Abstract
The constant increase of CO2 concentration in the atmosphere is recognized worldwide to severely impact the environment and human health. Zeolites possess a high adsorption capacity for CO2 removal, but their powdery form prevents their use in many practical applications. When binding agents are used, a partial occlusion of the porosity can severely compromise the adsorption capacity. In this regard, a great challenge is producing compact composite adsorbents while maintaining a high specific surface area to preserve the pristine performance of zeolites. Here, this goal was achieved by preparing beads with a high content of zeolite 13X (up to 90 wt %) using a chitosan aerogel as the binding agent. A facile preparation procedure based on the freeze-drying of hydrogel beads obtained by phase inversion led to a peculiar microstructure in which a very fine polymeric framework firmly embeds the zeolite particles, providing mechanical coherence and strength (compressive strain >40% without bead fragmentation, deformation <20% under 1 kgf-load) and yet preserving the powder porosity. This allowed us to fully exploit the potential of the constituents, reaching a high specific surface area (561 m2 g–1) and excellent CO2 uptake capacity (4.23 mmol g–1) for the sample at 90% zeolite. The beads can also be reused after being fully regenerated by means of a pressure swing protocol at room temperature.
Highlights
CO2 emissions due to anthropic activities are recognized as one of the main causes of global warming
A wide panorama of adsorbents can be used for this purpose, for example, graphene oxide,[5,6] mesoporous silica,[7,8] metal oxides,[9,10] activated carbons,[11,12] metal-organic frameworks (MOFs),[13,14] and zeolites.[15−18] The latter are suitable for fast and reversible CO2 adsorption devices because of good selectivity toward CO2 at low pressures and moderate temperatures[18] and the possibility to be fully regenerated with minimal energy consumption.[19,20]
The surface and internal microstructure of the beads are shown in Figure 2, where SEM micrographs are reported for pure CS and two CS-zeolite 13X (ZX) samples at different φZX
Summary
CO2 emissions due to anthropic activities are recognized as one of the main causes of global warming. While leading to relatively low performance, the previous studies indicate the direction one can take for maximizing the CO2 capture capacity of zeolite-based adsorbents: (i) working at a high zeolite content to maximize the amount of the active phase; (ii) using a highly porous matrix as a binding agent not to occlude the zeolite porosity and to allow the CO2 to reach the entire active surface.
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