Adsorbents with sustainable CO 2 capture capacity prepared from carboxymethylcellulose
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Adsorbents with high specific surface areas, developed porosities, and sustainable CO2 capture capacity (;180 mg/g at 25 °C, 1 bar) were prepared by KOH activation of hydrothermally carbonized carboxymethylcellulose (CMC). Condensed aromatic carbon materials (CSc) with particle diameters of 2–3 lm and many oxygen-containing groups on their surfaces can be obtained after hydrothermal treatment of CMC; these materials are similar to glucose-derived hydrothermal carbons. The activation conditions, including activation ratio and activation temperature, significantly influence the structure and morphology of the adsorbents. In turn, the pore structures, specific surface areas, and adsorption conditions significantly affect the adsorption capacities of these new adsorbents. For samples with the same activation ratio, those with higher specific surface areas show higher CO2 capture capacities at 25 °C and 1 bar. Under these conditions, for samples with different activation ratios, the capacity is dominated by the microporosity development and, in particular, the high volume of smaller micropores (d 5 0.4–0.9 nm); when the adsorption pressure is decreased to 0.1 bar, the CO2 capture ability becomes closely correlated with the number of ultramicropores (d , 0.7 nm).
I. INTRODUCTION
The greenhouse effect is the most serious environmental problem that people have encountered in recent times, and is expected to lead to climate change, including global warming, sea level rise, and El Nino phenomenon. CO2 derived from the burning of fossil fuels is the main reason for this, meaning that in addition to finding alternative renewable sources of energy, capture of CO2 is needed. The most widely used CO2 capture method is neutralization with strong alkali1; however, the high cost, nonrenewable, and toxic nature of the chemicals involved have limited the practical use of this approach. Porous solid adsorbents are an effective way to mitigate CO2 emissions; the strongly enhanced interaction energy between CO2 molecules and the adsorbents in the developed pores can enhance the filling of gas molecules,2,3 and allow high-performance adsorbents to exhibit high adsorption capacity and selectivity toward CO2. Zeolites have open crystal lattices containing pores with molecular dimensions, into which molecules can penetrate. The nature of the adsorption can depend on the geometry of the site, physisorption of CO2 occurs with CO2 in a linear orientation by an ion–dipole interaction, and chemisorption occurs when sites are bent
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.164 J. Mater. Res., Vol. 29, No. 14, Jul 28, 2014
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to allow coordination.4,5 However, the adsorption capacities of zeolites are highly sensitive to temperature and their selectivity to CO2 is still low. Metal organic frameworks (MOFs) are a new family of porous materials; the CO2 adsorption and desorption in MOFs are ascribed to changes in the framework structures. Although MO
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