Open-Tip Carbon Nanotubes for Enhanced Methane Adsorption Performance: A Comparative Study

Yanyan Feng,Guangyuan Ye,Di Yang,Yanjie Li,Wen Yang,Shufen Zhang

doi:10.1155/2018/8905204

Abstract

A series of open-tip carbon nanotubes (CNTs) were obtained by HNO3 modification with various concentrations of as-prepared carbon nanotubes via the CVD method, and this work aimed at investigating the structural features of open-tip CNTs for the methane capability. Modified CNTs had higher specific surface area and larger total pore volume, and importantly, greater micropore volume was obtained through HNO3 modification of the as-prepared CNTs. The remarkably high methane adsorption capacities were measured on the modified CNTs under pressure ranges of 0∼4.0 MPa at 298 K. The resulted H-CNT, which exhibited highest specific surface area and micropore volume, showed high methane uptake of 26.15 mg/g from the D-A model. This value was nearly as twice as the methane uptake of original CNTs (13.62 mg/g), along with an initial adsorption heat of 19.4 kJ/mol at lower coverage and 9.5 kJ/mol at higher methane coverage for H-CNT, indicating the physical nature for methane adsorption over open-tip CNTs.

Highlights

Methane (CH4) produced by coal seam and shale is widely regarded as one of the main greenhouse gases contributing to global warming, which is one of the most significant challenges today [1,2,3]. e ongoing use of fossil fuels makes it compelling to store CH4 via the adsorption technology
We investigated the open-tip effect of the as-prepared CNTs on their structure and adsorption Journal of Nanotechnology performance. e pristine CNTs was synthesized by CVD in a quartz tube reactor, and a series of open-tip carbon nanotubes (CNTs) were obtained by HNO3 modification with various concentrations of as-prepared CNTs. e structural property was determined by N2 adsorption/ desorption at 77 K, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fouriertransform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA), respectively. e data of methane adsorption equilibrium were measured by a volumetric method, and experimental results of methane adsorption by CNTs were described by the model isotherms such as Langmuir and Dubinin–Astakhov (D-A) models
The HNO3 modification process carried out provoked a continuous increase in the adsorption capacity of N2

Summary

Introduction

Methane (CH4) produced by coal seam and shale is widely regarded as one of the main greenhouse gases contributing to global warming, which is one of the most significant challenges today [1,2,3]. e ongoing use of fossil fuels makes it compelling to store CH4 via the adsorption technology. Carbon materials, depending on their properties, can be used in CH4 storage, due to their high specific surface area and pore volume that is able to host large amounts of CH4 [2, 3, 11, 12]. A higher adsorption capacity in CH4 storage of the open-tip CNTs than the as-prepared ones was obtained due to the larger specific surface area. E pristine CNTs was synthesized by CVD in a quartz tube reactor, and a series of open-tip carbon nanotubes (CNTs) were obtained by HNO3 modification with various concentrations of as-prepared CNTs. e structural property was determined by N2 adsorption/ desorption at 77 K, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fouriertransform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA), respectively. Heat of adsorption was evaluated based on the Clausius–Clapeyron equation

Experimental

Results and Discussion

Conclusions