Scalable, Microwave-Enabled Synthesis of Ternary WxTi1-xO2 and Heterostructured TiO2-WO3-x Colloidal Nanocrystals: Carrier Dynamics and Photocatalytic Properties

In solar-light-driven chemical processes, designing ever-new strategies for synthesizing functional, doped, or defective semiconducting oxide nanostructures remains key. Techniques like bandgap engineering and interface heterostructuring, among others, have driven the development of brand-new synthetic schemes that enable efficient charge carrier extraction. In this context, microwave (MW) chemistry has effectively established bottom-up synthetic strategies. This study details a fast MW hydroalcohothermal synthesis for the scalable production of ternary WxTi1-xO2 and heterostructured TiO2-WO3-x colloidal nanocrystals. MWs allow for size control at the nanoscale, and, in the case of heterostructures, support the anisotropic nucleation of oxygen-deficient plasmonic WO3-x nanobelts directly onto the surfaces of pre-existing TiO2 seeds, establishing unique reaction pathways. Femtosecond transient absorption spectroscopy reveals the formation and ultrafast cooling of hot electrons within the plasmonic domains at near-infrared (NIR) wavelengths. Both nanostructures exhibit significant photo-oxidant activity toward 4-methoxybenzyl alcohol in a liquid aerobic environment, concurrently demonstrating enhanced selectivity toward aldehyde products. While the ternary material shows activity and notable selectivity exclusively under UV excitation, the heterostructures provide compelling functionality, especially under solar-simulated light irradiation. This superior performance is ascribed to the synergistic coupling of the NIR-assisted photocatalytic effect driven by hot carriers, along with the photothermal effect arising from plasmon excitation.