Revealing the Adsorption Mechanisms of Methanol on Lithium-Doped Porous Carbon through Experimental and Theoretical Calculations

Abstract

Previous reports have shown that it is difficult to improve the methanol adsorption performance of nitrogen and oxygen groups due to their low polarity. Here, we first prepared porous carbon with a high specific surface area and large pore volume using benzimidazole as a carbon precursor and KOH as an activating agent. Then, we improved the surface polarity of the porous carbon by doping with Lithium (Li) to enhance the methanol adsorption performance. The results showed that the methanol adsorption capacity of Li-doped porous carbon reached 35.4 mmol g^-1, which increased by 57% compared to undoped porous carbon. Molecular simulation results showed that Li doping not only improved the methanol adsorption performance at low pressure, but also at relatively high pressure. This is mainly because Li-modified porous carbon has higher surface polarity than nitrogen and oxygen-modified surfaces, which can generate stronger electrostatic interactions. Furthermore, through density functional theory (DFT) calculations, we determined the adsorption energy, adsorption distance, and charge transfer between Li atom and methanol. Our results demonstrate that Li doping enhances the adsorption energy, reduces the adsorption distance, and increases the charge transfer in porous carbon. The mechanism of methanol adsorption by Li groups was revealed through experimental and theoretical calculations, providing a theoretical basis for the design and preparation of methanol adsorbents.

Keywords: adsorption mechanism; lithium doping; methanol adsorption; pore structure; porous carbon.

Figure 1

SEM images of LiPC-3, (a) 2 μm and (b) 500 nm.

Figure 2

XRD pattern of Li-doped porous carbon.

Figure 3

(a) N₂ sorption–desorption isotherms and (b) pore size distributions calculated with NLDFT of porous carbon.

Figure 4

XPS spectra of the LiPC-3: (a) survey spectrum, (b) N 1s, (c) C 1s, and (d) O 1s.

Figure 5

The adsorption isotherms of methanol on porous carbon at 25 °C.

Figure 6

Adsorption density of the slit pore model (a) and Li-doped slit pore model (b) on methanol.

Figure 7

Partial charge distribution of Li-doped slit pore model surface atoms.

Figure 8

(a) Adsorption density of Li-doped slit pore model with EI and without EI; (b) electrostatic contribution of Li-doped slit pore model on methanol.

Figure 9

Adsorption density of O-, N-, and Li-doped slit pore model on methanol.

Figure 10

Adsorption energies of perfect graphene (a) and Li-doped graphene (b).