Adsorption of Erythrosine Red onto Silica Synthesized with Ora-Pro-Nobis as a Natural Porogenic Template: Equilibrium, Kinetic, and Thermodynamic Evaluation

Abstract

In this study, a silica-based adsorbent was synthesized via a two-step sol–gel route. A branch of ora-pro-nobis (Pereskia aculeata Miller) was used as a porogenic template. The biomass was incorporated into the silica matrix and subsequently removed by calcination. The resulting material was characterized by nitrogen adsorption–desorption analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC), and its performance for erythrosine red adsorption from aqueous solution was evaluated. The incorporation of the biotemplate modified the pore structure of the silica, decreasing the BET specific surface area from 297.33 to 249.10 m2 g−1 while increasing the average BJH pore diameter from 2.26 to 3.66 nm. Adsorption was favored at pH 6 and rapidly approached equilibrium within approximately 5–7 min. The equilibrium data were satisfactorily described by the Langmuir model, with a maximum adsorption capacity of 108.81 mg g−1 at 25 °C. Adsorption capacity decreased with increasing temperature, and thermodynamic analysis indicated a spontaneous and exothermic process (ΔH° = −8.07 kJ mol−1). Overall, ora-pro-nóbis biomass acted as a renewable porogenic biotemplate, modifying the pore architecture of silica. The resulting TSOPN material exhibited competitive adsorption performance for erythrosine removal.