Tailoring of nanocrystals Bi2WO6 glass ceramics decorated with Sm3+ and Eu3+ ions for improving photocatalytic activity

Abstract

For the first time in glass ceramics, pure Bi2WO6 nanocrystals were synthesized. This was achieved by preparing glass samples have a specific composition of SiO2-B2O3-NaF-WO3-SeO2-Na2O-Bi2O3 with 0.05 mol.% (Sm3+ or/and Eu3+) via melt-quenching technique. Then through a differential scanning calorimetry (DSC) study, the controlled heat treatment process for the glass samples was determined at 500°C/2hrs to obtain their glass-ceramic counterparts. Doping by Sm3+ or/and Eu3+ decreased the glass transition temperature (Tg) from 467, 426, 350 to 344° C and the crystallization temperature from 535, 508, 481 to 433° C for the samples in the order of W, WSm, WEu, and WSE, respectively. Vibrational modes associated with SiO4, BO4 and BO3 units were confirmed by FTIR measurements. RE-doped glass showed characteristic visible - NIR absorption peaks due to the respective rare earth ions. Orthorhombic Bi2WO6 nanocrystals were obtained in glass ceramic samples, except WSE sample exhibited crystallization of Bi2WO6 as a major phase beside traces of Bi2O3, as shown by X-rays. Bi2WO6 crystallized in 2D sheet-like nanocrystals measuring less than 10 nm in size based on SEM and TEM studies. XPS analysis confirmed the triple valence of Eu3+ and Sm3+ ions into Bi2WO6. Photoluminescence measurements revealed distinct emission peaks from Sm and Eu ions in both glass and glass-ceramic samples, ranging from red to white light. Using UV–vis DRS, the optical band gap energy (Eopt) was estimated for glass-ceramic samples, showing values within the semiconductor range (∼2.8 eV). Photocatalytic activity was evaluated by degradation of methylene blue (MB) under UV and natural sunlight. All studied glass ceramics showed high photocatalytic efficiency. Remarkably, doping with Eu3+ significantly enhanced photocatalytic activity, exceeding 85% after 1 hour under UV or sunlight irradiation, followed by Sm3+ doping, and then doping with both Eu3++ Sm3+. Based on the obtained results, the studied samples are potentially useful as visible light photocatalysts, semiconductors, and photoluminescent glass ceramics.