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

Contamination of heavy metals, particularly chromium from industrial activities, represents a critical challenge for public health and the environment. The aim of this study is to evaluate the adsorption performance of green mesoporous silica (GMS-24 h), synthesized through a sustainable process from industrial sodium silicate, and its derivative functionalized with amino groups (GMS-24 h–NH2) for the removal of Cr(III) in aqueous systems. FTIR and CP–MAS NMR characterization confirmed the surface modification and textural property improvement of green mesoporous silica. The adsorption experiments, carried out under varying pH and Cr(III) concentration conditions, were fitted to the Langmuir and Freundlich models. The results showed that GMS-24 h reached a maximum capacity of 303 mg·g−1 at pH 3, while GMS-24 h–NH2 achieved 370 mg·g−1 at pH 5. The evaluated adsorbents showed up to a 44% increase in efficiency. Preliminary kinetic studies indicated that the pseudo-second-order model accurately describes the process (R2 > 0.99), with the rapid stabilization of the system. Diffusion analysis indicated combined mechanisms, with an additional chelation step (N → Cr) in GMS-24 h–NH2. These findings suggest that GMS–NH2 has the potential to be a sustainable and economical adsorbent for the remediation of wastewater from the tanning industry in León, Guanajuato, Mexico.