Microspherical core-shell MoO2-graphitic C3N4 heterojunction promoted integration leading to Kröhnke pyridines and degradation of xylenol orange

Abstract

In the current study, we fabricated a microspherical core-shell consisting of MoO2 and graphitic-C3N4 by a simple one-step calcination procedure. TEM analysis revealed MoO2 at the core (average diameter of 210 nm), surrounded by a graphitic-C3N4 shell. MoO2 of the core exhibited monoclinic symmetry. The Raman spectrum additionally confirmed the monoclinic MoO2. The sample was EPR active, indicating paramagnetic oxygen vacancies. It contained meso-sized pores and a high surface area. The core-shell’s optical bandgap was higher than the pure metallic MoO2. XPS results confirmed the existence of molybdenum in IV and VI oxidation states. The core-shell’s heterojunction catalyzed the degradation of xylenol orange (XO) dye into C8H9ONH3+, C6H5SO3− and C15H14ONH3+SO3−. The core-shell promoted the efficient synthesis of symmetrical and unsymmetrical 2, 4, 6-triaryl pyridines through the oxidative condensation of acetophenones with benzylamines in good to excellent yields using molecular oxygen as the oxidant. The catalyst is recyclable for both these reactions.