A novel structure and photochromism of heteropolyoxometalates dispersed in polymer networks

Nanocomposites based on Keggin structure tungstophosphate acid (PWA) with ‘branch-like’ nanometer well dispersed in poly(acrylamide-co-vinylamine) (PAM-co-PVAm) were fabricated. The microstructure and photochromic properties were studied via Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visible spectra (UV–vis) and electron resonance spectra (ESR). FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and hydrogen bonding and salt formation were built between PWA and polymer matrix. SEM and TEM images showed that PWA nanoparticles were finely dispersed in polymer matrix with ‘branch-like’ shape. Under UV irradiation, the film was reduced photochemically to yield a glaucous species. After UV light turned off, the color of film became green. Two photo-reduction processes (one was between acylamino and heteropoly acid, another was between amidocyanogen and heteropoly acid) occurred at the same time in PWA/PAM-co-PVAm system, which resulted in the formation of heteropolygreen.

Two absorption bands appeared after UV irradiated. In bleaching process, the peaks at 620–820 nm disappeared and those at 420 nm still presented. Due to synergies happened between heteropolyacid and PAM-co-PVAm, heteropolygreen was formed.Figure optionsDownload as PowerPoint slideHighlights
► ‘Branch-like’ composites were fabricated by dispersed PWA into PAM-co-PVAm system.
► Two photo-reduction processes occurred simultaneously in PWA/PAM-co-PVAm system.
► Heteropolygreen was formed by synergies of hydrogen bonding and salt formation.