Synergistic adsorption and oxidative degradation of polyvinyl alcohol by acidified OMS-2: Catalytic mechanism, degradation pathway and toxicity evaluation

Abstract

The present work introduced the use of acidified rod-like manganese dioxide (H-OMS-2) as effective peroxymonosulfate (PMS) activator and adsorbent for the removal of polyvinyl alcohol (PVA). The adsorption efficiency for PVA solution (80 mg/L) was 78 % after 60 min when H-OMS-2 (0.6 g/L) was used as adsorbent and the maximum adsorption capacity was 25.5 mg/g. After the addition of PMS (7 mM), PVA was entirely degraded within 40 min after adsorption/desorption equilibrium, and 64 % mineralization rate was reached after 5 h via the synergistic adsorption and oxidation process. The apparent activation energy (Ea) of H-OMS-2/PMS system was 11.14 kJ/mol that was lower than the value in OMS-2/PMS system (24.87 kJ/mol). And, H-OMS-2 could be recycled for 4 times with 90 % of degradation rate at 40 min and 56 % of mineralization rate after 24 h. Quenching test and electron paramagnetic resonance (EPR) results demonstrated that 1O2 was the primary reactive oxygen species rather than ·OH, SO4̇- and O2̇-. In addition, non-radical pathway via the direct electron transfer existed. The complex between Mn3+ and PMS (electron acceptor) acted as main active species to oxidize adsorbed PVA (electron donor). The characterization and degradation performance of catalyst indicated that abundant Lewis- and Brønsted-acid sites on H-OMS-2 are beneficial to CC cleavage of PVA, along with the void-confinement effects of H-OMS-2 due to its highly structured mesoporous pore size, which can result in the promotion of the degradation. Finally, study on the degradation pathway of PVA along with the aquatic toxicity experiment via zebrafish model system indicated that intermediates containing carbonyl groups are harmful for the survival and development of zebrafish.