Green remediation, mechanisms, and pathways of synthetic phenolic antioxidants by Fe-based antioxidant combined ball milling

Organic synthetic phenolic antioxidants (SPAs) and inorganic Fe-based antioxidants are widely used in daily life to prevent or delay oxidation and prolong storage and use. However, the ubiquitous occurrence of SPAs and the unreasonable disposal of Fe-based antioxidants (typically throwing them away) cause environmental issues and waste Fe resources. In this study, 16 solid SPAs and one important SPA intermediate were selected as target pollutants and destroyed via the ball milling Fe-based antioxidants collected from food bags packaged under a vacuum. Typical influencing factors, such as the co-grinder type, content, and grinding velocity, significantly affected the destruction efficiencies of the substrate (4- tert -octylphenol, 4- t OP, a representative commonly used SPA). Under optimal conditions, 0.1 g of 17 SPAs achieved high removal rates (35 %–97 %), with the highest first-order reaction rate constant ( k ) for propyl gallate (PG) being 1.00 h −1 , and the lowest k value for 2,6-di- tert -butyl-4-methylphenol (BHT) being 0.09 h −1 . Experimental and characterization (X-ray diffraction, Fourier transform-infrared spectroscopy, and X-ray photoelectron spectroscopy) observations showed that the reduction of Fe 0 , the oxidation of •OH, the reduction and oxidation of Fe(II) and Fe(III), oxygen vacancies, and mechanical forces exerted during ball-milling contributed to SPA destruction. Among these, the first two were the main mechanisms; however, the mechanical forces could not be ignored. Ten intermediates generated by 4- t OP during Fe-based ball milling were identified based on mass spectrometric results. Three pathways involved were hydroxylation, dealkylation, and polymer formation, and hydroxylation products were more abundant than others. According to ECOSAR and T.E.S.T program analyses, the ecotoxicity of most of the obtained intermediates was reduced. These findings reveal that Fe-based ball-milling technology can treat solid SPA pollution and achieve double-win performance.