Perborate accelerated copper-immobilized carbon nanofibers activating peroxymonosulfate process for sulfadiazine degradation: Performance and mechanisms understanding

Abstract

In this work, perborate (BO3−) was applied to promote the degradation of sulfadiazine (SDZ) in copper-immobilized carbon nanofibers (Cu-CNF-x) activated peroxymonosulfate (PMS) system. Results showed that in BO3−/Cu-CNF-3/PMS ternary system, 100% of SDZ (40 μM) could be efficiently eliminated in 5 min with 0.1 g/L Cu-CNF-3, 1 mM BO3− and 1 mM PMS; while Cu-CNF-3/PMS and BO3−/PMS systems only achieved 58.4% and 47.3% degradation in 30 min. In initial pH range of 5.0–9.0, the ternary system removed over 92.6% of SDZ, and the treated solution pH maintained neutral, effectively relieving the water acidification introduced by PMS. Electron paramagnetic resonance analysis and radical scavenger tests evidenced the production of SO4−•, •OH, 1O2 and H2O2BO•O•−. Mechanisms analysis proposed the activation process as follows: initially, BO3− promptly activated PMS to generate H2O2BO•O•− via electrophilic substitution reaction, and H2O2 was produced due to the decomposition of BO3−; thereafter, PMS was activated by Cu-CNF-x to yield SO4−•, •OH and 1O2; the obtained H2O2 was then utilized by Cu-CNF-x to produce •OH and 1O2 as well. Density functional theory (DFT) calculations showed that the adsorption energy (Ead) between PMS and Cu-CNF-x was 0.43 eV. BO3− greatly increased the Ead of PMS on Cu-CNF-x by ten times to 4.75 eV, which extremely promoted the PMS activation. This work provided a novel strategy of BO3−/Cu-CNF-3/PMS for the efficient degradation of refractory organic pollutants, and managed to understand the synergistic role of BO3− to PMS based heterogeneous catalytic processes.