The Effect of Solvothermal Conditions on the Properties of Three-Dimensional N-Doped Graphene Aerogels.

Alina Pruna,Alfonso Cárcel,Enrique Giménez,Adolfo Benedito

doi:10.3390/nano9030350

Abstract

Low-density three-dimensional (3D) N-doped graphene aerogels by a one-step solvothermal method in the presence of ethylenediamine (EDA) are reported. The gelation, formation, and properties of the aerogels were studied with solvothermal conditions, namely, operating temperature, time, graphene oxide (GO) concentration, and the GO/EDA w/w ratio. Two ranges of solvothermal conditions are employed: one involving an operating temperature below 100 °C and a conventional chemical reduction of GO with EDA at atmospheric pressure and a second one employing a higher temperature range up to 165 and a high pressure reduction with EDA. The results show that both solvothermal approaches allow for the fabrication of homogeneous N-doped 3D graphene aerogels with density values close to 10 mg cm−3. The measurements indicated that low values of GO concentration, temperature, and EDA are optimum for obtaining low-density 3D aerogels. N doping is improved with an EDA amount in lower temperature conditions. The N doping mechanism below 100 °C is dominated by the epoxy ring opening while at temperatures up to 165 °C both epoxy ring opening and amidation take place. The CO2 adsorption properties are strongly controlled by the nitrogen configuration, namely, pyridinic nitrogen in terms of its density.

Highlights

Strategies for mitigation of climate change due to anthropogenic sources are focused on reducing CO2 emissions from combustion of fossil fuels and on developing more selective and efficient CO2 capture systems [1].Many carbon-based porous materials are appropriated for CO2 adsorption [2]
The critical gel concentration of graphene oxide (GO) was another parameter to consider, e.g., gelation was reported to occur at values as low as 0.075–0.125 mg·mL−1, the aerogels obtained at such low values did not exhibit good mechanical strength [23]
While no monolith could be formed at 85 ◦C, the formation of hydrogel monoliths at higher temperature (HT route) indicates that the self-assembly of reduced graphene oxide (rGO) hydrogel is induced by the chemical reduction of GO

Summary

Introduction

Strategies for mitigation of climate change due to anthropogenic sources are focused on reducing CO2 emissions from combustion of fossil fuels and on developing more selective and efficient CO2 capture systems [1].Many carbon-based porous materials are appropriated for CO2 adsorption [2]. In order to improve the CO2 capture capacity along with high CO2/N2 selectivity, rGO materials can be employed as composite materials with other adsorbent materials such as metal organic frameworks (MOFs) [3] or can incorporate radicals such as amine groups [4,5]. They are likely to facilitate the cyclic process of CO2 desorption during adsorbent regeneration by proper microwave heating [6]. Three-dimensional graphene networks exhibit interesting characteristics, including the presence of graphene oxide (GO) features in bulk volume, the improvement of practical applications in the field of adsorption by the easy separation of the adsorbent, and the prevention of a restacking of sheets in macro-scaled agglomerates during the adsorption process [7]

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Results

Discussion

Conclusion