Bubbling-based method for direct carbon dioxide capture from ambient air using alkaline earth metal halides

Abstract

The high level of CO₂ in the atmosphere is a major global challenge, with excessive emissions continuing into the foreseeable future. Effective methods for CO₂ capture and utilization are therefore necessary to achieve environmental sustainability. In this study, a novel method to capture CO₂ directly from ambient air is developed based on the bubbling of alkaline earth metal solutions, utilizing a simple do-it-yourself (DIY) device. In the bubbling process, ambient air passes through a diffuser to produce tiny air bubbles in an aqueous solution of alkaline earth metal halides (i.e., MCl₂, where M=Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) and sodium hydroxide. During this process, dissolved metallic ions interact with CO₂ molecules confined in the tiny air bubbles, forming metal carbonates. The depletion of CO₂ in the air flux was monitored by operando Fourier-transform infrared (FTIR) spectroscopy. The CO₂ capture efficiency was found to be dependent on the type of metal halide, its concentration, and pH level. Specifically, 0.10 mol/L MCl₂ aqueous solutions at pH=11 demonstrated efficiencies ranging from 90% to 52% in the following order: Mg > Ca > Sr > Ba, with MgCl₂ exhibiting superior performance in the studied pH range of 6–11. The formed carbonates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy-dispersive spectroscopy (EDS), and FTIR. The high purity of the products enables their subsequent use in other applications, contributing to the sustainability of the proposed approach. In summary, this study compares the dynamics of CO₂ capture by MCl₂ in an alkaline medium and evaluates the efficiency of the process in yields of useful carbonates for various industrial applications.

Graphical abstract