Ultrafast Microwave Synthesis of WO<sub>3</sub> Nanostructured Films for Solar Photocatalysis
Daniela Nunes, Ana Fragoso, Tainá L. Freire, Maria Leonor Matias, Ana C. Marques, Rodrigo Martins, Elvira Fortunato, Ana Pimentel
Abstract
Tungsten oxide (WO 3 ) nanostructured films are synthesized under microwave radiation with synthesis times of 5 and 10 min, at 150 or 180 °C. This ultrafast synthesis route results in uniform and well‐crystallized WO 3 nanostructured films fully covering the substrates. A plate‐like hierarchical structure is observed at 150 °C, and closely packed rectangular nanorods are formed at 180 °C. For both temperatures, the nanostructures self‐organize into larger flower‐like structures. The increase of the synthesis time from 5 to 10 min at 180 °C results in thicker films, reaching ≈4 μm. X‐ray diffraction (XRD) and Raman spectroscopy reveal that the films grow with the WO 3 orthorhombic crystalline phase ( o ‐WO 3 ·0.33H 2 O). Photoluminescence (PL) measurements are performed for all the films, and their optical bandgaps are estimated through diffuse reflectance spectroscopy. The WO 3 films have their photocatalytic activity assessed from rhodamine B (RhB) degradation under solar radiation. The Mott–Schottky plots confirm the n‐type character of the films with the flat‐band potentials and electron concentrations being estimated for the best photocatalysts. This study associates the eco‐friendly, fast, and low‐cost aspects of the synthesis route to the production of highly photoactive materials, which can effectively contribute to environmental remediation.