Effects of PMMA/anisole hybrid coatings on discoloration performance of nano zerovalent iron toward organic dyes

• PMMA/anisole coatings decreased the discoloration reactivity of NZVI.
• Inhibition of PMMA/anisole to the discoloration reactivity of NZVI was evaluated.
• Discoloration kinetics by PNZVI and BNZVI was discussed.
• Possible inhibitory mechanisms of PMMA/anisole were proposed.

To elucidate the effects of poly(methylmethacrylate) (PMMA)/anisole coatings on discoloration performance of nano zerovalent iron (NZVI), PMMA/anisole co-modified NZVI (PNZVI) was fabricated. PMMA/anisole-assisted fabrication of NZVI, to form PNZVI, has enhanced the oxidation resistance of NZVI and reduced its agglomeration. However, such coatings on NZVI surface gave an inhibition to discoloration reactivity of NZVI toward the selected dyes (i.e. acid fuchsine, sunset yellow and methyl orange). Further exploration showed that increasing initial concentration of acid fuchsine demonstrated an enhanced inhibition of the hybrid coatings to its discoloration efficiency by NZVI, whereas increasing NZVI dosage and solution temperature demonstrated a decreased inhibition to its discoloration efficiency. Additionally, the increased pH value reduced the discoloration reactivity of NZVI toward acid fuchsine but weakened the inhibition of the hybrid coatings. Such inhibitory effects might be ascribed to the inhibited mass transfer, blocked reactive sites, restrained electron transfer and reactive species caused by the hybrid coatings. Interestingly, the chloride ions are favorable for the enhancement of PNZVI reactivity whereas unfavorable for bare NZVI, and the discoloration kinetics by PNZVI and bare NZVI can both be well-described by empirical rate equation. This study suggests that polymer coatings play a crucial role between particle stability and reactivity of NZVI.