Cr(III) Adsorption on Green Mesoporous Silica: Effect of Amine Functionalization and pH

This paper investigates the adsorption performance of green mesoporous silica (GMS-24h) and its amine-functionalized derivative (GMS-24h–NH2) for Cr(III) removal from aqueous systems. Adsorption isotherms were evaluated using the Langmuir and Freundlich models. GMS-24h achieved a maximum capacity of 303 mg·g⁻¹ at pH 3, while GMS-24h– NH2 showed a maximum capacity of 370 mg·g⁻¹ at pH 5. When compared to other silica-based materials, such as SRH and SRH–Triamine, the GMS materials demonstrated up to 44% higher adsorption capacity. Kinetic studies indicated that the pseudo-second-order (PSO) model provided the most accurate description of the adsorption process, as evidenced by high correlation coefficients (R2 > 0.99) and low deviation values (Δq < 20%). The equilibrium factor Rw showed rapid system stabilization. Intraparticle and external diffusion models demonstrated that both mechanisms contribute to the overall process, with external diffusion dominating at low Cr(III) concentrations and intraparticle diffusion at higher levels. The number of diffusion steps remained constant across a range of pH values, indicating a pH-independent mechanism. However, an additional chelation step (N→Cr) was observed in GMS-24h–NH2. These findings underscore the promise of GMS-based materials as effective adsorbents for the remediation of heavy metals in water treatment applications.