Enhancement of ionizing radiation-induced catalytic degradation of antibiotics using Fe/C nanomaterials derived from Fe-based MOFs

Highlights

• MOFs-derived Fe/C nanomaterial was used to enhance antibiotic removal by radiation.

• Degradation rate of CEP-C and SMT raised by 1.3 and 1.8 times using gamma/MOFs.

• Intermediates of bond cleavage of antibiotic molecule and OH addition were identified.

• Gamma radiation had no obvious influence on the structure and magnetism of MOFs.

Abstract

In present work, we studied a novel Fe/C nanomaterial fabricated using Fe-based metal organic frameworks (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 MOFs-derived Fe/C nanomaterials (DMOFs) had the regular octahedrons structure of MOFs and contained element C, Fe and O, while Fe° with a fraction of Fe₃O₄ and Fe₂O₃ were identified. Results showed that DMOFs addition could accelerate the generation of OH during gamma irradiation, while the intermediates of bonds cleavages of antibiotic molecules and OH addition were identified. DMOFs were more effective to improve the decomposition of antibiotic having the higher adsorption capacity like SMT. The degradation rate of CEP-C and SMT increased by 1.3 times and 1.8 times, and TOC reduction at 1.0 kGy reached 42 % and 51 %, respectively by gamma/DMOFs treatment, while only 20.2 % (CEP-C) and 4.5 % (SMT) of TOC reduction were obtained by γ-irradiation alone. The crystal structure, functional groups and magnetism of DMOFs changed slightly after gamma irradiation, which made it possible to be reused. DMOFs were promising to enhance the degradation of antibiotics during gamma irradiation.

Introduction

With the wide use of antibiotics to treat disease of bacterial infection and promote animal’s growth in livestock and poultry raising (Klein et al., 2018), concerns are growing about the hazardous effect of the residual antibiotics in water matrices (Kümmerer, 2009). Antibiotics, even in trace concentrations, could cause the development of antimicrobial resistance genes and pathogens (Martinez, 2009), which have become a serious issue to threaten public health (WHO, 2017). Since the conventional biological wastewater treatment is not effective in degrading antibiotics (Luo et al., 2014), various chemical/physical treatment technologies such as Fenton oxidation, ozonation, electrochemical oxidation, photo-catalysis and coagulation were developed to remove antibiotics in aqueous matrices, which is the hot topic in environmental research (Homem and Santos, 2011; Giraldo et al., 2015; Wang and Wang, 2016; Li et al., 2017; Wan and Wang, 2017; Liu et al., 2018; Wang and Wang, 2018, 2019a, 2019b, Wang and Chen, 2020).

Ionizing radiation by gamma-ray or e-beam irradiation is a new and efficient technique to decompose antibiotics in aqueous solution (Jiang and Iwahashi, 2019; Wang et al., 2019a,b,c). Through direct irradiation of high-energy γ-rays or e-beam and indirect reaction of radicals involving OH, H and e_aq⁻ formed in situ in water radiolysis (Eq. 1) (Spinks and Woods, 1990), most of antibiotics including macrolide, β-lactam and tetracycline are destroyed into intermediates and some of them are further mineralized into carbon dioxide and water (Wang and Chu, 2016; Changotra et al., 2018; Chu et al., 2019). In addition, 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. Besides, the intermediates with higher toxicity and antimicrobial activity were observed during ionizing radiation (Chen et al., 2019). To improve the mineralization and abatement of antimicrobial activity as well as to reduce the operation cost, ionizing radiation is often applied with addition of some oxidants like H₂O₂, ozone and the metal catalysts such as Fe²⁺ and TiO₂ (Kubesch et al., 2005; Torun et al., 2011; Illes et al., 2013; Liu et al., 2014; Chu et al., 2016; Wang and Zhuan, 2020). Among them, metal catalyst is attractive to accelerate the formation of OH which is noN–Selective strong oxidant and is mainly responsible for the decomposition and mineralization of antibiotics (Wang and Xu, 2012). Moreover, since antibiotics are existed in trace levels in real water, the substances, such as dissolved organic matters (DOM) and inorganic anions with large amount compete the radicals with antibiotics, leading to a great reduction in antibiotic removal. If the antibiotics are adsorbed into the metal catalyst and concentrated, the competition of antibiotics could be enhanced. The key point is to explore a metal catalytic material with a higher specific surface area and catalytic activity.

H₂O → OH(2.7) + e_aq⁻ (2.6) + H·(0.55) + H₂O₂(0.71) + H₂(0.45) + H₃O⁺(2.6)

MOFs are the hybrid porous crystalline materials constructed of central metal/clusters coordinated to organic ligands. MOFs materials are characterized with unique advantages involving the large surface area and controllable pore size, tunable topology and flexible structure (Corma et al., 2010), which makes the new porous materials to be widely used in many fields, for example, adsorption (Zhang et al., 2018b, c; Zhang et al., 2019d, e), photo-catalysis (Liu et al., 2019) and catalysis (Zhang et al., 2018a; Wang et al., 2019a,b,c; Zhang et al., 2019b). Fe-based materials have been widely applied for the environmental remediation (Wang and Bai, 2017; Liu and Wang, 2019). Recently, Fe-based metal organic frameworks (MOFs) have aroused increasing attention to catalyze the Fenton-like reaction and photocatalytic reaction to degrade organic pollutants in aqueous solution (Dias and Petit, 2015; Lv et al., 2015). Fe-based MOFs-derived Fe/C nanomaterials (DMOFs) were fabricated by using Fe-based MOFs as precursors through thermal pyrolysis under controlled temperatures and inert atmosphere. DMOFs could maintain the advantages of MOFs such as high specific surface area and flexible structure and exhibit more stable structure during catalyzing the Fenton-like oxidation (Andrew Lin and Hsu, 2015; Tang and Wang, 2018a). DMOFs might be promising to catalyze ionizing radiation-induced degradation of antibiotics in water matrices, which is scarcely available in literature as far as we know.

The aim of the present work was to enhance the efficiency of antibiotic degradation and mineralization during gamma irradiation catalyzed by DMOFs which was synthesized using MIL-100(Fe) as precursor. Two kinds of antibiotics, beta-lactam cephalosporin C (CEP-C) and sulfonamide sulfamethazine (SMT) were chosen as the target contaminants, which are used widely as broad-spectrum antibiotics and detected commonly in water matrices. The adsorption kinetics of the two antibiotics on DMOFs were firstly investigated. The performances of gamma/DMOFs system was evaluated in terms of antibiotic removal and mineralization extent, in comparison to gamma irradiation alone. The intermediates of antibiotic degradation were identified and the physicochemical properties of DMOFs before and after irradiation were assessed. This study will provide a new insight into an efficient technique to decompose antibiotics in water matrices by catalytic ionizing radiation.