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 NOx gas up to 8.05 × 10-2 mmol/g. Furthermore, it effectively restrained the release of NOx gas from NC by 60% in the NOx 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 NOx adsorption capacity and high stability. Additionally, the porous materials used in this work can also provide some inspiration on exhaust gases adsorption.