The performance and mechanism of persulfate activated by CuFe-LDHs for ofloxacin degradation in water

Abstract

Antibiotic-containing refractory organic wastewater is difficult to degrade via traditional physicochemical treatment technology because of its high stability. Therefore, an advanced oxidation process based on sulfate radicals was developed and received extensive attention because of its wider pH operating range and stronger oxidizing property, considering that the PS was easily activated by transition metals without excessive energy input. In this study, a layered double hydroxide (LDH) catalyst consisting of Cu(II) and Fe(III) (CuFe-LDHs) was synthesized to activate PS to degrade ofloxacin (OFL) in water effectively. The results showed that when the dosages of CuFe-LDHs and PS were set as 0.5 g L⁻¹ and 0.2 mM, respectively, the degradation efficiency of OFL was up to ∼80% within a wide pH operating range (3–11) and with low activation energy (E_a = 54.95 kJ mol⁻¹) under the condition that the initial OFL concentration was 10 mg L⁻¹. Interference experiments on OFL degradation demonstrated that Cl⁻, NO₃⁻, humic acid and HCO₃⁻ have almost no influence on the CuFe-LDHs/PS system, while the OFL degradation performance was significantly inhibited with increasing concentration of SO₄²⁻ and H₂PO₄⁻ (the degradation efficiency decreased by 44.4% and 60.1%, respectively). The results of quenching experiments and electron paramagnetic resonance analysis showed that SO₄·⁻ was the dominant free radical for OFL degradation, and SO₄·⁻ was generated via Cu-Fe electron transfer with surface-OH acting as active sites. That was the reason why the catalytic reaction process was easily affected by SO₄²⁻ and H₂PO₄⁻. In addition, the CuFe-LDHs/PS system exhibited excellent cycle performance: the OFL degradation efficiency remained at 66.8% after five cycles. In summary, this study provides theoretical and technical guidance for the application of CuFe-LDHs in antibiotic wastewater degradation by activating PS.