Enhanced Photocatalytic Performance of Non-stoichiometric WO 3-x Nanocrystals Via Near-Infrared Localized Surface Plasmon Resonance

The use of non-stoichiometric metal oxides as cheaper and abundant plasmonic materials is an effective way to increase photocatalytic performance. This report shows that WO _3-x nanocrystals exhibit a localized surface plasmon resonance (LSPR) band in the near-infrared (NIR) and photocatalytic activity towards the degradation of methylene blue (MB). In this report, the LSPR absorption spectrum was simulated using the Mie-Gans theory, and free carrier density (N _e ) was calculated. Our findings show that increasing the aspect ratio after calcination shifts the LSPR peak from 1213 to 1771 nm (a remarkable redshift at about 560 nm). In addition, we found that the calcination process leads to the values of N _e as high as 2.03 ×10 ²² cm ^–3 , which is close to that of plasmonic noble metals, and thus our oxide-based nanostructures can be considered as quasi-metallic. Furthermore, the photodegradation rate of W1.5NC for MB was 0.01228 min ^-1 , about 6.3 times higher than that of W3. This shows that the high photocatalytic performance of W1.5NC can be attributed to the significant enhancement of electron-hole pair generation and separation due to localized surface plasmon resonance. Finally, based on photoluminescence (PL) spectroscopy, we proposed a light-harvesting mechanism for WO _3-x nanocrystals.