Feeding silkworms with HPMC dispersed MoO2 NPs: An efficient strategy to enhance the supercapacitance performance of carbonized silk

https://doi.org/10.1016/j.compscitech.2021.109025Get rights and content

Highlights

  • Upon in vivo feeding, HPMC can ensure the separation of nanoparticles even after they are encapsulated within silk fibers.

  • Feeding HPMC to the silkworm enhances the degree of graphitization of the carbonized silk.

  • Compared with previous results, the specific capacitance of the carbonized silk increased from 245 F/g to 456 F/g.

  • Our work produced a silk precursor with potential utility as a high-power supercapacitor component.

Abstract

It was found in our previous study that feeding silkworms with MoO2 nanoparticles (NPs) as a food additive enabled the incorporation of MoO2 NPs into the as-spun silk, which, in turn, can be used to build electrodes for energy storage. However, aggregation of the MoO2 NPs was observed at high fractional feeding dosages. In order to disperse the MoO2 NPs in fibrous silk and enhance the specific capacitance of the carbonized silk more effectively, a 0.5% (w/v) hydroxypropyl methyl cellulose (HPMC) solution was utilized as the dispersant in this work. Transmission electron microscopy (TEM) results confirmed that HPMC increased the separation of MoO2 nanoparticles incorporated within the silk matrix. Furthermore, the electrochemical performance was characterized, revealing that the specific capacitance of carbonized silk from this HPMC-MoO2 NP feeding group reached 456 F/g, compared to the value of 245 F/g from the previous study, at a current density of 0.2 A/g, demonstrating a significant improvement. The feasibility of utilizing HPMC to maintain the segregated state of MoO2 NPs throughout all stages of silk encapsulation, with negligible impact of this feeding regimen on the growth of silkworms, is demonstrated in this work.

Introduction

Flexible electronics is an exciting emerging technological arena, enabling platforms for many types of wearable devices [1]. Among the various materials used in manufacturing flexible electronics, silkworm silk, spun by Bombyx mori, has attracted significant attention. Although recent research has shown that in vivo feeding of silkworms with functional nanomaterial-loaded mulberry leaves [2,3] enables the production of silkworm silk fibers with enhanced electrical properties [4,5], their performance is limited by the poor conductivity of the natural silk. Carbonized silkworm silk maintains excellent flexibility and conductivity, and therefore has been extensively studied as an appealing material in the construction of flexible electronics [6,7]. In our previous study [8], molybdenum dioxide nanoparticles (MoO2 NPs) were successfully introduced into spun silk through feeding silkworms with mulberry leaves coated with MoO2 NPs. The study broadened the possibility of utilizing carbonized silk in energy storage devices. However, it was found that the introduced MoO2 NPs suffered from aggregation which hinders surface-redox reactions and lowers the efficacy of MoO2 NPs in enhancing the capacitance of carbonized silk [[9], [10], [11]]. Therefore, increasing the level of dispersion of the MoO2 NPs would be beneficial for enhancing their pseudocapacitive behavior and give rise to higher energy storage kinetics [11].

Hydroxypropyl methyl cellulose (HPMC) is a cellulose derivative. It has been approved as a food additive by the Food and Agriculture Organization of the United Nations and by the World Health Organization (FAO/WHO) [12]. HPMC solutions are odorless and tasteless. It is widely used as a dispersant, a film forming agent, and an emulsifier, to name a few, in food and industrial products and systems [13]. In recent years, HPMC has also been used to increase the water dispersibility of additives that were sprayed on mulberry leaves in order to produce functionalized silk fibers [[14], [15], [16]]. However, none of these studies considered whether HPMC ensures the separation of nanoparticles once they enter the silk gland and are encapsulated within silk fibers.

In this work, 0.5% (w/v) HPMC solution was utilized to disperse MoO2 NPs and the mulberry leaves were soaked with this mixture to ensure that the MoO2 NPs were evenly distributed on the mulberry leaves used for feeding the silkworms. We explored and found that the use of HPMC significantly reduces the level of aggregation observed for MoO2 NPs encapsulated within the as-spun silk. Furthermore, it was found that the carbonized silk maintains its fibrous morphology and exhibits enhanced specific capacitance. For the first time, we investigated the impact of HPMC on silkworm growth, nanoparticle feed efficiency, silk production and several properties of the resulting silk.

Section snippets

Impact of feeding methods on larvae growth and the spun silk

Here, we compare results for silkworms which were fed using MoO2 NP suspensions prepared via two different approaches, then loaded onto mulberry leaves. The first feeding approach, the focus of this paper, was described in the methods section of supplementary material. The second feeding approach was HPMC-free and has been described previously [8]. In that previous study, different amounts of MoO2 NPs were first dispersed in DI-H2O and then sprayed on the surface of the mulberry leaves. These

Conclusion

In this study, a 0.5% HPMC solution was employed to disperse the MoO2 NPs fed to silkworms, in order to avoid aggregation of the MoO2 NPs incorporated into silk at high MoO2 NP feeding dosages. Such agglomeration was observed in our previous study [8]. The experimental results confirmed that HPMC, serving as the dispersant, could ensure the MoO2 NPs ultimately incorporated into the silk remain well separated. Our study reveals that feeding HPMC to silkworms did exhibit adverse effects on the

Credit author contribution statement

Jianwei Liang: Investigation, Conceptualization, Methodology, Writing – Original Draft. Xiaoning Zhang: Conceptualization, Methodology, Writing – Original Draft, Resources. Yansong Ji: Investigation, Formal analysis. Zhenyu Chen: Investigation. Micheal L Norton: Writing – Review & Editing. Yixuan Wang: Investigation. Chi Yan: Investigation. Xi Zheng: Resources. Yong Zhu: Resources. Guotao Cheng: Formal analysis.

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.

Acknowledgements

This research was funded by Venture & Innovation Support Program for Chongqing Overseas Returnees [grant number cx2019098]; the Fundamental Research Funds for the Central Universities [grant number SWU117036]; the 2020 National Training Program of Innovation and Entrepreneurship for Undergraduates in Southwest University [grant number 202010635088]. And this research was partially supported by the National Science Foundation under Award No. OIA-1458952. We specially thank Mr. David Neff from

References (43)

  • C. Dong et al.

    Green synthesis of monodisperse silver nanoparticles using hydroxy propyl methyl cellulose

    J. Alloys Compd

    (2014)
  • M. Santorum et al.

    Novaluron impairs the silk gland and productive performance of silkworm Bombyx mori (Lepidoptera: bombycidae) larvae

    Chemosphere

    (2020)
  • C. Brigham

    Chapter 3.22 - biopolymers: biodegradable alternatives to traditional plastics

  • M.M.R. Khan et al.

    Structural characteristics and properties of Bombyx mori silk fiber obtained by different artificial forcibly silking speeds

    Int. J. Biol. Macromol

    (2008)
  • W. Wei et al.

    Full-faradaic-active nitrogen species doping enables high-energy-density carbon-based supercapacitor

    J. Energy Chem

    (2020)
  • S.T. Senthilkumar et al.

    Flexible fiber hybrid supercapacitor with NiCo2O4 Nanograss@Carbon fiber and bio-waste derived high surface area porous carbon

    Electrochim. Acta

    (2016)
  • H.D. Yoo et al.

    Impedance analysis of porous carbon electrodes to predict rate capability of electric double-layer capacitors

    J. Power Sources

    (2014)
  • H. Gao et al.

    MoO2-loaded porous carbon hollow spheres as anode materials for lithium-ion batteries

    Mater. Chem. Phys

    (2014)
  • S. Fuchs et al.

    Outgrowth endothelial cells isolated and expanded from human peripheral blood progenitor cells as a potential source of autologous cells for endothelialization of silk fibroin biomaterials

    Biomaterials

    (2006)
  • S. Huang et al.

    Flexible electronics: stretchable electrodes and their future

    Adv. Funct. Mater

    (2019)
  • C. Wang et al.

    Silk-based advanced materials for soft electronics

    Acc. Chem. Res

    (2019)
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