Post-synthetic modification of aluminum trimesate and copper trimesate with TiO2 nanoparticles for photocatalytic applications

Abstract

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.

Iodine Uptake by Zr-/Hf-Based UiO-66 Materials: The Influence of Metal Substitution on Iodine Evolution

“…In this process, when an electron (e – ) jumps into the CB, it leaves a hole (h + ) in the VB, which is considered as a positive charge . Although these entities have relatively low lifetimes and can annihilate themselves by recombining due to electrostatic interactions, this effect is reduced for materials with low mobility of charge carriers (electrons and holes) . In this scenario, some materials can trap the produced electrons, the holes, or both .…”

“…58 Although these entities have relatively low lifetimes and can annihilate themselves by recombining due to electrostatic interactions, this effect is reduced for materials with low mobility of charge carriers (electrons and holes). 59 In this scenario, some materials can trap the produced electrons, the holes, or both. 60 Because UiO-66 compounds present a pure linker-based transition, 36 both the electrons and holes are created in the aromatic part of the UiO-66 network, which is confirmed by the absence of a redox phenomenon on the metal siteas demonstrated by EPRand can be related to the low binding energy of the d 0 orbitals of Zr 4+ and Hf 4+ .…”

Electron-Donor Functional Groups, Band Gap Tailoring, and Efficient Charge Separation: Three Keys To Improve the Gaseous Iodine Uptake in MOF Materials

“…A common method for assessing the E g energies of powdered materials is to first acquire optical absorbance data (α)in this case α ≈ F­(R), according to the Kubelka-Munk modeland then, to plot the (α h ν) n values against the photon energy h ν . The band gap value is then obtained in the interception between the (α h ν) n curve and the x -axis . It is worth mentioning that, when the compound presents a preabsorption band, a baseline correction must be performed before the E g measurement .…”

“…First, the presence of titanium oxide (as anatase or rutile) in the MIL-125(Ti) and MIL-125(Ti)_NH 2 samples was discarded after verifying that there is no sharp band at about 140−150 cm −1 related to TiO 2 species in the Raman spectra, which is in accord with the powder XRD results (Figure 1 and 4a). 39 When focusing on the inorganic cluster vibrational modes, the Raman spectra of MIL-125(Ti) and MIL-125(Ti) _NH 2 present a band related to the titanium cation with a typical octahedral coordination environment at 703 and 691 cm −1 , respectively. 32 Additionally, a similar signal was found for CAU-1(Al)_NH 2 at 697 cm −1 , which should be ascribed to the equivalent vibrational mode of the aluminum species in octahedral coordination.…”

“…51 The band gap value is then obtained in the interception between the (αhν) n curve and the x-axis. 39 It is worth mentioning that, when the compound presents a preabsorption band, a baseline correction must be performed before the E g measurement. 52 Also, the type of transition exhibited by the material is specified depending on the best fit for the n values (n = 2 for direct semiconductors or n = 1/2 for indirect semiconductors) in the (αhν) n vs hν plot.…”