Fe-based carbonitride as Fenton-like catalyst for the elimination of organic contaminants
Graphical abstract
Introduction
Organic pollutants in water such as dyes (He et al., 2018), phenols (Feng et al., 2020), and antibiotics (Wang et al., 2019) have become a serious issue, damaging the environment and health of living organisms. Therefore, there is an urgent need to develop effective treatment techniques to remove these contaminants from wastewater. Advanced oxidative processes (AOPs) (O'Shea et al., 2012) are promising candidates for wastewater treatment and can provide ROS, such as SO4- (Hu et al., 2016), OH (Su et al., 2016), O2- (Zhou et al., 2019) and 1O2 (Zhang et al., 2020), for the destruction of organic compounds. Among the various AOPs, the generation of SO4- (Luo et al., 2019) and OH (Li et al., 2018) based on a Fenton-like system via activation of PMS has received much attention because of the relatively high standard redox potentials of these radicals. There are several methods for the efficient activation of PMS, such as heat (Qi et al., 2017), UV irradiation (Jaafarzadeh et al., 2017a), ultrasound (Chakma et al., 2017) and transition metals (Song et al., 2018). In particular, the use of Fe2+ for activating PMS is more appealing because of its advantages of high efficiency (Yi et al., 2019), non-toxicity (Zhang et al., 2016) and low energy consumption (Kulandaivelu et al., 2019). However, the homogeneous catalyst of Fe2+ in aqueous solutions results in considerable amounts of iron sludge. Therefore, the development of heterogeneous Fe-based catalysts is of great significance in avoiding secondary pollution of Fe ions.
As promising crystalline porous materials (Li et al., 2018), metal organic frameworks (MOFs) have been widely employed as self-sacrificial templates (Chen et al., 2015) or precursors for the generation of nanoporous carbonitride (NC) frameworks (Tang et al., 2015) in catalysis. Significantly, recent progress has illustrated that MOFs as supporting materials for heterogeneous Fe-based catalysts present a substantial capability for the activation of superoxides and degradation of contaminants. Zeng et al. fabricated crystalline Fe-based nanoparticles with N-doped porous nanocarbon through the pyrolysis of Fe–N co-doped nanoscale MOF templates, which could remove 93% of 4-chlorine phenol in 60 min when coupled with PMS (Zeng et al., 2017). Liu et al. encapsulated Fe/Fe oxides nanoparticles into N-doped porous carbon with NH2-group MOF precursor for the degradation of acyclovir, and the elimination efficiency of the catalyst/PMS system reached 94% in 20 min (Liu et al., 2018). Liang et al. reported Fe- and N-containing graphene by calcination with mixed MIL-100 and dicyandiamide for PMS activation, and the removal efficiency of phenol reached 98% after 180 min (Liang et al., 2017). However, the overall performance of these Fe-based NC frameworks remains far from satisfactory, as indicated by the long degradation time. This can be ascribed to the limited electron transport resulting from the low graphitic carbon (Yao et al., 2019) and nitrogen (Gao et al., 2019) of these catalysts. Therefore, there is an urgent need to exploit an efficient heterogeneous catalyst of Fe-based NC with increased amounts of graphitic carbon and nitrogen.
In the present study, we developed a crystalline CNT interconnected Fe/Fe3C-doped NC framework derived from Fe-ZIF-8 as a highly active and stable heterogeneous catalyst for activating PMS and eliminating contaminants. The nitrogen element in ZIF-8 formed chemical bonds with the Fe species and served as the doping heteroatom in the NC. The crystalline CNTs were formed directly on the edge of the Fe/Fe3C-doped frameworks during the pyrolysis process. Thus, the synthesized catalyst of Fe/Fe3C-doped nanoporous carbonitrides (Fe-NC) possessed high degrees of graphitic carbon and nitrogen, which favored electron transfer in the catalytic system. It was found that the Fe-NC catalyst exhibited favorable catalytic performance and durability in accelerating PMS activation for the elimination of various organic contaminants, including dyes, phenols, and antibiotics. Moreover, the catalyst can be separated and recycled from the reaction solution conveniently under the action of a magnetic field owing to the magnetic properties of the Fe–NCs. Furthermore, the amount of Fe ions leaching in the catalytic system was extremely low, even after five cycles. Overall, this research provides a novel insight for the development of Fe-based heterogeneous catalysts with high efficiency, favorable stability, and environmental friendliness for the removal of organic contaminants.
Section snippets
Materials
2-Methylimidazole (2-MIM, 99%), zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 99%), methanol (MA, 99.9%), ethanol (EA, 99.7%), tertiary butyl alcohol (TBA, 99.5%), ferric nitrate nine hydrate (Fe(NO3)3·9H2O, 99%), peroxymonosulfate (2KHSO5·KHSO4·K2SO4, PMS, 47% KHSO5), 2,2,6,6-tetramethyl-4-piperidone (TEMP, 98%), and 5,5-dimethyl-pyrroline-oxide (DMPO, 97%) were obtained from Aladdin Reagent Co., Ltd. 2, 2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS, 98%), Reactive Red M-3BF (3BF, 99.9%),
Structural analysis of the catalyst
The morphologies of the prepared ZIF-8, NC, and Fe-NC are shown in Fig. 1. Both the ZIF-8 and NC particles have rhombic dodecahedral structures (Fig. 1a and b) (Wang et al., 2016), indicating that the high-temperature carbonization procedure had no influence on the shape of ZIF-8 (Yang et al., 2018). After doping the ZIF-8 with Fe3+ and the subsequent pyrolysis process, Fe-NC was obtained. A large number of nanoparticles were loaded on the NC, with slender nanowires wrapped around in the sample
Conclusions
In summary, a Fe-NC heterogeneous Fenton-like catalyst was developed via direct pyrolysis of Fe3+ loaded ZIF-8 and utilized to activate PMS for the degradation of multiple compounds. The results demonstrated that the removal efficiency of 3BF was 95.6% within 10 min by PMS (0.5 mM) in the presence of the Fe-NC (0.15 g/L). The removal efficiencies for other types of organic pollutants, such as AO7, MB, MO, RB19, 4-CP, BPA, SZ, SMX, ENR and CIP reached 96.2% within 10 min. The degradation of
Author contributions
Zhuo Shen: Conceptualization, Methodology, Investigation, Writing – original draft, Validation, Formal analysis, Experiment. Lingling Fan: Experiment, Data curation. Shangkun Yang: Experiment, Data curation. Yuyuan Yao: Review, Editing, Resources, Supervision. Haixiang Chen: Resources. Wentao Wang: Writing – review & editing, Resources, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 51772274, 21908201), the Postdoctoral Science Foundation of China (2020M671793),the Zhejiang Top Priority Discipline of Textile Science and Engineering (2018YBZX12), the Science Foundation of Zhejiang Sci-Tech University under Grant No. 18012217-Y, the Fundamental Research Funds of Zhejiang Sci-Tech University (2020Q007), and the General Scientific Research Project of Zhejiang Provincial Education Department
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