Catalytic oxidative degradation of bisphenol A using an ultrasonic-assisted tourmaline-based system: Influence factors and mechanism study

• BPA was completely removed in the ultrasonic-assisted tourmaline-catalytic system.
• BPA degradation kinetics were described well by a retarded first-order kinetic model.
• Electrostatic field assisted acceleration of the Fe(III)/Fe(II) cycle was proposed.
• BPA degradation involved hydroxylation, oxidative skeletal rearrangement, demethylation, dehydration.

Tourmaline was utilized as a heterogeneous catalyst for the oxidation of bisphenol A (BPA) with synergetic H2O2-catalytic ability and ultrasonic irradiation. Higher tourmaline concentration, an appropriate H2O2 dose and a lower pH favored BPA depletion. The removal of 5.0 mg L−1 BPA reached 98.4% at 120 min under the following optimized reaction conditions: sonication (40 kHz, 500 W), tourmaline concentration 5.0 g L−1, H2O2 50 mM and pH 2.0. This high BPA removal could be caused by coordinating heterogeneous and homogeneous processes, based on the observed iron leaching and H2O2 conversion data at different pHs. A retarded first-order kinetic model was employed to describe BPA degradation. The strong inhibition of BPA removal by radical scavengers indicated that the attack of hydroxyl radicals was mainly responsible for BPA removal. In view of the X-ray photoelectron spectroscopy (XPS) results during the reaction, a possible mechanism involving accelerated transfer in the Fe(III)/Fe(II) cycle on the tourmaline surface was proposed. Moreover, eight intermediates were evidenced by GC–MS and LC–MS/MS analyses, and a reaction pathway was also proposed, including the processes of hydroxylation, oxidative skeletal rearrangement, demethylation and dehydration.