Preparation and application of solid-state upconversion materials based on sodium polyacrylate

Abstract

By loading a microemulsion containing both sensitizer and emitter into porous sodium polyacrylate (PAAS), a water-absorbent resin (WAR) upconversion (UC) material was fabricated for photocatalysis applications. This WAR UC material showed a highly efficient UC process in the ambient environment owing to its liquid/solid encapsulation structure. In the application measurement, the UC emission from WAR UC materials can excite the catalyst Pt/WO₃ to produce hydroxyl radicals, yielding 7-hydroxycoumarin by reacting with coumarin. In another case, since the band gap of ZnCdS matches the energy of UC emission, hole-electron pairs can be obtained under the UC irradiation and capture electrons from rhodamine B, leading to the degradation of rhodamine B. The maximum of the photocatalysis efficiency can be up to 97%. This work solves the oxygen quenching problem by preparing a triplet-triplet annihilation upconversion (TTA-UC) O/W microemulsion and loading it into PAAS WAR, and opens a new avenue to solid-state devices for TTA-UC. The applications of photocatalytic synthesis and photocatalytic degradation lay a foundation for future practical applications for TTA-UC materials.

Fig. 1. Absorption and fluorescence spectra of PdTPP (a) and DPA (b) with solvent toluene at a concentration of 1 × 10⁻⁶ mol L⁻¹.

Fig. 2. (a) Photograph of WAR UC materials; (b) microstructure of WAR UC materials; (c) photograph of UC fluorescence of WAR materials; (d) schematic diagram of UC microemulsion in microcellular of WAR UC materials.

Fig. 3. (a) Spectrum of UC intensity under different excitation light power density of WAR UC materials; (b) logarithmic plots of upconversion intensity versus excitation light power density of WAR UC materials.

Fig. 4. (a) Fluorescence spectrum of 7-hydroxycoumarin under different irradiation time; (b) conversion rate of coumarin under different conditions.

Fig. 5. (a) Schematic diagram of photo-degradation test of WAR UC materials/ZnCdS/rhodamine B; (b) absorption fluorescence spectra of rhodamine B under different irradiation time; (c) photo-degradation curves of rhodamine B under different conditions.