Persulfate activation using leonardite char-supported nano zero-valent iron composites for styrene-contaminated soil and water remediation

Abstract

Effective in-situ technology to treat carcinogenic compounds in contaminated areas poses a major challenge. Our objective was to load nano-zero-valent iron (nZVI) onto leonardite char (LNDC), an alternative carbon source from industrial waste, for use as a persulfate (PS) activator for styrene treatment in soil and water. By adding a surfactant during synthesis, cetyltrimethylammonium bromide (CTAB) promotes a flower-like morphology and the nZVI formation in smaller sizes. Results showed that nZVI plays a crucial role in PS activation in both homogeneous and heterogeneous reactions to generate reactive oxygen species (ROS), which can remove 98% of styrene within 20 min. Quenching experiments indicated that singlet oxygen (1O2), superoxide radicals (O2•–), and sulfate radicals (SO4•–) were the main species working together to degrade styrene. XPS analysis also revealed a role of surface oxygen-containing groups (i.e., CO, C–OH) in activating PS for SO4•– and 1O2 generation. The possible reaction mechanism of PS activation by LNDC-CTAB-nZVI composite and factors affecting treatment efficiency (i.e., PS concentration, catalyst dosage, pH, and humic acid) were illustrated. The molarity/molality ratio of PS to nZVI should be set greater than 1 for effective styrene removal. GC-MS analysis showed that styrene was degraded to a less toxic benzaldehyde intermediate. However, the excessive use of PS and catalysts can harm plant growth, requiring a combining approach to achieve safer use for real applications. Overall results supported the use of the LNDC-CTAB-nZVI/PS system as an efficient in-situ treatment technology for soil and water remediation.