Regular Article
Efficient removal of methylene blue from aqueous solutions using magnetic graphene oxide modified zeolite

https://doi.org/10.1016/j.jcis.2019.02.030Get rights and content

Abstract

In this study, magnetic graphene oxide modified zeolite (Cu-Z-GO-M) composites with two different ratios of GO to zeolite (named Cu-Z-GO-M 1:2 and Cu-Z-GO-M 1:1) were synthesized by solid-state dispersion (SSD) method. The properties of zeolite-based composites were characterized by SEM, XRD, FTIR, XPS, and magnetization curves. In order to understand the pollutant removal performance of the as-prepared composites, methylene blue (MB) was used as the target pollutant in adsorption experiments. The removal efficiency of MB onto Cu-Z-GO-M composite was enhanced obviously with pH > 9. The adsorption capacities of MB onto Cu-Z-GO-M 1:1 were 82.147, 89.315, 97.346 mg/g at 298, 308, and 318 K, respectively. The removal ability of MB increased with the increase of GO content in modified composites. The adsorption behavior can be well described using a pseudo-second-order kinetic and Freundlich isotherm model. The thermodynamic analysis indicated the MB adsorption by Cu-Z-GO-M was a spontaneous and endothermic reaction. The results showed that the prepared Cu-Z-GO-M composite could be a promising adsorbent with good adsorption capacity and reusability for MB removal from wastewater.

Introduction

Dyes effluent discharged from textile, paper-making, printing, food additives, leather, cosmetic and other industries have caused serious environmental pollution [1], [2]. Nowadays, dye pollution has attracted great attention over the world, due to its toxicity to human being as well as the fauna and flora even at a low concentration [3]. The toxic effects of dyes effluent on human being will cause allergy, cutitis, skin stimulus, and even cancer [4], [5]. Therefore, the waste water containing dyes must be treated before discharging into the natural water bodies. Various approaches including precipitation [6], ion exchange [7], photocatalytic degradation [8], [9], biological oxidation [10], [11], adsorption [12], [13], membrane filtration [14] and electrochemical function have been applied to remove dyes from wastewater. Among these methods, adsorption has been regarded as a most commonly used method for water purification, because of its low cost, easy operation and flexibility [15].

Zeolite, a common mineral absorbent with adequate deposits, low cost, and organophilic cations [16], has been widely used for dye adsorption from wastewater. For example, the natural zeolite has been reported in many investigations for dye removal [17], [18], [19]. However, the lower adsorption capacity of natural zeolite limits its widely application as an absorbent. In order to improve its adsorption performance, various modified zeolite composites have been fabricated. Jin et al. [18] reported that the adsorption capacity of SDBS-modified zeolite was twice larger than that of original zeolite towards anionic orange II. Erol Alver et al. [20] also reported that the adsorption capacities of anionic dyes (reactive red 239 and reactive blue 250) onto zeolite with hexamethylenediamine modification were up to 28.57 and 17.63 mg/g at 293 K, respectively. Although, these reports showed that modified zeolites had higher adsorption capacity as compared to that of the unmodified zeolite, those modification approaches still could not obtain a satisfactory adsorption performance. Therefore, seeking an appropriate modification method to functionalize zeolite and improve its performance is still required.

Graphene oxide (GO), a typical product of graphene, has a particular structure of a two-dimensional (2D) honeycomb lattice with a single layer of sp2 carbon atoms [21], [22], [23]. To date, GO has been applied as an efficient adsorbent for pollutant removal owing to its unique structure and physicochemical properties, such as a large surface area, abundant oxygen-containing functional groups [24], [25] and excellent physicochemical abilities [26], [27]. However, it is difficult to separate GO from aqueous solution due to its excellent hydrophilicity. Therefore, the design of solid hybrid GO-based materials is a good method to improve its application in pollutants removal. Importantly, the pollutant removal performance of raw materials could be enhanced after its modification [28], [29]. To our knowledge, the research on the application of GO modified zeolite composite for cationic dye removal is limited. Thus, it is worth to explore the dye removal by GO modified zeolite composite. In order to make the synthesis of hybrid successfully, Cu2+ ions were used as a coordination cation to bond zeolite to GO sheets [30]. Nevertheless, composites modified by GO are difficult to collect after reaction. Magnetic separation technology has been widely applied for the solid-liquid separation. Herein, MnFe2O4 with short synthesis time, high crystallinity and low cost was introduced onto Cu-Zeolite/GO composites to make it possible to reuse the materials [31], which can be conveniently separated by an external magnet.

In this study, magnetic Cu-Zeolite/GO composites were fabricated using a facile method. In order to investigate their pollutant removal performance, methylene blue (MB), a typical cationic dye was selected as a model pollutant for adsorption experiments. A series of experiments were carried out to determine the influence of various factors such as pH, time, and temperature on dyes adsorption by magnetic Cu-Zeolite/GO composite.

Section snippets

Materials

GO was prepared according to the modified Hummer method [32], [33]. Artificial zeolite (Na2O·Al2O3·xSiO2·yH2O) was obtained from Sinopharm chemical Reagent Co., Ltd., Ethanol, CuSO4·5H2O, FeCl3·6H2O, MnSO4·H2O, MB, and all other chemicals used were analytical reagent grade and purchased from Sinopharm chemical Reagent Co., Ltd without further purification. Deionized water was used in all experiments.

Synthesis of MnFe2O4 nanoparticles

Magnetic nanoparticles were synthesized by the coprecipitation method [34], [35], [36], [37].

Characterizations of samples

The morphology of raw zeolite, GO and Cu-Z-GO-M samples was observed by SEM micrograph (Fig. 1). As shown in Fig. 1a, the crystal surface of zeolite is obvious. The typical properties of GO image, such as the smooth surface, the wrinkled ripples and a thinner layer are also observed (Fig. 1b) [39]. Additionally, Cu-Zeolite is more densely distributed on GO sheets in Fig. 1c comparing with that in Fig. 1d. The rough morphology of Cu-Z-GO-M sample (1:1) could provide more adsorption sites owing

Conclusions

Based on the previously published works [18], [19], [20], [28], [29], [30], this work demonstrated that the magnetic GO modified zeolite samples could be synthesized to facilitate surface characterizations and adsorption capacity towards MB. The introduction of GO to zeolite could enhance the removal ability of MB comparing with zeolite undecorated, which was attributed to the incremental surface area and active sites. The adsorption is better described by pseudo-second-order kinetic and

Acknowledgements

This study was financially supported by the National Natural Science Foundation of China (51579099, 51521006 and 51879105), Innovative Research Team in University (IRT-13R17), and the Hunan Provincial Innovation Foundation for Postgraduate (CX2016B134).

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