The drug metformin is the most prescribed drug to treat type II diabetes and has been recently reported to have anticancer activities. Because of its wide use, its potential risk on the environment is extremely concerning. In this study, the mechanism and the thermodynamics of the thermo-oxidative decomposition of the metformin were investigated as part of a new solution for the pharmaceutical contamination of water bodies. Thermogravimetry and mass spectrometry were used to demonstrate the metformin thermo-oxidative decomposition under air in the temperature range 25–800 °C. The isoconversional methods of Kissinger-Akahira Sunose (KAS) and Friedman (FR) were implemented to deduce the trends of effective activation energies. As expected, the effective activation energy (E_α) of the reaction was dependent on the reaction temperature, suggesting multi-step reactions. The E_α ranged from 100 to 145 kJ/mol and 200–300 kJ/mol for the KAS and FR methods, respectively. The kinetic triplet, A_α, ΔS^‡, and ΔG^‡ were also determined by finding the appropriate reaction model. Theoretical calculations were implemented to propose a full reaction mechanism. The oxidation of metformin was investigated with both molecular O₂(t) and atomic O(t) oxygen. The experimental results were then explained under the light of the computational data to explain the variation of E_α with temperature, and the competition between the O₂(t)/O(t) species.

Title

Thermochimica Acta

Publisher

Elsevier

Publisher Country

Netherlands

Indexing

Scopus

Impact Factor

3.1

Publication Type

Both (Printed and Online)

Volume

694

Year

2020

Pages

13