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Air pollution related to the release of industrial toxic gases,
represents one of the main
concerns of our modern world owing to its detrimental effect on the
environment. To tackle this growing issue, efficient ways to
reduce/control the release of pollutants are required. Adsorption
of gases on porous materials appears as a potential solution.
However, the physisorption of small molecules of gases such as
ammonia is limited at ambient conditions. For their removal,
adsorbents providing strong adsorption forces must be
used/developed.
In this study, new carbon-based materials are prepared and tested
for ammonia adsorption at ambient conditions. Characterization of
the adsorbents texture and surface chemistry is performed before
and after exposure to ammonia to identify the features responsible
for high adsorption capacity and for controlling the mechanisms of
retention. The characterization techniques include: nitrogen
adsorption, thermal analysis, potentiometric titration, FT-IR
spectroscopy, X-ray diffraction, Energy Dispersive X-ray
spectroscopy, X-ray photoelectron spectroscopy and Electron
Microscopy. The results obtained indicate that ammonia removal is
governed by the adsorbent s surface chemistry. On the contrary,
porosity (and thus physisorption) plays a secondary role in this
process, unless strong dispersive forces are provided by the
adsorbent. The surface chemistry features responsible for the
enhanced ammonia adsorption include the presence of
oxygen-(carboxyl, hydroxyl, epoxy) and sulfur- (sulfonic)
containing groups. Metallic species improve the breakthrough
capacity as well as they lead to the formation of Lewis acid-base
interactions, hydrogen-bonding or complexation. In addition to the
latter three mechanisms, ammonia is retained on the adsorbent
surface via Bronsted acid-base interactions or via specific
reactions with the adsorbent s functionalities leading to the
incorporation of ammonia into the adsorbent s matrix. Another
mechanism involves dissolution of ammonia in water when moisture is
present in the system. Even though this process increases the
breakthrough capacity of a material, it provides rather weak
retention forces since ammonia dissolved in water is easily
desorbed from the adsorbent s surface."
Air pollution related to the release of industrial toxic gases,
represents one of the main
concerns of our modern world owing to its detrimental effect on the
environment. To tackle this growing issue, efficient ways to
reduce/control the release of pollutants are required. Adsorption
of gases on porous materials appears as a potential solution.
However, the physisorption of small molecules of gases such as
ammonia is limited at ambient conditions. For their removal,
adsorbents providing strong adsorption forces must be
used/developed.
In this study, new carbon-based materials are prepared and tested
for ammonia adsorption at ambient conditions. Characterization of
the adsorbents texture and surface chemistry is performed before
and after exposure to ammonia to identify the features responsible
for high adsorption capacity and for controlling the mechanisms of
retention. The characterization techniques include: nitrogen
adsorption, thermal analysis, potentiometric titration, FT-IR
spectroscopy, X-ray diffraction, Energy Dispersive X-ray
spectroscopy, X-ray photoelectron spectroscopy and Electron
Microscopy. The results obtained indicate that ammonia removal is
governed by the adsorbent s surface chemistry. On the contrary,
porosity (and thus physisorption) plays a secondary role in this
process, unless strong dispersive forces are provided by the
adsorbent. The surface chemistry features responsible for the
enhanced ammonia adsorption include the presence of
oxygen-(carboxyl, hydroxyl, epoxy) and sulfur- (sulfonic)
containing groups. Metallic species improve the breakthrough
capacity as well as they lead to the formation of Lewis acid-base
interactions, hydrogen-bonding or complexation. In addition to the
latter three mechanisms, ammonia is retained on the adsorbent
surface via Bronsted acid-base interactions or via specific
reactions with the adsorbent s functionalities leading to the
incorporation of ammonia into the adsorbent s matrix. Another
mechanism involves dissolution of ammonia in water when moisture is
present in the system. Even though this process increases the
breakthrough capacity of a material, it provides rather weak
retention forces since ammonia dissolved in water is easily
desorbed from the adsorbent s surface."
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