Understanding the Hydrophilicity and Water Adsorption Behavior of Nanoporous Nitrogen-Doped Carbons

Abstract

Through molecular simulation we exposed the anomalous water adsorption behavior in slit-shaped and disordered nitrogen doped carbons. Instead of Langmuirian, water adsorption proceeds via mechanisms analogous to crystal nucleation: birth and spread of (poly) nucleation sites in one, two, and three dimensions forming water nanowires/pillars and water clusters before complete pore filling via capillary condensation. The adsorption of water and the adsorption hysteresis in N-doped carbons are strongly influenced by the poresize. The smaller the pore-size, the smaller is the pressure at which the abovementioned process tends to occur in N-doped carbons. The nucleation analogues are clearly visible in a pore that has a homogeneous pore structure, whereas in disordered pore structures, the complex and distributed pore-sizes disturb these nucleation analogue patterns especially at lower relative pressures. The effect of the adsorbed water molecules on the connectivity of the available pore volume is discussed. Adsorption at zero loading confirmed water molecules preferentially adsorb over specific zones, which corresponds to regions with a high local density of N atoms rather than specific sites or type of N (such as graphitic or pyridinic). Simulated adsorption isotherms showed the hydrophilicity introduced to the carbon pore via N doping is sensitive to impurities such as water, such that it can affect the ability of the carbon framework to host another guest molecule such as CO 2 , a prime fluid involved in flue gas.

Monolithic resorcinol–formaldehyde alcogels and their corresponding nitrogen-doped activated carbons

“…Its lower water uptake capacity is readily explained by a lower amount of micro-and mesoporosity. Also, the RF activated carbon adsorbs water at higher relative humidities than its N-bearing RMF and F1.5 counterparts do, which is in good agreement with the literature [53]. However, despite having the highest nitrogen content, the carbon from the F1.5 series displays a behavior similar to the RMF carbon and its isotherm is not shifted further towards earlier adsorption, which comes as somewhat of a surprise.…”

Advances in Porous Organic Polymers for Efficient Water Capture

“…Kumar et al . studied water adsorption on nitrogen‐doped carbons by using Monte Carlo simulations (Figure ), wherein they used model carbon structures doped with graphitic‐N and pyridinic‐N.…”

Characterization of the adsorption site energies and heterogeneous surfaces of porous materials

“…In other peculiar cases, as in water adsorption, it is common to expect secondary events like cluster formation, co-adsorption, creation of new active sites due to the adsorbed water molecules. 21,85,86 Obviously, such information cannot represent the actual heterogeneity of the material. So clearly for this case, the proposed methods should not be applied.…”

“…[4][5][6][7][8] Other applications of adsorption include heterogeneous catalysis, waste water treatment, removal of objectionable odor and taste; metal leaching, storage of logistically important gases like hydrogen and methane, molecular separations and molecular gas sensosrs. [9][10][11][12][13][14][15][16][17][18][19][20][21] In biological systems, adsorption equilibrium characterizes the ligand-binding systems. 22 Another important application of adsorption is the removal of pollutants from an unmanageable, large volume of liquid to a manageable solid phase using low cost adsorbents which are safely disposed of after the process.…”