Mechanochemical destruction of perfluorooctane sulfonate (PFOS) using boron carbide (B₄C)

Widespread detection in soils and sediments underscores the potential threats posed by persistent, bioaccumulative and toxic perfluorooctane sulfonate (PFOS) to ecosystems and organisms. Nevertheless, the formidable energy of the C-F bond imparts stability and hampers degradation. This study investigates the potential of boron carbide (B₄C), a hard-ceramic material often utilized in armor and abrasion contexts, for degrading solid-phase PFOS through ball milling. Following a 60-minute reaction period, PFOS degradation reached 100 %, while desulfurization stabilized at 13.9 %. Defluorination initially rose to 23.7 % but subsequently displayed a gradual decline. Fluoride ions, once released, were secured and the stable reservoir surface of B₄C during the ball-milling process, leading to the formation of B-C-B-F chemical bonds, which was confirmed through characterization by XPS, FTIR, and solid-state NMR analyses. Furthermore, intermediate byproducts formed during the degradation of PFOS, encompassing perfluoroalkyl sulfonic acids (PFSAs) and perfluoro carboxylic acids (PFCAs), were identified. Eventually, the generation of free electrons, contributing to the facilitation of degradation for both PFOS and its intermediates, was confirmed through the DPPH experiment. This identification underscores the intricacy of the PFOS degradation pathway, which encompasses the generation and subsequent breakdown of these intermediates. These discoveries hold significance for pioneering sustainable and inventive methods to combat PFOS pollution across diverse applications. Furthermore, they enrich the comprehension of how mechanical forces can be leveraged for the eco-friendly removal of PFOS contaminants.