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.

Enhanced photocatalytic degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) by the addition of H2O2

Photocatalytic remediation technology has been shown to be a favorable approach for the removal of a range of environmental pollutants in water treatment. While this approach can often achieve complete degradation, often overlooked are reaction intermediates that are potentially as harmful as the original parent compound. In the case of photocatalytic oxidation of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA), we have recently shown that 4-chloro-2-methylphenol (CMP) is formed as the primary intermediate. To ensure the continued development of the technology, it is crucial to ensure the removal of both MCPA and CMP can be achieved by photocatalysis. Reported here is the enhanced photocatalytic removal and subsequent suppression of MCPA and CMP respectively, by the addition of small quantities of H₂O₂. While the addition of H₂O₂ often accelerates degradation rates (via increased OH radical production), it was found to restrict the formation of CMP in this study through competitive adsorption at the surface of TiO₂. Based on the combination of MCPA removal coupled with supressed CMP formation, 0.5% H₂O₂ was determined to be an optimal loading for the process. Under these conditions 100% MCPA removal was achieved (to the limit of HPLC detection) after 45 min irradiation at a degradation rate of ∼1 mg L^-1 min^-1 (ƞ_photon = 4.4), which also resulted in a ∼83% reduction in CMP formation when compared to a system with no H₂O₂ present.

Photocatalytic ozonation of pesticides in a fixed bed flow through UVA-LED photoreactor

In this study, a fixed bed flow through UVA-LED photoreactor was used to compare the efficiency of ozone, photocatalysis and photocatalysis-ozone degradation, and mineralization of two pure pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), and a commercial one, Killex®. For the degradation of the parent compounds, ozone-based processes were more effective. While for mineralization, photocatalytic processes were more effective. Photocatalytic ozonation was the most efficient process for both the degradation and mineralization of the parent compounds. The degradation rates and mineralization by photocatalytic ozonation were higher than the summation of the corresponding rates by ozonation and photocatalysis, indicating a symbiotic relationship.Overall, the photocatalytic ozonation process with the fixed bed TiO₂ reduces the time needed for the degradation and mineralization of the pesticides, reduces the costs of powder catalyst separation and overcomes the reduced efficiency of immobilized catalysts, which makes the process quite attractive for practical applications.