Abstract
Polycrystalline bismuth phosphate BiPO4 was synthesized by solid-state reaction at different temperatures varying from 500 to 900 °C. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and Raman spectroscopy. The low-temperature phase of BiPO4 has monoclinic structure with a space group P21/n, and was transformed into the monoclinic phase P21/m with a slight distortion of monoclinic lattice when it was heated above 500 °C. The effect of the transformation on the structure, morphology and photocatalytic properties was examined. The photocatalytic activity of each sample, in presence of Rhodamine B (RhB) in aqueous solution, was carried out and analyzed under UV light irradiation. Photoexperiments showed that the material prepared at 500 °C is the best catalyst with degradation efficiency of the order of 96% after 12 min of reaction time under UV light irradiation. This high photocatalytic efficiency could be due to their structural and morphological changes. The photocatalytic degradation mechanism of RhB in the presence of the best photocatalyst BiP-500 °C is proposed. The stability of the catalyst was also examined by carrying out four successive tests of the degradation in the presence of BiP-500 °C. Total organic carbon (TOC) was used to further estimate the rate of mineralization in the presence of BiP-500 °C (83% TOC removal). Photoluminescence experiments performed under UV-laser light irradiation revealed emissions in the green-orange range, with optimal intensities for the mix systems observed at 550 °C.
Highlights
The mineralization of Rhodamine B (RhB) and its intermediates during the photocatalytic reaction was evaluated by the measurement of total organic carbon present in aqueous solution
All the detected diffraction peaks for the BiP-500 sample could be indexed into the monoclinic phase with space group P21 /n (M1 ) single phase
When the calcination temperature increases above 550 ◦ C, the nMBIP phase is progressively transformed into the monoclinic phase of BiPO4 with space group P21 /m (M2 ) (Figure 2)
Summary
Photocatalysis provides a powerful oxidation via the generation of highly oxidizing species, e.g., radicals OH [6,7,8,9] These latter are non-selective and can lead to a good removal of all types of non-biodegradable organic contaminants including dyes, pesticides and pharmaceuticals [10,11,12,13,14,15]. This high photocatalytic activity was explained by the inductive effect of PO4 3− leading to a good separation of the electron and hole pairs [45] For this reason, BiPO4 -based photocatalysts have been extensively studied for environmental remediation applications [40,46,47,48,49].
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