(354f) Ionizing Radiation-Induced Catalytic Degradation of Antibiotics in Water Matrices Using Fe/C Nanomaterials Derived from Iron-Based MOFs

The serious threat of antimicrobial resistance to human health has aroused the development of potential technologies to abate antibiotics from aqueous solutions. High-energy ionizing radiation, using electron beam or gamma rays, is considered to be more economic and efficient on a large-scale application than other AOPs such as UV radiation. H₂O molecules absorb radiation energy and water radiolysis occurs to generate the species involving the powerful oxidant ·OH and reductant e_aq^- and H·. ionizing irradiation has the advantages of good penetration in water matrices, insensitivity to suspended particles, no residuals produced and operation at room temperature. The public safety concern about radiation and high cost of investment and operation are the major factors to limit its application.

Recently, the iron-based metal organic frameworks (MOFs) have increasingly aroused great research attention in catalyzing the Fenton-like reaction and photocatalytic reaction to degrade organic pollutants in aqueous solution. MOFs are the hybrid porous crystalline materials constructed of the central metal /clusters coordinated to organic ligands, which have the large surface area and porosity, tunable topology and flexible structure. The Fe-based MOFs-derived Fe/C nanomaterials (DMOFs) are fabricated by using Fe-based MOFs as precursors through thermal pyrolysis under controlled temperatures and inert atmosphere. DMOFs remained the high specific surface area and porosity of MOFs and exhibited high catalytic activity and stability.

In present work, we proposed a novel Fe/C nanomaterial fabricated using Fe-based MOFs as precursors through thermal pyrolysis to catalyze gamma irradiation-induced degradation of antibiotics, cephalosporin C (CEP-C) and sulfamethazine (SMT) in aqueous solution. The adsorption kinetics of the two antibiotics on DMOFs were firstly investigated. The performances of gamma/DMOFs system was evaluated in terms of the antibiotics removal and mineralization extent in comparison to that using gamma irradiation alone. The degradation intermediates of antibiotics were identified and the physicochemical properties of DMOFs before and after irradiation was assessed. This study will provide a new insight about an efficient technique to decompose antibiotics in water matrices by catalytic ionizing radiation.

Results showed that DMOFs have the regular octahedrons structure of MOFs with high porosity. It consists of element C, Fe and O and Fe⁰ with a fraction of Fe₃O₄ and Fe₂O₃ were identified. DMOFs addition was more efficient to enhance the degradation of antibiotics having a higher adsorption capacity like SMT. The degradation rate of CEP-C and SMT raised by 1.3 times and 1.8 times, and the TOC reduction at 1.0 kGy reached 42% and 51%, respectively by gamma/DMOFs treatment, compared to TOC removal of 20.2% (CEP-C) and 4.5% (SMT) by gamma irradiation alone. This was attributed to the enhanced generation of ·OH catalyzed by DMOFs during gamma irradiation. Overall, the degradation rate of both CEP-C and SMT was higher at acidic conditions and declined at alkaline pH of 9.0. It is noted that the adsorption capacity of both antibiotics declined with increasing the solution pH, which might have negative effect on antibiotic degradation. Regarding to the iron leached, it was much higher (up to 0.9-1.2 mg/L) at pH 4.0, while it maintained at low levels (0-0.2 mg/L) when the solution pH was higher than 5.2. Taken into account of the higher antibiotic decomposition rate and the minor iron leaching, pH value of 5.7 ± 0.5 was suggested for practical application.

The antibiotic molecules were destroyed, leading to the formation of intermediates of the N-S bond cleavage for SMT, C-N bond cleavage and β-lactam ring and dihydrothiazine ring opening for CEP-C. DMOFs exhibited good stability and recyclability as exposed to gamma irradiation. The crystal structure, functional groups and magnetism of DMOFs changed slightly after gamma irradiation, which made it possible to be recycled and reused. DMOFs were promising to enhance the degradation of antibiotics during gamma irradiation.