A facile one-pot synthesis of TiO2-based nanosheets loaded with Mn O nanoparticles with enhanced visible light–driven photocatalytic performance for removal of Cr(VI) or RhB

This paper reports a facile one-pot approach for MnxOy (Mn = Mn2+, Mn3+) loaded TiO2-based nanosheets (Mn–TNSs) with surface enrichment of MnxOy nanoparticles via a simple hydrothermal route. The as-synthesized samples showed clearly sheet-like structure, with high specific surface area (200–300 m2/g) and small thickness (ca. 4 nm). The small MnxOy nanoparticles with uniform size (1–2 nm) were highly dispersed on the surface of the TNSs. Loaded MnxOy not only have influenced the crystal structure and surface area of the TNSs, but also resulted in considerable enhancement of visible-light absorption and red-shift for TNSs. The results of X-ray photoelectron spectroscopy showed that Mn2+ and Mn3+ co-exist in Mn–TNSs. The loading of MnxOy on TNSs resulted in changes in binding energies of Ti and O. The concentration of Ti3+ increased gradually with the amount of loaded MnxOy increasing. The photo-reactivity of the samples were evaluated by measuring the formation of photo-induced hydroxyl radical (OH) using coumarin (COU) as a probe molecule and photocatalytic degradation of Rhodamin B (RhB) and dichromate (Cr(VI)) under visible-light irradiation. It has been found that the Mn–TNSs photocatalysts showed better visible-light photocatalytic activity for aqueous RhB or Cr(VI) solution. The photocatalytic activity gradually increased with the content of MnxOy increasing initially, and then decreased after attaining a maximum value at an optimal content (2.5 at.%) of MnxOy in TNSs for degradation of aqueous RhB or Cr(VI) solution, respectively. The cyclic tests that performed five times demonstrated high stability and recyclable usability of the photocatalysts. A possible alternate mechanism for the enhancement of the photocatalytic activity under visible-light irradiation was also proposed.