How does water of crystallization influence the optical properties, band structure and photocatalytic activity of tungsten oxide?

Both experimental and computational approaches were conducted to elucidate the effect of water of crystallization on optical properties, band structure, and photocatalytic activity of tungsten oxide. WO3 center dot 2H(2)O powder was synthesized at room temperature by the liquid phase deposition (LPD) and, upon annealing, was converted to WO3 center dot 2H(2)O and WO3. The crystallite size was obtained using the Scherrer equation similar to 69 nm for WO3 center dot 2H(2)O, similar to 91 nm for WO3 center dot H2O, and similar to 23 nm for WO3. It was found that the optical band gap energy value for WO3 center dot 2H(2)O (similar to 2.25 eV) is lower than that for WO3 center dot 2H(2)O (similar to 2.55 eV) and WO3 (similar to 2.91 eV), and the electron-hole recombination for WO3 center dot 2H(2)O occurs at a lower rate. The computed data showed that water of crystallization does not change the band gap energy by creating new energy states; instead, it alters the crystal structure and hybridization with crystal atoms. The hybridization is stronger for WO3 center dot 2H(2)O compared to WO3 center dot H2O. The computed phonon-induced pure-dephasing times are faster for the hydrated crystals that, as a result, it leads to a long excited-state lifetime. The experimental results confirmed the computed data that WO3 center dot 2H(2)O showed better photocatalytic activity than WO3 center dot H2O and WO3 , as well as more stable cyclic performance. Instead, WO3 and WO3 center dot H2O acted as better adsorbents for the elimination of methylene blue. The cyclic performance of the photocatalysts decreased to 87.5, 60, and 50% of the initial performance for WO3 center dot 2H(2)O, WO3 center dot H2O, and WO3, respectively.

Automated summary

Both experimental and computational approaches were used to investigate the effect of water of crystallization on the optical properties, band structure, and photocatalytic activity of tungsten oxide. WO3 center dot 2H(2)O showed better photocatalytic performance and stability compared to WO3 and WO3 center dot H2O. The presence of water of crystallization altered the crystal structure and hybridization with crystal atoms, leading to different band gap energies and electron-hole recombination rates.