CO2 Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral

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Intercalation of CO2 Selected by Type of Interlayer Cation in Dried Synthetic Hectorite

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Influence of CO2 on Nanoconfined Water in a Clay Mineral

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Non-activated adsorption of methane on nickel surfaces induced by reduced work function

Adsorption of methane has been studied in ultrahigh vacuum environments on single crystalline as well as on Ni nano-particles on mica substrates. Experimental techniques have been X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and temperature programmed desorption spectroscopy (TPD). In accordance with previous observations only physisorption of is observed on pure nickel at temperatures below 130 K for exposures in the high vacuum regime. TPD in the temperature range from 200 to 300 K shows that chemisorption of methane takes place when the sample work function is lowered by about 0.7 eV by a surface treatment, which presumably exposes the surface to atomic hydrogen. The lowered work function enables charge transfer from the Ni conduction band to the methane affinity level which subsequent leads to dissociative chemisorption

CO desorption from nickel-decorated muscovite mica

Adsorption and desorption of CO from Ni nanostructures deposited on muscovite mica substrates have been studied by TPD and characterized by XPS and AFM. In agreement with previous reports it is found that CO does not adsorb on the bare mica substrate. The desorption spectra depend strongly on the Ni coverage on the mica substrate. Three coverage regimes have been found; for low Ni coverage of approximately 0.2 monolayers a dominant desorption peak is found near 400 K. For medium coverage of approximately 0.6 monolayers three distinct peaks appear in the temperature region from 250 to 550 K. For higher Ni coverage of approximately 3 monolayers a single peak is observed near 550 K. The high temperature peak was assigned to desorption from terrace sites, the medium temperature peak was assigned to step sites, and the low temperature peak was argued to stem from lateral interaction between adsorbed CO species and possible sites with low coordination, e.g. kink sites. Desorption parameters have been extracted from the low temperature part of the desorption spectra. Anomalous low values for the vibrational prefactors were obtained in the case of low Ni coverage. This is argued to be due to dissociation of CO

The Impact of Thermal History on Water Adsorption in a Synthetic Nanolayered Silicate with Intercalated Li+ or Na+

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CO2 Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral

Due to the compact two-dimensional interlayer pore space and the high density of interlayer molecular adsorption sites, clay minerals are competitive adsorption materials for carbon dioxide capture. We demonstrate that with a decreasing interlayer surface charge in a clay mineral, the adsorption capacity for CO2 increases, while the pressure threshold for adsorption and swelling in response to CO2 decreases. Synthetic nickel-exchanged fluorohectorite was investigated with three different layer charges varying from 0.3 to 0.7 per formula unit of Si4O10F2. We associate the mechanism for the higher CO2 adsorption with more accessible space and adsorption sites for CO2 within the interlayers. The low onset pressure for the lower-charge clay is attributed to weaker cohesion due to the attractive electrostatic forces between the layers. The excess adsorption capacity of the clay is measured to be 8.6, 6.5, and 4.5 wt % for the lowest, intermediate, and highest layer charges, respectively. Upon release of CO2, the highest-layer charge clay retains significantly more CO2. This pressure hysteresis is related to the same cohesion mechanism, where CO2 is first released from the edges of the particles thereby closing exit paths and trapping the molecules in the center of the clay particles

The Impact of Thermal History on Water Adsorption in a Synthetic Nanolayered Silicate with Intercalated Li+ or Na+

For applications benefitting from the swelling properties of nanolayered silicates (clay minerals), it is of paramount importance to understand the hysteresis in the clay–water interaction. In this context, the present work investigates how the thermal history of Na+- and Li+-intercalated fluorohectorite affects the hydration process. By combining X-ray diffraction and thermogravimetric analysis, water adsorption of preheated and non-preheated fluorohectorite was measured and analyzed in terms of the characteristic interlayer distance. The number of water molecules per cation was also inferred. We find that some of the hydration states in preheated samples are suppressed, and transitions to higher hydration states are achieved at higher relative humidity values. This could be due to the initial water content that facilities crystalline swelling. However, the data for Li-fluorohectorite do not exclude the possibility of a low temperature Hofmann–Klemen effect at 150 °C. Our study also provides strong hints that the so-called 1.5 water layer state, observed in previous studies on smectites, is a metastable state. In addition, the impact of a hydrogenous structure in the interlayer space of Li-fluorohectorite on the clay’s hydration behavior is demonstrated. The results, if generalized, would have strong implications on a wide range of applications, where the thermal history of smectites is important

The Impact of Thermal History on Water Adsorption in a Synthetic Nanolayered Silicate with Intercalated Li+ or Na+

For applications benefitting from the swelling properties of nanolayered silicates (clay minerals), it is of paramount importance to understand the hysteresis in the clay–water interaction. In this context, the present work investigates how the thermal history of Na+- and Li+-intercalated fluorohectorite affects the hydration process. By combining X-ray diffraction and thermogravimetric analysis, water adsorption of preheated and non-preheated fluorohectorite was measured and analyzed in terms of the characteristic interlayer distance. The number of water molecules per cation was also inferred. We find that some of the hydration states in preheated samples are suppressed, and transitions to higher hydration states are achieved at higher relative humidity values. This could be due to the initial water content that facilities crystalline swelling. However, the data for Li-fluorohectorite do not exclude the possibility of a low temperature Hofmann–Klemen effect at 150 °C. Our study also provides strong hints that the so-called 1.5 water layer state, observed in previous studies on smectites, is a metastable state. In addition, the impact of a hydrogenous structure in the interlayer space of Li-fluorohectorite on the clay’s hydration behavior is demonstrated. The results, if generalized, would have strong implications on a wide range of applications, where the thermal history of smectites is important