Intervention of HCHO on the FeSx structure transition during sulfidation of zero-valent iron

[Display omitted] •HCHO intervenes the FeSx structure transition during sulfidation of zero-valent iron.•SZVIHCHO has batter electrochemical properties and better Cr(VI) removal performance.•The bonds of –CHO with Fe-S makes the electron loss from Fe atom but not from S atom. Iron sulfides (FeSx) enhancing the properties of sulfidated zero-valent iron (SZVI) to contaminants removal has been extensively studied, however, it is difficult to further regulate the FeSx species to control the SZVI properties. Based on the transformation of formaldehyde (HCHO) on FeSx, this work introduced HCHO into SZVI preparation process to regulate the FeSx structure. Results show that the HCHO-intervened SZVI (SZVIHCHO) has better Cr(VI) removal performance, which is due to the batter electrochemical properties. The FeSx structure of SZVIHCHO is evidently changed by HCHO, that is flaky FeSx transforms into granular FeSx and locally aggregated on SZVIHCHO surface. The composition of FeSx species shows that HCHO can weaken the conversion of FeS to FeS2, but directionally induce the conversion of FeS to Fe3S4. The electrostatic attraction of Fe atom in FeSx to the –CHO and the electron-withdrawing property of –CHO are the causes of electron loss from Fe atom and thus increase the Fe valence state. This study provides the inspirations for the future regulation of SZVI by inserting organics with specific structure and functions during SZVI preparation.