Surface engineered VN-rGO nanocomposite for rapid and efficient cationic dye adsorption

Organic dyes are extremely carcinogenic and mutagenic pollutants that pose a serious threat to aquatic ecosystems and human health, necessitating the development of efficient remediation strategies. In this work, Vanadium nitride-reduced graphene oxide (VN-rGO) was synthesised using an ammonium peroxovanadate precursor and investigated as a novel adsorbent for the removal of cationic dyes, including methylene blue (MB) and rhodamine B (RhB). The synergistic effect of the high surface area of rGO and chemically active VN sites promotes multiple binding interactions with dye molecules, resulting in rapid and efficient dye removal. The VN-rGO achieved complete adsorption of MB (1 ppm) and RhB (0.7 ppm) within 30 s under the investigated conditions. The effect of parameters such as contact time, adsorbent dosage, adsorbate concentration, and reusability without regeneration was systematically investigated. To understand the adsorption mechanism, Freundlich, Langmuir, and Temkin isotherm models were employed. The linear and non-linear Freundlich models provide the best fit for both dyes (R 2 = 0.96-0.98), suggesting multilayer adsorption on a heterogeneous surface. The linear and non-linear pseudo-second-order kinetic model showed the best agreement with the experimental data (0.96-0.99), suggesting a chemisorption-dominated adsorption process. The adsorption behaviour is attributed to the combined effect of electrostatic interactions, surface complexation, hydrogen bonding, and π-π stacking. Furthermore, the VN-rGO demonstrated effective dye removal over multiple cycles without regeneration, highlighting its potential as a rapid and reusable adsorbent for wastewater treatment.