Capacitive and Charge Transfer Effects of Single-Walled Carbon Nanotubes in TiO2 Electrodes

The transfer of nanoscale properties from single-walled carbon nanotubes (SWCNTs) to macroscopic systems is a topic of intense research. In particular, inorganic composites of SWCNTs and metal oxide semiconductors are being investigated for applications in electronics, energy devices, photocatalysis, and electroanalysis. In this work, a commercial SWCNT material is separated into fractions containing different conformations. The liquid fractions show clear variations in their optical absorbance spectra, indicating differences in the metallic/semiconducting character and the diameter of the SWCNTs. Also, changes in the surface chemistry and the electrical resistance are evidenced in SWCNT solid films. The starting SWCNT sample and the fractions as well are used to prepare hybrid electrodes with titanium dioxide (SWCNT/TiO₂). Raman spectroscopy reflects the optoelectronic properties of SWCNTs in the SWCNT/TiO₂ electrodes, while the electrochemical behavior is studied by cyclic voltammetry. A selective development of charge transfer characteristics and double-layer behavior is achieved through the suitable choice of SWCNT fractions.     

Functional Group Modification and Bonding Characteristics of Ti3C2 MXene-Organic Composites from First-Principles Calculations

The unique physical structure and abundant surface functional groups of MXene make the grafted organic molecules exhibit specific electrical and optical properties. This work reports the results of first-principles calculations to investigate the composite systems formed by different organic molecular monomers, namely acrylic acid (AA), acrylamide (AM), 1-aziridineethanol (1-AD) and glucose, and Ti₃C₂ MXene saturated with different functional groups, namely −OH, −O and −F. The results show that the interaction between organic molecules and the MXene surface depends on the type of functional groups of the organic molecules, while the strength of the interaction is determined by the type of surface functional groups and the number of hydrogen bonds. The bare Ti₃C₂ and Ti₃C₂(OH)₂ can readily form strong chemical and hydrogen bonds with AA and AM molecules, leading to strong adsorption energy and a large amount of charge transfer, while the interaction between organic molecules and MXene saturated by −F or −O groups mainly exhibits physical interactions, accompanied by low adsorption energy and a small amount of charge transfer. This research provides theoretical guidance for the synthesis of high-performance MXene organic composite systems.     

A theoretical study on the effect of intercalating sulfur atom and doping boron atom on the adsorption of hydrogen molecule on (10,0) single-walled carbon nanotubes

Adsorption of molecular hydrogen on single-walled carbon nanotube (SWCNT), sulfur-intercalated SWCNT (S-SWCNT), and boron-doped SWCNT (BSWCNT), have been studied by means of density functional theory (DFT). Two methods KMLYP and local density approximation (LDA) were used to calculate the binding energies. The most stable configuration of H₂ on the surface of pristine SWCNT was found to be on the top of a hexagonal at a distance of 3.54 Å in good agreement with the value of 3.44 Å reported by Han and Lee (Carbon, 2004, 42, 2169). KMLYP binding energies for the most stable configurations in cases of pristine SWCNT, S-SWCNT, and BSWCNT were found to be ?2.2 kJ mol^?1, ?3.5 kJ mol^?1, and ?3.5 kJ mol^?1, respectively, while LDA binding energies were found to be ?8.8 kJ mol^?1, ?9.7 kJ mol^?1, and ?4.1 kJ mol^?1, respectively. Increasing the polarizability of hydrogen molecule due to the presence of sulfur in sulfur intercalated SWCNT caused changes in the character of its bonding to sulfur atom and affected the binding energy. In H₂-BSWCNT system, stronger charge transfer caused stronger interaction between H₂ and BSWCNT to result a higher binding energy relative to the binding energy for H₂-SWCNT.     

Sensing Characteristics of a Graphene‐like Boron Carbide Monolayer towards Selected Toxic Gases

By using first‐principles calculations based on density functional theory, we study the adsorption efficiency of a BC₃ sheet for various gases, such as CO, CO₂, NO, NO₂, and NH₃. The optimal adsorption position and orientation of these gas molecules on the BC₃ surface is determined and the adsorption energies are calculated. Among the gas molecules, CO₂ is predicted to be weakly adsorbed on the graphene‐like BC₃ sheet, whereas the NH₃ gas molecule shows a strong interaction with the BC₃ sheet. The charge transfer between the molecules and the sheet is discussed in terms of Bader charge analysis and density of states. The calculated work function of BC₃ in the presence of CO, CO₂, and NO is greater than that of a bare BC₃ sheet. The decrease in the work function of BC₃ sheets in the presence of NO₂ and NH₃ further explains the affinity of the sheet towards the gas molecules. The energy gap of the BC₃ sheets is sensitive to the adsorption of the gas molecules, which implies possible future applications in gas sensors.     

Thickness dependent sensing mechanism in sorted semi-conducting single walled nanotube based sensors

Single walled carbon nanotube (SWCNT) networks present outstanding potential for the development of SWCNT-based gas sensors. Due to the complexity of the transport properties of this material, the physical mechanisms at stake during exposure to gas are still under debate. Previously suggested mechanisms are charge transfer between gas molecules and SWCNT and Schottky barrier modulation. By comparing electrical measurements with an analytical model based on Schottky barrier modulation, we demonstrate that one mechanism or the other is predominant depending on the percolation of metallic carbon nanotubes. Below the metallic SWCNT percolation threshold, sensing is dominated by the modulation of the Schottky barrier, while above this threshold, it is only attributed to a charge transfer between SWCNT and gas molecules. Both mechanisms are discussed in terms of sensitivity and resolution leading to routes for the optimization of a gas sensor architecture based on highly enriched semiconducting carbon nanotube films.     

Extraction of Intercalated O2 from Aligned Carbon Nanotubes: The Breaking of Intertube Paths and Exponential Changes in Resistance

In carbon nanotube films, the alignment of carbon nanotubes creates Lennard–Jones potentials at intertube junctions and trapped O₂ appears to oscillate at elevated temperatures. Electrical measurements reveal a low hopping barrier along the transverse direction and an underlying mechanism that involves intercalated molecules acting as charge carriers between tubes. Ab initio calculations support dynamic intercalation and charge transfer through O₂ bouncing between tubes.     

Mössbauer spectra of (Fe0.5Zn0.5)PS3 and its pyridine intercalate

Mössbauer spectra of (Fe_0.5Zn_0.5)PS₃, which is isomorphous with FePS₃, were measured at 300 and 80 K, and were compared with those of FePS₃. We succeeded in preparing (Fe_0.5Zn_0.5)PS₃ intercalated with pyridine. In the XRD pattern of the intercalate the diffraction peaks corresponding to (Fe_0.5Zn_0.5)PS₃ were completely missing, suggesting that the intercalation was completely performed with pyridine. The Mössbauer spectra were changed significantly by the intercalation suggesting the charge transfer from guest molecules to the host matrix. The replacement of iron by zinc has no influence on the electronic state of the iron atom, except for the magnetic interaction.     

Mechanistic insights into the efficient intramolecular chemiexcitation of dioxetanones from TD-DFT and multireference calculations

Despite decades of research, it is still not clear what is the mechanism behind the efficient chemiexcitation of dioxetanones in chemiluminescent and bioluminescent reactions. In fact, long-standing theories (charge transfer-initiated luminescence and chemically induced electron-exchange luminescence) have been demonstrated to not be able to explain this phenomenon. Herein, a theoretical approach using reliable and up-to-date methodology was used to address this problem, by focusing on model dioxetanones. Time-dependent (TD)-Density functional theory (DFT) and multireference complete-active-space second-order perturbation theory (CASPT2) calculations provided evidence that points to efficient intramolecular chemiexcitation being the result of the reacting molecules having access to a long zone of the Potential energy surface (PES), within the biradicalar region, where S₀ and S₁ are degenerate. Molecules with inefficient chemiexcitation are unable to reach this zone of degeneracy. Our main finding is that access to the region of degeneracy appears to be given due to increased interaction between the keto and CO₂ moieties, as supported by the use of the activation strain model and Born-Oppenheimer molecular dynamics, which extends the biradical region by delaying the rupture of the peroxide ring. Increased interaction derives from attractive electrostatic interactions between the moieties of dioxetanone. Thus, we hypothesize that efficient chemiexcitation results not only from electron/charge transfer and subsequent charge annihilation but is instead based on the degree of interaction between the keto and CO₂ moieties, which controls the access to a region of degeneracy between the ground and excited states.     

Diameter‐Sorted SWCNT–Porphyrin and SWCNT–Phthalocyanine Conjugates for Light‐Energy Harvesting

A non‐covalent double‐decker binding strategy is employed to construct functional supramolecular single‐wall carbon nanotubes (SWCNT)–tetrapyrrole hybrids capable of undergoing photoinduced electron transfer and performing direct conversion of light into electricity. To accomplish this, two semiconducting SWCNTs of different diameters (6,5 and 7,6) were modified via π–π stacking of pyrene functionalized with an alkyl ammonium cation (PyrNH₃⁺). Such modified nanotubes were subsequently assembled via dipole–cation binding of zinc porphyrin with one ( 1 ) or four benzo‐18‐crown‐6 cavities ( 2 ) or phthalocyanine with four benzo‐18‐crown‐6 cavities at the ring periphery ( 3 ), employed as visible‐light photosensitizers. Upon charactering the conjugates using TEM and optical techniques, electron transfer via photoexcited zinc porphyrin and phthalocyanine was investigated using time‐resolved emission and transient absorption techniques. Higher charge‐separation efficiency is established for SWCNT(7,6) with a narrow band gap than the thin SWCNT(6,5) with a wide band gap. Photoelectrochemical studies using FTO/SnO₂ electrodes modified with these donor–acceptor conjugates unanimously demonstrated the ability of these conjugates to convert light energy into electricity. The photocurrent generation followed the trend observed for charge separation, that is, incident‐photon‐to‐current efficiency (IPCE) of a maximum of 12 % is achieved for photocells with FTO/SnO₂/SWCNT(7,6)/PyrNH₃⁺: 1 .     

Electroreduction of carbon dioxide: Part II. The mechanism of reduction in aprotic solvents

The mechanism of electroreduction of carbon dioxide in aprotic solvents on mercury, lead, tin, indium and platinum is studied using the photoemission method and the method of stationary polarization curves. When comparing the data of photoemission and “dark” (polarization) measurements it was found that in the first Tafel region of the polarization curves the rate-determining step is the transfer of the second electron to (CO₂)^.?₂ anion-radicals formed as a result of the interaction of initially generated CO^.?₂ anion-radicals with adsorbed CO₂ molecules. In the second Tafel region the rate-determining step is the transfer of the first electron to an adsorbed CO₂ molecule. The peculiarities of electroreduction of carbon dioxide in aprotic solvents can be explained provided that the effect of potential on adsorption of CO₂ and anion-radicals and the effect of repulsion of negatively charged radicals are taken into account.     

Electrolytic molybdenum sulfides for thin-layer lithium power sources

The active molybdenum sulfide compound Mo₂S₃, which should be considered as a cathode material for thin-layer rechargeable power source, has been produced by electrolysis. Using impedance spectroscopy and potential relaxation method after current interruption, the kinetic parameters of lithium intercalation in electrolytic Mo₂S₃ have been obtained. Activation energy of Li⁺ migration in electrolyte (13.76 kJ/mol), charge transfer through the Mo₂S₃ electrode/electrolyte interface (38.8 kJ/mol), and Li⁺ diffusion in a solid phase (57.3 kJ/mol) have also been established. Taking into account the coefficient data of charge mass transfer in a solid phase and the reaction rate coefficient of charge transfer through the interface electrode/electrolyte within the temperature range 20–50 °C, the stage of Li⁺ transfer in a solid phase has been determined as a limiting stage for lithium intercalation in electrolytic molybdenum sulfide Mo₂S₃.     

Functional Group-induced p-Doping of MoS2 by Titanium(IV) Bis(ammonium lactato) Dihydroxide Physisorption

P-type doping is of critical importance for the realization of certain high-performance electrical and optoelectronic devices based on molybdenum disulfide (MoS₂). Charge transfer doping is a feasible strategy for tuning the conductance properties via facile treatment. In this work, the electrical properties of few-layer MoS₂ were modulated with titanium(IV) bis(ammonium lactato) dihydroxide molecules (denoted as TALH) via physisorption. The functional groups such as electronegative hydroxyl (−OH) and carboxylate groups (−COO) included in TALH molecules are expected to induce p-doping effect through surface charge transfer when being attached to MoS₂. The p-doping is proved by X-ray photoelectron spectroscopy (XPS) with the downshift of Mo 3d and S 2p peaks. Control experiments and density functional theory calculations validate that the p-type doping mainly originated from the −OH group in TALH, which drew electrons from MoS₂. These results suggest that functional group-mediated p-doping effect show a path to modulate the carrier transition in MoS_2, and enrich the molecule series for device modification.     

A computational study on the nature of the halogen bond between sulfides and dihalogen molecules

The characteristics and nature of the halogen bonding in a series of B···XY (B = H₂S, H₂CS, (CH₂)₂S; XY = ClF, Cl₂, BrF, BrCl, Br₂) complexes were analyzed by means of the quantum theory of “atoms in molecules” (QTAIM) and “natural bond orbital” (NBO) methodology at the second-order Møller-Plesset (MP2) level. Electrostatic potential, bond length, interaction energy, topological properties of the electron density, the dipole moment, and the charge transfer were investigated systematically. For the same electron donor, the interaction energies follows the B···BrF > B···ClF > B···BrCl > B···Br₂ > B···Cl₂ > B···ClBr order. For the same electron acceptor, the interaction energies increase in the sequence of H₂S, H₂CS, and (CH₂)₂S. Topological analyses show these halogen bonding interactions belong to weak interactions with an electrostatic nature. It was found that the strength of the halogen-bonding interaction correlates well with the electrostatic potential associated with halogen atom and the amount of charge transfer from sulfides to dihalogen molecules, indicating that electrostatic interaction plays an important role in these halogen bonds. Charge transfer is also an important factor in the halogen bonds involved with dihalogen molecules.     

The π-hole tetrel bond between X2TO and CO2: Substituent effects and its potential adsorptivity for CO2

Quantum chemical calculations are applied to study the complexes between X₂TO (X = H, F, Cl, Br, CH₃; T = C, Si, Ge, Sn) and CO₂. The carbon atom of CO₂ as a Lewis acid participates in the C···O carbon bond, whereas its oxygen atom as a base engages in the O···T tetrel bond with X₂TO. Most of complexes are stabilized by a combination of both C···O and O···T interactions. The interaction energy increases in the T = C < Ge < Sn < Si sequence for most complexes. Both the electron-withdrawing halogen group and the electron-donating methyl group increase the interaction energy, up to 51 kJ/mol in F₂SiO···CO₂. One F₂SiO molecule can bind with different numbers of CO₂ molecules (1–4); as the number of CO₂ molecules increases, the average interaction energy for each CO₂ decreases and each CO₂ molecule can contribute with at least 27 kJ/mol. Therefore, silicon-containing molecules are good absorbents for CO₂.     

Ultrathin zinc selenide nanosheet-based intercalation hybrid coupled with CdSe quantum dots showing enhanced photocatalytic CO_2 reduction

Fabrication of well-designed heterojunctions is an extraordinarily attractive pathway for boosting the photocatalytic activity toward CO_2 photoreduction.Herein,a novel kind of na nosheet-based intercalation hybrid coupled with CdSe quantum dots(QDs) was successfully fabricated by a facile solvothermal method and served as photocatalyst for full-spectrum-light-driven CO_2 reduction.Ultra-small CdSe QDs were rationally in-situ introduced and coupled with lamellar ZnSe-intercalation hybrid nanosheet,resulting in the formation of CdSe Q.Ds/ZnSe hybrid heterojunction.Significantly,the concentration of Cd~(2+) could change directly the crystallinity and micromorphology of ZnSe intercalation hybrid,which in turn would impact on the photocatalysis activity.The optimized CdSe QDs/ZnSe hybrid-5 composite demonstrated a considerable CO yield rate of the 25.6 μmol g~(-1) h~(-1) without any additional cocatalysts or sacrificial agents assisting,making it one of the best reported performance toward CO_2 photoreduction under full-spectrum light.The elevated CO_2 photoreduction activity could be attributed to the special surface heterojunction,leading to improving the ability of light absorption and promoting the separation/transfer of photogenerated carriers.This present study developed a new strategy for designing inorganic-organic heterojunctions with enhanced photocatalyst for CO_2 photoreduction and provided an available way to simultaneously mitigate the greenhouse effect and alleviate energy shortage pressure.     

Enhancement of Mass and Charge Transfer during Carbon Dioxide Photoreduction by Enhanced Surface Hydrophobicity without a Barrier Layer

The CO₂ reduction reaction (CRR) represents a promising route for the clean utilization of renewable resources. But mass-transfer limitations seriously hinder the forward step. Enhancing the surface hydrophobicity by using polymers has been proved to be one of the most efficient strategies. However, as macromolecular organics, polymers on the surface hinder the transfer of charge carriers from catalysts to reactants. Herein, we describe an in-situ surface fluorination strategy to enhance the surface hydrophobicity of TiO₂ without a barrier layer of organics, thus facilitating the mass transfer of CO₂ to catalysts and charge transfer. With less obstruction to charge transfer, a higher CO_2, and lower H⁺ surface concentration, the photocatalytic CRR generation rate of methanol (CH₃OH) is greatly enhanced to up to 247.15 μmol g⁻¹ h⁻¹. Furthermore, we investigated the overall defects; enhancing the surface hydrophobicity of catalysts provides a general and reliable method to improve the competitiveness of CRR.     

CO2-activation and enhanced capture by C6Li6: A density functional approach

In this study, we propose a simple and yet effective approach for capture and storage of CO₂ by C₆Li₆. C₆Li₆ possesses a planar star-like structure, whose ionization energy is lower than that of Li atom and hence, it behaves as a superalkali. We have systematically studied the interaction of successive CO₂ molecules with C₆Li₆ using long-range dispersion corrected density functional ωB97xD/6-311 + G(d) calculations. We notice that these interactions lead to stable C₆Li₆-nCO₂ complexes (n = 1-6) in which the structure of CO₂ moieties is bent appreciably (122-125°) due to electron transfer from C₆Li₆, whose planarity is distorted only slightly (≤7°). This clearly suggests that the CO₂ molecules can successfully be activated and captured by C₆Li₆. It has been also noticed that the bond-length of CO₂ in C₆Li₆-nCO₂ complexes increases monotonically whereas adsorption energy decreases, ranging 3.18-2.79 eV per CO₂ with the increase in n. These findings establish the potential of C₆Li₆ for capture and storage of CO₂ molecules.     

Theoretical and experimental investigations of complexation with BF3.Et2O effects on electronic structures,energies and photophysical properties of Anil and tetraphenyl (hydroxyl) imidazol

The novel compounds (E)‐2‐(((4‐hydroxyphenyl)imino)methyl)phenol, Tetraphenyl (hydroxyl) imidazole and their corresponding Boron difluoride complexes were synthesized and characterized by spectroscopic techniques. Density functional theory calculations at B3LYP‐D3/6–311++G (d, p) level of theory were performed for the geometric parameters. The MEP surface studies were used to understand the behavior of molecules in terms of charge transfer and to determine how these molecules interact. We used the GIAO and the B3LYP‐D3 with a 6–311++ G (d, p) basis set to simulate the (¹H‐NMR and ¹⁹F‐NMR) and the IR spectra, respectively. The corresponding calculated results are in good agreement with the experimental data. The stability of the molecule arising from hyperconjugation interaction and charge delocalization were analyzed using NBO analysis. FMOs revealed the occurrence of charge transfer within the molecule. The complexation using BF₃.Et₂O was also found to have remarkable effects on the electrochemical properties of the studied molecules, where (b) and (d) present lower chemical stability, higher reactivity and higher polarizability than (a) and (c), respectively. Moreover, the energy gap of (a) and (c) decreased after complexation using BF₃.Et₂O, indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. These values are the factors explaining the possible charge transfer interaction within the molecule. The absorption and emission spectra of the model compound were also simulated and compared to experimental observations in the DMF solvent. The results of DFT calculations supported the structural and spectroscopic data and confirmed the structure modification of frontier molecular orbitals for BF₂ complexes as well as tunable potentials and energy levels.     

Magnetic field effects on the thermodynamic and kinetic parameters of intercalation of gallium selenide with nickel

The magnetic field effect on the thermodynamic and kinetic parameters of the formation of Ni _x GaSe intercalates became significant at nickel concentrations that provided interaction between the magnetic moments of the guest and the formation of supermagnetic phase nuclei. This interaction in Ni _x GaSe and the Zeeman delocalization of current carriers at room temperature increased the free energy of intercalation in a magnetic field. The highest resistance at the charge transfer stage of intercalation of gallium selenide with nickel was obtained for two-phase states without a magnetic field. The maximum change in the energy relief for charge transfer in Ni _x GaSe intercalates obtained in a magnetic field was recorded for high values of x in onephase regions, in which there were temperature neighborhoods of the inversion of the temperature coefficient of specific resistance, which coincided with a substantial increase in the real part of dielectric permittivity and correlated with the distinct maximum of dielectric permittivity measured at extra low frequencies. Original Russian Text ? N.T. Pokladok, I.I. Grigorchak, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 575–579.     

Ab Initio and DFT Studies on CO2 Interacting with Znq+–Imidazole (q=0, 1, 2) Complexes: Prediction of Charge Transfer through σ‐ or π‐Type Models

Using first‐principles methodologies, the equilibrium structures and the relative stability of CO₂@[Zn^q+Im] (where q=0, 1, 2; Im=imidazole) complexes are studied to understand the nature of the interactions between the CO₂ and Zn^q+–imidazole entities. These complexes are considered as prototype models mimicking the interactions of CO₂ with these subunits of zeolitic imidazolate frameworks or Zn enzymes. These computations are performed using both ab initio calculations and density functional theory. Dispersion effects accounting for long‐range interactions are considered. Solvent (water) effects were also considered using a polarizable continuum model approach. Natural bond orbital, charge, frontier orbital and vibrational analyses clearly reveal the occurrence of charge transfer through covalent and noncovalent interactions. Moreover, it is found that CO₂ can adsorb through more favorable π‐type stacking as well as σ‐type hydrogen‐bonding interactions. The inter‐monomer interaction potentials show a significant anisotropy that might induce CO₂ orientation and site‐selectivity effects in porous materials and in active sites of Zn enzymes. Hence, this study provides valuable information about how CO₂ adsorption takes place at the microscopic level within zeolitic imidazolate frameworks and biomolecules. These findings might help in understanding the role of such complexes in chemistry, biology and material science for further development of new materials and industrial applications.