Boosted micropollutant removal over urchin-like structured hydroxyapatite-incorporated nickel magnetite catalyst via peroxydisulfate activation

Abstract

In this work, urchin-like structured hydroxyapatite-incorporated nickel magnetite (NiFe₃O₄/UHdA) microspheres were developed for the efficient removal of micropollutants (MPs) via peroxydisulfate (PDS) activation. The prepared NiFe₃O₄/UHdA degraded 99.0 % of sulfamethoxazole (SMX) after 15 min in 2 mM PDS, having a first-order kinetic rate constant of 0.210 min^-1. In addition, NiFe₃O₄/UHdA outperformed its counterparts, i.e., Fe₃O₄/UHdA and Ni/UHdA, by giving rise to corresponding 3.6-fold and 8.6-fold enhancements in the SMX removal rate. The outstanding catalytic performance can be ascribed to (1) the urchin-like mesoporous structure with a large specific surface area and (2) the remarkable synergistic effect caused by the redox cycle of Ni³⁺/Ni²⁺ and Fe²⁺/Fe³⁺ that enhances multipath electron transfers on the surface of NiFe₃O₄/UHdA to produce more reactive oxygen species. Moreover, the effects of several reaction parameters, in this case the initial solution pH, PDS dosage, SMX concentration, catalyst loading, co-existing MPs and humic acid level on the catalytic performance of the NiFe₃O₄/UHdA + PDS system were systematically investigated and discussed in detail. The plausible catalytic mechanisms in the NiFe₃O₄/UHdA + PDS system were revealed via scavenging experiments and electron paramagnetic resonance analysis, which indicated a radical (^•OH and SO₄^•-) as the major pathway and a nonradical (¹O₂) as the minor pathway for SMX degradation. Furthermore, NiFe₃O₄/UHdA exhibited fantastic magnetically separation and retained good catalytic activity with a low leached ion concentration during the performance of four cycles. Overall, the prepared NiFe₃O₄/UHdA with outstanding PDS activation could be a promising choice for the degradation of persistent organic pollutants from wastewater.

Keywords: Heterogeneous catalysis; Persulfate-based advanced oxidation processes; Reactive oxygen species; Sulfamethoxazole; Urchin-like structured NiFe(3)O(4)/UHdA.