Efficient CO 2 adsorption and mechanism on nitrogen-doped porous carbons
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RESEARCH ARTICLE
Efficient CO2 adsorption and mechanism on nitrogen-doped porous carbons Yanxia Wang1, Xiude Hu1, Tuo Guo2, Jian Hao1, Chongdian Si1, Qingjie Guo (✉)1 1 State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, Ningxia University, Yinchuan 750021, China 2 College of Arts and Sciences, Ferris State University, Big Rapids, MI 49307, USA
© Higher Education Press 2020
Abstract In this work, nitrogen-doped porous carbons (NACs) were fabricated as an adsorbent by urea modification and KOH activation. The CO2 adsorption mechanism for the NACs was then explored. The NACs are found to present a large specific surface area (1920.72– 3078.99 m 2 $g –1 ) and high micropore percentage (61.60%–76.23%). Under a pressure of 1 bar, sample NAC-650-650 shows the highest CO2 adsorption capacity up to 5.96 and 3.92 mmol$g–1 at 0 and 25 °C, respectively. In addition, the CO2/N2 selectivity of NAC-650-650 is 79.93, much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650. The CO2 adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles. Analysis of the results show that the CO2 capacity of the NACs has a linear correlation (R2 = 0.9633) with the cumulative pore volume for a pore size less than 1.02 nm. The presence of nitrogen and oxygen enhances the CO2/N2 selectivity, and pyrrole-N and hydroxy groups contribute more to the CO2 adsorption. In situ Fourier transform infrared spectra analysis indicates that CO2 is adsorbed onto the NACs as a gas. Furthermore, the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat, and it is found to be controlled by CO2 diffusion. The CO2 adsorption kinetics for NACs at room temperature and in pure CO2 is in accordance with the pseudo-first-order model and Avramís fractional-order kinetic model. Keywords porous carbon, CO2 adsorption, nitrogendoped, adsorption mechanism, kinetics
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Introduction
The increasingly severe greenhouse effect has led to Received March 14, 2020; accepted June 7, 2020 E-mail: [email protected]
serious environmental problems, for instance, global warming and ecological deterioration [1–3]. The main reason for these problems is the large amount of greenhouse gas emissions, especially CO2. Carbon capture and storage technology [4] is a key technology to reduce the concentration of CO2 in the atmosphere. In addition to solving environmental problems, CO2, as a carbon precursor, is converted to carbon-containing fuels [5–7], such as CO, CH4, and methyl alcohol. Therefore, it is of great significance to achieve the effective capture of CO2. Many solid adsorbents have been reported for CO2 capture, such as metal-organic frameworks [8,9], zeolites [10,11], mesoporous silica [12,13] and porous carbon materials [14–16]. Porous carbon is the most promising adsorbent for CO2 capture because of its low cost, high porosity, good surface chemical modifiability, superior hydrophobic property, and excellent recycle performance under environmental pres
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