Elsevier

Journal of Molecular Liquids

Volume 294, 15 November 2019, 111598
Journal of Molecular Liquids

Feasibility of toxic metal removal from aqueous medium using Schiff-base based highly porous nanocomposite: Adsorption characteristics and post characterization

https://doi.org/10.1016/j.molliq.2019.111598Get rights and content

Highlights

  • Synthesis of magnetic porous organic polymer (MPOP) using Schiff base

  • The MPOP nanocomposite showed the high rates of adsorption for Cd(II) and Hg(II).

  • The adsorption was followed pseudo second order kinetics for both Cd(II) and Hg(II).

  • The MPOPC was regenerated by simply washing with 0.1 M HCl solution.

Abstract

Fabrication of novel adsorbent with high surface area and high adsorption capacity is in urgent demand for water treatment, Therefore, in this study, a nanocomposite include Schiff base polymer and magnetic Fe3O4 nanoparticles was synthesized and characterized using analytical techniques including FTIR, TGA, XRD, Raman, SEM, TEM, XPS and N2 adsorption-desorption studies. The fabricated magnetic porous organic polymer (MPOP) was used as an efficient adsorbent for the removal of Cd(II) and Hg(II) from aqueous solution. The adsorption kinetic results revealed that both metal ions; Cd(II) and Hg(II) supported the pseudo-second-order adsorption kinetic model. The Langmuir isotherm model supported the adsorption over MPOP with a maximum adsorption capacity of 308.9 mg g−1 and 284.6 mg g−1 for Cd(II) and Hg(II), respectively. The thermodynamic results indicated that the adsorption of both metal ions was spontaneous and endothermic. The regeneration results suggested that the novel MPOP was a promising reusable adsorbent for the adsorption of heavy metal ions from aqueous solution.

Introduction

Water is essential substance for life. However many millions of people around the world are facing water shortage and a daily struggle to secure safe water for their basic needs. The growth of industrialization and modernization has contributed negatively impact over the clean resources of water. Several toxic inorganic and organic pollutants are coming out mainly from mining, steel, machine industries, refineries and textile industry [1,2]. Specially, heavy metals are hazardous to human health, resulting in reduced growth and development, as well as diseases including cancer, organ and nerve system damage, along with the ecosystem [[3], [4], [5]]. Therefore, it is urgent demand of researcher for developing simple efficient technology to eliminate heavy metals from wastewater aqueous solution. For that reason, a variety of techniques, such as ion exchange, chemical precipitation, membrane separation, and adsorption, have been developed for the removal of heavy metal ions from contaminated water [2,6,7]. Among these techniques, adsorption is one of the valuable methods exclusive of any side effects and several advantages like high efficiency, most effective, sludge free, insensitivity to toxic material [[8], [9], [10]]. Several adsorbents including activated carbons, clays, zeolites and polymers are widely explored for the removal of heavy metal ions [1,11,12]. Among these adsorbents, polymers, including Schiff base polymers, polypyrrole, polyesters, polymeric resins, polyaniline, and polythiophene, have been used as active materials for the adsorption of heavy metals because of their extraordinary adsorption capacity and their excellent reusability [[13], [14], [15], [16]]. The Schiff base based polymers have attracted extensive research interest in recent years as an adsorbent. Because, Schiff based polymers have extraordinary surface area with azomethine (Cdouble bondN) donor groups which have strong ion exchange capacity towards metal ions [17,18]. However, the separation procedures for Schiff base polymer based absorbents are often complicated due to their high dispersibility in water, which could led to new environmental risks [19,20]. Therefore, the separation cost and time can reduce by using magnetic process which can be easily separated using external magnetic field [21,22]. In this regard, much effort has been made to improve the formation of polymer/Fe3O4 nanocomposite with potential functional group to attract the organic/inorganic pollutants form aqueous solution. Previously, several polymers have been used as ideal matrixes for Fe3O4nanoparticles, and many of magnetic–polymeric composite materials were produced by introducing Fe3O4 nanoparticles into the polymer matrix [[23], [24], [25]]. However, the surface area of the adsorbent plays a potential role for adsorption capacity. Therefore, the objective of the present study is to develop a new prototype for adsorption of heavy metals, in this paper, we have developed a magnetic porous organic polymer (MPOP) nanocomposites using Schiff base based polymer and magnetic nanoparticles. The fabricated nanocomposite was characterized using analytical techniques including FTIR, TGA, XRD, Raman, SEM, TEM, XPS and N2 adsorption-desorption studies. The fabricated nanocomposite was used as an effective adsorbent for the removal for Cd(II) and Hg(II) from aqueous solution.

Section snippets

Materials

Analytical grade chemicals such as sodium hydroxide (NaOH), iron (II) chloride (FeCl2·6H2O), iron (III) chloride (FeCl3·6H2O), mercury (II) chloride, cadmium (II) chloride, ethanol (CH3CH2OH), hydrochloric acid (HCl, 36.5 wt%), NH3·H2O (25–28 wt%), salicylaldehyde, o-phenylenediamine, and formaldehyde were purchased from Sigma-Aldrich. Magnetic nanoparticles, Fe3O4 were fabricated according to previous reported method [5]. In a 100 mL beaker, an aqueous solution of FeCl3·6H2O and FeCl2·6H2O

Characterization

The synthetic route for the preparation of MPOP is illustrated in Scheme 1, the elemental analysis results of the MPOP revealed that the prepared nanocomposite contains 50.2% C, 14.2% N and 18% Fe. The FTIR results of the MPOP was carried out using KBr and illustrated in Fig. 1(a). The broad peaks at 3438 cm−1 and 2954–2870 cm−1 were attributed to the stretching vibration of Osingle bondH and aliphatic Csingle bondH groups (sym/asym), respectively [26]. The peaks at 1680 cm−1 and 1584 cm−1 were attributed to the Cdouble bondN

Conclusion

The MPOP nanocomposites with azomethine and phenolic surface functional groups was successfully synthesized by the reaction of Schiff base and formaldehyde in basic medium. The fabricated magnetic nanocomposites was used for the removal of Cd(II) and Hg(II) from aqueous solution. The adsorption kinetics results revealed that the adsorption of both metal ions support pseudo-second order reaction. The adsorption process was better described by Langmuir model than Freundlich and Temkin isotherm

Acknowledgement

The authors extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for funding this Research Group (RG-1435-007).

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