Structural responses of metal–organic frameworks to non-thermal plasma treatment and their effects on CO2 adsorption and conversion performances†

Abstract

Non-thermal plasma (NTP)-assisted catalysis shows exceptional carbon dioxide (CO₂) conversion performance at atmospheric pressure and room temperature. However, the structural stability of MOFs under plasma treatment constrains their application in CO₂ adsorption and conversion. Moreover, the structural responses of MOFs to plasma treatment and the effects on their CO₂ adsorption and conversion performance remain poorly understood. Herein, changes in the crystal structure and physicochemical properties of several MOFs (i.e., Cu-BTC, Zr-BPDC, Zn-MeIM and Zr-BDC) under NTP treatment were investigated by SEM, XRD, FTIR and BET analyses, and the disparities in the CO₂ adsorption and conversion performances of these MOFs with different structures were analyzed. Results indicated that Cu-BTC formed using Cu²⁺ as the chelating ligand and Zr-BDC formed using the [Zr₆O₄(OH)₄] metal cluster and a ligand exhibited varied structural stability under NTP treatment. Ar plasma mainly attacked and broke the Cu–O₁ bond of Cu-BTC, causing an increase in crystal defects and a significant reduction in the micropore volume, accompanied by a 46.0% decrease in CO₂ adsorption capacity. The destruction of the Cu-BTC structure by the plasma weakened the discharge intensity of plasma and inhibited the conversion of CO₂. In contrast, Zr-BDC showed excellent coordination bonds and pore structural stability against NTP treatment, which promoted the synergistic effect of plasma and the catalyst in the CO₂ hydrogenation reaction. This study enhances our understanding of the structure and functions of MOFs against NTP treatment, which is significant for expanding the application of MOFs using NTP-assisted catalysis.