Ultralight, hydrophobic, sustainable, cost-effective and floating kapok/microfibrillated cellulose aerogels as speedy and recyclable oil superabsorbents

https://doi.org/10.1016/j.jhazmat.2020.124758Get rights and content

Highlights

  • Economic and advanced kapok/MFC aerogels were designed by introducing kapok.

  • A dual-scale hierarchically porous structure at micro-level was achieved.

  • The introduction of kapok results in improved formability and higher porosity.

  • The obtained aerogel exhibits rapid, selective and ultrahigh absorption ability.

  • Excellent reusability and sustainability of recycled aerogel was also performed.

Abstract

Cellulose aerogels achieve excellent absorption of waste oil and organic pollutant, which has received lots of attention recently. It is still a big challenge to obtain aerogels with both high cost-effectiveness and advanced oil absorption performance, since it is a time-consuming, and environmentally unfriendly process to obtain cellulose, compared with direct usage of natural fibers. In this manuscript, we develop highly porous and hydrophobic kapok/microfibrillated cellulose (MFC) aerogels with a dual-scale hierarchically porous structure at micro-level as cost-effective, sustainable, and floating superabsorbents via simple vacuum freeze-drying and surface modification. Kapok, a natural hollow fiber, has been recently considered as a new sustainable resource for oil cleanup. By partially replacing MFC with chopped kapok fibers in MFC aerogels (MMAs), the resultant kapok/MFC aerogels (KCAs) exhibit ultralow density (5.1 mg/cm−3), ultrahigh porosity (99.58%) and hydrophobicity (140.1°) leading to advanced oil sorption (130.1 g/g) that is 25.3% higher than that of MMAs. In addition, these KCAs can rapidly and selectively absorb waste oil from oil-water mixture with ultrahigh absorption ability of 104–190.1 g/g, which is comparable to other environmentally unfriendly and high-cost aerogels. Furthermore, the KCAs own excellent reusability and sustainability. These benefits enable the KCAs a suitable alternative to clean oil spills.

Introduction

The water pollution caused by oil spill has engaged wide attention because of its disastrous impact on the ecosystem (Jiang and Hsieh, 2014, Ventikos et al., 2004, Yuan et al., 2008). Aerogels, an ultralight three-dimensional (3D) highly porous material, have been widely utilized as efficient absorbents in oil and organic pollutant clean up due to its low density, high porosity, and superior absorption capacity (Wu et al., 2013, Gao et al., 2018). Recently, various aerogels, such as synthetic silicon (Sai et al., 2013), CNTs (Gui et al., 2011), and graphene (Ge et al., 2017, Chen et al., 2015), exhibit great potential for oil cleanup and have been largely developed and investigated. However, their disadvantages like the high cost in precursors and instruments, complicated manufacturing processes, especially environmental unfriendliness, greatly impede their practical applications (Korhonen et al., 2011). As an abundant, sustainable and economic natural material, cellulose has received tremendous attention in different fields including modern coatings, controlled release of actives, biodegradable plastics, composites and laminates, optical films, membranes and related separation media (Edgar et al., 2001).

Large amounts of efforts have been devoted to achieving sustainable cellulose-based aerogels with high oil absorption capacity (Bi et al., 2013, Zhou et al., 2020, Zhou et al., 2016). The nanocellulose aerogels extracted from cellulose pulp waste by mechanical grinding were chemically treated with methyltrimethoxysilane (MTMS), showing good performance in absorbing various oils, but the absorption capacity was still relatively low (less than 17 g/g) (Zanini et al., 2016). Then, sugarcane bagasse cellulose-based aerogels were produced using polyvinyl alcohol (PVA) binder for oil spill cleaning, showing good flexibility, high porosity (91.9–98.9%) and a slightly increased absorption capacity around 25 g/g (Thai et al., 2019). To further improve their oil absorption capacity, Duong et al. obtained aerogels by using Kymene crosslinker and recycled cellulose fibers from paper waste. After coating with MTMS via chemical vapor deposition, the aerogels yielded an oil absorption capacity up to 95 g/g (Feng et al., 2015). Moreover, Zhou et al. (2016). prepared hydrophobic and highly porous microfibrillated cellulose (MFC) aerogels from softwood kraft pulp via a facile silanization reaction. It could absorb a variety of oils and organic solvents with a relatively high absorption capacity around 159 g/g. Although these cellulose-based aerogels own lower cost and better sustainability than other carbon- (Gui et al., 2011; Ge et al., 2017) or silica-based (Sai et al., 2013) aerogels, the approaches to achieve cellulose or nanocellulose are still time-consuming, environmentally unfriendly and relatively expensive compared with direct usage of other natural fiber absorbents.

Kapok, a natural fiber with a cylindrical hollow structure, has limited spinnability, which is generally considered as a non-economic fiber and a pollen-pollution resource. It is reported that millions of metric tons of kapok fiber waste are produced worldwide each year, which can cause respiratory diseases and pollute the environment (Dong et al., 2016). While, due to its huge hollow structure (Yang et al., 2018) with a smooth surface coated with a layer of wax, kapok fiber owns high buoyancy, low density and good hydrophobicity. These properties have opened up possibilities for various new applications of kapok fiber, especially in oil absorption. It has been used as a natural absorbent in oil cleanup with an absorption capacity of 30–50 g/g diesel and engine oil (Wang et al., 2012, Hori et al., 2000, Lim and Huang, 2007, Abdullah et al., 2010). In addition, kapok could be used as an excellent filter material to selectively remove oil from oily water (Huang and Lim, 2006, Lim and Huang, 2006), with a removal efficiency above 99%. Our research group has also done a great amount of research on the oil absorption performance of kapok fiber. The absorption and adhesiveness of single kapok fiber to various oils were quantitatively evaluated based on Carroll’s theory of droplet morphology (Dong et al., 2015). Besides, the oil absorption capacity of kapok fiber assembly to diesel and motor oil was found to be 27 g/g and 44 g/g, respectively. After reaction with trichloromethylsilane, the oil absorption capacity was further increased by 35–53% (Dong et al., 2016). In addition, based on theoretical analysis, it was found that the huge hollow structure of kapok fiber contributed greatly to the oil absorption property of kapok fiber assembly (Dong et al., 2014). Therefore, non-spinnable and hollow kapok fiber is a sustainable and recyclable alternative for oil cleanup.

To adequately improve the oil absorption capacity and maximize the cost-effectiveness, we attempt to construct a dual-scale hierarchically porous architecture with improved porosity in microfibrillated cellulose (MFC) aerogels by partially introducing chopped kapok fibers. The obtained kapok/MFC aerogels (KCAs) were modified by Vinyltrimethoxysilane (VTMO) to build the hydrophobic and oleophilic surface. These KCAs exhibit exceptionally high porosity (99.58%), ultralow density (5.1 mg/cm−3) and hydrophobic property, resulting in an ultrahigh absorption (104–190.1 g/g) and retention (97.5%) capacity, outstanding oil-water selectivity performance and ultrahigh oil absorption rate. It is worth noting that the absorbed oil could be readily recovered and the absorbent can be recycled. To our knowledge, it is the first report of a dual-scale hierarchically porous kapok/MFC aerogels through chopped kapok fibers to achieve advanced oil absorption performance and high cost-effectiveness.

Section snippets

Materials

Microfibrillated cellulose (MFC) were commercial eucalyptus pulp and obtained from Guilin Qihong Technology Co, Ltd. (Guangxi, China) Vinyltrimethoxysilane (98%, VTMO) were purchased from Sigma-Aldrich trade co., LTD. (Shanghai, China) Acetic acid glacial (99.5%), Susan III, and other chemicals including Methyl blue, Acetone, Ethanol, Chloromethane, N,N-dimethylformamide (DMF) and Toluene were collected from Shanghai Adamas Reagent Co., Ltd. (Shanghai, China) All chemicals were used as received

Morphology of MMAs and KCAs

Herein, we report a facile and greener route to optimize the pore sizes and volume of 3D interconnected porous aerogels by utilizing chopped hollow kapok fiber powders (Fig. 1a) into microfibrillated cellulose (MFC) aerogels (MMAs). As shown in Fig. 1a, ultralight, hydrophobic, sustainable, cost-effective and floating kapok/MFC aerogels (KCAs) were developed by the freeze-drying method and silane treatment. The achieved KCAs own lower density (5.1 mg/cm−3) and higher porosity (99.58%), compared

Conclusion

In summary, a novel aerogel, comprising microfibrillated cellulose (MFC) and chopped hollow kapok fiber, was first developed to own a dual-scale hierarchically porous structure via vacuum freeze-drying and surface modification. Due to ultrahigh porosity, and hydrophobic performance, the obtained kapok/MFC aerogels (KCAs) achieved advanced oil absorption (104 g/g to 190.2 g/g) and retention (up to 97%) capacity and speedy oil absorption rate (0.74 g/s). In addition, these KCAs could selectively

CRediT authorship contribution statement

Huimin Zhang: Conceptualization, Methodology, Validation, Investigation, Writing - original draft. Guangbiao Xu: Writing - review & editing. Yanfang Xu: Validation, Formal analysis. Fumei Wang: Investigation, Review. Jilong Wang: Methodology, Data curation, Writing - review & editing. Hua Shen: Writing - review & editing, Funding acquisition.

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

The authors wish to acknowledge the National Natural Science Foundation of China [No. 51903034] and the Fundamental Research Funds for the Central Universities of China [Grant Numbers 2232019D3-12, 2232020G-01 and 2232019D-15].

References (43)

  • T.T. Lim et al.

    In situ oil/water separation using hydrophobic-oleophilic fibrous wall: a lab-scale feasibility study for groundwater cleanup

    J. Hazard. Mater.

    (2006)
  • H.Y. Mi et al.

    Highly compressible ultra-light anisotropic cellulose/graphene aerogel fabricated by bidirectional freeze drying for selective oil absorption

    Carbon

    (2018)
  • N. Ventikos et al.

    A high-level synthesis of oil spill response equipment and countermeasures

    J. Hazard. Mater.

    (2004)
  • J. Wang et al.

    Effect of kapok fiber treated with various solvents on oil absorbency

    Ind. Crops Prod.

    (2012)
  • H. Bidgoli et al.

    A functionalized nano-structured cellulosic sorbent aerogel for oil spill cleanup: synthesis and characterization

    J. Hazard. Mater.

    (2018)
  • H. Bi et al.

    Carbon fiber aerogel made from raw cotton: a novel, efficient and recyclable sorbent for oils and organic solvents

    Adv. Mater.

    (2013)
  • J. Chen et al.

    Synthesis of freestanding amorphous giant carbon tubes with outstanding oil sorption and water oxidation properties

    J. Mater. Chem. A

    (2018)
  • D. Chen et al.

    Renewable reduced graphene oxide-based oil-absorbent aerosols: preparation and essential oils absorption ability

    ACS Sustain. Chem. Eng.

    (2015)
  • R. Gao et al.

    Mussel adhesive-inspired design of superhydrophobic nanofibrillated cellulose aerogels for oil/water separation

    ACS Sustain. Chem. Eng.

    (2018)
  • J. Ge et al.

    Joule-heated graphene-wrapped sponge enables fast clean-up of viscous crude-oil spill

    Nat. Nanotechnol.

    (2017)
  • X. Gong et al.

    Highly porous, hydrophobic, and compressible cellulose nanocrystals/PVA aerogels as recyclable absorbents for oil-water separation

    ACS Sustain. Chem. Eng.

    (2019)
  • Cited by (0)

    1

    These two authors contributed equally to this paper.

    View full text