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Glyoxal (GLY) is an important precursor of aqueous secondary organic aerosol (aqSOA). Knowledge of the reaction mechanisms of GLY in the aqueous phase is not complete, and the oxidation mechanisms of GLY in the presence of different oxidants are under debate. Our recent experimental studies of GLY oxidation mediated by nitrate photolysis yielded formic acid instead of oxalic acid which was commonly found in bulk GLY oxidation experiments. In this work, we investigated the hydration and oligomer formation mechanism of GLY in the aqueous phase theoretically. Furthermore, we calculated the energetics for the mechanisms of GLY oxidation by OH radicals in the presence of O2and NO2. Results showed that the hydration reaction plays a significant role in GLY uptake into the aqueous phase, and oligomers are likely to form at intermediate RH. The formation of formic acid in the presence of OH and NO2is more favorable, while oxalic acid is the main product in the presence of OH and O2. The present study provides a theoretical insight into the aqueous-phase chemistry of GLY, and the results may be helpful for understanding the atmospheric evolution of GLY.

The heterogeneous Fenton-like reaction on metal-free graphene-based catalysts attracts great attention. However, a systematic and comprehensive understanding of the mechanisms for H2O2activation and pollutant oxidation is still lacking. In this study, the heterogeneous Fenton-like mechanisms on doped and oxygen-containing graphene are investigated using density functional theory. The H2O2tends to form a surface oxygen and a water molecule on the doped graphene. For the oxygen-containing graphene-based systems, relative to the groups in the basal plane, the separated groups on the edge including hydroxyl, carbonyl, and carboxyl readily activate H2O2to hydroxyls. However, when the groups are close to each other, more additional side reactions might occur upon H2O2adsorption, which may inhibit catalyst retrieval. Phenol is selected as a model pollutant to study its oxidation reaction with the adsorbed oxygen formed from the dissociated H2O2. The thermodynamics of the reactions depends significantly on the co-adsorption strengths over different catalysts. Our work provides key fundamental insights into the catalytic performance of various modified graphene-based systems, which could guide the future design and applications of heterogeneous Fenton reactions.

We propose a new constrained density functional theory (CDFT) approach which directly controls the oxidation state of the target atoms. In this new approach called oxidation-state constrained density functional theory (OS-CDFT), the eigenvalues of the occupation matrix obtained from projecting the Kohn–Sham wave functions onto the valence orbitals are constrained to obtain the desired oxidation states. This approach is particularly useful to study electron transfer problems in transition metal-containing systems due to the multivalent nature of the transition metal ions. The calculation of the forces on the ions and of the coupling constant was implemented under the OS-CDFT scheme to allow efficient and accurate study of electron transfer reactions. We demonstrated the application of this method in the study of different electron transfer reactions including the aqueous ferrous–ferric self-exchange reaction, polaron hopping in the TiO2anatase and bismuth vanadate, and photoexcited electron transfer in the sapphire.

Sodium-ion batteries (NIBs) are a potential low-cost alternative to lithium-ion batteries for large-scale energy storage, but many high-capacity NIB cathode materials undergo irreversible structural changes during charge and discharge, leading to fast capacity fading. Herein, monoclinic NaVO3exhibits good cycle performance with high capacity as a cathode material for NIBs. In situ synchrotron X-ray diffraction studies show that the material structure is virtually invariant during Na+(de-)intercalation, with the aand blattice parameters changing only by 0.13 and 0.19%, respectively. The material undergoes an oxygen redox reaction during initial charge while delivering a remarkable specific capacity of 245 mAh g–1(1.2–4.7 V) with contributions from cationic (V4+/V5+) and anionic (O2–/O–) redox couples during discharge. The stable VO4tetrahedral framework also enables the material to give superior rate and cycle capabilities, with a capacity of 164 mAh g–1(67% utilization) at a current of 1000 mA g–1(about 5C) and a capacity retention of 90% after 50 cycles. Density functional theory calculations further verify the stability of the material and the charge–discharge mechanism. This work can broaden the horizon for designing high-energy cathode materials with enhanced structural stability for sodium-ion batteries.

Modulated anodization synthesis is introduced here for the fabrication of porous Sn-doped iron oxide. Continuous square-wave modulation consisting of highly positive (+50 to +80 V range) and slightly negative potentials (−2 to −10 V range) at 100 Hz allowed the etching anodization of the metallic Fe foil and incorporation of Sn-dopant from the fluoride anion–containing electrolyte, respectively. Compared with the undoped iron oxide, the surface-enriched Sn-dopant (in the form of Sn4+) alleviates the trapping and recombination of surface holes, while enhancing the hole transfer at the surface states. As such, the overpotential for photoelectrochemical (PEC) water oxidation was reduced by 110 mV and photocurrent density doubled. The incorporation of Co-Pi co-catalyst further improved the hole transfer efficiency, resulting in further reduction in overpotential by another 330 mV with respect to the bare Sn-doped iron oxide and significant improvement in photocurrent density at potentials below +1.23 V vs. reversible hydrogen electrode. Lastly, the iron oxide electrodes exhibit highly stable PEC water oxidation with no degradation in activity throughout the 10 h assessment under simulated solar irradiation and Faradaic efficiency of 90%. We envisage that the modulated anodization technique can be conveniently incorporated for a wide range of other dopants in search of efficient solar water splitting electrodes.

The nature of electron and hole polaron transport in the mixed valence cobalt(II,III) oxide Co3O4in pristine conditions and with an oxygen vacancy are studied using Oxidation-State Constrained DFT (OS-CDFT). We find that the tetrahedral site repels electron polarons as hopping from a neighboring octahedral site toward the tetrahedral site is highly endothermic while hopping away toward a neighboring octahedral site is nearly instantaneous. Hence, electron polarons travel through bulk Co3O4using pathways through only octahedral Co ions. In contrast, while the purely octahedral pathways remain the dominant pathway for hole polaron transport, the pathways involving both the octahedral and tetrahedral sites are still viable with about two thirds the rate of the octahedral pathways. Moreover, the purely octahedral pathway is enhanced with an oxygen vacancy for both the electron and hole polarons. On the other hand, pathways involving both the octahedral and tetrahedral sites are impeded in the presence of an oxygen vacancy for both the electron and hole polarons due to increased magnitude of driving forces.

Although there have been tremendous breakthroughs in perovskite solar cells over the past few years, degradation of perovskite has been a huge problem. Recently, a number of experimental studies have demonstrated that organic–inorganic halide perovskite materials are sensitive to humid air, and several degradation mechanisms have been proposed. However, the decomposition process of perovskites is only partially known and controversial. In this paper, we theoretically study the structures of the tetragonal CH3NH3PbI3and CH3NH3PbBr3(110) surfaces and the degradation mechanism using density functional theory calculations both with and without the van der Waals correction. The computed results indicate that the CH3NH3+(MA) cations preferentially orient with the NH3group pointing into the surface. This allows the formation of more hydrogen···halide hydrogen bonds between the MA cations and the halides. Moreover, the interactions of water molecules, hydroxyl radicals, and hydroxide ions with the perovskite surfaces are investigated. It has been suggested that the deprotonation of the MA cations followed by the desorption of the CH3NH2molecules is a key step in the degradation mechanism. We found that the hydroxyl radicals and hydroxide ions facilitate this desorption process while water molecules have little effect on it. These present findings are pertinent to revealing the decomposition mechanisms of perovskite materials.

We use oxidation-state constrained density functional theory (OS-CDFT) to study the polaron dynamics in the monolayer and bulk MoS2as well as in MoS2with the S and Mo vacancies. OS-CDFT is used to calculate the reorganization energies and driving forces of the polaron dynamics in MoS2. From our study, we find similar polaron hopping energetics for both monolayer and bulk MoS2. However, polaron hopping near an S vacancy has a high driving force such that it is in the Marcus inverted regime for both monolayer and bulk MoS2. This can explain the low electron mobility of monolayer MoS2found in experiments. Similarly, polaron hopping near an Mo vacancy is in the Marcus inverted regime for both monolayer and bulk MoS2. However, the driving force near an Mo vacancy is not as large as the driving force near an S vacancy.

In catalysis by metalloenzymes and in electrocatalysis by clusters related in structure and composition to the active components of such enzymes transition‐metal atoms can play a central role in the catalyzed redox reactions. Changes to their oxidation states (OSs) are critical for understanding the reactions. The OS is a local property and we introduce a new, generally useful local method for determining OSs, their changes, and the associated bonding changes and electron flow. The method is based on computing optimally localized orbitals (OLOs). With this method, we analyze two cases, superoxide reductase (SOR) and a proposed hydrogen‐producing model electrocatalyst [FeS2]/[FeFe]P, a modification of the active site of the diiron hydrogenase enzymes. Both utilize an under‐coordinated Fe site where a one‐electron reduction (for SOR) or a two‐electron reduction (for [FeFe]P) of the substrate occurs. We obtain the oxidation states of the Fe atoms and of their critical ligands, the changes of the bonds to those ligands, and the electron flow during the catalytic cycle, thereby demonstrating that OLOs constitute a powerful interpretive tool for unraveling reaction mechanisms by first‐principles computations.

Classical and quantum-chemical computations are employed to probe the reaction intermediates and proton-transfer processes in superoxide reductase (SOR) from Desulfoarculus baarsii. Ab initio studies of the SOR active site, as well as classical and QM/MM MD simulations on the overall enzymatic reaction, are performed. We explore the use of a Hubbard Ucorrection to standard density functional theory (DFT) in order to obtain a better description of the strongly correlated d electrons in the transition-metal center. The results obtained from the standard and Hubbard-U-corrected DFT approaches are compared with those obtained using different hybrid-DFT functionals. We show that the Hubbard Ucorrection gives a significant improvement in the description of the structural, energetic, and electronic properties of SOR. We establish that adopting the Hubbard Ucorrection in the QM/MM approach leads to increased accuracy with essentially no additional computational cost. Our results suggest that Lys48is one of the likely sources of the first proton donation to the superoxide, either directly or through an interstitial water molecule. Our QM/MM calculations highlight the important role of the interactions and hydrogen-bond network created by the imidazole rings of the His ligands and the internal water molecules. Whereas the hydrogen-bonding pattern due to internal waters can facilitate the protonation event, the interactions with the His ligands and the hydrogen bonds with water can stabilize the dioxygen ligand in a side-on conformation, which, in turn, prevents the immediate proton transfer from Lys48, as indicated by recent experimental studies.

We present a density-functional theory (DFT) approach, with fractionally occupied orbitals, for studying the prototypical ferric−ferrous electron-transfer (ET) process in liquid water. We use a recently developed ab initio method to calculate the transfer integral (also named electronic-coupling or ET matrix element) between the solvated ions. The computed transfer integral is combined with previous ab initio values of the reorganization energy, within the framework of Marcus’ theory, to estimate the rate of the electron self-exchange reaction. The self-interaction correction incorporated (through an appropriate treatment of the electronic correlation effects) into a Hubbard Uextension to the DFT scheme leads to a theoretical value of the ET rate relatively close to an experimental estimate from kinetic measurements. The use of fractional occupation numbers (FON) turned out to be crucial for achieving convergence in most self-consistent calculations because of the open-shell d-multiplet electronic structure of each iron ion and the near degeneracy of the redox groups involved. We provide a theoretical justification for the FON approach, which allows a description of the chemical potential and orbital relaxation, and possible extension to other transition-metal redox systems. Accordingly, the methodology developed in this paper, which rests on a suitable combination of Hubbard Ucorrection and a FON approach to DFT, seems to offer a fruitful approach for the quantitative description of ET reactions in biochemical systems.

Despite previous reports showing that crystallization kinetics affects zeolite phase selectivity because zeolites are metastable species in their synthesis solution rather than thermodynamic end-points, the critical kinetics-controlling parameter is yet to be determined. This work elucidated the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis of 10-membered ring zeolites (MFI- or TON-type zeolites). The results showed that the dissolved silica concentration in the synthesis solution, which is controlled by varying the TEOS hydrolysis temperature and addition rate, induced heterogeneous nuclear growth. Specifically, in 1- butyl-3-methylimidazolium ([BMIM]Br)-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. The experimental results are supported by silica polymerization modeling using the Reaction Ensemble Monte Carlo (REMC) method and theoretical calculations on composite building unit formation. The results are valuable for understanding the nucleation mechanism in zeolite crystallization.

The heterogeneous Fenton process is one of the efficient methods for wastewater treatment, and the effects of dissolved organic matter (DOM) when treating actual wastewaters are anticipated. However, the impact of DOM on H2O2activation is not clearly understood yet. In this work, the α-Fe2O3(001) surfaces are chosen as the model materials and the effects of the major functional groups in DOM on H2O2activation are systematically investigated using density functional theory simulations. First, the adsorption and activation of H2O2on the surfaces are simulated, confirming the superior catalytic properties of the Fe sites on the α-Fe2O3(001) surface with an oxygen vacancy. Then, the adsorption configurations with various DOM functional group representations are obtained. Phenol, carboxyl, amide, and quinone groups adsorb more strongly on the surfaces than H2O2, while the hydroxyl and aldehyde groups show weaker adsorption. Finally, the coadsorption of the DOM molecules and H2O2is simulated and the influences on the activation barrier of H2O2are studied. For the pristine surface, the intermolecular interactions can promote or inhibit the H2O2cleavage with some DOM molecules. However, for the surface with an oxygen vacancy, due to the competition for adsorption sites, some DOM functional groups are found to substitute the H2O2at the most reactive Fe site, thus inhibiting its activation. The direct interactions between the DOM molecules and H2O2do not significantly affect H2O2activation. This work reveals the various effects of DOM on H2O2activation and contributes to the application of the heterogeneous Fenton technology.

The CO2reduction reaction is an imperative piece of technology that closes the carbon cycle in many critical energy-conversion and chemical-manufacturing processes. Here, we report two new Iridium(III) terpyridine-based photocatalysts capable of selective reduction of CO2to CO under visible light (λ ≥ 420 nm). The first photocatalyst, [Ir-COOH], was functionalized with carboxyl group on the phenylpyridine, while the second, [Ir-PhCOOH], was attached to a phenyl spacer on the terpyridine. The [Ir-PhCOOH] was characterized by a higher extinction coefficient than [Ir-COOH], thus allowing more absorption of photons. While both photocatalysts require a two-electron activation, the [Ir-PhCOOH] is more readily activated as a result of the more negatively charged Ir centre. These photocatalysts show exclusive selectivities in the production of CO. The turnover frequencies for [Ir-COOH] and [Ir-PhCOOH] were 19 and 10 h-1, respectively, under visible light irradiation. The e-e-H-H pathway was identified as the most favorable, consisting of the rate limiting step in the conversion of *COOH to *CO, and where the barrier is significantly lower for [Ir-PhCOOH] than for [Ir-COOH].

Recent experimental and theoretical studies on the family of Li-rich layered materials show that they can deliver much higher capacities than traditional Li-transitional metal oxides. This also leads to great interests in Na-rich layered oxides as alternative positive electrode materials for sodium-ion batteries for large-scale energy storage. Herein, we report a Na-rich material, Na2SeO3with an unconventional layered structure as a positive electrode material in NIBs for the first time. This material can deliver a discharge capacity of 232 mAh g−1after activation, one of the highest capacities from sodium-based positive electrode materials. X-ray photoelectron spectroscopy indicates the oxidation state of selenium remains unchanged during the charge process. Theoretical simulation shows that after removal of Na, spin is situated around oxygen atoms near the Na vacancy, and the projected density of state of oxygen electron is close to the Fermi level. These suggest the involvement of oxygen during charge-discharge. This work will propel new searches of high-capacity sodium-based positive electrode materials.