A simple methodology for obtaining novel heterojunction photocatalyst NiO/δ-FeOOH: a theoretical and experimental study

Abstract

A new type of photocatalyst was obtained by heterojunction between δ-FeOOH and NiO using a ball mill. The proportion of NiO in relation to δ-FeOOH was varied, resulting in the materials FN5, FN10 and FN20 (5, 10 and 20% w/w, NiO:δ-FeOOH). The diffractograms confirmed the heterojunction by the presence of crystalline planes of NiO. In addition, the heterojunction formed also reflected in the increase in the band gap of the material and, consequently, in the performance of photocatalysis, especially for FN20, which reached about 72% of dye removal in 4 h. Theoretical studies were carried out to elucidate the mechanisms of photocatalysis by optimization and single-point calculations of NiO and δ-FeOOH structures. The results indicated that, when the light is on, the holes pass from the valence band of NiO to the valence band of δ-FeOOH, whose photoexcited electrons go from its conduction band to the conduction band of NiO. This effect results in decreasing electron/hole recombination rates, improving the photocataylic process when compared to the δ-FeOOH photocatalyst alone. In addition, it was observed that the water oxidation occurs on δ-FeOOH surface, and that this reaction can be thermodynamically favorable.