Eco-friendly process for facile pore control in thermally stable cellulose acetate utilizing zinc(II) nitrate for water-treatment

https://doi.org/10.1016/j.jiec.2019.08.056Get rights and content

Highlights

  • Pore generation in cellulose acetate by hydrated Zn salts with water-pressure.

  • Facile pore control by intensity of water-pressure.

  • Enhanced plasticization effect by free hydrated NO3 ions.

Abstract

The generation of pores in cellulose acetate (CA) using water pressure and inorganic materials was investigated and succeeded in fabricating straight nanopores in polymer. In this study, we researched Zn(NO3)2·6H2O to have relatively larger ionic size instead of Ni(NO3)2·6H2O. When the CA/Ni(NO3)2·6H2O membrane was employed, the water flux was about 95 L/m2 h at water-pressure of 8 bar. However, the water flux through the CA/Zn(NO3)2·6H2O membrane was about 182 L/m2 h at the same water-pressure. This indicated that Zn(NO3)2·6H2O was more easily able to control the pore size than Ni(NO3)2·6H2O since both zinc salts and the plasticized parts by salts were readily removed by water-pressure.

Graphical abstract

Pore generation through cellulose acetate containing Zn(NO3)2·6H2O to have relatively larger ionic size with external water-pressure.

  1. Download : Download high-res image (136KB)
  2. Download : Download full-size image

Introduction

Nano or microporous materials have been used for various applications such as catalysis, battery separators, medicine, fibers, gas separation, and clean energy technologies [1], [2], [3], [4], [5]. There are various methods to synthesize porous materials. For example, Lei et al. fabricated porous hydroxyapatite/chitosan (HAP/CS) materials by removing Pb(II) ions from aqueous solutions using the freeze-drying method [6]. The size of the pores fabricated using this method ranged from less than 100 μm to over 300 μm. Yu et al. reported single-track etching for the fabrication of conical nanopores in polymer foils [7]. They showed that the nano-sized pore constriction deviates from the funnel-like shape. As a result, nanopores were successfully fabricated, and the radius of the pores was smaller than 10 nm. Schreiber et al. introduced the fabrication of cylindrical pores using the melting-and-freezing method [8]. The size of the pores generated in Mobil Composition of Matter No. 41 (MCM-41) was 2.9–3.7 nm. Additionally, the pores generated in Santa Barbara Amorphous-15 (SBA-15) were larger than those in MCM-41. In another study, this porous material was used to separate gas mixtures. The methods for pore formation were so diverse and have been studied continuously. In addition, studies on the generation of pores in materials having high stability based on the application with controlling the pore-shape, have been actively carried out. In gas separations, the effect of increasing the surface area via the porosity of the material has been utilized to adsorb a large number of gas molecules or to separate gas mixtures. Zhu et al. synthesized porous organic polymers (POPs) and used them to selectively separate CO2 gas molecules [9]. They demonstrated a one-pot catalyst-free synthesis of thiazolothiazole-linked POPs (TzTz-POPs) via a reaction between aldehydes and dithiooxamide. The final material showed good porosity of 488 m2/g, resulting in the high-uptake of CO2 molecules. Furthermore, covalent organic frameworks (COFs), porous aromatic frameworks (PAFs), covalent triazine frameworks (CTFs), and metal–organic frameworks (MOFs) have been interested due to various characteristics [10], [11], [12], [13]. Recently, Yoon et al. reported porous inorganic materials as additives for the separation of olefin–paraffin gas mixtures [14]. In that study, porous inorganic materials such as KIT-6 were used to increase the gas permeability. When KIT-6 was added to the polymer matrix, the mixed propylene/propane permeance reached to 10 GPU from 7.5 GPU. In addition, the selectivity for olefin–paraffin increased from 13 to 20.

On the other hand, porous materials used as battery separators have required high mechanical and chemical stability because of the risk of explosion from the contact of the anode with cathode. If these conditions were satisfied, nanoporous polymer materials would be promising candidates for highly efficient battery applications owing to their easy tunable morphology [15], [16], [17], [18], [19]. For example, Vijayakumar et al. applied the NiO/C porous nanocomposite as an electrode material [20]. The working electrode was formed by mixing 80 wt% NiO/C with 15 wt% activated carbon. To this mixture, 5 wt% polytetrafluoroethylene (PTFE) was added, along with ethanol, and the mixture was coated on a graphite sheet of 1 cm2 area. As a result, the NiO/C electrode exhibited a maximum specific capacitance of 644 F/g at 2 mV/s, and had a good cycling stability over 1000 cycles.

In an earlier study, we reported a method to fabricate pores using an inorganic complex and water pressure [21]. The hydrated nickel nitrate (Ni(NO3)2·6H2O) inorganic complex dissolves in water or acetone and it could be applied to cellulose acetate (CA) solution dissolved in acetone/water (8:2 (w/w)). As a result, the pore size in CA matrix could be controlled using the Ni(NO3)2·6H2O contents and water pressure [21]. The water flux of CA/Ni(NO3)2·6H2O was about 95 L/m2 h at 8 bar water pressure to generate the pores. As a result, pores in the cellulose acetate matrix were uniformly distributed.

In this study, we used Zn(NO3)2·6H2O to generate pores in a CA membrane. It was well-known that the Zn(NO3)2 has the higher solubility in water than Ni(NO3)2. Thus, we hypothesized that relatively larger Zn ions easily complexed with CA polymers by little solvation could increase the plasticizing effect of free NO3 ions on polymer chains. We proved the relationship between the plasticizing effect and the hydrated NO3 ion radius using Zn(NO3)2·6H2O.

Section snippets

Separator preparation

CA was dissolved in acetone/water (8:2 (w/w)) as 10 wt%. Then, the zinc(II) nitrate hexahydrate (Zn(NO3)2·6H2O) was added to solution containing CA polymer as various mole ratio of the Zn ions for monomeric unit of CA. Then, the solution was stirred for 30 min at room temperature. Subsequently, the solutions containing Zn salt and CA polymer were cast for preparation of free-standing film on glass plate and dried at 1 atm for 30 min. The dried polymer matrix containing Zn(NO3)2·6H2O was subjected

Results and discussion

SEM was used to investigate the pores formed in the CA polymer matrix using Zn(NO3)2·6H2O additive in acetone/water (8:2 (w/w)). Fig. 1(a) and (b) represented the surface morphology of the CA polymer matrix which was dissolved in acetone/water (8:2 (w/w)) along with the Zn(NO3)2·6H2O additive. The SEM image precisely exhibited that pores were formed on the surface when Zn salts were incorporated to the CA polymer matrix dissolved in acetone/water (8:2 (w/w)). Furthermore, the cross-section of

Conclusions

We demonstrated a method to generate pores using Zn(NO3)2·6H2O for porous cellulose acetate. A porous polymer matrix was successfully fabricated using Zn(NO3)2·6H2O and water pressure as shown in Scheme 1. When water pressure was applied to the CA polymer matrix, the pore size and porosity gradually increased. Also, the water flux increased with the water pressure. This indicated that pressurized water molecules were penetrated into the polymer chains loosened by the solvated Zn(NO3)2·6H2O.

Acknowledgements

This work was supported by the Basic Science Research Program (2017R1D1A1B03032583) through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT, and Future Planning. This study was also funded by Korea Environment Industry & Technology Institute (KEITI) as “Technology Program for establishing biocide safety management” (RE201805019).

References (25)

  • B. Dong et al.

    ChemComm

    (2016)
  • C. Gu et al.

    Polym. Chem.

    (2015)
  • K.W. Yoon et al.

    J. Membr. Sci.

    (2016)
  • M.A. Mohamed et al.

    Chem. Eng. J.

    (2016)
  • M.A. Mohamed et al.

    Carbohydrate Polym.

    (2017)
  • M.A. Mohamed et al.

    Int. J. Biol. Macromol.

    (2017)
  • M. Gratzel

    Inorg. Chem.

    (2005)
  • Y.-y. Pei et al.

    Korean J. Chem. Eng.

    (2018)
  • Y.S. Park et al.

    J. Membr. Sci.

    (2015)
  • J. Choi et al.

    Korean J. Chem. Eng.

    (2018)
  • N. Linares et al.

    Chem. Soc. Rev.

    (2014)
  • Y. Lei et al.

    RSC Adv.

    (2015)
  • Cited by (15)

    • Porous C<inf>2</inf>H<inf>3</inf>O<inf>2</inf>-substituted cellulose with thermal stability based on sodium chloride

      2023, Journal of Industrial and Engineering Chemistry
      Citation Excerpt :

      Therefore, it was possible to develop an eco-friendly and low-cost battery separator process. In previous studies, Lee et al., demonstrated that an advanced porous separator can be fabricated by adding an inorganic compound such as a metal salt to a ASC polymer solution [33,34]. Mg(NO3)2·6H2O was added to cellulose acetate to control the pore size on the surface of the ASC matrix.[33]

    • Low-cost process to utilize sodium salts for porous cellulose materials

      2022, Journal of Industrial and Engineering Chemistry
      Citation Excerpt :

      Moreover, Mg(NO3)2·6H2O was used as an additive to fabricate a separation membrane that was thermally stable at the optimal composition and demonstrated a flux of 70 LMH [35]. Research was conducted on inorganic hexahydrate composites containing Zn(NO3)2·6H2O [36]. The flux of a CA/Ni(NO3)2·6H2O membrane was approximately 95 L∙m−2∙h−1 at a water pressure of 8 bar, however, the flux of water passing through the CA/Zn(NO3)2·6H2O membrane was approximately 182 L∙m−2∙h−1 at the same water pressure.

    • Development of low-cost process for pore generation in cellulose acetate by utilizing calcium salts

      2021, Journal of Industrial and Engineering Chemistry
      Citation Excerpt :

      This method has the advantages that water could be an easily available resource and environmentally friendly, in particular useful to generate the straight pores. So far our group has used metal salts such as Mg, Zn and Ni salts based on cellulose acetate polymer [9,25,26]. Metal salts have the advantages of high mechanical strength and thermal stability, but are expensive and generally showed the poor porosity.

    View all citing articles on Scopus
    View full text