Important role of cellulose and lignin in controlling the crystal structure of iron-carbon composite: Fe3C surpassing Fe0 in activating peroxymonosulfate

The mechanism of producing iron-carbon composites with different crystal structures by varied wood-based biomass remains unclear. Herein, cellulose and lignin as the important components of wood-based biomass were used to investigate the influence on the crystal structure of iron-carbon composites. Results showed that Fe 3 C could only be produced in cellulose-containing pyrolysis processes, while the pyrolysis of lignin could reduce the iron salt to Fe 0 . Additionally, prolonging pyrolysis time and increasing the ratio of cellulose to Fe also favored the production of Fe 3 C. When applied to activate peroxymonosulfate (PMS), the Fe@Cel 0.5 -4 typically dominated by Fe 3 C showed better performance than Fe@Ln 1.0 -4 which was dominated by Fe 0 in the aspects of adsorption, electron transfer, retaining the iron species, sustainability, adaptability to complex water conditions, and the catalytic capability to degrade diclofenac (DCF). Quenching experiments and electron spin resonance results indicated the presence of free radicals ( OH, SO 4 − , SO 5 − and O 2 − ) and non-radical ( 1 O 2 and electron transfer process) pathways in both processes. However, the degradation of DCF in Fe@Cel 0.5 -4/PMS process was mainly dominated by 1 O 2 and electron transfer while was contributed by radical and nonradical pathways almost equally in Fe@Ln 1.0 -4/PMS process. This study may cast some light on the development of iron-carbon composites using wood-based biomass as the carbon source to synthesize the highly efficient catalyst for PMS activation.