Monthly Archives: September 2023

Role of Dipolar Organic Cations on Light‐triggered Charge Transfer at TiO2/CH3NH3PbI3 Interfaces

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Role of Dipolar Organic Cations on Light-triggered Charge Transfer at TiO2/CH3NH3PbI3 Interfaces

Light-triggered charge transfer across pristine and defective TiO2/CH3NH3PbI3 interfaces with different orientations of the organic cations is studied using first-principles calculations, indicating that the negatively (positively) charged CH3 (NH3) moieties of the CH3NH3 cations might promote (inhibit) the light-induced charge transfer.


Abstract

The TiO2/MAPbI3 (MA=CH3NH3) interfaces have manifested correlation with current-voltage hysteresis in perovskite solar cells (PSCs) under light illumination conditions, but the relations between the photo-induced charge transfer and the collective polarization response of the dipolar MA cations are largely unexplored. In this work, we adopt density functional theory (DFT) and time-dependent DFT approach to study the light-triggered charge transfer across the TiO2/MAPbI3 interfaces with MAI- and PbI-exposed terminations. It is found that regardless of the surface exposure of the MAPbI3, the photo-induced charge transfer varies when going from the ground-state geometries to the excited-state configurations. Besides, thanks to the electrostatic interactions between the ends of MA cations and the photogenerated electrons, the photo-induced charge transfer across the interfaces is enhanced (weakened) by the negatively (positively) charged CH3 (NH3) moieties of the MA species. Resultantly, the positively charged iodine vacancies at the TiO2/MAPbI3 interfaces tend to inhibit the charge transfer induced by light. Combining with the energy level alignment which is significantly modulated by the orientation of the MA species at the interfaces, the dipolar MA cations might be a double-edge sword for the hysteresis in PSCs with the TiO2/MAPbI3 interfaces.

Accessibility of Lithium Cations in VSH‐2 Zeotype: Structural Effects and Formation of Protonated Water Clusters

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Accessibility of Lithium Cations in VSH-2 Zeotype: Structural Effects and Formation of Protonated Water Clusters

Cooperative rotation of SiO4 and VO5 units in response to Li-ion exchange led to changes in symmetry in VSH-2 framework. The Cs sites are converted into new distorted tetrahedral sites for smaller Li+ ions via 2D ion transport along the [011] direction. Exchange of Cs+ by Li+ is incomplete suggesting the formation of protonated water clusters to counterbalance the net negative framework charge.


Abstract

The accessibility of lithium cations in microporous vanadosilicate VSH-2Cs of composition Cs2(VO)(Si6O14) ⋅ 3H2O was investigated by Single Crystal X-ray Diffraction, Attenuated Total Reflection Fourier Transformed Infrared Spectroscopy and Density Functional Theory calculations. The topological symmetry of VSH-2Cs is described in space group Cmca. After Li-ion exchange, the structure of VSH-2Li adopted monoclinic symmetry (space group C2/c) with a=17.011(2) Å, b=8.8533(11) Å, c=12.4934(16) Å, β=91.677(4)°, V=1880.7(4) Å3. The strong interactions between Li ions and oxygen-framework atoms drive the main deformation mechanism, which is based on cooperative rotation of SiO4 and VO5 units around their oxygen atoms that behave as hinges. Exchange of Cs+ by Li+ is incomplete and accompanied by the formation of protonated species to counterbalance the electrostatic charge. The incorporation of protons is mediated by the presence of water dimers in the structural channels. H2O molecules in VSH-2Li account not only as “space-fillers” after the removal of large Cs ions but also mediate proton transfer to compensate the negative charge of the host vanadosilicate framework.

Heterogeneous Electrocatalytic Oxygen Evolution Reaction by a Sol‐Gel Electrode with Entrapped Na3[Ru2(μ‐CO3)4]: The Effect of NaHCO3

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Heterogeneous Electrocatalytic Oxygen Evolution Reaction by a Sol-Gel Electrode with Entrapped Na3[Ru2(μ-CO3)4]: The Effect of NaHCO3

A sol-gel electrode containing the ruthenium complex Na3[Ru2(μ-CO3)4] is used as a stable working electrode in OER while showcasing the cathodic shift and the relatively increased current in the presence of NaHCO3.


Abstract

The Na3[Ru2(μ-CO3)4] complex is acting as a water oxidation catalyst in a homogeneous system. Due to the significance of heterogeneous systems and the effect of bicarbonate on the kinetic, we studied the bicarbonate effect on the heterogeneous electrocatalyst by entrapping the Na3[Ru2(μ-CO3)4] complex in a sol-gel matrix. We have developed two types of sol-gel electrodes, which differ by the precursor, and are demonstrating their stability over a minimum of 200 electrochemical cycles. The pH increases affected the currents and kcat for both types of electrodes, and their hydrophobicity, which was obtained from the precursor type, influenced the electrocatalytic process rate.

The results indicate that NaHCO3 has an important role in the catalytic activity of the presented heterogeneous systems; without NaHCO3, the diffusing species is probably OH−, which undergoes diffusion via the Grotthuss mechanism.

To the best of our knowledge, this is the first study to present a simple and fast one-step entrapment process for the Na3[Ru2(μ-CO3)4] complex by the sol-gel method under standard laboratory conditions. The results contribute to optimizing the WSP, ultimately helping expand the usage of hydrogen as a green and more readily available energy source.

Lanthanide‐FRET Molecular Beacons for microRNA Biosensing, Logic Operations, and Physical Unclonable Functions

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Lanthanide-FRET Molecular Beacons for microRNA Biosensing, Logic Operations, and Physical Unclonable Functions

This study demonstrates the application of terbium and europium based time-gated FRET molecular beacons for multiplexed microRNA biosensing, simplified molecular logic devices, and improved security identification and authentication.


Abstract

Time-resolved or time-gated (TG) biosensing and bioimaging with luminescent lanthanide probes and Förster resonance energy transfer (FRET) have significantly advanced bioanalytical chemistry. However, the development of lanthanide-based molecular beacons (MBs) has been rather limited. Here, we designed DNA stem-loop MB probes against two different microRNAs (miR-21 and miR-27b) using Tb and Eu FRET donors and quenching (BHQ2) and fluorescent (Cy3) FRET acceptors. Limits of detection down to 190 pM and duplexed miR-21/miR-27b quantification at low nanomolar concentrations with Tb-BHQ2 and Eu-BHQ2 TG-FRET MBs demonstrated the versatility and high analytical performance of lanthanide-based MBs. The particular donor-acceptor distances in the Tb-Cy3 MB resulted in inverted nucleic acid target concentration-dependent TG PL intensities in short (e. g., 0 to 40 μs) and long (e. g., 0.1 to 2.1 ms) TG detection windows after pulsed excitation. We showed that this specific feature of our TG-FRET MBs can be adapted to the design of molecular logic devices (NOR, OR, NAND, AND, XNOR, XOR, IMPLEMENT, and INHIBIT). Moreover, the almost unlimited choice of TG detection windows and the distinct spectral features of Tb and Cy3 over a broad visible spectral range could be exploited to devise biophotonic physical unclonable functions for highly secure authentication and identification. Our study manifests the versatility of lanthanides for advanced biophotonic applications.

A Novel Quasi‐Planar Two‐dimensional Carbon Sulfide with Negative Poisson’s Ratio and Dirac Fermions

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A Novel Quasi-Planar Two-dimensional Carbon Sulfide with Negative Poisson's Ratio and Dirac Fermions

The two-dimensional carbon sulfide, named subunene, is primarily designed using the experimentally synthesized sulflower molecule. It exhibits a dynamical, thermal, and mechanical stability with negative Poisson's ratio. Subunene furnishes linear band dispersion, Dirac cones, degenerate massless Dirac fermions and massive fermions in the electronic band spectrum.


Abstract

In the present study, a novel and unconventional two-dimensional (2D) material with Dirac electronic features has been designed using sulflower with the help of density functional theory methods and first principles calculations. This 2D material comprises of hetero atoms (C, S) and belongs to the tetragonal lattice with P4/nmm space group. Scrutiny of the results show that the 2D nanosheet exhibits a nanoporous wave-like geometrical structure. Quantum molecular dynamics simulations and phonon mode analysis emphasize the dynamical and thermal stability. The novel 2D nanosheet is an auxetic material with an anisotropy in the in-plane mechanical properties. Both composition and geometrical features are completely different from the conditions necessary for the formation of Dirac cones in graphene. However, the presence of semi-metallic nature, linear band dispersion relation, massive fermions and massless Dirac fermions are observed in the novel 2D nanosheet. The massless Dirac fermions exhibit highly isotropic Fermi velocities (vf=0.68×106 m/s) along all crystallographic directions. The zero-band gap semi metallic features of the novel 2D nanosheet are perturbative to the electric field and external strain.

Adaptive Data‐Driven Modeling Strategy Based on Feature Selection for an Industrial Natural Gas Sweetening Process

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Adaptive Data-Driven Modeling Strategy Based on Feature Selection for an Industrial Natural Gas Sweetening Process

A machine learning-based modeling approach is proposed that integrates an adaptive immune genetic algorithm with random forest to intelligently select process features as input variables for natural gas sweetening process modeling. This model can adaptively execute physical feature selection and possesses the advantages of strong predictive performance and tolerance to outliers and noise.


Abstract

As the core process of natural gas purification plant, natural gas sweetening directly affects the production efficiency and product quality of the purification plant. However, process modeling based on sulfur content prediction presents challenges in adaptability and accuracy. To tackle this, a machine learning-based modeling approach is proposed that integrates an adaptive immune genetic algorithm with random forest (RF) to intelligently select process features as input variables for RF modeling. The industrial result indicates that the proposed method is able to remove interfering variables and adaptively achieve optimal model precision for different scenarios. It offers a novel research instrument for product quality monitoring in natural gas sweetening plants.

Theoretical study on luminescence properties of a series of iridium complexes with high spin orbit coupling coefficients

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Theoretical study on luminescence properties of a series of iridium complexes with high spin orbit coupling coefficients

This article uses two theories, DFT and TD-DFT, to study a series of Ir complexes through theoretical calculations. By analyzing their luminescence color, molecular frontier orbitals, absorption and spin orbit coupling coefficients in CH2Cl2 solution, and other data, their performance is evaluated. Finally, complexes with high spin orbit coupling coefficients are obtained.


Abstract

In this paper, several Ir (III) complexes with transition metal as the central atom formed by the corresponding combination of two main ligands and three auxiliary ligands have been studied theoretically. The electronic structure, frontier molecular orbital, and spin orbit coupling data are used to analyze its application value in light emitting devices. The density functional theory is used to study (tbi)2Ir(bpp), (tbi-c)2Ir(bpp), (tbi)2Ir(dbm), (tbi-c)2Ir(dbm), (tbi)2Ir(pic), and (tbi-c)2Ir(pic). bpp = (2Z)-3-hydroxy-13-diphenylprop-2-en-1-one; dbm = 1,3-di-phenyl-1, 3-propanedione; pic = picolinate.

Electrical conductivity and species distribution of aluminum chloride and 1‐butyl‐3‐methylimidazolium chloride ionic liquid electrolytes

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Electrical conductivity and species distribution of aluminum chloride and 1-butyl-3-methylimidazolium chloride ionic liquid electrolytes

In this article, electrical conductivity of aluminum chloride (AlCl3) and 1-butyl-3-methylimidazolium chloride (BMIC) ionic liquid electrolytes was reported as a function of temperature and AlCl3 mole fraction. Electrical conductivity increases when the mole fraction of AlCl3 is between 0 and 0.50 and decreases when the concentration of AlCl3 exceeds 0.50. An anionic species distribution profile was developed to correlate electrical conductivity, and it was found that AlCl4− anion mainly influences the electrical conductivity of AlCl3:BMIC electrolytes.


Abstract

Electrical conductivity (σ) of aluminum chloride (AlCl3) and 1-butyl-3-methylimidazolium chloride (BMIC) ionic liquid (IL) was investigated as a function of temperature and AlCl3 mole fraction ( XAlCl3). Electrochemical impedance spectroscopy was used to measure the electrical conductivity. Composition of AlCl3:BMIC ionic liquid was varied by changing the XAlCl3 from 0 to 0.67. The temperature was changed from 70°C to 110°C at 10°C intervals. It was found that the electrical conductivity increases with an increase in temperature. Electrical conductivity increases with XAlCl3 from 0 to 0.5 and then starts to decrease after XAlCl3 = 0.5. A species concentration profile was developed based on thermodynamic model at room temperature for the IL containing BMI+, Cl−, AlCl4−, Al2Cl7−, Al3Cl10−, Al4Cl13−, and Al2Cl6 at different XAlCl3. The only anion species presents between 0 and 0.5 XAlCl3 are Cl− and AlCl4−. Anions like Al2Cl7−, Al3Cl10−, Al4Cl13−, and Al2Cl6 are found at higher XAlCl3. A good agreement between the model and the experimental data was obtained. The variations in anion concentration, molecular structure, and cation–anion interactions are to be the causes of the changes in electrical conductivity of AlCl3:BMIC system.

On the nonexistent Nobel Prizes for two pioneers of modern physical organic chemistry: Sir Christopher K. Ingold and Saul Winstein

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On the nonexistent Nobel Prizes for two pioneers of modern physical organic chemistry: Sir Christopher K. Ingold and Saul Winstein†

The careers of two pioneers of modern physical organic chemistry, Sir Christopher K. Ingold (photograph on the left) and Saul Winstein, are reviewed. That neither of these eminent scholars received the Nobel Prize in Chemistry is discussed in light of their numerous and timely nominations for this award. Nomination data comes from the Nobel Foundation's Nomination Archive.


Abstract

The careers of two pioneers of modern physical organic chemistry, Sir Christopher K. Ingold and Saul Winstein, are discussed and compared. Despite the fact that Ingold received 112 nominations from 77 nominees for the Nobel Prize in Chemistry (NPch), he never received that award. Winstein, also a non-recipient of the NPch, died prematurely at the age of 57. In his last 3 years, Winstein received 22 nominations from 18 nominators, seven of whom received or would receive the NPch themselves. Analyses of the Nobel Nomination Archive along with other evidence are used to explain Ingold's experience. A detailed examination of Winstein's career along with relevant historical data suggests that Winstein was a highly probable Nobelist had he lived just a few years longer. The relationship of Ingold's and Winstein's careers and the politics of the Nobel Prize selection process including the possibility that they would have shared a Nobel Prize are presented.