PbS shares several features with the other lead chalcogenides PbX (X: Te, Se), which are good thermoelectric materials. PbS has a potential advantage in that it is quite earth abundant and inexpensive. In this work we tune the transport properties in n-type, single-phase polycrystalline PbS 1−x Cl x (x ≤ 0.008) with different carrier densities. Lead chloride provides a nearly 100% effi cient doping control up to 1.2 × 10 20 cm − 3 . The maximum zT achieved at 850 K is 0.7 with a predicted zT ∼ 1 at 1000 K. This is about twice as high as what was previously reported ( ∼ 0.4) for binary PbS. Compared with the other lead chalcogenides the higher effective mass and higher lattice thermal conductivity makes binary PbS an inferior thermoelectric material. However this study also predicts greater potential of zT improvement in PbS by material engineering such as alloying or nanostructuring compared to PbSe or PbTe. Considering their abundance and low cost, PbS based materials are quite competitive among the lead chalcogenides for thermoelectric applications. 489

Inspired by the promising thermoelectric properties in the Zintl compounds Ca 3 AlSb 3 and Ca 5 Al 2 Sb 6 , we investigate here the closely related compound Sr 3 GaSb 3 . Although the crystal structure of Sr 3 GaSb 3 contains infinite chains of corner-linked tetrahedra, in common with Ca 3 AlSb 3 and Ca 5 Al 2 Sb 6 , it has twice as many atoms per unit cell (N ¼ 56). This contributes to the exceptionally low lattice thermal conductivity (k L ¼ 0.45 W m À1 K À1 at 1000 K) observed in Sr 3 GaSb 3 samples synthesized for this study by ball milling followed by hot pressing. High temperature transport measurements reveal that Sr 3 GaSb 3 is a nondegenerate semiconductor (consistent with Zintl charge-counting conventions) with relatively high p-type electronic mobility ($30 cm 2 V À1 s À1 at 300 K). Density functional calculations yield a band gap of $0.75 eV and predict a light valence band edge ($0.5 m e ), in qualitative agreement with experiment. To rationally optimize the electronic transport properties of Sr 3 GaSb 3 in accordance with a single band model, doping with Zn 2+ on the Ga 3+ site was used to increase the p-type carrier concentration. In optimally hole-doped Sr 3 Ga 1Àx Zn x Sb 3 (x ¼ 0.0 to 0.1), we demonstrate a maximum figure of merit of greater than 0.9 at 1000 K.

Photosynthesis is an efficient mechanism for converting solar light energy into chemical energy. We report on a strategy for the aerobic photocyanation of tertiary amines with visible and near-infrared (NIR) light. Panchromatic sensitization was achieved by functionalizing TiO 2 with a 2methylisoquinolinium chromophore, which captures essential features of the extended π-system of 2,7-diazapyrenium (DAP 2+ ) dications or graphitic carbon nitride. Two phenolic hydroxy groups make this ligand highly redoxactive and allow for efficient surface binding and enhanced electron transfer to the TiO 2 surface. Non-innocent ligands have energetically accessible levels that allow redox reactions to change their charge state. Thus, the conduction band is sufficiently high to allow photochemical reduction of molecular oxygen, even with NIR light. The catalytic performance (up to 90% chemical yield for NIR excitation) of this panchromatic photocatalyst is superior to that of all photocatalysts known thus far, enabling oxidative cyanation reactions to the corresponding α-cyanated amines to proceed with high efficiency. The discovery that the surface-binding of redox-active ligands exhibits enhanced light-harvesting in the red and NIR region opens up the way to improve the overall yields in heterogeneous photocatalytic reactions. Thus, this class of functionalized semiconductors provides the basis for the design of new photocatalysts containing non-innocent donor ligands. This should increase the molar extinction coefficient, permitting a reduction of nanoparticle catalyst concentration and an increase of the chemical yields in photocatalytic reactions.

Localized surface plasmon resonance properties in unconventional materials like metal oxides or chalcogenide semiconductors have been studied for use in signal detection and analysis in biomedicine and photocatalysis. We devised...

Polycrystalline samples of Ca 3 Al 1Àx Zn x Sb 3 , with x ¼ 0.00, 0.01, 0.02, and 0.05 were synthesized via a combined ball milling and hot pressing technique and the influence of zinc as a dopant on the thermoelectric properties was studied and compared to the previously reported transport properties of sodium-doped Ca 3 AlSb 3 . Consistent with the transport in the sodium-doped material, substitution of aluminum with zinc leads to p-type carrier conduction that can be sufficiently explained with a single parabolic band model. It is found that, while exhibiting higher carrier mobilities, the doping effectiveness of zinc is lower than that of sodium and the optimum carrier concentration for a maximum figure of merit zT is not reached in this study. We find that the grain size influences the carrier mobility, carrier concentration, and lattice thermal conductivity, leading to improved properties at intermediate temperatures, and highlighting a possible approach for improved figures of merit in this class of materials.

Metal oxide based polymer nanocomposites find diverse applications as functional materials, and in particular thiol-ene/TiO2 nanocomposites are promising candidates for dental restorative materials. The important mechanical and thermal properties of the nanocomposites, however, are still not well understood. In this study, the elastic modulus and thermal conductivity of thiol-ene/TiO2 nanocomposite thin films with varying weight fractions of TiO2 nanoparticles are investigated by using Brillouin light scattering spectroscopy and 3ω measurements, respectively. As the TiO2 weight fraction increases from 0 to 90%, the effective elastic longitudinal modulus of the films increases from 6.2 to 37.5 GPa, and the effective thermal conductivity from 0.04 to 0.76 W/m K. The former increase could be attributed to the covalent cross-linking of the nanocomposite constituents. The latter one could be ascribed to the addition of high thermal conductivity TiO2 nanoparticles and the formation of possible conductive channels at high TiO2 weight fractions. The linear dependence of the thermal conductivity on the sound velocity, reported for amorphous polymers, is not observed in the present nanocomposite system.

Many natural materials are complex composites whose mechanical properties are often outstanding considering the weak constituents from which they are assembled. Nacre, made of inorganic (CaCO3 ) and organic constituents, is a textbook example because of its strength and toughness, which are related to its hierarchical structure and its well-defined organic-inorganic interface. Emulating the construction principles of nacre using simple inorganic materials and polymers is essential for understanding how chemical composition and structure determine biomaterial functions. A hard multilayered nanocomposite is assembled based on alternating layers of TiO2 nanoparticles and a 3-hydroxy-tyramine (DOPA) substituted polymer (DOPA-polymer), strongly cemented together by chelation through infiltration of the polymer into the TiO2 mesocrystal. With a Young's modulus of 17.5 ± 2.5 GPa and a hardness of 1.1 ± 0.3 GPa the resulting material exhibits high resistance against elastic as well as plastic deformation. A key feature leading to the high strength is the strong adhesion of the DOPA-polymer to the TiO2 nanoparticles.

Numerous catechol-containing polymers, including biodegradable polymers, are currently heavily discussed for modern biomaterials. However, there is no report combining poly(phosphoester)s (PPEs) with catechols. Adhesive PPEs have been prepared via acyclic diene metathesis polymerization. A novel acetal-protected catechol phosphate monomer was homo- and copolymerized with phosphoester comonomers with molecular weights up to 42000 g/mol. Quantitative release of the catechols was achieved by careful hydrolysis of the acetal groups without backbone degradation. Degradation of the PPEs under basic conditions revealed complete and statistical degradation of the phosphotri- to phosphodiesters. In addition, a phosphodiester monomer with an adhesive P-OH group and no protective group chemistry was used to compare the binding to metal oxides with the multicatechol-PPEs. All PPEs can stabilize magnetite particles (NPs) in polar solvents, for example, methanol, due to the binding of the phosphoester groups in the backbone to the particles. ITC measurements reveal that multicatechol PPEs exhibit a higher binding affinity to magnetite NPs compared to PPEs bearing phosphodi- or phosphotriesters as repeating units. In addition, the catechol-containing PPEs were used to generate organo- and hydrogels by oxidative cross-linking, due to cohesive properties of catechol groups. This unique combination of two natural adhesive motives, catechols and phosphates, will allow the design of novel future gels for tissue engineering applications or novel degradable adhesives.