Publication: Development of photochromic paper based on zinc oxide / polyvinylpyrrolidone composite
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Date
2025-08-01
Authors
Teoh, Ao
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Abstract
Zinc oxide (ZnO) is an II-VI semiconductor with 3.37 eV bandgap and 60 meV excitation binding energy. This makes it suitable for ultraviolet (UV) photochromic (PC) applications such as ink-free printing to address pollution from traditional paper and printing industries. The development of ZnO-based PC paper still faces several challenges, including the lack of a reliable image-based characterization technique to quantify the colour change and intensity of the photochromic response. Current research has predominantly focused on rod-like ZnO, which have relatively small polarized (002) surface area. This project aims to develop a UV-sensitive PC paper based on a ZnO spherical/polyvinylpyrrolidone (PVP) composite synthesized via a
sol-gel method. The formulation parameters such as paper substrate types, concentrations of PVP and phosphomolybdic acid (PMoA), and heating temperature were optimized. The ZnO spherical/PVP PC paper showed that filter paper was the most suitable substrate, with optimal coating uniformity at 0.06 g/ml PVP, fastest PC coloration at 0.08 g/ml PMoA and weak PC thermal reversibility. Additionally, an image-based RGB colorimetric analysis method using ImageJ software was successfully developed to quantitatively evaluate the colour change and intensity of
the photochromic paper. Finally, the photochromic paper based on ZnO disk/PVP, despite having a larger (002) polar surface, did not show improved performance in terms of coating uniformity, colour contrast and response time. This was attributed to the agglomeration of ZnO disk, poor dispersion of ZnO disk in PVP matrix and limited penetration into paper fibres.