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

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.

Highly efficient nanostructured CoFe2 O4 thin film electrodes for electrochemical degradation of rhodamine B.

In this work, we report the application of highly efficient electrodeposited cobalt ferrite (CoFe2 O4 ) thin films in electrochemical degradation of rhodamine B. XRD, FTIR and Raman spectroscopic studies confirmed the formation of single phase CoFe2 O4 . SEM analysis revealed a very fine nanorods dispersed uniformly with average size around 30 nm. UV-Vis spectrophotometry emphasized that the optical band gap value is 1.6 eV. Moreover, the elaborated CoFe2 O4 thin films showed a good efficiency for the electrochemical degradation of an aqueous solution of rhodamine B (RhB) attaining 99% during the first 3 min of reaction time. The trapping experiments revealed that the hydroxyl radicals were the main active species leading to the removal of RhB initial concentration of 10 mg/L in a very short time. PRACTITIONER POINTS: A simple electrodeposition technique was used to fabricate CoFe2 O4 thin. XRD and FTIR studies revealed the formation of pure cubic spinel phase. Nano-rod like morphology has been successfully synthesized. The rhodamine B aqueous solution has been completely decolorized using the obtained CoFe2 O4 thin films.