Porous and flexible membrane derived from ZIF-8-decorated hyphae for outstanding adsorption of Pb2+ ion

https://doi.org/10.1016/j.jcis.2020.01.035Get rights and content

Highlights

  • Mucor was used as a template for the assembly of ZIF-8.

  • ZIF-8@Mucor membrane was formed by the in-situ growing of ZIF-8 on hyphae.

  • In-situ growing ZIF-8@Mucor has smaller size and more uniform distribution of ZIF-8.

  • ZIF-8 in the membrane exhibited high adsorption capacity for Pb2+ (1443.29 mg/g).

Abstract

Metal-organic frameworks (MOFs) based membranes with superior mechanical properties are of particular interest in purification, separation, and catalysis. Nevertheless, their fabrication still remains a grand challenge. Here, fungus hyphae (Mucor) were used as a robust scaffold to load the MOFs and induced the formation of porous and flexible membranes. ZIF-8 was used as a representative of MOFs. The ZIF-8@Mucor membrane was formed by the in-situ growth of ZIF-8 on hyphae and then a vacuum filtration of the ZIF-8/hyphae composite. ZIF-8 was effectively dispersed on the ZIF-8@Mucor membrane, and the shear modulus of ZIF-8@Mucor-3 was 864 MPa by calculation. The ZIF-8@Mucor membrane exhibited promising properties for adsorption application to remove the highly toxic Pb2+. The adsorption capacity of this membrane was as high as 1443.29 mg/g. Results from dynamic adsorption indicated that the penetration concentration of Pb2+ ions was less than 5% of the original level before 80 min whereas after 160 min, penetration concentration of Pb2+ ions was more than 90%. This study would open a new way of how to synthesize composite MOFs/bacterial membranes for energy and environment purposes.

Introduction

Nowadays, heavy metals are becoming one of the most severe environmental problems. Typically, natural aquatic systems that are exposed to leads (Pb) suffer many treats to their biodiversity [1], [2], [3]. Unlike organic contaminants, Pb(II) is non-biodegradable and tends to accumulate in living organisms. Once Pb (II) finds its way into the human body, it causes sustained harm, such as the central nervous system breakdown, because of its high toxicity and accumulative effect [4]. There are various methods applied to remove Pb(II) from wastewater, such as membrane filtration [5], coagulation [6], adsorption [7], ion exchange [8], precipitation [9]. Adsorption proves to be one of the most potent and cost-saving techniques [10]. And many adsorbents for removing of Pb(II) from wastewater were investigated [10], [11], [12].

In the adsorbent family, metal-organic frameworks (MOFs) have emerged as potential candidates for removing heavy metal ions effectively [13], [14], [15], [16]. MOFs are capable for the treatment of a broad range of pollutants due to the fact that they have a tunable texture properties [17], [18], [19]. MOFs have significant optical and mechanical properties originating from its small size when they are as nanomaterials [20], [21]. Yu et al. prepared various ZIFs to adsorb three typical dyes, neutral rhodamine, anionic methyl orange, and cationic methylene blue, which achieved an adsorption capacity of about 20 mg g−1 [22]. Wang et al. used six kinds of MOFs to adsorb Pb (II) and Zn (II) and found that zinc-based MOFs showed high selectivity in the adsorption of Pb (II) [23]. Despite all these enumerable advantages, MOFs are still facing myriad of challenges because of the small size of particles. Consequently, MOFs cannot be directly used in practical applications, resulting in different operations, waste of resources and secondary pollution [24]. To alleviate these problems, some researchers combined membrane materials with MOFs crystal. Zhang et al. combined 6FDA-DAM polyimide with a zeolitic imidazolate framework (ZIF-8) to fabricate mixed matrix membranes. The ZIF-8 crystal was prone to fall off due to only a physical bond between the ZIF-8 crystal and the membrane [25].

The study employed a bio-assembly method, an advanced micro-particle method for solving problems. Microorganisms as vectors of microparticles have received extensive attention due to their high reproduction and cheap resource [26], [27]. Filamentous fungus, such as Mucor, is a kind of unique microorganism, which possesses both microscale and macroscale features [26]. Besides, fungus hyphae have abundant functional groups on the cell wall, such as phosphonate, hydroxy, and amino group. However, as for MOFs, the high reactivity of metal ions and organic ligands generally promotes their intramolecular self-assembly via coordination effect. For instance, Marion Gualino et al successfully prepared ZIF-8@Al2O3 membrane using Zn(NO3)2·6H2O and 2-methylimidazole solution through the modified alumina film [28]. Aguado et al. synthesized in-situ, a substituted imidazolate-based MOF (SIM-1) membrane [29]. Bux et al. prepared a continuous ZIF-8 layer by putting ZIF-8 seed alumina discs into solvothermal secondary growth solutions [30]. In these conventional assembly processes, the formation and aggregation of MOFs molecules predominantly tend to occur in bulk solution rather than around support material surface, which greatly wastes expensive raw materials and lower performance.

In this study, a special phased growth of MOFs (ZIF-8) on hyphae surface was successfully induced to produce layer-by-layer assembly, avoiding the self-aggregation of MOFs molecules in bulk solution. This approach not only achieved the macro-construction of MOFS molecules but also realized the controllable load of MOFs nanoparticles on a one-dimensional scale. Simultaneously, a very high adsorption capacity of Pb2+ (>1000 mg/g) in water was obtained, far beyond most previous reports. Adsorption behavior was carefully explored.

Section snippets

Synthesis of ZIF-8/Mucor

Mucor. Mucor was cultured on 200 mL potato culture medium (PDA) in 300 mL Erlenmeyer flasks, shaking at 160 rpm and 30 °C for three days. Each liter of PDA contains 200 g potato, 0.5 g MgSO4, 1.0 g KH2PO4, and 20 g glucose. PDA was autoclaved at 115 °C for 15 min before inoculation which was processed on an aseptic bench. The cultured Mucor was then filtered (G-2 sand core funnel filter) and rinsed with ultrapure water. The obtained Mucor was dispersed into ultrapure water to form 5.0 g L−1

Synthesis of the ZIF-8@Mucor composites

Mucor was inoculated in a suitable liquid medium under a rotating shock culture. The water shear force would lead to the continuous growth of hypha, which was a necessary condition conducive for improving the stability of the Mucor membrane made through vacuum filtration. The Mucor membrane underwent a stepwise reaction process. First, it reacted with Zn2+ and the second reaction was with 2-MeIm to form ZIF-8@Mucor composite. With this strategy, a series of mycelial nanocomposite membranes with

Conclusion

Based previously reported to the modification of MOFs, this paper had provided a good way of interface science that grew MOFs on the thallus. These composite materials were used to acquire carbon materials and other materials, applying in environment and energy, etc. In summary, ZIF-8/Mucor membranes were successfully synthesized. ZIF-8/Mucor-O was synthesized by in situ reaction, while ZIF-8/Mucor-N was synthesized by stage adsorption reaction. According to the comparison of adsorption

CRediT authorship contribution statement

Lei Huang: Writing - original draft, Data curation, Formal analysis. Bichao Wu: Writing - original draft, Data curation. Yanjing Wu: Investigation. Zhihui Yang: Software. Tao Yuan: Validation. Sikpaam Issaka Alhassan: Validation. Weichun Yang: Supervision. Haiying Wang: Writing - review & editing, Funding acquisition. Liyuan Zhang: Writing - review & editing.

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 research is financially supported by the Key R&D Program of Hunan Province (2018SK2026), National Key R&D Program of China (2016YFC0403003), and the National Natural Science Foundation of China (51634010).

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