Research Paper
High-efficiency water purification for methyl orange and lead(II) by eco-friendly magnetic sulfur-doped graphene-like carbon-supported layered double oxide

https://doi.org/10.1016/j.jhazmat.2021.126406Get rights and content

Highlights

  • Magnetic sulfur-doped graphene-like carbon-supported layered double oxide (MG/S-LDO) was prepared.

  • The MG/S-LDO exhibited an ultrafast and superior methyl orange (MO) and Pb2+ removal.

  • Sulfur functionalization played a vital role in MO and lead removal.

  • LDO with “memory effect” and released ions benefited for MO and Pb2+ removal as well.

Abstract

Traditional disposal techniques for the spent layered adsorbents after capturing organics suffer from intractable obstacles, such as resource waste and secondary pollution. To address this diploma, we here developed the “resource-utilization” strategy, i.e., converting the organic layered double hydroxide (as representative) to magnetic sulfur (S)-doped graphene-like carbon-supported layered double oxide (MG/S-LDO) to be reutilized in water purification. The as-prepared MG/S-LDO exhibited outstanding remediation ability toward methyl orange (MO) and lead(II), with the adsorption capacity of 1456 and 656 mg g−1, respectively. Specifically, the residue concentration of Pb2+ was reduced to 0.15 mg L−1 within 1 h, which met the discharge limit of the secondary industrial wastewater. MG/S-LDO could also maintain the preeminent adsorption capability under various interferences (such as wide pH and co-existing ions), even in the authentic water matrices. The removal mechanisms were systematically investigated to unveil that MO removal was dominated by metal-complexation, “memory effect”, and π-π electron donor–acceptor (EDA). While for Pb2+ removal, besides the released OH- from LDO as precipitate agent, the vacancy defect resulting from the S doping played a crucial role in electron interaction between Pb2+ and S-doped graphene. Additionally, the MG/S-LDO was further confirmed as an eco-friendly adsorbent with excellent reusability via the acute toxicity tests using green algae and multiple cycle experiments. This work provides a novel resource-utilization strategy for organic layered wastes to construct the functional eco-friendly materials in wastewater purification realm.

Introduction

Water purification, especially for organic pollutants elimination from aqueous, is of vital importance to deal with the critical global challenge. Over recent decades, adsorption is considered to be one of the most versatile, effective and economical methods for organic pollutants removal (Ai et al., 2016, Zhang et al., 2018a, Zhang et al., 2018b, Dutta et al., 2019). Among various available adsorbents, layered materials with intriguing properties (e.g., large surface areas, exchangeable ions, hydrophilicity) have attracted considerable attention (Li et al., 2020, Cruz-Guzmán et al., 2004, Zhang et al., 2018a, Zhang et al., 2018b, Guo et al., 2019). Besides paying attention to the exceptional performance, the smart disposal of the spent layered adsorbents after organics adsorption (i.e., organic layered waste) is also critical due to its underlying risk to the environment and human health. Traditional disposal techniques for organic layered wastes are mainly direct landfill or combustion (Yang et al., 2020, Ghenai et al., 2020). Nevertheless, some bottlenecks exist like occupying a large amount of land, releasing greenhouse gases (CO2, SO2 and/or NOx), and wasting precious resources from the spent materials. With respect to the conception of green and sustainable chemistry, it is imperative, but also challenging, to develop a reliable disposal strategy for better applying the layered materials on organics elimination as well as improving economic effectiveness.

Graphene family nanomaterials, constituted by a group of sp2 hybridized carbon atoms monolayer, have been the research hotspot in materials science field due to their special hexagonal honeycomb structure and unique physicochemical properties (Ruiz-Hitzky et al., 2011, Novoselov et al., 2004). In particular, heteroatom (e.g., sulfur, oxygen, nitrogen) doping of graphene has recently stimulated immense interest, where the doped heteroatom can dramatically influence the structure and enhance the performance of substances (Ma et al., 2016, Saha et al., 2016). Currently, various synthetic routes including chemical vapor deposition, ball milling, and bottom-up synthesis are well developed for fabricating heteroatom-doped graphene-like materials (Wang et al., 2014). Yet, these approaches face limitations such as high cost, low yield, and difficulty on controlling the doping process. In this context, thermal annealing the inexpensive organic precursors under oxygen-limited conditions is emerging as an alternative method (Sheng et al., 2011, Nguyen et al., 2015). Zhang et al. used gelatin to prepare boron and nitrogen co-doped graphene like-carbon nanosheets with annealing treatment (Zhang et al., 2016, Zhang et al., 2016). Niu et.al calcinated sugarcane bagasse pith/chitosan to construct nitrogen-doped graphene-like carbon (Niu et al., 2017). However, these synthesis methods usually suffer from the stacked layers structure, which is caused by the strong π–π interactions between the interlayers of graphene (Witomska et al., 2019). In 1988, Kyotani et al. first employed a typical layered clay mineral, montmorillonite (MONT), as template to successfully transfer the intercalated polyacrylonitrile to highly orientated graphite without stacking, via calcination under N2 protection (Kyotani et al., 1988). More recently, several groups reported that the layered double hydroxides (LDHs) with lamellar structure as template can also fabricate the graphene like-materials with single layer under the protection of inert gases (Laipan et al., 2015, Zhang et al., 2016). Obviously, the utilization of layered materials to synthesize graphene-like material can efficiently avoid the aggregation among graphene sheets in virtue of the existence of interlayer confinement. Unfortunately, the layered materials mentioned in the above studies are only employed as templates, which are etched via acid treatment. In fact, it has been extensively demonstrated that the calcinated layered materials can serve as cost-effective platforms to be used in versatile practical realms (Jiang et al., 2019, Lin and Juang, 2002, Darder et al., 2017, Lei et al., 2017). For example, layered double oxides (LDOs), derived from LDHs’ precursors upon calcination, have signified their superiority in supercapacitors, catalysis, and electrodes for batteries in terms of their flexible and homogeneously dispersed metallic phases (Kuljiraseth et al., 2019, Li et al., 2017, Xu et al., 2019). Notably, LDOs are also broadly adopted as desirable adsorbents in capturing anionic contaminants in wastewater due to its specific “memory effect”, i.e., the calcinated products can reconstruct the original layered structure of LDHs via rehydration and simultaneously incorporate anions into the interlayer (Lee et al., 2018, Mourid et al., 2019, Cheng et al., 2019). However, to our knowledge, there are fewer papers reporting that the used layered materials embedded with organics can not only be employed as template to fabricate the graphene like-material, but also take full advantage of their calcinated products as valuable materials, further broadening the reuse benefits of economic.

In view of our previous works reported the organic three-dimensional MgAl-LDH containing sodium dodecyl sulfate (O3D-SDS) (Zhang et al., 2019a, Zhang et al., 2019b), we herein attempted to employ it as organic precursor to fabricate the magnetic sulfur (S)-doped graphene-like carbon-supported LDO (abbreviated as MG/S-LDO), based on the “resource-utilization” strategy. Two basic toxic contaminants, i.e., methyl orange (MO) and lead (II), were chosen to determine the environmental-remediation performance of MG/S-LDO. We found that MG/S-LDO had superhigh adsorption capacity for MO (1456 mg g−1) and Pb2+ (656 mg g−1). Furthermore, multiple characterizations and DFT calculations illuminated that the possible removal mechanisms were closely linked to the synergistic interactions of LDO and doped S in graphene-like carbon. Given that the absorbents are inevitably leaked into the aqueous system (Lv et al., 2018, Zhang et al., 2017), the underlying toxic effect of MG/S-LDO on aquatic organisms was explored via the acute toxicity tests using green algae (Scenedesmus obliquus and Chlorella vulgaris) as model organisms, which further confirmed that MG/S-LDO was an eco-friendly adsorbent. In addition, the feasibility of this strategy was demonstrated by verification experiments via utilizing spent LDHs after capturing three S-containing organic surfactants. As such, this work is expected to open a new avenue for the reuse/recycling of organic waste to construct functional, exceptional adsorption-performing and eco-friendly adsorbents for environmental remediation.

Section snippets

Materials

Mg(NO3)2·6H2O, Al(NO3)3·9H2O, urea (CO(NH2)2), and sodium dodecyl sulfonate (SDS) were purchased from Aladdin chemicals reagent company (Shanghai, China). NaAc·3H2O and ethylene glycol (EG) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). FeCl3·6H2O was purchased from the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All chemicals were analytically pure (more than 99% purity) and used as received without further treatment. Deionized (DI) water was used to

Characterization

Based on our previous work, the organic-intercalated LDH precursor (i.e., O3D-SDS) was successfully prepared (Zhang et al., 2019a, Zhang et al., 2019b), as evidenced by XRD (Fig. S1). The possible chemical formula was calculated as Mg0.69Al0.31(OH)2(C12H25OSO3)0.31·0.42 H2O, with a high organic content of 55.27%, according to TG-DTA, ICP and CHN analyses (Fig. S2 and Table S2). After calcination, a series of peaks belonged to MgAl-LDO, graphene-like carbon, and Fe3O4 were clearly identified in

Conclusion

In summary, a facile, green and efficient “resource-utilization” strategy was rationally designed and developed to dispose the organic layered wastes, which employing it as available-template carbon sources fabricates the magnetic sulfur (S)-doped graphene-like carbon-supported LDO (MG/S-LDO) absorbents. The unique characteristics of two major components of the composite, i.e., LDO phase with “memory effect” and released ions as well as the S-doped graphene-like carbon with rich functional

CRediT authorship contribution statement

Ping Zhang: Conceptualization, Methodology, Writing - review & editing, Supervision, Project administration, Funding acquisition. Mingxue Xiang: Methodology, Formal analysis, Writing - original draft. Tao He: Methodology, Visualization. Huiling Liu: Validation, Methodology. Shuqi Yu: Resources, Methodology. Xuemei Pan and Fangfang Qiu: Validation, Methodology. Zhongbang Zhu and Youqin Zou: Conceptualization, Supervision, Project administration. Yu Chen: Project administration, Writing - review

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

We would like to thank the support of Analysis and Test Center of Nanchang University for infrastructure and morphology characterizations. This project is financially supported by National Nature Science Foundation of China (No. 21767018), Major Discipline Academic and Technical Leaders Training Program of Jiangxi Province (No. 2019BCJ22002), the Natural Science Foundation of Jiangxi Province (No. 2020BAB203013), the Postdoctoral Science Foundation of China (No. 2017M612164). Earmarked Fund for

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