Fabrication of starch-graft-poly(acrylamide)/graphene oxide/hydroxyapatite nanocomposite hydrogel adsorbent for removal of malachite green dye from aqueous solution

https://doi.org/10.1016/j.ijbiomac.2017.07.182Get rights and content

Highlights

  • A novel nanocomposite hydrogel adsorbent was synthesized in the presence of graphene oxide nano sheets and nono-hydroxyapatite.

  • The adsorbent exhibited high selectivity for removal of various cationic dyes with regenerated properties.

  • The thermodynamic parameters affirm the spontaneous and feasibility nature of biosorption process.

  • The experimental adsorption data fitted better the Langmuir isotherm and pseudo-second-order kinetic models.

Abstract

This article reports the efficient removal of malachite green (MG) dye from aqueous solution using a novel polysaccharide-based nanocomposite hydrogel adsorbent (NHA). The NHAs of different compositions were prepared through a simple free radical graft copolymerization of acrylamide (AM) monomer onto starch backbones in the presence of graphene oxide (GO) nano sheets and nono-hydroxyapatite (n-HAp). The surface morphology and chemical properties of the prepared NHAs were fully examined by using FTIR, SEM, TEM, XRD and TGA.

The biocompatibility, biodegradability, porosity, water content and water uptake of the synthesized NHAs were also evaluated. The NHA was employed as bioadsorbents for the adsorption of MG dye. The temperature dependence data also revealed that MG sorption process was feasible, spontaneous and endothermic. The MG adsorption rates were described by the pseudo-second-order model. Furthermore, the adsorption isotherm data fitted well with the Langmuir isotherm model with a maximum adsorption capacity of 297 mg g−1 for MG dye. The NHA also showed an excellent regeneration capacity after five consecutive cycles of dye adsorption-desorption. According to the results, the prepared NHAs could be environment friendly and promising adsorbents for the adsorption of different cationic dyes from contaminated water.

Introduction

Hydrogels are hydrophilic crosslinked, linear or branched polymers with the ability to absorb large quantities of water and still maintain a distinct three-dimensional structure [1]. They have gained tremendous importance off late in many applications such as wound dressings [2], contact lenses [3], artificial organs [4], tissue engineering [5] and drug delivery systems [6] where water absorbance or water retention is important [7]. Hydrogels, however, do not have sufficient mechanical properties for certain applications. Recently, many efforts have been made to incorporate hard filler particles as physical cross-linkers into soft hydrogels for providing necessary and desired applications [8], [9], [10]. Hydrogels consisting of polymers and inorganic materials, which combine their synergistic benefits, have been developed to make hydrogel composites with enhanced mechanical properties [11], [12], [13]. In recent years, hydroxyapatite (HAp, [Ca10(PO4)6(OH)2]) as a major inorganic ceramic material and an essential component of the bone and teeth, is widely used to enhance the mechanical, swelling behavior, bioactive and osteoconductive properties of biopolymers [14], [15], [16]. HAp has numerous exceptional properties such as high surface area to volume ration, bioactivity, biocompatibility, osteoconductivity, availability, non-toxicity, non-immunogenicity and easy synthesizability [17], [18], [19], [20]. Therefore, HAp is being used for various applications like tissue engineering [21], dental filling material [22], [23] and water treatment [24], [25], [26].

Dyes as non-biodegradable, highly toxic and carcinogenic pollutants are present in large amounts in the effluents of many industries [27]. Therefore, it is very necessary to remove dyes from industrial effluents before discharging them into the environment. Many physical and chemical treatment processes have been used to remove dyes from wastewater, such as oxidation [28], coagulation [29], biological treatment [29] and membrane filtration [30]. Among these methods, adsorption is one of the most useful techniques for dye removal because it is a cheap, efficient, simple and flexible [31], [32], [33], [34], [35].

However, few studies on the sorption of dyes from aqueous solutions have been recently investigated using HAp-based nanocomposites [36] due to strong interaction between the HAp particles and dye molecules. On the other hand, graphite oxide (GO) with many hydrophilic oxygenated functional groups has positional applications to remove dyes from wastewater [37], [38], [39] due to its reactive and large specific surface. Therefore, loading HAp nanoparticles onto GO could combine the relatively high adsorption capacity of GO and have excellent performances in water purification. So, the main objective of the present is to fabricate a novel nano-adsorbent based on HAp and GO with improved dye sorption capacity in aqueous solutions. The effect of various reaction conditions on dye adsorption behavior as well as kinetics, thermodynamic and isothermic models of adsorption were investigated in detail.

Section snippets

Materials

Native cassava starch with an amylose contain of about 25% (white powder, from Merck), N,N′-methylene bisacrylamide (MBA, from Merck), ammonium persulfate (APS, from Fluka), disodium hydrogen phosphate (from Merck), and calcium chloride (from Merck) were of analytical grade and used without further purification. Acrylamide (AM, from Fluka) was used after crystallization in acetone. The high-purity graphite powder (99.99%) with an average particle size of 23 μm was obtained from Merck. The

Preparation of NHA

In the present work, the starch-graft-poly(acrylamide)/graphene oxide/hydroxyapatite nanocomposite with different n-Hap contents were synthesized via free radical cross-linking copolymerization reaction and in situ preparation of n-HAp particles. Scheme 1 shows a simple and general schematic illustration of the preparation of NHA product. In the first step, n-HAp was prepared within starch solution using precipitation of disodium hydrogen phosphate and calcium chloride. After adding GO

Conclusions

In this work, nono-hydroxyapatite were incorporated into starch-graft-poly(acrylamide)/graphene oxide network to form a nano-adsorbent composite for removal of malachite green dye from aqueous solutions. The maximum of dye adsorption (297 mg g−1) was achieved under the optimum conditions that found to be: agitation time 60 min, n-HAp content 3 wt%, solution pH 10 and initial dye concentration 100 mg L−1. The thermodynamic parameters exhibited that the adsorption of MG was a spontaneous, endothermic

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