Physical and photo-electrochemical characterization of natural phosphate material. Application to basic dyes photodegradation

Abstract

Photocatalytic degradation of methyl violet (MV) and rhodamine B (RhB), in single and binary systems, using natural phosphate rock was investigated, motivated by its low cost, abundance, and environmental friendliness. The physical and photo-electrochemical properties of the material were studied. The diffuse reflectance spectrum indicated a direct allowed optical transition at 2.66 eV. The thermal variation of the electrical conductivity showed semiconductor behavior following an exponential type law with low activation energy. Photo-electrochemical studies revealed that the phosphate material exhibited n-type behavior with conduction band of 0.16 VRHE and valence band of 2.82 VRHE, permitting production of both $${\text{O}}_{2}^{ \cdot - }$$ and HO· oxidizing radicals, respectively, responsible of photodegradation of MV and RhB. In single solutions, both dyes were degraded under ultraviolet (UV) light, within 240 min for MV and 330 min for RhB. However, in binary systems, degradation of RhB was effective only when most of the MV had disappeared. Photocatalytic degradation of MV and RhB on natural phosphate.