Elsevier

Journal of Hazardous Materials

Volume 353, 5 July 2018, Pages 166-172
Journal of Hazardous Materials

A superfast hexavalent chromium scavenger: Magnetic nanocarbon bridged nanomagnetite network with excellent recyclability

https://doi.org/10.1016/j.jhazmat.2018.03.059Get rights and content

Highlights

  • A brand new nanocarbon bridged nanomagnetite network is prepared through electrospinning of functionalized polystyrene.

  • This new framework can superfast remove Cr(VI) from polluted water within 15 s benefiting from its gridding structure.

  • The carbon nanocomposites exhibit a prominent stability and an excellent recyclability for Cr(VI) adsorption.

  • Both electrostatic attraction and network structure are responsible for this superior Cr(VI) adsorption performance.

Abstract

In this work, a nanocarbon bridged nanomagnetite network (NC-NMN) is developed through the electrospinning of epichlorohydrin functionalized polystyrene (f-PS), followed by the direct calcination of f-PS and ferric nitrate, which is capable of superfast removing hexavalent chromium (Cr(VI)) from polluted water within only 15 s benefiting from its gridding framework, with an adsorption rate constant of 1.64 g mg−1 min−1 according to the pseudo-second-order kinetics. The well-fitted Langmuir isotherm model indicates a monolayer adsorption for Cr(VI) on NC-NMN. The thermodynamic parameters including negative ΔG° and positive ΔH° demonstrate that the Cr(VI) adsorption on NC-NMN is spontaneous and endothermic. The Cr(VI) adsorption retention, which is only 3.8%, is achieved for NC-NMN after five cycles, exhibiting a prominent stability and an excellent recyclability. X-ray photoelectron spectroscopy (XPS), zeta potential and energy-filter transmission electron spectroscopy (EFTEM) results illustrate that both the electrostatic attraction and the network structure of NC-NMN are responsible for the superior Cr(VI) adsorption performance. This work intends to provide a new method for designing the novel structure materials for polluted water treatment.

Introduction

Recently, with increasing awareness of environmental sustainability in modern society, the environmental contamination especially water pollution is a common threat faced by human and wildlife. [1] Hexavalent chromium (Cr(VI)) is a major pollutant in the environment coming from the industrial and agricultural activities of human being. [2] Owing to its high mobility and toxicity, the US Environmental Protection Agency (US-EPA) has set a standard for total Cr lower than 100 μg L−1 in drinking water. [3] Thus, it’s imperatively demanded to seek efficient and economical methods to remove Cr(VI) from polluted water systems. [4,5] Among various technologies for water system clean-up, adsorption is identified as a favourable and feasible strategy for industrial applications due to its low cost, high efficiency and easy handling. [6] Even though activated carbon made from coconut wood, lignin and coke etc. has been widely served as the adsorbents for Cr(VI) adsorption due to its unique pore structures, [7] the recycle and reusage are still challenges for their applications in water purification. In addition, the adsorption performance of activated carbon is normally related to its resources and activation process used. Especially, it’s reported that the regeneration of activated carbon is commonly conducted at a high temperature around 800 °C, which brings relatively high costs. [8] Fortunately, magnetic carbon nanocomposites are emerging more recently, which combine carbon materials with magnetic nanoparticles for polluted water treatment and provide the opportunity for the nanocomposites to be easily recycled with a permanent magnet. [9] Therefore, the design and the fabrication of the new magnetic carbon nanocomposites towards heavy metal removal with fast adsorption kinetics and high adsorption capacity as well as excellent recyclability have attracted considerable attention. [10] Even polystyrene has been widely used in CD covers, lids, and containers, the placed serious white pollution to the environment requires the new technology for the reclamation of PS waste. [11]

In this work, a unique and facile procedure to synthesize a novel magnetic network consisting of nanocarbon bridged nanomagnetite (NC-NMN), fabricated through the electrospinning of epichlorohydrin functionalized polystyrene (f-PS), followed by the direct calcination of f-PS and ferric nitrate has been developed. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), scanning electron microscope (FE-SEM) and thermogravimetric analysis (TGA) have been used to characterize the chemical structures and morphologies of NC-NMN. The formation mechanism of this novel structure in NC-NMN and the optimal synthesis condition of NC-NMN is explored. Meanwhile, the as-received PS has also been electrospun and calcined via the same procedure as the fabrication of NC-NMN under the optimal conditions for comparison. A comprehensive Cr(VI) adsorption and desorption behaviours on NC-NMN has been studied in details. The results confirm that NC-NMN can superfast adsorb Cr(VI) on its surface through a monolayer process within a period of 15 s. More importantly, after five cycles of magnetic separation, this network only has 3.8% Cr(VI) adsorption retention, exhibiting an excellent recyclability. The kinetics and thermodynamics as well as Cr(VI) adsorption mechanism are evaluated. This network demonstrates a superb ability as a Cr(VI) scavenger. This work is aiming to provide a new insight for devising an original materials in environmental remediation.

Section snippets

Materials

Polystyrene (PS, Mw ≈57,700) was provided by Taizhou Suosi education equipment Co., Ltd. Ethyl acetate (CH3COOC2H5), cyclohexane (C6H12), epichlorohydrin (C3H5ClO), acetone (CH3COCH3), dichromate (K2Cr2O7), anhydrous ethanol (C2H5OH), anhydrate aluminum trichloride (AlCl3), dimethylformamide (DMF, C3H7NO), ferric nitrate (nonahydrate, Fe(NO3)3·9H2O), sodium hydroxide (NaOH), concentrated sulfuric acid (H2SO4, 98.0 wt%), hydrochloric acid (HCl, 36.0–38.0 wt%), and nitric acid (HNO3,

Synthesis and characterization of magnetic nanocarbon bridged nanomagnetite network

The NC-NMN in this work has been fabricated via an electrospinning of 25.0 wt% of epichlorohydrin functionalized polystyrene (f-PS)/dimethylform-amide (DMF) solution, followed by direct calcination of f-PS with ferric nitrate at a temperature of 500 °C under a hydrogen (5.0 vol%)/argon atmosphere. This synthesis process is illustrated in Scheme S1. The XRD patterns of NC-NMN (Fig.1(A)) and NMN (Fig. S1(A)) display strong diffraction peaks located at 18.3, 30.1, 35.4, 37.1, 43.1, 53.4, 56.9, and

Conclusions

To sum up, the magnetic network composed of nanocarbon bridged nanomagnetite (NC-NMN) with superior Cr(VI) adsorption performance is reported in this work and its formation mechanism is proposed as well. NC-NMN is competent to superfast adsorb Cr(VI) within 15 s and perform an outstanding recyclability with only 3.8% Cr(VI) adsorption retention after five cycles. The Cr(VI) adsorption process on NC-NMN is spontaneous and endothermic. The network structure of NC-NMN is devoted to this

Acknowledgements

The authors are grateful for the support and funding from the Foundation of National Natural Science Foundation of China (Nos. 51703165, 51403175 and 81400765), Shanghai Science and Technology Commission (14DZ2261100), Young Elite Scientist Sponsorship Program by CAST (YESS, No. 2016QNRC001). This work is supported by Shanghai Science and Technology Commission (14DZ2261100). This project is supported by special fund of State Key Joint Laboratory of Environment Simulation and Pollution Control

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