Structural and dynamical properties of Li+-dibenzo-18-crown-6(DB18C6) complex in pure solvents and at the aqueous-organic interface

Role of Dibenzo Crown Additive for Improving the Stability of Inorganic Perovskite Solar Cells

Photovoltaics are being transformed by perovskite solar cells. The power conversion efficiency of these solar cells has increased significantly, and even higher efficiencies are possible. The scientific community has gained much attention due to perovskites' potential. Herein, the electron-only devices were prepared by spin-coating and introducing the organic molecule dibenzo-18-crown-6 (DC) to CsPbI₂Br perovskite precursor solution. The current-voltage (I-V) and J-V curves were measured. The morphologies and elemental composition information of the samples were obtained by SEM, XRD, XPS, Raman, and photoluminescence (PL) spectroscopies. The distinct impact of organic DC molecules on the phase, morphology, and optical properties of perovskite films are examined and interpreted with experimental results. The efficiency of the photovoltaic device in the control group is 9.76%, and the device efficiency gradually increases with the increase of DC concentration. When the concentration is 0.3%, the device efficiency is the best, reaching 11.57%, short-circuit current is 14.01 mA/cm², the open circuit voltage is 1.19 V, and the fill factor is 0.7. The presence of DC molecules effectively controlled the perovskite crystallization process by inhibiting the in-situ generations of impurity phases and minimizing the defect density of the film.

Competitive Adsorption of Ions at the Oil-Water Interface: A Possible Mechanism Underlying the Separation Selectivity for Liquid-Liquid Solvent Extraction

Adsorption, especially competitive adsorption of ions at the interfaces, governs a wealth of physicochemical processes. Understanding the mechanism behind these interfacial behaviors is crucial for developing novel strategies to intensify reactions or transfer processes. Herein, as an example, we found that in the case of liquid-liquid transport of V(V) and Cr(VI) ions, the competitive adsorption of V(V) and Cr(VI) ions against coexisting SO₄^2- ions at the oil-water interface exhibits a significant impact on the selective separation behaviors of V(V) and Cr(VI) ions. The transport of Cr(VI) ions would be hindered by adding Na₂SO₄ into the aqueous solutions because of the competitive adsorption of SO₄^2- ions at the interface being stronger than that of Cr(VI) ions, whereas the transport of V(V) ions would not be affected because of the stronger affinity of V(V) ions to the interfaces compared to that of SO₄^2- ions. The present work provides new inspirations for developing efficient strategies to improve the separation efficiency of target ions with similar physic-chemical properties by regulating their adsorption behaviors at the interface. It is beneficial to get a deeper understanding into the microscopic nature of competitive adsorption behaviors of ions at interfaces from the interface-molecular level.

Structure, Dynamics, and Adsorption of Charged Guest within the Nanocavity of Polymer-Functionalized Neutral Macrocyclic Host

Host-guest encapsulation has been widely applied for purification and seizing of the metal ions. Macrocyclic crown ethers are one of the most popular hosts in the field of host-guest chemistry, which on functionalization with polymers are employed as an effective adsorbent. In spite of their vast applications, the microscopic information about their sensing mechanism toward cations/molecules is very scarce. Therefore, the present study is focused on the molecular insights of ion-exchange mechanism within the cavity of crown ether-functionalized polymers using molecular dynamics (MD) simulations. This present study investigates the molecular-level events of chloromethylated polystyrene (CMPS) bearing dibenzo-18-crown-6 (DB18C6) in the aqueous and acidic environment, which has been found to be particularly successful in sensing of various alkali and alkali earth metal ions. A strategy has been envisaged to design a crown ether-based functionalized polymeric resin, which exhibits good match of properties with the in-house-synthesized resin. The MD studies well capture the experimentally observed Langmuir-type adsorption isotherms of Li⁺ ions on crown ether-grafted polymer resins. The presence of acid reduces the adsorption of Li⁺ ions due to the competition with H₃O⁺ ions. In addition, the results revealed that the "adsorption in crown cavity" follows a dual residence time function. To the best of our knowledge, this is the first report on the adsorption isotherm of functionalized crown ether using MD simulations. The structure and dynamics of binding sites were explored using radial distribution functions and diffusion coefficients. All of these effects have been studied for different Li⁺-ion concentrations, acid concentrations, and counterions as well as different lengths of polymer chains and degrees of polymerization. Overall, the present study provides insights into and quantitative information about adsorption on the CMPS-DB18C6 resin, which might be useful in myriads of host-guest-based adsorption experiments.

Interfacial Behavior of Cs+, K+, Na+, and Rb+ Extraction in the Presence of Dibenzo-18-Crown-6 from the Nitrobenzene-Water Biphasic System: Experimental, Quantum Chemical, and Molecular Dynamic Studies

Extraction of metal ions (i.e., Cs⁺, K⁺, Na⁺, and Rb⁺) in the presence of ionophore such as dibenzo-18-crown-6 (DB18C6) from the nitrobenzene-water biphasic system is reported by COSMO-RS (conductor-like screening model for real solvents) predictions, molecular dynamics simulation, along with experimental validation. The predicted values of selectivity as obtained for the Na⁺-DB18C6 complex were 4.571, 4.877, and 4.947 at 298.15, 308.15, and 318.15 K, respectively. This was then confirmed by the experimental distribution coefficient (D) as obtained in the diluent systems along with by varying the metal ion to crown ether ligand (M-L) mole ratios: 10:1 (0.1 M M⁺ and 0.01 M DB18C6), 1:1 (0.01 M M⁺ and 0.01 M DB18C6), and 1:10 (0.001 M M⁺ and 0.01 M DB18C6). The experimentally determined values of D _Na (i.e., 0.059, 0.060, and 0.056) were found to be very large as compared to the values of D _Cs (i.e., 0.001, 0.010, and 0.024) in the nitrobenzene phase. It indicates an excellent extraction ability of DB18C6 for Na⁺. The rate of phase separation for the Cs⁺NO₃ ^- system was slow as compared to other metal ion systems. The binding energies, free energies, and nonbonded interaction energies of the complexed metal ion in solution were calculated with both explicit and implicit solvent models. A higher interaction energy between Na⁺-DB18C6 complex and nitrobenzene was observed (i.e., -289.92 in the explicit model and -143.12 kcal/mol in the implicit model) when compared with other metal ions (i.e., Cs⁺, K⁺, and Rb⁺).

Partitioning of Cs+ and Na+ ions by dibenzo-18-crown-6 ionophore in biphasic aqueous systems of octanol and ionic liquid

Molecular dynamics (MD) simulations were carried out to obtain molecular level insights on the behavior of Cs+/Na+ ions at the water–ionic liquid and water–octanol interface in the presence of dibenzo-18-crown-6 (DB18C6) ionophore with an aim to compare an ionic liquid (IL) to a octanol as receiving organic solvent phase. It was observed that the rate of phase separation for the octanol system was rapid as compared to the IL system. The free crown ethers (CE) were found to be highly solvated by the IL phase. A dual cationic exchange mechanism was observed at the [BMIM]/water interface. The [BMIM]+ cation was found to exchange with both the metal ions in aqueous phase as well as with the metal ion aided by the ionophore. The self-diffusion coefficient of the 1:2 complex (0.07×10−9 m2/s) at the octanol/water interface were found to be smaller than that of 1:1 complex (0.37 and 0.14×10−9 m2/s). It was observed that the surface tension of ILs decreased in the presence of complexes and free CE, whereas the surface tension of water was found to increase in presence of salts (Cs+NO3 − and Na+NO3 −). The experimentally determined value of D Cs was found to be quite high in IL phase (1.595) compared to the octanol phase (0.139) in presence of CE. The kinetics of Cs+ was found to be very fast having rate with values of k 1 ^ $\widehat {{k_1}}$ =1.79×10−12 s−1 and k 2 ^ $\widehat {{k_2}}$ =0.205×10−12 s−1 in IL and water phase, respectively. The present results may help us in understanding the role of diluents in the assisted metal ion extraction but also in the future design of diluents and ionophore.

Extraction of Gd3+ and UO22+ Ions Using Polystyrene Grafted Dibenzo Crown Ether (DB18C6) with Octanol and Nitrobenzene: A Molecular Dynamics Study

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd³⁺) and uranium dioxide (UO₂) with dibenzo crown ether (DBCE) in nitrobenzene (NB) and octanol (OCT) solvents. The effect of polystyrene graft length, on DBCE, on the binding behavior of Gd³⁺ and UO₂²⁺ is investigated for the first time. Our simulation results demonstrate that the binding of Gd³⁺ and UO₂²⁺ onto the oxygens of crown ethers is favorable for polystyrene grafted crown ether in the organic solvents OCT and NB. The metal ion binding free energy (ΔG_Binding) in different solvent environments is calculated using the thermodynamic integration (TI) method. ΔG_Binding becomes more favorable in both solvents, NB and OCT, with an increase in the polystyrene monomer length. The metal ion transferability from an aqueous phase to an organic phase is estimated by calculating transfer free-energy calculations (ΔG_Transfer). ΔG_Transfer is significantly favorable for both Gd³⁺ and UO₂²⁺ for the transfer from the aqueous phase to the organic phase (i.e., NB and OCT) via ion-complexation to DBCE with an increase in polystyrene length. The partition coefficient (log P) values for Gd³⁺ and UO₂²⁺ show a 5-fold increase in separation capacity with polystyrene grafted DBCE. We corroborate the observed behavior by further analyzing the structural and dynamical properties of the ions in different phases.

TBP Assisted Uranyl Extraction in Water-Dodecane Biphasic System: Insights from Molecular Dynamics Simulation

In the PUREX (Plutonium Uranium Recovery by Extraction Process) process, the extraction of uranyl ion from dissolver solution to the organic phase is influenced by co extraction of the other species, such as water and nitric acid and it is assumed that the presence of water or acid droplets in the organic phase intensifies the coordination mechanism of TBP. The present study illustrates the uranyl extraction from the aqueous phase to the organic phase using molecular dynamics (MD) simulation. Here, we consider the biphasic systems to gain insights into the characteristics of the interface and humidity of the organic phase under different acidic and neutral conditions. MD being a force field method, can’t satisfactorily model the bond making and breaking process therefore a priori choice has been made concerning the different status of proton for the acidic phase. Further, the importance of charge species transferability during uranyl-TBP complexation have been investigated considering two different models of uranyl nitrate; united UO2(NO3)2 complex and separate UO2 2+ and NO3 – ions. From the results, it is recommended to use the ionic uranyl model with separate UO2 2+ and NO3 – to study the structural and dynamical properties of extracted uranyl ions in the organic phase. Also, it was noticed that extracted uranyl ions in the organic phase are not completely dehydrated but are surrounded by water molecules. In other words the results show co extraction of other species such as water and acid molecules to the organic phase. Most remarkably, the present study evident that the neutral HNO3 effectively represents the acidity effect for the receiving phase in terms of acid/water extraction and their aggregation to form water droplet, especially when ionic model of uranyl nitrate is considered.

Passage of TBP–uranyl complexes from aqueous–organic interface to the organic phase: insights from molecular dynamics simulation

Water/organic interface representing TBP orientation for neutral versus acidic interface and occurrence of UO₂²⁺–TBP–NO₃⁻ species in various stoichiometry.

Quantum mechanical calculations of the interactions between diazacrowns and the sodium cation: an insight into Na+ complexation in diazacrown-based synthetic ion channels

Quantum mechanical calculations were performed to study the conformational behavior and complexation between a sodium cation and a diazacrown (diaza-18-crown-6) using density functional theory (DFT), Møller–Plesset (MP2) and molecular mechanics methods.