Extended light absorption and enhanced visible-light photocatalytic degradation capacity of phosphotungstate/polyimide photocatalyst based on intense interfacial interaction and alternate stacking structure

In previous research, phosphotungstic acid (H₃PW₁₂O₄₀, PW)/polyimide (PI) composites were constructed using insoluble heptazine melem. We found that the introduction of PW can cause a slight increase in the light absorption of the composites. To further study the effects of polyoxometallate on the light absorption and photocatalytic activity of photocatalysts, a novel phosphotungstate/polyimide photocatalyst (MPWPI) was constructed via in situ solid-state thermal polymerization using melamine phosphotungstate ((C₃N₆H₇)_x[PW₁₂O₄₀], MPW) synthesized by water-soluble triazine melamine (C₃H₆N₆, MA) and PW. The structural and morphological results confirm the successful construction and the alternate stacking structure of MPWPI. The alternate stacking structure is more favorable for the contact between polyoxometallate and polyimide, and it also facilitates the electron delocalization through the intermolecular phosphotungstate anions-π interactions. This will lead to the extended light absorption and enhanced visible-light photocatalytic degradation capacity. The UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) results display that the light absorption of MPWPI can be obviously extended to 800 nm. Compared to the inactive polyimide and phosphotungstate, MPWPI exhibits extraordinary photocatalytic activity of imidacloprid under visible light irradiation (λ > 400 nm) for the extended light absorption and suppressed carriers recombination. For this photocatalytic system, the OH and O₂⁻ are the main active species. Furthermore, the encapsulated phosphotungstate anions in the specific structure of MPWPI give it excellent recyclability for the inhibited polar solvent dissolution.