Conjugated polymer coated MIL-125(Ti) as an efficient photocatalyst for selective oxidation of benzylic C-H bond under visible light

Abstract Selective oxidation of saturated C-H bonds to value-added chemicals under mild conditions is of great importance in chemical community. In this work, conjugated polymer (PMPTA) coated MIL-125(Ti) composites with type I heterojunction structure were obtained from the mixture of MIL-125(Ti), melamine and terephthalaldehyde via a solvent-free hydrothermal method. The MP-30 with optimal composition has excellent photocatalytic activity for the selective oxidation of benzylic C-H bonds to their corresponding aldehydes and ketones under the illumination of 420 nm light using O2 as oxidant and N-Hydroxyphthalimide (NHPI) as co-catalyst. The conversions of fluorene catalyzed by MIL-125(Ti) and PMTPA are 32% and 65%, respectively, while the conversions of fluorene over MP-20, MP-30 and MP-40 are significantly improved, which are 86%, 99% and 77%, respectively. The characterization results from photoluminescence spectroscopy, photocurrent and band gap positions demonstrate that the one-way transfer of electrons and holes between the MIL-125(Ti) and PMTPA through the heterojunction structure allows the substrate to react rapidly on the outer layer of heterostructured MIL-125(Ti)/PMTPA, resulting an increase in photocatalytic efficiency. Moreover, the introduced heterojunction structure reduces the recombination of photo-generated electrons and holes and improves the efficiency of the conversion of holes into reaction intermediates.