Abstract
Mg2+ doped hexagonal ZnO nanoparticles with different Mg2+ contents (0%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20% and 25%) were prepared from oxalate precursors synthesized by direct reaction in the solid state between oxalic acid dihydrate (H2C2O4.2H(2)O), nitrate salts of zinc (Zn(NO3)(2).6H(2)O) and magnesium (Mg(NO3)(2).6H(2)O) at 150 degrees C. The resulting precursors were subsequently calcined at 500 degrees C to produce the corresponding oxides. In addition, the oxalates of the single metals were also prepared by heating at 180 degrees C to dehydrate the complexes, before using TGA thermal gravimetric analysis to determine the temperature range of the decomposition. The obtained oxides were characterized using X-ray Diffraction (XRD), Brunauer-Emmett-Teller technique (BET), transmission electron microscopy (TEM) and tested as photocatalysts in the degradation of methylene blue (MB) under UV irradiation. The results show a segregation of phases starting at an Mg2+ content of 10%. The crystallites' sizes, calculated using Scherer formula from the XRD data, are in the nanoscale for all the samples (19.8 to 29.8 nm), in good agreement with the particle size observed in TEM (20 to 50 nm). However, larger particles sizes were obtained from BET, ranging from 70 to 123 nm, due the agglomerated state of the powder. On the other hand, the highest efficiency as a photocatalyst in the photodegradtion of MB was observed for samples 7 and 8 corresponding to 10% and 15% in Mg2+ content respectively. The reaction rates were found to be 0.57min(-1) for undoped ZnO and 1.17 min(-1) for samples 7 and 8. In this range, the substituted compounds are twice more efficient than the undoped ZnO.