Order Of Reactivity Research Articles

The impact of apatite on sulfuric acid baking of a monazite concentrate and the benefit of goethite addition on rare earth leaching

Sulfuric acid baking of monazite ((Ce,La,Th)PO4) bearing ores is one of the major processes used in commercial production of rare earth elements. In hydrothermal vein type rare earth deposits, apatite is often found together with monazite. Rare earth enriched fluorapatite ores may also contain significant amounts of rare earths hosted in monazite. An understanding of the effect of apatite on the sulfuric acid baking of monazite is therefore important for the development of effective sulfuric acid based treatment methods for such ores. In this work, the addition of a natural hydroxyapatite (Ca5(PO4)3(OH)) sample to a monazite acid bake followed by acid leach was investigated using a combination of chemical analyses, SEM-EDS, XRD and TG-DSC. Hydroxyapatite addition significantly decreased the dissolution of rare earth elements from monazite in the leach after baking at temperatures above 300 °C. For a bake temperature of 500 °C, the rare earth dissolution in the leach dropped from 80% for monazite alone, to 30% for a 1:1 (w/w) addition of hydroxyapatite. This decrease in rare earth leaching was attributed to the formation of an insoluble thorium and rare earth bearing polyphosphate. The rare earth elements were incorporated into this polyphosphate phase in preference to calcium. At 800 °C, monazite was re-formed, causing a further reduction in rare earth extraction, while simultaneous formation of calcium pyrophosphate (Ca2P2O7) led to an increase in calcium and phosphorus dissolution. The detrimental effect of apatite could be partially overcome by the addition of goethite. Addition of goethite to the acid bake of a monazite/apatite mixture at 500 °C improved the total rare earth dissolution from 29% to 85% in the subsequent leach. Results also demonstrated that the order of reactivity, in terms of formation of polyphosphates is Fe > REE > Ca.

Lanthanum partial substitution by basic cations in LaNiO3/CeO2 precursors to raise DFM performance for integrated CO2 capture and methanation

The influence of the adsorbent nature on the CO2 capture and in situ methanation efficiency of novel Dual Function Materials (DFMs) is studied. Several 20% La0.7A0.3NiO3/CeO2–type precursors, with La3+ partially substituted by basic metal oxides (Na, K, Ca and Ba) are prepared. Samples are deeply characterized before and after catalytic tests by XRD, N2 adsorption-desorption, H2-TPR, H2-TPD, STEM-EDS, XPS, CO2-TPD and H2-TPSR. Characterization results show that Ca2+ and Ba2+ cations accommodate better inside the perovskite structure, due to their similarity in oxidation state and ionic radius to La3+. Corresponding DFMs result in enhanced textural properties, more homogenous phase distribution and promoted surface basic sites accessibility and concentration. Finally, the higher proximity and interactions between CO2 adsorption and active sites enhances CH4 formation in a wider temperature window. The order of reactivity has been observed in terms of CH4 production: Ca-doped ≥ Ba-doped > non-doped ≫ Na-doped > K-doped. The 20% La0.7Ca0.3NiO3/CeO2-derived DFM improves methane production of the conventional 15% Ni-15% CaO/Al2O3 DFM (128.0 vs. 118.0 μmol CH4 g−1 at 400 ºC) in the presence of CO2 during the adsorption period, whereas the incorporation of O2 and/or NOx during the adsorption period shows similar detrimental effect in both cases. However, the partial confinement of Ni nanoparticles (NPs) on Ni-La2O3, Ni-CaO or La-Ce-O interfaces prevents synthesized DFM from deactivation and promotes its regenerability related to the conventional formulation. Thus, Ca doping emerges as the more effective way of tailoring CO2 adsorption and in-situ hydrogenation to CH4 efficiency of 20% LaNiO3/CeO2-derived DFMs.

χ-Anderson type polyoxometalates and anhydride based polyimides: Synthesis, characterization and photovoltaic response in dye sensitized solar cells

Efficient electron transport and minimizing recombination losses are crucial for optimizing DSSC performance, necessitating strategies to improve electron diffusion and reduce charge recombination. Two new eco-friendly polyimides based on χ-type polyoxometalates namely Tris@ZnPOM, and Tris@NiPOM, one with the Zn-containing Anderson-type POM(ADP), and the other with the Ni-containing Anderson-type POM, respectively have been synthesized and characterized by FT-IR, UV–vis. spectral analysis, TGA,1H NMR, fluorescence and cyclic voltametric analysis. The fluorescence quenching in Tris@ZnPOM, and Tris@NiPOM was observed as98% and 99.7% as compared to Tris@anhydride, referring the photo-induced transfer of electrons between POM and Tris@anhydrides. The dielectric loss is found to be higher in Tris@anhydride as compared to the Tris@NiPOM, and Tris@ZnPOM. From the MEP analysis it has been seen that POM act as an electron with drawing subunit when conjugated with the anhydride. Different global reactivity parameters (μ, η and ω) were estimated from the frontier molecular orbitals (FMO) analysis, and the order of reactivity for Tris@anhydride, Tris@NiPOM, and Tris@ZnPOM is determined to be in accordance with their increasing band gap i.e., Tris@anhydride > Tris@NiPOM > Tris@ZnPOM. The increase in efficiency (η) of photovoltaics response for Tris@ZnPOM (2.35) is found to be higher as compared to Tris@NiPOM (1.25) and Tris@anhydride(0.62). The presence of Zn in ADP is responsible for increasing the efficiency of Tris@ZnPOM due to its low band gap that causes the easiest transfer of electron.

Graphullerene: A Fully Atomistic Analysis of the Tensile Characteristics Under Temperature Variation

Based on the molecular dynamics simulations, mechanical properties of the most recently synthesized covalent fullerene network, i.e., graphullerene sheet, under uniaxial tension, are determined. These properties include Young's modulus, ultimate stress, failure strain, tensile toughness, and Poisson's ratio. Due to the lack of existing data on mechanical properties of graphullerene, a comprehensive study is performed to get an insight into the effects of defect density, size, and temperature on all tensile characteristics. In the results, it is indicated that the tensile behavior of graphullerene structure is comparable with graphene allotropes. Moreover, it is observed that the presence of defect reduces stiffness, ultimate stress, and tensile toughness, while it has a negligible effect on the failure strain. It is further observed that unlike stiffness, increasing the temperature reduces other tensile characteristics. Interestingly, it is found that graphullerene exhibits auxetic behavior with negative Poisson's ratio which categorizes it as a unique auxetic material ever synthesized. At the end, three types of potential functions for hydrocarbons including adaptive intermolecular reactive empirical bond order, reactive empirical bond order, and Tersoff are considered to study the tensile behavior of graphullerene. This new auxetic nanosheet is a promising analogous to the existing 2D nanostructures with fascinating potential applications.

Deformation behaviors of hydrogen filled boron nitride and boron nitride - carbon nanotubes: Molecular dynamics simulations of proposed materials for hydrogen storage, gas sensing, and radiation shielding

Boron nitride nanotubes (BNNTs) have been extensively studied for hydrogen storage, sensing, and radiation shielding applications. The deformation behaviors of pristine, defective, and H2-encapsulated closed-end armchair BNNTs and BNNT-carbon nanotube (CNT) heterostructures are investigated using molecular dynamics employing the ReaxFF interatomic potential and a combination of Tersoff, adaptive intermolecular reactive empirical bond order, and Lennard-Jones potentials. The calculated elastic properties for pristine BNNTs and CNTs are in excellent agreement with published reliable data. The nanotube length and diameter, defects, entrapped hydrogen content, and temperature all affect the mechanical properties significantly. The ReaxFF potential predicts H2 molecule adsorption on B atoms of undeformed BNNTs whilst under strain, the H2 molecules show preference for the N atoms. Hydrogen adsorption leads to lowering of the elastic and fracture strength of BNNTs. The ReaxFF potential is shown to be a reliable forcefield for investigating the interaction of H2 molecules with BNNTs and BNNT-CNT heterotubes.

The Effect of Conformational Freedom vs Restriction on the Rate in Asymmetric Hydrogenation: Iridium-Catalyzed Regio- and Enantioselective Monohydrogenation of Dienones.

Transition metal-catalyzed asymmetric hydrogenation constitutes an efficient strategy for the preparation of chiral molecules. When dienes are subjected to hydrogenation, control over regioselectivity still presents a large challenge and the fully saturated alkane is often yielded. A few successful monohydrogenations of dienes have been reported, but hitherto these are only efficient for dienes comprised of two distinctly different olefins. Herein, the reactivity of a conjugated carbonyl compound as a function of their conformational freedom is studied, based on a combined experimental and theoretical approach. It was found that alkenes in the (s)-cis conformation experience a large rate acceleration while (s)-trans restrained alkenes undergo hydrogenation slowly. Ultimately, this reactivity aspect was exploited in a novel method for the monohydrogenation of dienes based on conformational restriction ((s)-cis vs (s)-trans). This mode of discrimination conceptually differs from existing monohydrogenations and dienones constructed of two olefins similar in nature could efficiently be hydrogenated to the chiral alkene (up to 99 % ee). The extent of regioselection is even powerful enough to overcome the conventional reactivity order of substituted olefins (di>tri>tetra). This high yielding and atom-economical protocol provides an interesting opportunity to instal a stereogenic center on a carbocycle, while leaving a synthetically useful alkene untouched.

Reactions of the ˙NO3 radical with nuclear extraction ligands in alkane solution.

The reactivity of the nitrate radical (NO3˙) with organophosphorus and amidic actinide and lanthanide complexing agents of interest to nuclear solvent extraction applications was measured, resulting in the first-ever reported bimolecular rate constants for this radicals' reactions in dodecane solution. The order of reactivity for neutral organophosphorus compounds showed faster rate constants with increasing electron density on the phosphoryl phosphorus atom, indicating an increasing facility for electron abstraction reactions occurring in addition to H-atom abstraction from the ligand alkane chains. The only acidic organophosphorus compound investigated, HEH[EHP], showed low reactivity with the NO3˙ radical, attributed to its dimerization in this non-polar solvent. Amide ligand reaction rates were faster than for organophosphorus molecules, suggesting more facile H-atom abstraction from carbonyl activated methylene and amyl groups. While all rate constants were slower than the diffusion-limited rate they were still rapid enough to result in significant oxidation of solvent extraction ligands in dodecane solution.

Theoretical study of the catalytic hydrodeoxygenation of furan, methylfuran and benzofurane on MoS2.

Herein, we have studied the direct deoxygenation (DDO) (without prior hydrogenation) of furan, 2-methylfuran and benzofuran on the metal edge of MoS2 with a vacancy created under pressure of dihydrogen. For the three molecules, we found that the desorption of the water molecule for the regeneration of the vacancy is the most endothermic. Based on the thermodynamic and kinetic aspects, the reactivity order of the oxygenated compounds is furan ≈ 2-methylfuran > benzofuran, which is in agreement with literature. We present the key stages of the mechanisms and highlight the effects of substituents.

The interplay of covalency, cooperativity, and coupling strength in governing C-H bond activation in Ni2E2 (E = O, S, Se, Te) complexes.

Dinickel dichalcogenide complexes hold vital multifaceted significance across catalysis, electron transfer, magnetism, materials science, and energy conversion. Understanding their structure, bonding, and reactivity is crucial for all aforementioned applications. These complexes are classified as dichalcogenide, subchalcogenide, or chalcogenide based on metal oxidation and coordinated chalcogen, and due to the associated complex electronic structure, ambiguity often lingers about their classification. In this work, using DFT, CASSCF/NEVPT2, and DLPNO-CCSD(T) methods, we have studied in detail [(NiL)2(E2)] (L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane; E = O, S, Se and Te) complexes and explored their reactivity towards C-H bond activation for the first time. Through a comprehensive analysis of the structure, bonding, and reactivity of a series of [(NiL)2(E2)] complexes with E = O, S, Se, and Te, our computational findings suggest that {Ni2O2} and {Ni2S2} are best categorised as dichalcogenide-type complexes. In contrast, {Ni2Se2} and {Ni2Te2} display tendencies consistent with the subchalcogenide classification, and this aligns with the earlier structural correlation proposed (Berry and co-workers, J. Am. Chem. Soc. 2015, 137, 4993) reports on the importance of the E-E bond strength. Our study suggests the reactivity order of {Ni2O2} > {Ni2S2} > {Ni2Se2} > {Ni2Te2} for C-H bond activation, and the origin of the difference in reactivity was attributed to the difference in the Ni-E bond covalency, and electronic cooperativity between two Ni centres that switch among the classification during the reaction. Further non-adiabatic analysis at the C-H bond activation step demonstrates a decrease in coupling strength as we progress down the group, indicating a correlation with metal-ligand covalency. Notably, the reactivity trend is found to be correlated to the strength of the antiferromagnetic exchange coupling constant J via developing a magneto-structural-barrier map - offering a hitherto unknown route to fine-tune the reactivity of this important class of compound.

A density functional theory analysis of the C-H activation reactivity of iron(IV)-oxo complexes with an 'O' substituted tetramethylcyclam macrocycle.

In this article, we present a meticulous computational study to foresee the effect of an oxygen-rich macrocycle on the reactivity for C-H activation. For this study, a widely studied nonheme Fe(IV)O molecule with a TMC (1,4,8,11-tetramethyl 1,4,8,11-tetraazacyclotetradecane) macrocycle that is equatorially attached to four nitrogen atoms (designated as N4) and acetonitrile as an axial ligand has been taken into account. For the goal of hetero-substitution, step-by-step replacement of the N4 framework with O atoms, i.e., N4, N3O1, N2O2, N1O3, and O4 systems, has been considered, and dihydroanthracene (DHA) has been used as the substrate. In order to neutralise the system and prevent the self-interaction error in DFT, triflate counterions have also been included in the calculations. The study of the energetics of these C-H bond activation reactions and the potential energy surfaces mapped therefore reveal that the initial hydrogen abstraction, which is the rate-determining step, follows the two-state reactivity (TSR) pattern, which means that the originally excited quintet state falls lower in the transition state and the product. The reaction follows the hydrogen atom transfer (HAT) mechanism, as indicated by the spin density studies. The results revealed a fascinating reactivity order, in which the reactivity increases with the enrichment of the oxygen atom in the equatorial position, namely the order follows N4 < N3O1 < N2O2 < N1O3 < O4. The impacts of oxygen substitution on quantum mechanical tunneling and the H/D kinetic isotope effect have also been investigated. When analysing the causes of this reactivity pattern, a number of variables have been identified, including the reactant-like transition structure, spin density distribution, distortion energy, and energies of the electron acceptor orbital, i.e., the energy of the LUMO (σ*z2), which validate the obtained outcome. Our results also show very good agreement with earlier combined experimental and theoretical studies considering TMC and TMCO-type complexes. The DFT predictions reported here will undoubtedly encourage experimental research in this biomimetic field, as they provide an alternative with higher reactivity in which heteroatoms can be substituted for the traditional nitrogen atom.

Identification of reaction sites and chlorinated products of purine bases and nucleosides during chlorination: a computational study.

Hypochlorous acid (HOCl) released from activated leukocytes plays a significant role in the human immune system, but is also implicated in numerous diseases due to its inappropriate production. Chlorinated nucleobases induce genetic changes that potentially enable and stimulate carcinogenesis, and thus have attracted considerable attention. However, their multiple halogenation sites pose challenges to identify them. As a good complement to experiments, quantum chemical computation was used to uncover chlorination sites and chlorinated products in this study. The results indicate that anion salt forms of all purine compounds play significant roles in chlorination except for adenosine. The kinetic reactivity order of all reaction sites in terms of the estimated apparent rate constant kobs-est (in M-1 s-1) is heterocyclic NH/N (102-107) > exocyclic NH2 (10-2-10) > heterocyclic C8 (10-5-10-1), but the order is reversed for thermodynamics. Combining kinetics and thermodynamics, the numerical simulation results show that N9 is the most reactive site for purine bases to form the main initial chlorinated product, while for purine nucleosides N1 and exocyclic N2/N6 are the most reactive sites to produce the main products controlled by kinetics and thermodynamics, respectively, and C8 is a possible site to generate the minor product. The formation mechanisms of biomarker 8-Cl- and 8-oxo-purine derivatives were also investigated. Additionally, the structure-kinetic reactivity relationship study reveals a good correlation between lg kobs-est and APT charge in all purine compounds compared to FED2 (HOMO), which proves again that the electrostatic interaction plays a key role. The results are helpful to further understand the reactivity of various reaction sites in aromatic compounds during chlorination.

Electronic Structure and Reactivity of Mononuclear Nonheme Iron-Peroxo Complexes as a Biomimetic Model of Rieske Oxygenases: Ring Size Effects of Macrocyclic Ligands.

We report the macrocyclic ring size-electronic structure-electrophilic reactivity correlation of mononuclear nonheme iron(III)-peroxo complexes bearing N-tetramethylated cyclam analogues (n-TMC), [FeIII(O2)(12-TMC)]+ (1), [FeIII(O2)(13-TMC)]+ (2), and [FeIII(O2)(14-TMC)]+ (3), as a model study of Rieske oxygenases. The Fe(III)-peroxo complexes show the same δ and pseudo-σ bonds between iron and the peroxo ligand. However, the strength of these interactions varies depending on the ring size of the n-TMC ligands; the overall Fe-O bond strength and the strength of the Fe-O2 δ bond increase gradually as the ring size of the n-TMC ligands becomes smaller, such as from 14-TMC to 13-TMC to 12-TMC. MCD spectroscopy plays a key role in assigning the characteristic low-energy δ → δ* LMCT band, which provides direct insight into the strength of the Fe-O2 δ bond and which, in turn, is correlated with the superoxo character of the iron-peroxo group. In oxidation reactions, reactivities of 1-3 toward hydrocarbon C-H bond activation are compared, revealing the reactivity order of 1 > 2 > 3; the [FeIII(O2)(n-TMC)]+ complex with a smaller n-TMC ring size, 12-TMC, is much more reactive than that with a larger n-TMC ring size, 14-TMC. DFT analysis shows that the Fe(III)-peroxo complex is not reactive toward C-H bonds, but it is the end-on Fe(II)-superoxo valence tautomer that is responsible for the observed reactivity. The hydrogen atom abstraction (HAA) reactivity of these intermediates is correlated with the overall donicity of the n-TMC ligand, which modulates the energy of the singly occupied π* superoxo frontier orbital that serves as the electron acceptor in the HAA reaction. The implications of these results for the mechanism of Rieske oxygenases are further discussed.

A combined catalytic and kinetic study of the aqueous-biphasic hydrogenation of allylbenzenes by using a dihydride-ruthenium complex containing tri(sodium-o-sulfonatedphenylphosphine) ligands

The water-soluble complex Ru(H)2(CO)(o-TPPTS)3 was used as a catalyst precursor for the hydrogenation of naturally occurring allylbenzenes, such as eugenol, estragole, and safrole, in an aqueous biphasic system. Under the best-operating conditions, P = 900 psi (62 atm), Tθ = 90 °C (363.15 K), S/C ratio = 80/1, time = 6 h, and stirring rate = 800 rpm, this catalyst precursor showed a good activity and selectivity towards C = C bond hydrogenation. When working with eugenol, the isomerization by-product (isoeugenol) was obtained in addition to the hydrogenation product. Preliminary kinetics studies indicate that the individual reactivity order was estragole > allylbenzene > safrole > eugenol. In contrast, a quaternary olefin mixture showed that the hydrogenation rate was somewhat similar to that of individual allylbenzene. The classic Hg test confirmed the molecular nature of the Ru water-soluble complex. Finally, the catalyst recycling study indicates that this complex can be used up to three times, maintaining the same catalytic activity.

Palladium-catalyzed chemoselective Suzuki–Miyaura cross-coupling reaction of poly(pseudo)halogenated arenes

This paper presents general examples of the palladium-catalyzed chemoselective Suzuki–Miyaura cross-coupling reaction of polyhalogenated aryl triflates with a reactivity order of C–Br > C–Cl > C–OTf. A diverse array of bromo(hetero)aryl triflates was successfully coupled with (hetero)aryl boronic acids, achieving excellent reactivity and chemoselectivity. This was accomplished using a catalyst system composed of Pd(OAc)2 and SelectPhos (L1), with catalyst loadings reducible to as low as 0.02 mol% Pd. The sequential double functionalization of bromochloroaryl triflates was also demonstrated successfully, paving the way for the synthesis of terphenyl derivatives.

ReaxFF molecular dynamics simulation and experimental validation about chemical reactions of water and alcohols on SiC surface

The high chemical inertness of silicon carbide (SiC) makes it difficult for surface chemical reactions to occur. Surface oxidation reactions are crucial for improving the processing efficiency and surface quality of SiC wafers. Extensive research has been conducted on conventional aqueous polishing slurries, while investigations on non-aqueous solvent-based polishing slurries have emerged as alternative options for enhancing SiC surface processing, as evidenced by recent scholarly reports. However, the surface chemical reaction mechanism of silicon carbide in either water or other hydroxyl groups containing solvents remains still unclear and is not well understood. In this work, ReaxFF molecular dynamics simulation was used to study the dynamic reaction processes between solvents and 6H SiC (001) surfaces. The oxidation of SiC surface in water and alcohol solvent is found to go through three stages: in the first stage, the solvent molecules move towards the SiC surface and react with the uncoordinated Si atoms and C atoms on the surface; in the second stage, the solvent molecules adsorbed on the surface of SiC reduces the Si–C bonding energy and promotes the breaking of Si–C bonds; in the third final stage, the migration of OH and H on the SiC surface induces the formation of Si–O–Si bonds, which promotes the continuous oxidation of the SiC surface. The order of simulated chemical reactivity between solvent and silicon carbide surface is consistent with experimental polishing removal rates. The reaction mechanism of solvent on silicon carbide surface was proposed by combining ReaxFF simulation results with polishing experiments, AFM, and XPS data analysis, shedding new insights on better understanding the mechanism of SiC chemical mechanical polishing.

Modular Synthesis of Fluoro-Substituted Furan Compounds via Controllable Fluorination of Biomass-Based 5-HMF and Its Derivatives.

5-Hydroxymethylfurfural (5-HMF) is regarded as one of the most promising platform feedstocks for producing valuable chemicals, fuels, and materials. In this study, we present a controllable fluorination technique for biomass-based 5-HMF and its oxygenated derivatives. This technique allows us to synthesize mono-fluoromethyl, difluoromethyl, and acylfluoro-substituted furan compounds by adjusting experimental conditions such as different fluorine sources and mole ratio. To gain a deeper understanding the reactivity order, we conducted intermolecular and intramolecular competition experiments. The results revealed that the hydroxyl group exhibited the highest reactivity, followed by the aldehyde group. This finding provides important theoretical support and opens up the possibility of selective fluorination. The reaction offers several advantages, including mild conditions, no need for inert gas protection, and easy operation. Furthermore, the fluoro-substituted furan compounds can be further transformed for the preparation of drug analogs, offering a new route for the high-value utilization of biomass molecules.

Photocatalytic degradation of non-ionic, anionic, and cationic surfactants: from batch experiments through equilibrium/kinetic study to ecotoxicology analysis

Surface-active compounds constitute a group of important and widespread environmental pollutants. Among different methods used for their treatment, photocatalytic degradation is a promising and efficient solution. Nevertheless, the exact outcome of photodegradation of surfactants may be difficult to predict in case of concentrations used at the industrial scale and considering that the associated mechanism involves radicals which may potentially result in the formation of toxic by-products. In consequence, the aim of this study was to analyze the catalytic photodegradation of three groups of surfactants (three structurally diverse representatives of cationic, anionic, and non-ionic surfactants). Nanoparticles of zinc oxide were synthesized and used as a photocatalyst. The efficiency of photodegradation ranged from 93 to 100% at 10 mg/L, from 38 to 94% at 100 mg/L, and from 15 to 66% when the surfactants were supplied at 1000 mg/L, and the results depended on the structure of the compound subjected to treatment. Subsequent investigation of kinetics revealed that Freundlich, Langmuir or Dubinin-Radushkevich isotherms may be used to describe the adsorption of surfactants (1–65%) and allowed to establish the following order of reactivity: cationic > non-ionic > anionic. Subsequent LC–MS/MS studies of the residues were the basis for identification of photodegradation products for each respective compound. Ultimately, due to the fact that treated graywater is often used as potable water, the phytotoxicity of the degradation products was tested toward sorghum. It was established that in the majority of cases the treatment was efficient (in some cases stimulation of plant growth compared to control samples was observed), whereas an increase in toxicity was observed in case of two cationic surfactants (CTAB and benzalkonium chloride). Overall, the results presented in this study support the application of photocatalytic degradation as an efficient solution for treatment of surfactant-rich effluents.

Investigation of fullerene cluster growth mechanisms by carbon atom addition using classical molecular dynamics.

The mechanisms of carbon sticking reactions to C36 and C-C80 fullerenes were investigated with molecular dynamics simulations (MD) using the Second-generation Reactive Empirical Bond Order (SREBO) and Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potentials that were specifically optimized for carbon-carbon interactions. Results showed the existence of three possible sticking configurations where the projectile atom can stick either to one, two or three atoms of the target fullerene. They also showed that although the two potentials give similar magnitudes for the sticking cross-sections, they yield fairly different results as far as sticking mechanisms and configurations at thermal collision-energies, i.e., in the range 0.05-0.5eV, are concerned. While AIREBO, that takes into account the long-range Lennard-Jones interaction, essentially results in a surface-sticking configuration with a single atom of the target fullerene, SREBO potential yields both surface- and two neighbors-sticking (2N-sticking) configurations. The fullerene structure is preserved in the last configuration while it can be recovered by a 2000K annealing in the former configuration. Results obtained with SREBO eventually showed larger sticking probabilities for C36 as compared with C80. In spite of this, the sticking cross-sections obtained for C80 are similar to or even larger than those obtained for C36 due to the larger size of C80 that compensates for its smaller sticking probabilities.

Adsorption of Multi-Collector on Long-Flame Coal Surface via Density Functional Theory Calculation and Molecular Dynamics Simulation

The quantum chemical properties of long-flame coal (LFC) and collectors (kerosene, diesel, diethyl phthalate (DEP), biodiesel collector (BDC), and emulsified biodiesel collector (EBDC)) were analyzed via the density functional theory (DFT). The molecular dynamics (MD) of the coal–collector–water system and the adsorption of collectors on LFC were conducted based on the first principles. The results showed that the frontier molecular orbitals of kerosene, diesel, DEP, and BDC were 0.38 eV, 0.28 eV, 0.27 eV, and 0.20 eV, respectively. The chemical reactivity order of the above mentioned collectors was BDC &gt; DEP &gt; diesel &gt; kerosene. Kerosene, diesel, and DEP adsorbed with carbonyl, hydroxyl, and carboxyl groups in LFC, respectively. Carboxyl groups in BDC and carboxyl groups in LFC bilaterally adsorbed, while BDC repelled water molecules via hydrogen bonds on the LFC surface. In the systems of BDC and EBDC, the diffusion coefficients of a water molecule were 2.83 × 10−4 cm2/s and 3.73 × 10−4 cm2/s. The emulsifier that adsorbed onto the oil–water interface of the coal–BDC–water system improved the dispersion of BDC during flotation, while at the same time increasing the number of hydrogen bonds between BDC and LFC, which accelerated the migration of water molecules from the LFC surface.

Orientation-dependent etching of silicon by fluorine molecules: A quantum chemistry computational study

Anisotropic etching is a widely used process in semiconductor manufacturing, in particular, for micro- and nanoscale texturing of silicon surfaces for black silicon production. The typical process of plasma-assisted etching uses energetic ions to remove materials in the vertical direction, creating anisotropic etch profiles. Plasmaless anisotropic etching, considered here, is a less common process that does not use ions and plasma. The anisotropy is caused by the unequal etching rates of different crystal planes; the etching process, thus, proceeds in a preferred direction. In this paper, we have performed quantum chemistry modeling of gas-surface reactions involved in the etching of silicon surfaces by molecular fluorine. The results confirm that orientation-dependent etch rates are the reason for anisotropy. The modeling of F2 dissociative chemisorption on F-terminated silicon surfaces shows that Si–Si bond breaking is slow for the Si(111) surface, while it is fast for Si(100) and Si(110) surfaces. Both Si(100) and Si(110) surfaces incorporate a larger number of fluorine atoms resulting in Si–Si bonds having a larger amount of positive charge, which lowers the reaction barrier of F2 dissociative chemisorption, yielding a higher etch rate for Si(100) and Si(110) surfaces compared to Si(111) surfaces. Molecular dynamics modeling of the same reactions has shown that the chosen reactive bond order potential does not accurately reproduce the lower reaction barriers for F2 dissociative chemisorption on Si(100) and Si(100) surfaces. Thus, reparameterization is necessary to model the anisotropic etching process that occurs at lower temperatures.