Hydrophobic bifunctionalized hexagonal mesoporous silicas as efficient adsorbents for the removal of Orange IV

Abstract

A novel hydrophobic bifunctionalized hexagonal mesoporous silica (Ph-Am-HMS) material was synthesized with the simultaneous immobilization of phenyl and amino groups on its surface. The composition and structure of Ph-Am-HMS were studied by FT-IR, XRD, N₂ adsorption–desorption, and sessile water droplet contact angle measurements, etc., which revealed that this novel bifunctionalized material showed hydrophobicity and good porous properties. When applied to the adsorption of the azo dye Orange IV in aqueous solutions, Ph-Am-HMS exhibited a high adsorption capacity and a rapid adsorption rate. The theoretical maximum adsorption capacity could reach 246.3 mg g⁻¹ in 60 min at 293 K. A kinetic study indicated that the adsorption of Orange IV on Ph-Am-HMS fitted perfectly to the Freundlich adsorption model and followed pseudo-second-order kinetics. The changes in Gibbs free energy (−10.55 kJ mol⁻¹), enthalpy (−7.06 kJ mol⁻¹), and entropy (11.83 J mol⁻¹ K⁻¹) at 293 K showed that the adsorption process was spontaneous and exothermic.