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.