Adsorption of methyl violet from aqueous solution using gum xanthan/Fe3O4 based nanocomposite hydrogel

https://doi.org/10.1016/j.ijbiomac.2016.04.050Get rights and content

Highlights

  • Hydrogel nanocomposites of Gx-cl-PAA with Fe3O4 nanoparticles were synthesized.

  • Hydrogel nanocomposite showed excellent MV adsorption capacity of 642 mg/g.

  • Adsorption process followed Langmuir adsorption isotherm and pseudo-second-order kinetics model.

  • The nanocomposite showed very good recyclability.

Abstract

This research paper reports the utilization of gum xanthan-grafted-polyacrylic acid and Fe3O4 magnetic nanoparticles based nanocomposite hydrogel (NCH) for the highly effective adsorption of methyl violet (MV) from aqueous solution. Synthesized NCH was characterized using various techniques, such as FTIR, XRD, SEM-EDS, TEM and BET. Adsorption behavior of NCH was studied for the adsorption of MV and it was found to remove 99% dye from the solution. Adsorption process followed Langmuir isotherm model (qe = 642 mg/g) and pseudo-second-order kinetics model. Thermodynamic studies suggested that the adsorption process was endothermic and spontaneous. Moreover, the adsorbent was successfully utilized for successive five cycles of adsorption-desorption.

Introduction

Discharge of dyes-containing industrial effluents in different water bodies is one of the major reasons of water pollution. Most of the dyes are highly carcinogenic and even the trace amounts of these dyes have adverse effects on the human health [1], [2]. Synthetic dyes have a number of applications in different industries and more than 10,000 dyes have been produced annually because of their low cost and easy availability. Although the use of synthetic dyes in various industries is very important from economical point of view but at the same time their harmful effects on our ecosystem should be taken into consideration. Therefore, the proper and efficient treatment of dyes contaminated waste material before their discharge is of prime importance. The waste produced by the dye effluents is difficult to process using the conventional wastewater treatment methods because it can withstand degradation by water, microbes, light and chemicals [3], [4], [5]. Most of the conventional methods of dye removal from wastewater, such as coagulation and flocculation, reverse osmosis, activated sludge, bacterial action, chemical oxidation, ozonation and physical methods like membrane filtration, ion exchange and electrochemical techniques, are either very expensive and/or inefficient for the complete removal of dyes [6], [7]. Adsorption is one of the most promising and widely used techniques for the removal of pollutants from wastewater [1], [5], [8], [9]. Different adsorbents have been used previously for removing impurities from wastewater but most of them were found to be either non-biodegradable or very expansive [10], [11]. To overcome these drawbacks biopolymers based adsorbents being introduced in the water treatment applications [12], [13], [14]. Biopolymers mainly gum polysaccharides are fully biodegradable large organic molecules and most of them have many hydroxyl and carboxylate functionalities in their internal structure [15], [16], [17], [18]. The adsorption of dyes onto polysaccharide based adsorbents takes place through the electrostatic attractions between opposite charges of adsorbents and pollutants [19]. Therefore, due to the presence of a large concentration of anionic functionalities, they are considered as novel adsorbents for the removal of cationic impurities from wastewater. Polysaccharide based adsorbents have a lot of advantages over other adsorbents such as low cost, biodegradability, easily availability and the ability of modification as per the target pollutant [1], [8], [19], [20].

Biopolymers based nanocomposites have also shown promising results in water treatment applications and the introduction of nanoparticles within a polymer matrix not only improves the surface properties but also mechanical, thermal as well as the chemical stability of the polymer matrix which increases the reusability of the polymeric adsorbent [21], [22], [23]. Inclusion of nanoparticles within the polymer matrix also provides additional adsorption sites for binding the pollutants. Recently iron oxide magnetic nanoparticles (Fe3O4 MNPs) based adsorbents have attracted the attention of a number of research groups due of their basic properties like very small size and high surface area to volume ratio [24], [25]. In the field of separation science and technology, the main advantage of using magnetic adsorbents is generally based on their solid phase magnetic property that endows a rapid and easy separation of the adsorbent and the recovery of contaminants from the polluted environment by applying an external magnetic field. Moreover, using magnetic separation large amount of polluted water can be treated within a very short period of time [26], [27], [28], [29]. The nanocomposites prepared by the combination of gum polysaccharides with Fe3O4 MNPs have all the desired properties of modern adsorbents [22], [23], [24], [25], [30], [31]. In view of the advantages of the gum polysaccharides and Fe3O4 MNPs, in this research work we have reported the development of Fe3O4 MNPs filled gum xanthan (Gx)-crosslinked-polyacrylic acid (PAA) based nanocomposite hydrogel (NCH) for adsorption of methyl violet (MV) from the aqueous solution. The NCH showed excellent adsorption capacity of 642 mg/g. Effect of different adsorption parameters, adsorption kinetics, adsorption isotherms and different thermodynamic parameters were also evaluated. Furthermore, the reusability of the NCH was tested using adsorption-desorption experiments for the successive five cycles.

Section snippets

Materials

Gx, acrylic acid (AA), potassium persulphate (KPS), ascorbic acid (ABC), N,N’-methylene-bis-acrylamide (MBA), MV and Fe3O4 MNPs were purchased from Sigma Aldrich, South Africa and were used as received. Stock solution of MV (1000 mg/L) was prepared by dissolving appropriate amount of dye in the 1000 mL of deionized water and the stock solution was further diluted for batch experiments using deionized water.

Synthesis of the NCH

For the synthesis of NCH, crosslinked network of AA with Gx was prepared through free

Mechanism of the synthesis of NCH

The NCH was synthesized by incorporating the Fe3O4 MNPs within the polymer matrix of Gx-cl-PAA hydrogel. In the first step, the polymer matrix, i.e., Gx-cl-PAA was synthesized via the free radical graft co-polymerization of AA onto the Gx where the redox mixture of KPA and ABC was used as the initiator and MBA was used as crosslinker. Initially, the active sites were generated on the backbone polymer, i.e., Gx and the monomer which further propagated the polymerization reaction and formed

Conclusion

In this study, we have successfully synthesized magnetic nano-adsorbents based on Fe3O4 MNPs filled Gx-cl-PAA. The successful incorporation of the Fe3O4 MNPs with the polymer matrix was confirmed by FTIR, XRD, TEM and SEM-EDS analyses. Moreover, the thermal stability of the polymer matrix was increased after the incorporation of Fe3O4 MNPs. The increased surface area and pore volume was also confirmed by BET analyses. NCH effectively removed MV from the aqueous solution and followed Langmuir

Acknowledgements

The authors are grateful to the National Research Foundation (NRF), South Africa for awarding a Postdoctoral research fellowship to Dr. Hemant Mittal. The authors would also like to thank the University of Johannesburg, Department of Science and Technology and the Council for Scientific and Industrial Research, South Africa for their financial support.

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