Selective synthesis of scheelite/perovskite CdWO₄ nanoparticles: a mechanistic investigation of phase formation and property correlation

We proposed a simple solution combustion strategy to fabricate CdWO₄ nanoparticles for the first time in two different polymorphs: a stable monoclinic and metastable tetragonal phase. The selective synthesis of polymorphs has been achieved by optimizing oxidizer to fuel ratio. Influence of oxidizer to fuel ratio on the formation of CdWO₄ polymorphs is of particular relevance to this study and the significant effects are discussed. A mechanistic comparison of properties between two phases has been carried out. Rietveld analyzes of powder X-ray diffraction patterns were performed using GSAS program. Transmission electron microscope images of as synthesized products show the particle sizes of t-CdWO₄ (10–20 nm) are smaller than the particle size of m-CdWO₄ (≈30 nm). The specific surface area was found to be 12 and 25 m²/g for tetragonal and monoclinic phases, respectively. Photocatalytic activities were investigated by the degradation of methylene blue solution under UV light irradiation. It was found that the photocatalytic activity of tetragonal phase was higher than monoclinic phase, this can be attributed to smaller particle size and active sites of the catalyst that rely sensitively on synthetic conditions. We also explored the photoluminescence (PL) properties of t-CdWO₄ and compared with the PL results of m-CdWO₄.