Co-incorporation of nitrogen and boron into microscale zero-valent iron via mechanochemical ball-milling method improved Cr(Ⅵ) elimination: Performance and mechanism investigation

• N 0.1 B 0.2 mZVI was prepared via simple mechanochemical ball-milling method. • The co-doping of N and B significantly enhanced the hydrophilicity of mZVI . • Fe-N and pyridine-N accelerated the electrons transfer to Cr(Ⅵ). • The B-B bond generated in ball milling process promoted the Fe(Ш)/Fe(Ⅱ) cycle. • N 0.1 B 0.2 mZVI exhibited excellent environmental adaptability on Cr(Ⅵ) removal. The passivation layer of microscale zero-valent iron (mZVI) limits its electronic efficiency in removing contaminants from water. Herein, nitrogen and boron co-doped mZVI ( N 0.1 B 0.2 mZVI ) was prepared via simple ball-milling method to regulate the electron transfer performance of mZVI. The co-doping of N and B significantly improved the electron efficiency of mZVI, resulting in complete Cr(Ⅵ) elimination within 60 min, and the k obs of N 0.1 B 0.2 mZVI was 17.33, 5.43, and 2.64 times higher than mZVI, N 0.1 mZVI , and B 0.2 mZVI . Additionally, N 0.1 B 0.2 mZVI demonstrated the ability to eliminate Cr(Ⅵ) across a broad pH range, while maintaining excellent removal performance in the presence of dissolved oxygen and co-existing ions. Mechanistic exploration revealed that the Fe-N and pyridine-N species were primarily responsible for accelerating electron transfer to Cr(Ⅵ). Furthermore, the B-B bond generated during the ball milling process, which did not originally exist in B 2 O 3 , could facilitate the Fe(Ш)/Fe(Ⅱ) cycle, promoting the generation of Fe(Ⅱ) on the surface of ( N 0.1 B 0.2 mZVI ) to reduce Cr(Ⅵ). This study optimized the electronic properties of mZVI through multi-heteroatom doping via the mechanochemical method, providing a reference for Cr(Ⅵ) elimination.