Density Functional Method Research Articles

Effect of number of intramolecular double bonds on photophysical properties and ESIPT processes for Cha-NH2 and its derivatives: A theoretical study

In recent years, the research on excited-state intramolecular proton transfer (ESIPT) reactions has aroused increasingly attention theoretically and experimentally. For a deep exploration, we designed three derivatives of Cha-NH2 with different numbers of carbon–carbon double bonds: Cha-NH2-1, Cha-NH2-2, and Cha-NH2-3. Using density functional theory and time-dependent density functional theory methods, we systematically studied the photophysical properties and ESIPT processes of Cha-NH2 and its derivatives. Detailed analysis revealed that the number of carbon–carbon double bonds within the molecule has a significant impact on the ESIPT behavior and spectral properties of Cha-NH2 and its derivatives. Specifically, as the number of carbon–carbon double bonds increases, the strength of intramolecular hydrogen bond is gradually weakened, leading to a red shift in the spectrum and a increase in the forward energy barrier for ESIPT, which is unfavorable for the occurrence of the ESIPT reaction. Therefore, this finding opens up broad application prospects for the adjustment and optimization of future ESIPT process.

Charge transfer regulates electrocatalytic CO2 reduction on one-dimensional carbon nanotube/boron nitride nanotube heterostructures

Driving the electrochemical carbon dioxide reduction reaction (CO2RR) to generate high-value chemicals is one of the effective solutions to promote carbon–neutral cycles. Herein, we use a heterostructure strategy to enhance the catalytic performance of single-atom catalysts (SACs) for CO2RR. A series of catalysts formed by doping some transition metal atoms (TM = Cr, Mn, Fe, Co, Ni, Cu) into heterostructures which include the single-wall carbon nanotube in boron nitride nanotube (CNT@BNNT) and the hybridization of carbon nanotube and boron nitride nanotube (CNT/BNNT) are respectively named as TM-CNT@BNNT and TM-CNT/BNNT, and their catalytic activity of CO2RR is systematically studied using density functional theory methods. After forming a heterostructure, the number of charges transferred from the metal center to the substrate and the d-band center will change, which will, to some extent, regulate the catalytic activity of the catalyst. Due to the effective activation of CO2 and significant inhibition ability of competitive hydrogen evolution reaction, nine catalysts are considered effective candidates for CO2RR. Finally, seven catalysts with high CO2RR activity are selected by calculating the Gibbs free energy. The moderate linear relations between charge transfer and adsorption energy of CO2/free energy change of reaction intermediates/limiting potential indicate that charge transfer can regulate activity to a certain extent. The improvement of CO2RR activity comes from the smaller charge transfer in the metal center, which is more likely to result in moderate binding strength between the catalyst and the key intermediate (*OH) to generate high catalytic performance.

Revealing the potential of a C6BN/black phosphorene nanocomposite as an anode material for sodium-ion batteries by atomistic simulation: DFT and AIMD

Black phosphorus (BP) has recently been regarded as a promising anode for sodium-ion batteries (SIBs) owing to its high storage capacity, rapid Na mobility in its lamellar structure, and low redox potential. However, its poor cyclability due to structural instability hampers its further implementation in SIBs. Here, we propose to design a novel two-dimensional nanocomposite by vertically stacking a C6BN sheet on a black phosphorene layer (C6BN/Black-Pn). Atomistic simulations by the van der Waals corrected density functional theory method were conducted to assess the suitability of the designed C6BN/Black-Pn model as a potential anode in SIBs. Benefiting from C6BN's electronic and chemical features, Black-Pn's band gap in C6BN/Black-Pn is diminished to 0.14 eV, which disappears and indicates metallic character upon sodiation. Additionally, the optimized Na adsorption energy within the nanocomposite is decreased to −2.06 eV, compared to −1.76 eV in pure Black-Pn and −0.98 eV in C6BN, with a modest diffusion barrier of 0.23 eV. A maximal theoretical capacity of 568.77 mAh/g and a low potential of 0.48 V are predicted for the nanocomposite. The above evaluation of C6BN/Black-Pn electrode for SIBs may provide better insights into adopting a physical approach to address BP electrochemical failures for advanced energy storage.

A quantum mechanistic investigation into the unusual reactions of nitrilimine and nitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone.

The theoretical study investigates the [3 + 2] cycloaddition (32CA) reactions between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone and benzonitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone. Nitrilimines and nitrile oxides are dipoles used in the synthesis of several heterocyclic compounds, including spiropyrazoline oxindoles and isoxazolines. The derivatives of these compounds are found with different biological activities, such as ion channel blockers, anti-inflammatory and anticancer agents as well as antimalarial. Conceptual density functional theory (CDFT) analysis, along with the activation energies of the 32CA reaction between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone, demonstrates concordance with the empirical findings. The 32CA reaction is found to proceed through a very polar single-step asynchronous mechanism. While deductions from the activation energies of the 32CA reaction between benzonitrile oxide and 2,3,4,5-tetraphenylcyclopentadienone are found to lead to the experimental product, the parr function analysis could not explain the observed chemo- and regioselectivity. This 32CA reaction is also found to proceed through a one-step asynchronous mechanism, though with a non-polar character. The modulation of substituents positioned at the reactive sites of the reactants is found to influence the kinetics, thermodynamics, and CDFT parameters of the two 32CA reactions, consequently impacting the observed selectivities. The 32CA reactions between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone and benzonitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone have been explored theoretically using the density functional theory method at the hybrid ωB97X-D coupled with the split valence triple-ξ (TZ) basis set as implemented in the Gaussian 09. Solvent effects were taken into account by full optimization of the gas phase geometries through the polarizable continuum model developed within the self-consistent reaction field.

First-principles study on the microstructure, band structure, mechanical and optical properties of AB-stacked bilayer graphene under constant neutron irradiation with different electric field magnitudes and directions

Carbon-based devices have superior performance and lower power consumption compared to silicon-based devices. However, graphene and related two-dimensional materials are easily influenced by radiation due to their extremely high surface-to-volume ratio. Under constant neutron irradiation conditions, there have been no studies on the effects of the magnitude and direction of an external electric field on various properties of the AB system. This study systematically investigated the neutron irradiation effects on the AB system and the influence of the different electric fields on the properties of the AB system under constant irradiation conditions using the density functional theory and ab initio molecular dynamics method that assigns energy to the primary knock-on atom. The results indicate that under constant neutron irradiation with different electric fields, the changes in system configuration dominate the influence on band structure, while the impact of surface ripples is relatively limited. Reducing the interlayer spacing of the system can make the configuration more stable, which makes the band structure under the electric field more stable. The primary factors influencing the Young's modulus (Y) of the system are changes in the microstructure and the appearance of surface ripples, while the influence of system configuration is relatively limited. Under the irradiation conditions, the electric field can to some extent accurately modulate the band gap of the system. However, it will also correspondingly reduce the system's Y to a certain extent, causing negative impacts on the electrical and thermal conductivity.

Integrated Study on Methane Activation: Exploring Main Group Frustrated Lewis Pairs through Density Functional Theory, Machine Learning, and Machine-Learned Force Fields.

Frustrated Lewis Pairs (FLP) are an important advance in metal-free catalysis due to their ability to activate a variety of small molecules. Many studies have focused on a very limited sample of Lewis acids and bases. Herein, we disclose an automated exploration algorithm using density functional methods, artificial neural networks (ANNs), and a molecule builder that incentivizes the exploration of favorable FLP space for the activation of methane via two mechanisms: deprotonation and hydride abstraction. The exploration algorithm creates FLPs with different Lewis acids (LA), Lewis bases (LB), and their substituents (LA/LB), which proved successful in quickly converging in the favorable chemical space, suggesting chemically sound structures, and generating thousands of potential candidates for methane activating FLPs. By modeling thousands of reactions, an FLP database of methane activation was created, allowing one to data mine properties, e.g., adduct bond length, highest occupied molecular orbital-lowest-unoccupied molecular orbital (HOMO-LUMO) gap, global electrophilicity index, favored Lewis acids/bases/substituents, and substituent steric volume. These properties not only successfully narrow the FLP chemical space but also provide meaningful insight into the chemical nature of competent methane activators. The machine learning discovery strategy disclosed here is general enough to be applicable to many chemical optimization tasks. This study also investigates the efficacy of a Machine-Learned Force Field (MLFF) in predicting the formation energies of Frustrated Lewis Pairs (FLPs). Our model, exhibiting a test error of ±10 kcal/mol, highlighted impressive computational efficiency by enabling the calculation of all possible FLP permutations within our chemical space. The MLFF demonstrated proficiency in predicting energies, providing a significant acceleration compared to quantum mechanics methods. However, challenges emerged in accurately capturing forces, necessitating recourse to classical force fields for reliable structure relaxation. The present study sheds light on the MLFF's potential as a tool for rapid energy predictions, emphasizing the need for further refinement to enhance its accuracy, particularly in force predictions, to expand its utility in chemical simulations.

Core Hole Effect to Valence Excitations: Tracking and Visualizing the Same Excitation in XPS Shake-Up Satellites and UV Absorption Spectra.

Introducing a core hole significantly alters the electronic structure of a molecule, and various X-ray spectroscopy techniques are available for probing the valence electronic structure in the presence of a core hole. In this study, we visually demonstrate the influence of a core hole on valence excitations by computing the ultraviolet absorption spectra and the shake-up satellites in X-ray photoelectron spectra for pyrrole, furan, and thiophene, as complemented by the natural transition orbital (NTO) analysis over transitions with and without a core hole. Employing equivalent core hole time-dependent density functional theory (ECH-TDDFT) and TDDFT methods, we achieved balanced accuracy in both spectra for reliable comparative analysis. We tracked the same involved valence transition in both spectra, offering a vivid illustration of the core hole effect via the change in corresponding particle NTOs introduced by a 1s core hole on a Cα, Cβ, or O atom. Our analysis deepens the understanding of the core hole effect on valence transitions, a phenomenon ubiquitously observed in general X-ray spectroscopic analyses.

Effect of Substitutional Metallic Impurities on the Optical Absorption Properties of TiO2.

(TiO2) is both a natural and artificial compound that is transparent under visible and near-infrared light. However, it could be prepared with other metals, substituting for Ti, thus changing its properties. In this article, we present density functional theory calculations for Ti(1-x)AxO2, where A stands for any of the eight following neutral substitutional impurities, Fe, Ni, Co, Pd, Pt, Cu, Ag and Au, based on the rutile structure of pristine TiO2. We use a fully unconstrained version of the density functional method with generalized gradient approximation plus the U exchange and correlation, as implemented in the Quantum Espresso free distribution. Within the limitations of a finite-size cell approximation, we report the band structure, energy gaps and absorption spectrum for all these cases. Rather than stressing precise values, we report on two general features: the location of the impurity levels and the general trends of the optical properties in the eight different systems. Our results show that all these substitutional atoms lead to the presence of electronic levels within the pristine gap, and that all of them produce absorptions in the visible and near-infrared ranges of electromagnetic radiation. Such results make these systems interesting for the fabrication of solar cells. Considering the variety of results, Ni and Ag are apparently the most promising substitutional impurities with which to achieve better performance in capturing the solar radiation on the planet's surface.

Hydrogen adsorption, desorption, sensor and storage properties of Cu doped / decorated boron nitride nanocone materials: A density functional theory and molecular dynamic study

The hydrogen storage and sensor properties of Cu-modified boron nitride nanocone (BNNC) structure were comprehensively investigated using the density functional theory method (DFT). By replacing nitrogen atoms with copper atoms on the BNNC structure, the hydrogen molecule's adsorption enthalpy and Gibbs free energy values were calculated as −48.6 and −16.9 kJ/mol, respectively. 4 Cu-doped BNNC structure achieved a notable hydrogen storage capacity of 5.38 wt%. The molecular dynamics calculations demonstrate that the structure modified with four Cu atoms maintains its dynamic stability. Furthermore, this study reveals that the desorption temperatures tend to rise with an increase in the number of adsorbed hydrogen molecules, and the average desorption temperature under 1 atm pressure is determined to be 332 K. The changes of work function values after hydrogen adsorption point out that the Cu-modified BNNC has Φ-sensor feature. Overall, Cu-modified BNNC structures show promising potential as hydrogen storage materials in ambient conditions.

Thermal properties of ZrSe2 and HfS2/ZrSe2 heterojunctions subjected to tensile strain

In this paper, the phonon spectra of ZrSe2, HfS2, and HfS2/ZrSe2 heterojunctions are calculated based on the density-functional perturbation method for biaxial tensile strains to study their stability and thermal properties. It was found that monolayers of ZrSe2 and HfS2 should not be subjected to >8 % biaxial tensile strain, and HfS2/ZrSe2 heterojunctions should not be subjected to >6 %. By looking at the graphs of enthalpy, entropy, free energy, and heat capacity under strain for the three systems, it is found that the effect on heat capacity is greater after destabilization in the monolayer system and after destabilization in the heterojunction structure, it is greater for the free energy. Enthalpy, entropy and free energy all increase continuously with increasing temperature, and heat capacity increases continuously with the rising temperature at temperatures <200 K and tends to remain constant when the temperature is >200 K.

Putative reaction mechanism of nitrogenase with a half-dissociated S2B ligand.

We have studied whether dissociation of the S2B sulfide ligand from one of its two coordinating Fe ions may affect the later parts of the reaction mechanism of nitrogenase. Such dissociation has been shown to be favourable for the E2-E4 states in the reaction mechanism, but previous studies have assumed that S2B either remains bridging or has fully dissociated from the active-site FeMo cluster. We employ combined quantum mechanical and molecular mechanical (QM/MM) calculations with two density-functional theory methods, r2SCAN and TPSSh. To make dissociation of S2B possible, we have added a proton to this group throughout the reaction. We study the reaction starting from the E4 state with N2H2 bound to the cluster. Our results indicate that half-dissociation of S2B is unfavourable in most steps of the reaction mechanism. We observe favourable half-dissociation of S2B only when NH or NH2 is bound to the cluster, bridging Fe2 and Fe6. However, the former state is most likely not involved in the reaction mechanism and the latter state is only an intermittent intermediate of the E7 state. Therefore, half-dissociation of S2B seems to play only a minor role in the later parts of the reaction mechanism of nitrogenase. Our suggested mechanism with a protonated S2B is alternating (the two N atoms of the substrate is protonated in an alternating manner) and the substrate prefers to bind to Fe2, in contrast to the preferred binding to Fe6 observed when S2B is unprotonated and bridging Fe2 and Fe6.

Well-defined asymmetric nitrogen/carbon-coordinated single metal sites for carbon dioxide conversion

Asymmetric nitrogen/carbon-coordinated single metal sites (M-NxC4-x) outperform symmetric M-N4 sites in carbon dioxide (CO2) electroreduction. However, the challenge of crafting well-defined M-NxC4-x sites complicates the understanding of their structure-catalytic performance relationship. In this study, we employ metallized N-confused tetraphenylporphyrin (M-NCTPP) to investigate CO2 conversion on M-N3C1 sites using both density functional theory and experimental methods. The optimal cobalt (Co)-N3C1 site (Co-NCTPP) achieves a current density of 500 mA cm−2 and a carbon monoxide Faraday efficiency exceeding 90 % at −1.25 V vs. the reversible hydrogen electrode, surpassing the performance of Co-N4 (Co-TPP). This research introduces a novel approach for designing and synthesizing high-activity heteroatom-anchored single metal sites, advancing fundamental understanding in the field.

Corrosion resistance of aluminum against acid activation in 1.0 M HCl by symmetrical ball − type zinc phthalocyanine

The inhibition effect of symmetrical Ball − type Zinc Phthalocyanine on Aluminum in 1mol/L hydrochloric acid was analyzed by electrochemical techniques. A novel ball-type zinc phthalocyanine (Zn-Pc) inhibitor has been synthesized and verified utilizing FTIR, nuclear magnetic resonance (1H NMR and 13C NMR), MALDI-TOF MS, and absorption spectroscopy (UV-Vis). In addition, laser-induced breakdown and photoluminescence spectroscopy were employed for additional study. Weight loss technique was employed to investigate the corrosion inhibition effectiveness of the synthesized Zn-Pc on Aluminum in 1mol/L hydrochloric acid at the range of variation temperatures (293–333 K). The inhibition efficiency of Zn-Pc increased with higher concentrations of Zn-Pc and decreased as the temperature increased. Furthermore, Zn-Pc demonstrated outstanding outcomes, achieving 72.9% at a very low inhibitor concentration (0.4 mmol/L) at 298 K. The experimental data for Zn-Pc Aluminum in 1mol/L hydrochloric acid obeys the Langmuir adsorption isotherm. Moreover, the corrosion system’s thermodynamic parameters and activation energy were determined. Quantum chemical calculations applying the (DFT) Density Functional Theory method was conducted and applied in this study. These calculations played a pivotal role in elucidating molecular structures and reactivity patterns. Through DFT, numerous reactivity indicators were computed, providing valuable insights into the chemical behavior of the studied compounds. These indicators, such as frontier molecular orbitals, electron density, and molecular electrostatic potential, were subsequently correlated with experimental data.

Energetics of the OH radical H-abstraction reactions from simple aldehydes and their geminal diol forms.

Carbonyl compounds, especially aldehydes, emitted to the atmosphere, may suffer hydration in aerosols or water droplets in clouds. At the same time, they can react with hydroxyl radicals which may add or abstract hydrogen atoms from these species. The interplay between hydration and hydrogen abstraction is studied using density functional and quantum composite theoretical methods, both in the gas phase and in simulated bulk water. The H-abstraction from the aldehydic and geminal diol forms of formaldehyde, acetaldehyde, glycolaldehyde, glyoxal, methylglyoxal, and acrolein is studied to determine whether the substituent has any noticeable effect in the preference for the abstraction of one form or another. It is found that abstraction of the H-atom adjacent to the carbonyl group gives a more stable radical than same abstraction from the geminal diol in the case of formaldehyde, acetaldehyde, and glycolaldehyde. The presence of a delocalizing group in the Cα (a carbonyl group in glyoxal and methylglyoxal, and a vinyl group in acrolein), reverts this trend, and now the abstraction of the H-atom from the geminal diol gives more stable radicals. A further study was conducted abstracting hydrogen atoms from the other different positions in the species considered, both in the aldehydic and geminal diol forms. Only in the case of glycolaldehyde, the radical formed by H-abstraction from the -CH2OH group is more stable than any of the other radical species. Abstraction of the hydrogen atom in one of the hydroxyl groups in the geminal diol is equivalent to the addition of the •OH radical to the aldehyde. It leads, in some cases, to decomposition into a smaller radical and a neutral molecule. In these cases, some interesting theoretical differences are observed between the results in gas phase and (simulated) bulk solvent, as well as with respect to the method of calculation chosen. DFT (M06-2X, B2PLYP, PW6B95), CCSD(T), and composite (CBS-QB3, jun-ChS, SCVECV-f12) methods using Dunning basis sets and extrapolation to the CBS limit were used to study the energetics of closed shell aldehydes in their keto and geminal-diol forms, as well as the radical derived from them by hydrogen abstraction. Both gas phase and simulated bulk solvent calculations were performed, in the last case using the Polarizable Continuum Model.

Accurate NMR Shieldings with σ-Functionals.

In recent years, density-functional methods relying on a new type of fifth-rung correlation functionals called σ-functionals have been introduced. σ-Functionals are technically closely related to the random phase approximation and require the same computational effort but yield distinctively higher accuracies for reaction and transition state energies of main group chemistry and even outperform double-hybrid functionals for these energies. In this work, we systematically investigate how accurate σ-functionals can describe nuclear magnetic resonance (NMR) shieldings. It turns out that σ-functionals yield very accurate NMR shieldings, even though in their optimization, exclusively, energies are employed as reference data and response properties such as NMR shieldings are not involved at all. This shows that σ-functionals combine universal applicability with accuracy. Indeed, the NMR shieldings from a σ-functional using input orbitals and eigenvalues from Kohn-Sham calculations with the exchange-correlation functional of Perdew, Burke and Ernzerhof (PBE) turned out to be the most accurate ones among the NMR shieldings calculated with various density-functional methods including methods using double-hybrid functionals. That σ-functionals can be used for calculating both reliable energies and response properties like NMR shieldings characterizes them as all-purpose functionals, which is appealing from an application point of view.

Predicting decomposition temperatures and carbonization feasibility of heterocycles with their decomposition mechanism

Pyrolysis of heterocyclic compounds such as Meldrum’s acid (MA) derivatives has been studied with focus on two key mechanisms analysing their energy barrier diagrams using the hybrid density functional theory method M06-2X. The feasibility of these decomposition reactions was calculated specifically for MA, monomethyl Meldrum’s acid (MMA), dimethyl Meldrum’s acid (DMMA), methylene Meldrum’s acid (MeMA) and (dimethylamino)methylene Meldrum’s acid (DMAMeMA), based on previous experimental analysis. The barrier to initial decomposition products (ketene or substituted ketenes with CO2 and acetone) were found to be endothermic requiring activation energies (∼180 – 230 kJ/mol) at decomposition temperatures of 280, 299, 301, 503 and 414 K respectively. Transition state theory calculations show MeMA and DMAMeMA are thermally more stable than other derivatives with low values for the rate constants and high energy barriers to produce initial decomposition products, suggesting they can produce fine carbon materials during carbonization. DMMA is found the best option for obtaining heteroatoms-doped carbon material formation.

Pyrolysis mechanistic study on sulfated polysaccharide from marine algal biomass with density functional theory method

Sulfated polysaccharide (SPS) derived from marine algae represents a promising renewable carbon biomass source. Through pyrolysis, SPS can be converted into C5 platform chemicals, including furfural (FF) and 5-methylfurura (5-MF). Understanding the fundamental reaction mechanisms during pyrolysis is essential for the advancing pyrolysis techniques. This work presents a detailed reaction mechanism that reveal new pathways leading to the most important products and intermediates. Simulations focusing on the initial steps in SPS pyrolysis showed that the unimolecular degradation of SPS is dominated by SO3 elimination, with a barrier height of 157.2 kJ/mol; ring-opening and glycosidic bond fission were identified as important competitive reactions, both of which have a barrier height of 207.6 kJ/mol and 260.1 kJ/mol, respectively. The 4,5-unsaturated acyclic rhamnose derived from the glycosidic bond fission of acyclic reducing end group can transform into 5-MF with high selectivity. In addition, the acyclic reducing end group is readily dehydrated to form a 2,3-unsaturated acyclic reducing end group, a reactive unsaturated intermediate. Its decomposition involves an 8-membered ring transition state that requires a low barrier height and results in the formation of a C5 fragment, which can be cyclized directly and dehydrated to form 5-MF. The majority of CO2 is mostly formed by the synergistic breakage of C-Ccarboxyl bonds and glycosidic bonds, with a barrier height of 197.9 kJ/mol. Moreover, a mechanism is uncovered for the formation of formic acid (FA) from a 4,5-unsaturated no-reducing end group. The major pyrolysis channel is initiated by a retro Diels-Alder reaction and followed by a retro-ene reaction to produce a 3,4-unsaturated non-reducing end group, which further decomposes into FA and a new 4,5-unsaturated non-reducing end group.

An Ab Initio Journey toward the Molecular‐Level Understanding and Predictability of Subnanometric Metal Clusters

Current advances in synthesizing and characterizing atomically precise monodisperse metal clusters (AMCs) at the subnanometer scale have opened up new possibilities in quantum materials research. Their quantizied “molecule‐like” electronic structure showcases unique stability, and physical and chemical properties differentiate them from larger nanoparticles. When integrated into inorganic materials that interact with the environment and sunlight, AMCs serve to enhance their (photo)catalytic activity and optoelectronic properties. Their tiny size makes AMCs isolated in the gas phase amenable to atom‐scale modeling using either density functional theory (DFT) or methods at a high level of ab initio theory, even addressing nonadiabatic (e.g., Jahn–Teller) effects. Surface‐supported AMCs can be routinely modeled using DFT, enabling long real‐time molecular dynamics simulations. Their optical properties can also be addressed using time‐dependent DFT or reduced density matrix (RDM) theory. These theoretical–computational efforts aim to achieve predictability and molecular‐level understanding of the stability and properties of AMCs as function of their composition, size, and structural fluxionality in different thermodynamical conditions (temperature and pressure). In this perspective, the potential of ab initio and DFT‐based modeling is illustrated through recent studies of unsupported and surface‐supported AMCs. Future directions of research are also discussed, including applications and methodological enhancements beyond the state‐of‐the‐art.

A theoretical study on the electronic and optical properties of M-TiO2/ZnO (M=Li, Na, K, Fe) toward application in photocatalysis

This study employs the tight-binding density functional method GFN1-xTB to investigate the structural and electronic properties of TiO2-ZnO and TiO2-ZnO composite materials modified by Li, Na, K, and Fe metals. Computational analyses reveal the formation of weak covalent bonds between the TiO2 and ZnO components within the composite system. Doping TiO2-ZnO with metals induces significant alterations in the electronic structure, particularly in terms of ionization energy and global electrophilic index. The UV-VIS spectra are calculated using real-time time-dependent density functional theory with xTB Hamiltonians. The obtained results demonstrate minimal impact of metal presence on the absorption spectrum of TiO2-ZnO, but significant influence on the recombination potential of photogenerated charge carriers. It is suggested that Fe/TiO2-ZnO and Li/TiO2-ZnO will demonstrate higher photocatalytic activity than the pristine TiO2-ZnO material.

Enhanced Degradation of Micropollutants in a Peracetic Acid/Mn(II) System with EDDS: An Investigation of the Role of Mn Species.

Extensive research has been conducted on the utilization of a metal-based catalyst to activate peracetic acid (PAA) for the degradation of micropollutants (MPs) in water. Mn(II) is a commonly employed catalyst for homogeneous advanced oxidation processes (AOPs), but its catalytic performance with PAA is poor. This study showed that the environmentally friendly chelator ethylenediamine-N,N'-disuccinic acid (EDDS) could greatly facilitate the activation of Mn(II) in PAA for complete atrazine (ATZ) degradation. In this process, the EDDS enhanced the catalytic activity of manganese (Mn) and prevented disproportionation of transient Mn species, thus facilitating the decay of PAA and mineralization of ATZ. By employing electron spin resonance detection, quenching and probe tests, and 18O isotope-tracing experiments, the significance of high-valent Mn-oxo species (Mn(V)) in the Mn(II)-EDDS/PAA system was revealed. In particular, the involvement of the Mn(III) species was essential for the formation of Mn(V). Mn(III) species, along with singlet oxygen (1O2) and acetyl(per)oxyl radicals (CH3C(O)O•/CH3C(O)OO•), also contributed partially to ATZ degradation. Mass spectrometry and density functional theory methods were used to study the transformation pathway and mechanism of ATZ. The toxicity assessment of the oxidative products indicated that the toxicity of ATZ decreased after the degradation reaction. Moreover, the system exhibited excellent interference resistance toward various anions and humid acid (HA), and it could selectively degrade multiple MPs.