Role of thermal decomposition process in the photocatalytic or photoluminescence properties of BiPO4 polymorphs.

Abstract

Thermal decomposition process was used to obtain modified photocatalytic and/or photoluminescence properties of bismuth phosphate polymorphs. The precursor BiPO4 , 0.7H2 O was synthesized by a coprecipitation route. The observed polymorphs were the hexagonal P31 21 hydrate phase BiPO4 , 0.7H2 O at 25°C, a mix system of hexagonal and monoclinic P21 /n phases at 200°C and 400°C, a mix system of monoclinic phases P21 /n and P21 /m at 600°C, and a unique monoclinic phase P21 /m at 900°C. The X-ray diffraction analyses allowed evidencing lattice deformations due to structural defects. The photocatalytic activities in the presence of rhodamine B in aqueous solution were determined using UV light irradiation. The best photocatalytic efficiencies were observed with the mix systems resulting from thermal decomposition at 400 and 600°C. Photoluminescence experiments performed under UV-laser light irradiation revealed unexpected emissions in the green-orange range, with optimal intensities for the mix systems observed at 400°C. The role of structural defects resulting from decomposition process is discussed. PRACTITIONER POINTS: Thermal decomposition is used to introduce structural defects in BiPO4 polymorphs The BiPO4 intermediate systems are used to photodegrade rhodamine B Active species trapping experiments are performed Photoluminescence experiments highlight green-orange emissions Structural defects are at the origin of this photoluminescence.