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

Abstract

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.