Adsorption and characterization of MCPA on DDTMA- and raw-montmorillonite: Surface sites involved

Detection and adsorption of 2-methyl-4-chlorophenoxyacetic acid in vegetables via dual-functional molecularly imprinted polymer doping with carbon dot

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is one of the most widely used herbicides, so adsorption and detection of MCPA in the environment is critical. Blue fluorescent carbon dot (CD) was synthesized from citric acid and urea, which could be quenched by MCPA. Herein, bifunctional molecularly imprinted polymer (CD@MIP) was prepared on monodisperse poly (glycidyl methacrylate-co-ethylene glycol dimethacrylate) microspheres, with 4-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate as the cross-linking agent, and doped with CD. The enrichment ability of CD@MIP for MCPA and fluorescence detection performance were determined. The maximum adsorption amount of MCPA was 93.9 mg g-1 as determined by isothermal adsorption experiments and was in accordance with the Langmuir adsorption model. The results of the kinetic experiments showed that the adsorption equilibrium reached within 30 min, which possessed a relatively fast adsorption rate and was in accordance with the pseudo-second-order adsorption model. Both MIP without CD and non-imprinted polymers were also fabricated and tested as references. Fluorescence experiments showed good linearity of CD@MIP in the range of 0-80 μmol. The cabbage samples were analyzed by high performance liquid chromatography with a linear range of 0.02-15 μg mL-1, recoveries of 90.5%-98% and low relative standard deviations (RSD, n = 3) of 1.5%-5.9%. CD@MIP with excellent performance provides a feasible practical application in the detection and enrichment of MCPA.

Comparison of pesticide adsorption efficiencies of zeolites and zeolite-carbon composites and their regeneration possibilities

The presence of pesticides in our environment is a consequence of intensive industrial and civilizational development, necessitating the search for effective and safe methods to remove them. We suggest utilizing zeolite X and a zeolite-carbon composite, obtained through the chemical transformation of fly ash, as pesticide sorbents. To increase the sorption efficiency of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), carbendazim, and simazine, we functionalized the zeolite materials with cationic (hexadecyltrimethylammonium) and nonionic (Triton X-100) surfactants. We used transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric/differential thermal analysis (TG/DTA) and point of zero charge (pHpzc) analysis to characterize the functionalized sorbent materials. Our results indicate that cationic surfactants significantly enhance the adsorption of 2,4-D and MCPA. In contrast, carbendazim and simazine exhibit maximum sorption on the unmodified zeolite-carbon composite. The sorption mechanism is intricate, with physical sorption predominating, primarily due to electrostatic interactions between the protonated binding sites of the adsorbents and the negatively charged pesticide molecules. Regeneration tests demonstrated that ethanol is the most effective in regenerating zeolite-carbon composite with adsorbed MCPA and 2,4-D, while thermal regeneration was not possible. Adsorbents with simazine and carbendazim can be regenerated using both thermal and ethanol methods, but the thermal regeneration of zeolite with adsorbed simazine is more efficient. Utilizing functionalized zeolite materials obtained from industrial waste, such as fly ash, could provide an efficient way to remove pesticides from the environment.

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.

Adsorption of picloram on clays nontronite, illite and kaolinite: equilibrium and herbicide-clays surface complexes

The picloram (PCM) adsorption on nontronite, illite and kaolinite was studied at pH 3, 5 and 7. The adsorption isotherms had well-fitted to Langmuir and Freundlich models equations. The interactions of PCM with the clay mineral surfaces exhibited an anionic profile adsorption, with a decrease in adsorption when the pH increases. The PCM adsorption capacity increases in the following order: kaolinite < illite < nontronite. The X-ray diffraction (XRD) analysis of PCM-clay samples revealed that the picloram molecule does not enter into the clays basal space. The interaction of PCM with clays surface sites through nitrogen of the pyridine ring was confirmed by X-ray photoelectron spectroscopy (XPS). Due to the anionic form of PCM, the adsorption onto the external and edges surface sites of the clay minerals was proposed.

OPAC (orange peel activated carbon) derived from waste orange peel for the adsorption of chlorophenoxyacetic acid herbicides from water: Adsorption isotherm, kinetic modelling and thermodynamic studies

This study presents the orange peel activated carbon (OPAC), derived from biowaste precursor (orange peel) by single step pyrolysis method and its application for the adsorption of chlorophenoxyacetic acid herbicides from the water. The OPAC exhibited the surface area of 592.471 m² g^-1, pore volume and pore diameter of 0.242 cc g^-1 and 1.301 nm respectively. The adsorption kinetics and thermodynamic equilibrium modelling for all chlorophenoxyacetic acid herbicides were investigated. The various parametric effects such as pH and temperature were evaluated. A pseudo-second-order kinetic model was well fitted for all the herbicides. The Langmuir isotherm was obeyed for all the herbicides and the maximum Langmuir capacity of 574.71 mg g^-1 was achieved. The thermodynamic studies revealed that the adsorption increases with increase in temperature. The results shows that the orange peel derived carbon (OPAC) as effective and efficient adsorbent material for the removal of chlorophenoxyacid herbicides from the water.