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Among various techniques for treating polybrominated diphenyl ethers (PBDEs), adsorption and removal methods using carbon materials are widely applied to remove and decompose organic pollutants with high efficiency. Of many carbon allotropes, theoretically developed graphyne has numerous promising applicabilities for its strong carbon chemical bond, large conjugate system, good chemical stability, and excellent electrical conductivity. To evaluate the PBDE removal capability of graphyne as an adsorbent, we investigated the adsorption properties of ten PBDE species on graphyne using the density functional theory calculation. Furthermore, we analyzed the correlation between the hydrophobicity and adsorption characteristics of PBDEs and found that the adsorption energy increased with the hydrophobicity and the bromination number, indicating a linear relationship for only seven samples. In BDE154, BDE183, and BDE209, however, this linearity was not clearly found because when the bromine groups of the PBDE structures were located at 6,6′, two phenyl rings repelled each other to limit adsorption. From a water solvation model, graphyne also indicated a high adsorption capacity of PBDEs. It is worth noting that graphyne is considered to be a suitable material for PBDE adsorption, and the adsorption reaction may vary depending on the structural characteristics and hydrophobicity of the PBDEs. [ABSTRACT FROM AUTHOR]

Studies on hydrogen storage materials are proceeding worldwide to enhance adsorptive capacity with a proper adsorption energy between physisorption and chemisorption. Graphyne is the carbon allotropes having sp- and sp2-hybridized carbon atoms. It has not been synthesized yet, but have taken the center stage for decades owing to its promising electronic properties and applicability. Therefore, we performed geometry optimization using density functional theory calculation to determine the adsorptive behaviors of graphyne with decoration and doping approaches for improving hydrogen storage. Graphyne decorated with alkali metal cations showed highly adsorptive properties owing to the enhanced basicity by cations, whereas doped graphyne showed a lower adsorption energy within the desirable hydrogen storage range (−0.20 eV to −0.70 eV). Therefore, we applied bimodal surface modification using doped/co-doped graphyne in the presence of alkali decoration. We found that both decoration and doping approaches compensated each other, yielding an energy suitable for hydrogen storage (min: −0.24 eV, max: −0.32 eV), which elucidates the promising properties of a hydrogen storage material. [ABSTRACT FROM AUTHOR]

The introduction of a protogenic group such as sulfonic acid enables the operation of polymer electrolyte membrane for fuel cells at intermediate temperatures (> 100 °C) and very low humidity. It has been reported that the addition of a strongly acidic sulfonic acid group to hydrophobic polyether ether ketone (PEEK) creates the water permeability and proton transfer. In order to understand how sulfonic acid develops hydrophilicity, we conducted density functional theory calculations to determine the adsorption affinity of water for sulfonated PEEK (SPEEK), which represents the binding energy and band gap between HOMO (highest occupied molecular orbital) of SPEEK and LUMO (lowest unoccupied molecular orbital) of water molecules. Moreover, we designed disulfonated PEEKs (DSPEEK) with cis- and trans-conformations and found that cis-DSPEEK exhibits higher adsorption affinity for water with strong hydrogen bonds. This is attributed to the narrow energy gap of water molecules on cis-DSPEEK. Furthermore, we investigated proton adsorption in the presence of water to determine the effect of hydrophilic environment on the proton exchange in SPEEK. We found that cis-DSPEEK shows high repulsion for hydrogen transfer and moderate adsorption affinity for protons. Theoretical findings confirm that sulfonation ultimately yields hydrophilicity and developed proton transfer ability for PEEK, leading to a suitable structure for preferable proton exchange membrane. [ABSTRACT FROM AUTHOR]

ABSTRACT High transmittance is an important parameter for polyimide (PI) films used as flexible display substrates. However, thermal treatment during film fabrication can cause an undesired phenomenon affecting color change in the films, which is called haze. Until now, haze formation in PI films has remained mostly unexplored, suggesting that originates in the composition. In this work, the effect of fluorination on haze reduction was investigated. Both experiments and density functional theory calculations suggest that a high degree of fluorination of PI repeating units results in weaker intra/intermolecular conjugations between polymer chains and higher haze resistance in the following order: one fluorinated group (−1.43 eV) > two fluorinated groups (−0.76 eV) > three fluorinated groups (−0.52 eV) > four fluorinated groups (−0.43 eV). The differences in the haze resistance can influence on haziness in the PI films by thermal gradient inside a lab scale cavity in a furnace. The obtained results indicate that slow heat transfer facilitates the manufacturing process to obtain high transparency in PI films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44375. [ABSTRACT FROM AUTHOR]

The introduction of a protogenic group such as sulfonic acid allows the operation of polymer electrolyte membranes for fuel cells at intermediate temperature (>100 °C) and very low humidity. A sulfonated polyethersulfone (SPES) membrane with additional sulfonation was simulated by density functional theory calculations to determine the beneficial effect of the sulfonic group, which induces hydrophilicity for increased hydrogen conductivity. A higher degree of sulfonation enhances the H2O adsorption. In particular, trans-di-SPES ( trans-DSPES), with higher charge transfer to H2O and more hydrogen bonds, is more favorable for H2O adsorption than cis-DSPES; this is attributed to its narrow band gap (2.84 eV) and high adsorption energy (−0.81 eV) compared to cis-DSPES (2.96 and −0.69 eV, respectively). Theoretical findings suggest that adding the sulfonic acid group ultimately yields greater H2O adsorption on DSPES, increasing the hydrophilicity. [ABSTRACT FROM AUTHOR]

CO2 adsorption on a barium oxide ( BaO) surface saturated with a monolayer of H2O molecules was studied; a monolayer of H2O molecules on the BaO surface exhibits nondissociative or dissociative adsorption. During the nondissociative reaction, a hydroxyl ion-terminated surface is produced, resulting in the formation of barium hydroxide (Ba( OH)2) on the surface. The Ba( OH)2 from the substrate associates with the tightly bound CO2 molecule, resulting in the formation of barium carbonate ( BaCO3). In contrast, during the dissociative H2O adsorption, a hydrogen-terminated surface is produced, which strongly adsorbs CO2 molecules. The H2O molecules on a fully saturated BaO surface (containing multiple layers of H2O molecules) readily aggregate, and Ba dissociation takes place on the hydrated surface, possibly resulting in a surface containing Ba defects. [ABSTRACT FROM AUTHOR]

In this study, we investigated the adsorption of multiple CO 2 on Mg-rich minerals such as magnesium oxide (MgO) and olivine (MgSi 2 O 4 ) surface in order to understand the adsorption mechanism of CO 2 using density functional theory (DFT) approach. It is found that the energy required for the adsorption of CO 2 onto Mg 2 SiO 4 surface is 2.5 times (−1.30 eV) and 2.7 times (−0.70 eV) higher than that onto MgO surface for single and multiple CO 2 chemisorption, respectively. The surface coverage ( θ ) of Mg 2 SiO 4 surface is 1, which is four times higher than that of MgO surface. By analyzing the charge distribution of each atom of the MgO and Mg 2 SiO 4 surfaces before and after the adsorption of CO 2 molecules, we observed that charge redistribution occurs more readily in CO 2 –Mg 2 SiO 4 than in CO 2 –MgO. [ABSTRACT FROM AUTHOR]

• Synergic effect of bimodal structure on CO 2 adsorption with truncated architectures. • The truncated crystal phase of the adsorbents, exposing active facet sites. • Enhanced adsorption kinetics by the porous calcium-based materials. • CO 2 chemisorption by active charge reorganization between the adsorbent and CO 2. To increase the mineralization capabilities for the adsorption of carbon dioxide, we prepared bimodal calcium-based materials such as calcium oxide and calcium hydroxide with porous structures using a precipitation method with various drying processes. The various drying methods on porous structure develop different composition ratio of CaO and Ca(OH) 2 in bimodal materials, and in particular, formation of different morphology and structure, which leads different adsorption characteristics. Samples prepared with such methods attained porous structure and more active adsorption sites. It is worth noting that the freeze drying (FD) and aerogel drying (AD) methods created the truncated crystal phase of the adsorbents, exposing active facet sites in the place of the vertices. The results of CO 2 temperature programmed desorption and dynamic flow experiments reveal that porous calcium-based materials, synthesized through a process combining FD and AD sequentially, show high CO 2 adsorption capacity (up to 26.1 wt% at 650 °C) with enhanced adsorption kinetics. To gain insight into CO 2 adsorptive configuration at the atomistic scale and the adsorption mechanism, the adsorption of multiple CO 2 molecules on the CaO (1 0 0) surface is investigated using density functional theory calculation. The CO 2 molecules are chemisorbed through active charge reorganization between the CaO surface and CO 2 molecules while the adsorption energy is highly stabilized at –1.56 eV. The experimental and theoretical findings both suggest that CO 2 mineralization is feasible on calcium-based bimodal structured materials. [ABSTRACT FROM AUTHOR]

We calculated the band structures of a variety of N- and S-doped graphenes in order to understand the effects of the N and S dopants on the graphene electronic structure using density functional theory (DFT). Band-structure analysis revealed energy band upshifting above the Fermi level compared to pristine graphene following doping with three nitrogen atoms around a mono-vacancy defect, which corresponds to p-type nature. On the other hand, the energy bands were increasingly shifted downward below the Fermi level with increasing numbers of S atoms in N/S-co-doped graphene, which results in n-type behavior. Hence, modulating the structure of graphene through N- and S-doping schemes results in the switching of "p-type" to "n-type" behavior with increasing S concentration. Mulliken population analysis indicates that the N atom doped near a mono-vacancy is negatively charged due to its higher electronegativity compared to C, whereas the S atom doped near a mono-vacancy is positively charged due to its similar electronegativity to C and its additional valence electrons. As a result, doping with N and S significantly influences the unique electronic properties of graphene. Due to their tunable band-structure properties, the resulting N- and S-doped graphenes can be used in energy and electronic-device applications. In conclusion, we expect that doping with N and S will lead to new pathways for tailoring and enhancing the electronic properties of graphene at the atomic level. [ABSTRACT FROM AUTHOR]

Toughness and high elastic elongation are important requirements for polyimide films used as substrates in flexible displays. However, these properties can be altered by imidization during the thermal treatment. In the present study, we investigated a probable mechanism to enhance the toughness by shrinking fluorinated polyimide films containing benzidine moieties. A higher degree of fluorination leads to weaker intermolecular charge transfer and optically clearer films, but it also degrades the mechanical properties. Moreover, β -transition originating from the molecular rotation around benzidines makes the film dependent on the elongation conditions during solvent drying. According to frequency-sweeping measurements and simulations based on density functional theory and molecular dynamics, the β -transition temperature increases and the phase lag in elastic energy loss decreases with increasing shrinkage. Both experimental and theoretical findings suggest that the change in frequency dependence can be attributed to the variation in elasticity retardation, which possibly originates from the chain-entanglement density. [ABSTRACT FROM AUTHOR]