Dechlorinating transformation of propachlor through nucleophilic substitution by dithionite on the surface of alumina

Abstract

Purpose The aim of this study was to evaluate the roles of aluminum-based minerals, especially their surface Lewis acid sites (LASs), on the transformation and fate of chloroacetanilide herbicide contaminants when nucleophilic reagents are present. Materials and methods Batch experiments were used to study propachlor transformation processes under different reaction conditions. The surface bonding of aluminas before and after interacting with propachlor and dithionite were characterized by Fourier transform infrared (FTIR) spectra. The LASs on different aluminas, acting as the key role for accelerating the propachlor transformation, were analyzed by pyridine adsorption/FTIR spectroscopic technique. Results and discussion Rates of dithionite-initiated propachlor dechlorination were increased in the presence of aluminas. Transformation efficiencies of propachlor on different aluminas were found to be as γ-Al 2 O 3 >γ-AlOOH>α-Al 2 O 3 . A higher reaction temperature, higher pH, and higher alumina dosage can further increase the propachlor dechlorination rate.The addition of citric acid may block the active sites on alumina and reduce propachlor transformation by dithionite. FTIR and pyridine adsorption/diffuse reflectance Fourier transform infrared spectroscopy indicated that Al-S and Al-O bonds on the LASs of alumna play a key role in accelerating propachlor transformation. Conclusions LASs on alumina surfaces can effectively accelerate the propachlor transformation by dithionite. The strong electron accepting ability of LASs gives dithionite a favorable affinity to form surface sulfur compounds, which are stronger reductants and nucleophilic reagents for propachlor dechlorination. The intensities of LASs on alumina surfaces can be used to control the rate of propachlor transformation by dithionite.

Enhanced Dechlorination of 1,2-Dichloroethane by Coupled Nano Iron-Dithionite Treatment

“…Dithionite is capable of degrading select chlorinated compounds and pesticides (Castillo et al, 1997, Rodriguez and Rivera, 1997, Nzengung et al, 2001, Liu et al, 2012. However, when combined with a reactive surface (e.g., alumina or iron) the reaction rate of the system increases (Nzengung et al, 2001, Liu et al, 2012.…”

“…However, when combined with a reactive surface (e.g., alumina or iron) the reaction rate of the system increases (Nzengung et al, 2001, Liu et al, 2012. Therefore, a heterogeneous solution with nZVI is expected to show a higher reaction rate than a homogeneous solution of only dithionite.…”

“…The pseudo-first order rate constant of the dithionite + nZVI (4.5 x 10 -3 d -1 ) treatment is twice that of only dithionite (2.1 x 10 -3 d -1 ). Liu et al (2012) reported an increase in the reaction rate of dithionite when combined with alumina for the dechlorination of propachlor. The higher reaction rate was attributed to the density of Lewis Acid Sites (LASs) on alumina surfaces.…”

Heterogeneous Nucleophilic Transformation of Metolachlor by Bisulfide on Alumina Surface

“…With regard to g-Al 2 O 3 and a-Al 2 O 3 , only Al-O bond stretching was found after the reaction and the intensities on these two aluminas also varied slightly. However, according to our previous report, the higher intensity of active LAS on g-Al 2 O 3 than on a-Al 2 O 3 may lead to the higher metolachlor transformation rate with g-Al 2 O 3 [32].…”

“…The limit of detection was 7 mg L À1 , and the relative standard deviation was within 5%. The qualitative determination of the metolachlor transformation intermediates was performed by LC/MS analysis using an HPLC system (Shimadazu, Japan) accompanying an API 3000 mass analyzer with the detailed procedure described in our previous study [32].…”