Carbon dioxide adsorption and cycloaddition reaction of epoxides using chitosan–graphene oxide nanocomposite as a catalyst

Abstract

One of today's major challenges is to provide green materials for a cleaner environment. We have conducted studies on carbon dioxide (CO₂) adsorption and conversion to valuable products by an ecofriendly approach based in chitosan/graphene oxide (CSGO) nanocomposite film. Rheological behavior indicates that the CSGO has a better solvation property than the pure chitosan. An adsorption capacity of 1.0152 mmol CO₂/g of CSGO nanocomposite at 4.6 bar was observed. The catalytic behavior of the CSGO nanocomposite in the presence of tetra-n-butylammonium iodide (n-Bu₄NI) as co-catalyst was evaluated for the cycloaddition of CO₂ to epoxides, to give cyclic carbonates, in the absence of any solvent. These results strongly suggest that the CSGO nanocomposite may open new vistas towards the development of ecofriendly material for catalytic conversion and adsorption of CO₂ on industrial scale.

Introduction

Burning of fossil fuels has caused a steady increase in atmospheric carbon dioxide concentration which is considered to be the most important provider to the increase in atmospheric temperatures in the 21st century (Kintisch, 2008). In response to this, and growing needs of modern society and rapid industrial development, it is necessary to design environmentally friendly and low-cost CO₂ storage methods and CO₂ conversion catalysts. Graphene has attracted great interest for its potential use in various applications, such as hydrogen storage (Kumar et al., 2014, Ma et al., 2009, Srinivas et al., 2010, Yuan et al., 2011), carbon dioxide capture (Balasubramanian and Chowdhury, 2015, Kumar et al., 2015c, Liu et al., 2015, Shen et al., 2015) and solar energy (Dai, 2013, Lightcap and Kamat, 2013, Tu et al., 2013). Graphene oxide (GO) possesses various reactive functional groups such as hydroxyl, epoxy, and carboxylic groups (Kumar and Koh, 2014). GO-based materials have attracted wide and intense interest for energy and environment related applications due to its excellent chemical stability, environmental friendliness and abundance. GO can be readily functionalized, which renders it useful in a wide range of synthetic transformations (Fan et al., 2015, Su and Loh, 2013, Zhang et al., 2014). Graphene has been suggested for storage of different gases in theoretical studies and its CO₂ adsorption capacity was demonstrated at − 78.15°C temperature, which has not much practical application (Ghosh et al., 2008). Therefore, there is a need to investigate and improve the CO₂ adsorption and conversion ability of graphene based materials.

CO₂ is a thermodynamically stable molecule due to the negative adiabatic electron affinity and large ionization potential, thus making its conversion into useful products difficult under normal conditions. The formation of cyclic organic carbonates using CO₂ as a renewable carbon feed stock is a highly vibrant area of research. Since these organic carbonates are useful building blocks and nontoxic reagents. Several different catalysts have been designed for the conversion of CO₂ to useful products such as cyclic carbonates (Kumar et al., 2015c, Wani et al., 2016). Cyclic carbonates can be used as electrolytes in lithium ion batteries, as precursors for pharmaceutical intermediates, raw materials for plastics, and as environmentally friendly nonprotic solvents (Fujita et al., 2014).

Chitosan (CS) is a biopolymer, used in biomedical and industrial applications due to its biodegradability, biocompatibility and low cytotoxicity (Chattopadhyay et al., 2013, Dang and Leong, 2006, Dutta et al., 2013, Fan et al., 2013, Garg et al., 2013, Jayakumar et al., 2010, Kumar et al., 2010, Kumar et al., 2015a, Kumar et al., 2015b, Kumar and Koh, 2013, Muzzarelli, 1977, Srivastava et al., 2011, Wan Ngah et al., 2011). Recently, we have studied the carbon dioxide capture on a porous CS derivative (Kumar et al., 2016, Silva et al., 2013). Chitosan–graphene oxide organic aerogels for CO₂ capture and effect of pyrolysis on chitosan–graphene oxide hybrid aerogels have also been studied (Alhwaige et al., 2013). However, to the best of our knowledge, CO₂ adsorption and conversion on chitosan/graphene oxide (CSGO) nanocomposite films have not yet been reported. Pure CS polymer is not efficient for adsorption applications. We have demonstrated that dispersing GO into a CS matrix in the form of nanocomposite film leads to higher CO₂ adsorption and improves its catalytic performance for cycloaddition of CO₂ to epoxides. The preparation and applications of GO hydrogels and their composites are becoming a rapidly growing area in modern chemistry (Li and Shi, 2014). Herein, we report the development of CSGO nanocomposite for CO₂ adsorption and chemical conversion to cyclic carbonates.