Effectively accelerated degradation of bisphenol A in Fe3O4/PMS system by caffeic acid

Bisphenol A (BPA) is an endocrine disruptor widely used in industry and the increased incidence of many cancers has been shown to be related to their exposure. Effective removal of BPA is causing concern. In this article, it was found that the introduction of caffeic acid (CFA) might significantly improve BPA degradation in Fe3O4/PMS system. The use of Fe3O4/CFA/PMS system offers a number of advantages compared to previously used homogeneous systems, including a wider pH range for application, ease of production, and minimal biotoxicity. Based on the analysis and discussion of the experimental data, it is clear that BPA can be almost completely degraded within 40 minutes under the most efficient conditions of 0.4 mM PMS, 0.5 g/L Fe3O4, and 0.05 mM CFA. BPA was successfully removed over a broad pH range of 3.0–9.0. Due to the presence of reactants in different states, the inhomogeneous system is less significantly disturbed by H+ and OH- compared to the homogeneous system. The presence of Cl-, HCO3-, NO3- and humic acid influences the removal of BPA. The intermediate product (benzoquinone) of CFA was found to be involved in the reaction and effectively promoted the recycling of Fe(II) and Fe(III). By the formation of CFA-Fe chelates, the reducing and chelating ability of CFA accelerates Fe(III)/Fe(II) cycling and thus promotes the activation of PMS. Ethanol scavenging studies and chemical probe experiments showed that the presence of hydroxyl radicals (HO·), sulphate radicals (SO4.-) and singlet oxygen (1O2) plays a role in the elimination of BPA in Fe3O4/CFA/PMS system. The contribution rate is found to be SO4.->HO·>1O2. The current research provides a low-cost, environmentally friendly method to remove BPA.