A Study on the Aggregation and Dehydration Behavior of Aqueous Boric Acid Solutions Confined in Carbon Nanotubes

The properties and structure of boric acid aqueous solutions confined in different carbon nanotubes (CNTs) with pore sizes are investigated using multiscale simulations. The study shows that a CNT pore size of 2.56 nm is a critical value for the properties and structure of confined boric acid solutions. When the pore size of a CNT is less than 2.56 nm, the properties of boric acid solutions show a noticeable confinement effect, which gradually decreases with increasing pore size and approaches those of a bulk solution. In small-sized CNTs (0.82 and 0.96 nm), boric acid molecules do not polymerize with each other. With further increasing pore size, polymerization occurs between boric acid molecules in a bidentate manner. In small CNTs (0.82 and 0.96 nm), boric acid molecules undergo dehydration and transform into metaboric acid molecules. This study provides a theoretical basis for green enrichment, separation, and high-value utilization of boron resources.