A novel polylysine–resorcinol base γ-alumina nanotube hybrid material for effective adsorption/preconcentration of cadmium from various matrices

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Highlights

  • Alumina nanotube was synthesized by hydrothermal route.

  • Polylysine–resorcinol polymer was synthesized on alumina surface.

  • Alumina polymer nanocomposite was used for cadmium adsorption.

  • Response surface methodology was used for optimizing effective parameters.

Abstract

Polylysine–resorcinol coated alumina nanotube has been synthesized based on Mannich reaction. Synthetic polymer has been obtained using lysine and resorcinol as monomer and p-formaldehyde as linker by condensation reaction. The nanosorbent was employed for cadmium adsorption from aqueous samples. Effective parameters on sorption process have been optimized with Box–Behnken design (BBD). Equilibrium time was 11 min as well as adsorption capacity was 220 mg g−1. Regeneration of the sorbent was performed with HNO3 solution (0.5 mol L−1). The accuracy of the method was evaluated by determination of cadmium in various real samples.

Graphical abstract

Polylysine–alumina nanotube was employed for cadmium adsorption.

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Introduction

Pollution of water resources by heavy metal is a common environmental problem in today’s communities, that will destroy the living surrounding. Numerous metals such as mercury, lead, cadmium, cobalt and nickel are known to be highly toxic because of their non-biodegradable and carcinogenic nature [1], [2]. Cadmium like other heavy metals can be introduced into surface waters by effluents from mining, metallurgical alloying, electroplating, photography, production of alkaline batteries and agricultural activities contain high concentrations of trace elements [3], [4]. Prolonged exposure to elevated level of Cd could cause damage to cardiovascular system, bone and kidney [5]. The WHO has stipulated that the maximum concentrations of Cd in water for human consumption should not exceed 10 μg L−1 [6]. Therefore, many efforts have been made to purify wastewaters from cadmium pollution, among which the adsorption has an inevitable place [7]. Adsorption technique is of special advantages such as low cost, simplicity of operation, low generation of residues and recycling of the adsorbent [8]. Till now, many adsorbents have been used to remove metal ions, especially cadmium, including biomaterials, carbon, zeolite, kaolinite, activated alumina, metal oxide, and etc. [9], [10], [11], [12], [13], [14]. However, these adsorbents have low adsorption capacity and are not highly efficient for metal ion removal. Therefore, it is quite necessary to develop new promising adsorbents.

It is known that, the unique properties of nanosorbents are providing highly efficient and cost-effective approaches for the removal of pollutants. In fact, nanoparticles exhibit unprecedented opportunities for metallic pollutant manipulation especially due to higher surface area and greater active sites [15], [16]. Besides, by using nanomaterials the adsorption process is rapid and the operation is simple. So there is a growing interest in the application of nanoparticles as adsorbents [17]. Among various nanomaterials, nano alumina is one of the most important ceramic materials widely used for microelectronic, membrane applications and water and wastewater treatment. But, some metal cations are poorly adsorbed on it hence, surface modification of the nanoparticles with certain functional groups containing some donor atoms is necessary [18], [19].

The use of inorganic–organic hybrid materials is regarded as one of the most effective adsorbent for the abatement of heavy metal ions from aqueous phase. Among organic–inorganic hybrid materials, polymeric composites, which can be applied in the field of desalination technology, are expected to display some of major merits such as structural flexibility, mechanical stability, rigidity, high thermal stability and potential applications in harsh environmental conditions [20], [21] as well as present relatively high metal ion adsorption capacities due to the synergism between the constituents [22], [23]. Several routes to synthesize polymer nanocomposite as well as the applicability of them for removing heavy metals from aqueous solutions have already been proposed [24], [25], [26], [27]. Considering the merits of aforementioned polymeric adsorbents for heavy metal ions removal from aqueous phase, we have synthesized novel polylysine–resorcinol hybridized alumina nanotube based on Mannich reaction which takes place with a variety of substances having reactive hydrogen atoms, such as phenols with formaldehyde and a primary or secondary amine [28]. The introduction of nitrogen-containing groups can increase the heavy metal adsorption capability due to the nitrogen-containing bases favored to chelating with metallic ions. Lysine which apply in biosynthesis of proteins were used as amine source hence it can be noted that the final nanocomposite is a biocompatible green material. To the best of our knowledge, the research on the synthesis of polylysine–alumina composite has not been forthcoming. Therefore, in this paper, Mannich base polymer coated alumina nanotube was synthesized and applied for heavy metal adsorption. After immobilization of polymer at the surface of alumina, target ions are not only removed by adsorption but it could be removed by a chemical-bonding phenomenon on the newly material. The sorbent was used for cadmium adsorption and preconcentration from water and food samples moreover, effective parameters on cadmium adsorption were optimized by response surface methodology (RSM).

Section snippets

Materials and methods

Al(NO3)3.9H2O, urea, cetyltrimethylammonium bromide (CTAB), l-lysine, resorcinol, para-formaldehyde and aminopropyl-triethoxysilane (APTES) were purchased from Merck (Darmstadt, Germany). Ethanol was supplied from Bidestan Company (Qazvin, Iran). Standard solutions of Cd(II) ions (1000 mg L−1) were prepared by dissolving of Cd(NO3)2 salt in distilled water. The pH adjustment was performed with 0.1 mol L−1 of NH3 and HNO3 solutions.

The prepared nanomaterials were characterized by energy dispersive

Characterization

EDX analysis is a useful nondestructive technique which exhibits some qualitative and quantative elemental information. In other words, back scattered electrons as well as X-rays which are generated by primary electron bombardment can be correlated to the atomic number of the element within the sampling volume and gives quantitative elemental information. Typical EDX spectra correspond to the elements in nanocomposite structure and quantitative values of them are shown at Fig. 1a. As can be

Conclusions

In this work polylysine–resorcinol wrapped γ-alumina nanotube was synthesized by one step Mannich based condensation reaction. The nanocomposite was demonstrated as a novel system for cadmium adsorption and preconcentration. Response surface methodology was employed to investigate effective adsorption parameters and their interaction. Result showed that solution pH is a main factor which affects cadmium adsorption behavior. Adsorption of the target ions is fast as well as the sorbent showed

Acknowledgment

Support of this investigation by the Research Council of the University of Tehran through grant is gratefully acknowledged.

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