Effective near-infrared absorbent: ammonium tungsten bronze nanocubes

Abstract

Hardly any other compound has realized better optical absorption of near-infrared (NIR) rays (780–2500 nm) than tungsten bronze nanoparticles in terms of absorption coefficient, widths of the working spectrum, photothermal transformation efficiency and their own physicochemical stability. However, efforts concerning the development of tungsten bronze nanoparticles for serving as a NIR absorbent are very limited due to the shortage of effective approaches to obtain these nanoparticles, especially for tungsten bronzes with insertion of bigger cations, such as Cs_xWO₃ and (NH₄)_xWO₃. In this work, we describe how to fabricate (NH₄)_xWO₃ using a high-temperature but short-time solvothermal process, which involves employing oleic acid–oleylamine as the solvent and WCl₆ as the W resource, together with the inspection of its NIR-absorption related properties. The nanocubes of 100 nm have been characterized by XRD, TG-MS, XPS and TEM to examine the crystal phase and nanostructures. Moreover, the dispersion of the nanocubes in the form of a thin film was used to investigate the NIR absorption properties. As determined by the optical test, the thin film consisting of the nanocubes exhibits extraordinary features as a solar control window, which can transmit the majority of visible light while absorbing nearly all of the NIR rays from 780 nm to 2500 nm. Meanwhile, the (NH₄)_xWO₃ thin film can maintain its high shielding effect for the 1064 nm NIR light up to 35.3 kW m⁻² radiation and has excellent cyclic stability for 100 cycles without obvious optical changes. Finally, it has been found that the (NH₄)_xWO₃ nanocubes show a remarkable photothermal conversion phenomenon even when dispersed in a thin film.