Vol. 25, No. 3 (2026), IA26888 https://doi.org/10.24275/rmiq/IA26888

Mechanistic insights into metformin sorption onto natural, sodium-exchanged, HDTMA-modified, and cerium-loaded clinoptilolite zeolites

 

Authors

A.M. Dávila-Estrada, J.J. Ramírez-García

Abstract

Metformin is a persistent antidiabetic drug frequently detected in aquatic environments due to its incomplete removal in conventional wastewater treatment plants. In this study, the dominant sorption mechanisms of metformin onto natural clinoptilolite (ZN), sodium-conditioned zeolite (ZNa), hexadecyltrimethylammonium bromide-modified zeolite (ZMS), and cerium-loaded zeolite (ZCe) were investigated. Experiments were conducted at intrinsic pH (5–6), where metformin is predominantly present in its protonated form. The materials were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM–EDS), Thermogravimetric Analysis (TGA), CHNS elemental analysis, and point of zero charge (pHpzc).
Kinetic assays performed at 100 mg L-1 and 25 °C showed that ZNa exhibited the highest sorption capacity (2.42 mg g-1), followed by ZMS (1.90 mg g-1), ZN (1.62 mg g-1), and ZCe (1.23 mg g-1). The Elovich model provided the best fit (R2 > 0.90), indicating heterogeneous, activation-controlled sorption. The release of Na+ provided qualitative evidence supporting cation exchange as the predominant sorption mechanism under the evaluated conditions.

Overall, sodium conditioning enhanced metformin sorption by increasing the availability of exchangeable Na+ sites.

Keywords

Clinoptilolite, cation exchange, metformin, pharmaceutical pollution, sorption mechanism.

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