MOFs derived Co/Cu bimetallic nanoparticles embedded in graphitized carbon nanocubes as efficient Fenton catalysts

https://doi.org/10.1016/j.jhazmat.2020.122567Get rights and content

Highlights

  • Metal organic frameworks derived Co/Cu bimetallic carbon nanocubes (CuxCo10-x/CNC) have been prepared.

  • CuxCo10-x/CNC have been first used as Fenton catalysts in degradation of dye.

  • The optimized catalytic activity of CuxCo10-x/CNC was at Cu/Co ratio of 4/6.

Abstract

In this work, Cu-Co bimetallic nanoparticles embedded carbon nanocubes (CuxCo10-x/CNC) are synthesized by direct carbonization of Cu-Co bimetal ZIF. The ratio of Cu and Co nanoparticles in CuxCo10-x/CNC as well as morphology, pore structure and graphitization degree of carbon substrates can be tuned by adjusting the molar ratio of Cu/Co (0:10, 1:9, 2:8, 3:7, 4:6 and 5:5) in ZIF precursors. The Fenton catalytic performances of CuxCo10-x/CNC are further studied by degrading a typical azo dye, Acid Orange II (AOII). The results show the CuxCo10-x/CNC with a Cu/Co ratio of 4/6 display the highest catalytic activity with faster dye degradation rate than other catalysts, which may be ascribed to the synergetic effects of optimized ratio of Cu/Co bimetals, high surface area and graphitized carbon framework. The stability and reusability of the catalyst has been investigated, showing a good performance after five consecutive runs. The catalysts prepared in this study can be used as an attractive alternative in heterogeneous Fenton chemistry and wastewater treatment.

Introduction

Fenton technology is a powerful process that can generate free hydroxyl radicals (•OH) from H2O2 and degrade various organic pollutants (Fenton, 1894; Shi et al., 2014; Rusevova et al., 2012). Traditional homogeneous Fenton reaction is catalyzed by Fe2+/Fe3+ ions, however, the requirements of low pH values (2–3), poor recyclability and accumulation of iron-containing sludge have limited their practical applications (Min et al., 2015; Zhan et al., 2011; Wang et al., 2015a). Alternatively, iron-based heterogeneous Fenton catalysts such as metallic iron or iron oxides have been developed (Dhakshinamoorthy et al., 2012; Pereira et al., 2012; Munoz et al., 2015; Wang et al., 2018). Nevertheless, the problems of low activity at neutral pH and poor stability due to metal ions leaching still exist (Wang et al., 2014; Nekoeinia et al., 2018). In addition to iron, other elements such as cerium, manganese, chromium, copper, cobalt and ruthenium with multiple redox states also have the ability to activate H2O2 (Bokare and Choi, 2014). Among them, cobalt-based materials with a wide pH adapting range and excellent stability have attracted much attention (Torres-Luna et al., 2019; Zhong et al., 2019; Ribeiro et al., 2017, 2016). It has been reported that the transformation of Co3+ to Co2+ redox pair is the limiting step in Fenton-like reactions (Lyu et al., 2017; Lu et al., 2018), which is highly desirable in enhancing the catalytic activity of cobalt-based heterogeneous catalysts. Light (Kalam et al., 2018), electricity (Liang et al., 2016) and ultrasound (Behling et al., 2017) have been widely used to improve the Co3+ to Co2+ transformation process, however, the additional energy input and extra processes are unfavorable for applications.

Recently, another widely used and cheap transition metal species, copper, which also possesses the ability to activate H2O2 and generate hydroxyl radicals, has drawn researcher’s attention (Lyu et al., 2020; Sun et al., 2019a; Wang et al., 2017a; Xu et al., 2019; Chen et al., 2018; Su et al., 2019). Copper can also be introduced into cobalt-based heterogeneous Fenton systems to fabricate copper-cobalt based Fenton catalysts with enhanced catalytic performance, mainly due to the synergistic effect between copper and cobalt during catalytic reaction (Shen et al., 2015; Qi et al., 2019). For example, Shen and coworkers (Shen et al., 2015) reported that Co0.5Cu0.5O catalyst showed better Fenton activity than CoO for the degradation of Congo red. Pine-needle-like CuCo2O4 catalysts also showed superior catalytic activity than only cobalt containing catalysts (Qi et al., 2019). It is noted that most of the reported copper-cobalt based Fenton catalysts are metal oxides, while metallic copper-cobalt Fenton catalysts have rarely been reported.

Supporting catalysts on various substrates such as zeolite (Fan et al., 2008), clay (Timofeeva et al., 2009), porous silica (Karthikeyan et al., 2016a) and porous carbons (Wang et al., 2015b) is an efficient strategy to enhance the catalytic activity and stability. Among these supports, porous carbon materials possess excellent chemical and thermal stability, high specific surface area and favorable adsorption ability, which can improve the dispersity/stability of metal particles and enrich organic pollutants (Wu et al., 2012; Lee et al., 2009). As an important family of crystalline porous materials with excellent physicochemical properties, metal-organic frameworks (MOFs) have received extensive interest in various applications (Sue et al., 2014; Shieh et al., 2015; Liao et al., 2018; Kaneti et al., 2017), such as gas storage (Li et al., 2016), environmental remediation (Wang et al., 2017b), catalysis (Jiao et al., 2018) and energy storage (Zhou and Wang, 2017). Generally, MOFs are constructed by organic linkers and metal centers, which are also the desirable precursors for synthesis of carbon or metal-carbon materials (Li et al., 2018), e.g., bimetallic copper-cobalt incorporated porous carbon materials (Kuang et al., 2017; Kang et al., 2019). By using thermal conversion of zeolitic imidazolate frameworks (ZIF-67) pre-grown on Cu (OH)2 nanowires Cu (Kuang et al., 2017) or Cu-Co-ZIF synthesized by a microwave-assisted hydrothermal method (Kang et al., 2019), Cu,Co-embedded nitrogen-enriched carbon materials were synthesized for electrocatalytic applications. However, there are few reports on the synthesis of bimetallic Cu-Co incorporated carbon composites derived from MOFs as Fenton catalysts. Moreover, the bimetallic Cu/Co ratio and structure confined in the carbon substrates are hardly adjusted in previous reports (Kuang et al., 2017; Kang et al., 2019), which is important in understanding the relationship between structure and Fenton catalytic performance of Cu/Co-carbon based Fenton catalysts.

Herein, carbon nanocubes embedded with bimetallic Cu-Co nanoparticles (CuxCo10-x/CNC) are synthesized by direct carbonization of Cu-Co bimetal ZIF. The ratio of Cu and Co nanoparticles in CuxCo10-x/CNC materials, their morphology, pore structure and graphitization degree of carbon substrates are tuned by adjusting the ratio of Cu/Co (0:1, 1:9, 2:8, 4:6, 3:7 and 5:5) in ZIF precursors. The Fenton catalytic performance of CuxCo10-x/CNC have been studied by degrading a typical azo dye, Acid Orange II (AOII). The effect of Cu/Co ratios on the catalytic activity is also investigated. The results show that Cu4Co6/CNC displays the highest catalytic activity among all catalysts under study, and can be used as effective Fenton catalysts with excellent cycling performance.

Section snippets

Chemicals

Cetyltrimethylammonium bromide (CTAB), 2-methylimidazole (2-MeIM) and anhydrous ethanol were purchased from Shanghai Titan Scientific Co., Ltd. Cobalt nitrate hexahydrate [Co(NO3)2⋅6H2O], copper nitrate trihydrate [Cu(NO3)2⋅3H2O] and Acid Orange II (AOII) and H2O2 (30 wt%) were purchased from Sinopharm Chemical Reagent Co., Ltd. 5,5-dimethy-1-pyrroline N-oxide (DMPO) was obtained from J&K Scientific Ltd. All chemicals are of analytical grade and used as received. Millipore deionized water was

Morphology and physicochemical properties of catalyst

Cu4Co6-ZIF was synthesized and characterized as a typical example. The SEM image of Cu4Co6-ZIF (Fig.1A) shows a dispersed and uniform cubic morphology with an average diameter of ∼435 nm and smooth surface. TEM image (Fig.1D) also displays a solid structure of Cu4Co6-ZIF. By direct carbonization of Cu4Co6-ZIF at 600 °C in N2 atmosphere, Cu4Co6/CNC were generated. During this carbonization process, the ligands and metal ions were turned into carbon matrix and metal nanoparticles with CTAB

Conclusion

In the present work, Cu-Co bimetallic nanoparticles embedded carbon nanocubes (CuxCo10-x/CNC) are synthesized by using Cu-Co bimetal ZIF as precursor. By regulating the molar ratio of Cu/Co in ZIF, the ratio of Cu and Co nanoparticles, morphology, pore structure and graphitization degree of carbon substrates in CuxCo10-x/CNC can be tuned. The Fenton catalytic performances show the CuxCo10-x/CNC with a Cu/Co ratio of 4/6 display the highest catalytic activity than catalysts with other ratios,

CRediT authorship contribution statement

Jing Wang: Conceptualization, Writing - original draft. Chao Liu: Methodology, Writing - original draft. Jiayou Feng: Investigation, Resources. Dan Cheng: Investigation. Chaoqi Zhang: Formal analysis. Yining Yao: Validation. Zhengying Gu: Investigation. Wenli Hu: Formal analysis. Jingjing Wan: Funding acquisition. Chengzhong Yu: Supervision, Writing - review & editing.

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant No. 51908218, 21905092, 21705107), project funded by China Postdoctoral Science Foundation, Science and Technology Commission of Shanghai Municipality (Grant No. 19JC1412100), the support from the Australian National Fabrication Facility and the Australian Microscopy and Microanalysis Research Facility at the Centre for Microscopy and Microanalysis and University of Queensland.

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