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A porous coating assembled with hierarchical 3D Co 3 O 4 urchin-like particles was synthesized by Pulsed Laser Deposition (PLD) and thermal oxidation. Laser ablation of Co B powder, used as the target material, in oxygen atmosphere formed core–shell particles on the coating surface with mainly a metallic Co core and a mixture of Co, B and O accommodating the shell. The thermal oxidation of these core–shell particles in air at 600 °C induces the morphological transformation to urchin-like particles consisting of nanowires (NWs) (diameter: 30–60 nm and length 1–3 μm) grown radially from the core surface. The extrusion marks on the surface of NWs indicate that the stress induced growth process is caused by difference in the thermal expansion coefficient. XRD, Raman, EXAFS and HRTEM analysis confirmed that the NWs are polycrystalline consisting of pure Co 3 O 4 phase. A wet-chemistry hydrothermal procedure was also employed to synthesize nanostructured urchin-like particles which are hollow and the structure is held together by the radially oriented nanorods (diameter: 40–150 nm). During photocatalysis, urchin-like particles synthesized by PLD displayed significantly higher (∼5 times) degradation rates when compared to chemical urchins for degradation of methylene blue dye via a photo-Fenton reaction in presence of H 2 O 2 and visible light. This is mainly attributed to poor stability of the nanorods in the chemical urchin structure. Features such as high surface area, enhanced stability against agglomeration, polycrystalline nature of the NWs, porous surface and superior adhesion, are responsible for the enhanced photocatalytic activity of Co 3 O 4 urchin-like particles assembled in a porous coating synthesized by PLD and thermal oxidation. Reusability tests also demonstrate the robust nature of the catalyst coating. [ABSTRACT FROM AUTHOR]

Highlights: [•] V–N-codoped TiO2 thin films have been prepared using RF-magnetron sputtering. [•] The band gap was narrowed up to 2.5eV when V and N were codoped in TiO2. [•] V–N-codoped TiO2 thin film was able to degrade organic water pollutants much faster than mono-doped and undoped TiO2. [•] Increased visible light absorption and charge separation are mainly responsible for enhanced photocatalytic activity for codoped-TiO2. [ABSTRACT FROM AUTHOR]

Abstract: V- and N-codoped TiO2 photo-catalyst is synthesized by sol–gel method to sensitize TiO2 to visible light. The concentrations of V and N were varied and optimized to enhance photo-catalytic activity. In order to increase the active surface area, the crystalline powder was ball milled to obtain nanosized particles. The photo-catalysts were characterized by Micro-Raman, TEM, XPS and UV–vis (in diffused reflectance mode) techniques. The co-doped TiO2 photocatalyst displayed narrower band gap (2.3eV) compared to singly doped TiO2 catalyst, namely V (2at.%)-doped (2.42eV), N (4at.%)-doped (2.95eV), and undoped TiO2 (3.13eV). The photocatalytic activity for the degradation of Rhodamine B (an organic dye) under visible light irradiation obtained with co-doped TiO2 photo-catalyst is significantly better as compared to the undoped, V-doped, and N-doped TiO2. The incorporation of V and N in TiO2 lattice induces isolated energy levels near the conduction and valence bands, respectively, causing an effective narrowing of the band gap. In addition, due to the low dopants concentrations, these energy levels can also act as traps for photoexcited holes or electrons thus reducing the recombination between photo-generated charges. Both these effects, namely band narrowing and enhanced charge separation produce synergistic effects to increase the photocatalytic activity of V-N-codoped TiO2. [Copyright &y& Elsevier]