Fast plasma nanomodification of graphitic carbon nitride by amide and carboxyl groups for enhanced sulfamethoxazole degradation in wastewater: detailed experimental and DFT study

Abstract

In this study, we developed an efficient plasma nanomodification strategy of graphitic carbon nitride (gCN) prepared from melamine (M-gCN) and 3-amino-1,2,4-triazole (3AT-gCN). For the first time, we report the surface functionalization of gCN by amide (CONH₂) groups formed simultaneously with carboxyl (COOH) groups and amine (NH₂) groups. The plasma treatment was performed using a large-area surface low-temperature plasma generated in the open air, proving to be a non-destructive, rapid (4 minutes), and environmentally friendly approach for enhancing the photocatalytic efficacy of gCN. To comprehensively examine the effect of nanomodification, we conducted deep X-ray Photoelectron Spectroscopy (XPS) analysis complemented by Density Functional Theory (DFT) simulations. The surface functionalization has profound impact on the electronic properties of plasma-treated samples (M-gCN-PT and 3AT-gCN-PT) as demonstrated by valence band XPS spectra. The plasma nanomodification led to pronounced separation and migration of photogenerated charge carriers. These findings have been supported by the efficient degradation of sulfamethoxazole (SMX), both with and without the presence of peroxymonosulfate (PMS), showcasing significant SMX removal of 88% (M-gCN-PT) and 76% (3AT-gCN-PT) after 2 h in pure water or 83% (M-gCN-PT) and 71% (3AT-gCN-PT) after 12 h in effluents from a municipal wastewater treatment plant (WWTP) in Bratislava.