Framework and Channel Modifications in Mayenite (12CaO·7Al₂O₃) Nanocages By Cationic Doping

Mayenite (Ca₁₂Al₁₄O₃₃, C₁₂A₇), and its electride variant (C₁₂A₇:2e^–) have attracted attention as functional materials with high ionic conductivity, and for potential uses in oxidation catalysis, fuel cells, and hydrogen storage. In contrast to anionic substitutions into C₁₂A₇, less is known about the influence of cationic substitutions on this material. This study applies DFT methods to rigorously understand the influences of Mg²⁺, Cu²⁺, Sr²⁺, Fe³⁺, Ir⁴⁺, P⁵⁺ and V⁵⁺ (2+ ≤ <i>Z</i>_V ≤ 5+, where <i>Z</i>_V is the cation valence, unitless) substitutions on the structural and electronic features of C₁₂A₇ and its electride variant. Substitutions alter the lattice parameters, in relation to their size, and alter charge localization. Substitutions also affect mayenite’s cage framework, resulting in the formation of a “window” that connects two adjacent cages. While Mg²⁺, Sr²⁺, P⁵⁺, and V⁵⁺ substitutions maintain their F⁺-like attractive nature, Cu²⁺, Fe³⁺, and Ir⁴⁺ neutralize such a tendency in the cages of their corresponding C₁₂A₇ electride. Therefore, the conduction mechanism of mayenite electride (i.e., containing Cu²⁺, Fe³⁺, and Ir⁴⁺) switches from e^–-hopping to band conduction electrons. The insertion of Cu²⁺-substitutions makes the window between two adjacent nanocages collapse, resulting in the formation of a <i>transport channel</i> between two neighboring [Ca–Al–O] cages for localized electrons. The outcomes suggest novel means to induce electron coupling between nearest-neighbor cages in mayenite, an aspect of interest for tailoring the electron transport properties of mayenite and other light-metal oxide electrides

Heats of Adsorption of CO and CO₂ in Metal–Organic Frameworks: Quantum Mechanical Study of CPO-27-M (M = Mg, Ni, Zn)

Density functional theory is applied with a hybrid functional to which a parametrized damped 1/<i>r</i>⁶ term has been added to account for dispersion (B3LYP+D*). This method is used with periodic boundary conditions to get the structures of the adsorption complexes. Dispersion has a substantial share on the calculated adsorption energies (46–77%). For these structures, adsorption energies are also calculated with a hybrid high-level (MP2 with complete basis set extrapolation):low level (B3LYP+D*) method. The MP2 calculations are performed on cluster models. Comparison is made with experimental heats of adsorption. B3LYP+D* underestimates heats of adsorption by about 5 kJ/mol, whereas hybrid MP2:B3LYP+D* slightly overestimates them by about 2 kJ/mol. With MP2:B3LYP+D*, also the mean absolute error is somewhat smaller, 3.8 kJ/mol compared to 5.6 kJ/mol for B3LYP+D*. Both the B3LYP+D* and the hybrid MP2/CBS:B3LYP+D* method predict the same sequence of binding energies for carbon monoxide (Ni > Mg > Zn) and carbon dioxide (Mg > Ni > Zn) adsorption on open metal cation sites in the CPO-27 metal–organic frameworks

Influence of (Al, Fe, Mg) Impurities on Triclinic Ca₃SiO₅: Interpretations from DFT Calculations

Ca₃SiO₅ and its polymorphic representations are the dominant phase(s) present in ordinary portland cement (OPC). As environmental pressures bracket the production of OPC, there is increasing emphasis on designing newer, more efficient OPC chemistries. While minor impurities in the form of (Al, Fe, Mg) are long understood to have substantial influences on the structure and reactivity of the siliceous cementing phases, specific details at the atomistic level remain unclear. In this paper, we report the results of first-principles calculations performed at the density functional level of theory (DFT), on triclinic Ca₃SiO₅, a template phase of relevance to OPC doped with (Al, Fe, Mg) species. Focus is devoted toward understanding modifications induced in (a) the lattice and crystallographic parameters, (b) the mechanical properties, and (c) the electronic descriptors of the silicate. Special efforts are devoted to identify preferred atomic substitution sites and to rank the stability of different phases using thermochemical descriptors. The results suggest that the presence of (Al, Fe, Mg) impurities in the silicate lattice modifies charge localization and exchange, contributing a new means toward interpreting and steering cementing phase reactivity, by careful manipulations of their impurity distributions

Electronic Origin of Doping-Induced Enhancements of Reactivity: Case Study of Tricalcium Silicate

Systematic manipulation of the reactivity of silicate materials in aqueous environment remains a challenging topic. Herein, by combining first-principles and reactive molecular dynamics simulations, we present a complete picture of the influence of impurity species on hydration reactivity, using the reactive triclinic tricalcium silicate phase as an example. We show that although initial hydration is influenced by the surface’s chemistry and structure, longer-term hydration is primarily controlled by proton transport through the bulk solid. Both shorter- and longer-term hydration processes are noted as being intrinsically correlated with electronic features. These outcomes provide the first direct evidence of the linkages between electronic structure and the longer-term (i.e., on the order of several nanoseconds) hydration behavior and sensitivity of hydrophilic crystalline materials and also offer a pathway to efficient compositional design for similar materials

Unusual Fluorescent Responses of Morpholine-Functionalized Fluorescent Probes to pH via Manipulation of BODIPY’s HOMO and LUMO Energy Orbitals for Intracellular pH Detection

Three uncommon morpholine-based fluorescent probes (<b>A</b>, <b>B</b>, and <b>C</b>) for pH were prepared by introducing morpholine residues to BODIPY dyes at 4,4′- and 2,6-positions, respectively. In contrast to morpholine-based fluorescent probes for pH reported in literature, these fluorescent probes display high fluorescence in a basic condition while they exhibit very weak fluorescence in an acidic condition. The theoretical calculation confirmed that morpholine is unable to function as either an electron donor or an electron acceptor to quench the BODIPY fluorescence in the neutral and basic condition via photoinduced electron transfer (PET) mechanism because the LUMO energy of morpholine is higher than those of the BODIPY dyes while its HOMO energy is lower than those of the BODIPY dyes. However, the protonation of tertiary amines of the morpholine residues in an acidic environment leads to fluorescence quenching of the BODIPY dyes via d-PET mechanism. The fluorescence quenching is because the protonation effectively decreases the LUMO energy which locates between the HOMO and LUMO energies of the BODIPY dyes. Fluorescent probe <b>C</b> with deep-red emission has been successfully used to detect pH changes in mammalian cells