Molecular‐Level Insights into the Oxidative Degradation of Grafted Amines

Abstract

The oxidative degradation of CO2 adsorbents consisting of amine-grafted pore-expanded mesoporous MCM-41 silica was investigated. The adsorbents were treated under flowing air at various temperatures, and the degree of deactivation was evaluated through the measurement of their CO2 adsorption capacity prior and subsequent to exposure to air. To decipher the chemical structure of surface species upon air-deactivation of grafted amines, a solvent extraction procedure was developed using a deuterated basic solution. The obtained solutions were analyzed by a variety of 1D and 2D NMR spectroscopy techniques, such as (29)Si, (13)C, (1)H, [(1)H,(15)N] HMBC, [(1)H,(13)C] HMQC, COSY and DOSY. The surface species generated by oxidative degradation of amine-grafted silica were found to contain functional groups such as imine, amide and carboxylic groups. Several structural units were conclusively demonstrated.

Oxidative degradation of silica-supported polyethylenimine for CO2adsorption: insights into the nature of deactivated species

“…The NMR spectrum of the air-deactivated BPEI was obtained in DMSO-d 6 , as well as in KOH/D 2 O following the method reported in our earlier work. 39 Interestingly, the data obtained for the extracted deactivated BPEI using both methods were consistent with each other (Fig. 5 and Fig.…”

“…Interestingly, our results further validate the solvent-extraction methodology we developed earlier for the removal of grafted species from the silica samples. 39 Indeed, although deactivated polymeric species were separated in this work by simple solvent dissolution, their structure was consistent with the grafted deactivated species removed under basic conditions. 39 Thus, the occurrence of the identified species in deactivated materials could be extrapolated to other amine-containing adsorbents.…”

“…To overcome this problem, we developed a solvent-extraction procedure for the removal of oxygen-deactivated species in amine-grafted CO 2 adsorbents under basic conditions, allowing us to use more powerful NMR techniques and gain unprecedented insights into the nature of deactivated products. 39 Both grafted propylamine and propyldiethylenetriamine were investigated, and a number of structural units containing CQO and -CHQN-species were conclusively identified. The current work is devoted to in-depth investigation of the oxidative degradation products of PEI-impregnated mesoporous silica.…”

Aminosilane‐Grafted Zirconia–Titiania–Silica Nanoparticles/Torlon Hollow Fiber Composites for CO2 Capture

“…In addition to the activation reaction of the aminosilane with water in the first step, the aminosilane can also undergo self‐polymerization in the presence of water, which is present in the toluene solvent. Sayari and co‐workers showed that the presence of water in the aminosilane solution increases aminosilane coupling on the silica surfaces, which leads to the formation of multilayers instead of a simple monolayer of grafted amines. The activated aminosilane undergoes condensation, involving the Si−OH groups of the silanol and the OH groups of the zirconia, titania, and silica nanoparticles in the fiber pores.…”

Surface functionalization of carbon fibers with active screen plasma

“…Unfortunately, the degradation sequence is difficult to identify by XPS surface analysis because of technique limitations. 40 It is speculated that the NH functional groups undergo oxidative scissions and evaporative loss upon their exposure to air, although the elucidation of the degradation mechanism requires further study.…”