Computational Study of Adsorption and Separation of CO₂, CH₄, and N₂ by an <i>rht</i>-Type Metal–Organic Framework

In this work, a computational study is performed to evaluate the adsorption-based separation of CO₂ from flue gas (mixtures of CO₂ and N₂) and natural gas (mixtures of CO₂ and CH₄) using microporous metal organic framework Cu-TDPAT as a sorbent material. The results show that electrostatic interactions can greatly enhance the separation efficiency of this MOF for gas mixtures of different components. Furthermore, the study also suggests that Cu-TDPAT is a promising material for the separation of CO₂ from N₂ and CH₄, and its macroscopic separation behavior can be elucidated on a molecular level to give insight into the underlying mechanisms. On the basis of the single-component CO₂, N₂, and CH₄ isotherms, binary mixture adsorption (CO₂/N₂ and CO₂/CH₄) and ternary mixture adsorption (CO₂/N₂/CH₄) were predicted using the ideal adsorbed solution theory (IAST). The effect of H₂O vapor on the CO₂ adsorption selectivity and capacity was also examined. The applicability of IAST to this system was validated by performing GCMC simulations for both single-component and mixture adsorption processes

A Calcium Coordination Framework Having Permanent Porosity and High CO₂/N₂ Selectivity

A thermally stable, microporous calcium coordination network shows a reversible 5.75 wt % CO₂ uptake at 273 K and 1 atm pressure, with an enthalpy of interaction of ∼31 kJ/mol and a CO₂/N₂ selectivity over 45 under ideal flue gas conditions. The absence of open metal sites in the activated material suggests a different mechanism for selectivity and high interaction energy compared to those for frameworks with open metal sites

A Calcium Coordination Framework Having Permanent Porosity and High CO₂/N₂ Selectivity

A thermally stable, microporous calcium coordination network shows a reversible 5.75 wt % CO₂ uptake at 273 K and 1 atm pressure, with an enthalpy of interaction of ∼31 kJ/mol and a CO₂/N₂ selectivity over 45 under ideal flue gas conditions. The absence of open metal sites in the activated material suggests a different mechanism for selectivity and high interaction energy compared to those for frameworks with open metal sites

A Calcium Coordination Framework Having Permanent Porosity and High CO₂/N₂ Selectivity

A thermally stable, microporous calcium coordination network shows a reversible 5.75 wt % CO₂ uptake at 273 K and 1 atm pressure, with an enthalpy of interaction of ∼31 kJ/mol and a CO₂/N₂ selectivity over 45 under ideal flue gas conditions. The absence of open metal sites in the activated material suggests a different mechanism for selectivity and high interaction energy compared to those for frameworks with open metal sites

A Multifunctional Organic–Inorganic Hybrid Structure Based on Mn^III–Porphyrin and Polyoxometalate as a Highly Effective Dye Scavenger and Heterogenous Catalyst

A two-step synthesis strategy has led to a unique layered polyoxometalate–Mn^III–metalloporphyrin-based hybrid material. The hybrid solid demonstrates remarkable capability for scavenging of dyes and for heterogeneous selective oxidation of alkylbenzenes with excellent product yields and 100% selectivity

Effects of Nanofiber Architecture and Antimony Doping on the Performance of Lithium-Rich Layered Oxides: Enhancing Lithium Diffusivity and Lattice Oxygen Stability

Li-rich layered oxides (LLOs) with high specific capacities are favorable cathode materials with high-energy density. Unfortunately, the drawbacks of LLOs such as oxygen release, low conductivity, and depressed kinetics for lithium ion transport during cycling can affect the safety and rate capability. Moreover, they suffer severe capacity and voltage fading, which are major challenges for the commercializing development. To cure these issues, herein, the synthesis of high-performance antimony-doped LLO nanofibers by an electrospinning process is put forward. On the basis of the combination of theoretical analyses and experimental approaches, it can be found that the one-dimensional porous micro-/nanomorphology is in favor of lithium-ion diffusion, and the antimony doping can expand the layered phase lattice and further improve the lithium ion diffusion coefficient. Moreover, the antimony doping can decrease the band gap and contribute extra electrons to O within the Li₂MnO₃ phase, thereby enhancing electronic conductivity and stabilizing lattice oxygen. Benefitting from the unique architecture, reformative electronic structure, and enhanced kinetics, the antimony-doped LLO nanofibers possess a high reversible capacity (272.8 mA h g^–1) and initial coulombic efficiency (87.8%) at 0.1 C. Moreover, the antimony-doped LLO nanofibers show excellent cycling performance, rate capability, and suppressed voltage fading. The capacity retention can reach 86.9% after 200 cycles at 1 C, and even cycling at a high rate of 10 C, a capacity of 172.3 mA h g^–1 can still be obtained. The favorable results can assist in developing the LLO material with outstanding electrochemical properties

Atomistic Insights into FeF₃ Nanosheet: An Ultrahigh-Rate and Long-Life Cathode Material for Li-Ion Batteries

Iron fluoride with high operating voltage and theoretical energy density has been proposed as a high-performance cathode material for Li-ion batteries. However, the inertness of pristine bulk FeF₃ results in poor Li kinetics and cycling life. Developing nanosheet-based electrode materials is a feasible strategy to solve these problems. Herein, on the basis of first-principles calculations, first the stability of FeF₃ (012) nanosheet with different atomic terminations under different environmental conditions was systematically studied, then the Li-ion adsorption and diffusion kinetics were thoroughly probed, and finally the voltages for different Li concentrations were given. We found that F-terminated nanosheet is energetically favorable in a wide range of chemical potential, which provide a vehicle for lithium ion diffusion. Our Li-ion adsorption and diffusion kinetics study revealed that (1) the formation of Li dimer is the most preferred, (2) the Li diffusion energy barrier of Li dimer is lower than isolated Li atom (0.17 eV for Li dimer vs 0.22 eV for Li atom), and (3) the diffusion coefficient of Li is 1.06 × 10^–6 cm²·s^–1, which is orders of magnitude greater than that of Li diffusion in bulk FeF₃ (10^–13–10^–11 cm²·s^–1). Thus, FeF₃ nanosheet can act as an ultrahigh-rate cathode material for Li-ion batteries. More importantly, the calculated voltage and specific capacity of Li on the FeF₃ (012) nanosheet demonstrate that it has a much more stable voltage profile than bulk FeF₃ for a wide range of Li concentration. So, few layers FeF₃ nanosheet provides the desired long-life energy density in Li-ion batteries. These above findings in the current study shed new light on the design of ultrahigh-rate and long-life FeF₃ cathode material for Li-ion batteries

Photochemical Water Oxidation by Crystalline Polymorphs of Manganese Oxides: Structural Requirements for Catalysis

Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn­(III) and Mn­(IV) only, with particular emphasis on the five known structural polymorphs of MnO₂. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn₂O₃ > Mn₃O₄ ≫ λ-MnO₂, where the latter is derived from spinel LiMn₂O₄ following partial Li⁺ removal. No catalytic activity is observed from LiMn₂O₄ and four of the MnO₂ polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn₂O₃ (bixbyite), Mn₃O₄ (hausmannite), and λ-MnO₂ (spinel), all containing Mn­(III) possessing longer Mn–O bonds between edge-sharing MnO₆ octahedra. Electronically degenerate Mn­(III) has antibonding electronic configuration e_g¹ which imparts lattice distortions due to the Jahn–Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface