Theoretical study of noncovalent functionalization of BN nanotubes by various aromatic molecules

The unsatisfactory stability of CNT under high temperature or subject to strong oxidants has limited the potential use of p- and n-type field-effect transistors (FETs). Promisingly, boron nitride (BN) nanotubes are known to have the excellent resistance to oxidant and thermal stability at high temperature as well as the uniform electronic properties, which rends their possible application as alternative FET device. In this paper, through the theoretical computation of the noncovalent functionalization of BN nanotube by various aromatic molecules (including C₁₀H₈, C₁₄H₁₀, porphyrin, DDQ, and TCNQ molecules), we for the first time evaluate its possibility as a candidate of stable FET device. We find that: (i) these aromatic molecules can be stably adsorbed on the studied BN with the adsorption energy ranging from ? 0.22 (C₁₀H₈) to ? 0.42 eV (porphyrin); (ii) the adsorption of electrophilic molecules on the outer sidewall of BN nanotube realizes a p-type semiconductor with a smaller band gap (~ 0.90 eV); (iii) exoherdral adsorption of nucleophilic aromatic molecules leads to an n-type semiconductor. This novel BN nanotube-based material offers great promise for molecule electronics in terms of their good stability.     

Lanthanide-based metal–peptide frameworks prepared by ionothermal method: Anion direct effect,DFT calculation and luminescence property

A series of new isomorphic lanthanide-based metal–peptide frameworks, [Ln(PODC)(H₂O)₂]Br (Ln = La(1), Nd(2), Eu(3), Tb(4), H₂PODC = 2, 5-piperazinedione-1, 4-diacetic acid), were synthesized under the ionic liquid medium. Crystal structure measure results exhibit that they are new three-dimensional frameworks, where bromine anions of ionic liquid are enveloped in the pore. Interestingly, it is found that bromine anions can effectively counteract the effects of lanthanide ions (e.g. lanthanide contraction). Via the first-principles DFT calculation, it is obtained that bromine anions of ion liquid influence the electronic properties of PODC^2 − ligand and thereby directly control the structure. Luminescence analysis demonstrates that compounds 3 and 4 have good fluorescence properties, where the emission peaks can be ascribed to the transitions of ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) for 3 and ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) for 4.     

Synthesis,structure and fluorescence properties of a uranyl-2,5-pyridinedicarboxylic acid coordination polymer: The missing member of the UO22+-2,n-pyridinedicarboxylic series

A 3D uranium-pyridinedicarboxylate, compound (1) [UO₂(C₇H₃NO₄)], represents the final member of a series of materials incorporating a series of 2,n-pyridinedicarboxylic (pydc) acids (n = 3,4,5,6). The resulting crystal structure [FW = 419.13, monoclinic, P2₁/n, a = 9.0096(3) Å, b = 8.1371(2) Å, c = 11.6954(4) Å, V = 852.45 ų, Z = 4] was determined by single crystal X-ray diffraction and fluorescent properties were investigated. Additionally, the complete series of uranium-2,n-pydc materials was examined on a basis of fluorescent behaviors and architectural similarities.     

Adsorption of perchlorate onto raw and oxidized carbon nanotubes in aqueous solution

Perchlorate (ClO₄^?) is an emerging trace contaminant. The adsorption of ClO₄^? on raw and oxidized carbon nanotubes (CNTs) was investigated to elucidate the affinity mechanism of CNTs with anion pollutants. The adsorption of ClO₄^? into different CNTs increased in the order multi-walled CNTs < single-walled CNTs < double-walled CNTs (DWCNTs). Co-existing anions (SO₄^2?, NO₃^?, Cl^?) significantly weakened ClO₄^? adsorption, while the co-existence of Fe³⁺ and cetyltrimethylammonium cations increased ClO₄^? adsorption 2- to 3-fold. ClO₄^? adsorption was promoted by oxidized DWCNTs due to the introduction of more oxygen-containing functional groups, which served as additional adsorption sites. The pH values significantly affected the zeta potential of raw and oxidized DWCNTs and thus ClO₄^? adsorption. The pH-dependent curves of ClO₄^? adsorption on CNTs were distinct from those of conventional sorbents (e.g., activated carbon and resin). Maximum ClO₄^? adsorption occurred at pH = the isoelectric point (pH_IEP) + 0.85 rather than at pH < pH_IEP, which cannot be explained by electrostatic interactions alone. Hydrogen bonding is proposed to be a dominant mechanism at neutral pH for the interaction of ClO₄^? with CNTs, and variations of ClO₄^? affinity with CNTs in different pH ranges are illustrated.     

Selection of ionic liquids for the extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures

The separation of aromatic hydrocarbons (benzene, toluene, ethyl benzene and xylenes) from C₄ to C₁₀ aliphatic hydrocarbon mixtures is challenging since these hydrocarbons have boiling points in a close range and several combinations form azeotropes. In this work, we investigated the separation of toluene from heptane by extraction with ionic liquids.Several ionic liquids are suitable for extraction of toluene from toluene/heptane mixtures. The toluene/heptane selectivities at 40 °C and 75 °C with several ionic liquids, [mebupy]BF₄, [mebupy]CH₃SO₄, [bmim]BF₄ (40 °C) and [emim] tosylate (75 °C), are a factor of 1.5–2.5 higher compared to those obtained with sulfolane (S_tol/hept = 30.9, D_tol = 0.31 at 40 °C), which is the most industrially used solvent for the extraction of aromatic hydrocarbons from a mixed aromatic/aliphatic hydrocarbon stream. From these five ionic liquids, [mebupy]BF₄ appeared to be the most suitable, because of a combination of a high toluene distribution coefficient (D_tol = 0.44) and a high toluene/heptane selectivity (S_tol/hept = 53.6). Therefore, with [mebupy]BF₄ also extraction experiments with other aromatic/aliphatic combinations (benzene/n-hexane, ethylbenzene/n-octane and m-xylene/n-octane) were carried out. The aromatic/aliphatic selectivities were all in the same range, from which it can be concluded that the toluene/heptane mixture is a representative model system for the aromatic/aliphatic separation.     

Selection of ionic liquids for the extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures

The separation of aromatic hydrocarbons (benzene, toluene, ethyl benzene and xylenes) from C₄ to C₁₀ aliphatic hydrocarbon mixtures is challenging since these hydrocarbons have boiling points in a close range and several combinations form azeotropes. In this work, we investigated the separation of toluene from heptane by extraction with ionic liquids.Several ionic liquids are suitable for extraction of toluene from toluene/heptane mixtures. The toluene/heptane selectivities at 40 °C and 75 °C with several ionic liquids, [mebupy]BF₄, [mebupy]CH₃SO₄, [bmim]BF₄ (40 °C) and [emim] tosylate (75 °C), are a factor of 1.5–2.5 higher compared to those obtained with sulfolane (S_tol/hept = 30.9, D_tol = 0.31 at 40 °C), which is the most industrially used solvent for the extraction of aromatic hydrocarbons from a mixed aromatic/aliphatic hydrocarbon stream. From these five ionic liquids, [mebupy]BF₄ appeared to be the most suitable, because of a combination of a high toluene distribution coefficient (D_tol = 0.44) and a high toluene/heptane selectivity (S_tol/hept = 53.6). Therefore, with [mebupy]BF₄ also extraction experiments with other aromatic/aliphatic combinations (benzene/n-hexane, ethylbenzene/n-octane and m-xylene/n-octane) were carried out. The aromatic/aliphatic selectivities were all in the same range, from which it can be concluded that the toluene/heptane mixture is a representative model system for the aromatic/aliphatic separation.     

Organic–inorganic hybrid oxides: Structure and magnetic properties of [{Cu(terpy)}2Mo6O17(H2O)(O3PCH2NH2CH2PO3)2] · H2O,a bimetallic oxide constructed from novel {Mo6O17(H2O)(O3PCH2NH2CH2PO3)2}4− clusters

The hydrothermal reaction of MoO₃, CuSO₄ · 5H₂O, 2,2′:6′:2″-terpyridine (terpy) and bis-N,N-(methylphosphonic acid) amine (H₂O₃PCH₂NHCH₂PO₃H₂) provided blue crystals of the bimetallic oxide [{Cu(terpy)}₂Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂] · H₂O (1 · H₂O). The three-dimensional structure of 1 is constructed from {Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂}⁴⁻ clusters linked through {Cu(terpy)}²⁺ subunits. The cluster consists of three pairs of edge-sharing {MoO₆} octahedra linked through corner-sharing interactions into a {Mo₆O₆} ring. One phosphonate ligand spans the diameter of the ring, bridging four molybdenum sites and leaving at a pendant {PO} group at each terminus. The second diphosphonate ligand exploits one {–PO₃} unit to cap the hexamolybdate ring and bridge all six molybdenum sites while the second {–PO₃} terminus bridges two molybdenum sites, leaving a pendant {PO} unit. Crystal data: C₃₄H₄₅Cu₂Mo₆N₈O₃₅P₄: monoclinic, P2₁/n, a = 11.9431(7) Å, b = 17.382(1) Å, c = 27.524(2) Å, β = 90.429(1)°, V = 5713.7(6) Å³, Z = 4, D_calc = 2.270 g cm⁻³, R₁ = 0.0466.     

Microwave dielectric properties and cation distributions of Zn1-3xAl2+2xO4 ceramics with defect structures

The spinel-structured Zn_1-3xAl_2+2xO₄ (x = 0–0.2) ceramics having defective structures were synthesized using the molten salt method, and their microwave dielectric properties and cation distributions were assessed. The ²⁷Al solid-state nuclear magnetic resonance spectra of these ceramics demonstrate that they have an intermediate spinel structure in which the tetrahedral site occupancy increases from 0.03 to 0.64 as x increases. Moreover, crystal structure refinements suggest that cation vacancies are located at octahedral sites for x = 0.1 and 0.2. Based on these data, the introduction of cation vacancies at octahedral sites appears to enhance the preferential occupation of tetrahedral sites by Al³⁺. The ε_r of these ceramics slightly decreased from 8.5 to 8.2 with increasing x, while the Q·f value increased significantly, from 127,532 to 202,468 GHz, upon the introduction of cation vacancies. An intermediate spinel structure with preferential occupancy of tetrahedral sites by trivalent cations exhibits an enhanced Q·f value.     

Ionothermal synthesis,fluorescence, and DFT calculation of three lanthanide-based metal-organic frameworks

Three lanthanide-based metal-organic frameworks (MOFs), [Ln(SIP)(HSIP)][EMIm]₂, (Ln = La(1), Nd(2) Eu(3); H₂SIP = 5-sulfoisophthalic acid; EMImBr = 1-ethyl-3-methyl-imidazole bromine), were obtained under the ionic liquid medium. Crystal structure analysis reveals that there are two-dimensional metal-organic frameworks, which are built from the connection of {Ln_n} chains by SIP^3 − ligands. It is found that EMIm⁺ cations are filled in the void between 2D layers. Interestingly, the whole framework shows one new topology with the symbol of [3 · 4²]₂[3⁴ · 4⁶ · 5⁶ · 6⁸ · 7³ · 8]. Luminescence measurement exhibits that compound 3 has good emission property. Furthermore, DFT calculation results confirm that the emission mechanism can be attributed to the transition of f–f transition of Eu(III) ions, where SIP^3 − ligand acts as the role of electron carrier.     

An expeditious synthesis of benzimidazole derivatives catalyzed by Lewis acids

An expeditious and efficient route for the synthesis of benzimidazole derivatives by the reaction of o-phenylenediamines with orthoesters in the presence of Lewis acids was described. ZrCl₄, SnCl₄ · 5H₂O, TiCl₄, BF₃ · Et₂O, ZrOCl₂ · 8H₂O and HfCl₄ exhibited high catalytic activity for this transformation.     

Spark plasma sintering of MgAl2O4–YCr0.5Mn0.5O3 composite NTC ceramics

New high temperature negative temperature coefficient (NTC) thermistor ceramics based on a xMgAl₂O₄–(1 − x)YCr_0.5Mn_0.5O₃ (x = 0.1, 0.4, 0.6) composite system have been successfully fabricated through spark plasma sintering (SPS) with a low sintering temperature and a short sintering period. The X-ray diffraction analysis indicates that the SPS-sintered composite ceramics consist of a cubic spinel MgAl₂O₄ phase and an orthorhombic perovskite YCr_0.5Mn_0.5O₃ phase isomorphic to YCrO₃. The SPS-sintered composite ceramics have high relative density ranging from 94.1 to 97.4% of the theoretical density. X-ray photoelectron spectroscopy analysis corroborates the presence of Cr³⁺, Cr⁴⁺, Mn³⁺, and Mn⁴⁺ ions on lattice sites, which may result in the hopping conduction. The obtained ρ₂₅, B_25–150, and B_700–1000 of the SPS-sintered composite NTC thermistors are in the range of 1.53 × 10⁶–9.92 × 10⁹ Ω cm, 3380–5172 K, and 7239–9543 K, respectively. These values can be tuned by adjusting the MgAl₂O₄ concentration.     

Activation of graphene aerogel with phosphoric acid for enhanced electrocapacitive performance

We present a facile and efficient route to introduce in-plane nanopores on the graphene sheets by activation of graphene aerogel (GA) with phosphoric acid (H₃PO₄). Results from N₂ adsorption and TEM images showed that H₃PO₄ activation created mesopores with pore size of 2–8 nm on the graphene sheets. With such nanopores on graphene sheets, the activated GA exhibits a specific capacitance of 204 F g⁻¹, enhanced rate capability (69% capacitance retention from 0.2 to 30 A g⁻¹), reduced equivalent series resistance (3.8 mΩ) and shortened time constant (0.73 s) when comparing with the hydrothermally-derived pristine GA and thermally annealed GA in the absent of H₃PO₄. The excellent capacitive properties demonstrate that introduction of nanopores on GA by H₃PO₄ activation not only provides large ion-accessible surface area for efficient charge storage, but also promotes the kinetics of electrolyte across the graphene two-dimensional planes.     

Linked macrocyclic systems. Interaction of copper(I) with tris-ring N2S2-donor macrocycles and their single-ring analogues

The interaction of two tri-linked N₂S₂-donor macrocyclic ligands, 1 (R = H) and 2 (R = H), and their related single ring derivatives, 3 (R = H) and 4 (R = CH₂C₆H₅), with copper(I) is reported. Solid 3:1 (metal:ligand) complexes of type [Cu₃L](PF₆)₃ (L = 1 and 2, R = H) and single ring derivatives of type [CuL]PF₆ (L = 3, R = H; L = 4, R = CH₂C₆H₅) were isolated; the X-ray structure of [CuL]PF₆ (L = 3, R = H) showed that the four macrocyclic donor atoms coordinate to the copper(I) in a quasi-tetrahedral manner (Cu–N 2.089, 2.096(4); Cu–S 2.239, 2.264(2) Å, X–Cu–Y 104.5(1)–115.4(1))°.     

Synthesis of 1,1′-ferrocene bis(carboxypyrazole) compounds and displacement of the pyrazole ligands

The reaction of 1,1′-ferrocenedicarbonyl chloride with pyrazole or 3,5-dimethyl pyrazole generates novel 1,1′-ferrocene bis(amide) compounds 1 and 2, respectively. The crystal structure of 1 shows that the pyrazole rings are essentially co-planar with each other and with the cyclopentadienyl rings. Attempts to use the complexes as a chelating ligand were unsuccessful. Instead, treatment of 1 or 2 with Mo(CO)₄(pip)₂, pip = piperidine, led to displacement of the pyrazole ligands and formation of the known amide compound, 1,1′-ferrocene bis carbonyl piperidine. Replacement of the pyrazole is ascribed to the weakness of the amide bond caused by the aromaticity of the pyrazole ring. Crystal data for C₁₈H₁₄FeN₄O₂ (1): monoclinic P2(1)/c, a = 13.3907(18) Å, b = 10.2112(14) Å, c = 11.3082(16) Å, β = 105.209(2)°, V = 1492.1(4) Å³, Z = 4.     

A new trinuclear zinc(II) complex possessing five- and six-coordinated central ions and its photoluminescent property

A aromatic Schiff base ligand, N, N′-bis((4, 4′-diethylamino)salicylidene)-1, 2-phenylenediamine (H₂L), and its trinuclear zinc(II) complex, Zn₃L₂(CH₃COO)₂, were synthesized. The X-ray crystal structure of the complex reveals that two zinc ions show the coordination number of five and the third one has the coordination number of six. The complex exhibits blue-green emission as the result of the fluorescence from the intraligand emission excited state.     

Dissolution of platinum in acidic media

To understand the degradation of the Pt/C cathode for use in polymer electrolyte fuel cells, the solubility and the dissolution mechanism of platinum in acidic media was very important fundamentally. In this study, the platinum solubility has been determined in acidic electrolytes as a function of temperature and pH. The solubility was 3 × 10^?6 mol dm^?3 at 25 °C in 1 mol dm^?3 of H₂SO₄, HClO₄, and CF₃SO₃H under air. It increased at higher temperature and decreased in pH. The apparent enthalpy of the dissolution reaction was ca. 25 kJ mol^?1, and the solubility was proportional to [H⁺] in these acids. The platinum solubility in oxygen was slightly higher than that in air. The detected dissolved Pt species was 4 valent. On the other hand, the solubility of platinum in nitrogen was much lower than the oxygen-containing atmosphere. Based on these results, the platinum solubility in an oxygen-containing atmosphere would mainly be the following acidic dissolution reaction: PtO₂ + H⁺ + H₂O = Pt(OH)₃⁺.     

Hydrothermal synthesis,structure and fluorescent property of a novel cuprous thiocyanate inorganic polymer directed by 1,5-bis(pyridinium) pentane cation

A novel cation-templated 3D cuprous thiocyanate polymer, {(bppt)[Cu₂(NCS)₄]}_n, bppt = 1,5-bis (pyridinium) pentane, was hydrothermally synthesized and structurally characterized. The compound crystallizes in monoclinic system, space group P2(1)/c with cell parameters of a = 10.1571(8) Å, b = 15.9785(13) Å, c = 15.3983(12) Å, V = 2407.4(3) Å³, Z = 4, D_c = 1.622 g cm^?3, F(0 0 0) = 1192, μ = 2.133 mm^?1, R₁ = 0.0551, wR₂ = 0.1246. In the polymeric architecture, Cu₂(NCS)₄ dimer is connected by NCS^? bridging ligand to constitute a infinite 3D framework with the organic cation bppt trapped in it. Photoluminescence investigation reveals that a slightly red shift of 27 nm for the complex takes place comparing with the organic cation.     

Quantitative characterization of the solid acidity of montmorillonite using combined FTIR and TPD based on the NH3 adsorption system

The complete parameters of montmorillonite solid acidity, namely amount, strength, and types of acidity, were determined and the properties of the acid sites after heating were proposed by combining the temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR) based on the NH₃ adsorption system. The total amount of montmorillonite acid sites was 1.15 mmol/g, which was higher than the value obtained by the Hammett indicator method because of the detection of solid acid sites in the montmorillonite interlayer space. These acid sites were composed of 1.00 mmol/g Brønsted and 0.15 mmol/g Lewis acid sites. The acidity of montmorillonite was primarily derived from the interlayer polarized water, Si–OH, H₃O⁺ adsorbed by negatively charged tetrahedral AlO₄, and unsaturated Al^3 + ions, all of which were attributed to the Brønsted acid sites with the exception of the unsaturated Al^3 + ions (Lewis acid sites). Heating led to an increase in the acid strength and the acid amount and altered the type of the partial acid sites. The interlayer polarized water provided more protons after heating at 120 °C and exhibited higher acid strength than that of raw montmorillonite. After heating at 400 °C, the interlayer polarized water acted as very strong acid sites. The H₃O⁺ adsorbed by tetrahedral AlO₄ was attributed to weak-strength acid sites and transformed into Si–O(H)–Al after dehydration, while displaying strong-strength acidity. The unsaturated Al^3 + ions showed medium-strength Lewis acidity, although a portion of these ions adsorbed water molecules and exhibited weak Brønsted acidity. After dehydroxylation at 600 °C, an abundance of unsaturated Al^3 + ions appeared and the amount of Lewis acid sites increased.     

Photoluminescence and structural characteristics of double tungstates A(M1−X PrX)W2O8 (A = Li,Cs, M = Al,Sc, La)

In this article, photoluminescence of Pr³⁺ ions in the double tungstate A(M_1?X Pr_X)W₂O₈ (A = Li, Cs, M = Al, Sc, La; 0.0 ≤ X ≤ 0.1) are characterised. By varying ion radius in A and M sites the crystal structure was modified and even in crystals with similar structural characteristics three distinctive types of luminescence are observed. When the substitution ions in both A and M sites are relatively small the host lattice exhibits luminescence dominantly. With the small A site ion (Li⁺) and the large M site ion (La³⁺, 1.03 Å) the Pr³⁺ ion exhibits prominent luminescence. With the very large A site ion (Cs⁺, 1.67 Å) and relatively small M site ion (Sc³⁺, 0.75 Å) the Pr³⁺ exhibits both the 4f²–4f5d excitation and the ³P_J manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr³⁺. PL characteristics are discussed with respect to crystal structural criteria.     

Methanation of carbon dioxide over mesoporous Ni–Fe–Al2O3 catalysts prepared by a coprecipitation method: Effect of precipitation agent

Mesoporous nickel (30 wt%)–iron (5 wt%)–alumina (denoted as NiFeAl–X) catalysts were prepared by a coprecipitation method with a variation of precipitation agent (X = (NH₄)₂CO₃, Na₂CO₃, NH₄OH, and NaOH), and they were applied to the methane production from CO₂ and H₂. Metal particle size of reduced NiFeAl–X catalysts decreased in the order of NiFeAl–NaOH > NiFeAl–NH₄OH > NiFeAl–Na₂CO₃ > NiFeAl–(NH₄)₂CO₃. In the methanation of CO₂, yield for CH₄ increased in the order of NiFeAl–NaOH < NiFeAl–NH₄OH < NiFeAl–Na₂CO₃ < NiFeAl–(NH₄)₂CO₃. This indicates that the catalytic performance in the methanation of CO₂ was strongly influenced by the identity of precipitation agent.