Pulsed laser deposition of nanostructured tungsten oxide films: A catalyst for water remediation with concentrated sunlight

The increasing interest for addressing photocatalyst materials towards an effective application with sunlight is an important topic in materials science. We present here a novel investigation of tungsten trioxide (WO3) coatings fabricated by pulsed laser deposition (PLD) with the aim of providing a nanostructured photocatalyst capable of working with concentrated sunlight and exhibiting good stability in acidic environment. This is important since: (1) acidic pH is common in industrial wastewaters and (2) acidic pH is also known to enhance photo-Fenton reactions. Samples produced by PLD were deposited on glass slides with area of 19 cm2 and then thermally annealed at different temperatures (200, 400 and 600 °C) for 8 h to investigate the growth mechanism of WO3. Material characterization was performed by scanning electron microscopy (SEM), X-Ray diffraction (XRD) and micro-Raman, revealing the growth of a crystalline monoclinic phase of WO3 with a highly structured surface featuring nanoflakes in a flower-shape like structure with an energy bandgap of 2.6 eV. To study its photocatalytic properties, the catalyst annealed at the temperature of 600 °C evolved into a complete WO3 oxide presenting monoclinic phase and was investigated under labscale artificial visible light in both direct photocatalysis and in presence of H2O2 as a radical source (photo-Fenton-like process) using 10 ppm solutions of the Methylene Blue (MB) dye as a model pollutant. The study was then replicated in higher volume scale under concentrated solar light from a parabolic dish concentrator (PDC) apparatus to demonstrate application. Results highlighted high surface adsorption of 15%, 54% total MB degradation on direct photocatalysis and 85% in the photo-Fenton-like mode after 120 min of experiment.