Insight into Organic Pollutant Adsorption Characteristics on a g-CN Surface by Attenuated Total Reflection Spectroscopy and Molecular Dynamics Simulation.

Herein the adsorption characteristics of zwitterionic dye pollutant Rhodamine B (RhB) on a g-CN surface were investigated by both an attenuated total reflection spectroscopy (ATRS) experiment and a molecular dynamics simulation (MDS). For experimental investigation, g-CN was coated on a silica optical fiber (SOF) surface to fabricate an adsorption film. According to the ATRS response, adsorption thermodynamics and thermodynamics results were in situ obtained and evaluated. The isothermal Langmuir model was used to calculate the adsorption equilibrium constants () and adsorption energies (Δ) for RhB as 27.25 × 10 M and -31.01 kJ mol, respectively, which indicated the spontaneous adsorption behavior of RhB at the g-CN surface. Using dynamic Elovich modeling, the rate constants of RhB were found to be = 0.0063 min and = 0.0004 min, which indicated two-stage adsorption at the g-CN surface. For theoretical simulation, adsorption configurations and adsorption energies were systematically calculated by a molecular dynamics simulation (MDS) . RhB molecules were inclined to orient in a parallel position at the g-CN surface during low concentration but a perpendicular position at the g-CN surface during high concentration. Combined with experimental and calculation results, this work revealed the microscopic adsorption performance and elucidated the intermolecular interaction between localized interfaces of g-CN and hazardous dye pollutant. We propose an adsorption model to explain the process of surface interaction, which is based on molecular orientation and a force-driven mechanism. Electrostatic attraction and π-π interaction dominated the adsorption interaction with an adsorption energy of Δ = -38.96 kJ mol for low RhB concentration, and electrostatic attraction dominated the adsorption interaction with an adsorption energy of Δ = -25.76 kJ mol for high RhB concentration. This work can provide a fundamental basis for a dye-pollutants removal application by g-CN in both adsorption and photocatalyzation.