Stone-Wales Defect in Graphene

2D graphene the most investigated structures from nanocarbon family studied in the last three decades. It is projected as an excellent material useful for quantum computing, artificial intelligence, and next generation advanced technologies. Graphene exists in several forms and its extraordinary thermal, mechanical, and electronic properties, principally depend on the kind of perfection of the hexagonal atomic lattice. Defects are always considered as undesired components but certain defects in graphene could be an asset for electrochemistry and quantum electronics due to the engineered electronclouds and quantum tunnelling. The authors carefully discuss the Stone-Wales imperfections in graphene and its derivatives comprehensively. A specific emphasis is focused on the experimental and theoretical aspects of the Stone-Wales defects in graphene with respect to structure-property relationships. The corroboration of extrinsic defects like external atomic doping, functionalization, edge distortion in the graphene consisting of Stone-Wales imperfections, which are very significant in designing graphene-based electronic devices, are summarized.

Synergistic mechanism of formaldehyde adsorption by intrinsic defects and carboxyl groups on the surface of carbon materials

The adsorption of formaldehyde on the original carbon material is limited. Determining the synergistic adsorption of formaldehyde by different defects on the carbon material is necessary for comprehensively understanding the mechanism of formaldehyde adsorption on the surface of the carbon material. The synergistic effect of intrinsic defects and oxygen-containing functional groups on formaldehyde adsorption on the surface of carbon materials was simulated and verified by experiments. Based on the density functional theory, the adsorption of formaldehyde on different carbon materials was simulated by quantum chemistry. The synergistic adsorption mechanism was studied by energy decomposition analysis, IGMH, QTAIM, and charge transfer, and the binding energy of hydrogen bonds was estimated. The results showed that the energy for the adsorption of formaldehyde adsorbed by the carboxyl group on the vacancy defect was the highest, at -11.86 kcal/mol, the hydrogen bond binding energy was -9.05 kcal/mol, and a larger charge transfer was recorded. The mechanism of synergy was studied comprehensively, and the simulation results were verified at multiple scales. This study provides valuable insights into the effect of carboxyl groups on the adsorption of formaldehyde by activated carbon.

Adsorption-induced clustering of CO2 on graphene

Utilization of graphene-based materials for selective carbon dioxide capture has been demonstrated recently as a promising technological approach. In this study we report results from density functional theory calculations and molecular dynamics simulations on the adsorption of CO2, N2, and CH4 gases on a graphene sheet. We calculate adsorption isotherms of ternary and binary mixtures of these gases and reproduce the larger selectivity of CO2 to graphene relative to the other two gases. Furthermore it is shown that the confinement to two-dimensions, associated with adsorbing the CO2 gas molecules on the plane of graphene, increases their propensity to form clusters on the surface. Above a critical surface coverage (or partial pressure) of the gas, these CO2-CO2 interactions augment the effective adsorption energy to graphene, and, in part, contribute to the high selectivity of carbon dioxide with respect to nitrogen and methane. The origin of the attractive interaction between the CO2 molecules adsorbed on the surface is of electric quadrupole-quadrupole nature, in which the positively-charged carbon of one molecule interacts with the negatively-charged oxygen of another molecule. The energy of attraction of forming a CO2 dimer is predicted to be around 5-6 kJ mol-1, much higher than the corresponding values calculated for N2 and CH4. We also evaluated the adsorption energies of these gases to a graphene sheet and found that the attractions obtained using the classical force-fields might be over-exaggerated. Nevertheless, even when the magnitudes of these (classical force-field) graphene-gas interactions are scaled-down sufficiently, the tendency of CO2 molecules to cluster on the surface is still observed.

Roll-to-roll graphene oxide radon barrier membranes

Graphene oxide as a radon barrier in living environments was introduced by intercalating the polymer resin-coated layer inside a multilayer membrane with an area of 1 × 10 m and a thickness of 2.5 mm, prepared by the roll-to-roll method. A 5 μm-thick graphene oxide polymer resin (GOPR) layer was coated on polyethylene terephthalate (PET) film (100 μm) between the two styrene-butadiene-styrene (SBS)-modified bitumen asphalt layers fitted for construction sites. The inserted graphene oxide materials were characterized by means of infrared, Raman, and X-ray photoelectron spectroscopy (XPS). Dispersion-corrected density functional theory (DFT) calculations suggested weaker binding energies on the oxide surfaces and higher penetration energy barriers of graphene nanopores for radon (²²²Rn) than in the cases of the atmospheric gas molecules Ar, H₂O, CO₂, H₂, O₂, and N₂. Theoretical calculations of the graphene nanopores supported the higher barrier energies of ²²²Rn than most ambient gases. The roll-to-roll prepared graphene materials exhibited good barrier properties for ²²²Rn as well as for the ambient gases. The purpose of our experimental and theoretical study is to provide a better understanding of using graphene-based materials to reduce the risk of carcinogenic radon gas in construction sites and residential buildings for practical applications.