Molar absorptivities of 2,4-D, cymoxanil, fenpropidin, isoproturon and pyrimethanil in aqueous solution in the near-UV

2,4-Dichlorophenoxyacetic acid (2,4-D) photodegradation on WO3-TiO2-SBA-15 nanostructured composite

A current environmental problem is the uncontrolled use of various pesticides that are harmful to the environment and public health. The herbicide 2,4-D is widely used, making it a vector of contamination for aquatic bodies, air, soil, and biomass. In recent decades, researchers have studied remediation of this compound in the environment. In this work, WO₃ and TiO₂ were supported on SBA-15 molecular sieve by the in situ anchoring (ISA) method, with different molar percentages of WO₃ in relation to the oxide content: X = 25%, 50%, and 75%. The W-Ti-S (X) samples were characterized by XDR, XRF, Raman, FTIR, diffuse reflectance of UV-vis, and adsorption and desorption of N₂. SBA-15 mesoporous structure was not destroyed even after the incorporation of the oxides. XRD analyses associated with Raman result found a predominance of the anatase phase for titanium oxide, and the FRX showed low incorporation of nanoparticles. Photocatalytic tests indicated that the catalytic activity depends on WO₃ and TiO₂ content, although all W-Ti-S (X) samples exhibited similar TOF value. The W-Ti-S (25) sample had the highest photocatalytic activity, 76% herbicide photodegradation under ultraviolet irradiation, at 270 min. The analysis of the catalytic cycles indicated that W-Ti-S (25) keeps out 70% of photocatalytic activity in the fourth catalytic cycle. In addition, the W-Ti-S (25) catalytic activity under direct sunlight irradiation was similar to that under artificial UV irradiation.

Adsorption kinetic and thermodynamic studies of the 2, 4 - dichlorophenoxyacetate (2,4-D) by the [Co-Al-Cl] layered double hydroxide

[Co-Al-Cl] layered double hydroxide (LDH) obtained by co-precipitation at constant pH 8 presented a single phase in a hexagonal unit cell parameters similar to the hydrotalcite (JCPDS 14-191) belonging to the rhombohedral crystal system and space group R (-3)m . The adsorption kinetics of 2,4-D onto [Co-Al-Cl] LDH was better described by the Pseudo Second-Order (best adjust R2 = 0.9998 for 60 mg L-1 2,4-D adsorption). Intra-particle diffusion model was not the sole rate-controlling factor, indicating the adsorption of 2,4-D by the [Co-Al-Cl] LDH is a complex process for the experimental conditions performed, involving both boundary layer and intra-particle diffusion. The adsorption isotherm adjusted better to the Freundlich model (R2 = 0.9845) and the ΔH° value of - 51.18 kJ mol-1 indicated the predominance of the physical adsorption. The FT-IR spectrum of LDH after adsorption presented 2,4-D bands together with those of LDH and XRD showed an increase in the interlamellar distance (d 003) due to the intercalation of 2,4-D in the interlayer structure of the [Co-Al-Cl] LDH, corroborating inter and intra-particle adsorption data. Thus, [Co-Al-Cl] LDH, commonly used as electrodes in supercapacitors, can be effectively used as an adsorbent for the removal of 2,4-D from contaminated waters.

Fungicide volatilization measurements: inverse modeling, role of vapor pressure, and state of foliar residue

Few data sets of pesticide volatilization from plants at the field scale are available. In this work, we report measurements of fenpropidin and chlorothalonil volatilization on a wheat field using the aerodynamic gradient (AG) method and an inverse dispersion modeling approach (using the FIDES model). Other data necessary to run volatilization models are also reported: measured application dose, crop interception, plant foliage residue, upwind concentrations, and meteorological conditions. The comparison of the AG and inverse modeling methods proved the latter to be reliable and hence suitable for estimating volatilization rates with minimized costs. Different diurnal/nocturnal volatilization patterns were observed: fenpropidin volatilization peaked on the application day and then decreased dramatically, while chlorothalonil volatilization remained fairly stable over a week-long period. Cumulated emissions after 31 h reached 3.5 g ha(-1) and 5 g ha(-1), respectively (0.8% and 0.6% of the theoretical application dose). A larger difference in volatilization rates was expected given differences in vapor pressure, and for fenpropidin, volatilization should have continued given that 80% of the initial amount remained on plant foliage for 6 days. We thus ask if vapor pressure alone can accurately estimate volatilization just after application and then question the state of foliar residue. We identified adsorption, formulation, and extraction techniques as relevant explanations.