Houyu Zhu

A NbO-type copper metal–organic framework decorated with carboxylate groups exhibiting highly selective CO2 adsorption and separation of organic dyes

A porous Cu metal–organic framework (1) based on a pentacarboxylate ligand and paddlewheel SBU was synthesized and structurally characterized. Complex 1 possesses a NbO-type framework with uncoordinated –COO− groups, resulting in its good selectivity for CO2/N2 (36) and CO2/CH4 (12) as well as a large CO2-uptake capacity of 140 cm3 g−1 at 273 K and 1 bar. Grand Canonical Monte Carlo (GCMC) simulations revealed that strong CO2 adsorption sites exist near the open CuII sites and the uncoordinated –COO− groups. Significantly, complex 1 exhibits water resistance and selective adsorption of cationic methylene blue (MB+) in aqueous solution and the adsorbed MB+ can be released in saturated NaCl solution, making it also a promising porous material for charge and pore-size dependent large-molecule capture and separation. The existence of coordinatively unsaturated metal sites as well as the exposed –COO− groups in the framework of 1 is responsible for its selective gas adsorption and dye separation.

Decomposition of methanthiol on Pt(111): a density functional investigation.

Decomposition of methanthiol on Pt(111) is systematically investigated using self-consistent periodic density functional theory (DFT), and the decomposition network has been mapped out. The most stable adsorption of the involved species tends to form the sp(3) hybridized configuration of both C and S atoms, in which C is almost tetrahedral and S has the tendency to bond to three atoms. Spontaneous dissociation rather than desorption is preferred for adsorbed methanthiol. Based on the harmonic transition state theory calculations, the decomposition rate constants of the thiolmethoxy and thioformaldehyde intermediates are found to be much lower than those for their formation, leading to long lifetimes of the intermediates for observation. Under the ultrahigh vacuum (UHV) condition, the most possible decomposition pathway for methanthiol on Pt(111) is found as CH(3)SH --> CH(3)S --> CH(2)S --> CHS --> CH + S --> C + S, in which the C-S bond cleavage mainly occurs at the CHS species. However, the decomposition pathway is CH(3)SH --> CH(3)S --> CH(3) + S under the hydrogenation condition; the C-S bond scission mainly occurs at CH(3)S. The Brønsted-Evans-Polanyi relation holds for each of the S-H, C-H, and C-S bond scission reactions.

Initial Hydrogenations of Pyridine on MoP(001): A Density Functional Study

The initial hydrogenations of pyridine on MoP(001) with various hydrogen species are studied using self-consistent periodic density functional theory (DFT). The possible surface hydrogen species are examined by studying interaction of H(2) and H(2)S with the surface, and the results suggest that the rational hydrogen source for pyridine hydrogenations should be surface hydrogen atoms, followed by adsorbed H(2)S and SH. On MoP(001), pyridine has two types of adsorption modes, i.e., side-on and end-on; and the most stable η(5)(N,C(α),C(β),C(β),C(α)) configuration of the side-on mode facilitates the hydrogenation of pyridine. The optimal hydrogenation path of pyridine with surface hydrogen atoms in the Langmuir-Hinshelwood mechanism is the formation of 3-monohydropyridine, followed by producing 3,5-dihydropyridine, in which the two-step hydrogenations take place on the C(β) atoms. When adsorbed H(2)S is considered as the source of hydrogen, slightly higher hydrogenation barriers are always involved, while the energy barriers for hydrogenations involving adsorbed SH are much lower. However, the hydrogenation of pyridine should be suppressed by the adsorption of H(2)S, and the promotion effect of adsorbed SH is limited.

Methanol oxidation on Ru(0001) for direct methanol fuel cells: analysis of the competitive reaction mechanism

The competitive oxidation reaction mechanism of methanol on the Ru(0001) surface has been investigated by periodic density functional theory (DFT). Stable adsorption configurations, elementary reaction energies and barriers, the potential energy surface (PES), and the electrochemical potential analysis were elucidated. The results showed that O–H bond activation was more competitive than C–H and C–O bond activation during the initial methanol oxidation. Competitive pathways occurred for CH3OH oxidation to CH2O via CH3OH → CH3O → CH2O versus CH3OH → CH2OH → CH2O, further to COOH via the CO pathway CH2O → CHO → CO → COOH versus the non-CO pathway CH2O → CH2OOH → CHOOH → COOH, and finally oxidation to CO2. Taking PES and the electrochemical potential analysis into account, CH3OH → CH2OH → CH2O → CH2OOH → CHOOH → COOH → CO2 appeared to be the preferred oxidation pathway. The OH group could inhibit CO formation by directly reacting with CH2O to yield CH2OOH but could not efficiently remove the CO that had already been produced by the reactions.

Initial reduction of CO2 on perfect and O-defective CeO2 (111) surfaces: towards CO or COOH?

First-principle calculations were performed to explore the initial reduction of CO2 on perfect and O-defective CeO2 (111) surfaces via direct dissociation and hydrogenation, to elucidate the product selectivity towards CO, COOH, or HCOO. The results showed that CO2 prefers a bent configuration with the C atom of CO2 occupying the oxygen vacancy site. Reductive hydrogenation CO2 + H → COOH* was more competitive than CO2 + H → HCOO* on both perfect and O-defective CeO2 (111) surfaces. Comparatively, CO2 hydrogenation towards COOH was slightly more favorable on the perfect surface, whereas reductive dissociation of CO2 was predominant on the O-defective CeO2 (111) surface. Electronic localization function, charge density difference, and density of states were utilized to analyze the effect of charge accumulation and redistribution on the adsorption and reductive dissociation of CO2 caused by the presence of O vacancies. The results of this study provided detailed insight into the initial reduction mechanisms of CO2 towards different products on perfect and O-defective CeO2 (111) surfaces.

Enhancing light hydrocarbon storage and separation through introducing Lewis basic nitrogen sites within a carboxylate-decorated copper–organic framework

A novel nanoporous Cu metal–organic framework (NEM-4) with open CuII sites, Lewis basic nitrogen sites, and uncoordinated –COO− groups exhibits both outstanding uptake capacities (in cm3 (STP) g−1) for C2H2 (204), C2H4 (164.1), C2H6 (172.2), C3H6 (197.4), and C3H8 (196.1) and high selectivities for C2H2/CH4 (63.2), C3H6/CH4 (174.8), and C3H8/CH4 (168.3) under ambient conditions. After eight cycles of adsorption–desorption tests, only 8.2% and 10.3% decrease in the acetylene and propene storage capacities was observed, indicating an excellent repeatability. Compared with 1 (carboxylate decorated NOTT-101), when nitrogen sites are inserted, the C2–C3 hydrocarbon uptakes of NEM-4 can be significantly enhanced. Grand Canonical Monte Carlo and first-principles calculations reveal that not only the open CuII sites but also the uncoordinated –COO− groups and the nitrogen sites play significant roles in its high C2–C3 hydrocarbon uptakes. Moreover, the adsorption and separation of cationic dyes in NEM-4 are highly size and charge state dependent, and the adsorbed methylene blue (MB+) in NEM-4 can be efficiently released in an NaCl-containing CH3OH solution. This study reveals that the combination of open metal sites, carboxylate groups, Lewis basic pyridyl sites, and appropriate pore geometry is responsible for the high adsorption/separation of light hydrocarbons in NEM-4.

Porous Carbon Materials Based on Graphdiyne Basis Units by the Incorporation of the Functional Groups and Li Atoms for Superior CO2 Capture and Sequestration

The graphdiyne family has attracted a high degree of concern because of its intriguing and promising properties. However, graphdiyne materials reported to date represent only a tiny fraction of the possible combinations. In this work, we demonstrate a computational approach to generate a series of conceivable graphdiyne-based frameworks (GDY-Rs and Li@GDY-Rs) by introducing a variety of functional groups (R = -NH2, -OH, -COOH, and -F) and doping metal (Li) in the molecular building blocks of graphdiyne without restriction of experimental conditions and rapidly screen the best candidates for the application of CO2 capture and sequestration (CCS). The pore topology and morphology and CO2 adsorption and separation properties of these frameworks are systematically investigated by combining density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. On the basis of our computer simulations, combining Li-doping and hydroxyl groups strategies offer an unexpected synergistic effect for efficient CO2 capture with an extremely CO2 uptake of 4.83 mmol/g at 298 K and 1 bar. Combined with its superior selectivity (13 at 298 K and 1 bar) for CO2 over CH4, Li@GDY-OH is verified to be one of the most promising materials for CO2 capture and separation.