Functional groups regulate ion concentration and pH in nanopores

 

To understand the chemical reactions occurring inside the nanopores of nanostructured materials—whether synthetic or natural, such as those found in membranes or ion channels in biological systems—it is essential to determine the ion concentration within them. For this purpose, nanopores are functionalized with specific chemical groups.

Until now, it had not been possible to determine how functional groups influence ion concentration inside nanopores.

In this study, a group of researchers from the United States reported the development of a core–shell-type plasmonic nanosensor, consisting of a gold nanorod coated with mesoporous silica functionalized with phenyl and methyl groups. This nanosensor can measure the local concentration of protons, anions (such as phosphates, nitrates, sulfates, and arsenates), as well as cations (such as mercury, lead, and copper) in functionalized nanopores. The measurements were performed using Surface-Enhanced Raman Spectroscopy (SERS), applied in situ.

The obtained values were compared with those of bulk silica. Moreover, results indicated that ion concentrations differ in pristine and hydrophobic nanopores compared with those functionalized with phenyl and methyl radicals. In the latter, an increase in anion concentration and a concurrent decrease in cation concentration were reported. Additionally, the pH within the nanopores was found to depend on the composition of the solution. In some cases, the pH inside the nanopores decreased by as much as 2.5 units compared to the bulk value.

These findings provide insight into ion–nanopore chemical interactions and enable precise and selective control of contaminants, with direct applications in water chemistry for membrane-based desalination processes, CO₂ storage, and catalysis in porous materials.

More information at: ACS Applied Materials and Interfaces