# Porous Organic Polymers with Azo, Azoxy, and Azodioxy Linkages: Design, Synthesis, and CO2 Adsorption Properties

## TL;DR

This review explores how porous organic polymers with nitrogen-nitrogen linkages can be designed and used for capturing CO2 efficiently.

## Contribution

The paper provides a comprehensive review of azo-linked POPs and computational methods to guide CO2 adsorption design.

## Key findings

- Azo-linked POPs show tunable properties for CO2 capture based on building blocks and framework topology.
- Computational models link structure to CO2 adsorption behavior in amorphous or partially ordered networks.
- Reversible nitroso/azodioxide chemistry offers a pathway to ordered porous materials for CO2 capture.

## Abstract

Rising atmospheric CO2 levels have increased the demand for robust, scalable adsorbents for practical CO2 capture and separation. Porous organic polymers (POPs) are attractive candidates because their pore architecture and binding site properties can be precisely tuned via building blocks and linkage formation. This review summarizes experimental and computational studies of azo-linked POPs and, more broadly, nitrogen–nitrogen (N–N) linked systems, emphasizing how synthetic routes, building blocks, and framework topology govern CO2 uptake. We highlight key synthetic strategies and representative systems, including porphyrin–azo networks, and discuss the relatively sparse experimental literature on alternative N–N linked POPs incorporating azoxy and azodioxy motifs. Emphasis is placed on reversible nitroso/azodioxide chemistry as a potential pathway to ordered porous organic materials. Computational studies provide a practical route to connect structure with adsorption behavior in largely amorphous or partially ordered networks. We review hierarchical workflows combining periodic DFT and electrostatic potential properties, grand canonical Monte Carlo (GCMC) simulations, and binding energy calculations to rationalize trends and identify favorable binding environments. Computational findings demonstrate that pore accessibility and stacking models can strongly influence predicted CO2 adsorption. This review provides guidelines for designing POPs with enhanced CO2 adsorption, offering an outlook and discussing challenges for future studies.