Fe-based carbonitride as Fenton-like catalyst for the elimination of organic contaminants

https://doi.org/10.1016/j.envres.2020.110486Get rights and content

Highlights

  • Carbon nanotubes interconnected Fe/Fe3C-doped carbonitride was facilely prepared.

  • This Fe-based catalyst possessed high graphitic carbon and nitrogen degree.

  • The Fe-NC/PMS system exhibited excellent performance for the removal of organics.

  • The degradation of pollutants was due to the generated SO4radical dot-, radical dotOH, O2radical dot- and 1O2.

Abstract

The Fenton-like process has been regarded as a clean and efficient approach to generate reactive oxygen species (ROS) to deal with the ever-growing environmental pollution. However, developing improved catalysts with adequate activity and stability remains a long-term goal for practical application. Herein, crystalline carbon nanotubes (CNTs) interconnected Fe/Fe3C-doped nanoporous carbonitride (Fe-NC) was easily prepared by the pyrolysis of ZIF-8 confined with Fe3+. The obtained Fe–NCs possessed high degrees of graphitic carbon and nitrogen. Such Fe–NCs can enhance the activation of peroxymonosulfate (PMS) for the removal of multiple organic contaminants. The optimized Fe-NC/PMS system exhibited impressive catalytic performance, with a TOF as high as 4.43 min−1 for 3BF degradation, and the removal efficiency of other dyes, phenols and antibiotics was up to 96.2% within 10 min. The removal efficiency of 3BF was 93.4% within 10 min with extremely low iron ions leaching (<0.052 mg/L) even after five cycles. In addition, the effects of pH on the catalytic performance demonstrated that the decomposition of 3BF exceeded 95.6% even when the initial pH varied from 5 to 10. We confirmed that SO4radical dot-, radical dotOH, O2radical dot- and 1O2 were generated in the catalytic system of Fe-NC/PMS, which played a critical role in degrading the organics. These findings provide new insights into the design of environmental-friendly Fenton-like catalysts with high efficiency and favorable stability in environmental remediation.

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 SO4radical dot- (Hu et al., 2016), radical dotOH (Su et al., 2016), O2radical dot- (Zhou et al., 2019) and 1O2 (Zhang et al., 2020), for the destruction of organic compounds. Among the various AOPs, the generation of SO4radical dot- (Luo et al., 2019) and radical dotOH (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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