Structural characterization of the crystalline nanocellulose and nanocellulose-reinforced carbon buckypaper

https://doi.org/10.1016/j.diamond.2020.107821Get rights and content

Highlights

  • Compared to the non-ground and ground CNC structures, crystallinity and morphology were not able to maintain, dispersibility in aqueous media improved but not the dispersion stability.

  • The composite structure of obtained BP was revealed by TEM analysis, filtration, salt rejection and absorption ability of the fabricated buckypaper determined by UV–Vis spectral analysis and electrical conductivity measurement.

  • The obtained nanocomposite CNT/CNC buckypaper exhibited 48% of improved salt rejection and excellent filtration and adsorption ability which can compete with traditional water filtration counterparts.

  • Besides, the natural abundance and biodegradability of nanocellulose are the big-tickets to the low-cost and eco-friendly production of the nanocomposite paper substrate.

Abstract

Recently, nanostructured cellulose materials have been taking great attention due to their excellent mechanical properties, nanostructure, and non-toxic nature. According to these amazing properties, nanocellulose has been suggested as an excellent reinforcement material to empower the carbon paper structure. In this study, experimental investigations were conducted to establish a comprehensive understanding of the fundamental characterizations of crystalline nanocellulose (CNC) material such as structure, morphology, crystallinity, dispersion characterizations, and thermal and electrical behavior. Moreover, the grinding effect on the CNC structure and morphology, the advantage of CNC reinforcement in carbon buckypaper (BP) properties and performances were investigated. As a result, structural and morphological studies indicated that the relative amount of crystal domain in the CNC is 66% which contains numerous sphere-shaped crystal nanoparticles composed of small crystallites with an approximate size of 42.33 nm. Therefore, the electrical conductivity of CNC aqueous dispersion was greatly improved with an increase of concentration but the opposite results found for the thermal conductivity. Compared to the non-ground and ground CNC structures, crystallinity and morphology were not able to maintain, dispersibility in aqueous media improved but not the dispersion stability. Moreover, the composite structure of obtained BP was revealed by TEM analysis, filtration, salt rejection and absorption ability of the fabricated buckypaper determined by UV–Vis spectral analysis and electrical conductivity measurement. The obtained nanocomposite CNT/CNC buckypaper exhibited 48% of improved salt rejection and excellent filtration and adsorption ability which can compete with traditional water filtration counterparts. Besides, the natural abundance and biodegradability of nanocellulose are the big-tickets to the low-cost and eco-friendly production of the nanocomposite paper substrate.

Introduction

Due to natural abundance, strong mechanical quality, and non-toxic biodegradable behavior, nanocellulose has expected to be utilized in numerous applications including synthesis of the functional materials such as sensors, optical devices, paper membranes, flexible paper batteries, supercapacitors and transistors [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]]. Particularly, crystalline nanocellulose (CNC) has unusual mechanical properties for use in material applications, for instance, their tensile strength is about 500 MPa, similar to aluminum and stiffness is about 140–220 GPa. [[14], [15], [16], [17]]. Thereby, the mechanical properties of the nanocellulose appear to be occupied a prominent position in both the scientific and industrial fields according to reported articles and commercialized products [[18], [19], [20], [21], [22], [23], [24], [25]]. For further application, more details regarding the other aspects such as structure, morphology, dispersion characteristics and the thermal and electrical properties of nanocellulose are needed to be explored.

Meantime, nanostructured carbon allotropes, particularly CNTs are been well-regarded candidates in all-embracing applications due to their novel properties [[26], [27], [28], [29]]. Wherefore, a cohesive carbon buckypaper structure has become a far-reaching vital substitute in the field of electronics, biomedical engineering, military, filtering, thermal systems and so on [[30], [31], [32], [33], [34]]. Carbon buckypapers are a self-supporting randomly oriented sheet structure of the CNT bounded by van der Waals attraction. The BPs were originated from the revelation of the Buckyballs in 1985 by a team of scientists Smalley and Kroto [35] and further reported as “Buckypaper” in 1998 [36]. Since then, the paper-structure of carbons has attracted efforts of researches due to the high surface area, elasticity, biodegradability, and the possibility of large scale production. However, the commercialization of carbon BPs seems hindered by a lack of mechanical strength and cost-effectivity [[30], [31], [32], [33], [34],[37], [38], [39], [40]]. In this context, cost-effective, natural polymer matrices have been involved in BP synthesis as reinforcement that supports the mechanical properties of BP [41,42]. As another major challenge facing, the dispersibility of both materials in water becomes critical because of the hydrophobic nature of carbon and the agglomeration caused by enhanced viscosity and strong attractive interaction of the CNT/polymer composite [43,44]. For this reason, improved carbon dispersion and downscale reinforcement requisites for the composite synthesis. As an effective nanoscale reinforcement, nanostructured cellulose materials (cellulose nanofibrils CNF and cellulose nanocrystals CNC) have attracted great interest in the research community.

To empower the carbon buckypaper (BP) structure and obtain advanced composite with multifunctional properties, several efforts have been directed to optimize effective nanocellulose reinforcement for fabricating BPs with the full potential and reducing the consumption of the related toxic materials [32,[43], [44], [45], [46], [47], [48]]. For instance, Salajkova et al. fabricated CNT nano paper structure with a tensile strength of 183 MPa by using nano fibrillated cellulose (NFC) reinforcement. Later, Yang et al. synthesized graphene/NFC nanocomposite paper with excellent conductivity and satisfactory mechanical properties such as 61 MPa of tensile strength [45,46].

Not only the mechanical properties, but nanocellulose nanomaterials also hold great potential in environmental applications including water purification, air filtration, and oil recovery, for instance, a team of Zhu.M synthesized bio-based antibacterial composite air filtration membrane which has superior multifunctional features [49]. Meanwhile, Lv.D et all have developed highly efficient (filtration efficiency of the membrane for ultrafine particles was higher than 99.99%) eco-friendly electrospun membrane recently [50]. Also, membrane filtration methods have been developed and antibacterial and self-cleaning activities have been investigated as well [51,52]. Nanostructured cellulose can be a compatible candidate for the next generation of filter membranes which demands strong mechanical qualities along with advanced filtration ability while maintaining exceptional permeability [[49], [50], [51]]. According to the published article of the team of Carpenter, nanocellulose materials found a sustainable replacement of CNTs and a CNF was seen as an effective alternative adsorbent for removing heavy metal contaminants Pb2+, Cd2+, Cr3+ from the environment [52].

Besides, the dispersive nature of nanostructured cellulose materials attracted great attention in nanofluid synthesis, particularly, carbon-based nanofluid production lately [[53], [54], [55], [56]]. As shown in the literature, nano fibrillated cellulose (CNF) can be associated with other nanoparticles in colloidal suspension due to the multi-point interaction which provides improved dispersion and stability which ease the dispersion complication of the carbon nanoparticles in the BP production process. Our previous study was also focused on the ability of nanocellulose (CNC) on carbon dispersion in nanofluid synthesis due to the static dispersion supported by non-covalent functionalization, resulting in excellent dispersion characterizations and thermal and electrical properties [56]. The result suggested that nanocellulose acts as a stabilizing agent in highly conductive carbon nanofluid production, obtained nanofluid can be further employed for the synthesis of the buckypaper and the nanocellulose can be a structural element in nanocomposite material due to the excellent mechanical properties, crystalline structure, and adsorption ability.

In this work, the crystalline structure, surface morphology, thermal and electrical properties of the CNC were studied. Therefore, the nanocomposite structures of MWCNTs and CNC was synthesized as composite buckypaper to understand the advantage of CNC in buckypaper production and performance. Morphological analysis and structural characteristics of the buckypaper were examined by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). UV–Vis spectral analysis and electrical conductivity measurement carried out on the feed and filtrate solutions to estimate the organic compound filtering, ion adsorption, and salt rejection activity of the obtained buckypaper.

Section snippets

Materials

MWCNTs with an approximately 20 nm diameter, ~5 μm length, greater than 95% purity and less than 3% impurities (Carbon Nanomaterial Technology Co., Ltd, South Korea), a concentrated stock dispersion of CNC with a 99.0% purity (SKB TECH, South Korea) were employed as main material in this study.Hydrochloric acid (HCl) (98%), sulfuric acid (H2SO4) (98%) and Nitric acid (HNO3) (63%) were purchased from Junsei Chemicals Co., Ltd. Japan used for chemical modification of MWCNTs. Potassium

Crystalline nanocellulose characterizations

The functional groups were confirmed by Fourier Transform Infrared (FTIR) spectrophotometer (Bruker VERTEX). FTIR spectra of CNC shown in Fig. 1A, the absorption peaks at 3451 cm−1 and around 2899 cm−1 were attributed to the Osingle bondH and Csingle bondH stretching vibrations, respectively. The peak absorption at 1644 cm−1 was reported as the Osingle bondH vibration of absorbed water. The peak for Csingle bondH and Csingle bondO vibrations contained in the polysaccharide rings of cellulose is around 1382 cm−1. The vibration of C-O-C in the

Conclusion

This experimental study was aimed to understand the fundamental characterization of the crystalline nanocellulose materials and the effect of the nanocellulose reinforcement in carbon-based buckypaper properties and performances. As included in the aims of the study, the structure, surface morphology, dispersion characterizations, and thermal and electrical conductivity of the nanocellulose, and filtration ability of the obtained BPs were investigated respectively.

Furthermore, comparative

CRediT authorship contribution statement

Otgonbayar Dovjuu:Conceptualization, Investigation, Validation, Writing - original draft.Sedong Kim:Formal analysis, Methodology, Writing - review & editing.Ajeong Lee:Data curation.Seungyeop Baek:Data curation.Junhyo Kim:Formal analysis, Methodology.Jungpil Noh:Formal analysis, Methodology.Sunchul Huh:Validation.Byeongkeun Choi:Writing - review & editing.Yonmo Sung:Writing - review & editing.Hyomin Jeong:Conceptualization, Investigation.

Declaration of competing interest

The authors declare that they have no known competing financial interest or personal relationships that c ould have appeared to influence the work reported in this paper.

Acknowledgement

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (No. 2017R1A2B4007620).

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