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 O-2(center dot-) radicals are the main reactive species, although photogenerated (OH)-O-center dot radicals and electrons also contribute to the degradation. The stability of the most active photocatalyst was confirmed upon three successive runs.