Density Functional Theory Findings Research Articles

Absence of magnetic order in RuO2: insights from μSR spectroscopy and neutron diffraction

Altermagnets are a novel class of magnetic materials, where magnetic order is staggered both in coordinate and momentum space. The metallic rutile oxide RuO2, long believed to be a textbook Pauli paramagnet, recently emerged as a putative workhorse altermagnet when resonant X-ray and neutron scattering studies reported nonzero magnetic moments and long-range collinear order. While some experiments seem consistent with altermagnetism, magnetic order in RuO2 remains controversial. We show that RuO2 is nonmagnetic, both in bulk and thin film. Muon spectroscopy complemented by density-functional theory finds at most 1.14 × 10−4 μB/Ru in bulk and at most 7.5 × 10−4 μB/Ru in 11 nm epitaxial films, at our spectrometers’ detection limit, and dramatically smaller than previously reported neutron results that were used to rationalize altermagnetic behavior. Our own neutron diffraction measurements on RuO2 single crystals identify multiple scattering as the source for the false signal in earlier studies.

Removal of lead ions (Pb2+) from aqueous solution using chitosan/starch composite material: Experimental and density functional theory findings

AbstractTreatment of wastewater has become vital to prevent environmental pollution in recent years. Adsorption is an easily applicable, low-cost and efficient method and is the subject of this study. In this study, an adsorbent was synthesized to be used in heavy metal removal using chitosan and starch. The composite was characterized by Fourier transform infrared (FTIR) spectrophotometry, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis. It was determined that the composite had an amorphous and compact structure. Adsorption experiments were carried out under the optimized parameters such as solution pH, concentration, adsorbent amount, equilibrium time, and temperature. It shows that during adsorption, with the increase in pH, the adsorption efficiency and adsorption capacity first increase and then a fluctuation occurs. The highest adsorption efficiency and Q value were reached at pH 3.46 as 78% and 0.038 mol/kg, respectively. Moreover, the adsorption capacity (Q) reached its highest value with a value of 0.067 mol/kg in the presence of 30 mg adsorbent. Equilibrium experiments were validated by the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models. To investigate the adsorption mechanism, pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models were used. It was determined that the adsorption process followed the D-R isotherm (R2 = 0.99) and PSO (R2 = 0.99). Therefore, the existence of chemical adsorption can be mentioned. Thermodynamic parameters enthalpy (∆H), Gibbs free energy (∆G) and entropy change (∆S) were investigated. The adsorbate-adsorbent interactions were studied by density functional theory (DFT).

Removal of erythrosine B dye from wastewater using chitosan boric acid composite material: Experimental and density functional theory findings

AbstractIn this study, the chitosan boric acid (Ch‐B) composite has been prepared and characterized with sophisticated analytical techniques such as FT‐IR, SEM, and EDX. The prepared Ch‐B adsorbent was applied for the adsorption of erythrosine B (EB) dye from water samples under the optimized parameters of pH, adsorbent dosage, time, and temperature. Results shows that the Ch‐B adsorbent removes 96.5% of EB dye at pH 5, using 0.05 g of adsorbent. The adsorption equilibrium data have been subject to the Langmuir, Freundlich, and D‐R adsorption equilibrium models, which demonstrates that the Freundlich model was the best fit with good correlation coefficient value (R2 = 0.991), while energy E (9.18 KJ·mol−1) calculated from D‐R model suggested that the physical adsorption nature of the adsorption. Beside this, the thermodynamic and kinetic experiments were performed to check the feasibility and adsorption mechanism of EB‐dye onto Ch‐B adsorbent, which shows that the adsorption is endothermic (∆H = 0.124) and spontaneous in nature due to the negative values of Gibbs free energy (i.e., ∆G KJ·mol−1 = −13.01, −17.06, and −17.60). The kinetic models show that the adsorption equilibrium is best fitted with pseudo second order kinetic model due to good correlation coefficient (R2 = 0.99). Moreover, the interaction phenomenon between adsorbent and adsorbate was analyzed through DFT calculations.

A relativistic DFT probe of polypyrrolic macrocyclic diuranium(III) complexes with terminal solvents and iodines.

Relativistic density functional theory finds that two isomers of a diuranium(III) complex of a polypyrrolic macrocycle (H4L) feature active sites on uranium moieties, allowing for their potential application in activating industrially and economically important small molecules. To address this, a series of adducts [(X)nU2(L)]((2-m)+) (X = THF, I(-) and HI; n = 1 and 2; m = 0, 1 and 2) have been examined. The coordination from X to the exposed uranium(s) changes the general geometry and electronic structure slightly. Thermodynamic calculations reveal that iodine termination is energetically favored over THF/HI coordination. Graphical abstract Scalar and spin-orbit coupling relativistic DFT calculation reveals that the active sites on the uranium moieties of [U2(L)](2+) lead to formation of adducts [(THF)nU2(L)](2+), [InU2(L)]((2-n)+) and [(HI)nU2(L)](2+) (n = 1 and 2). Coordination to the exposed uranium(s) changes geometrical and electronic properties slightly, but iodine termination is the most energetically favored.