Deep eutectic solvent-mediated synthesis of W-Mo oxide nanocomposites for enhanced and tunable photochromic response

Abstract

This study details the synthesis and characterization of photochromic tungsten-molybdenum oxide (W-Mo) nanocomposites using a deep eutectic solvent (Ethaline) composed of choline chloride and ethylene glycol in a 1:2 molar ratio, providing a green and efficient fabrication route. FTIR analysis confirmed the successful incorporation of metal oxides into the DES matrix, evidenced by characteristic metal-oxygen (W-O and Mo-O) stretching vibrations observed within the 947-767 cm^-1 and functional group interactions. Scanning electron microscopy imaging revealed agglomerated, irregularly shaped particles with porous morphologies, while energy dispersive X-ray spectroscopy confirmed the homogeneous distribution of W and Mo within the composite. X-Ray diffraction patterns indicated a predominantly amorphous structure with broad peaks corresponding to semicrystalline tungsten and molybdenum oxide phases. Ultraviolet-visible spectroscopy showed strong absorption in the 259-476 nm range, confirming efficient light-induced activation. The nanocomposites exhibited excellent photochromic performance, transitioning rapidly from cream-yellow to blue within three seconds under UV exposure, and reversibly fading in an oxygen-rich environment within 50 min. Electrochemical impedance spectroscopy (EIS) further revealed that the W-Mo (0.8:0.2) composite had the lowest charge transfer resistance, enhancing electron transport and accelerating photo-switching behaviour. The combined structural, optical, and electrochemical properties of these materials underscore their promise for use in smart windows, UV sensors, and dynamic display technologies.