NH 3 , essential for producing artificial fertilizers and several military and commercial products, is being produced at a large scale to satisfy increasing demands. The inevitable leakage of NH 3 during its utilization, even in trace concentrations, poses significant environmental and health risks because of its highly toxic and reactive nature. Although numerous techniques have been developed for the removal of atmospheric NH 3 , conventional NH 3 abatement systems possess the disadvantages of high maintenance cost, low selectivity, and emission of secondary wastes. In this context, highly tunable porous materials such as metal-organic frameworks, covalent organic frameworks, hydrogen organic frameworks, porous organic polymers, and their composite materials have emerged as next-generation NH 3 adsorbents. Herein, recent progress in the development of porous NH 3 adsorbents is summarized; furthermore, factors affecting NH 3 capture are analyzed to provide a reasonable strategy for the design and synthesis of promising materials for NH 3 abatement.

Although CO 2 insertion is a predominant phenomenon in diamine-functionalized Mg 2 (dobpdc) (dobpdc 4À = 4,4-dioxidobiphenyl-3,3'-dicarboxylate) adsorbents, a high-performance metal-organic framework for capturing CO 2 , the fundamental function of the diamine carbon chain length in the mechanism remains unclear. Here, Mg 2 (dobpdc) systems with open metal sites grafted by primary diamines NH 2 À (CH 2 ) n À NH 2 were developed, with en (n = 2), pn (n = 3), bn (n = 4), pen (n = 5), hn (n = 6), and on (n = 8). Based on CO 2 adsorption and IR results, CO 2 insertion is involved in frameworks with n = 2 and 3 but not in systems with n � 5. According to NMR data, bn-appended Mg 2 (dobpdc) exhibited three different chemical environments of carbamate units, attributed to different relative conformations of carbon chains upon CO 2 insertion, as validated by firstprinciples density functional theory (DFT) calculations. For 1-hn and 1-on, DFT calculations indicated that diamine intercoordinated open metal sites in adjacent chains bridged by carboxylates and phenoxides of dobpdc 4À . Computed CO 2 binding enthalpies for CO 2 insertion (À 27.8 kJ mol À 1 for 1-hn and À 20.2 kJ mol À 1 for 1-on) were comparable to those for CO 2 physisorption (À 19.3 kJ mol À 1 for 1-hn and À 20.8 kJ mol À 1 for 1on). This suggests that CO 2 insertion is likely to compete with CO 2 physisorption on diamines of the framework when n � 5.