Noncovalent Interactions Dictate Surface Chemical Functionalization of Carbon Nitrides with Demonstration from Methylation

Polymeric carbon nitride (CNx) is promising for removing pollutants from water due to its high surface area and chemical stability. As a photocatalyst, CNx can degrade pollutants under light irradiation. However, its efficiency can be limited by the lack of reactive sites, and modifying its surface is challenging due to its unreactive nature. This study focuses on the postsynthetic methylation of the surface of CNx to convert amino groups into quaternary ammonium groups to impart positive charge and enhance water remediation activity. Through experimental characterization and quantum mechanical calculations, we explore the chemical reactivity of the amino groups of CNx and its analogues within the carbon nitride family (CNF)melamine, melam, and melem. Our findings demonstrate successful methylation of the CNF members except for bulk CNx. Disrupting noncovalent interactions is shown to enhance amino groups’ reactivity, and forming CNx nanosheets (CNNS) allows successful methylation of the polymer. The effectiveness of the methylation of CNNS to generate positively charged surface groups was demonstrated via a proof-of-concept application in As­(V) remediation: methylated CNNS displayed a significant reduction of As­(V) concentration in water, in contrast to nonmethylated CNNS and CNx, which showed poor As­(V) adsorption capabilities. This study provides valuable insights into surface modification strategies for CNx and CNNS, highlighting the impact of noncovalent interactions on function and offering a promising approach for sustainable water remediation solutions.