Synergistic Physisorption-Chemisorption Mechanism Enables High-Capacity NO₂ Capture in Nitrogen-Rich Conjugated Microporous Polymers

The limited number of active sites of small-molecule stabilizers makes it difficult to inhibit the autocatalytic reaction of nitrocellulose (NC) in complex environments. The high thermal stability and sufficient active sites of conjugated microporous polymers (CMPs) provide a new solution for NC stabilizers under harsh conditions. In this work, N-rich CMPs networks were presented for NC stabilizers, namely, 3D polyamine (PTPA) networks synthesized via Buchwald-Hartwig (BH) coupling between tris(4-aminophenyl)amine (TAPA) and aryl bromine. Among them, PTPA-2 exhibited a rich microporous structure with a high specific surface area of up to 700 m²·g^-1 and showed excellent thermal stability. With 3% PTPA-2, the NC reduced outgassing by 58% in the vacuum stability test (VST) and prolonged the time to color change of the methyl violet paper by two times. In addition, PTPA-2 adsorbed NO_x gas up to 8.05 × 10^-2 mmol/g. Furthermore, it effectively restrained the release of NO_x gas from NC by 60% in the NO_x titration test. The TG-DSC-FTIR-GC-MS method was employed to analyze the generation of NO₂ from the thermal decomposition of NC, confirming that PTPA-2 absorbed NO₂ to stabilize NC in several ways. The possibilities of the adsorption effect and chemical bonding at different positions in PTPA-2 were simulated by density functional theory (DFT). Furthermore, it was revealed that the -N-Ar-NH- active site absorbed NO₂ molecules in a coordinated process, including physical adsorption and chemical immobilization. The results disclosed in this work are supposed to propose and design stabilizers with high NO_x adsorption capacity and high stability. Additionally, the porous materials used in this work can also provide some inspiration on exhaust gases adsorption.