ZnO-TiO2 Nanoparticles Coated by the Dioxomolybdenum (VI) bis-Schiff Base Complex for Catalytic Oxidation of Sulfides

Theoxygenation processes for the organic compounds have greatapplications in fine organic fabrications. To speed up progress inthe industrialization of such oxidation systems, a monometallic dioxomolybdenum(VI) bis-Schiff base complex (MoO2L2) was synthesized through coordination of easily accessible4-hydroxyiminophenol ligand (HL) with cis-MoO2 (2+) ion in an octahedral geometry. The structuralconformation of MoO2L2 and its coordinated ligand(HL) was determined using modern spectrophotometric tools. A heterogeneouscatalyst (MoO2L2@ZnO-TiO2)was successfully prepared by immobilization of MoO2L2 on the surface of ZnO-TiO2 nanostructuredparticles through the deprotonation of 4-OH group in its coordinatedligand. Various analytical techniques were used to examine the surfacemorphology and internal structure features of ZnO-TiO2 and MoO2L2@ZnO-TiO2 nanocomposites.To study the catalytic efficiency of MoO2L2 andMoO(2)L(2)@ZnO-TiO2-based catalysts,they were employed in the oxygenation process of Ph2S (diphenylsulfide) and MePhS (methylphenyl sulfide) using the most environmentallyfriendly oxidant (an aqueous H2O2) under anaerobic environment. A high degree of selectivity was observed forthe productivity of diphenyl sulfoxide (Ph2SO) and methylphenylsulfoxide (MePhSO), with some contamination of overoxidation sideproducts (Ph2SO2 and MePhSO2). Thecatalytic oxidative ability was not observably superior for the heterogeneouscoated catalyst by ZnO-TiO2 over its homogeneousone (MoO2L2) due to the less redox activityof ZnO and TiO2 nanoparticles in the catalytic cycles forthe oxygen-transfer mechanism. Both catalysts were successfully recycled,in which the homogeneous catalyst sustained its high catalytic potentialfor up to three cycles, while the heterogeneous catalyst was ableto be reused up to six times.