Solar-Light-Responsive Titanium-Sheet-Based Carbon Nanoparticles/B-BiVO4/WO3 Photoanode for the Photoelectrocatalytic Degradation of Orange II Dye Water Pollutant.

We report the preparation and application of a heterostructured photoelectrocatalyst comprising carbon nanoparticles (CNPs) and boron codoped BiVO4 and WO3 for the removal of an organic dye pollutant in water. The materials, synthesized by hydrothermal method, were characterized by X-ray diffraction, diffuse reflectance UV-visible spectroscopy, energy-dispersive X-ray spectroscopy, and electron microscopy. The catalysts were immobilized on treated titanium sheets by drop-casting. The fabricated electrodes were characterized by linear sweep voltammetry (LSV) and chronoamperometry. Diffuse reflectance spectroscopy of the catalysts reveals that the incorporation of CNPs and B into the structure of monoclinic BiVO4 enhanced its optical absorption in both UV and visible regions. The LSV measurements carried out in 0.1 M Na2SO4 showed that the BiVO4- and WO3-based photoelectrode demonstrated significant photoactivity. CNP/B-BiVO4 and CNP/B-BiVO4/WO3 photoanodes gave photocurrent densities of approximately 0.83 and 1.79 mA/cm2, respectively, at 1.2 V (vs 3 M Ag/AgCl). The performance of the electrodes toward degradation of orange II dye was in the order BiVO4 < B-BiVO4 < WO3 < CNP-BiVO4 < CNP/B-BiVO4 < CNP/B-BiVO4/WO3, and the apparent rate constants obtained by fitting the experimental data into the Langmuir Hinshelwood kinetic model are 0.0924, 0.1812, 0.254, and 0.845 h-1 for BiVO4, WO3, CNP/B-BiVO4, and CNP/B-BiVO4/WO3, respectively. The chemical oxygen demand abatement after 3 h of electrolysis at the best performing photoanode was 58%. The study showed that BiVO4 and WO3 are promising anodic materials for photoelectrocatalytic water treatment plant.

Photoelectrocatalytic application of palladium decorated zinc oxide-expanded graphite electrode for the removal of 4-nitrophenol: experimental and computational studies.

A novel Pd-ZnO-expanded graphite (EG) photoelectrode was constructed from a Pd-ZnO-EG nanocomposite synthesised by a hydrothermal method and characterised using various techniques such as X-ray diffractometry (XRD), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, nitrogen adsorption-desorption analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Cyclic voltammetry and photocurrent response measurements were also carried out on the electrode. The Pd-ZnO-EG electrode was employed in the photoelectrocatalytic removal of 4-nitrophenol as a target water pollutant at a neutral pH and with a current density of 7 mA cm-2. Optical studies revealed that the Pd-ZnO-EG absorbed strongly in the visible light region. The Pd-ZnO-EG electrode showed improved photoelectrocatalytic activity in relation to ZnO-EG and EG electrodes for the removal of the 4-nitrophenol. The photocurrent responses showed that the Pd-ZnO-EG nanocomposite electrode could be employed as a good photoelectrode for photoelectrocatalytic processes and environmental remediation such as treatment of industrial waste waters. Density functional theory method was used to model the oxidative degradation of 4-nitrophenol by the hydroxyl radical which generates hydroquinone, benzoquinone, 4-nitrocatechol, 4-nitroresorcinol and the opening of the 4-nitrophenol ring. Furthermore, the hydroxyl radical is regenerated and can further oxidise the ring structure and initiate a new degradation process.