Fabrication of host–guest UV-blocking materials by intercalation of fluorescent anions into layered double hydroxides

Abstract

Materials for blocking UV light play important roles in a variety of areas such as protecting the human skin and increasing the lifetime of polymers. In this work, a new type of host–guest UV-blocking material has been synthesized by the introduction of a fluorescent anion, 2-[2-[4-[2-(4-carboxyphenyl)vinyl]phenyl]vinyl]benzoate (CPBA), into the interlayer galleries of a ZnAl–NO₃ layered double hydroxide (LDH) precursor by an anion-exchange method. The structure and the thermal and photostability of the intercalated ZnAl–CPBA-LDH were investigated by powder X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), fluorescence spectroscopy and UV-vis spectroscopy. The supramolecular layered host–guest structure of ZnAl–CPBA-LDH enables both physical shielding and absorption of UV light. Furthermore, in contrast to conventional UV blocking materials—which convert UV light into thermal energy—the CPBA anions in the LDH interlayer galleries convert UV light (in the range 250–380 nm) into lower energy fluorescence emission (λ^em_max = 430 nm), thus reducing the thermal aging of the polymer composite materials. Intercalation of the CPBA anions into the LDH host also markedly enhances the thermal stability of CPBA. In polypropylene (PP) aging performance tests, after adding 1–5 wt% ZnAl–CPBA-LDH to PP, the resistance to UV degradation of the resulting ZnAl–CPBA-LDH/PP composites is higher than that of pristine PP or a CPBA/PP composite. Therefore, this work provides a way to construct a new type of host–guest layered material for UV-blocking applications.