Highly reversible photochromism in composite WO3/nanocellulose films

Reversible photochromic hybrid organic–inorganic films containing nanocrystalline cellulose as a matrix and tungsten oxide as a photochromic component (CNC/WO3) were obtained via a simple and quick solvent casting method. The films were studied by scanning electron microscopy, together with element mapping, FT-IR spectroscopy and X-ray diffraction, confirming successful incorporation of WO3 nanoparticles into a nanocellulose matrix. Thermal analysis data indicated that the modification of a nanocellulose matrix with WO3 increases its thermal stability. The CNC/WO3 films showed a quick coloration-bleaching transition with good reversibility within 20 min, without notable degradation of photochromic properties after 10 cycles. The synthetic method proposed allows for scalable preparation of highly efficient low-cost WO3-based photochromic materials.