Adsorption of Methylene Blue using Poly(N-vinylpyrrolidone)-Graphene Oxide Composite: Kinetics, Equilibrium, Thermodynamics, and Mechanisms

A poly( N -vinylpyrrolidone)-graphene oxide (NVP-GO) composite with high adsorption capacity for methylene blue (MB) was synthesized and comprehensively characterized using SEM, XRD, FT-IR, TG, elemental analysis, nitrogen physical adsorption, and XPS. The adsorption of MB onto NVP-GO was examined in relation to several variables, including contact time, adsorption temperature, initial concentration of MB, and pH. Adsorption kinetics, isotherms, and thermodynamics were thoroughly investigated. The adsorption kinetics followed the pseudo-second-order model, and the Langmuir isotherm model indicated a monolayer adsorption pattern of MB onto NVP-GO, with the maximum adsorption capacities ranging from 116.6 to 161.3 mg·g −1 at temperatures between 25 and 45 °C. Thermodynamic assessments and activation energy calculations demonstrated that the adsorption process was spontaneous, endothermic, and ​controlled by chemical activation. XPS analysis highlighted the significance of electrostatic interactions, n–π interactions, π–π stacking, and hydrogen bonding in mediating the adsorption mechanisms between NVP-GO and MB. Notably, NVP-GO maintained stable adsorption efficiency over three consecutive adsorption–desorption cycles, highlighting its potential as a promising adsorbent for wastewater treatment. Graphical