Post-synthetic modification of aluminum trimesate and copper trimesate with TiO 2 nanoparticles for photocatalytic applications.

Organic pollutants have been a significant source of concern in recent years due to their facile dissemination and harmful effects. In this work, two different metal-organic frameworks (MOFs) were initially prepared by hydrothermal treatment, namely aluminum trimesate (MIL-100(Al)) and copper trimesate (HKUST-1). These materials were subsequently submitted to a post-synthetic modification step to grow titania nanoparticles on their surface. Anatase nanoparticles with sizes around 5 nm were successfully anchored on MIL-100(Al), and the concentration of TiO 2 in this sample was about 68 wt.%. This is the first time that this composite (TiO 2 @MIL-100(Al)) is reported in the literature. It showed an improved photocatalytic activity, removing 90% of methylene blue ( k app  = 1.29 h -1 ), 55% of sodium diclofenac ( k app  = 0.21 h -1 ), and 62% of ibuprofen ( k app  = 0.37 h -1 ) after four hours of illumination with UV-A light. A significant concentration (14 µM) of reactive oxygen species (ROS) was detected for this composite. HKUST-1 showed a structural collapse during its post-synthetic modification, leading to a non-porous material and providing fewer sites for the heterogeneous nucleation of titania. This behavior led to a low concentration of rutile nanoparticles on HKUST-1 (9 wt.%). However, the obtained composite (TiO 2 @HKUST) also showed an improved photoactivity compared to HKUST-1, increasing the photodegradation rates evaluated for methylene blue (0.05 h -1 vs. 0.29 h -1 ), sodium diclofenac (negligible vs. 0.03 h -1 ), and ibuprofen (0.01 h -1 vs. 0.02 h -1 ). This work brings new insights concerning the preparation of photocatalysts by growing semiconductor nanoparticles on trimesate-based MOFs.