Enhanced CO₂ Adsorption on Activated Carbon Fibers Grafted with Nitrogen-Doped Carbon Nanotubes.

Yu-Chun Chiang,Ruey-Shin Juang,Wei-Lien Hsu,Shih-Yu Lin

doi:10.3390/ma10050511

Abstract

In this paper, multiscale composites formed by grafting N-doped carbon nanotubes (CNs) on the surface of polyamide (PAN)-based activated carbon fibers (ACFs) were investigated and their adsorption performance for CO2 was determined. The spaghetti-like and randomly oriented CNs were homogeneously grown onto ACFs. The pre-immersion of cobalt(II) ions for ACFs made the CNs grow above with a large pore size distribution, decreased the oxidation resistance, and exhibited different predominant N-functionalities after chemical vapor deposition processes. Specifically, the CNs grafted on ACFs with or without pre-immersion of cobalt(II) ions were characterized by the pyridine-like structures of six-member rings or pyrrolic/amine moieties, respectively. In addition, the loss of microporosity on the specific surface area and pore volume exceeded the gain from the generation of the defects from CNs. The adsorption capacity of CO2 decreased gradually with increasing temperature, implying that CO2 adsorption was exothermic. The adsorption capacities of CO2 at 25 °C and 1 atm were between 1.53 and 1.92 mmol/g and the Freundlich equation fit the adsorption data well. The isosteric enthalpy of adsorption, implying physical adsorption, indicated that the growth of CNTs on the ACFs benefit CO2 adsorption.

Highlights

Global warming is one of the most important recent environmental concerns, which is mostly caused by anthropogenic activities
After the conventional chemical vapor deposition (CVD) process, the spaghetti-like and a slightly randomly oriented N-doped carbon nanotubes (CNTs) with a high density and homogeneity were grown onto the activated carbon fibers (ACFs)
The nanotubes on CN2/ACF had a larger range of diameters with a mean diameter of CN2 of about 25–83 nm

Summary

Introduction

Global warming is one of the most important recent environmental concerns, which is mostly caused by anthropogenic activities. CO2 capture and sequestration (CCS) is a set of technologies that can greatly reduce CO2 emissions from new and existing emission sources and is considered as an effective approach in mitigating global warming. Since most anthropogenic CO2 was a byproduct of the combustion of fossil fuels from coal-fired plants and large industrial sources, CO2 capture technologies were commonly classified as pre-combustion capture, post-combustion capture, and Materials 2017, 10, 511; doi:10.3390/ma10050511 www.mdpi.com/journal/materials. Among the different CCS methods available, post-combustion capture appears to be the most feasible approach as it can be retrofitted to existing power plants without upgrading or modifying the existing systems [4]. Much effort has been expended to develop various physical and chemical methods for post-combustion CO2 capture [5]

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