Iron-based metal organic framework MIL-88-A for the degradation of naproxen in water through persulfate activation

In this work, particular interest is given to synthetized iron-based MOF e.g. MIL-88-A especially for its ability to catalytically activate persulfate (PS) in an advanced oxidation process (AOP) toward the degradation of naproxen (NPX) in solution in batch systems. NPX solution (50 mg L-1) was subjected to specific added amount of MIL-88-A followed by PS spiking after equilibrium was reached. The system was optimized for its recyclability and matrix variations by studying parameters including ionic strength, pH, phosphates and bicarbonates content, oxidant nature (S2O82- vs H2O2) as well as UVA irradiation. Results showed that (i) MIL-88-A is a good activator of PS where 65-70% degradation of NPX was noticed within 2 h of reaction at room temperature; (ii) MIL-88-A is recyclable up to 4 successive cycles with significant removal extent; (iii) phosphates had no effect on the degradation of NPX however, bicarbonates exhibited a strong inhibition; (iv) PS activation and NPX degradation were optimal at acidic conditions (pH = 4) and (v) PS generated HRs and SRs in the medium and was shown to be superior oxidant over H2O2 in the presence of MIL88-A. Moreover, experiments under UVA irradiation showed significant improvement of the degradation process of NPX in solution reaching almost complete vanishing after 2 h of reaction. The removal mechanism of NPX was investigated using, for the first time, in addition to traditional analytical techniques e.g. HPLC/DAD/MS-Ion trap, XPS and EPR, the Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). TOF-SIMS technique confirmed that adsorption/degradation mechanism of NPX took place at the surface of MIL-88-A making this heterogeneous catalysis AOP-based technology very successful for the elimination of pharmaceutical compounds from water effluents.