The importance of outgassing conditions when using water vapour to characterize activated carbons

Velasco, Leticia F.; Devos, Anneleen; Lodewyckx, Peter

doi:10.1016/j.carbon.2019.06.054

Cited by 5 publications

(2 citation statements)

References 22 publications

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“…On the other hand, their differences in surface chemistry are highlighted by the higher surface oxygen content of CGranular, which was chemically activated. More precisely, the surface of CGranular is rich in carboxylic groups, as studied in a previous work by infrared and thermogravimetric techniques [16]. Sample R1 displays a similar thermogravimetric profile, but with a considerably lower mass loss.…”

Section: Characterization Of the Materialsmentioning

confidence: 65%

Factors Influencing the Kinetics of Water Vapour Adsorption on Activated Carbons

Boutillara

Richelet

Velasco

et al. 2021

Eurasian Chem. Tech. J.

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The performance of porous carbon materials as sorbents is often compromised by the presence of humidity. Studying the kinetics of water vapour adsorption on activated carbons will undeniably help to overcome this issue. This has been approached in this work by evaluating the influence of several operational factors on the dynamic adsorption of water vapour in these materials. Specifically, different carbon types, particle sizes, air flows and ambient conditions (temperature and relative humidity (RH)) were systematically investigated. The impact of each isolated parameter on both the maximum water uptake and the uptake rate was analyzed by fitting the experimental data to the Linear Driving Force (LDF) kinetic model. The results show that except for the particle size, the studied variables play a role in the water sorption kinetics, although to a different extent. It was also confirmed that the LDF model can adequately describe the kinetics of water vapour adsorption independently of the experimental conditions. Finally, the complete water vapour adsorption process can be described by this model, obtaining a different value of the kinetic constant for the sequential stages, involving different adsorption mechanisms.

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Section: Characterization Of the Materialsmentioning

confidence: 65%

Factors Influencing the Kinetics of Water Vapour Adsorption on Activated Carbons

Boutillara

Richelet

Velasco

et al. 2021

Eurasian Chem. Tech. J.

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“…Since water is sensitive to the surface groups of the materials, mild outgassing conditions (100°C, overnight) were used. This guarantees an optimal compromise between the cleaning of the surface and avoiding the modification of the surface chemistry (Velasco et al, 2019 ).…”

Section: Methodsmentioning

confidence: 99%

Influence of Fluorine Doping of Activated Carbon Fibers on Their Water Vapor Adsorption Characteristics

et al. 2021

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The characterization of fluorinated carbon fibers by water sorption has been broadly investigated in this work. In brief, a pitch-based activated carbon fiber (ACF) was submitted to a fluorination process under different conditions of partial pressure (F2:N2 ratio) and temperature. This led to samples with varied fluorine content and C-F type bonding. The effect of the fluorination treatment on the textural properties of the ACF was studied by means of nitrogen and carbon dioxide adsorption at −196 and 0°C, respectively, while the changes induced in the surface chemistry of the materials were analyzed by XPS. Also, the affinity and stability of the materials toward water was evaluated by single and cycling isotherms. The obtained results show that a mild fluorination not only can preserve most of the textural properties of the parent ACF, but enhance the water uptake at the first stages of the water sorption process, together with a shift in the upswing of the water isotherms toward lower relative humidities. This indicates that fluorination under certain conditions can actually enhance the surface hydrophilicity of carbon materials with specific properties. On the contrary, higher partial pressures led to highly fluorinated fibers with lower porosity and more hydrophobic character. Moreover, they presented a lower chemical stability as demonstrated by a change in the shape of the water isotherms after two consecutive measurements. The kinetics of water sorption in the ACFs provided further insights into the different sorption phenomena involved. Hence, water sorption can definitely help to tailor the water affinity, stability and performance of fluorinated porous carbon materials under humid conditions.

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On the Low‐Pressure Hysteresis (LPH) in Gas Sorption Isotherms of Porous Carbons

Zelenka,

Zelená,

Abreu‐Jaureguí

et al. 2024

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This study investigates the origin of low‐pressure hysteresis (LPH) in the adsorption and desorption of three different probe molecules: carbon dioxide, nitrogen, and argon, across various adsorption temperatures (from cryogenic to room temperature), and within five different carbon materials: synthetic carbons (pristine and one post‐synthetically oxidized) and natural coal. Significant attention is dedicated to elucidating LPH in oxidized samples outgassed at various temperatures (120–350 °C). Experimental results show that insufficient outgassing temperature can lead to unreliable data due to artificial LPH and significantly underestimated textural properties, primarily caused by porosity blockage from substances like moisture. Conversely, in samples where heteroatoms have a stabilizing effect on texture, such as natural coal, careful consideration of outgassing temperature is crucial due to the risk of thermal degradation. Other factors contributing to LPH are adsorption temperature, and especially, kinetic limitations at cryogenic temperatures for cellulose‐based carbons. Minor factors responsible for LPH are the physical state of the sample (monolith vs powder) and the flexibility of the porous system, both studied by carbon dioxide sorption. This study constitutes an important piece in the evaluation of LPH, providing practical recommendations and underlining the importance of experimental design, with implications for further research in this complex field.

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The importance of outgassing conditions when using water vapour to characterize activated carbons

Cited by 5 publications

References 22 publications

Factors Influencing the Kinetics of Water Vapour Adsorption on Activated Carbons

Factors Influencing the Kinetics of Water Vapour Adsorption on Activated Carbons

Influence of Fluorine Doping of Activated Carbon Fibers on Their Water Vapor Adsorption Characteristics

On the Low‐Pressure Hysteresis (LPH) in Gas Sorption Isotherms of Porous Carbons

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