CO Separation from H₂ via Hydrate Formation in Single-Walled Carbon Nanotubes

Hydrogen is an alternative fuel without generating greenhouse gas or other harmful emissions. Industrial hydrogen production, however, always contains a small fraction of carbon monoxide (CO) (∼0.5–2%) that must be removed for use in fuel cells. Here, we present molecular dynamics simulation evidence on facile separation of CO from H₂ at ambient pressure via the formation of quasi-one-dimensional (Q1D) clathrate hydrates within single-walled carbon nanotubes (SW-CNTs). At ambient pressure, Q1D CO (or H₂) clathrates in SW-CNTs are formed spontaneously when the SW-CNTs are immersed in CO (or H₂) aqueous solution. More interestingly, for the CO/H₂ aqueous solution, highly preferential adsorption of CO over H₂ occurs within the octagonal or nonagonal ice nanotubes inside of SW-CNTs. These results suggest that the formation of Q1D hydrates within SW-CNTs can be a viable and safe method for the separation of CO from H₂, which can be exploited for hydrogen purification in fuel cells

Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture

Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture

Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture

Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture

Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture

Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture

Preparation of Mesoporous Carbon from Sodium Lignosulfonate by Hydrothermal and Template Method and Its Adsorption of Uranium(VI)

A novel adsorbent of mesoporous carbon with high specific surface area was successfully prepared by hydrothermal and template method, using sodium lignosulfonate (LSs) as a raw material and cetyltrimethylammonium bromide (CTAB) as a template agent. The mesoporous carbon was characterized by SEM, TEM, BET, FTIR, and XPS. The formation mechanism of the mesoporous carbon was analyzed. The adsorption of uranium­(VI) on the mesoporous carbon from the simulated aqueous solution and actual radioactive wastewater was respectively investigated. The optimum conditions for U­(VI) adsorption were determined by studying experimental variables including pH, contact time, sorbent dose, initial concentration, and temperature. The results indicated that the maximum adsorption capacity of the mesoporous carbon for U­(VI) in the simulated aqueous solution and actual radioactive wastewater was respectively 109.46 mg/g at pH 5.5 and 328.15 K and 195.6 mg/g at pH 5.5 and the initial U­(VI) concentration of 189.75 mg/L. The adsorption data could be well described by the pseudo-second-order model and Freundlich isotherm model. The adsorption of U­(VI) on the mesoporous carbon was an endothermic and spontaneous process. The adsorption mechanism may be a complex chemical reaction between uranium and the oxygen-containing functional groups on the mesoporous carbon

Molecular Simulations of Methane Adsorption Behavior in Illite Nanopores Considering Basal and Edge Surfaces

The adsorption properties of methane (CH₄) have a great influence on shale gas exploration and development. The surface chemistry characteristics of nanopores are key factors in adsorption phenomena. The clay pores in shale formations exhibit basal surface and edge surfaces (mainly as A and C chain and B chain surfaces in illite). Little research regarding CH₄ adsorption on clay edge surfaces has been carried out despite their distinct surface chemistries. In this work, the adsorption of CH₄ confined in nanoscale illite slit pores with basal and edge surfaces was investigated by grand canonical Monte Carlo and molecular dynamics simulations. The adsorbed phase density, adsorption capacity, adsorption energy, isosteric heat of adsorption, and adsorption sites were calculated and analyzed. The simulated adsorption capacity compares favorably with the available experimental data. The results show that the edge surfaces have van der Waals interactions that are weaker than those of the basal surfaces. The adsorption capacity follows the order basal surface > B chain surface > A and C chain surface. However, the differences of adsorption capacity between these surfaces are small; thus, edge surfaces cannot be ignored in shale formation. Additionally, we confirmed that the adsorbed phase has a thickness of approximately 0.9 nm. The pore size determines the interaction overlap strength on the gas molecules, and the threshold value of the pore size is about 2 nm. The preferential adsorption sites locate differently on edge and basal surfaces. These findings could provide deep insights into CH₄ adsorption behavior in natural illite-bearing shales

Molecular Simulations of Methane Adsorption Behavior in Illite Nanopores Considering Basal and Edge Surfaces

The adsorption properties of methane (CH₄) have a great influence on shale gas exploration and development. The surface chemistry characteristics of nanopores are key factors in adsorption phenomena. The clay pores in shale formations exhibit basal surface and edge surfaces (mainly as A and C chain and B chain surfaces in illite). Little research regarding CH₄ adsorption on clay edge surfaces has been carried out despite their distinct surface chemistries. In this work, the adsorption of CH₄ confined in nanoscale illite slit pores with basal and edge surfaces was investigated by grand canonical Monte Carlo and molecular dynamics simulations. The adsorbed phase density, adsorption capacity, adsorption energy, isosteric heat of adsorption, and adsorption sites were calculated and analyzed. The simulated adsorption capacity compares favorably with the available experimental data. The results show that the edge surfaces have van der Waals interactions that are weaker than those of the basal surfaces. The adsorption capacity follows the order basal surface > B chain surface > A and C chain surface. However, the differences of adsorption capacity between these surfaces are small; thus, edge surfaces cannot be ignored in shale formation. Additionally, we confirmed that the adsorbed phase has a thickness of approximately 0.9 nm. The pore size determines the interaction overlap strength on the gas molecules, and the threshold value of the pore size is about 2 nm. The preferential adsorption sites locate differently on edge and basal surfaces. These findings could provide deep insights into CH₄ adsorption behavior in natural illite-bearing shales