Supported MOCVD TiO₂ Thin Films Grown on Modified Stainless Steel Mesh for Sensing Applications

Among semiconductor metal oxides, that are an important class of sensing materials, titanium dioxide (TiO₂) thin films are widely employed as sensors because of their high chemical and mechanical stability in harsh environments, non-toxicity, eco-compatibility, and photocatalytic properties. TiO₂-based chemical oxygen demand (COD) sensors exploit the photocatalytic properties of TiO₂ in inducing the oxidation of organic compounds to CO₂. In this work, we discuss nanostructured TiO₂ thin films grown via low-pressure metal organic chemical vapor deposition (MOCVD) on metallic AISI 316 mesh. To increase the surface sensing area, different inorganic acid-based chemical etching protocols have been developed, determining the optimal experimental conditions for adequate substrate roughness. Both chemically etched pristine meshes and the MOCVD-coated ones have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) microanalysis, and X-ray photoelectron spectroscopy (XPS). We demonstrate that etching by HCl/H₂SO₄ at 55 °C provides the most suitable surface morphology. To investigate the behavior of the developed high surface area TiO₂ thin films as COD sensors, photocatalytic degradation of functional model pollutants based on ISO 10678:2010 has been tested, showing for the best performing acid-etched mesh coated with polycrystalline TiO₂ an increase of 60% in activity, and degrading 66 µmol of MB per square meter per hour.