Electrodeposition of nanostructured γ-MnO2 film for photodegradation of Rhodamine B

Abstract

In this work, we report the results of the electrodeposition of MnO2 film on stainless steel (SS) electrode in aqueous MnSO4 solution which was used as photocatalyst to degrade the Rhodamine B (RhB). Different techniques such as field emission gun scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Braunauer Emett and Teller (BET), and UV-visible diffuse reflectance spectroscopy (UV-vis DRS) were used to characterize the deposited MnO2 film. It was found that MnO2 is electrodeposited as a γ-MnO2 nanoparticle film with a low rate of crystallinity and high specific surface area of about 140 m2 g−1. The particle size is less than 20 nm. In addition, the diffuse reflectance measurements show that the γ-MnO2 presents a direct band gap of about 1.41 eV. The Mott-Schottky plot confirms that γ-MnO2 is a n-type semiconductor with the flat band potential VFB = 0.016 V vs. Ag/AgCl and the electron concentration ND = 0.8 × 1020 cm−3. The conduction and valence energy band values were estimated at Ec = 4.498 eV and Ev = 5.908 eV, respectively. It was shown also that these films exhibit good ability for the degradation of RhB especially under visible light irradiation. Indeed, degradation rates of about 90 and 55% were obtained after 60 min of visible and UV light irradiation, respectively. Finally, the degradation process mechanism of RhB is discussed.