From highly reactive amorphous tantalum oxide to tantalum nitride. Impact of the nitridation temperature on the optical and photocatalytic properties
Résumé
Recently, much further attention has been paid to functional (oxy)nitrides as emerging materials for environmental and energy applications considering the specific tuning properties offered by the nitrogen/oxygen substitution. Among them, red tantalum nitride Ta3N5 is particularly regarded as a visible-light driven photocatalyst because its narrow bandgap of 2.2 eV allows harvesting of most of the visible range of the solar spectrum. In order to enhance the photocatalytic activity of the material, the morphology of the powder is an important parameter, thus soft chemistry route are usually required to for the synthesis of the oxide precursor Ta2O5 as conventional commercial product are usually not suited due to micrometric grain size. A better control of the particle size and specific surface area of the oxide precursor also allows to lower nitridation reaction time and temperature and limit the generation of reduced defects detrimental to optical and photocatalytic properties of Ta3N5. However, there is only a few options for the starting materials for the synthesis of the Ta2O5 using soft chemistry routes, such as oxalate (Ta(C2O4)x), chloride (TaCl5) or alkoxydes (Ta(OEt)5) that are costly and highly moisture sensitive for some. We propose here a simple approach for the amorphization of commercial Ta2O5, involving the use of potassium bisulfate (KHSO4), in order to improve its reactivity towards ammonia and thus lower nitridation temperature. Structural, optical and photocatalytic properties of the as-prepared Ta3N5 will be discussed based on XRD, UV/Vis, O/N, SEM characterizations as well as methylene blue (MB) photodegradation experiments under visible irradiation.
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