Elsevier

Applied Surface Science

Volume 359, 30 December 2015, Pages 602-608
Applied Surface Science

Synthesis and characterization of organic–inorganic core–shell structure nanocomposite and application for Zn ions removal from aqueous solution in a fixed-bed column

https://doi.org/10.1016/j.apsusc.2015.10.143Get rights and content

Highlights

  • The γ-Fe2O3 nanoparticles were prepared in one step using ultrasonic radiation and coated by polyrhodanine.

  • Nanocomposite synthesized with core average diameter of 15 nm and polyrhodanine as shell with thickness of 1.5 nm

  • Application of products was investigated to separate zinc ions from aqueous solution in a fixed-bed column.

  • The Adams–Bohart, BDST, Thomas and Yoon–Nelson models used to predict model parameters.

  • The models were nearly in good agreement with the experimental data.

Abstract

An organic–inorganic core/shell structure, γ-Fe2O3/polyrhodanine nanocomposite with γ-Fe2O3 nanoparticle as core with average diameter of 15 nm and polyrhodanine as shell with thickness of 1.5 nm, has been synthesized via chemical oxidation polymerization and applied for adsorption of Zn ions from aqueous solution in a fixed-bed column. The properties of nanocomposite were characterized with transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometer (VSM). The performance of the column was assessed under variable bed heights (10, 15 and 20 cm) and influent Zn concentrations (50, 100 and 150 ppm) at a constant flow rate (0.5 mL/min). The results demonstrated that the breakthrough curves are S-shaped and the breakthrough time increases with increasing bed height and decreases with increasing influent concentration. Moreover, the dynamics of the adsorption process were evaluated by using Adams–Bohart, bed depth service time (BDST), Thomas and Yoon–Nelson kinetic models. The models were nearly in good agreement with the experimental data.

Introduction

Heavy metal ion pollution is currently of great concern due to increasing awareness of the potentially hazardous effects of elevated levels of these materials in the environment [1]. Zinc is one of the most important pollutants in surface and ground water [2]. Although, Zinc is considered as an essential trace element for life, at high concentrations it could be damaging to human health. Zinc is widely used in many important industrial applications such as dry batteries, electroplating industry, insecticides, foundry, metallurgy, newsprint paper production and inorganic pigments industry [3], [4]. Since, Zn is not biodegradable and accumulates in living organisms causing diseases and other toxic effects, the recovery of Zn and other heavy metals from contaminated water is of environmental and agricultural importance [5]. Various treatment processes for the removal of metal ions including adsorption [6], [7], precipitation [8], ion exchange [9], membrane processes [10], [11], etc., have been proposed. Among them, adsorption is found to be cheap, effective and easy to adapt and has been confirmed as one of the most promising technologies for removing heavy metals from wastewaters [12]. Magnetic nanoparticles, especially maghemite as an efficient adsorbent have been receiving continuous attention because of their high adsorption capacity regarding their high surface area, low cost, environmental sustainability, easy separation and easy recovery via an external magnetic field [13], [14]. On the other hand, there are major limitations in the application of magnetic nanoparticles originating from the magnetically induced aggregation, surface oxidation, and deficiency of functional groups [15]. Aggregation reduces their high surface area to volume ratio and subsequently reduces effectiveness [16]. Inorganic nanoparticles coated with conducting polymer that form core/shell structured materials has been demonstrated to be an effective strategy to enhance the stability of composites and widen the applications because of the strong electronic interaction between the inorganic core and polymer shell [17]. The polymer shell provides a flexible functional group to magnetic nanoparticles and protects them from surface oxidation and aggregation, while increasing their stability [18]. The main idea in a composite is to integrate several component materials and their properties in a single material [19]. Conductive polymers have been the center of attention in the last several years, due to variety of their applications. Among the conductive polymers, polyrhodanine has attracted considerable attention in various application fields such as anticorrosion [20], antibacterial [21], and antihistaminic agents [22]. In addition, they can be used for detecting or adsorbing metal ions because the Rhodanine monomeric unit has metal-binding functional groups [23], [24]. Furthermore, the appropriate choice of polymer host with specific functional groups may even lead to enhancing the properties of nanoparticles [16]. Many polymerization methods have been applied to prepare magnetic polymer nanocomposites, for example, Pickering suspension polymerization [25], microemulsion polymerization [26], in situ polymerization and oxidative polymerization [27], [28].

The two main methods of synthesis of the polymer supported nanoparticles are ex situ and in situ method. In this work, the ex situ method is applied for synthesis of the polymer supported nanoparticles. Ex situ method of synthesis can be obtained by first synthesizing the inorganic nanoparticles and then dispersing them in a polymer solution or a three-dimensional matrix. This method of synthesis is a popular one because it does not set limitation on the nature of nanoparticles and the host polymer which is used [16].

In this study, the γ-Fe2O3/polyrhodanine core–shell structure nanocomposite was fabricated by chemical oxidation polymerization [18]. At first, the synthesis of maghemite (γ-Fe2O3) nanoparticles was carried out in an ultrasonic bath in one step via chemical precipitation [29], then the polymer shell coated on the surface of maghemite nanoparticles was synthesized using FeCl3 as an oxidant. Eventually, the potential of the synthesized nanocomposite was studied in a fixed-bed column at different bed heights and influent Zn ion concentrations. There are few studies reporting on employing the maghemite/polyrhodanine nanocomposite as an adsorbent for removing metals and other pollutant from water in batch mode, this is one of the first studies on Zn ion separation from aqueous solution by maghemite/polyrhodanine nanocomposite in the fixed-bed column. Noticeably, to scale up a process, continuous flow fixed-bed column investigations are essential. Moreover, to analyze the breakthrough curves for Zn adsorption, Adams–Bohart, BDST, Thomas and Yoon–Nelson models were used.

Section snippets

Materials

The chemical materials used for fabrication of γ-Fe2O3 nanoparticles and γ-Fe2O3/polyrhodanine nanocomposite were Iron(II) Chloride Tetra hydrate (FeCl2.4H2O), Iron(III) Chloride FeCl3, Rhodanine (C3H3NOS2), ammonium hydroxide (NH4OH), Ethanol (C2H5OH) and Hydrochloric acid (HCl) from Merck Co. All these chemicals were used as received without any further Purification. Distilled water was used throughout the experiment.

Instrumentation

The morphology and nano-structure of the γ-Fe2O3 core–shell nanocomposite

Particle size and morphology of nanocomposite

TEM image of nanocomposite is shown in Fig. 2. From Fig. 2(a), it can be obviously seen that the synthesized nanocomposite had a core–shell structure which surface of γ-Fe2O3 coated with a thin layer of polyrhodanine. The dark color in the center is attributed to γ-Fe2O3 and the light colored around the center can be attributed to polyrhodanine. The average size of γ-Fe2O3/polyrhodanine core/shell nanoparticles is about 18 nm The maghemite core diameter is about 15 nm and thickness of the polymer

Conclusions

In summary, the maghemite nanoparticles were successfully synthesized by chemical precipitation method using ultrasonic radiation and γ-Fe2O3/polyrhodanine core–shell structure nanocomposite, via ex situ chemical oxidation polymerization. The characterization of the obtained products shows that nanoparticles are spherical, monodisperse and have an average core diameter of around 15 nm and shell thickness of 1.5 nm. The structural characterization of magnetic nanoparticles and nanocomposite was

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