Phase-Transition Induced Conversion into a Photothermal Material: Quasi-Metallic WO_2.9 Nanorods for Solar Water Evaporation and Anticancer Photothermal Therapy

Phase transition from WO₃ to sub-stoichiometric WO_2.9 by a facile method has varied the typical semiconductor to be quasi-metallic with a narrowed band gap and a shifted Femi energy to the conduction band, while maintaining a high crystallinity. The resultant WO_2.9 nanorods possess a high total absorption capacity (ca. 90.6 %) over the whole solar spectrum as well as significant photothermal conversion capability, affording a conversion efficiency as high as around 86.9 % and a water evaporation efficiency of about 81 % upon solar light irradiation. Meanwhile, the promising potential of the nanorods for anticancer photothermal therapy have been also demonstrated, with a high photothermal conversion efficiency (ca. 44.9 %) upon single wavelength near-infrared irradiation and a high tumor inhibition rate (ca. 98.5 %). This study may have opened up a feasible route to produce high-performance photothermal materials from well-developed oxides.