Enhanced CO2 adsorption in Cux-MOF-5: Optimal doping and regeneration performance

Abstract

This paper introduces a method for synthesizing Cu_x-MOF-5 material in one step by doping with Cu²⁺. The synthesized Cu_x-MOF-5 materials at different doping concentrations were characterized using XRD, FT-IR, TGA, SEM, and N₂ adsorption-desorption isotherms techniques. The CO₂ adsorption capacity of the adsorbent was tested using a gas adsorption instrument ASAP 2020 at 274.15 K and 0–1 bar. It was concluded that the optimal process conditions were hydrothermal synthesis at 150 °C with Cu²⁺:Zn²⁺ is 0.05:1. The maximum CO₂ adsorption capacity of Cu_x-MOF-5 material was 4.6052 mmol/g, which was nearly 31 % higher than that of MOF-5 without Cu²⁺ doping. Even after eight consecutive adsorption-desorption cycles, the regeneration rate of the composite material remained above 97 %, demonstrating complete regenerability. Factors enhancing the material's dynamic adsorption capacity for CO₂ include the presence of micropores, Cu²⁺'s affinity for CO₂, and the imbalance of surface electrostatics due to Cu²⁺ and Zn²⁺ exchange. However, when Cu²⁺:Zn²⁺ exceeds 0.25:1, a large amount of Cu-BDC is generated, leading to a rapid decline in the material's adsorption performance. The obtained adsorbent parameters indicate that Cu-MOF-5 material is a promising CO₂ adsorbent.