Elsevier

Carbon

Volume 68, March 2014, Pages 210-220
Carbon

Solid-state dechlorination pathway for the synthesis of few layered functionalized carbon nanosheets and their greenhouse gas adsorptivity over CO and N2

https://doi.org/10.1016/j.carbon.2013.10.081Get rights and content

Abstract

A simple solid-state dechlorination route has been demonstrated to synthesize few layered functionalized carbon nanosheets (FCNS) utilizing hexachloroethane as carbon source and copper as reducing agent under the autogenic pressure at 300 °C. The obtained FCNS possesses the sheet thickness of 6–12 nm as analyzed by transmission electron microscopy. The particle nature of the FCNS provides the excess porosity having the surface area 836 m2/g. The equilibrium gas adsorption study of FCNS for greenhouse gases (CO2 and CH4), toxic gas (CO) and light gas (N2) showed the maximum adsorption capacity for CO2 (2.95 mmol/g; at 288 K) with maximum capacity selectivity of 10.1 at 318 K. The very strong adsorbate–adsorbent interaction was observed in case of CO compare to other gases resulted in higher heat of adsorption for CO. The gas adsorption and FT-IR study showed that the interaction of CO with copper present in minute quantities in FCNS improves the CO adsorption due to π complexation. The FCNS obtained under present methodology showed the very high equilibrium selectivity for CO over N2 (197) followed by CH4 (61) and CO2 (7.3) at 288 K.

Introduction

Carbon nanosheets (CNS) is a two-dimensional carbon nanostructure of stacked graphene sheets with few nanometers thickness [1], [2]. CNS is one of the interesting material in the carbon family due to its potential applicability in various fields such as gas storage [3], catalyst support [4], nano-electronics [5], electrode [6] and adsorption [7] etc. The chemical vapor deposition method has been well elaborated for the synthesis of CNS [8], [9], whereas different synthesis methods such as close-packing assembly [10], carbonization [11], catalytic thermal pyrolysis [12] and template-like method [13] have also been reported. Most of the synthesis methods of CNS included the use of graphite as a carbon source [14]. Very few methods utilized different carbon sources for the synthesis of graphene like CNS, but the use of the advanced techniques and low yield are the major disadvantages associated with it. Ando et al. [15] have reported the synthesis of petal-like graphite sheets using the hydrogen arc discharge method. The dechlorination of chloro-hydrocarbon using metal catalysts under solvothermal condition is one of the promising and easy routes for the synthesis of different carbon nanostructures [16]. Qian et al. [17] and Xiong et al. [18] synthesized carbon nanotubes with claw-like end and carbon hollow spheres by the dechlorination of halocarbon using metal as reducing agent, respectively. Similarly, Kuang et al. [19] reported the low temperature solvothermal synthesis of crumpled CNS using metallic potassium and methane tetrachloride at 60 °C.

The drastic increase in the emission of greenhouse gases mainly CO2, due to industrial exhaust and burning of fossil fuel creates the environmental hazard like global warming [20], [21]. The direct emission of carbon monoxide into the atmosphere is restricted because of its high toxicity. Zeolite and activated carbon are the well known commercial adsorbents for the gas storage and separation [22], [23], [24], [25]. Clay [26], metal organic framework [27], [28] and the porous silica materials [29] have also been developed and studied as adsorbent for the CO2 sequestration. Recently, our group reported the horn shaped carbon nanotubes synthesized using copper catalyzed dechlorination of tetrachloroethylene as potential adsorbent for greenhouse gases [30].

Herein we described the solid-state dechlorination of hexachloroethane using copper to few layered functionalized CNS (FCNS) under autogenic pressure and its greenhouse gas adsorptivity (carbon dioxide and methane) over carbon monoxide and nitrogen at different temperatures.

Section snippets

Synthesis of FCNS

All chemicals were procured from S.D. Fine Chem. India and used as received. Synthesis of FCNS was carried by heating the SS autoclave (50 ml capacity) containing hexachloroethane (6.2 g) and copper powder (5 g), at 300 °C for 5 h. After cooling the autoclave to room temperature, the obtained black color product was treated with 500 ml of 1:1 HNO3 aqueous solution for 24 h under continuous stirring. The product was recovered by filtration, washed with deionized water till free from chloride ions (AgNO3

FCNS formation

The structural arrangement or morphology of the obtained carbon product investigated under SEM depicts an agglomerated form of FCNS. Fig. 1 also indicated the particle nature of FCNS which provides the additional porosity to it. TEM analysis (Fig. 2a) also reflects the sheets like-arrangement of the synthesized carbon product with randomly arranged wrinkled structure. The dark edges appear in the TEM image (Fig. 2a) are the folded region of the FCNS with varying edge thickness of 6–12 nm. This

Conclusion

Few layered FCNS was successfully synthesized using hexachloroethane as carbon source and copper powder as reducing agent under autogenic pressurized condition. The obtained CNS showed the varying layer thickness of 6–12 nm (as characterized by TEM analysis) and possesses the surface and textural oxygen; and chlorine functionality. The equilibrium gas adsorption study of greenhouse gases (CO2 and CH4), toxic gas (CO) and light gas (N2) showed that the CNS possesses the high adsorption capacity

Acknowledgments

The authors are grateful to Council of Scientific and Industrial Research (CSIR), New Delhi, India for financial support under Network project CSC-102. Sandesh Sawant acknowelegdes CSIR, New Delhi for the award of Senior Research Fellowship.

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