Highly effective ammonia removal in a series of Brønsted acidic porous polymers: Investigation of chemical and structural variations
Articolo
Data di Pubblicazione:
2017
Abstract:
Although a widely used and important industrial gas, ammonia (NH3) is also highly toxic and presents
a substantial health and environmental hazard. The development of new materials for the effective
capture and removal of ammonia is thus of significant interest. The capture of ammonia at ppm-level
concentrations relies on strong interactions between the adsorbent and the gas, as demonstrated in
a number of zeolites and metal–organic frameworks with Lewis acidic open metal sites. However, these
adsorbents typically exhibit diminished capacity for ammonia in the presence of moisture due to
competitive adsorption of water and/or reduced structural stability. In an effort to overcome these
challenges, we are investigating the performance of porous polymers functionalized with Brønsted acidic
groups, which should possess inherent structural stability and enhanced reactivity towards ammonia in
the presence of moisture. Herein, we report the syntheses of six different Brønsted acidic porous
polymers exhibiting –NH3Cl, –CO2H, –SO3H, and –PO3H2 groups and featuring two different network
structures with respect to interpenetration. We further report the low- and high-pressure NH3 uptake in
these materials, as determined under dry and humid conditions using gas adsorption and breakthrough
measurements. Under dry conditions, it is possible to achieve NH3 capacities as high as 2 mmol g1 at
0.05 mbar (50 ppm) equilibrium pressure, while breakthrough saturation capacities of greater than
7 mmol g1 are attainable under humid conditions.Chemical and structural variations deduced from
these measurements also revealed an important interplay between acidic group spatial arrangement and
NH3 uptake, in particular that interpenetration can promote strong adsorption even for weaker Brønsted
acidic functionalities. In situ infrared spectroscopy provided further insights into the mechanism of NH3
adsorption, revealing a proton transfer between ammonia and acidic sites as well as strong hydrogen
bonding interactions in the case of the weaker carboxylic acid-functionalized polymer. These findings
highlight that an increase of acidity or porosity does not necessarily correspond directly to increased
NH3 capacity and advocate for the development of more fine-tuned design principles for efficient NH3
capture under a range of concentrations and conditions.
Tipologia CRIS:
03A-Articolo su Rivista
Keywords:
Chemistry (all)
Elenco autori:
Barin, Gokhan; Peterson, Gregory W.; Crocellà , Valentina; Xu, Jun; Colwell, Kristen A.; Nandy, Aditya; Reimer, Jeffrey A.; Bordiga, Silvia; Long, Jeffrey R.
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