Density Functional Theory Assessment of Molecular Structures and Energies of Neutral and Anionic Al_<i>n</i> (<i>n</i> = 2–10) Clusters

We report the results of a benchmarking study on hybrid, hybrid-meta, long-range-corrected, meta-generalized gradient approximation (meta-GGA), and GGA density functional theory (DFT) methods for aluminum (Al) clusters. A range of DFT functionals, such as B3LYP, B1B95, PBE0, mPW1PW91, M06, M06-2X, ωB97X, ωB97XD, TPSSh, BLYP, PBE, mPWPW91, M06-L, and TPSS, have been used to optimize the molecular structures and calculate the vibrational frequencies and four energetic parameters for neutral and anionic Al_<i>n</i> (<i>n</i> = 2–10) clusters. The performances of these functionals are assessed systematically by calculating the vertical ionization energy for neutral Al clusters and the vertical electron detachment energy for anionic Al clusters, along with the cohesive energy and dissociation energy. The results are compared with the available experimental and high-level ab initio calculated results. The calculated results showed that the PBE0 and mPW1PW91 functionals generally provide better results than the other functionals studied. TPSS can be a good choice for the calculations of very large Al clusters. On the other hand, the B3LYP, BLYP, and M06-L functionals are in poor agreement with the available experimental and theoretical results. The calculated results suggest that the hybrid DFT functionals like B3LYP do not always provide better performance than GGA functionals

Performance of Density Functional Theory and Relativistic Effective Core Potential for Ru-Based Organometallic Complexes

Herein a performance assessment of density functionals used for calculating the structural and energetic parameters of bi- and trimetallic Ru-containing organometallic complexes has been performed. The performance of four popular relativistic effective core potentials (RECPs) has also been assessed. On the basis of the calculated results, the MN12-SX (range-separated hybrid functional) demonstrates good performance for calculating the molecular structures, while MN12-L (local functional) performs well for calculating the energetics, including that of the Ru–Ru bond breaking process. The choice of appropriate density functional is a crucial factor for calculating the energetics. The LANL08 demonstrates the lowest performance of the RECPs for calculating the molecular structures, especially the Ru–Ru bond length

Rational Synthesis of Metal–Organic Framework-Derived Noble Metal-Free Nickel Phosphide Nanoparticles as a Highly Efficient Cocatalyst for Photocatalytic Hydrogen Evolution

Facile preparation of metal–organic framework (MOF) derived earth-abundant nickel phosphide (Ni₂P) by a simple, cost-effective procedure is described. Ni₂P is recognized as a suitable replacement for expensive noble metal cocatalysts used for H₂ production by water splitting. Ni₂P nanoparticles were used to prepare a Ni₂P/CdS composite with improved photocatalytic properties. Crystal structure and surface morphology studies showed that Ni-MOF spheres readily transform into Ni₂P particles, and TEM images indicated the presence of Ni₂P nanoparticles on CdS. The optical properties and charge carrier dynamics of the composite material exhibited better visible light absorption and improved suppression of charge carrier recombination. X-ray photoelectron spectra confirmed the presence of Ni₂P on CdS. The synthesized materials were tested for photocatalytic hydrogen production with lactic acid as a scavenger under irradiation in a solar simulator. The rate of H₂ production with Ni₂P/CdS was 62 times greater than that with pure CdS. The superior activity of the composite material is attributed to the ability of Ni₂P to separate the photoexcited charge carriers from CdS and provide good electrical conductivity. The optimized composite material also exhibited better photocatalytic activity than Pt cocatalyzed CdS. Based on the experimental results, a possible electron–hole transfer mechanism is proposed

Optimization of Active Sites of MoS₂ Nanosheets Using Nonmetal Doping and Exfoliation into Few Layers on CdS Nanorods for Enhanced Photocatalytic Hydrogen Production

Transition metal dichalcogenides (TMDs) have emerged as promising nonprecious noble-metal-free catalysts for photocatalytic applications. Among TMDs, MoS₂ has been extensively studied as a cocatalyst due to its exceptional activity for photocatalytic hydrogen evolution. However, the catalytic activity of MoS₂ is triggered only by the active S atoms on its exposed edges, whereas the majority of S atoms present on the basal plane are catalytically inactive. Doping of foreign nonmetals into the MoS₂ system is an appealing approach for activation of the basal plane surface as an alternative for increasing the concentration of catalytically active sites. Herein, we report the development of earth-abundant, few-layered, boron-doped MoS₂ nanosheets decorated on CdS nanorods (FBMC) employing simple methods and their use for photocatalytic hydrogen evolution under solar irradiation, with lactic acid as a hole scavenger, under optimal conditions. The FBMC material exhibited a high rate of H₂ production (196 mmol·h^–1·g^–1). The presence of few-layered boron-doped MoS₂ (FBM) nanosheets on the surface of CdS nanorods effectively separated the photogenerated charge carriers and improved the surface shuttling properties for efficient H₂ production due to their extraordinary number of active edge sites with superior electrical conductivity. In addition, the observed H₂ evolution rate of FBMC was much higher than that for the individual few-layered MoS₂-assisted CdS (FMC) and bulk boron-doped MoS₂/CdS (BBMC) photocatalysts. To the best of our knowledge, this is the highest H₂ production rate achieved with MoS₂-based CdS photocatalysts for water splitting under solar irradiation. Considering its low cost and high efficiency, this system has great potential as a photocatalyst for use in various fields

Time-Resolved X‑ray Spectroscopy in the Water Window: Elucidating Transient Valence Charge Distributions in an Aqueous Fe(II) Complex

Time-resolved nitrogen-1s spectroscopy in the X-ray water window is presented as a novel probe of metal–ligand interactions and transient states in nitrogen-containing organic compounds. New information on iron­(II) polypyridyl complexes via nitrogen core-level transitions yields insight into the charge density of the photoinduced high-spin state by comparing experimental results with time-dependent density functional theory. In the transient high-spin state, the 3d electrons of the metal center are more delocalized over the nearest-neighbor nitrogen atoms despite increased bond lengths. Our findings point to a strong coupling of electronic states with charge-transfer character, facilitating the ultrafast intersystem crossing cascade in these systems. The study also highlights the importance of local charge density measures to complement chemical interaction concepts of charge donation and back-bonding with molecular orbital descriptions of states

Tuning Band Alignments and Charge-Transport Properties through MoSe₂ Bridging between MoS₂ and Cadmium Sulfide for Enhanced Hydrogen Production

Transition-metal dichalcogenide materials play a major role in the state-of-the-art innovations for energy conversion because of potential applications resulting from their unique properties. These materials additionally show inordinate potential toward the progress of hygienic power sources to deal with increasing environmental disputes at the time of skyrocketing energy demands. Herein, we report earth-abundant, few-layered, MoSe₂-bridged MoS₂/cadmium sulfide (CdS) nanocomposites, which reduce photogenerated electron and hole recombination by effectively separating charge carriers to achieve a high photocatalytic efficiency. Accordingly, the MoSe₂-bridged MoS₂/CdS system produced effective hydrogen (193 μmol·h^–1) as that of water using lactic acid as a hole scavenger with the irradiation of solar light. The presence of few-layered MoSe₂ bridges in MoS₂/CdS successfully separates photogenerated charge carriers, thereby enhancing the shuttling of electrons on the surface to active edge sites. To the best of our knowledge, this few-layered MoSe₂-bridged MoS₂/CdS system exhibits the most effective concert among altogether-reported MoS₂-based CdS composites. Notably, these findings with ample prospective for the development of enormously real photocatalytic systems are due to their economically viable and extraordinary efficiency

Electronic and Molecular Structure of the Transient Radical Photocatalyst Mn(CO)₅ and Its Parent Compound Mn₂(CO)₁₀

We present a time-resolved X-ray spectroscopic study of the structural and electronic rearrangements of the photocatalyst Mn₂(CO)₁₀ upon photocleavage of the metal–metal bond. Our study of the manganese K-edge fine structure reveals details of both the molecular structure and valence charge distribution of the photodissociated radical product. Transient X-ray absorption spectra of the formation of the Mn­(CO)₅ radical demonstrate surprisingly small structural modifications between the parent molecule and the resulting two identical manganese monomers. Small modifications of the local valence charge distribution are decisive for the catalytic activity of the radical product. The spectral changes reflect altered hybridization of metal-3d, metal-4p, and ligand-2p orbitals, particularly loss of interligand interaction, accompanied by the necessary spin transition due to radical formation. The spectral changes in the manganese pre- and main-edge region are well-reproduced by time-dependent density functional theory and <i>ab initio</i> multiple scattering calculations

Femtosecond Soft X-ray Spectroscopy of Solvated Transition-Metal Complexes: Deciphering the Interplay of Electronic and Structural Dynamics

We present the first implementation of femtosecond soft X-ray spectroscopy as an ultrafast direct probe of the excited-state valence orbitals in solution-phase molecules. This method is applied to photoinduced spin crossover of [Fe(tren(py)₃)]²⁺, where the ultrafast spin-state conversion of the metal ion, initiated by metal-to-ligand charge-transfer excitation, is directly measured using the intrinsic spin-state selectivity of the soft X-ray L-edge transitions. Our results provide important experimental data concerning the mechanism of ultrafast spin-state conversion and subsequent electronic and structural dynamics, highlighting the potential of this technique to study ultrafast phenomena in the solution phase

Light-Induced Radical Formation and Isomerization of an Aromatic Thiol in Solution Followed by Time-Resolved X‑ray Absorption Spectroscopy at the Sulfur K‑Edge

We applied time-resolved sulfur-1s absorption spectroscopy to a model aromatic thiol system as a promising method for tracking chemical reactions in solution. Sulfur-1s absorption spectroscopy allows tracking multiple sulfur species with a time resolution of ∼70 ps at synchrotron radiation facilities. Experimental transient spectra combined with high-level electronic structure theory allow identification of a radical and two thione isomers, which are generated upon illumination with 267 nm radiation. Moreover, the regioselectivity of the thione isomerization is explained by the resulting radical frontier orbitals. This work demonstrates the usefulness and potential of time-resolved sulfur-1s absorption spectroscopy for tracking multiple chemical reaction pathways and transient products of sulfur-containing molecules in solution