Yang Li,Wenjing Wei,Jiaqi Chen,Lijie Zu,Yan Zhou,Jinzhu Wu,Xiaohong Wu
In spaceflight applications, molecular contamination control has become one of the most challenging issues. Porous zeolites are a potent molecular adsorbent with advantages of efficient adsorption at low pressure and/or high temperature, high interaction with adsorbates, and superior durability in extreme environments. Herein, zeolite 13X pellets were selected for adsorption of stearyl alcohol (C 18 H 37 OH) as a target molecular contaminant. Considering the excellent hydrophilicity of the zeolite 13X which limits the adsorption of most hydrophobic organic molecules, modification of the zeolite 13X by deposition of TiO 2 via atomic layer deposition (ALD) technology was performed. Results show that ALD-grown TiO 2 not only improves hydrophobicity but also renders high activity, whilst retains the hierarchical pores of the zeolites. As a result, the as-prepared zeolite 13X@TiO 2 exhibits efficient adsorption toward trace stearyl alcohol under low pressure through the synergistic contribution of physisorption and chemisorption. Monte Carlo (MC) simulation, molecular dynamic (MD) and Density Functional Theory (DFT) calculations further discover that pore wall surfaces are primary adsorption sites for the physisorption while ALD-grown TiO 2 provides active sites for the chemisorption.
Aminophenazone (AP) is one kind of harmful additives in transformer oil. It results in a significant drop of the insulation property of transformer oil and thus leads to substation accidents. Adsorption method has proved to be an efficient approach for AP removal. In this work, activated bentonite, zeolite 13X, and activated carbon were chosen as adsorbents for the separation of AP from the polluted transformer oil. At 25 ℃ and initial AP content is 400 ppmw, the AP uptake of activated bentonite (151.2 mg/g) is much higher than that of zeolite 13X (52.1 mg/g) and activated carbon (45.0 mg/g). The desorption activation energy (E d ) of AP on the three adsorbents follow in the order: activated bentonite (115.73 kJ/mol) > activated carbon (52.51 kJ/mol) > zeolite 13X (51.23 kJ/mol). Activated bentonite exhibits the highest AP uptake due to the existence of acidic sites that can strongly interact with alkaline AP and the pore sizes that facilitate AP molecules to more easily enter into the adsorbent channels. Activated bentonite is an industrially promising adsorbent for the removal of AP from the polluted transformer oil.
Recently, zeolites have been selected as a potential adsorbent for capturing space molecular contaminants owing to their strong adsorption ability and extreme stability in a harsh environment. Considering the adsorption process in a vacuum environment, enhancement of the adsorption performance of the zeolites is required. Unfortunately, up to now, the improved adsorption behavior for the space molecular contaminants of the modified zeolite adsorbent under ultralow pressure has rarely been reported. Herein, a 13X/ZnO adsorbent was prepared by incorporating ZnO nanoislands into the nanoporous zeolite 13X via atomic layer deposition (ALD). It is found that a representative 13X/ZnO-50 exhibits an increased adsorption capacity toward dimethyl phthalate and the outgassing species of J133 adhesive even under the ultralow pressure of 10–5 Pa. This could be attributed to the synergistic effects of physical interactions and chemical adsorption associated with the unique cage structure of the zeolite and the incorporated ALD-grown ZnO nanoislands. This work provides a useful strategy for developing the adsorbents used in space molecular contamination control during space missions.
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