Bryophyte-Bioinspired Nanoporous AAO/C/MgO Composite for Enhanced CO₂ Capture: The Role of MgO

Abstract

A composite material composed of anodized aluminum oxide (AAO), carbon (C), and magnesium oxide (MgO) was developed for CO2 capture applications. Inspired by the bryophyte organism, the AAO/C/MgO composite mirrors two primary features of these species—(1) morphological characteristics and (2) elemental composition—specifically carbon, oxygen, and magnesium. The synthesis process involved two sequential steps: electroanodization of aluminum foil followed by a hydrothermal method using a mixture of glucose and magnesium chloride (MgCl2). The concentration of MgCl2 was systematically varied as the sole experimental variable across five levels—1 mM, 2 mM, 3 mM, 4 mM, and 5 mM—to investigate the impact of MgO formation on the samples’ chemical and physical properties, and consequently, their CO2 capture efficiency. Thus, scanning electron microscopy analysis revealed the AAO substrate’s porous structure, with pore diameters measuring 250 ± 30 nm. The growth of MgO on the AAO substrate resulted in spherical structures, whose diameter expanded from 15 nm ± 3 nm to 1000 nm ± 250 nm with increasing MgCl2 concentration from the minor to major concentrations explored, respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that carbon serves as a linking agent between AAO and MgO within the composite. Notably, the composite synthesized with a 4 mM MgCl2 concentration exhibited the highest CO2 capture efficiency, as determined by UV-Vis absorbance studies using a sodium carbonate solution as the CO2 source. This efficiency was quantified with a ‘k’ constant of 0.10531, significantly higher than those of other studied samples. The superior performance of the 4 mM MgCl2 sample in CO2 capture is likely due to the optimal density of MgO structures formed on the sample’s surface, enhancing its adsorptive capabilities as suggested by the XPS results.

Keywords

• CO₂ capture efficiency
• alumina template
• hydrothermal synthesis
• MgO XPS
• magnesium oxide nanostructures