Indirect Grafting of Alkyl Ammonium Ions onto Glassy Carbon and Coal Surface. Enhancing the Performance of Heterogeneous Asymmetric Membranes

Glassy carbon (GC) and lignite coal powder surfaces are functionalized—either electrochemically or chemically—with alkylammonium groups. The modified coal powder is then embedded within cellulose acetate asymmetric membranes. The surface functionalization process involves the reduction of 2,6‐dimethylbenzene diazonium salt (2,6‐DMBD), which generates the 2,6‐dimethylphenyl radical. Owing to steric hindrance, this radical does not react directly with the surface; instead, it undergoes a radical crossover reaction with brominated alkylammonium salts, generating alkylammonium radicals that subsequently graft onto GC and coal surfaces. In contrast, the reduction of 4‐nitro‐ and 3,5‐dicarboxybenzenediazonium salts produces aryl radicals that bind directly to the coal surface while simultaneously generating alkylammonium radicals. This dual mechanism enables the formation of mixed alkylammonium–aryl layers. On GC, the modification yields a surface layer of alkylammonium groups, as confirmed by cyclic voltammetry using redox probes and by X‐ray photoelectron spectroscopy (XPS), particularly through the N 1s signal, which attests to the presence of alkylammonium groups. When coal modified with alkylammonium ions—either alone or in combination with aryl groups—is incorporated into heterogeneous asymmetric membranes, the resulting membranes exhibit enhanced productivity, product flux, and solute separation compared to both unmodified membranes and those modified without ammonium groups.