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The nature of interaction between coal surface and collector molecule affects the yield of fine coal flotation. The interaction depends on coal surface characteristics and collector polarity as well as collector size. In this work, a detail understanding on the interaction nature of nonpolar such as dodecane (C1) and polar collectors such as tetrahydrofurfuryl oleate (C2) and 2-[2-[2-[2-[2-[2-(2-hydroxyethoxy)ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethyl(Z)-octadec-9-enoate (C3) with low-rank coal is presented using density functional theory calculations and finite temperature large scale ReaxFF molecular dynamics simulations. It has been shown that collector consisting of more electronegative elements (i.e. with larger polarity) show stronger interaction with low-rank coal. Moreover, larger aliphatic chain helps to interact via van der Walls interactions and polar functional groups through electrostatic interaction (hydrogen bond formation) due to flexibility in the collector backbone. Interestingly, the collectors did not show any spike like attachment to the low-rank coal surface, rather lies along the coal surface to maximize the possible interactions. This contrasts with commonly presented picture for collector-(low-rank) coal surface interaction. Optimal requirement of aliphatic chain length and polar functional groups was discussed by analyzing structure properties relationship. [ABSTRACT FROM AUTHOR]

Inorganic binders like bentonite, used for pelletization of low-grade iron ore, generate iron ore slimes with comparatively high silica and alumina content necessitating extra steps for their removal during iron making process. This demands the usage of organic binders as full or partial replacement of bentonite for iron ore pelletization. In this work, adsorption of organic binders with saccharides skeleton and –H, –OH, –CH 2 OH and –CH 2 CH 2 OH as polar substituents, on goethite surface was studied using density functional theory, molecular dynamics and machine learning. It was observed that adsorption energy of binders on goethite surface had weak dependence on number of hydrogen bonds between them. With this favorable interaction in mind, a library containing 64 organic binders was constructed and adsorption energy of 30 of these binders was computed using molecular dynamics, followed by training of a linear regression model, which was then used to predict the adsorption energy of rest of the binders in the library. It was found that the introduction of –CH 2 CH 2 OH at R2 position resulted in statistically significant higher adsorption energy. Binder34 and Binder44 were identified as viable candidates for both goethite and hematite ore pelletization and adsorption of their n-mers on goethite and hematite surfaces was also quantified. Designing of Organic binders for Low-grade iron ore palletization using molecular dynamics simulations, quantum chemical calculations and machine learning methods. By using the quantum chemical data, the machine learning model was built and trained followed by the prediction of most probable adsorbed organic binders from a binders library. [Display omitted] • Organic polymers based on sugars used as binders for goethite ore pelletization. • A library of binders was constructed and its adsorption on Goethite was quantified. • Polar group –CH 2 CH 2 OH at R2 position resulted in higher adsorption energy. • Binder34 and Binder44 were identified as candidates for goethite ore pelletization. [ABSTRACT FROM AUTHOR]

Reactive force field (ReaxFF) based molecular dynamics simulations were performed to study the interaction nature of grafted dextrin with hematite. Nature of interaction further explained by doing periodic density functional theory (DFT) calculations. It was observed that in presence of moisture, the polymer adsorbed on the hematite surface via hydrogen bond formation mediated by water. Upon heating, the interfacial water evaporated and boding interactions with the surface was were established. The oxygens present in the polymer backbone also took part in bonding interactions in addition to −COOH, −OH and −COOCH3 functional groups. The binding energies were estimated as −35.8 (Dextrin), −42.6 (Dextrin grafted with polyacrylic acid) and −38.0 kcal/mol (Dextrin grafted with polyacrylic acid and poly (methyl acrylate)) which indicated chemisorption and effect of molecular weight. Grafted dextrin, having higher molecular weight exhibited stronger interaction and it is anticipated that it will have better thermal stability. Binding energy estimated from DFT calculations as −34.8 kcal/mol. DFT charge density difference calculation showed that the oxygen present in the ring polymer structure also interacted with Fe d‐orbitals. [ABSTRACT FROM AUTHOR]

• Molecular level presentation of coal. • Molecular structure development using machine learning (ML) and density functional theory (DFT) methods. • ReaxFF MD simulations to understand thermal decomposition of coal. • DFT IR spectra. • Characterization of coal using FTIR and NMR techniques. The nature of interaction between coal surface and reagent affects fine coal flotation yield. Hence, it is crucial to understand the nature of coal surface to improve flotation yield. Therefore, determination of coal surface at the molecular level is important to optimize the flotation performance. But coal is a complex material, and its molecular presentations depend highly on its geographical origin. In this work, various experimental techniques such as ultimate analysis, proximate analysis, TGA, FTIR and solid state 13C NMR were used to characterize the structure of low-rank Indian coal. The data extracted from these experiments were then used to develop molecular level presentation of coal using machine learning (ML) and DFT. Five stable molecular level structures were proposed for this Indian coal. DFT calculated FTIR spectra matches reasonably with the experimental FTIR data. Finally, a 3D model of the coal sample was developed, and reactive force field (ReaxFF) molecular dynamics simulations were performed for thermal decomposition analysis. [Display omitted] [ABSTRACT FROM AUTHOR]

High temperature quantum chemical molecular dynamics simulations on the polycyclic aromatic hydrocarbon (PAH) formation during combustion of benzene were performed using the density-functional tight-binding (DFTB) method. Systems with varying H/C of 0.8, 0.6, 0.4, and 0.2 and temperatures of Tn=2500 K and Tn=3000 K were employed for the study of the PAH formation and growth mechanism, and trajectories were analyzed by recording average C:H compositions, common elementary reactions and molecular species, ring count, and other characteristic quantities as functions of time. We found that at H/C=0.8 mostly short polyacetylenic hydrocarbons were formed, and no significant PAH growth was found. At lower H/C ratio, longer polyacetylenic chains started to form and new five- and six-membered rings were created due to chain entanglement. Significant PAH growth forming only pericondensed PAHs was observed at lower H/C ratios of 0.4 and 0.2. In addition, smaller hydrocarbon species, such as C2H2, C2H, and C2, are constantly produced by fragmentation of hydrocarbons (unimolecular reactions) and remain common species, although they are simultaneously consumed by the H-abstraction-C2H2-addition growth mechanism. Hydrogen is found to have a clear inhibitive effect on PAH and carbon cluster growth in general, in agreement with recent experimental observations. [ABSTRACT FROM AUTHOR]

Excited-state geometries and electronic spectra of butadiene, acrolein, and glyoxal have been investigated by the symmetry adapted cluster configuration interaction (SAC-CI) method in their s-trans conformation. Valence and Rydberg states below the ionization threshold have been precisely calculated with sufficiently flexible basis sets. Vertical and adiabatic excitation energies were well reproduced and the detailed assignments were given taking account of the second moments. The deviations of the vertical excitation energies from the experiment were less than 0.3 eV for all cases. The SAC-CI geometry optimization has been applied to some valence and Rydberg excited states of these molecules in the planar structure. The optimized ground- and excited-state geometries agree well with the available experimental values; deviations lie within 0.03 Å and 0.7° for the bond lengths and angles, respectively. The force acting on the nuclei caused by the excitations has been discussed in detail by calculating the SAC-CI electron density difference between the ground and excited states; the geometry relaxation was well interpreted with the electrostatic force theory. In Rydberg excitations, geometry changes were also noticed. Doubly excited states (so-called 2 1Ag states) were investigated by the SAC-CI general-R method considering up to quadruple excitations. The characteristic geometrical changes and large energetic relaxations were predicted for these states. [ABSTRACT FROM AUTHOR]

Intermolecular energy transfer for the vibrationally excited propylbenzene cation (C9H12+) in a helium bath was studied with chemical dynamics simulations. The bond energy bond order relationship and electronic structure calculations were used to develop an intramolecular potential for C9H12+. Spin component scaled MP2/6-311++G** calculations were used to develop an intermolecular potential for He + C9H12+. The He + He intermolecular potential was determined from a previous explicitly correlated Gaussian electronic structure calculation. For the simulations, C9H12+ was prepared with a 100.1 kcal/mol excitation energy to compare with experiment. The average energy transfer from C9H12+, ⟨ΔEc⟩, decreased as C9H12+ was vibrationally relaxed and for the initial excitation energy ⟨ΔEc⟩ = 0.64 kcal/mol. This result agrees well with the experimental ⟨ΔEc⟩ value of 0.51 ± 0.26 kcal/mol for collisions of He with the ethylbenzene cation. The ⟨ΔEc⟩ value found for He + C9H12+ collisions is compared with reported values of ⟨ΔEc⟩ for He colliding with other molecules. [ABSTRACT FROM AUTHOR]

A one-dimensional nanostructure with sp3-hybridized carbon atoms, namely, poly[5]asterane (PA), is predicted by means of electronic structure calculations and reactive molecular dynamics simulations. Thermochemical analysis based on homodesmotic reactions showed that the formation of poly[5]asterane is more favorable than that of polytriangulane and comparable to that of polytwistane. A plane-wave DFT approach gave a computed Young's modulus of about 0.84 TPa, which is quite promising and comparable to those of other sp3-hybridized nanothreads. Simulations of the desorption of hydrogen atoms from PA showed a high activation energy ( Ea≈52 kcal mol−1), which again indicates substantial chemical stability. Interestingly, PA was shown to exhibit auxetic behavior (negative Poisson's ratio). Thus, PA is advocated as a new mechanically and chemically stable nanothread with exotic auxetic behavior. [ABSTRACT FROM AUTHOR]

The carbonization mechanism in polyacrylonitrile (PAN)based carbonnanofibers is studied using ReaxFF molecular dynamics simulations.Simulations are performed at two carbonization temperatures, 2500and 2800 K, and also at two densities, 1.6 and 2.1g/cm3, that are relevant to the experimental carbonizationconditions. The results are analyzed by examining the evolution ofspecies with time, including carbon-only ring structures and gaseousspecies. Formation mechanisms are proposed for species like N2, H2, NH3, and HCN and five-, six-,and seven-membered carbon-only rings, along with polycyclic structures.Interestingly, the formation of five-membered rings follows N2formation and usually occurs as a precursor to six-memberedrings. Elimination mechanisms for the gaseous molecules are foundthat are in agreement with previously proposed mechanisms; however,alternative mechanisms are also proposed. [ABSTRACT FROM AUTHOR]

Abstract: Emission of (n =1, 2, … etc.) molecular ions has been studied under the joint influence of electropositive (cesium) and electronegative (oxygen) elements in the secondary ion mass spectrometry (SIMS) process. The kinetic energy distributions, measured for Cs+, , AgCs+ and ions at different oxygen pressures exhibited changing slopes in their leading parts that hinted at appreciable change in the surface work function. The maximum observed change in the surface work function Δϕ max was ∼0.44eV. The measured integrated counts of all ionic species showed a strong variation with the changing oxygen environment. The observations are explained in the light of surface work function changes at the sputtering site. Formation mechanisms of , AgCs+ and ions are explained in the framework of sputter-ion emission models. [Copyright &y& Elsevier]

Detailed studies were carried out on the initial stages of carbonization of sub-bituminous coal using reactive force field (ReaxFF) molecular dynamics simulations. Evolution of different gaseous species during carbonization were analyzed at different temperatures and densities. Elementary reactions were identified leading to the formation of small gaseous species. Cleavage of homolytic O–H bond was found to be the first step of sub-bituminous coal carbonization. CH 4 formed mainly due to reaction of ·CH 3 with hydrogen radical/hydrogen abstraction. Among others, C 9 H m O n radicals were the most abundant species at any simulations condition considered here, where m = 9, 8 or 7 and n = 1, 2 or 3. Bond dissociation energy (BDE) of the identified reactions decreased by ∼3.0 kcal/mol for endothermic reactions and increased by ∼3.0 kcal/mol for exothermic due to change in enthalpy at higher temperature. It was observed that the formation of 5-membered carbon only rings and sp-hybridized carbon species played crucial role in the subsequent growth. The results agree with available experimental observations and computational studies. This work provides new insights on the carbonization mechanism of sub-bituminous coal. [Display omitted] • Initial reaction mechanism of small species formation during carbonization in coal. • Initial reactions begin with intramolecular bond breaking. • Role of sp-hybridized carbon chains and 5-memebred carbon only ring to form nucleus. • Growth of nucleus and formation mechanism of graphitic structure. [ABSTRACT FROM AUTHOR]

Reactive (ReaxFF) molecular dynamic simulations were performed to elucidate the nature of interaction between hematite and carboxymethyl cellulose (CMC) considering effect of moisture and temperature. Simulations showed that the presence of moisture prohibited CMC to interact directly with hematite surface. However, the moisture helps to disperse CMC along the hematite surface thus maximizing the interaction. In dry condition, it was found that the negatively charged oxygen present in the functional groups and in CMC backbone (–CH 2 OCH 2 –) take part to form chemical bond with the positively charged surface Fe. The bonding interaction with polymer back bone is a new finding from this simulation. The binding energy estimated as −56.2 kcal/mol clearly indicates chemisorption with bond length ∼2.00 Å. Upon heating up the complex in presence of atmospheric oxygen it was observed that CMC decomposed at high temperature rather than desorbed from the surface. This study clearly shows that CMC is a suitable binder for iron ore pelletization and will pave the way for more rationale design of organic binders. Image 1 • Chemisorption of carboxymethyl cellulose on α-Fe 2 O 3 (001) surface. • Bonding interaction with the oxygen in –CH 2 OCH 2 - like unit of carboxymethyl cellulose. • Carboxymethyl cellulose remains attached to hematite surface up to higher temperature. • Effect of moisture and temperature on interaction nature. [ABSTRACT FROM AUTHOR]