Impact of nanoceria shape on degradation of diethyl paraoxon: Synthesis,catalytic mechanism, and water remediation application

摘要

A series of nanomaterials have been demonstrated to be powerful for direct degradation of diethyl paraoxon (EP) to diethyl phosphate and 4-nitrophenol in aqueous solution. However, comparison of catalytic activity of different nanomaterials toward EP is rarely explored. In the present study, four different morphological nanoceria (cubes, rods, polyhedral, and spheres) were synthesized, characterized, and evaluated as a catalyst for the degradation of EP in comparison to other commercially available nanomaterials. Among the tested nanoceria, the cerium dioxide (CeO_2) nanopolyhedra possess the best catalytic activity toward the hydrolysis of EP owing to their abundant oxygen vacancy sites, optimal ratio of Ce(Ⅲ) to Ce(Ⅳ), and specific exposed facets. Under the conditions of 0.2 M NH_3/NH_4C1 buffer and 25 °C, the CeO_2 nanopolyhedra catalyzed the reduction of EP to 4-nitrophenol with a > 99% conversion at pH 8.0 for 50 h, at pH 10.0 for 12 h, and at pH 12.0 for 2.5 h. The catalytic degradation of nearly 100% EP in NH_3/NH_4C1 buffer (pH 10.0) at 25 °C is in the decreasing order of CeO_2 nanopolyhedra > CeO_2 nanorods > ZnO nanospheres (NSs) > CeO_2 nanocubes > TiO_2 NSs > CeO_2 NSs > Fe_3O_4 NSs ~ Co_3O_4 NSs ~ control experiment. The mechanism for the degradation of EP was confirmed by monitoring catalytic kinetics of the CeO_2 nanopolyhedra in the presence of EP, dimethyl paraoxon, 4-ni-trophenyl phosphate, and parathion. The nanocomposites were simply fabricated by electrostatic self-assembly of the CeO_2 nanopolyhedra and polytdiallyldimethylammonium chloride)-capped gold nanoparticles (PDDA-AuNPs). The resultant nanocomposites still efficiently catalyzed NaBH4-mediated reduction of 4-nitrophenol to 4-aminophenol with a normalized rate constant of 6.68 ± 0.72 s~(-1) g~(-1) and a chemoselectivity of > 99%. In confirmation of the robustness and applicability of the as-prepared nanocomposites, they were further used to catalyze the degradation of EP to 4-amionphenol in river water and seawater.