Research paper
Synthesis of MnO2 derived from spent lithium-ion batteries via advanced oxidation and its application in VOCs oxidation

https://doi.org/10.1016/j.jhazmat.2020.124743Get rights and content

Highlights

  • Manganese is selectively and efficiently recovered from spent LIBs.

  • Metal-doped α-, β-MnO2 were one-step prepared for catalytic oxidation of VOCs.

  • Metal-doped α-, β-MnO2 exhibited better catalytic performance in VOCs removal.

  • Metal-doped α-, β-MnO2 showed better physicochemical properties.

  • The reaction pathway of metal-doped α-MnO2 for toluene oxidation was proposed.

Abstract

In this work, manganese is selectively and efficiently recovered from spent lithium-ion batteries via advanced oxidation by using potassium permanganate and ozone, and the transition metal-doped α-MnO2 and β-MnO2 are one-step prepared for catalytic oxidation of VOCs. The recovery rate of manganese can be approximately 100% while the recovery efficiency of cobalt, nickel, and lithium is less than 15%, 2%, and 1%, respectively. Compared with pure α-MnO2 and β-MnO2, transition metal-doped α-MnO2 and β-MnO2 exhibit better catalytic performance in toluene and formaldehyde removal attributed to their lower crystallinity, more defects, larger specific surface area, more oxygen vacancies, and better low-temperature redox ability. Besides, the introduction of the appropriate proportion of cobalt or nickel into MnO2 can significantly improve its catalytic activity. Furthermore, the TD/GC-MS result indicates that toluene may be oxidized in the sequence of toluene − benzyl alcohol − benzaldehyde-benzoic acid − acetic acid, 2-cyclohexen-1-one, 4-hydroxy-, cyclopent-4-ene-1,3-dione − carbon dioxide. This method provides a route for the resource utilization of spent LIBs and the synthesis of MnO2.

Introduction

Volatile organic compounds (VOCs), such as toluene and formaldehyde, have been regarded as the major influencing factor of global air pollution (Huang et al., 2015). They are associated with the formation of ozone, photochemical smog and secondary organic aerosol (SOA), which affect human health and worldwide climate (Park et al., 2013). Considering the environmental impact, toxicity and increasingly stringent emission standards of VOCs, it is highly critical to developing effective and practical approaches to dispose of VOCs (Yang et al., 2019, Scire and Liotta, 2012, He et al., 2019). Catalytic oxidation at low temperatures (293–673 K) is recognized as one of the efficient, energy-saving, and eco-friendly methods for end-of-pipe treatment which can convert VOCs into harmless CO2 and water (Wen et al., 2019, Zhang et al., 2016). Generally, transition metal oxides and noble metals are two main types of essential catalysts for total VOCs oxidation (Zhang et al., 2019, Sun et al., 2019). However, the high cost of noble metal catalysts still hinders its extensive and large-scale application. By contrast, transition metal oxide catalysts such as CoOx and MnOx gradually emerge with bright prospects owing to their low cost and strong resistance to sintering and poisoning (Jiang et al., 2019, Jiang et al., 2019, Dong et al., 2019). Among various transition metal oxides, MnO2 stands out because of its phenomenal adsorption capacity for oxygen species and desirable reducibility at low temperatures (Wang et al., 2012). Besides, MnO2 shows innate superiority such as multivalence (Mn2+, Mn3+, and Mn4+), structural flexibility and polymorphism (α-MnO2, β- MnO2, γ-MnO2 and δ- MnO2). The α-MnO2 with a unique [2 × 2] tunnel structure is considered to be one of the best MnO2 catalysts for VOCs removal (Uematsu et al., 2016). Previous studies (Dong et al., 2020, Li et al., 2018, Vu et al., 2009) have shown that the catalytic activity of MnO2 is supposed to be associated with surface defects and oxygen vacancies, which could be further facilitated by doping with specific metal cations such as Ce2+, Co2+, Cu2+ and Ni2+. For example, Li et al. Li et al., (2018) successfully synthesized Ce-doped and Co-doped γ-MnO2 by a one-step hydrothermal method. They found doping of 2.97% Ce and 0.4% Co both enhanced the catalytic efficiency of γ-MnO2, which could be ascribed to the regulation of physicochemical properties like specific surface area. Moreover, further characterization indicated that the increase of oxygen vacancies and surface defects was the key role.

In recent years, spent lithium-ion batteries (LIBs) have been triggered more and more attention due to their potential economic value and environmental hazard. On the one hand, they contain a range of metals such as lithium (Li), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu) and aluminum (Al), and can be considered as a kind of “artificial mineral”, of which Co, Ni and Li have the relatively higher value (Xiao et al., 2020). It is predicted that the global spent LIBs recycling market will grow from USD 1.5 billion in 2019 to USD 18.1 billion by 2030 (Lithium-ion Battery Recycling Market). On the other hand, heavy metals and toxic electrolytes in LIBs pose a severe threat to human health and ecosystems (Zheng et al., 2018). Therefore, the recovery of spent LIBs is highly desirable and beneficial from both economic and environmental perspectives (Zhang et al., 2018). The state-of-the-art recycling process of spent LIBs is mainly composed of pretreatment for obtaining electrode materials, metal-extraction from electrode materials, and step-by-step separation and purification of different metal elements (Xiao et al., 2020). However, it has the disadvantages of complex operation and high solvent cost due to the wide use of solvent extraction in the separation and purification step.

In our previous work, the manganese-based multi-oxide catalysts have been successfully prepared from spent LIBs by a combustion method (Guo et al., 2019), while the operational procedures are complicated owing to the additional Li and Al removal process. Besides, the high-value elements like Co, Ni will be wholly entered into the catalyst, which is not economically efficient. In this work, Mn in the leaching solution of spent LIBs was one-step selectively oxidized to transition metal-doped α-MnO2 and β-MnO2 by using potassium permanganate and ozone which could also achieve the separation of Mn from other high-value metals. Toluene and formaldehyde were selected as the particular pollutants to compare the catalytic activity of obtained MnO2 with the pure one. Additionally, the effect of Co and Ni dopant on the catalytic performance of MnO2 was also investigated. Furthermore, the possible oxidation pathway of toluene was proposed by the Thermal Desorption/Gas Chromatograph-Mass Spectrometer experiment.

Section snippets

Catalyst preparation from spent LIBs

The flow chart of catalyst preparation from spent LIBs was shown in Fig. 1, which mainly consists of three steps. Step 1 was the pretreatment process. Spent LIBs were first discharged completely, then disassembled manually and divided into two parts: the cathode and the others (anode, iron shell, separator and electrolyte). After that, the cathode materials were cut into 2 cm × 2 cm pieces before calcined at 600 °C in a muffle furnace to remove polyvinylidene fluoride (PVDF). Then the calcined

Crystal structures and surface areas

XRD patterns of the catalysts were tested to study their crystal structures. As shown in Fig. 2(A), a-350 and b-350 exhibit eleven identical broad peaks at 12.8º, 18.1º, 25.7º, 28.8º, 37.5º, 42.0º, 49.9º, 56.4º, 60.3º, 65.1º and 69.7º in the range from 10º to 80º, corresponding to (110), (200), (220), (310), (211), (301), (411), (600), (521), (002) and (541) of α-MnO2 (JCPDS 44–0141) (Zhang et al., 2015), respectively. c-350 and d-350 have three identical broad peaks at 37.3º, 42.8º and 56.7º,

Conclusion

The transition metal-doped α-MnO2 and β-MnO2 were prepared from spent LIBs via advanced oxidation using potassium permanganate and ozone, respectively. The recovery rate of manganese can be approximate 100% and meanwhile, the recovery efficiency of cobalt, nickel, and lithium is less than 15%, 2%, and 1%. Under the optimum calcination temperature of 350 °C, the transition metal-doped α-MnO2 and β-MnO2 exhibit significantly higher VOCs removal efficiency compared with pure α-MnO2 and β-MnO2.

The

CRediT authorship contribution statement

Xin Min: Conceptualization, Formal analysis, Writing - original draft. Mingming Guo: Writing - review & editing. Lizhong Liu: Writing - review & editing. Lu Li: Visualization. Jia-nan Gu: Writing - review & editing. Jianxing Liang: Writing - review & editing. Chen Chen: Data curation. Kan Li: Project administration, Resources. Jinping Jia: Project administration, Resources. Tonghua Sun: Supervision, Project administration, Resources.

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 financially supported by the National Natural Science Foundation of China (grant nos. 21876107 and 21607103) and Open Funding from Shanghai Engineering Research Center of Solid Waste Treatment and Resource Recovery.

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