt-resistance glyphosate adsorbent. The loading amount of Fe3+ on D113-Fe3+ is 3.5 mmol/g. The adsorption mechanism revealed that Fe3+ in D113-Fe3+ formed Fe-O-P bond with the phosphonate group of glyphosate. At 293 K, the maximum complex ratio of the adsorbed glyphosate to Fe3+ in D113-Fe3+ was 2.4:1. At 293 K, the remarkable saturated glyphosate adsorption capacity of D113-Fe3+ reached 1420.2 mg/g. In pK2 state of glyphosate, D113-Fe3+ featured its maximum adsorption capacity at the zero charge point 2.43 of D113-Fe3+ and 293 K. In glyphosate solution coexisting 0–16 % NaCl, D113-Fe3+ exhibited stable glyphosate adsorption capacity and salt-resistance compared with D201, D301 and 330 resin. The endothermic and spontaneous adsorption of glyphosate on D113-Fe3+ can fit Freundlich model and pseudo-second-order model. 2 mol/L NH3·H2O, 2 mol/L FeCl3 and 2 mol/L H2SO4 could all regenerate D113-Fe3+. The characteristics of salt-resistance and the remarkable saturated adsorption capacity made D113-Fe3+ comparable to all reported glyphosate adsorbents.

Near-infrared light-promoted engineering oxygen vacancy of Fe3Ov-Mo/P nanozyme for sensitive detection of glyphosate

The rapid and sensitive detection of glyphosate herbicide in agricultural products is urgent need. Herein, we develop a photosensitive Fe3Ov-Mo/P nanozyme with defect-rich rough surface by the co-precipitation method. In particular, the Fe3Ov-Mo/P nanozyme with high-percentage oxygen vacancy (OV) defects and rough surface exhibited superior peroxidase (POD)-like activity and kinetics. More intriguingly, Fe3Ov-Mo/P nanozyme with strong optical absorption in near-infrared (NIR) region showed excellent light-promoted POD-like activity. It was found that the defect-rich rough surface is conducive to the adsorption of glyphosate to inhibit the POD-like activity of Fe3Ov-Mo/P. Under near-infrared laser irradiation, the inhibitory effect of glyphosate on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by Fe3Ov-Mo/P was increased by 2.64 times. A colorimetric platform was developed for the detection of glyphosate with a low detection limit of 0.032 mg L-1 and good selectivity. The method was used to determine the residual glyphosate in coffee, and the recovery efficiency was between 91.20–104.00 %. This work that combines the advantage of defect engineering and NIR provides a strategy for developing high-active nanozyme in pesticide assay.

Adsorption of Glyphosate in Water Using Iron-Based Water Treatment Residuals Derived from Drinking Water Treatment Plants

Glyphosate, a broad-spectrum herbicide, poses a potential threat to human health and the ecosystem due to its toxicity. In this study, iron-based water treatment residuals (Fe-WTRs) were employed for glyphosate removal. The adsorption kinetics, isotherms, and thermodynamics, as well as the effects of pH, Fe-WTR particle size, and temperature, were explored. The results show that Fe-WTRs are an effective adsorbent for glyphosate adsorption, and the maximum uptake capacity was recorded as 30.25 mg/g. The Fe-WTR surface was positively charged, and low-valent iron dominated under acidic conditions, favoring glyphosate adsorption. Furthermore, smaller Fe-WTR particles (<0.125 mm) showed a faster absorption rate and 20% higher adsorption capacity than larger particles (2–5 mm). The kinetic analysis indicated that the adsorption process exhibits a two-step profile, conforming to the pseudo-second-order model, and the thermodynamic analysis indicated that it is a spontaneous, endothermic, and entropy-driven reaction. Finally, the Fourier transform infrared spectral analysis revealed that this process is mainly associated with the formation of metal phosphate through the ligand exchange of the phosphate groups of glyphosates with the hydroxyl groups of iron present in Fe-WTRs. In this study, we demonstrated the potential of Fe-WTRs as a cost-effective and efficient adsorbent for glyphosate removal.

Quantum Simulations and Experimental Insights into Glyphosate Adsorption Using Graphene-Based Nanomaterials.

The increasing global demand for food and agrarian development brings to light a dual issue concerning the use of substances that are crucial for increasing productivity yet can be harmful to human health and the environment when misused. Herein, we combine insights from high-level quantum simulations and experimental findings to elucidate the fundamental physicochemical mechanisms behind developing graphene-based nanomaterials for the adsorption of emerging contaminants, with a specific focus on pesticide glyphosate (GLY). We conducted a comprehensive theoretical and experimental investigation of graphene-based supports as promising candidates for detecting, sensing, capturing, and removing GLY applications. By combining ab initio molecular dynamics and density functional theory calculations, we explored several chemical environments encountered by GLY during its interaction with graphene-based substrates, including pristine and punctual defect regions. Our results unveiled distinct interaction behaviors: physisorption in pristine and doped graphene regions, chemisorption leading to molecular dissociation in vacancy-type defect regions, and complex transformations involving the capture of N and O atoms from impurity-adsorbed graphene, resulting in the formation of new GLY-derived compounds. The theoretical findings were substantiated by FTIR and Raman spectroscopy, which proposed a mechanism explaining GLY adsorption in graphene-based nanomaterials. The comprehensive evaluation of adsorption energies and associated properties provides valuable insights into the intricate nature of these interactions, shedding light on potential applications and guiding future experimental investigations of graphene-based nanofilters for water decontamination.

Linkage between glyphosate adsorption/desorption and mineralization in Central European agricultural soils

The pesticides bioavailability in soil is primarily governed by sorption behaviors of soil. This study aimed to study adsorption, desorption, and bioavailability of glyphosate in agricultural soils and to find relationships to its mineralization. We examined 21 soil samples from Germany and Slovenia, varied widely in soil texture (8–86% sand), soil organic matter (1.2–4.5%), pH (5.0–7.1), exchangeable ions (7.5–32.9 mmolc 100 g−1) parameters. A batch experiment based on OECD guideline 106 was utilized to assess adsorption/desorption characteristics in soil of the herbicide glyphosate. Experimental results indicated that glyphosate was strongly adsorbed (77 and 100%) at Kelheim and Brezje soils, and weakly desorbed (5.7 and 49.0 %) at Brezje and Skrinjar soils, respectively. A significant variance in glyphosate mineralization was observed across different soils. Among evaluated parameters, exchangeable acidity was found to be the primary factor influencing adsorption and desorption of glyphosate, revealing a significant negative correlation at p < 0.0001. Additionally, a statistically significant relationship (R2 = 0.5299 at p = 0.0002) was obtained between adsorption/desorption and mineralization in soils of glyphosate herbicide. The study revealed that adsorption/desorption of glyphosate is heavily influenced by exchangeable acidity, and the mineralization of glyphosate is closely tied to a soil's capacity for glyphosate adsorption/desorption.

Adsorption of commercial glyphosate by MOF-808: a new ZrMOF for water purification

Adsorption of commercial glyphosate by MOF-808: a new ZrMOF for water purification

Application of mid-infrared spectroscopy to the prediction and specification of pesticide sorption: A promising and cost-effective tool

The cocktail of pesticides sprayed to protect crops generates a miscellaneous and generalized contamination of water bodies. Sorption, especially on soils, regulates the spreading and persistence of these contaminants. Fine resolution sorption data and knowledge of its drivers are needed to manage this contamination. The aim of this study is to investigate the potential of Mid-Infrared spectroscopy (MIR) to predict and specify the adsorption and desorption of a diversity of pesticides. We constituted a set of 37 soils from French mainland and West Indies covering large ranges of texture, organic carbon, minerals and pH. We measured the adsorption and desorption coefficients of glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D) and difenoconazole and acquired MIR Lab spectra for these soils. We developed Partial Least Square Regression (PLSR) models for the prediction of the sorption coefficients from the MIR spectra. We further identified the most influencing spectral bands and related these to putative organic and mineral functional groups. The prediction performance of the PLSR models was generally high for the adsorption coefficients Kdads (0.4 < R2 < 0.9 & RPIQ >1.8). It was contrasted for the desorption coefficients and related to the magnitude of the desorption hysteresis. The most significant spectral bands in the PLSR differ according to the pesticides indicating contrasted interactions with mineral and organic functional groups. Glyphosate interacts primarily with polar mineral groups (OH) and difenoconazole with hydrophobic organic groups (CH2, CC, COO−, C–O, C–O–C). 2,4-D has both positive and negative interactions with these groups. Finally, this work suggests that MIR combined with PLSR is a promising and cost-effective tool. It allows both the prediction of adsorption and desorption parameters and the specification of these mechanisms for a diversity of pesticides including polar active ingredients.

Statistical physics modelling and density functional theory calculations for glyphosate adsorption using zinc oxide-doped activated carbon

Glyphosate (GPS), an organophosphorus herbicide known for its genotoxic and carcinogenic effects, poses environmental and health risks. Addressing the need for sustainable removal methods, adsorption emerges as a promising, eco-friendly, and cost-effective approach. To enhance GPS removal, a bio-fabricated ZnONP-doped activated carbon (Zn@AC) was proposed and investigated for its adsorption mechanism. The adsorbent was created by pyrolyzing activated carbon derived from coconut fiber and introducing ZnO nanoparticles synthesized using Jatropha curcas leaf extract. Subsequently, the material underwent thorough characterization. The adsorption mechanism was explored using statistical physical modeling and Density Functional Theory (DFT) under different conditions: temperatures (303–353 K), pH levels (4.5–6), and GPS concentrations (5–50 mg/L). The monolayer, double layer, and multilayer models were used to gain comprehensive insight into GPS removal performance, and the results showed that Zn@AC was superior to AC and ZnONP. The adsorption capacity for monolayer quantity for GPS-Zn@AC was found to be 511.49 mg/g, and the density of receptor sites for Zn@AC was observed to be 85.68 ± 1.71. These values were obtained using the M5 model, which is a statistical physical modeling approach. The study provides insights into the adsorption of GPS on modified materials and the use of advanced statistical physics models for interpretation. The temperature-dependent changes and energy profiles (∊1 > 10 kJ/mol > ∊2) confirmed that the reaction was endothermic and driven by electrostatic interference. The alignment of experimental and DFT highlighted Zn-O interactions, showing the hierarchy of GPS-Zn@AC complexes (IV > II > III > I > V). These findings offer valuable insights for engineering and material science.

Removal characteristics of high concentration glyphosate in bioretention cells

ABSTRACT Glyphosate, as one of the most widely used pesticides, has been found in rainwater runoff. A bioretention cell with two types of fillers was constructed to explore removal of glyphosate in runoff an transformation of glyphosate in the filler. The type of filler had a significant impact on adsorption and degradation of glyphosate in the bioretention cell. The glyphosate removal efficiencies of coal cinder modified loess (CLB) and zeolite modified loess (ZLB) were 33.13–99.7% and 55.04–99.7%, respectively. Conversion of glyphosate in the bioretention cell occurred mainly in the upper layer of the filler. When the concentration of glyphosate in the runoff was 0.25 or 0.5 mg/L, the concentration of glyphosate degradation products at the two outlets along the way was as much as 26 times higher than that at the lowest outlet. Rainfall events promoted the migration of glyphosate and its degradation products within the filler. Glyphosate and its degradation products in ZLB were mainly distributed at 15 and 25 cm deep in the filler layer, while the highest concentrations in CLB were at 5 and 35 cm. Discontinuous runoff into the bioretention cell leads to continuous leaching and adsorption of glyphosate in the bioretention cell until complete degradation occurs.

Isolation of aqueous pesticides on surface-functionalized SBA-15: glyphosate kinetics and detailed empirical insights for atrazine.

Atrazine and glyphosate are two of the most used pesticides around the world causing serious water contamination. In this study, amine-functionalized Santa Barbara Amorphous-15 silica (SBA-15-NH2) was synthesized and employed for the aqueous adsorption of atrazine and glyphosate. The adsorbent was mesoporous post-functionalization with lower surface area, pore volume, size, and stability when compared to the SBA-15. The pesticides adsorption rates were high with over 85% of potential adsorption having occurred within the initial 180 min. The equilibria for atrazine and glyphosate adsorption were 60 and 360 min, respectively, and the rate data fit the fractal pseudo-second-order and pseudo-second-order models, respectively. Atrazine adsorption was higher at lower solution pH with reduced adsorption as the pH value increased. There was enhanced atrazine adsorption as temperature increased from 22 to 32 °C, but further temperature rise resulted in lower adsorption compared to that recorded at 22 °C. The processes comprise electrostatic interaction, trapping of atrazine within mesopores, and multi-layer adsorption of atrazine on surface-adsorbed atrazine. The equilibrium data fitted the Langmuir adsorption isotherm model better than the Freundlich. The SBA-15-NH2 adsorption capacity for atrazine and glyphosate was better than many adsorbents reported in literature, the adsorbent is reusable, and exhibited sustained efficiencies for atrazine that was ≥82% even after 3-cycles, an indication of chemical stability and renewability.

Assessment of chitosan-based adsorbents for glyphosate removal

Exposure to glyphosate produces various toxic effects, due to this, different methods have been evaluated for its elimination. The objective of this work was to formulate chitosan-based adsorbents and evaluate their efficiency in the removal of glyphosate in vitro. Four films were made by varying the weight ratio of silica/chitosan particles, and four sponges were made by varying the chitosan/chitosan ratio in a reticulated manner. Both adsorbents were characterized based on their porosity, water absorption, glyphosate removal, and reusability. It was found that increasing the porosity in both films and sponges resulted in an increase in the adsorption efficiency of glyphosate. The adsorption process exhibited a better fit in both adsorbents to the pseudo-second-order model. The adsorption of glyphosate to the films fit better with the Langmuir model, demonstrating that the process occurs in the form of a monolayer. In the case of sponges, the adsorption of glyphosate fit better with the Freundlich model, indicating that the process takes place in a multilayer form. Finally, when the reusability was evaluated, the adsorbents showed a loss of effectiveness. However, they still proved to be an efficient alternative for the removal of glyphosate in water, providing a cost-effective and environmentally friendly solution.

Removal of glyphosate (GLY) and aminomethylphosphonic acid (AMPA) by ultrafiltration with permeate-side polymer-based spherical activated carbon (UF–PBSAC)

Glyphosate (GLY) is the most commonly used herbicide worldwide, and aminomethylphosphonic acid (AMPA) is one of its main metabolites. GLY and AMPA are toxic to humans, and their complex physicochemical properties present challenges in their removal from water. Several technologies have been applied to remove GLY and AMPA such as adsorption, filtration, and degradation with varied efficiencies. In previous works, an ultrafiltration membrane with permeate-side polymer-based spherical activated carbon (UF–PBSAC) showed the feasibility of removing uncharged micropollutants via adsorption in a flow-through configuration. The same UF–PBSAC was investigated for GLY and AMPA adsorption to assess the removal of charged and lower molecular weight micropollutants. The results indicated that both surface area and hydraulic residence time were limiting factors in GLY/AMPA adsorption by UF–PBSAC. The higher external surface of PBSAC with strong affinity for GLY and AMPA showed higher removal in a dynamic process where the hydraulic residence time was short (tens of seconds). Extending hydraulic residence times (hundreds of seconds) resulted in higher GLY/AMPA removal by allowing GLY/AMPA to diffuse into the PBSAC pores and reach more surfaces. Enhancement was achieved by minimising both limiting factors (external surface and hydraulic residence time) with a low flux of 25 L/m2.h, increased PBSAC layer of 6 mm, and small PBSAC particle size of 78 µm. With this configuration, UF–PBSAC could remove 98 % of GLY and 95 % of AMPA from an initial concentration of 1000 ng/L at pH 8.2 ± 0.2 and meet European Union (EU) regulation for herbicides (100 ng/L for individuals and 500 ng/L for total herbicides). The results implied that UF−PBSAC was able to remove charged micropollutants to the required levels and had potential for application in wastewater treatment and water reuse.

Glyphosate/AMPA adsorption on magnetite under different conditions: The effect of pH and electrolytes

As a result of the frequent use, glyphosate (GLY) and its major metabolite, aminomethylphosphonic acid (AMPA), have emerged as ubiquitous environmental contaminants worldwide. Glyphosate, applied in agriculture, adsorbs on soil minerals, such as iron oxides, facilitating its fixation in soils and preventing leaching into groundwater sources. However, the adsorption capacity of various types of soils exhibits substantial variability. In this work the adsorption of GLY and AMPA on magnetite nanoparticles (MNPs) was studied under different conditions: at pH ∼ 6 and ∼ 8, and in the presence of 10 mmol/L NaCl, an indifferent electrolyte, and 10 mmol/L CaCl2, which contains a specific cation mainly present in soils. The pH-dependent zeta potential measurements revealed the difference between the effect of Na+ and Ca2+ ions on the charge state and aggregation of MNPs. The adsorption of GLY/AMPA shows significant pH dependence, with the bound amounts decreasing rapidly above pH ∼ 7 in both 10 mmol/L NaCl and CaCl2 solutions. The phosphonate adsorption capacity of MNPs, as determined from the fitting of the Langmuir isotherm equation, was approximately 0.35 mmol/g and 0,09 mmol/g at pH ∼ 6 and pH ∼ 8, respectively. The diverse bound amounts at different pHs are of environmental importance: under alkaline soil conditions, the mobilization of GLY may be more probable. GLY and AMPA bind to the surface of MNPs via complex formation at ≡Fe-OH sites, primarily involving phosphate groups, preferably at acidic pH, where the MNPs carry positive charges, and the near-surface concentration of phosphonate anions is higher due to electrostatic attraction. Furthermore, in the presence of Ca2+ ions, Ca-bridging occurs, as supported by the findings from the ATR-FTIR spectra. Additionally, it is worth noting that the complex formation between Ca2+ and phosphonates in the solution phase reduces the probability of Ca-bridge and surface complex formation, hindering the fixation of GLY/AMPA in soils.

La3+ and Al3+ loaded D151 as salt‐resistant resins for efficient adsorption of glyphosate: Effects of ionic radius

AbstractLa3+ and Al3+ loaded D151 resin [R‐La and R‐Al, respectively] were used as salt‐resistant resins for the efficient adsorption of glyphosate. The results showed that La3+ with a larger ionic radius could accommodate more glyphosate as ligands, resulting in higher glyphosate adsorption capacity of R‐La than that of R‐Al. Both R‐La and R‐Al exhibited maximum adsorption capacities at pH 2.52, where glyphosate existed in its ionization equilibrium of pKa2. Consistent with the larger ionic radius of La3+, R‐La featured larger qm and KL than R‐Al at the same temperature. Owing to the smaller radius of Al3+, the enthalpy values for the coordination adsorption of glyphosate by R‐Al were larger than those of R‐La at the same adsorption capacity. Owing to the smaller radius of Al3+, R‐Al exhibited stronger coordination adsorption for glyphosate and significantly higher salt tolerance than R‐La. The adsorption mechanisms indicated that both R‐La and R‐Al could adsorb glyphosate through the coordination of La3+ and Al3+ with O atoms of the phosphonate group of glyphosate. At a NaCl concentration range of 0–16%, R‐Al featured excellent salt tolerance and highly stable glyphosate adsorption capacity than 330, D301, R‐La, and the 14 adsorbents reported in the literature.

Phosphorus and Glyphosate Adsorption and Desorption Trends across Different Depths in Sandy Soil

The unintended loss of glyphosate and P from cropland may pose an environmental risk to downstream water quality and marine ecosystems. Glyphosate and P compete for exchange sites, and since glyphosate is an organophosphate, it reacts similarly to phosphates in soil. The competition for exchange sites between glyphosate and P could lead to an increased risk of loss due to leaching, leading to water quality degradation and harm to aquatic wildlife. The focus of this study was to (i) determine the sorption tendencies of P and orthophosphate in Florida Entisols and (ii) determine the sorption tendencies of glyphosate in Florida Entisols. Adsorption and desorption experiments were performed for both P and glyphosate. The data from the sorption experiments were fitted to linear, Freundlich, and Langmuir models. Orthophosphate-P (ortho-P) was best represented by the linear isotherm. Glyphosate adsorption was best represented by the linear isotherm, and desorption was best represented by both the linear and Freundlich models. Phosphorus and glyphosate sorption and desorption increased with soil depth, likely due to the higher concentrations of Fe and Al with greater depth. These results could improve P and glyphosate application rates when applied in tandem to citrus trees, increasing overall tree health and improving soil quality.

Insights into Glyphosate Adsorption in Aqueous Solutions Using Zn-Al Layered Double Oxide

AbstractContamination of surface and groundwater with glyphosate, used widely on crops to control weeds, can cause severe environmental damage. Processes for glyphosate removal from water bodies have been developed, but few are effective and all are expensive. This objective of the present study was to investigate the use of a layered double oxide as a potentially effective and inexpensive material to remove glyphosate from water. Equilibrium, kinetics, and adsorption mechanisms were evaluated, in addition to the effects of competing anions and temperature on glyphosate adsorption. Up to 95% of glyphosate was removed from a synthetic solution in 50 min by Zn2Al-LDO (layered double oxide in Zn/Al ratio of 2:1) at pH 10. The adsorption isotherms were type L and the Langmuir model best fitted the experimental data, with a qmax value of 191.96 μg mg–1 at 25°C. The XRD pattern did not support the hypothesis of intercalation of glyphosate anions, whereas Fourier-transform infrared and solid-state 13C and 31P magic angle spinning nuclear magnetic resonance confirmed the adsorption of glyphosate anions on the Zn2Al-LDO surface, through carboxylate and phosphonate moiety interactions with end-on and side-on modes. The degree of removal of glyphosate increased with increasing temperature and decreased with increasing concentration of competing anions, with carbonate anions having the most prominent effect on the inhibition of glyphosate adsorption. The adsorption kinetics fitted a pseudo-first order law. Moreover, the intraparticle diffusion model suggested that the adsorption process depends on the formation and thickness of the film at the solution/solid interface.

Unraveling the role of polysaccharide-goethite associations on glyphosate’ adsorption–desorption dynamics and binding mechanisms

HypothesisGlyphosate retention at environmental interfaces is strongly governed by adsorption and desorption processes. In particular, glyphosate can react with organo-mineral associations (OMAs) in soils, sediments, and aquatic environments. We hypothesize mineral-adsorbed biomacromolecules modulate the extent and rate of glyphosate adsorption and desorption where electrostatic and noncovalent interactions with organo-mineral surfaces are favored. ExperimentsHere we use in-situ attenuated total reflectance Fourier-transform infrared, X-ray photoelectron spectroscopy, and batch experiments to characterize glyphosate’ adsorption and desorption mechanisms and kinetics at an organo-mineral interface. Model polysaccharide-goethite OMAs are prepared with a range of organic (polysaccharide, PS) surface loadings. Sequential adsorption–desorption studies are conducted by introducing glyphosate and background electrolyte solutions, respectively, to PS-goethite OMAs. FindingsWe find the extent of glyphosate adsorption at PS-goethite interfaces was reduced compared to that at the goethite interface. However, increased polysaccharide surface loading resulted in lower relative glyphosate desorption. At the same time, increased PS surface loading yielded slower glyphosate adsorption and desorption kinetics compared to corresponding processes at the goethite interface. We highlight that adsorbed PS promotes the formation of weak noncovalent interactions between glyphosate and PS-goethite OMAs, including the evolution of hydrogen bonds between (i) the amino group of glyphosate and PS and (ii) the phosphonate group of glyphosate and goethite. It is also observed that glyphosate’ phosphonate group preferentially forms inner-sphere monodentate complexes with goethite in PS-goethite whereas bidentate configurations are favored on goethite.