Value Of Energy Barrier Research Articles

An investigation of the effect of clay type on coal flotation along with DLVO theoretical analyses

ABSTRACTCoals generally exist with clay minerals, which are very fine-sized minerals, and adversely affect the flotation of coal. For instance, they make the coal surface hydrophilic by coating coal surfaces and therefore, they inhibit bubble-particle attachment. Clay minerals can also cause over-consumption of reagents due to their high surface area. Additionally, clay minerals can transfer into the concentrate during the flotation process by entrainment because of their low weight and small particle size, and thus, increase pulp viscosity and changing froth stability. In this study, the influence of various clay minerals (kaolinite, illite, and bentonite) on the flotation behavior of coal sample was studied in detail by conventional flotation tests. In addition, the values obtained from flotation tests were correlated with theoretical energy barrier values established with classical DLVO theory based on zeta potential values of coal and clay samples measured at different pH values. According to the results of this study, no significant effect of clay minerals was observed on coal flotation. This was probably because of the high floatability of the coal used for this study. Both the results obtained from the experiments and theoretical analysis, DLVO calculations, showed that the type of clay mineral is the main indicator parameter for coal flotation.

Low-Scaling Algorithm for Nudged Elastic Band Calculations Using a Surrogate Machine Learning Model.

We present the incorporation of a surrogate Gaussian process regression (GPR) atomistic model to greatly accelerate the rate of convergence of classical nudged elastic band (NEB) calculations. In our surrogate model approach, the cost of converging the elastic band no longer scales with the number of moving images on the path. This provides a far more efficient and robust transition state search. In contrast to a conventional NEB calculation, the algorithm presented here eliminates any need for manipulating the number of images to obtain a converged result. This is achieved by inventing a new convergence criteria that exploits the probabilistic nature of the GPR to use uncertainty estimates of all images in combination with the force in the saddle point in the target model potential. Our method is an order of magnitude faster in terms of function evaluations than the conventional NEB method with no accuracy loss for the converged energy barrier values.

New metal complexes derived from S-benzyldithiocarbazate (SBDTC) and chromone-3-carboxaldehyde: synthesis, characterization, antimicrobial, antitumor activity and DFT calculations

Novel monobasic tridentate ONS donor ligand (HL) was synthesized from the condensation reaction of chromone-3-carboxaldehyde with S-benzyldithiocarbazate (SBDTC). Reaction of the ligand with the metal ions copper(II), nickel(II), cobalt(II), oxidovanadium(IV), cerium(III), manganese(II), zinc(II), and cadmium(II) afforded dimeric complexes with the general formula [ML(Y)m(H2O)x]2·(Y)m·nH2O·zCH3OH, Y = NO3 or Cl, m = 0–2, x = 0–2, n = 0–2, and z = 0–1 for all complexes except oxidovanadium(IV) complex which has the formula [VOL(H2O)]2(SO4). Structures of the ligand and its metal complexes were established through elemental, spectroscopic data (FT-IR, UV-Vis, and mass), thermal analyses, as well as conductivity and magnetic susceptibility measurements. The geometrical structures of the metal complexes are octahedral and square planar. The ligand and its complexes were subjected to in vitro bioassays against the gram-negative and gram-positive bacteria and the fungus strain with good results for some of these compounds. The antitumor activity of the ligand and its copper(II) and oxidovanadium(IV) complexes were investigated against HepG2 cell line. The molecular parameters of the ligand and its metal complexes have been calculated on the basis of DFT level implemented in the Gaussian 09 program, and computed data were correlated with the experimental results. The HOMO→LUMO electron transition potentially occurs from S-benzyldithiocarbazate to chromone moieties with 4.048 eV. The Mn(II) complex has the highest value of energy barrier, while Cu(II) complex has the lowest value among the complexes. All synthesized complexes have energy gap lower than free ligand and therefore these complexes are more reactive than the free ligand.

Quantum Paraelastic Two-Dimensional Materials

We study the elastic energy landscape of two-dimensional tin oxide (SnO) monolayers and demonstrate a transition temperature of T_{c}=8.5±1.8 K using abinitio molecular dynamics (MD) that is close to the value of the elastic energy barrier J derived from T=0 K density functional theory calculations. The power spectra of the velocity autocorrelation throughout the MD evolution permit identifying soft phonon modes likely responsible for the structural transformation. The mean atomic displacements obtained from a Bose-Einstein occupation of the phonon modes suggest the existence of a quantum paraelastic phase that could be tuned with charge doping: SnO monolayers could be 2D quantum paraelastic materials with a charge-tunable quantum phase transition.

Interaction Energy in a Suspension of Gypsum and Dispersed Limestone

The article describes results of the determination of the interaction energy between particles of a hydrating binder and filler, a solution and base. It was found that in the case of particles having a diameter of 17 μm, a mineral suspension should be practically stable, since the energy barrier is much higher than the thermal motion energy of the particles and is 166 kT (100% gypsum), 125 kT (100% CaCO3), 63 kT (gypsum-filler 90:10), and 41kT (gypsum-filler 80:20). A further increase in the amount of CaCO3 particles leads to a significant reduction in the barrier, which at the gypsum-to-filler ratio of 70:30 is 6 kT, and at the ratio of 50:50 completely disappears. In the interaction of the smallest particles (5 μm), the energy barrier values are: 44 kT (100% gypsum), 28 kT (100% CaCO3), 18 kT (gypsum-filler 90:10), 7 kT (80:20) and 2 kT (70:30). With the component ratio of 50:50, the energy barrier completely disappears, and the particles become denser in the first potential well.

Mononuclear Lanthanide(III)-Salicylideneaniline Complexes: Synthetic, Structural, Spectroscopic, and Magnetic Studies

The reactions of hydrated lanthanide(III) [Ln(III)] nitrates and salicylideneaniline (salanH) have provided access to two families of mononuclear complexes depending on the reaction solvent used. In MeCN, the products are [Ln(NO3)3(salanH)2(H2O)]·MeCN, and, in MeOH, the products are [Ln(NO3)3(salanH)2(MeOH)]·(salanH). The complexes within each family are proven to be isomorphous. The structures of complexes [Ln(NO3)3(salanH)2(H2O)]·MeCN (Ln = Eu, 4·MeCN_Eu, Ln = Dy, 7·MeCN_Dy; Ln = Yb, 10·MeCN_Yb) and [Ln(NO3)3(salanH)2(MeOH)]·(salanH) (Ln = Tb, 17_Tb; Ln = Dy, 18_Dy) have been solved by single-crystal X-ray crystallography. In the five complexes, the LnIII center is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms from the two monodentate zwitterionic salanH ligands, and one oxygen atom from the coordinated H2O or MeOH group. The salanH ligands are mutually “cis” in 4·MeCN_Eu, 7·MeCN_Dy and 10·MeCN_Yb while they are “trans” in 17_Tb and 18_Dy. The lattice salanH molecule in 17_Tb and 18_Dy is also in its zwitterionic form with the acidic H atom being clearly located on the imine nitrogen atom. The coordination polyhedra defined by the nine oxygen donor atoms can be described as spherical tricapped trigonal prisms in 4·MeCN_Eu, 7·MeCN_Dy, and 10·MeCN_Yb and as spherical capped square antiprisms in 17_Tb and 18_Dy. Various intermolecular interactions build the crystal structures, which are completely different in the members of the two families. Solid-state IR data of the complexes are discussed in terms of their structural features. 1H NMR data for the diamagnetic Y(III) complexes provide strong evidence that the compounds decompose in DMSO by releasing the coordinated salanH ligands. The solid complexes emit green light upon excitation at 360 nm (room temperature) or 405 nm (room temperature). The emission is ligand-based. The solid Pr(III), Nd(III), Sm(III), Er(III), and Yb(III) complexes of both families exhibit LnIII-centered emission in the near-IR region of the electromagnetic spectrum, but there is probably no efficient salanH→LnIII energy transfer responsible for this emission. Detailed magnetic studies reveal that complexes 7·MeCN_Dy, 17_Tb and 18_Dy show field-induced slow magnetic relaxation while complex [Tb(NO3)3(salanH)2(H2O)]·MeCN (6·MeCN_Tb) does not display such properties. The values of the effective energy barrier for magnetization reversal are 13.1 cm−1 for 7·MeCN_Dy, 14.8 cm−1 for 17_Tb, and 31.0 cm−1 for 18_Dy. The enhanced/improved properties of 17_Tb and 18_Dy, compared to those of 6_Tb and 7_Dy, have been correlated with the different supramolecular structural features of the two families. The molecules [Ln(NO3)3(salanH)2(MeOH)] of complexes 17_Tb and 18_Dy are by far better isolated (allowing for better slow magnetic relaxation properties) than the molecules [Ln(NO3)3(salanH)2(H2O)] in 6·MeCN_Tb and 7·MeCN_Dy. The perspectives of the present initial studies in the Ln(III)/salanH chemistry are discussed.

First-principles investigation of water adsorption on FeCrAl (1 1 0) surfaces

Using the first-principles calculations, the adsorption of the water on the FeCrAl surfaces is studied based on the density functional theory. The atomic structure of various configurations of water adsorption on the (1 1 0) surface is studied. Compared with the Zr (0 0 0 1) system which is widely used as the reactor cladding material, the FeCrAl (1 1 0) surface shows lower adsorption energy. The calculated results show that top site adsorption is energy favorable compared with the hollow and bridge sites. Besides, the charge transfer induced by the adsorption of water is studied as well as the electron density. It is found that charge accumulation happens around water molecules while charge depletion occurs the around surface metal atoms after the water adsorption. The surface element effect on the on the adsorption has been studied in details, and the Cr element on the surface shows stronger interaction with water compared with the Fe or Al elements. Furthermore, the water dissociation calculations show that the FeCrAl alloy has similar energy barrier value on the (1 1 0) surface compared with the pure Fe(1 1 0) surface. FeCrAl alloy has exhibited excellent potential serving as a good candidate for the cladding materials from the aspect of water adsorption.

The significance of acid-base properties in the key ligand for $$\hbox {CO}_{2}$$ CO 2 hydrogenation: role of amido ligand

Using the density functional theoretical calculations, a series of aliphatic amido pincer based Mn-complexes are proposed for base-free $$\hbox {CO}_{2}$$ hydrogenation. We report here that the acid-base nature of the amido ligand plays a crucial role in heterolytic $$\hbox {H}_{2}$$ cleavage and proton transfer mechanism. The reaction free energy barrier values suggest that such amido ligand-assisted $$\hbox {CO}_{2}$$ hydrogenation requires a lower activation barrier compared to the previously reported noble and non-noble metal-based catalysts. Furthermore, the Mn-NNN complex is the most promising catalyst by far and this could be due to the optimum acid-base nature of the amido ligand. Such acid-base properties of the pincer ligand can be tuned by ligand substitution, which in turn controls the catalytic activity. SYNOPSIS A series of aliphatic amido pincer ligand-based Mn-complexes are proposed for base-free $$\hbox {CO}_{2}$$ hydrogenation. The acid-base nature of the amido ligand is very important in heterolytic $$\hbox {H}_{2}$$ cleavage and proton transfer mechanism. This acid-base property of the amido ligand plays a crucial role in base-free $$\hbox {CO}_{2}$$ hydrogenation.

Estimation of structural film viscosity based on the bubble rise method in a nanofluid

When a single bubble moves at a very low capillary number (10−7) through a liquid with dispersed nanoparticles (nanofluid) inside a vertical tube/capillary, a film is formed between the bubble surface and the tube wall and the nanoparticles self-layer inside the confined film. We measured the film thickness using reflected light interferometry. We calculated the film structural energy isotherm vs. the film thickness from the film-meniscus contact angle measurements using the reflected light interferometric method. Based on the experimental measurement of the film thickness and the calculated values of the film structural energy barrier, we estimated the structural film viscosity vs. the film thickness using the Frenkel approach. Because of the nanoparticle film self-layering phenomenon, we observed a gradual increase in the film viscosity with the decreasing film thickness. However, we observed a significant increase in the film viscosity accompanied by a step-wise decrease in the bubble velocity when the film thickness decreased from 3 to 2 particle layers due to the structural transition in the film.

Density functional theory study on the hydrolysis process of COS and CS2 on a graphene surface

The adsorption behavior and hydrolysis mechanism of COS and CS2 on a graphene surface were studied by using density functional theory. It could be concluded that the most stable adsorption configuration for COS was in the form of straight line at the B site, and the adsorption energy was − 0.830 eV. However, the most stable adsorption structure for CS2 with an adsorption energy of − 0.867 eV was the three atoms in CS2 interacting with the C atoms on the graphene surface. By contrasting the two values, the conclusion that the CS2 would adsorb on the graphene surface firstly when the COS and CS2 exist simultaneously was easy to draw. Meanwhile, for the H2O, the maximal adsorption energy was − 0.244 eV and the corresponding configurations were in the form of a downward and upward “V”. So the COS and CS2 will adsorb on the graphene surface first when they react with H2O. Then, the gaseous H2O and adsorptive COS/CS2 create a low-energy system. The energy barrier values of COS and CS2 were 122.648 and 314.108 kcal/mol, respectively, during the hydrolysis process on the graphene surface. And the reaction energies were − 6.335 and 167.561 kcal/mol, respectively. Namely, when the two molecules resulted in the same final products, the COS initiated the reaction more easily.

Flexible proton-responsive ligand-based Mn(i) complexes for CO2 hydrogenation: a DFT study.

A series of flexible proton-responsive group substituted N^N-bidentate ligand based Mn(i) complexes have been studied for base free CO2 hydrogenation. We show here that proton responsive ligands play a critical role in base free CO2 hydrogenation. Our calculated reaction free energy barrier values for heterolytic H2 cleavage show that such flexible proton-responsive ligands require a very low activation energy (∼3 kcal mol-1) barrier. Such flexible proton responsive ligands improve the strong dihydrogen (HH) bonding, which in turn improves heterolytic H2 cleavage - an important step for base free CO2 hydrogenation. Therefore, we believe that such flexible proton responsive ligand-substituted metal complexes can be promising for base free CO2 hydrogenation reactions.

Theoretical insights on the oxygen-reduction reaction mechanism of LaN4-embedded graphene.

We studied the structural stability, adsorption behavior of the key intermediates in the oxygen-reduction reaction (ORR) process, and ORR mechanism on LaN4-embedded graphene (LaN4-Gra) theoretically in an acid environment. The geometry optimization and energy calculations in this study were performed using the generalized gradient approximation (GGA) within the Perdew-Burke-Ernzerhof (PBE) functional. The thermodynamic stability of LaN4-Gra is confirmed by its negative formation energy. The sequential hydrogenation of O2 to generate H2O molecules is the most favorable pathway and it is a four-electron process. The last hydrogenation of OH species to form H2O molecules is the rate-determining step in the whole ORR process. Compared with the energy barrier of pure Pt electrocatalyst (0.8eV), the close energy barrier value for LaN4-Gra (0.89eV) is quite favorable. This implies that LaN4-embedded graphene could be a potential ORR catalyst. Finally, the ORR free energy of LaN4-Gra electrocatalyst was also analyzed.

Thermal racemization of biaryl atropisomers

Many biaryl compounds possess atropisomerism due to the steric hindrance of substituents at the ortho-position of the two aromatic moieties. Upon heating, atropisomers may have enough energy to surpass the rotational energy barrier and racemize. The thermal stability of five atropisomers was studied using chiral chromatography by following the change in enantiomeric excess ratio at different temperatures. The first order racemization reaction rate was obtained at a given temperature as the slope of the change in enantiomeric excess ratio versus time. For each atropisomer, the racemization rates at different temperatures led to the value of the rotational energy barrier for racemization, ΔG‡, and to the racemization half lifetime, t1/2, indicating the atropisomer thermal stability. Binaphthol started to racemize significantly at temperature of 190°C and above while binaphthyldiamine was much more stable showing little or very minor racemization up to 210°C. A chloro-substituted phenylamino-naphthol was very sensitive to thermal racemization starting at a low 40°C.

A quantum chemical investigation of the photodissociation of the nitrosyl hematoporphyrin complex

The photodissociation process of the nitrosyl hematoporphyrin complex has been studied using quantum-chemical methods. Photolysis of hematoporphyrin complexes is of high biological usefulness and is widely employed in laser-therapy methods. However, the mechanism of photodissociation of these complexes is not entirely clear. Based on the computations, we propose a detailed mechanism for the photolysis of the nitrosyl hematoporphyrin complex. A transition “dissociative” excited state has been described, which has an energy barrier value of only 0.4 eV for NO dissociation.

First-principles investigation of adsorption and diffusion of Li on doped silicenes: Prospective materials for lithium-ion batteries

In this report, we investigate the adsorption energies and diffusion characteristics of Li atom on doped silicenes using first principles density functional theory (DFT) calculations. Our results show that the Li adsorption energy on doped silicenes is larger than pristine silicene. Based on our calculations, Al- and B-doped silicenes, due to creating an electron-deficient center in silicene, show a stronger interaction with Li atom compared to P- and N-doped silicenes. The obtained data for surface and perpendicular diffusion of Li atom show the easier mobility of Li on some doped silicenes compared to pristine silicene. According to our results, doping silicene with nitrogen and phosphorus atoms facilitates the Li surface mobility (diffusion barrier of 0.05 and 0.11 eV, respectively versus 0.18 eV for pure silicene) while, doping with aluminum, speed Li perpendicular diffusion (1.47 eV versus 1.67 eV for pristine silicene). The adsorption energy and diffusion barrier values, show the advantage of doped silicenes for use in LIBs with respect to pure silicene.

Effect of Temperature on Diffusion Parameters for 2-Dimensional Copper 5-Atom Island

The effect of temperature during the diffusion of Cu pentamer on Ag(111) surface has been studied by using molecular dynamics (MD) technique at 300, 500 and 700 K. The diffusion coefficient, effective energy barrier and diffusion prefactor for Cu pentamer on Ag(111) have been calculated. The effective energy barrier of 205.25 ± 10 meV and diffusion prefactor of 5.549 × 1012 A2/s have been deduced from the Arrhenius plot. The semi-empirical potentials based on MD simulation shows that the diffusivity obeys the Arrhenius Law and is independent of temperature from 300 to 700 K. The pop-up of single-atom among Cu pentamer has also been observed at 700 K. The value of effective energy barrier is in close agreement with that found from early Monte Carlo simulation.

Densities and viscosities of binary mixtures N , N -dimethyl-N-(3-sulfopropyl)cyclohexylammonium tosylate with water and methanol at T = (303.15 to 328.15) K

Abstract Densities, ρ and viscosities, η of N , N -dimethyl-N-(3-sulfopropyl)cyclohexylammo-nium tosylate ([CyN 1,1 PrSO 3 H][Tos]) with water and methanol were measured, at temperatures from 303.15 K to 328.15 K with 5 K interval and 0.1013 MPa, as a function of [CyN 1,1 PrSO 3 H][Tos] molality (or mass fraction). The isobaric thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy of the pure IL were obtained based on the density data of pure IL. The apparent molar volume, V φ , infinite dilution apparent molar expansibility, E φ ∞ and energy barrier, E were calculated from the experimental data. The Redlich-Mayer equation was used to evaluate infinite dilution apparent molar volume, V φ ∞ . In addition, viscosities can be described satisfactorily by Vogel-Fulcher-Tammann (VFT) equation. The V φ ∞ values of the IL in water are higher than those in methanol, which suggests that the ion-solvent interactions for [CyN 1,1 PrSO 3 H][Tos] + water binary system are stronger than those for [CyN 1,1 PrSO 3 H][Tos] + methanol. And the energy barrier values decrease with the drop of IL mass fraction in both systems, indicating that the viscosity changes of binary mixtures are more sensitive to the temperature at high composition of the IL.

Enhanced hydrogen diffusion in magnesium based hydride induced by strain and doping from first principle study

Magnesium based hydride (MgH2) is a promising hydrogen storage material. However, the sluggish sorption rate impedes its practical applications. To improve the dehydrogenation kinetics of MgH2, the influences of external strains with different dimension (uniaxial/biaxial/triaxial), direction (tensile/compressive) and magnitude (−3% ∼ +3%) on H atom diffusion properties within MgH2 lattice are investigated for the first time using first-principles calculations method. In addition, the synergistic effects of strain and doping of transition metal Nb are further studied. The results show that the diffusion energy barrier of H atom is sensitive to the strain applied to MgH2 lattice. The energy barrier value decreases significantly upon no matter uniaxial, biaxial or triaxial strain, leading to the remarkable increase of H atom diffusion rate. By contrast, the uniaxial tensile strains of ε ≥ 0.5% along [100] or [010] crystal direction, biaxial and triaxial compressive strains of ε ≤ −2% are more beneficial to improving the dehydrogenation kinetics of MgH2. What's more, the strain and Nb doping play the synergistic enhancement effect in increasing H atom diffusion rate, which is superior to their separate role. Analysis of electronic structures reveals that the dehydrogenation kinetics of different MgH2 systems is associated with the energy gap value near Fermi level and the covalent bond strength between hydrogen and metal ions within MgH2 lattice. These results prompt a new insight to enhance the dehydrogenation kinetics of MgH2 by synergistically introducing external strain and transition metal catalysts.

Steady-State CO Oxidation on Pd(111): First-Principles Kinetic Monte Carlo Simulations and Microkinetic Analysis

Using a kinetic Monte Carlo (KMC) approach with parameters derived from first-principles calculations, we modeled the steady-state of CO oxidation on Pd(111), a prototypical catalytic system with various practical applications, including the treatment of automotive gas exhausts. Focusing on the metallic phase of the catalyst, we studied how the rate of CO oxidation depends on temperature and pressure, at fixed gas phase composition. Comparing the results of our simulations with experimental data, we found that all the qualitative features of this catalytic system are correctly reproduced by our model. We show that, when raising the temperature, the system transitions from a CO-poisoned regime with high apparent activation energy to a regime where the rate is almost independent of the temperature. The almost zero apparent activation energy at high temperature stems from approximately equal and opposite values of the O2 adsorption energy and dissociation barrier, as revealed by a simple microkinetic analysis. In the CO-poisoned regime, the precursor-mediated dissociative adsorption of oxygen plays a crucial role: we find that small changes (within DFT error) in the parameters controlling this elementary step have large effects on the kinetics of CO oxidation at low temperature.

Study on the nucleation aspects and morphology of reverse osmosis desalination scales with and without scale inhibitor at different supersaturation ratios

Nucleation and crystallization studies of CaSO4.2H2O were carried out under simulated conditions of scale formation in the reverse osmosis desalination technique. Equal molar ratios of CaCl2 and NaSO4 aqueous solutions were mixed with saline solution of NaCl (40 g/L). Turbidity measurements were carried out for the mixed solutions at different time intervals to determine induction period for the crystal formation of gypsum at ambient temperature (25 °C). Induction period was measured under different high supersaturation ratios ranging from 4.47 to 6.71. Induction period decreases exponentially with increasing supersaturation ratios. Free energy barrier values, critical nucleus radius and nucleation rates were calculated with and without addition of antiscalant {(scale inhibitor) [sodium hexametaphosphate (NaPO3)6, SHMP]} using crystallization equations that relate induction period with supersaturation ratios. The radius of critical nucleus increased by about 30% with SHMP addition compared with the baseline at all the studied supersaturation ratios. Most importantly, scanning electron microscope (SEM) photomicrographs show that, the shapes of crystals of the uninhibited solutions are needle-like and plate-like crystals at supersaturation ratios of 4.47 and 6.71, respectively. Addition of 4.0 mg/L SHMP antiscalant modify the shape of crystals to be similar to that at low supersaturation ratio.