Semiconducting properties of hydrothermally synthesized libethenite application to orange G photodegradation

The photo-electrochemical properties of the libethenite Cu2(PO4)(OH) were studied to assess the oxidation of orange G (OG) under both solar and artificial lights. The compound was synthesized by hydrothermal route and characterized by X-ray diffraction, scanning electron microscopy, thermal and chemical analyses, UV–vis diffuse reflectance and electrochemical impedance spectroscopy. The libethenite possesses an optical gap of 1.52 eV and exhibits n type semiconducting behavior with an activation energy of 20 meV. On the basis of photo-electrochemical properties, it was concluded that the conduction band of the material (=4.81 eV/+0.30 VRHE) permits the formation of O2·− radicals for the OG oxidation. A maximum elimination of 94% was obtained upon sunlight within 120 min exposure. The injection process of orange G into the conduction band of the libethenite is confirmed by the photocurrent measurements at different concentrations. The decolorization process proceeds like a photo-Fenton reaction, based on copper ions. Referring to the energetic diagram, a degradation mechanism is proposed. Cu2PO4(OH) catalyst permits to activate H2O2 and initiate the decomposition of OG molecules. The OG removal follows a pseudo-first order kinetic with an apparent rate constant of 6.2×10−3 min−1 under sunlight.