Recent work on quasi-2D Ruddlesden–Popper phase organolead halide perovskites has shown that they possess many interesting optical and physical properties. Most notably, they are significantly more stable when exposed to moisture when compared to the typical 3D perovskite methylammonium lead iodide (MAPI); direct evidence for the chemical source of this stability remains elusive, however. Here, we present a detailed study of the superior moisture stability of a quasi-2D Ruddlesden–Popper perovskite, n-butylammonium methylammonium lead iodide (nBA-MAPI), compared to that of MAPI, and examine a simple, yet efficient, methodology to improve the stability of MAPI devices through the application of a thin layer of nBA-MAPI to the surface. By employing a variety of analytical techniques (photoluminescence, time-of-flight secondary ion mass spectrometry, cyclic voltammetry, X-ray diffraction) we determine that the improved stability of Ruddlesden–Popper perovskites is a consequence of a unique degradation pathway which produces a passivating surface layer, composed of increasingly stable phases of the 2D perovskite, via disproportionation. Our work establishes that this protective material isolates the bulk of the perovskite from a newly identified hydration layer which is found to accumulate at the C60/perovskite interface of full devices, slowing further hydrolysis reactions that would damage the device. As MAPI devices degrade quickly without any protection, a surface treatment of nBA-MAPI is an efficient way to delay device deterioration by creating an artificial 2D surface layer that similarly inhibits interaction with the hydration layer.

A series of adsorbents containing different amines including diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, branched poly­(ethylenimine), and spermine were exposed to flowing O2 at accelerated temperatures of 80 and 100 °C. Herein, we evaluated the structural effects of amines on the stability of CO2 adsorbents in dry and wet O2-containing environments. Various techniques were used to characterize the adsorbents. The CO2 adsorption capacity of the sorbents was drastically reduced after exposure to dry O2-containing environments. Sorbents modified with amines with a high molecular weight and a long chain of alkyl linkers between amine functional groups exhibited high resistance to O2. The viscosity of the amines played an important role in the oxidative stability of the amine composites as it affected the mass transfer of O2 to the amine sites of the composites. Furthermore, we report for the first time that the presence of steam in O2 medium could suppress or accelerate the oxidative degradation of amine-based CO2 sorbents depending on the amine structure.

The stability of silica impregnated with commercial tetraethylenepentamine (TEPA) under accelerated oxidizing conditions was evaluated, and the changes in the composition of sorbents during oxidative degradation were first reported. The oxidative stability of sorbents depended on the TEPA loading, oxidation duration, temperature, and O2 concentration. The marked loss of the CO2 adsorption capacity of the sorbents in O2-containing environments was mainly caused by changes in the functional groups of TEPA and the sorbent composition, as supported by thermogravimetric, elemental, infrared spectroscopic, and gas chromatography analyses. The results suggested that the hydroxyl groups of silica help to protect TEPA from oxidation. The pore and surface characteristics of sorbent have a significant influence on the O2 diffusion, regulating the oxidation rate. Among isolated components in commercial TEPA, 1,4,7,10,13-pentaazatridecane, 4-(2-aminoethyl)-N-(2-aminoethyl)-N′-[2-[(2-aminoethyl)­amino]­ethyl]-1,2-ethanediamine, and 1-[2-[[2-[(2-aminoethyl)­amino]­ethyl]­amino]­ethyl]­piperazine were revealed to be sensitive to O2, whereas 1-(2-aminoethyl)-4-[[(2-aminoethyl)­amino]­ethyl]­piperazine displayed strong O2 resistance.

A series of efficient adsorbents for CO 2 capture was prepared by a wet-impregnation method. Mesostructured cellular silica foam (MF) was selected as a support and modified with a mixture of tetraethylenepentamine (TEPA) and imidazoles (Ims) to improve the initial and working CO 2 -adsorption capacity. The heat of adsorption was also evaluated. The impact of different amines and the adsorption temperature on CO 2 -adsorption performance was investigated. Some Ims showed a synergistic effect with TEPA regarding adsorption/desorption performance. Impregnating MF with such Ims and TEPA increased CO 2adsorption performance and decreased the heat of absorption compared with those obtained for MF impregnated only with TEPA. MF modified with 30 wt % 4-methylimidazole and 40 wt % TEPA exhibited a high first-pass CO 2 adsorption capacity of 4.88 mmol/g at 100 kPa and 40 °C. Following vacuum regeneration, a working capacity of 4.15 mmol/g was observed for the same conditions.

Amine-functionalized materials have been widely investigated as promising candidates for CO 2 capture. However, they are prone to degradation in the presence of O 2 , resulting in loss in the CO 2 capture ability as well as a decrease in the sorbent lifetime. In this study, we evaluated the effect of different oxidation inhibitors on degradation of polyamines, including tetraethylenepentamine-and polyethylenimine-impregnated mesoporous silica. Sulfur-containing compounds and traditional antioxidants were selected as additives. Oxidative degradation tests of the amine solid sorbents were performed in a packed-bed reactor equipped with a temperature controller. The results showed that traditional antioxidants, such as butylated hydroxytoluene, N,N′-diphenyl-1,4-phenylenediamine, N,N′-di-2-butyl-1,4-phenylenediamine, 2,2′-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and pentaerythritol tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], catalyzed oxidative degradation. In contrast, sulfur-containing additives, which owe their effectiveness to free-radical scavenging and peroxide decomposition actions, decreased the oxidation rate. Amine solid sorbents containing such additives had 1.5−2 times higher CO 2 adsorption capacity retention values than the nonadditive sorbents under accelerated oxidation conditions. Furthermore, the long-term stability of the amine solid sorbents over 15 months storage was demonstrated. These sulfur-containing additives also delayed sorbent degradation.