Hydrogen storage in M(BDC)(TED)0.5 metal-organic framework: physical insights and capacities.

Finding renewable energy sources to replace fossil energy has been an essential demand in recent years. Hydrogen gas has been becoming a research hotspot for its clean and free-carbon energy. However, hydrogen storage technology is challenging for mobile and automotive applications. Metal-organic frameworks (MOFs) have emerged as one of the most advanced materials for hydrogen storage due to their exceptionally high surface area, ultra-large and tuneable pore size. Recently, computer simulations allowed the designing of new MOF structures with significant hydrogen storage capacity. However, no studies are available to elucidate the hydrogen storage in M(BDC)(TED)0.5, where M = metal, BDC = 1,4-benzene dicarboxylate, and TED = triethylenediamine. In this report, we used van der Waals-dispersion corrected density functional theory and grand canonical Monte Carlo methods to explore the electronic structure properties, adsorption energies, and gravimetric and volumetric hydrogen loadings in M(BDC)(TED)0.5 (M = Mg, V, Co, Ni, and Cu). Our results showed that the most favourable adsorption site of H2 in M(BDC)(TED)0.5 is the metal cluster-TED intersection region, in which Ni offers the strongest binding strength with the adsorption energy of -16.9 kJ mol-1. Besides, the H2@M(BDC)(TED)0.5 interaction is physisorption, which mainly stems from the contribution of the d orbitals of the metal atoms for M = Ni, V, Cu, and Co and the p orbitals of the O, C, N atoms for M = Mg interacting with the σ* state of the adsorbed hydrogen molecule. Noticeably, the alkaline-earth metal Mg strongly enhanced the specific surface area and pore size of the M(BDC)(TED)0.5 MOF, leading to an enormous increase in hydrogen storage with the highest absolute (excess) gravimetric and volumetric uptakes of 1.05 (0.36) wt% and 7.47 (2.59) g L-1 at 298 K and 7.42 (5.80) wt% and 52.77 (41.26) g L-1 at 77 K, respectively. The results are comparable to the other MOFs found in the literature.

Unravelling the effects of functional groups on the adsorption of 2-mercaptobenzothiazole on a copper surface: a DFT study.

The adsorption of organic compounds onto metal surfaces holds significant importance across various applications, where understanding the intricate interactions between the compounds and the metal surfaces is indispensable. By using density functional theory calculations, this study investigated the impact of functional groups on the interaction between the thione form of 2-mercaptobenzothiazole (MBT) and the Cu(111) surface. The results indicated that substituting functional groups at the C6 position exerts a dual influence on the covalent and non-covalent interactions (NCI). Electron-donating groups enhanced both covalent and non-covalent interactions, whereas electron-withdrawing groups decreased covalent while increasing non-covalent interactions. The covalent interaction between MBTs and Cu(111) is mainly governed by the electron donation from the occupied orbitals of the molecules to the conduction band of copper, with the absolute interaction energies (eV) increasing in the order of MBT-NO2 (0.629) < MBT-COOH (0.660) < MBT-Cl (0.699) < MBT (0.715) < MBT-SH (0.727) < MBT-OH (0.733) < MBT-CH3 (0.735) < MBT-OCH3 (0.749) < MBT-NH2 (0.781) < MBT-NHCH3 (0.792). The influence of functional groups on covalent interactions is clarified by examining changes in the molecule's electronic structure, revealing a linear relationship between covalent interaction energy and HOMO energy, or the Hammett substituent constant. However, the impact of functional groups on non-covalent interactions is more complex and cannot be described by changes in the electronic structure. A novel parameter, the substitution interaction energy, was proposed to capture the effect of functional groups on the NCI-included adsorption energy of MBT derivatives on the Cu(111) surface. The stronger the substitution interaction, the stronger the NCI-included interaction of MBTs on Cu(111). The absolute NCI-included interaction energies follow the order of MBT (2.141) < MBT-Cl (2.213) < MBT-COOH (2.266) < MBT-CH3 (2.294) < MBT-OH (2.331) < MBT-OCH3 (2.379) < MBT-NO2 (2.461) = MBT-NH2 (2.461) < MBT-SH (2.530) < MBT-NHCH3 (2.565). These insights offer valuable guidance for manipulating the adsorption of organic substances on metal surfaces through functional groups in diverse applications.

Photoswitchable Photochromic Chelating Spironaphthoxazines: Synthesis, Photophysical Properties, Quantum-Chemical Calculations, and Complexation Ability.

The stable and efficient photochromic and photoswitchable molecular systems designed from spirooxazines are of increasing scientific and practical interest because of their present and future applications in advanced technologies. Among these compounds, chelating spironaphthoxazines have received widespread attention due to their efficient optical response after complexation with some metal ions being of biomedical interest and environmental importance, as well as their good cycle performance and high reliability, especially by metal ion sensing. In this mini-review, we summarize our results in the design of novel photoswitchable chelating spironaphthoxazines with specific substituents in their naphthoxazine or indoline ring systems in view of recent progress in the development of such molecular systems and their applications as metal ion sensors. The design, synthesis methods, and photoresponse of such spirooxazine derivatives relevant to their applications, as well as quantum-chemical calculations for these compounds, are presented. Examples of various design concepts are discussed, such as sulfobutyl, hydroxyl, benzothiazolyl, or ester and carboxylic acid as substituents in the chelating spironaphthoxazine molecules. Further developments and improvements of this interesting and promising kind of molecular photoswitches are outlined.

Carbon dioxide conversion to methanol on a PdCo bimetallic catalyst.

The CO2 conversion to methanol (CO2-to-CH3OH conversion) is a promising way to resolve greenhouse gas emissions and global energy shortage. Many catalysts are of interest in improving the efficiency of the conversion reaction. The PdCo alloy is a potential catalyst, but no research is available to clarify the CO2-to-CH3OH reaction mechanism of this alloy. Here, using density functional theory combined with the thermodynamic model, we elucidated the reaction mechanism of the CO2-to-CH3OH conversion on the Pd-skin/PdCo alloy catalyst via thermo- and electro-catalytic processes. The adsorption of CO2-to-CH3OH intermediates with key stable intermediates such as HCOO, COOH, and CO was explored. Free-energy diagrams for the CO2-to-CH3OH conversion were constructed. We found that the formate pathway is the most favorable one. The charge transfer plays a crucial role in the substrate-adsorbate interaction via electronic structure analysis. This work provides valuable guidance for designing Pd-based catalysts for the CO2-to-CH3OH conversion.

Bandgap engineering of germanene for gas sensing applications.

Gas sensors are used to detect gas components in human breath to diagnose diseases, such as cancers. However, choosing suitable two-dimensional materials for gas sensors is a challenge. Germanene can be a good candidate because of its outstanding electronic and structural properties. Based on the density functional theory calculations with various schemes, such as PBE + vdW-DF2, HSE06 + PBE, and HSE06 + vdW-DF2, we elucidated the structural and electronic properties of germanene substrates (perfect, vacancy-1, and vacancy-2) while adsorbing hepatocellular carcinoma-related volatile organic compounds (VOCs), i.e., acetone, 1,4-pentadiene, methylene chloride, phenol, and allyl methyl sulfide. These gases have been selected for investigation because of their most frequent occurence in diagnosing the disease. We found that vacancy substrates enhanced the adsorption strength of the VOCs compared to the perfect one, where the phenol adsorbed most strongly and exhibited the most profound influence on the structural deformation of the substrates over the other VOCs. Besides, the adsorbed VOCs significantly modified the energy bandgap of the considered germanene substrates. In particular, the gases, except allyl methyl sulfide, vanished the bandgap of the vacancy-1 germanene and converted this substrate from a semiconductor to a metal, while they widened the bandgap of the vacancy-2 structure compared to the isolated case. Therefore, the perfect and vacancy-2 germanene sheets could maintain their semiconducting state upon gas adsorption, implying that these substrates may be suitable candidates for gas sensing applications. The nature of the interaction between the VOCs and the germanene substrates is a physical adsorption with a weak charge exchange, which mainly comes from the contribution of the pz orbital of the VOCs and the pz orbital of Ge.

Theoretical investigation of CO2 capture in the MIL-88 series: effects of organic linker modification.

CO2 capture is a crucial strategy to mitigate global warming and protect a sustainable environment. Metal-organic frameworks with large surface area, high flexibility, and reversible adsorption and desorption of gases are good candidates for CO2 capture. Among the synthesized metal-organic frameworks, the MIL-88 series has attracted our attention due to their excellent stability. However, a systematic investigation of CO2 capture in the MIL-88 series with different organic linkers is not available. Therefore, we clarified the topic via two sections: (1) elucidate physical insights into the CO2@MIL-88 interaction by van der Waals-dispersion correction density functional theory calculations, and (2) quantitatively study the CO2 capture capacity by grand canonical Monte Carlo simulations. We found that the 1πg, 2σu/1πu, and 2σg peaks of the CO2 molecule and the C and O p orbitals of the MIL-88 series are the predominant contributors to the CO2@MIL-88 interaction. The MIL-88 series, i.e., MIL-88A, B, C, and D, has the same metal oxide node but different organic linkers: fumarate (MIL-88A), 1,4-benzene-dicarboxylate (MIL-88B), 2,6-naphthalene-dicarboxylate (MIL-88C), and 4,4'-biphenyl-dicarboxylate (MIL-88D). The results exhibited that fumarate should be the best replacement for both the gravimetric and volumetric CO2 uptakes. We also pointed out a proportional relationship between the capture capacities with electronic properties and other parameters.

Effects of functional groups in iron porphyrin on the mechanism and activity of oxygen reduction reaction.

The activity of the oxygen reduction reaction (ORR) on the cathode is one of the dominant factors in the performance of proton exchange membrane fuel cells. Iron porphyrin has low cost, environmental benignity, and maximum efficiency of metal usage. Therefore, this material can be a promising single-atomic metal dispersion catalyst for fuel cell cathodes. The variation of functional groups was proven to effectively modify the activity of the ORR on the iron porphyrin. However, the influences of functional groups on the mechanisms of the ORR remain ambiguous. This work paid attention to the substitution of carboxyl (-COOH), methyl (-CH3), and amino (-NH2) functional groups at the meso positions of the porphyrin ring. By using van der Waals density functional theory (vdW-DF) calculations, we found that the ORR mechanisms can follow the associative and dissociative pathways, respectively. The Gibbs free energy diagrams revealed that the rate-limiting step occurs at the second hydrogenation step for the first pathway and the O2 dissociation step for the second pathway for all considered functional groups. The thermodynamic energy barrier at the rate-limiting step was found to be in the following order: porphyrin-(CH3)4 < porphyrin-(NH2)4 < original porphyrin < porphyrin-(COOH)4 for the associative mechanism and porphyrin-(NH2)4 < porphyrin-(CH3)4 < porphyrin-(COOH)4 < original porphyrin for the dissociative pathway. The findings suggested that porphyrin-(CH3)4 and porphyrin-(NH2)4 should be the best choices among the considered substrates for the oxygen reduction reaction. Furthermore, the interaction between the ORR intermediates and the substrates was attributed to the resonance of the d z 2 , d xz , and d yz components of the Fe d orbital and the C and N p orbitals of the substrates with the p orbitals of the oxygen atoms in the intermediates. Finally, the nature of the interaction between the adsorbent and adsorbate was charge transfer.

Physical insights into the Au growth on the surface of a LaAlO3/SrTiO3 heterointerface.

Researchers investigated the modification of the LaAlO3/SrTiO3 interface with Au overlayers and nanoparticles, which led to the change of various physical properties. However, no research is available to elucidate insights into the interaction of Au with the LaAlO3/SrTiO3 substrate. Therefore, this study is devoted to solving the question using density functional theory calculations. We also studied the optical properties of the LaAlO3/SrTiO3 system before and after the Au adsorption. We found that an additional optical peak occurs with significant intensity in the wavelength region of 600 nm to 1200 nm depending on the LaAlO3 film thickness. This peak is attributed to the increase in the hole states in the presence of Au adsorption with the increase in the LaAlO3 film thickness.

Selectivity of volatile organic compounds on the surface of zinc oxide nanosheets for gas sensors.

The detection of volatile organic compounds by gas sensors is of great interest for environmental quality monitoring and the early-stage and noninvasive diagnosis of diseases. Experiments found hexane, toluene, aniline, butanone, acetone, and propanol gases in the exhaled breath of patients suffering from COVID-19, lung cancer, and diabetes. However, no studies are available to systematically elucidate the selectivity of these gases on nanosheets of zinc oxide for chemiresistive and direct thermoelectric gas sensors. Therefore, this work performed the elucidation by studying the electronic, electrical, and thermal properties of the bilayered ZnO nanosheets with polar (0001) and non-polar (112̄0) surfaces under the adsorption of the gases. The interaction between the gases and the nanosheets belongs to two groups: electrostatic attraction and charge exchange. The second one occurs due to the peak resonance of the same type of orbitals between the substrates and the gases along the surface normal and the first one for the other cases. The characteristics of the Seebeck coefficient exhibited distinct selectivity of butanone and acetone.

Antimicrobial Properties of TiO2 Microparticles Coated with Ca- and Cu-Based Composite Layers.

The ability of TiO2 to generate reactive oxygen species under UV radiation makes it an efficient candidate in antimicrobial studies. In this context, the preparation of TiO2 microparticles coated with Ca- and Cu-based composite layers over which Cu(II), Cu(I), and Cu(0) species were identified is presented here. The obtained materials were characterized by a wide range of analytical methods, such as X-ray diffraction, electron microscopy (TEM, SEM), X-ray photoelectron (XPS), and UV-VIS spectroscopy. The antimicrobial efficiency was evaluated using qualitative and quantitative standard methods and standard clinical microbial strains. A significant aspect of this composite is that the antimicrobial properties were evidenced both in the presence and absence of the light, as result of competition between photo and electrical effects. However, the antibacterial effect was similar in darkness and light for all samples. Because no photocatalytic properties were found in the absence of copper, the results sustain the antibacterial effect of the electric field (generated by the electrostatic potential of the composite layer) both under the dark and in light conditions. In this way, the composite layers supported on the TiO2 microparticles' surface can offer continuous antibacterial protection and do not require the presence of a permanent light source for activation. However, the antimicrobial effect in the dark is more significant and is considered to be the result of the electric field effect generated on the composite layer.

Preliminary Study on Light-Activated Antimicrobial Agents as Photocatalytic Method for Protection of Surfaces with Increased Risk of Infections.

Preventing and controlling the spread of multidrug-resistant (MDR) bacteria implicated in healthcare-associated infections is the greatest challenge of the health systems. In recent decades, research has shown the need for passive antibacterial protection of surfaces in order to reduce the microbial load and microbial biofilm development, frequently associated with transmission of infections. The aim of the present study is to analyze the efficiency of photocatalytic antimicrobial protection methods of surfaces using the new photocatalytic paint activated by light in the visible spectrum. The new composition is characterized by a wide range of analytical methods, such as UV-VIS spectroscopy, electron microscopy (SEM), X-ray powder diffraction (PXRD) or X-ray photoelectron spectroscopy (XPS). The photocatalytic activity in the UV-A was compared with the one in the visible light spectrum using an internal method developed on the basis of DIN 52980: 2008-10 standard and ISO 10678-2010 standard. Migration of metal ions in the composition was tested based on SR EN1186-3: 2003 standard. The new photocatalytic antimicrobial method uses a type of photocatalytic paint that is active in the visible spectral range and generates reactive oxygen species with inhibitory effect against all tested microbial strains.

Polymorphism of chitosan-based networks stabilized by phytate investigated by molecular dynamics simulations.

Chitosan can associate in the presence of polyphosphates into insoluble hydrogels capable of drug encapsulation and safe and efficient release. On the one hand, chitosan hydrogels were synthesized using the phytate anion as a crosslinking agent and were characterized by employing dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR). On the other hand, an effective chitosan-phytate model with atomistic details was created to examine the underlying physical crosslinking pattern, and the structure and dynamics of the chitosan-phytate complex were systematically investigated by using molecular dynamics (MD) simulations. To harbor the crosslinker potential for obtaining chitosan-based hydrogels, the impact of the phytate concentration and the functional groups of the chitosan on the reticulation process was addressed. The phytate association was determined by the phosphates' capacity for H-bonding to the amine and hydroxyl groups belonging to two consecutive glucosidic units. The physical crosslinking pattern was determined by the number of chitosan chains bound by one phytate anion and the phytate orientation relative to the glucopyranose neighbors. Cross-linking of two up to six chitosan chains mediated by a phytate anion represented favorable states, and the number distribution of cross-linked chains depended on the phytate concentration. The circular distribution of the cross-linkable phosphates regulated the nearly isotropic orientation of the chitosan chains and phytate at the junction, and the variety of topological crosslinking demonstrated the phytate ion's potential for developing chitosan-based hydrogels with improved structural attributes.

N-type and p-type molecular doping on monolayer MoS2.

Monolayer MoS2 has attracted much attention due to its high on/off current ratio, transparency, and suitability for optoelectronic devices. Surface doping by molecular adsorption has proven to be an effective method to facilitate the usage of MoS2. However, there are no works available to systematically clarify the effects of the adsorption of F4TCNQ, PTCDA, and tetracene on the electronic and optical properties of the material. Therefore, this work elucidated the problem by using density functional theory calculations. We found that the adsorption of F4TCNQ and PTCDA turns MoS2 into a p-type semiconductor, while the tetracene converts MoS2 into an n-type semiconductor. The occurrence of a new energy level in the conduction band for F4TCNQ and PTCDA and the valence band for tetracene reduces the bandgap of the monolayer MoS2. Besides, the MoS2/F4TCNQ and MoS2/PTCDA systems exhibit an auxiliary optical peak at the long wavelengths of 950 and 850 nm, respectively. Contrastingly, the MoS2/tetracene modifies the optical spectrum of the monolayer MoS2 only in the ultraviolet region. The findings are in good agreement with the experiments.

How do the doping concentrations of N and B in graphene modify the water adsorption?

Understanding the interaction of water and graphene is crucial for various applications such as water purification, desalination, and electrocatalysis. Experimental and theoretical studies have already investigated water adsorption on N- and B-doped graphene. However, there are no reports available that elucidate the influences of the N and B doping content in graphene on the microscopic geometrical structure and the electronic properties of the adsorbed water. Thus, this work is devoted to solving this problem using self-consistent van der Waals density functional theory calculations. The N and B doping contents of 0.0, 3.1, 6.3, and 9.4% were considered. The results showed that the binding energy of water increases almost linearly as a function of doping content at all concentrations for N-doped graphene but below 6.3% for B-doped graphene. In the linear range, the binding energy increases by approximately 30 meV for each increment of the doping ratio. Analyses of the geometric and electronic structures explained the enhancement of the water-graphene interaction with the variation in doping percentage.

Electronic and optical properties of monolayer MoS2 under the influence of polyethyleneimine adsorption and pressure.

MoS2 is one of the well-known transition metal dichalcogenides. The moderate bandgap of monolayer MoS2 is fascinating for the new generation of optoelectronic devices. Unfortunately, MoS2 is sensitive to gases in the environment causing its original electronic properties to be modified unexpectedly. This problem has been solved by coating MoS2 with polymers such as polyethyleneimine (PEI). Furthermore, the application of pressure is also an effective method to modify the physical properties of MoS2. However, the effects of polyethyleneimine and pressure on the electronic and optical properties of monolayer MoS2 remain unknown. Therefore, we elucidated this matter by using density functional theory calculations. The results showed that the adsorption of the PEI molecule significantly reduces the width of the direct bandgap of the monolayer MoS2 to 0.55 eV because of the occurrence of the new energy levels in the bandgap region due to the contribution of the N-2p z state of the PEI molecule. Remarkably, the transition from semiconductor to metal of the monolayer MoS2 and the MoS2/PEI system occurs at the tensile pressure of 24.95 and 21.79 GPa, respectively. The bandgap of these systems approaches 0 eV at the corresponding pressures. Importantly, new peaks in the optical spectrum of the clean MoS2 and MoS2/PEI appear in the ultraviolet region under compressive pressures and the infrared region under tensile strains.

Mechanism and activity of the oxygen reduction reaction on WTe2 transition metal dichalcogenide with Te vacancy.

WTe2 transition metal dichalcogenide is a promising candidate for the cathode of proton-exchange membrane fuel cells. In this paper, we investigated the mechanism and activity of the oxygen reduction reaction on the monolayer of the WTe2 transition metal dichalcogenide with Te vacancy denoted as WTed 2. By using density functional theory calculations, we studied the reaction intermediates on the surface of WTed 2. The Gibbs free energy was calculated to clarify the thermodynamic properties of the reaction. We discovered that the ORR mechanisms are more favorable outside than inside the vacancy. The ORR activity was found to be comparable to that of the well-known transition metal electro-catalysts.

Simultaneous adsorption of SO2 and CO2 in an Ni(bdc)(ted)0.5 metal-organic framework.

The metal-organic framework Ni(bdc)(ted)0.5 is a promising material for simultaneous capture of harmful gases such as SO2 and CO2. We found that SO2 performs much better than CO2 during adsorption, and the lack of physical insight was clarified through detailed analyses of the electronic structures obtained from density functional theory calculations. Our results showed that strong interactions of the d band of Ni atoms with the valence states (2n, 3n, and 4n) of SO2 but almost not with those of CO2 are the main reasons. Our finding is useful for the rational design of new metal-organic frameworks with suitable interactions for the simultaneous capture of not only SO2 and CO2 but also other gases.

Monte Carlo Simulations of the Magnetic Behavior, Ordering Temperature and Magnetocaloric Effects in 1D, 2D and 3D Ferrimagnetic Systems.

As for the systematic investigations of magnetic behaviors and its related properties, computer simulations in extended quantum spin networks have been performed in good conditions via the generalized Ising model using the Monte Carlo-Metropolis algorithm with proven efficiencies. The present work, starting from a real magnetic system, provides detailed insights into the finite size effects and the ferrimagnetic properties in various 1 D, 2D and 3D geometries such as the magnetic moment, ordering temperature, and magnetocaloric effects with the different values of spins localized on the different coordinated sites.

Hydrogen bond network topology in liquid water and methanol: a graph theory approach.

Networks are increasingly recognized as important building blocks of various systems in nature and society. Water is known to possess an extended hydrogen bond network, in which the individual bonds are broken in the sub-picosecond range and still the network structure remains intact. We investigated and compared the topological properties of liquid water and methanol at various temperatures using concepts derived within the framework of graph and network theory (neighbour number and cycle size distribution, the distribution of local cyclic and local bonding coefficients, Laplacian spectra of the network, inverse participation ratio distribution of the eigenvalues and average localization distribution of a node) and compared them to small world and Erdos-Rényi random networks. Various characteristic properties (e.g. the local cyclic and bonding coefficients) of the network in liquid water could be reproduced by small world and/or Erdos-Rényi networks, but the ring size distribution of water is unique and none of the studied graph models could describe it. Using the inverse participation ratio of the Laplacian eigenvectors we characterized the network inhomogeneities found in water and showed that similar phenomena can be observed in Erdos-Rényi and small world graphs. We demonstrated that the topological properties of the hydrogen bond network found in liquid water systematically change with the temperature and that increasing temperature leads to a broader ring size distribution. We applied the studied topological indices to the network of water molecules with four hydrogen bonds, and showed that at low temperature (250 K) these molecules form a percolated or nearly-percolated network, while at ambient or high temperatures only small clusters of four-hydrogen bonded water molecules exist.

Interaction between graphene and the surface of SiO2.

The interaction between graphene and a SiO(2) surface has been analyzed with first-principles DFT calculations by constructing the different configurations based on α-quartz and cristobalite structures. The fact that single-layer graphene can stay stably on a SiO(2) surface is explained based on a general consideration of the configuration structures of the SiO(2) surface. It is found that the oxygen defect in a SiO(2) surface can shift the Fermi level of graphene down which opens up the mechanism of the hole-doping effect of graphene adsorbed on a SiO(2) surface observed in a lot of experiments.