Green, economical synthesis of nitrogen enriched carbon nanoparticles from seaweed extract and their application as invisible ink and fluorescent film

Abstract

In this article, we synthesized fluorescent nitrogen-enriched carbon nanoparticles (N-CNPs), which were prepared via the hydrothermal treatment of pyrolyzed seaweed extract and ethylene diamine at 160 °C for 12.0 h. These N-CNPs demonstrated a 12 nm average diameter with carbonyl, hydroxyl, and imine functionality on their surface. The zeta potential value was found to be negative which further confirms the presence of acid/imine groups on the surface of N-CNPs. The prepared N-CNPs showed strong blue fluorescence with 24% quantum yield under UV light illumination. Here, we introduced metal-free water dispersed N-CNPs as invisible ink for security purposes. The information was written by the N-CNPs in TLC plate and N-CNPs/PVA flexible composite film is invisible in daylight and can be readable in UV light illumination.