*3.1. General Materials*

All materials and reagents were purchased from commercial sources and used without further purification. K8SiW11O39·13H2O and azo-functionalized compounds **1**, **3** and **4** were prepared according to the literature [15]. Fourier transform infrared (FT-IR) spectra were recorded on JASCO FT-IR 410 spectrometeror or a JASCO FT-IR 4100 spectrometer (JASCO, Tokyo, Japan). 1H NMR spectroscopy was performed on a Bruker DPX 400 spectrometer (Bruker, Zurich, Switzerland) using the solvent's signal as an internal standard. Quantitative elemental analyses of C, H, and N were determined by microanalysis services within the College of Chemistry, Beijing University of Chemical Technology.
