Electron transfers in a TiO₂-containing MOR zeolite: synthesis of the nanoassemblies and application using a probe chromophore molecule

Abstract

New assemblies constituted by a microporous matrix of mordenite (MOR) zeolite on which TiO2 nanoclusters are deposited were synthesized using ionic oxalate complexes and TiCl3 titanium precursors. The samples were used to investigate the transfer of electrons produced by spontaneous or photo-induced ionization of a guest molecule (t-stilbene, t-St) occluded in the porous volume towards the conduction band of a conductive material placed nearby, in the pores or at least close to their entrance. The reaction mechanisms were compared in these Ti-rich solids and in a Ti-free mordenite sample. The characterization by XRD, N2 physisorption, TEM, XPS and DRIFT spectroscopy of the supramolecular TiO2/MOR systems before t-St adsorption showed the preservation of the crystalline structure after Ti addition and thermal activation treatments. They also revealed that titanium is mainly located at the external surface of the zeolite grains, in the form of highly dispersed and/or aggregated anatase. After incorporation of the guest molecule in the new assemblies, diffuse reflectance UV-visible and EPR spectroscopies indicate that the electron transfer processes are similar with and without TiO2 but strongly stabilized t-St˙(+) radicals are detected in the TiO2-MOR samples whereas such species were never detected earlier in TiO2-free mordenite using these techniques. The stabilization process is found to be more efficient in the sample prepared with TiCl3 as the precursor than with titanium oxalates. It is proposed that the proximity of TiO2 with the formed t-St˙(+) radicals provokes the stabilization of the radical through capture of the ejected electron by the semi-conductor and that confinement effects can also play a role.

Fly Ash Waste Recycling by Pt/TiO₂ Incorporation for Industrial Dyes Removal

“…ln C/Co= -kobs t (13) where: co and c are initial dye concentration and the concentration at the moment t and kobs is the overall observed pseudo first-order degradation rate constant.…”

“…One of the shortcomings of this procedure is the difficulty to separate the liquid and the solid photocatalyst after removing the pollutants. For this reason, the researchers have been explored many solid substrate [11][12][13] to immobilize WO3, TiO2 [14]. Thus, FA, by its composition (especially SiO2, Al2O3 and unburned carbon) could be a suitable support material to be optimized as an adsorbent with potential photo-catalytic properties (depending on the burned coal source and composition, small quantities of TiO2, MnO2 can be found in FA).…”

Electron Transfers in Donor–Acceptor Supramolecular Systems: Highlighting the Dual Donor and Acceptor Role of ZSM-5 Zeolite

“…In a first approach, TiO 2 nanoclusters were synthesized directly within the porous network and electron transfer mechanisms were investigated after photoionization of the adsorbed molecule. 41 The results showed that the presence of the semiconductor within the channels slowed considerably the electron transfers after ionization. However, even if this result is consistent with a possible transfer of electrons to the conduction band of TiO 2 , the yield of this reaction was found to be limited because of the diffusion of TiO 2 nanoclusters to the pore entry and aggregate formation.…”

“…To take advantage of these persistent charge-separated states, the following stage would be, for instance, to transfer the unpaired electrons to semiconductor materials present nearby. In a first approach, TiO 2 nanoclusters were synthesized directly within the porous network and electron transfer mechanisms were investigated after photoionization of the adsorbed molecule . The results showed that the presence of the semiconductor within the channels slowed considerably the electron transfers after ionization.…”

Fly Ash Waste Recycling by Pt/TiO2 Incorporation for Industrial Dye Removal

“…One of the shortcomings of this procedure is the difficulty to separate the liquid and the solid photocatalyst after removing the pollutants. For this reason, researchers have explored many solid substrates [17][18][19] to immobilize WO 3 and TiO 2 [20]. Thus, FA, given its composition (especially SiO 2 , Al 2 O 3 and unburned carbon), could be a suitable support material to be optimized as an adsorbent with potential photocatalytic properties depending on the burned coal source and composition, as small quantities of TiO 2 , MnO 2 can be found in FA.…”