Fabrication of PA-PEI-MOF303(Al) by Stepwise Impregnation Layer-by-Layer Growth for Highly Efficient Removal of Ammonia

Abstract

NH3 is a typical alkaline gaseous pollutant widely derived from industrial production and poses great risks to humans and other biota. Metal-organic frameworks (MOFs) have excellent adsorption capacities relative to materials traditionally used to adsorb NH3. However, in practice, applications of MOFs as adsorbents are restricted because of its powder form. We prepared a polyamide (PA) macroporous polyester substrate using an emulsion template method and modified the surface with polyethylenimine (PEI) to improve the MOF growth efficiency on the substrate. The difficulty of loading the MOF because of the fast nucleation rate inside the PA macroporous polyester substrate was solved using a stepwise impregnation layer-by-layer (LBL) growth method, and a PA-PEI-MOF303(Al) hierarchical pore composite that very efficiently adsorbed NH3 was successfully prepared. The PA-PEI-MOF303(Al) adsorption capacity for NH3 was 16.07 mmol·g−1 at 298 K and 100 kPa, and the PA-PEI-MOF303(Al) could be regenerated repeatedly under vacuum at 423 K. The NH3 adsorption mechanism was investigated by in situ Fourier transform infrared spectroscopy and by performing two-dimensional correlation analysis. Unlike for the MOF303(Al) powder, the formation of multi-site hydrogen bonds between Al–O–Al/C–OH, N–H, –OH, C=O, and NH3 in PA-PEI-MOF303(Al) was found to be an important reason for efficient NH3 adsorption. This study will provide a reference for the preparation of other MOF-polymer composites.

Efficient Adsorption of Ammonia by Surface-Modified Activated Carbon Fiber Mesh

“…This is consistent with the aforementioned increase in the content of surface acidic oxygen-containing functional groups, suggesting that the increase in acidic oxygen-containing functional groups promotes the chemical adsorption of ammonia on the ACF surface. As the adsorption proceeded, the heat of adsorption of ammonia on ACF-N-6 gradually decreased to 40 kJ•mol −1 , indicating that the chemical adsorption dominated the entire adsorption process [47]. The curves of ACF-N-2 and ACF-N-4 showed that before the heat of adsorption reached 30 mL•g −1 and 55 mL•g −1 , respectively, the heat of adsorption was greater than 40 kJ•mol −1 , indicating that chemical adsorption dominated.…”