Elsevier

Applied Catalysis A: General

Volume 544, 25 August 2017, Pages 10-20
Applied Catalysis A: General

Efficient transformation in characteristics of cations supported-reduced graphene oxide nanocomposites for the destruction of trichloroethane

https://doi.org/10.1016/j.apcata.2017.07.007Get rights and content

Highlights

  • Novel heterogeneous graphene supported iron and iron-copper nanocomposites were synthesized.

  • Solvothermal technique showed better catalytic performance compared to chemical reduction.

  • Aggregation was significantly eliminated in ST synthesized composite.

  • The surface area of the ST composites increased significantly.

  • Significantly improved efficiency with lower catalyst dosage.

Abstract

Experiments were conducted to investigate the use of graphene-oxide supported metallic nanocomposites for improving the degradation of trichloroethane (TCA) by sodium percarbonate (SPC). Two methods of production, chemical reduction (CR) and solvo-thermal (ST), were tested for preparation of single (Fe) and binary (Fe-Cu) nanocomposites supported by reduced graphene oxide (rGO). A variety of analytical techniques including N2 adsorption Brunauer-Emmett-Teller (BET), x-ray diffraction (XRD), fourier-transfrom infrared spectroscopy (FTIR), and transmisison electron microscopy (TEM) were applied to characterize the physicochemical and microstructural properties of the synthesized nanocomposites. The characterization indicated that the CR method produced nanocomposites that comprised only mesoporous structure. Conversely, both micro and mesoporous structures were present for samples produced with the ST method. The synthesized single and bimetallic composites produced from the ST method showed higher surface areas, i.e. 93.6 m2/g and 119.2 m2/g as compared to the ones synthesized via the CR method, i.e. 13.8 m2/g and 38.0 m2/g respectively. The results of FTIR and XRD analyses confirmed that the ST method produced highly crystalline nanocomposites. SEM and TEM analysis validated that metallic particles with definite morphology well distributed on the surface of rGO. X-ray photoelectron spectroscopy (XPS) analysis confirmed the homogeneity nanocomposites and occurrence of variation in copper oxidation states during degradation process. EDS mapping validate the homogeneous distribution of Cu and Fe at reduced graphene oxide surface. The Fe-Cu/rGO (ST) activated SPC system effectively degraded TCA (92%) in 2.5 h at low nanocomposite dose compared to the Fe-Cu/rGO (CR) and only Fe, for which the maximum degradation efficiencies achieved were 81% and 34%. In conclusion, excellent catalytic characteristics were observed for the ST-synthesized single and bimetallic (Fe/rGO, Fe-Cu/rGO) catalysts. These catalysts were successful in improving the degradation of TCA via activated SPC.

Introduction

Trichloroethane (TCA) has been extensively used for a wide variety of industrial purposes including metal degreasing, textile manufacturing, and adhesive production, and it is identified as a major groundwater pollutant. The presence of TCA is of particular concern due to its recalcitrant properties and risk to human health from long-term exposures. Among various groundwater remediation techniques, advanced oxidation processes (AOP) are considered as one of the most effective for treating recalcitrant contaminants [1]. The Fenton-based AOP is a favorable and efficient method for the treatment of a variety of organic compounds, such as organic solvents, pesticides, personal care products, pharmaceuticals, and synthetic dyes [2]. Recently, sodium percarbonate (SPC) has achieved considerable attention as an efficient, selective, and environmentally friendly reagent for Fenton-based AOP [3], [4].

The conventional homogeneous Fenton process destroys the organic contaminants by generating highly reactive species from the reaction of Fe2+/Fe3+ with hydrogen peroxide (H2O2). However, there are several drawbacks such as: (i) production of large quantities of iron salts as effluent, (ii) additional steps required to separate the sludge, (iii) generation of strong acidic conditions that inhibits the catalyst activity [5]. To address these issues, heterogeneous-catalysis technology is being investigated as a substitute for homogeneous-reaction based AOP with desire to provide extended stability over a wider pH range and improve recycling and reuse ability [6]. In previous studies, several organic pollutants have been treated by Fenton-based AOP using nano zero valent iron (nZVI) and iron minerals in heterogeneous catalysis to activate H2O2 for the generation of reactive hydroxyl radicals (OHradical dot) [7], [8], [9], [10]. For example, Fe-pillared clay was studied as a heterogeneous composite for the effective degradation of cinnamic acid [11]. Doong and Hussain et al. studied the effectiveness of nanoscale iron as a reductant for the dechlorination of organic solvents [12], [13].

Concerted efforts have been made to enhance the activity of heterogeneous Fenton catalysts by introducing a second metal. These bimetallic nanocomposites have been also used for the degradation of organic pollutants in groundwater [14]. Luadthong et al. used copper-ferrite/spinal-oxide catalyst for methnolysis of palm oil [15]. Porous Fe-Ni oxide nano sheets have been studied as a catalyst for groundwater contaminant treatment [16]. Nano zero valent Fe/Cu have been used by Zhu et al. for the remediation of chromium in soil [17]. Doping iron oxides with metallic elements, e.g. Ce, Ti, Co, Zr and Mn, to prepare bimetallic catalysts is a current focus of research in Fenton chemistry [18].

One limitation assocaited with the use of nanocomposites is that these nanoparticles tend to agglomerate and aggregate, which can lead to deterioration of the catalyst performance [19]. To address this problem, the metallic particles can be distributed on solid supports. Carbon based materials such as graphene could be an alternative solid support since the graphene has large surface area with high delocalized π-stacking interaction that could immobilize nanoparticles and could enhance the catalytic activity [20]. In addition, the use of carbon materials as a support is promising owing to their excellent stability under both acidic and alkaline conditions.

To the best of our knowledge, the degradation of TCA using single and bimetallic catalyst supported on rGO, and the comparison of their effectiveness via different synthesis routes have not yet been reported. In the present study, the single and bimetallic (Fe and Fe-Cu) heterogeneous nanocomposites supported on rGO were synthesized. TCA was selected as a model chlorinated organic compound to investigate the catalytic activity of the synthesized composites. Sodium percarbonate (SPC) was used as the oxidant for the TCA degradation. The aim of this work is to delineate the effects of synthesis methods on the characteristics and activity of the heterogeneous composites, and to determine their overll effeciveness in improving Fenton-based AOP.

Section snippets

Materials and chemicals

The TCA and the graphite powder were purchased from Aladdin Corporation (Shanghai, China). The potassium permanganate (KMnO4), hydrochloric acid (HCl, 37%), sulfuric acid (H2SO4, 99%), ethylene glycol (EG), sodium acetate anhydride (NaAc), hydrogen peroxide (H2O2, 30% wt.), and n-hexane were obtained from Shanghai Lingfeng Reagent Co. Ltd. China. The sodium borohydride (NaBH4, 99.5%), sodium percarbonate (SPC, 98%), ferrous sulfate hydrate (FeSO4·7H2O, 99%), sodium nitrate (NaNO3, 98%), ethanol

XRD analysis

The composites were analyzed using x-ray diffraction (XRD) as shown in Fig. 1. The sharp and broadest peak at 2Ɵ of 10.9° clearly indicates that the graphite powder totally exfoliated to GO. The diffraction peak disappeared and a new broad peak appeared at approxiamtely 24°, which shows reduction of GO by EG or NaBH4 [29], [30]. The characteristic peak of monoclinic tenorite CuO was observed at 35.49° (0 0 2) in the case of Fe-Cu/rGO (CR) and Fe-Cu/rGO (ST) catalysts, in agreement with JCPDS

Conclusions

In this study, single (Fe) and bimetallic (Fe-Cu) nanocomposite catalysts supported on rGO were tested for SPC-based TCA degradation. The materials were produced with two methods, chemical reduction and solvo-thermal. The ST approach produced Fe/rGO and Fe-Cu/rGO catalysts with larger specific surface areas and high particle dispersion, exhibiting higher catalytic activity for TCA degradation compared to the catalysts prepared by the CR method.

The eminent appearance of peaks in XRD analysis of

Acknowledgements

This study was financially supported by grants from the National Natural Science Foundation of China (No.s. 41373094 and 51208199). One of the authors would like to thank KKS-the Knowledge Foundation of Sweden and industrial partners (Mälarenergi and Eskilstuna Energi och Miljö) for their funding. The contributions of Mark Brusseau were supported by the NIEHS Superfund Research Program (P42 ES04940) and by SERDP (ER-2302).

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