Abstract
In this study, nanoparticles of five photocatalytic systems based on pure zinc oxide and with rare earths ions M-ZnO (M = La3+, Ce3+, Pr3+ or Nd3+) calcined at 500 °C or 700 °C were synthesized and investigated as potential photocatalysts for the removal of dyes. The addition of rare earth ions causes a decrease in the bandgap of ZnO; therefore, it can be well used to improve the photocatalytic properties. The photocatalytic activity of the synthesized nanoparticles was evaluated by the degradation of Rhodamine B in the presence of H2O2 under ultraviolet illumination. The results indicate that all the synthesized nanoparticles show good dye degradation efficiency. The highest degradation efficiency was 97.72% for the Ce-ZnO sample calcined at 500 °C and was achieved in 90 min with an excellent constant of the dye degradation rate k = 0.0363 min−1 following a first-order kinetic mechanism. The presence of oxychlorides as secondary phases inhibits the rate of the photocatalytic reaction.
Highlights
The preparation and study of nanoscale zinc oxide is currently of great interest.ZnO is a semiconductor material, which crystallizes in two main well-known forms: hexagonal wurtzite and cubic zinc blende
Zinc oxide with a rock salt structure can be obtained at high pressures; it can exist in nanostructured forms and, due to stabilization in matrices, a cubic structure [2]
The results indicate that the morphological, crystalline, optical, surface properties and photocatalytic activity of the synthesized nanoparticles were influenced by the presence of rare earths (RE) ions and calcination temperature
Summary
ZnO is a semiconductor material, which crystallizes in two main well-known forms: hexagonal wurtzite and cubic zinc blende. Zinc oxide with a rock salt structure can be obtained at high pressures; it can exist in nanostructured forms and, due to stabilization in matrices, a cubic structure (for example, MgO, NaCl) [2]. ZnO with wurtzite-like structure is thermodynamically stable, due to its tetrahedral structure, where each zinc atom is coordinated with four oxygen atoms. In any of the existing forms, ZnO is a semiconductor material with a wide and direct bandgap ranging from 3.1 to 3.3 eV and a gap bond energy of 60 meV, making it a material with low photocatalytic activity [3,4]. Due to its excellent dielectric, ferroelectric, piezoelectric and pyroelectric properties, ZnO is considered a multifunctional materials and has a wide range of applications such as solar cells [5], gas sensors [6], piezoelectric devices and field emission devices [7]
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