Is N-Doping in Porous Carbons Beneficial for CO₂ Storage? Experimental Demonstration of the Relative Effects of Pore Size and N-Doping

Abstract

The relative influence of nitrogen doping and pore size of highly microporous carbon materials, with virtually identical porosity, on CO2 uptake capacity at low pressure (≤1 bar) is presented in this article. The carbon materials are prepared via a range of synthesis methods, including activation of a variety of carbon precursors (biomass, polypyrrole, or carbon nanotube superstructures) and carbonization of an organic salt (potassium hydrogen phthalate), which generated a series of carbons with closely matched porosity but which are either N-free or N-doped. The carbons have a total surface area of 920 ± 60 m2/g and micropore surface area of 860 ± 40 m2/g, values that are within ±5% of each other and within the repeatability range (or experimental error) of the porosity measurements. The carbons have identical micropore volume of 0.39–0.40 cm3/g, and similar overall pore size and apparent pore size distribution. The similar porosity values allowed a simple and straightforward analysis of the influence of N-doping on CO2 uptake without any ambiguities associated with changes in surface area and pore volume. Contrary to many previous reports wherein both N-doping and porosity varied, we show that the presence of N has no beneficial effect on the adsorption of CO2. Rather, we show that the low-pressure adsorption of CO2 on carbons is critically sensitive to the pore size, and in particular to minute changes in micropore size distribution within the pore size range 5–10 Å. The pore size also exerts greater influence on both the isosteric heat of CO2 adsorption and the selectivity for CO2 over N2.

Templating of carbon in zeolites under pressure: synthesis of pelletized zeolite templated carbons with improved porosity and packing density for superior gas (CO2 and H2) uptake properties

“…This finding is consistent with the fact that the CO2 uptake at low pressure (1 bar) is very dependent on the pore size of the carbons. [33][34][35][36][37][38][39] On the other hand, the greater CO2 uptake of the pelletized samples at 20 bar may be ascribed to their higher overall surface area and pore volume. It is known that the CO2 uptake of porous carbons at high pressure (such as 20 bar) is determined by the total surface area.…”

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] This has included preparation of ultra-high surface area nanostructures for gas uptake at high pressures, 21,22 and on the other hand, synthesis of highly microporous materials for CO2 uptake at low pressure. 7,[33][34][35][36][37][38][39] Unfortunately, at the present time, the materials with the highest surface area generally tend to have low packing density and therefore low volumetric uptake. Enhancements in packing density and consequently volumetric storage capacity of porous materials may be achieved by material densification or compaction.…”

High yield and high packing density porous carbon for unprecedented CO2 capture from the first attempt at activation of air-carbonized biomass

“…This is surprising because most previous studies have noted a widening of the adsorption knee at higher activation temperature. 29,56,57,[61][62][63][64][65][66][67][68][69][70][71][72][73][74] The level of porosity generated, as judged by the amount of nitrogen adsorbed, increases modestly for samples prepared at higher activation temperature despite the non-changing nature and shape of the isotherms. The isotherms of the compactivated carbons are similar to those of analogous conventionally activated carbons except that they exhibit higher amounts of nitrogen sorption.…”

“…This is particularly interesting since the nature of the carbon feedstock has a significant impact on porosity development in activated carbons derived from various sources. [24][25][26][27][28][29][30] This work is also a departure from known practice given that although activated carbons can be produced using biomass feedstock, the biomass is first carbonized, usually via thermal decomposition of carbonaceous matter into an essentially all-carbon material. The carbonisation process is usually performed by heat treatment (400 -900 o C) under a non-oxidising (e.g.…”

Simple synthesis of porous melamine-formaldehyde resins by low temperature solvothermal method and its CO2 adsorption properties

“…To mitigate the effect of global warming, many porous materials, such as metal organic frameworks (MOFs) [5][6][7][8][9], porous co-ordination polymers [10,11], porous carbons [12][13][14][15][16], porous organic polymers (POPs) and covalent organic frameworks (COFs) [17][18][19][20], have been investigated for CO 2 storage. In recent years, many amine functionalized or nitrogen-rich porous materials were found to show good CO 2 adsorption properties because of the existence of strong interactions between the nitrogen functionality and CO 2 molecules [21][22][23][24][25][26][27].…”