Tuning the electronic and structural properties of WO3 nanocrystals by varying transition metal tungstate precursors

Abstract

Oxygen vacancy is one type of the most important defects affecting the photocatalytic performance of WO₃. In this paper, WO₃ nanoplates with a high density of oxygen vacancies were synthesized from MWO₄ (M = Zn, Cd, Co, Ni) precursors using a sacrificial template method. The structures and morphologies of WO₃ nanoplates were investigated by field emission scanning electron microscopy (FE-SEM), high resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis, Photoluminescence (PL), Diffuse Reflectance UV-Vis (DRS UV-Vis) and Time-correlated single-photon counting (TCSPC). The metal tungstates were found to not only act as the precursors but also as structure-directing agents during the growth of WO₃ nanoplates. XRD data revealed that two phases of WO₃·xH₂O (x = 1 or 2) were obtained after acid treatment of MWO₄. WO₃ nanoplates derived from NiWO₄ were found to have the highest ratio of WO₃·2H₂O, highest concentration of oxygen vacancies, narrowest band gap, longest electron–hole recombination time, and in turn the highest rate of photodegradation of azo dye methylene blue. These results show that the structural, electronic and photocatalytic properties of synthesized WO₃ nanoplates can be tuned by varying the transition metal tungstate precursors.