Investigation Of D-Spacing Control And Gas Sorption And Separation For Multi-Layered Graphene

With the economic growth and industrial development,the excess fossil fuel combustion leads to serious environmental deterioration.Therefore,reducing the anthropogenic emission of CO₂ and improving the utilization of H₂ and CH₄ new energy have recently become a political and technological priority.However,the gas capture and purification requires high-performance adsorbents.Among various materials,graphene-based materials have large surface area,mechanical robustness,and high impermeability,and thus,they are considered as one of the most potential classes of adsorbents.To deeply understand the mechanism of gas adsorption and separation in graphene-based materials,in this paper,the experimental technologies combined with molecular simulations are used to systematically investigate the gas adsorption capacity of graphene oxides?GO?intercalated by diminoalkanes,mineral acids,and mineral salts and the gas transport through two-dimensional graphene channels.The intercalated diaminoalkane graphene oxides?IGOs?were fabricated.Interlayer distances of GO were tuned by intercalation of three diaminoalkanes?NH₂?CH₂?_nNH₂,n=4,8,12?with different length of alkyl chain.The effect of structural parameters?such as interlayer distances?of intercalated composites on their CO₂,CH₄,H₂,N₂ adsorption properties was studied.At low pressures?0-100 kPa?,when the interlayer distance increases,the CH₄,H₂ and N₂ uptake in IGOs increases,whereas the CO₂ uptake in IGOs decreases.In the former,the adsorption is dominanted by the BET surface area and the amount of oxygen-containing group,while the heat of adsorption has a large contribution to the adsorption in the later.When the pressure increases,CO₂ uptake in IGO-12 increases sharply and surpasses those of both IGO-4 and IGO-8 at 3.0?10³ kPa,where the dominant interaction is pore volume.The influence of the pore width and functionalization at the sheet edge on the CH₄/H₂and CH₄/CO₂ permeation and separation were systematically studied for the 2D graphene channels.The edge-functionalization by–H,–F,–OH,–NH₂ and–COOH groups could significantly alter gas permeability by modifying the active surface area of the pore and tuning attractive and/or repulsive interaction with molecules at the entrance of channel.For CH₄/H₂ mixture,the H₂ permeability of molecular sieve at the small pore width of 0.600 nm is enhanced by–H,–F,and–OH groups but restrained by–NH₂,especially–COOH.At pore widths of 0.640 and 0.728 nm,–H,–F,and–OH edge-functionalized graphene membranes?GMs?show a preferential CH₄/H₂ selectivity.For GM–NH₂,it exhibits an excellent H₂/CH₄selectivity at 0.728 nm.Meanwhile,small H₂ molecules start to enter the channel of GM–COOH at the pore width up to 0.728 nm.For the largest pore width of 1.366 nm,the influence of edge functionalization becomes small,and a comparable CH₄/H₂ selectivity is observed for all the considered membranes.In the case of CH₄/CO₂,pristine GM with pore width of 0.600 nm is found to be a CO₂molecular sieve.When the pore increases,it allows both CH₄ and CO₂ molecules to enter.However,the 0.640 nm GM shows a preferential selectivity of CO₂ over CH₄,while GMs with pore width of 0.728¹.366 nm favor a selectivity of CH₄ over CO₂.The functionalized GMs reduce the amount of CO₂ entering the pore of 0.600 nm,especially GM–OH,GM–NH₂,and GM–COOH,with a passing rate of zero.For the pore with the width of 1.366 nm,the influence of edge functionalization is relatively small,and all the pores favor CH₄/CO₂selective transport.A series of intercalated graphene oxides were synthesized using sulfuric acid,phosphoric acid,and potassium sulfate.The relation among the concentrations of acid/salt,physicochemical properties?such as interlayer distances?,and gas adsorption capacity was studied.With the increasing concentrations of acid/salt,the interlayer distances and BET surface area of intercalated complexes increase gradually,but the CO₂ adsorption capacity decreases.The sulfuric acid and phosphoric acid intercalated complexes show a large CO₂adsorption capacity,but the CO₂ uptake of potassium sulfate intercalated complexes is relatively poor.