Mn-modified HfO2 nanoparticles with enhanced photocatalytic activity

Abstract Round shaped Mn-modified HfO2 nanoparticles were prepared by the Pechini type sol-gel method. The effects of Mn ions on the structure, particle growth, composition, optical properties and photocatalytic performance of HfO2 particles were investigated. The structure analysis revealed that the insertion of Mn2+, Mn3+, and Mn4+ ions inhibited the complete stabilization of tetragonal HfO2. Also, the decrease of particle size to values lower than 5 nm and the shift of optical band gap from 5.7 to 2.1 eV was obtained as effect of increasing the Mn content. HfO2 nanoparticles modified with 10 w% Mn exhibited the highest photocatalytic performance, reaching an efficiency of 91.93% in the decomposition of methylene blue, after 120 min of sunlight irradiation. The efficient trapping of photogenerated electrons on the surface of these nanoparticles generated •O2− radicals, which were the main oxidative species involved in the degradation of the dye. The improved photocatalytic performance of these nanoparticles is then attributable to their increased surface area, suitable photoactivation, and effective transport of photoexcited charge carriers. Based in studies of band gap, valence band position and active species, a mechanism of photodegradation for this photocatalyst was also proposed and discussed.