Microwave-assisted synthesis of NH2-MIL-125(Ti) for the solar photocatalytic degradation of aqueous emerging pollutants in batch and continuous tests

NH2-MIL-125(Ti) MOFs have been prepared by microwave-assisted synthesis under different conditions of temperature (140–200 ºC) and holding time (15 min to 4 h). The resulting materials have been tested as photocatalysts for the breakdown of six pharmaceuticals in aqueous solution under solar simulated irradiation. A full characterization of the solid samples by X Ray Diffraction, N2 adsorption-desorption, UV–visible DRS, and photoluminescence techniques was carried out. The MOF prepared at 200 ºC under 15 min microwave radiation displayed the best-defined crystalline structure and most developed porosity (1030 m2 g-1 BET surface area and 0.45 cm3 g-1 pore volume), with good optical properties for visible light absorption (bandgap 2.59 eV). This photocatalyst showed the best performance in the removal of diclofenac (complete conversion in 3 h; pseudo-first order rate constant of 1.11 ± 0.09 h-1) in batch tests. Further diclofenac photo-degradation experiments under continuous flow confirmed the high stability of the MOF with no loss of photocatalytic activity (10 h of time on stream). The degradation of a mixture of six other pharmaceutical compounds (acetaminophen, ciprofloxacin, tetracycline, sulfamethoxazole, diclofenac and ibuprofen) was also studied to learn more on the efficiency of the process against compounds of different chemical structure.