Probing the role of hydrolytically stable, 3-aminopropyl triethoxysilane crosslinked chitosan/graphene oxide membrane towards Congo red dye adsorption
Graphical abstract
Introduction
During the last decade Graphene oxide (GO) has emerged as an interesting material for polymer composites and in particular, has markedly increased the efficiency of wastewater treatment in many cases [[1], [2], [3]]. The presence of carboxyl and hydroxyl groups on the surface of GO renders it hydrophilic, and quite reactive towards adsorbents [4,5]. Another important advantage of GO is its potential for interaction through strong π-π interactions [[6], [7], [8]]. Congo red (CR) is a benzidine-based anionic dye which is discharged [9] into water courses from the printing, dyeing, paper and textile industries [10,11]. CR is believed to metabolize into benzidine, a known human carcinogen [12,13], so its removal from waste resources is very important. The potential advantages of GO led Debnath et al. [14] to investigate the adsorption of CR by powdered GO. Their results showed good adsorption, but handling GO and its removal from water requires extra time and effort and traces of the material may be left behind. To address this issue, GO supported material can be used. Using a biopolymer-based support would offer a more environmentally benign, and greener approach [15,16].
Chitosan extracted from the exoskeletons of shellfish [17]or Fungi [18], is a natural polysaccharide which shows good biocompatibility and biodegradability [19]. It is non-toxic and can be easily functionalized with other materials. Chitosan is also a strongly adsorbed material due to the presence of large numbers of amino and hydroxyl groups [20]. Its cationic nature could give additional benefit for the removal of anionic dyes such as CR [21,22]. Chitosan readily forms thin membranes or films [23] and can also be blended with other polymers to enhance its mechanical properties [24], an example being PVP. Ch-PVP blends which are miscible [25,26] due to the interactions between the hydroxyl groups in Ch and the carbonyl groups in PVP.
In this paper, we report efforts to improve the adsorptive performance of Ch/PVP membranes by incorporating GO as a nanofiller. Ch/PVP/GO nanocomposite membranes were prepared using a simple solution-casting technique. The swelling, oxidative and hydrolytic constancy and adsorptive performance of membranes have been determined.
Section snippets
Materials and methods
Chitosan (C3646, 75% de-acetylated), 3-(aminopropyl)triethoxysilane (3-APTES), PVP (average MW: 40,000), sulphuric acid, phosphoric acid, congo red, acetic acid, ethanol, potassium permanganate, and hydrochloric acid (HCl) were purchased from Sigma Aldrich. Ferrous sulphate and hydrogen peroxide were purchased from Merck. All chemicals were analytical grade and used without further purification.
Synthesis of graphene oxide (GO)
Expanded graphite was prepared [27] from commercial graphite by treating it with 25 mL of
Morphological analysis
Fig. 1 shows SEM micrographs of Ch/PVP/GO, Ch/PVP and CR-adsorbed nanocomposites membranes. Graphene sheets are visible in the micrographs of the GO containing membranes (the inset (Fig. 1a) shows a TEM of GO dispersed in ethanol) and also indicate homogeneous blending of PVP with the chitosan. Uniform dispersion of filler throughout the polymer matrices is shown in Fig. 1b. Fig. 1c shows the SEM image of Ch/PVP film while Fig. 1d represents the surface morphology of films after dye uptake.
Structural analysis
In
Conclusion
This work describes the fabrication and adsorptive characteristics of nanocomposite membranes consisting of GO dispersed in a Ch/PVP matrix. These combinations not only improve the adsorptive properties but also enhanced the thermal ability of the chitosan. Swelling, as well as hydrolytic results, confirmed that level of GO of 2%-Ch/PVP gave the most stable membrane while increasing the amount of 3-APTES crosslinker reduced the stability towards aqueous media due to the increased amount of
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 would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding of this research through the Research Group Project no. RGP-293.
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