Bioinspired synthesis of SnO crosses as backbone in artificial sponges.

The distinct electronic properties, including p-type semiconducting and a wide optical band gap, renders SnO suitable for applications such as microelectronic devices, gas sensors and electrodes. However, the synthesis of SnO is rather challenging due to the instability of the oxide, which is usually obtained as a by-product of SnO2 fabrication. In this work, we developed a bioinspired synthesis, based on a hydrothermal approach, for the direct production of SnO nanoparticles. The amount of mineralizer, inducing the precipitation, was identified, which supports a template-free formation of the nanosized SnO particles at low temperature and mild chemical conditions. Moreover, the SnO nanoparticles exhibit a shape of unique three-dimensional crosses similar to the calcite crosses present in the calcareous sponges. We demonstrated that SnO crosses are evenly distributed and embedded in an organic scaffold by an ice-templating approach, in this way closely mimicking the structure of calcareous sponges. Such scaffolds, reinforced by an active material, here SnO, could be used as filters, sensors or electrodes, where a high surface area and good accessibility are essential. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 2)'.

Peptide Controlled Shaping of Biomineralized Tin(II) Oxide into Flower-Like Particles.

The size and morphology of metal oxide particles have a large impact on the physicochemical properties of these materials, e.g., the aspect ratio of particles affects their catalytic activity. Bioinspired synthesis routes give the opportunity to control precisely the structure and aspect ratio of the metal oxide particles by bioorganic molecules, such as peptides. This study focusses on the identification of tin(II) oxide (tin monoxide, SnO) binding peptides, and their effect on the synthesis of crystalline SnO microstructures. The phage display technique was used to identify the 7-mer peptide SnBP01 (LPPWKLK), which shows a high binding affinity towards crystalline SnO. It was found that the derivatives of the SnBP01 peptide, varying in peptide length and thus in their interaction, significantly affect the aspect ratio and the size dimension of mineralized SnO particles, resulting in flower-like morphology. Furthermore, the important role of the N-terminal leucine residue in the peptide for the strong organic⁻inorganic interaction was revealed by FTIR investigations. This bioinspired approach shows a facile procedure for the detailed investigation of peptide-to-metal oxide interactions, as well as an easy method for the controlled synthesis of tin(II) oxide particles with different morphologies.

Genetically Induced In Situ-Poling for Piezo-Active Biohybrid Nanowires.

Polycrystalline piezo-active materials only exhibit a high macroscopic piezoresponse if they consist of particles with oriented crystal directions and aligned intrinsic dipole moments. For ferroelectric materials, the postsynthesis alignment of the dipoles is generally achieved by electric poling procedures. However, there are numerous technically interesting non-ferroelectric piezo-active materials like zinc oxide (ZnO). These materials demand the alignment of their intrinsic dipoles during the fabrication process. Therefore, in situ-poling techniques have to be developed. This study utilizes genetically modified M13 phage templates for the generation of force fields, which directly control the ZnO dipole poling. By genetic modification of M13 phage template, the piezoelectric response of the ZnO/M13 phage hybrid nanowire is doubled compared to the hybrid nanowire based on unmodified M13 wild type (wt) phage templates. Thus, the formation of piezo-active domains consisting of oriented ZnO nanocrystals is directly induced by the genetic modification. By the combination of the fiber-like structure of individual M13 phages with the bioenhanced electromechanical properties of ZnO, hybrid nanowires with a length of ≈1.1 µm and a thickness of ≈63.5 nm are fabricated with a high piezoelectric coefficient of up to d33 = 7.8 pm V-1 for genetically modified M13 phage templates.

Ultrahigh Damping Capacities in Lightweight Structural Materials.

The demand to outperform current technologies pushes scientists to develop novel strategies, which enable the fabrication of materials with exceptional properties. Along this line, lightweight structural materials are of great interest due to their versatile applicability as sensors, catalysts, battery electrodes, and acoustic or mechanical dampers. Here, we report a strategy to design ultralight (ρ = 3 mg/cm3) and hierarchically structured ceramic scaffolds of macroscopic size. Such scaffolds exhibit mechanical reversibility comparable to that of microscopic metamaterials, leading to a macroscopically remarkable dynamic mechanical performance. Upon mechanical loading, these scaffolds show a deformation mechanism similar to polyurethane foams, and this resilience yields ultrahigh damping capacities, tan δ, of up to 0.47.

Tailoring the structure and thermoelectric properties of BaTiO3via Eu2+ substitution.

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 (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 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.