Octavinylsilsesquioxane-based Organic–Inorganic hybrid polymers with double-decker silsesquioxane (DDSQ) derivative: Hierarchical structures with enhanced CO₂ and dye adsorption performance

In this work, we report the preparation and comprehensive investigation of octavinylsilsesquioxane (OVS)-based porous organic-inorganic polymers (POIPs) derived from bromo-functionalized double-decker silsesquioxane (DDSQ-Br) and 1,4-dibromobenzene (PD-Br) with OVS monomer. The DDSQ-Br monomer was prepared via both the Heck and Grubbs reactions, with detailed analyses performed using Fourier-transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, including ¹H, ¹³C, and ²⁹Si NMR. The FT-IR spectra confirmed the characteristic stretching vibrations of the corresponding monomer derivatives. At the same time, NMR data indicated that the Heck reaction tends to yield DDSQ oligomers, in contrast to the well-resolved signals observed for the monomer produced via the Grubbs reaction. Subsequent polymerization from cubic OVS with DDSQ-Br or 1,4-dibromobenzene resulted in the formation of two distinct POIPs: OVS-DDSQ POIP and OVS-PD POIP. These materials exhibit hierarchical pore structures, as confirmed by N₂ adsorption/desorption isotherms and pore size analyses, with BET surface areas of 692 m²/g and 407 m²/g, respectively. Thermogravimetric analysis (TGA) profiles revealed enhanced thermal stability for these POIPs, attributed to their highly crosslinked networks. Moreover, these POIPs demonstrate promising adsorption performance for both CO₂ capture and organic dye removal. At 298 K, the CO₂ uptake capacities of OVS-DDSQ and OVS-PD POIPs were 0.25 and 0.15 mmol/g, respectively, increasing significantly at 273 K to 0.74 and 0.45 mmol/g, respectively. Dye adsorption studies using Rhodamine B (RhB) showed rapid decolorization, with kinetic analyses indicating that the adsorption process in OVS-DDSQ POIP is predominantly governed by pseudo-first-order kinetics, while OVS-PD POIP fits both kinetic models well. The superior performance of OVS-DDSQ POIP is ascribed to its enhanced surface area, abundant micropores, and rich phenyl content, which promote stronger polar-π interactions with CO₂ and dye molecules.