Elsevier

Applied Surface Science

Volume 263, 15 December 2012, Pages 795-803
Applied Surface Science

Magnetically recoverable Ni@carbon nanocomposites: Solid-state synthesis and the application as excellent adsorbents for heavy metal ions

https://doi.org/10.1016/j.apsusc.2012.09.175Get rights and content

Abstract

Various magnetic nanocomposites with carbon-coated nickel structure (Ni@Cs) for selective adsorption of Pb2+ and Cu2+ have been prepared by a simple solid-state method, in which citric acid and nickel nitrate were selected as carbon resource and magnetic substance, respectively. Ni@C-1:5/1:10/1:20 were obtained with various mass ratios (nickel nitrate/citric acid) under the experimental conditions. FESEM and TEM results reveal that the nanocomposite particles exhibit relatively homogeneous distribution in shape/size, possessing mostly carbon-coated structure. Based on the analysis of N2 adsorption–desorption isotherm, the surface areas and pore volumes of the nanocomposites (Ni@C-1:5/1:10/1:20) are (183, 220, 149) m2 g−1 and (0.29, 0.22, 0.08) cm3 g−1, respectively. The saturation magnetization values for the Ni@Cs are as high as (11.82, 5.20 and 3.84) emu g−1 obtained by the VSM. Following, the application of the Ni@Cs for the removal of heavy metal ions (Pb2+ and Cu2+) from wastewater as potential and effective adsorbents was investigated. The results reveal the adsorbents possess more accessible active sites and good dispersibility in water, exhibiting excellent performance for selectivity of Pb2+ than that of Cu2+. The results of adsorption behavior are followed the pseudo-second-order kinetics and Freundlich model between the adsorbents and the heavy metal ions. Furthermore, the adsorbents can be recovered easily with an external magnetic field, having a higher remove efficiency after several times.

Highlights

► The use of solid-state method for Ni@Cs is effective and simple. ► Ni@Cs has higher adsorption capacity and chemical stability. ► Ni@Cs can be separated and reused by an external magnetic field.

Introduction

With the development of industry and technology, environmental pollution is becoming one of the most serious problems and having attracted widely attention all over the world, especially water pollution caused by heavy metal ions. These heavy metal ions commonly exist in the waste streams and water for life from many manufacturing units such as metal-plating facilities, electronic device manufacturing units, and tanneries [1], [2]. As the heavy metal ions have varying degrees of toxicity, which causes much severe health problems in animals and human beings [3], [4], [5]. Thus, it is necessary to remove them from the contaminated waters. Developing an efficient and economical method to achieve the purge of such toxic metal ions from wastewaters is a crucial issue. Various technologies have been employed for the removal of pollutants, including chemical precipitation [6], membrane filtration [7], ion exchange [8] and electrochemical treatment [9] methods, etc. However, these methods are limited due to the different disadvantages of expensive equipments, using of chemicals or complex technical process [10].

Adsorption is one of the effective, economical and easily regenerated ways among those methods for the of removal heavy metal from the wastewaters. In recent years, carbonaceous materials, such as activated carbon, carbon nanotubes, natural substances and bio-adsorbents [11], [12], [13], [14] have been demonstrated to be very effective adsorbents for heavy metal ions adsorption because of its large specific surface areas, abundant micropores and a series of surface functional groups [15]. However, the main shortcoming of practical application of these materials is their collection and recycling from a large volume of water. Hence, finding a route to realize the double-function purposes of heavy metal pollution control and cyclic utilization is indispensible. Recently, magnetic composites with nanometer size have been promising subjects applied in the area of adsorbents owing to their interesting electrical, optical magnetism and chemical properties [16], [17]. Moreover, the nanocomposites can not only remove kinds of heavy metal ions quickly from the polluted water, but also can be easily separated by external magnetic field due to the presence of magnetism. These properties make them turn into promising adsorbents in the area of metal ions adsorption from aqueous solutions [18], [19], [20]. Meanwhile, the preparation of magnetic nanocomposites with a larger surface area and higher saturation magnetization intensity by a simple and inexpensive method still is a considerable issue.

Ning et al. [21] synthesized the carbon-encapsulated ferronickel nanoparticles by a detonation method. Yu and Qiu [22] and Ni et al. [23] reported the preparations of carbon-encapsulated Co and Ni nanoparticles and honeycomb-like Ni@C composite nanostructures using a catalytic carbonization method and a two-step solution strategy, respectively. However, the preparations of Ni nanospheres and the complex steps were obviously presented to the references. Herein, we has demonstrated a simple, economical and environmentally benign solid-state synthetic method for preparing magnetic carbon-coated nickel nanocomposites (Ni@Cs), which is further applied as adsorption agents for waste water purification. The influences of uptake capacity of Ni@Cs according to the different contact times and initial concentrations were investigated. Furthermore, the adsorption isotherms, kinetics and recycle curves were also studied in order to understand the adsorption mechanism between the synthesized Ni@Cs and the heavy metal ions. Experimental results reveal that the present Ni@Cs exhibit good capacities for selective adsorption of Pb2+ and Cu2+ ions, which can be easily separated from water, also holding the high recovery efficiency after several times.

Section snippets

Experimental

Sodium hydroxide (NaOH), nitric acid monohydrate (C6H8O7·H2O), absolute ethyl alcohol (C2H5OH), lead nitrate (Pb(NO3)2), copper nitrate trihydrate (Cu(NO3)2·3H2O), nickel nitrate hexahydrate (Ni(NO3)2·6H2O). All the analytical chemicals were purchased from Sinopharm Chemical Reagent (Shanghai) Co. Ltd. and used as received without further purification.

Characterization of nanocomposites

The crystalline structure of the Ni@C-1:5 nanocomposite was determined by powder X-ray diffraction (XRD) at different temperature (400 °C, 600 °C and 800 °C) and employed a scan from 10° to 70° (2θ) as shown in Fig. 1. At the low temperature (400 °C), several diffraction peaks are observed from the XRD pattern in Fig. 1a corresponding to the cubic phase NiO (JCPDS card no. 47-1049), which illustrates an incomplete reduction reaction happening to the nickel(II) nitrate. But two characteristic peaks

Conclusions

In summary, magnetically separable Ni@Cs nanocomposites with larger surface areas were synthesized by an effective and simple solid-state method. The Ni@Cs were used as potential and intriguing adsorbents with an higher adsorption capacity and chemical stability for the removal of heavy metal ions (Pb2+ and Cu2+) from wastewater in a very short time. The adsorption processes were investigated by the kinetics and adsorption isotherms. The results show that the adsorption of metal ions on the

Acknowledgment

This work was supported by the Science and Technology Project of Land and Resources of Anhui Province (2010-g-19 and 2011-k-11).

References (31)

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