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Half-Heusler compounds with a valence electron count of 18, including ZrNiSn, ZrCoSb, and NbFeSb, are good thermoelectric materials owing to favorable electronic structures. Previous computational studies had predicted a high electrical power factor in another half-Heusler compound NbCoSn, but it has not been extensively investigated experimentally. Herein, the synthesis, structural characterization, and thermoelectric properties of the heavy-element Pt-substituted NbCoSn compounds are reported. Pt is found to be an effective substitute enabling the optimization of electrical power factor and simultaneously leading to a strong point defect scattering of phonons and the suppression of lattice thermal conductivity. Post-annealing significantly improves the carrier mobility, which is ascribed to the decreased grain boundary scattering of electrons. As a result, a maximum power factor of ∼3.4 mW m−1 K−2 is obtained at 600 K. In conjunction with the reduced lattice thermal conductivity, a maximum figure of merit zT of ∼0.6 is achieved at 773 K for the post-annealed NbCo0.95Pt0.05Sn, an increase of 100% compared to that of NbCoSn. This work highlights the important roles that the dopant element and microstructure play in the thermoelectric properties of half-Heusler compounds. [ABSTRACT FROM AUTHOR]

The development of thermoelectrics for high-temperature applications imposes several essential requirements on the material properties. In some energy-conversion scenarios, the cost and thermal stability requirements may dominate over efficiency issues, making abundant, high-temperature-stable and low-toxic oxides attractive alternative thermoelectric materials. As compared to "traditional" thermoelectrics, oxides possess unique redox flexibility and defect chemistry, which can be precisely tuned by external temperature and oxygen partial pressure conditions. This work aims to demonstrate how, by redox-sensitive substitutions, the thermoelectric properties of oxides can be tuned and enhanced. The proposed strategy is exemplified by considering molybdenum-containing strontium titanate within nominally single-substituted and nanocomposite concepts. The involved materials design allows us to proceed from an in-depth understanding of the redox-promoted effects to the demonstration of the enhanced thermoelectric performance attained by redox engineering. Synergistic enhancement of the Seebeck coefficient and suppression of the thermal conductivity due to combined carrier filtering effects and efficient phonon scattering at redox-induced interfaces provided up to 25% increase in the thermoelectric performance. The results demonstrate extraordinary flexibility of the perovskite lattice towards retaining a rich combination of the molybdenum redox states and shifting their ratio by tuning the A-site stoichiometry, and the prospects for developing new materials combining thermoelectric and (electro)catalytic functionalities. [ABSTRACT FROM AUTHOR]

A MoS2 quantum dot/reduced graphene oxide (MoS2 QD/rGO) nanocomposite has been synthesized by a simple hydrothermal approach. For the first time, the MoS2 QD/rGO composite is used as a highly sensitive and stable surface enhanced Raman scattering (SERS) substrate to detect trace amounts of molecular species. The lowest detection limit (LOD) for rhodamine 6G (R6G) is as low as 1 × 10−9 M with the maximum enhancement factor (EF) of up to 1.20 × 107, which is the best among the non-noble metal SERS materials. For practical applications, the MoS2 QD/rGO SERS substrate is also used to detect methylene blue (MB) in deionized water and river water. The LOD (1 × 10−8 M) is obtained in river water, which demonstrates the high feasibility for multi-molecule detection and vast potential ability for the detection of chemical and biological molecules. The enhancement mechanism of the MoS2 QD/rGO SERS substrate is studied, and the large enhancement of the SERS signal is due to the charge transfer (CT) state formed at the interface of the 1T-phase MoS2 QDs with small size and ultrathin slices and organic molecules. The chemical enhancement of rGO also contributes to the SERS enhancement. The study paves a new way for designing a novel MoS2 QD-based SERS substrate. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) has a very broad and versatile range of applications provided by its high abundance and optical and electrical properties, which can be further tuned by donor substitution. Al-doped ZnO is probably the most thoroughly investigated material with regard to thermoelectric properties. Fairly reasonable electrical properties of donor-doped zinc oxide are usually combined with high thermal conductivity limiting potential applications. Here we report a new self-forming nanocomposite concept for ZnO-based thermoelectrics, where a controllable interplay between the exsolution of the nanophases and modification of the host matrix suppresses the thermal transport while imparting enhanced electrical performance. The thermoelectric performance of the best-obtained composite, described by the dimensionless figure-of-merit ZT, at 920–1200 K is almost twice that of the pure matrix composition and reaches up to 0.11. The proposed approach invokes controlled interactions between composite components as a novel tool for decoupling the electrical and thermal transport parameters and shows clear prospects for an implementation in other thermoelectric oxide systems. The results indicate that the proposed concept may also constitute a promising pathway to achieve stable electrical performance at high temperatures, which currently represents one of the major challenges towards achieving ZnO-based thermoelectrics. [ABSTRACT FROM AUTHOR]

A 2D layered structure {[Co4(TC4A)Cl](L)2][(CH3CH2)4N]}n (+solvent)(1) has been solvothermally synthesized by assembly of Co4-TC4A (H4TC4A = p-tert-butylthiacalix[4]arene) subunits and L (H2L = 4-(1H-tetrazol-5-yl)benzoic acid) ligands. The layers arranged in an edge-to-edge (AAAA) manner, which represented the only example of 2D porous coordination polymers (PCPs) with 1D uniform channels of metal–thiacalix[4]arene. The activated PCP 1 exhibited high selectivity for C3H8/C2H6, C3H6/C2H4, and C3H8/C2H4, which makes it a competitive porous material for C3/C2 alkane and/or olefin separations. Frequency response investigations for C3H8 and C2H6 indicated that the 1D channels and inter-layer voids of the activated crystalline samples are primarily responsible for the observed gas adsorption and separation performances. [ABSTRACT FROM AUTHOR]

A series of Cd(ii) compounds, abbreviated as {[Cd·L·(BTC)0.5·H2O]·(H2O)3}n (1), [Cd5·(PO4)2·(HPO4)2·(H2O)4]n (2) and {[Cd2.5·L·(BTC)1.5·(H2O)1.5·(DMF)]·(H2O)2.35}n (3), were obtained by using a zwitterionic ligand (1,1′,1′′-(2,4,6-trimethybenzene-1,3,5-triyl)-tris(methylene)tris(4-carboxypyridinium) tribromide, H3LBr3) and an aromatic secondary ligand (H4BTC). Structure determination confirmed that compounds 1 and 3 possess the structure of 1D and 2D metal–organic frameworks respectively while compound 2 belongs to a novel inorganic crystal, which may be produced by introducing different categories and concentrations of inorganic acids. In addition to reasonable thermal stability (up to 300 °C), the titled Cd(ii) compounds exhibited different photoluminescence emissions in the solid state resulting from coordination environments and crystal structures. Moreover, compound 3 also exhibited a ferroelectric behavior with a saturated spontaneous polarization (Ps) of 0.20 μC cm−2, indicating that compound 3 is a potential ferroelectric material at room temperature. [ABSTRACT FROM AUTHOR]

Inhibition of amyloid β (Aβ) aggregation holds considerable promise as a therapeutic strategy for Alzheimer's disease (AD). However, successful inhibition is hard to achieve due to the blood–brain barrier (BBB) and the non-selective distribution of drugs. Herein, two targeting peptides (LPFFD and TGN) were conjugated to selenium nanoparticles (SeNPs). We found that the concentration ratio of LPFFD to TGN taken as 1 : 1 could form the most effective dual-functional SeNPs (L1T1–SeNPs) for inhibiting Aβ aggregation and crossing the BBB. L1T1–SeNPs can cross the BBB and have a strong affinity toward Aβ species, and thus, they can efficiently suppress extracellular Aβ fibrillation by disrupting hydrophobic and electrostatic interactions that are important for Aβ40 nucleation. Also, L1T1–SeNPs can suppress the Aβ40 fiber mediated generation of reactive oxygen species (ROS) and their corresponding neurotoxicity in PC12 cells. In addition, L1T1–SeNPs exert synergistic effects on the inhibition of Aβ aggregation and cross the BBB efficiently. Collectively, these results demonstrate that dual-functional SeNPs might be a valuable targeting system for inhibiting Aβ aggregation. [ABSTRACT FROM AUTHOR]

Doping (or substitution)-induced modification of the electronic structure to increase the electronic density of states (eDOS) near the Fermi level is considered as an effective strategy to enhance the Seebeck coefficient, and may consequently boost the thermoelectric performance. Through density-functional theory calculations of Mn-substituted TiFe2−xMnxSn compounds, we demonstrate that the d-states of the substituted Mn atoms induce a strong resonant level near the Fermi energy. Our experimental results are in good agreement with the calculations. They show that Mn substitution results in a large increase of the Seebeck coefficient, arising from an enhanced eDOS in Heusler compounds. The results prove that a proper substitution position and element selection can increase the eDOS, leading to a higher Seebeck coefficient and thermoelectric performance of ecofriendly materials. [ABSTRACT FROM AUTHOR]

A series of Ba1−xEuxTiO3−δ (0.1 ≤x≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu2+ substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 Å (equal to ∼5 unit cells) deviations from the cubic structure model (Pm3̅m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3−δ. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along 〈110〉 of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1−xEuxTiO3−δ. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium–europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K ＜ T ＜ 1123 K) the conduction mechanism of Ba1−xEuxTiO3−δ (0.1 ≤x≤ 0.9) is a polaron hopping when 0 ＜ x≤ 0.6 and is a thermally activated process when 0.6 ＜ x ＜ 1. Besides, the thermal conductivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3−δ showed a ZT value of 0.24 at 1123 K. [ABSTRACT FROM AUTHOR]

Using an assembly method, dinuclear CoCo and CoFe complexes supported by a bdt ligand, [Cp*Co(μ–η2:η2-bdt)(μ-I)CoCp*][PF6] (1[PF6], Cp* = η5-C5Me5, bdt = benzene-1,2-dithiolate), and [Cp*Co(μ–η2:η4-bdt)FeCp′][PF6] (3[PF6], Cp′ = η5-C5Me4H) were synthesized in high yields. Upon chemical reduction with CoCp2, complexes 1[PF6] and 3[PF6] were converted to [Cp*Co(μ-η2:η2-bdt)CoCp*] (2) and [Cp*Co(μ–η2:η4-bdt)FeCp′][PF6] (3), respectively. Treatment of 2 with HBF4 resulted in the protonation of two cobalt centers to generate a hydride bridged complex, [Cp*Co(μ–η2:η2-bdt)(μ-H)CoCp*][BF4] (4[BF4]), which was identified by spectroscopy and X-ray crystallography. When treating 3 with HBF4, a one-electron oxidation occurred to afford complex 3[BF4] along with the formation of H2. Importantly, heterodinuclear complex 3[PF6] and hydride bridged complex 4[BF4] can serve as effective catalysts to promote proton reduction for hydrogen evolution, as evidenced by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

A 2D layered structure {[Co4(TC4A)Cl](L)2][(CH3CH2)4N]}n (+solvent)(1) has been solvothermally synthesized by assembly of Co4-TC4A (H4TC4A = p-tert-butylthiacalix[4]arene) subunits and L (H2L = 4-(1H-tetrazol-5-yl)benzoic acid) ligands. The layers arranged in an edge-to-edge (AAAA) manner, which represented the only example of 2D porous coordination polymers (PCPs) with 1D uniform channels of metal-thiacalix[4]arene. The activated PCP 1 exhibited high selectivity for C3H8/C2H6, C3H6/C2H4, and C3H8/C2H4, which makes it a competitive porous material for C3/C2 alkane and/or olefin separations. Frequency response investigations for C3H8 and C2H6 indicated that the 1D channels and inter-layer voids of the activated crystalline samples are primarily responsible for the observed gas adsorption and separation performances.

Doping (or substitution)-induced modification of the electronic structure to increase the electronic density of states (eDOS) near the Fermi level is considered as an effective strategy to enhance the Seebeck coefficient, and may consequently boost the thermoelectric performance. Through density-functional theory calculations of Mn-substituted TiFe 2-x Mn x Sn compounds, we demonstrate that the d-states of the substituted Mn atoms induce a strong resonant level near the Fermi energy. Our experimental results are in good agreement with the calculations. They show that Mn substitution results in a large increase of the Seebeck coefficient, arising from an enhanced eDOS in Heusler compounds. The results prove that a proper substitution position and element selection can increase the eDOS, leading to a higher Seebeck coefficient and thermoelectric performance of ecofriendly materials.

A series of Ba 1-x Eu x TiO 3-δ (0.1 ≤ x ≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu 2+ substitution on the BaTiO 3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 Å (equal to ∼5 unit cells) deviations from the cubic structure model (Pm3[combining macron]m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO 3-δ . The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along 〈110〉 of the parent unit cell as observed for BaTiO 3 . Density functional calculations delivered an insight into the electronic structure of Ba 1-x Eu x TiO 3-δ . From the obtained density of states a significant reduction of the band gap by the presence of filled Eu 2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium-europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu 2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K < T < 1123 K) the conduction mechanism of Ba 1-x Eu x TiO 3-δ (0.1 ≤ x ≤ 0.9) is a polaron hopping when 0 < x ≤ 0.6 and is a thermally activated process when 0.6 < x < 1. Besides, the thermal conductivity increases with increasing Eu 2+ concentration. Due to a remarkable improvement of the power factor, Ba 0.1 Eu 0.9 TiO 3-δ showed a ZT value of 0.24 at 1123 K.