Effects of sulfur-deficient defect and water on rearrangements of formamide on pyrite (100) surface

Emerging Trends of Computational Chemistry and Molecular Modeling in Froth Flotation: A Review

Froth flotation is the most versatile process in mineral beneficiation, extensively used to concentrate a wide range of minerals. This process comprises mixtures of more or less liberated minerals, water, air, and various chemical reagents, involving a series of intermingled multiphase physical and chemical phenomena in the aqueous environment. Today's main challenge facing the froth flotation process is to gain atomic-level insights into the properties of its inherent phenomena governing the process performance. While it is often challenging to determine these phenomena via trial-and-error experimentations, molecular modeling approaches not only elicit a deeper understanding of froth flotation but can also assist experimental studies in saving time and budget. Thanks to the rapid development of computer science and advances in high-performance computing (HPC) infrastructures, theoretical/computational chemistry has now matured enough to successfully and gainfully apply to tackle the challenges of complex systems. In mineral processing, however, advanced applications of computational chemistry are increasingly gaining ground and demonstrating merit in addressing these challenges. Accordingly, this contribution aims to encourage mineral scientists, especially those interested in rational reagent design, to become familiarized with the necessary concepts of molecular modeling and to apply similar strategies when studying and tailoring properties at the molecular level. This review also strives to deliver the state-of-the-art integration and application of molecular modeling in froth flotation studies to assist either active researchers in this field to disclose new directions for future research or newcomers to the field to initiate innovative works.

Microbe Regulates the Mineral Photochemical Activity and Organic Matter Compositions in Water

Photochemical reactions that widely occur in aquatic environments play important roles in carbon fate (e.g., carbon conversion and storage from organic matter) in ecosystems. Aquatic microbes and natural minerals further regulate carbon fate, but the processes and mechanisms remain largely unknown. Herein, the interaction between Escherichia coli and pyrite and its influence on the fate of carbon in water were investigated at the microscopic scale and molecular level. The results showed that saccharides and phenolic compounds in microbial extracellular polymeric substances helped remove pyrite surface oxides via electron transfer. After the removal of surface oxides on pyrite, the photochemical properties under visible-light irradiation were significantly decreased, such as reactive oxygen species and electron transfer capacity. Unlike the well-accepted theory of minerals protecting organic matter in the soil, the organic matter adsorbed on minerals preferred degradation due to the enhanced photochemical reactions in water. In contrast, the minerals transformed by microbes suppressed the decomposition of organic matter due to the passivation of the chemical structure and activity. These results highlight the significance of mineral chemical activity on organic matter regulated by microbes and provide insights into organic matter conversion in water.

Aminohydroxymethylene (H2N-C̈-OH), the Simplest Aminooxycarbene

We generated and isolated hitherto unreported aminohydroxymethylene (1, aminohydroxycarbene) in solid Ar via pyrolysis of oxalic acid monoamide (2). Astrochemically relevant carbene 1 is persistent under cryogenic conditions and only decomposes to HNCO + H₂ and NH₃ + CO upon irradiation of the matrix at 254 nm. This photoreactivity is contrary to other hydroxycarbenes and aminomethylene, which undergo [1,2]H shifts to the corresponding carbonyls or imine. The experimental data are well supported by the results of CCSD(T)/cc-pVTZ and B3LYP/6-311++G(3df,3pd) computations.

Exploring the Evolution Mechanism of Sulfur Vacancies by Investigating the Role of Vacancy Defects in the Interaction between H2S and the FeS(001) Surface

Vacancy defects are inherent point defects in materials. In this study, we investigate the role of Fe vacancy (V_Fe) and S vacancy (V_S) in the interaction (adsorption, dissociation, and diffusion) between H₂S and the FeS(001) surface using the dispersion-corrected density functional theory (DFT-D2) method. V_Fe promotes the dissociation of H₂S but slightly hinders the dissociation of HS. Compared with the perfect surface (2.08 and 1.15 eV), the dissociation energy barrier of H₂S is reduced to 1.56 eV, and HS is increased to 1.25 eV. Meanwhile, S vacancy (V_S) significantly facilitates the adsorption and dissociation of H₂S, which not only reduces the dissociation energy barriers of H₂S and HS to 0.07 and 0.11 eV, respectively, but also changes the dissociation process of H₂S from an endothermic process to a spontaneous exothermic one. Furthermore, V_Fe can promote the hydrogen (H) diffusion process from the surface into the matrix and reduce the energy barrier of the rate-limiting step from 1.12 to 0.26 eV. But it is very hard for H atoms gathered around V_S to diffuse into the matrix, especially the energy barrier of the rate-limiting step increases to 1.89 eV. Finally, we propose that V_S on the FeS(001) surface is intensely difficult to form and exist in the actual environment through the calculation results.

Unimolecular decomposition of formamide via direct chemical dynamics simulations

Classical chemical dynamics simulations show that formamide (NH₂CHO) can dissociate via multiple pathways, either by direct dissociations or via intramolecular rearrangements to different isomers followed by dissociation.

Theoretical study of formamide decomposition pathways over (6,0) silicon-carbide nanotube

In this study, we systematically identified possible reaction pathways for the catalytic decomposition of formamide (FM) on a (6,0) silicon-carbide nanotube surface by means of density functional theory. To gain insight into the catalytic activity of the surface, the interaction between the FM and SiCNT is analyzed by detailed electronic analysis such as adsorption energy, charge density difference and activation barrier. The energy barriers for the dehydrogenation, decarbonylation, and dehydration processes are found to be in the range of 0.2-49 kcal. Our results indicate that dehydrogenation and decarbonylation pathways are possible routes to get gaseous HNCO, H2, NH3, and CO molecules. In contrast, the reaction of HCONH → CONH + H presents a large activation energy (about 49 kcal mol(-1)) which makes the FM dehydration an unfavorable reaction. Moreover, the dehydrogenation appears to be particularly favorable at low temperatures. The theoretical insights gained in this study could be useful for designing and developing metal-free catalysts based on SiC nanostructures.

Decomposition pathways of formamide in the presence of vanadium and titanium monoxides

Thermally feasible decomposition pathways of formamide (FM) in the presence of vanadium VO(X⁴Σ⁻) and titanium TiO(X³Δ) monoxides are determined using density functional theory (the BP86 functional) and coupled-cluster theory (CCSD(T)) computations with large basis sets.