Kinetics and thermodynamics of NPX adsorption by γ-FeOOH in aqueous media

Naproxen (NPX) is a common PPCPs in wastewater treatment plants which is influenced by the coexistence on its photodegradation. Most research on reasons for NPX photodegradation has focused on the soluble substances in water mainly, and the adsorption effect of solid particles is less. The effects of initial concentration, temperature, and pH on the adsorption of NPX on γ-FeOOH were studied. It was found that the equilibrium time of γ-FeOOH adsorbed NPX was 240 min. The increase of initial concentration and temperature were favorable for the adsorption. The optimal adsorption pH was 7.0, and the adsorption capacity attained 28.05 mg·g−1. It was learned, through model fitting, that the adsorption reaction was in accordance with the Laggenren quasi-second-order kinetic model; the internal diffusion process was the control step, where the adsorption was close to the Langmuir isothermal adsorption model. The thermodynamic calculation showed that ΔG < 0, ΔH < 0, ΔS < 0, which inferred that the adsorption was a spontaneous, endothermic, and entropy increasing process, which is the common action of chemical bond forces and static electricity.