Crystalline boron significantly accelerates Fe(III)/PMS reaction as an electron donor: Iron recycling, reactive species generation, and acute toxicity evaluation

Abstract

Crystalline boron (C-boron) could provide redox active sites in Fenton-like reactions due to the surface B-B bonds and interfacial suboxide boron in the surface structure of B12 icosahedra. However, related research on boron chemistry is limited. We demonstrate here that addition of C-boron to the Fe(III)/peroxymonosulfate(PMS) system effectively improves the degradation of flunixin meglumine, aspirin, nitrobenzene, and benzoic acid at pH 4.0–10.0 (without buffer). Compared with the Fe(III)/PMS system, the kobs of the C-boron/Fe(III)/PMS system for degradation of these four contaminants at pH 7.0 was approximately 8.7–65.1 times higher. C-boron enhanced the homogeneous Fe(II) concentration in the Fe(III)/PMS system from 5.4 to 16.2 mg/L in a 20-min reaction, whereas Fe(IV) was generated from the Fe(II) produced in the system.Electron paramagnetic resonance and quenching experiments revealed the presence of ·OH, 1O2, and O2·− in the reaction, and the corresponding contributions of ·OH to oxidizing flunixin meglumine and aspirin were 16.7 % and 28.1 % at pH 7.0. The C-boron/Fe(III)/PMS solution significantly inhibited Microcystis aeruginosa growth, with the rate increasing in the first 24 h and then decreasing from 48 to 96 h. This toxicity was resulted by the inhibition of the chlorophyll a and chlorophyll b in the photosynthetic system. Overall, this work reported the feasibility of C-boron enhancement for pollutants degradation in Fe(III)/PMS system for the first time.