Reaction of bisphenol A with synthetic and commercial MnOx(s): spectroscopic and kinetic study

Abstract

The reaction of bisphenol A (BPA) using laboratory synthesized (Syn-MnO_x) and commercially available (Com-MnO_x) MnO_x(s) media was investigated using spectroscopic and aqueous chemistry methods. The surface area of Syn-MnO_x (128 m² g⁻¹) and Com-MnO_x (13.6 m² g⁻¹) differed by an order of magnitude. The impurities were less than 1% by weight for Syn-MnO_x while Com-MnO_x contained 29% impurity by weight, mainly Al, Si and Fe. The removal of 99.7% BPA was observed applying Syn-MnO_x, while 71.2% BPA removal was observed applying Com-MnO_x after 44 hours of reaction of 10 mM MnO_x(s) media with 1 mM BPA at pH 5.5. The reduction of Mn was detected in the surface of both BPA reacted media, but a higher content of reduced Mn was observed in Syn-MnO_x (52% in Syn-MnO_x compared to 29% in Com-MnO_x). The release of soluble Mn was an order of magnitude higher in batch experiments reacting BPA with Syn-MnO_x compared with Com-MnO_x. The C 1s and O 1s XPS high resolution spectral analyses identified the presence of functional groups that likely correspond to BPA oxidation products, such as dimers and quinones associated with MnO_x(s) surfaces on both reacted media. The reaction of BPA with Syn-MnO_x fit the electron transfer-limited model (R² = 0.96), while the reaction of BPA with Com-MnO_x had a better fit for surface complex formation-limited model (R² = 0.95). These results suggest that BPA removal and the reactivity of MnO_x(s) are affected by the differences in surface area and impurities present in these media. Thus, this study has relevant implications for the reaction of MnO_x(s) with emerging organic contaminants in natural biogeochemical processes and water treatment applications.