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

Abstract

We proposed a simple solution combustion strategy to fabricate CdWO 4 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 CdWO 4 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-CdWO 4 (10-20 nm) are smaller than the particle size of m-CdWO 4 (≈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-CdWO 4 and compared with the PL results of m-CdWO 4 .

Modulation of Magnetic and Luminescence Properties via Control Cu-Doped in CdWO4 Nanorods for Photocatalytic Applications

“…17−21 Hydrothermal is the most commonly utilized method for synthesizing monoclinic and tetragonal CdWO 4 nanostructures. 22 Furthermore, syntheses of CdWO 4 nanostructures with different morphologies (e.g., nanowires, nanorods, and nanoparticles) have been reported using the hydrothermal method by tuning the experimental conditions. 16 Among these, CdWO 4 nanorods exhibited a more enhanced luminescence than nanowires and nanoparticles, which is attributed to the difference in the preferred growth directions and crystallinity.…”

“…Cadmium tungstate CdWO 4 with a monoclinic wolframite structure is one of the widely studied materials in the vast tungstate family because of its high refractive index, chemical/thermal stability, X-ray absorption coefficient, good scintillation, low-radiation damages, and afterglow. − The above unique properties have triggered intense research on the uses of CdWO 4 for potential applications in X-ray and γ-ray detectors, phosphorescence, optical devices, and photocatalysts. − However, the monoclinic CdWO 4 exhibits a diamagnetic property with a wideband gap of 3.7 eV, much larger than the conventional photocatalyst TiO 2 (3.2 eV), limiting its widespread applications. Thanks to technological advancements, the properties of pure compounds can be modulated through size reduction, surface modification, composites, different morphologies, and the introduction of a foreign impurity atom. ,− Many preparation methods have been introduced to form crystalline CdWO 4 nanostructures like microwave, sol–gel, sonochemical, molten salt, and hydrothermal. − Hydrothermal is the most commonly utilized method for synthesizing monoclinic and tetragonal CdWO 4 nanostructures . Furthermore, syntheses of CdWO 4 nanostructures with different morphologies (e.g., nanowires, nanorods, and nanoparticles) have been reported using the hydrothermal method by tuning the experimental conditions .…”

Review of Recent Studies on Solution Combustion Synthesis of Nanostructured Catalysts

“…ZnWO 4 nanopowder photocatalyst has been successfully delivered by the employment of Zn(NO 3 ) 2 .6H 2 O as metal precursor, sucrose as reducer and peroxo tungstic acid as tungsten source, while its photocatalytic performance was investigated by Eranjaneya and Chandrappa for the degradation of methylene blue (MB) solution under UV light irradiation.…”

CdWO4:Eu3+ Nanostructures for Luminescent Applications

“…Recently, luminescent materials with different emission colors have been developed in optical, sensing, biomedical, and energy-related applications . As one kind of important inorganic luminescent materials, tungstate has been widely investigated due to the luminescent applications in diverse fields (e.g., lasers, sensors, and optical fibers). − Cadmium tungstate (CdWO 4 ) possessing monoclinic wolframite crystal structure has attracted great attention because of its many advantages such as high average refractive index, good scintillation properties, low-radiation damages, high chemical stability, and high X-ray absorption coefficient. − Therefore, extensive researches have been focused on the development of CdWO 4 for applications in X-ray detectors, phosphors, and optical devices. − As a self-activating phosphor, its luminescence is due to the charge transfer between excited O 2– 2p orbitals and the empty W 6+ 5d orbitals or structure defects. , Many efforts have been made to form CdWO 4 crystals like sol–gel, hydrothermal, molten salt, and microwave methods. − For example, the structure of CdWO 4 (e.g., monoclinic and tetragonal) can be tuned by a hydrothermal method, and the morphologies can be controlled via a sonochemical method . Furthermore, CdWO 4 can be deposited by reduced graphene oxide under hydrothermal conditions, leading to the enhancement of photocatalytic performance .…”