超声辅助法制备PWA-PVP多层膜及其可见光光致变色

利用超声波对前驱体进行预处理, 采用逐层组装法（LbL）合成由磷钨酸（PWA）和聚乙烯吡咯烷酮（PVP）组成的新型可见光光致变色无机-有机多层膜. 在可见光照射下, 无色膜变成蓝色, 当薄膜在黑暗中与氧气接触或在空气中加热时发生褪色. 在X射线光电子能谱(XPS)中, 进一步将超声辅助LbL膜的W中W⁶⁺还原为W⁵⁺, 表明PWA颗粒与PVP基质间发生光还原反应. 超声辅助分散PWA颗粒可增强两光致变色性能, 将PWA的尺寸减小到量子点尺寸（10 nm至3.4 nm）, 诱导质子转移效应和介电限制效应. 在相同的照射时间内, 吸收峰的强度增加（0.23→0.45）, 激发能变小（2.51 eV→2.23 eV）, 扩大了吸收波长的范围和特征峰吸收强度, 从而获得较高的着色速率.

Ultrasound-Assisted Preparation of PWA-PVP Multilayer Film and Its Visible Light Photochromism

The precursor was ultrasonically pretreated by the layer-by-layer (LbL) assembly method, and a new type of visible light photochromic inorganic organic multilayer film composed of phosphotungstic acid (PWA) and polyvinylpyrrolidone (PVP) was synthesized. Under visible light irradiation, the colorless film turned blue with a reversible photochromic effect. The bleaching process occurred when the film was in contact with oxygen in the dark or heated in the air. In the X-ray photoelectron spectroscopy (XPS), the W⁶⁺ in the W of the ultrasound-assisted LbL film was further reduced to W⁵⁺, indicating that a photoreduction reaction occurred between the PWA particles and the PVP matrix. Ultrasound assisted dispersion of PWA particles could enhance two photochromic properties, reduce the size of PWA to the size of quantum dots (10 nm to 3.4 nm), induce conversion effects and dielectric confinement effects. Within the same irradiation time, the intensity of the absorption peak increased (0.23 to 0.45), the excitation energy decreased (2.51 eV→2.23 eV), which expanded the range of absorption wavelength and absorption intensity of characteristic peak, and a higher coloring speed was obtained.