A facile one-pot solvothermal method to produce superparamagnetic graphene–Fe₃O₄ nanocomposite and its application in the removal of dye from aqueous solution

Abstract

A superparamagnetic graphene–Fe₃O₄ nanocomposite (G/Fe₃O₄) was synthesized by a facile one-pot solvothermal method. The nanocomposite G/Fe₃O₄ prepared by the new method was firstly used as an adsorbent to remove dye for water pollution remediation. In comparison with G/Fe₃O₄ prepared by the in situ chemical coprecipitation, the newly prepared G/Fe₃O₄ had a higher adsorption efficiency for the dye. The adsorption characteristics of the nanocomposite adsorbent were examined using the organic dye pararosaniline as the adsorbate. The adsorption kinetics, adsorption capacity of the adsorbent, and the effect of the adsorbent dosage and solution pH on the removal efficiency of pararosaniline were investigated. The adsorption capacity of G/Fe₃O₄ for pararosaniline was evaluated using the Freundlich and Langmuir adsorption isotherm models. The G/Fe₃O₄ hybrid composite can be easily manipulated in magnetic field for desired separation, leading to an easy removal of the dye from polluted water. The G/Fe₃O₄ hybrid composite would have a great potential in removing organic dyes from polluted water.

Introduction

The control of water pollution and remediation of water environment have become of increasing importance in recent years. It is well known that dyes are widely used in various fields, but their discharge into water could cause environmental pollutions since most of the dyes are harmful. Some of them are considered carcinogenic for human health and some others could reduce light penetration and photosynthesis [1]. So, it is highly desired to develop eco-friendly, simple and economical techniques for the removal of the hazardous dyes. To date, a variety of methods have been developed for the removal of dye pollutants from colored effluents, such as biological treatment [2], coagulation/flocculation [3], ozone treatment [4], chemical oxidation [5], membrane filtration [6], ion exchange [7], photocatalytic degradation [8] and adsorption [9]. Among them, adsorption technology with no chemical degradation is attractive due to its advantages of the effectiveness and economy [10]. The commonly used adsorbents primarily include activated carbons, zeolites, clays, biodegradable polymers and synthetic polymer sorbents [11]. However, such adsorbents can suffer from low adsorption capacities and separation inconveniences. Therefore, the exploration of new promising adsorbents is still desirable.

Graphene (G), discovered in 2004, is a kind of novel and interesting carbon material and has attracted tremendous attentions from both the experimental and theoretical scientific communities in recent years [12], [13], [14]. In addition to being the principle component of the most carbon based nanomaterials, graphene also exhibits extraordinary properties, such as excellent mechanical, electrical, thermal, optical properties and very high specific surface area. As the large delocalized π-electron system of G can form strong π-stacking interactions with the benzene ring [15], [16], it might be also a good candidate as an adsorbent for the adsorption of benzenoid form compounds. Recently, graphene-based composites have been applied for the extraction of polycyclic aromatic hydrocarbons [17] and pyrethroid pesticides [18] with excellent results. Li et al. reported the adsorption of methylene blue from aqueous solution by graphene [19]. Graphene oxide (GO), as a precursor for graphene preparation, has also been used as an adsorbent for the removal of tetracyclines antibiotics [20], Cu²⁺ [21] and methyl blue [22] from aqueous solutions. However, to separate the adsorbent G and GO from the aqueous solution, high speed centrifugation was needed.

Magnetic separation has been one of the promising techniques for environmental water purification because of its producing no contaminants such as flocculants and having the capability of treating large amount of wastewater within a short time [11]. Moreover, this approach is particularly desirable in industry because it can overcome many of the issues present in filtration, centrifugation or gravitation separation. In the past few years, magnetic separation technology have been widely used in the fields of separations and adsorptions [11], [23], [24], [25], [26]. The introduction of magnetic properties into G will combine the high adsorption capacity of G and the separation convenience of the magnetic materials. The preparations of graphene-based magnetic nanocomposites have been reported recently [27], [28], [29], [30]. However, the applications of G-based magnetic nanoparticles as the adsorbent for the extraction of organic pollutants are still very few in the literature [31], [32], [33], [34], [35].

In this work, a graphene-based magnetic nanocomposite (G/Fe₃O₄) was synthesized by a facile one-pot solvothermal method. Its practical application potential in the removal of dyes from aqueous solution was investigated. In order to evaluate the adsorption performance of the G/Fe₃O₄, pararosaniline was selected as model organic pollutant. The adsorption characteristics and the impact of some experimental factors were also investigated.