Enhanced resolution of ultra micropore size determination of biochars and activated carbons by dual gas analysis using N2 and CO2 with 2D-NLDFT adsorption models

Abstract

In this study, biochars obtained by either direct carbonization or hydrothermal treatment of corn stems were used as precursors of two series of activated carbons (ACs). The pore size distributions (PSDs) of biochars and ACs were evaluated from N 2 and CO 2 adsorption isotherms using models based on the two-dimensional version of the non-local density functional theory (2D-NLDFT). We showed that more detailed carbon PSDs might be obtained from simultaneous (dual) gas analysis of both N 2 and CO 2 isotherms than from single isotherms. The dual gas method showed a peak at about 0.4 nm which was not detected by the single N 2 analysis. This fact is related to the restricted diffusion of N 2 into very narrow micropores at low temperatures and pressures. By modifying the lower pore width limit w min in the nitrogen model, we obtained an excellent fit of the dual model to both isotherms for all studied samples, which demonstrates the reliability and robustness of this refined method. Finally, we demonstrated that this approach would allow measuring N 2 isotherms at relative pressures starting at about 0.001 rather than at 10-6 , which would save time without losing resolution of the calculated PSD.

Exploiting the adsorption of simple gases O2 and H2 with minimal quadrupole moments for the dual gas characterization of nanoporous carbons using 2D-NLDFT models

“…The char derived from corn stigmata was labeled C-CS, and its two activated carbon derivatives were labeled C-CS-0.5 and C-CS-1.0, where the number in the sample label represents the time of activation in hours. Preparation and properties of the samples used in this work were described earlier for the PET series [16,23] and the CS series [24]. In addition to the porous carbons, a sample carbon black BP 280 (Cabot) was used to obtain H 2 adsorption reference data.…”

“…The limited sensitivity to larger pore sizes of CO 2 and H 2 implies that to calculate the carbon PSD in a full range of micro and mesopores, it is necessary to use an additional adsorbate that will condense in the larger pores. The concept of using two adsorbates that are sensitive to different pore sizes was implemented for CO 2 and N 2 in the dual gas analysis method [16,24].…”

Importance of Pore Structure and Surface Chemistry in Carbon Dioxide Adsorption on Electrospun Carbon Nanofibers

“…2(a). The results indicated that the HS-2D NLDFT model could detect the existence of a peak at about 0.4 nm, but the slit-NLDFT model only could probe down to 0.6 nm; (23) thus, the HS-2D-NLDFT model was subsequently used. The PSD patterns of carbonized samples [ Fig.…”

Lignin-graphene oxide inks for 3D printing of graphitic materials with tunable density

“…The corresponding results are given in Table 2. The pore size distributions (PSDs) were also obtained by applying the 2D-NLDFT-HS method, which provides more accurate results by combining N 2 and CO 2 adsorption data simultaneously [50][51]. By integration of the PSDs over the entire range of pore sizes [52] (not shown), the S NLDFT surface areas and the total pore volumes could be calculated and are also presented in Table 2.…”