Mixed Ti-Zr metal-organic-frameworks for the photodegradation of acetaminophen under solar irradiation

Mixed Ti-Zr metal-organic-frameworks (MOFs) have been synthesized and tested as photocatalysts under solar-simulated radiation using acetaminophen (ACE) as target pollutant. These materials were obtained upon partial substitution of Ti by Zr atoms in the crystalline structure of NH2-MIL-125(Ti) MOF. The effect of the Ti:Zr molar ratio on their characteristics and catalytic behaviour has been analysed. Materials with high Zr relative amount (60–80%) showed amorphous structure and low solar-photocatalytic activity. In contrast, lower Zr proportions resulted in new MOFs with well-defined crystalline structure and high activity for the solar photocatalytic degradation of ACE, even higher than that of the bare Ti MOF. Results with scavengers allowed concluding that O2− radicals are the main reactive species, although photogenerated OH radicals and electrons also contribute to the degradation. The stability of the most active photocatalyst was confirmed upon three successive runs.