Photocatalytic degradation of rhodamine B using Mo heterogeneous catalysts under aerobic conditions

MCM-41 based materials were prepared with immobilized MoII and MoVI active sites based on [MoI2(CO)3] and [MoO2Cl2] cores, respectively, using a 2-aminopyridine glycidyloxypropyl derivative as anchoring ligand. Suitable characterization by powder X-ray diffraction, FTIR and, 13C and 29Si solid state NMR spectroscopy was accomplished. All new materials were successfully used in photodegradation experiments of rhodamine B under aerobic conditions. Control experiments using neat MCM-41 and direct photolysis of rhodamine B were also carried out. All experiments were run without any external source of oxygen other than air. Photocatalytic results show that the presence of Mo and its oxidation state is not innocent in this process. In addition, Mo catalysts act most probably by quenching rhodamine B excited state leading to extended degradation of the dye, through secondary photochemistry, beyond a simple de-ethylation process. Density functional theory (DFT) results corroborate with this showing that when rhodamine B is in excited state the xanthene moiety bond orders change.

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► MCM-41 is a high-capacity mass-transfer agent for rhodamine B.
► Mo catalysts are very effective under aerobic conditions.
► Rhodamine B photodegradation by Mo arises from a secondary photochemistry process.
► Mo catalysts quench rhodamine B excited state leading to extended photodegradation.
► Results are sustained by UV–vis and ESI-MS measurements along with TD-DFT data.