Kinetic characteristics of enhanced photochromism in tungsten oxide nanocolloid adsorbed on cellulose substrates, studied by total internal reflection Raman spectroscopy

Abstract

The nanostructured tungsten(VI) oxide (WO₃)/cellulose derivatives (cellulose (CE) and triacetyl cellulose (TACE)) hybrid films were prepared by a solution-dipping adsorption process, and their structure and optical properties have been investigated. Various techniques, including adsorption isotherm, transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), in situUV-Vis absorption, and in situ total internal reflection Raman spectroscopy, were used for the characterization of the WO₃/CE and WO₃/TACE hybrid materials. Under UV irradiation, the photochromism (colorless → blue) was confirmed from the WO₃/CE hybrid film, although no coloration of the WO₃/TACE hybrid film was observed. This distinct difference in the coloration suggested that the interfacial interaction between hydroxyl groups present on the surface of the CE substrate and WO₃ nanoparticlesviahydrogen bonding plays a major role in the enhancement of photochromism in the WO₃/CE hybrid system. Moreover, the joint evidence in in situUV-Vis absorption and in situ total internal reflection Raman studies clearly revealed that the photogenerated coloration is related to a partial reduction of W⁶⁺ cations into W⁵⁺ cations in the WO₃/CE hybrid film. The findings in this study have great implications for the development of the novel green-functional inorganic/organic hybrid materials in optical devices.