Reusable and effective polyacrylic membranes for mecoprop and bentazon extractions

Water-soluble pesticides, while offering advantages like rapid plant uptake, pose a significant risk of water contamination through runoff and leaching. Mecoprop (MCP) and bentazon (BTZ) are water-soluble herbicides with leaf-level sorption. MCP is a neurotoxic phenoxypropionic herbicide used in non-crop areas, while BTZ is a benzothiazinone herbicide used in various crops. Both show relatively high soil mobility and have been detected in various environments, highlighting their toxicity. This study presents a novel, 100% commercially-available monomer-based material for efficient extraction of these pesticides. The membrane format offers excellent manageability and durability, eliminating the need for personal protective equipment (PPE). Its reusability and environmental friendliness make it suitable for large-scale applications. The study investigates the influence of polymeric composition and charged aminoethyl groups on membrane properties and sorption performance.

Existing methods for removing mecoprop and bentazon from water sources include the use of nanocrystalline TiO2 powder (requiring UV radiation), granulated compounds in wetlands, calcinated hydrotalcites (reusable for 4 cycles), magnetic ion exchange resins, and various activated carbons. While some show high removal capacities, many are not reusable or operate under complex conditions. The existing literature highlights a need for a reusable, efficient, and easily applicable method for removing these pesticides.

Membrane-shaped polymers were synthesized via bulk radical polymerization of 1-vinyl-2-pyrrolidone (VP), methyl methacrylate (MMA), and 2-isocyanatoethyl methacrylate (NCO) at different molar ratios, using ethylene glycol dimethacrylate (E) as a crosslinker. A reference membrane without the NCO group was also prepared. The membranes were characterized using TGA, DSC, mechanical testing, N2 adsorption (BET), and FTIR. Sorption kinetics were studied by fitting a solution of Fick's 2nd law equation to experimental data obtained from immersing the membranes in solutions of BTZ and MCP at different concentrations and measuring the remaining pesticide concentrations after 24 hours. Sorption isotherms were analyzed using the Langmuir and BET models. Transport properties (permeability, diffusion coefficients) were determined using a horizontal communicating vessel system. The interaction between mecoprop and a soluble linear polymer (POL10) with the same composition as MEM10 was investigated using 1H NMR, applying the continuous variation method. The interaction between MEM10 and both pesticides was studied using FT-IR. Molecular dynamics (MD) simulations using GROMACS software were performed to investigate the sorption behavior and interactions at the molecular level, analyzing binding enthalpies and noncovalent interactions (NCI) using the Independent Gradient Method (IGM). A competitive interaction study examined the removal efficiency of BTZ and MCP in the presence of urea and ammonium nitrate as interferents. Finally, the reusability of the membranes was evaluated over four sorption/desorption cycles, with desorption performed using distilled water and 0.1 mol dm⁻³ NaOH solutions.

The membranes effectively removed mecoprop (RE >99%) and bentazon (RE ≈95%) at low concentrations. The presence of charged aminoethyl groups significantly enhanced sorption. Sorption kinetics were non-Fickian at short times, suggesting coupled diffusional and relaxational mechanisms. Bentazon sorption followed a Langmuir isotherm (monolayer formation), while mecoprop sorption followed a BET isotherm (multilayer formation). MD simulations revealed a scorpion-like conformation of the macromolecular chains surrounding the pesticides, suggesting hydrophobic interactions as the primary removal mechanism. The NH3+ groups played a crucial role in facilitating this interaction, particularly in the case of bentazon. The membranes exhibited good mechanical and thermal properties, suitable for various applications. The membranes were reusable for at least four cycles with minimal performance loss after washing with NaOH. The presence of common nitrogen fertilizers (urea and ammonium nitrate) did not significantly affect bentazon removal, but did impact mecoprop removal efficiency, with the impact of ammonium nitrate being greater. The cost-effectiveness increased with lower NCO percentages while maintaining high removal efficiency.

The findings demonstrate the efficacy of the developed polyacrylic membranes for removing mecoprop and bentazon from aqueous solutions. The high removal efficiency, reusability, and ease of handling make these membranes a promising alternative to existing methods. The molecular-level insights from MD simulations and NMR analysis provide a comprehensive understanding of the underlying sorption mechanism, emphasizing the importance of hydrophobic interactions and the role of charged aminoethyl groups. The ability to reuse the membranes significantly improves cost-effectiveness and reduces environmental impact. The observed selectivity for bentazon over mecoprop in competitive sorption experiments highlights the potential for tailoring membrane properties to selectively target specific pesticides. The impact of nitrogen fertilizers on mecoprop removal underscores the need for further research into optimizing membrane performance in complex environmental matrices.

This study successfully developed reusable polyacrylic membranes for efficient removal of mecoprop and bentazon. The membranes exhibit high removal efficiency, reusability, and ease of handling. Molecular-level insights revealed hydrophobic interactions and the crucial role of charged aminoethyl groups. Future research could focus on optimizing membrane selectivity for specific pesticides and evaluating performance in real-world scenarios.

The study primarily focused on laboratory-scale experiments using purified water. Further research is needed to evaluate the performance of the membranes in complex real-world water matrices containing other organic and inorganic contaminants. The long-term stability and durability of the membranes under continuous use in various environmental conditions also warrant further investigation.