Development of an innovative capsule with three-dimension honeycomb architecture via one-step titration-gel method for the removal of methylene blue

https://doi.org/10.1016/j.ijbiomac.2019.02.001Get rights and content

Highlights

  • A novel capsule with 3D honeycomb architecture was fabricated via the one-step titration-gel method.

  • The GO capsules performed comparatively much better than the neat ones.

  • The capsules have a brodened pH tolerance property and reusable for the removal of MB.

  • The GO capsules could be regenerated multiple cycles by water.

Abstract

In this study, the capsules were prepared via the one-step titration-gel method by injecting spherical droplets of polyvinyl alcohol (PVA), sodium alginate (SA) and graphene oxide (GO) gelled mixture into the bath with calcium chloride (CaCl2) and oversaturated boric acid (H3BO3) solutions. The prepared capsules were then further modified with glutaraldehyde (GA). The formation mechanism of the prepared capsules was investigated. The morphology of the prepared capsules exhibited distinct micro-porous “3D honeycomb” pattern and hierarchical pore sizes distribution. It was also observed that GA not only acted as a co-cross-linked reagent in the fabricating process to increase the specific surface area of the capsules, but also offered exceptional tolerance property to work under a wide pH range (i.e. 2–12). The PVA-SA-GO capsules performed comparatively much better than PVA-SA capsules and they improved the adsorption capacity by up to 21.94%. Their adsorptive performance well followed the Langmuir isotherm. Moreover, the pH of the MB solution was evidently declined after adsorption, demonstrating the electrostatic attraction or ion-exchange might be the governing removal mechanism of methylene blue (MB) dye by the capsules. Importantly, the prepared capsules could be regenerated by simply washing with water and reused for at least 6 consecutive treatment cycles.

Introduction

Currently, urbanization and industrialization are deepening constantly, which raises the need of water and wastewater treatment experts to manage and treat a huge amount of contaminated waters with discharged toxic and harmful pollutants that are seriously destroying people's aquatic and the surrounding environment. Different physical, chemical and biological ways of removing these harmful pollutants from the aqueous environment have been drawn up and employed for controlling water pollution [[1], [2], [3]]. Among them, adsorption, has become fairly widely used; its rapid acceptance is due to the fact that it has overcome several of the drawbacks of conventional technologies, such as higher removed efficacy and cost efficiency [4,5].

In most studies of the adsorption, the adsorbed capacity of the adsorbents has been widely emphasized with attention being given to its real performance in application [6]. The previous work on this topic has indicated that the adsorptive performance of the nano-adsorbents, especially, graphene, is comparatively better than other materials due to possessing higher specific surface area and adsorbed sites, which is widely used for the removal of herbicides and metal ions, i.e., lead, cadmium and copper, etc., from the environment [[7], [8], [9], [10], [11]]. Nevertheless, it is very difficult to separate and recycle them from aqueous solutions after eliminating the contaminants because of their brilliant dispersibility [12,13]. It is also noticed that parts of graphene are directly/indirectly released into the environment, which not only pollutes the environment but also causes a waste of resources [14]. Widespread research indicates that it has negative influences on human health and ecological balance [[15], [16], [17]]. Nowadays, though some tasks have been started to find practical solutions to re-cycle the graphene materials after adsorption, the results are not always satisfactory. For example, graphene materials are separated from water through magnetic force or gravity after adsorption via loading them onto the magnetic or other larger nanoparticles, but its adsorbed capacity is seriously demolished in this progress [[18], [19], [20]]. Also, high-speed centrifuge has been used to collect the graphene after adsorption, but this technique is expensive and unrealistic for commercial sewage treatment [21].

By way of contrast, hydrogels are rich in hydrophilic functional groups such as carboxyl, amide, hydroxyl and sulfonic acid, and so on [[22], [23], [24]]. Based on this, they are successfully used for encapsulating and hybridizing some organic and inorganic materials to rapidly capture the pollutants from wastewaters, hold much water and can be permeated by oxygen and nutrients freely, etc. For instance, porous CTS-PVA/GO hydrogel is used for researching bone regeneration potential [25]; MNPs embedded in an SA/PVA matrix is applied to solve CMPW [26]; photo-catalysis efficiency of TiO2/poly [acrylamide-co-(acrylic acid)] composite material is used in the textile dye degradation [27]. Moreover, the inorganic nanoparticles can sufficiently interact with the radicals of the hydrogels then embed tightly into the polymers matrix, thereby minimizing the potential environmental damage which might be caused by the free-diffusion. However, most hydrogels are soft and vulnerable in adsorbed process. In addition, these hydrogels do not be provided with such polymer cellular pores as larger pore volume and higher porosity honeycomb architectures which have already described by the TIPS and NIPS methods for producing thin flat-sheets in spite of possessing multi-aperture and micro-porous pattern [[28], [29], [30], [31]]. Their weak chemical stability, low surface area and the porosity severely restrict their adsorption properties [32,33].

It is reported that the organic-inorganic composite hydrogels with IPNs structure have more excellent performance in a series use [34,35]. In addition, the mechanical property of the hydrogel could be further improved after chemical and physical modification [36]. On the basis of existing literature data, we carried out the studies in an effort to prepare the hybrid hydrogel adsorbents with specialized porous morphology, chemical stability and low toxicity, which can be recycled and applied to the overly acid or alkali situation. Herein, to the best of the knowledge of the researchers in this research, it was the very first time to present this novel capsule absorbent with 3D honeycomb architecture just through the one-step titration-gel method by injecting PVA and SA-GO spheroidal sol into the CaCl2 and oversaturated H3OB3 mixture, and these capsules were modified by GA then. The robust capsule loaded with GO could be reused for MB adsorption for at least 6 times by washing with acid eluent and water.

Section snippets

Materials

PVA (MW 146,000–186,000, 99+% hydrolyzed) was purchased from Sigma-Aldrich. GA (50.0 vol% in H2O) was applied by Aladdin Reagents Co., Ltd. (China). Commercial GO (Single layer GO powder, diameter 0.8 nm–1.2 nm, thickness 0.5 μm–5 μm) were obtained from XFNANO Co., Ltd. (China). Other chemicals were supplied by Sinopharm Chemical Reagent Co., Ltd. (China) and used as received. The ultra-pure water was produced by a Milli-Q BIOCEL unit (Millipore, The USA) with the resistivity of 18 MΩ cm.

Preparation of the casting sol

At

Morphology analysis of the prepared capsules

The FE-SEM analysis was conducted for clear depicting the morphology transmutation of the prepared capsules from the surface to the interior (Fig. 2, A to C).

Generally, from A to C, the overall microscopic-morphology of the prepared capsules exhibited distinct “3D honeycomb” architectures (Fig. 3). Moreover, the fenestra population and the diameter of the capsules were varied from ‘dense and small’ to ‘sparse and large’, which displayed a cascade distribution. The reason behind the results

Conclusion

In summary, the formation mechanism of the capsules contained a chelation process that the sol of the PVA-SA-GO was covalently bonded with H3BO3 and CaCl2. GA could co-cross-link with the polymer and had a brilliant ‘healing’ potency to regrow and reinforce the fractured fibers of the capsules, which increased the density of the pores and narrowed the average pore size distribution of the capsules. The capsule with faviform architectures and wide pH tolerance nature in this research could be

Acknowledgments

The authors acknowledge the support of the Key Project of the Joint Fund Between the State Fund Committee and Shandong Province (U1806210) and the State Key Laboratory of Environmental Criteria and Risk Assessment (SKLECRA2013FP12).

References (46)

  • Y. Tang et al.

    Magnetic TiO2-graphene composite as a high-performance and recyclable platform for efficient photocatalytic removal of herbicides from water

    J. Hazard. Mater.

    (2013)
  • T. Du et al.

    Photochlorination-induced transformation of graphene oxide: mechanism and environmental fate

    Water Res.

    (2017)
  • X. Huang et al.

    Bromate inhibition by reduced graphene oxide in thermal/PMS process

    Water Res.

    (2017)
  • C. Ren et al.

    Ultra-trace graphene oxide in a water environment triggers Parkinson's disease-like symptoms and metabolic disturbance in zebrafish larvae

    Biomaterials

    (2016)
  • W. Yao et al.

    Synergistic coagulation of GO and secondary adsorption of heavy metal ions on ca/Al layered double hydroxides

    Environ. Pollut.

    (2017)
  • Y.H. Cho et al.

    Water and ion sorption, diffusion, and transport in graphene oxide membranes revisited

    J. Membr. Sci.

    (2017)
  • N. Li et al.

    Recent advances in graphene-based magnetic composites for magnetic solid-phase extraction

    TrAC Trends Anal. Chem.

    (2018)
  • V. Jabbari et al.

    Green synthesis of magnetic MOF@GO and MOF@CNT hybrid nanocomposites with high adsorption capacity towards organic pollutants

    Chem. Eng. J.

    (2016)
  • V. Kumar et al.

    Development of bi-metal doped micro- and nano multi-functional polymeric adsorbents for the removal of fluoride and arsenic(V) from wastewater

    Desalination

    (2011)
  • W. Liang et al.

    A facile and controllable method to encapsulate phase change materials with non-toxic and biocompatible chemicals

    Appl. Therm. Eng.

    (2014)
  • J. Huang et al.

    Shape memory polymer-based hybrid honeycomb structures with zero Poisson's ratio and variable stiffness

    Compos. Struct.

    (2017)
  • A. Bée et al.

    Magnetic alginate beads for Pb(II) ions removal from wastewater

    J. Colloid Interface Sci.

    (2011)
  • Y. Zhang et al.

    Bio-inspired layered chitosan/graphene oxide nanocomposite hydrogels with high strength and pH-driven shape memory effect

    Carbohydr. Polym.

    (2017)
  • Cited by (16)

    • Fabrication of high boron removal reverse osmosis membrane with broad industrial application prospect by introducing sulfonate groups through a polyvinyl alcohol coating

      2022, Journal of Membrane Science
      Citation Excerpt :

      It can be found that all membranes have a characteristic peak of O* = C–O/OC–N at 532.3 eV, which is associated with PA [43,44]. The C–O–C peak at 531.5 eV and the R–OH peak at 533.5 eV appeared in the spectra of the RO1 and RO3 membranes (Fig. 6(b) and (c)), which were attributed to the acetal reaction of PVA with GA/BADSA Na and the presence of PVA, respectively [45]. Besides, the SO peak at 530.0eV appeared for the spectra of RO3 membranes [46,47], indicating the introduction of the sulfonate group.

    • Development of novel MOF-mixed matrix three-dimensional membrane capsules for eradicating potentially toxic metals from water and real electroplating wastewater

      2022, Environmental Research
      Citation Excerpt :

      According to the results, the peaks observed at 3600–3300 cm−1 can be attributed to O–H stretching vibrational peaks of polyphenolic groups and the peaks at 3192–2899 cm−1 could be attributed to the C–H stretching vibrational peaks of alkanes (Lin et al., 2019c; Ozcan et al., 2010). While the peaks at 1560–1375 cm−1 were allocated to C–OH stretching/the –COO− groups of SA (Ali et al., 2019a, 2019b; Lin et al., 2019a). Moreover, the peaks that appeared at 1640 and 892 cm−1 were attributed to CO stretching and the manifestation of O–Na bonds in the –COONa radical of SA, respectively (Lin et al., 2019b).

    • Boric acid-loosened polyvinyl alcohol/glutaraldehyde membrane with high flux and selectivity for monovalent/divalent salt separation

      2022, Journal of Membrane Science
      Citation Excerpt :

      Besides, the peak at 1100 cm−1 is attributed to the reaction of PVA and GA to form C–O–C bonds. The peak of C–OH in PVA is around 1000 cm−1 [36]. The peak at 1720 cm−1 represents an un-reacted aldehyde group (CO) of GA.

    • Fabrication of polyethylenimine functionalized magnetic cellulose nanofibers for the sorption of Ni(II), Cu(II) and Cd(II) in single-component and multi-component systems

      2021, International Journal of Biological Macromolecules
      Citation Excerpt :

      The XPS deconvolution spectra of C 1s before and after sorption are shown in Fig. 5a. The C 1s spectrum of PEI-CNFs@Fe3O4 is composed of C=O (287.26 eV), C-O (286.22 eV), C-O-C (285.28 eV) and C-N/C=N (284.41 eV) [28]. And the C=O is derived from the -COOH groups of CNFs [29].

    View all citing articles on Scopus
    View full text