CuCo2_{2}S4_{4} Deposited on TiO2_{2}: Controlling the pH Value Boosts Photocatalytic Hydrogen Evolution

Metallic spinel-type CuCo$_{2}$S$_{4}$ nanoparticles were deposited on nanocrystalline TiO$_{2}$ (P25®), forming heterostructure nanocomposites. The nanocomposites were characterized in detail by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), nitrogen sorption (BET) and UV/Vis spectroscopy. Variation of the CuCo$_{2}$S$_{4}$:TiO$_{2}$ ratio to an optimum value generated a catalyst which shows a very high photocatalytic H$_{2}$ production rate at neutral pH of 32.3 µmol/h (0.72 mLh$^{–1}$), which is much larger than for pure TiO$_{2}$ (traces of H$_{2}$). The catalyst exhibits an extraordinary long-term stability and after 70 h irradiation time about 2 mmol H$_{2}$ were generated. An increased light absorption and an efficient charge separation for the sample with the optimal CuCo$_{2}$S$_{4}$:TiO$_{2}$ ratio is most probably responsible for the high catalytic activity

Tuning ZnO Sensors Reactivity toward Volatile Organic Compounds via Ag Doping and Nanoparticle Functionalization

Nanomaterials for highly selective and sensitive sensors toward specific gas molecules of volatile organic compounds (VOCs) are most important in developing new-generation of detector devices, for example, for biomarkers of diseases as well as for continuous air quality monitoring. Here, we present an innovative preparation approach for engineering sensors, which allow for full control of the dopant concentrations and the nanoparticles functionalization of columnar material surfaces. The main outcome of this powerful design concept lies in fine-tuning the reactivity of the sensor surfaces toward the VOCs of interest. First, nanocolumnar and well-distributed Ag-doped zinc oxide (ZnO:Ag) thin films are synthesized from chemical solution, and, at a second stage, noble nanoparticles of the required size are deposited using a gas aggregation source, ensuring that no percolating paths are formed between them. Typical samples that were investigated are Ag-doped and Ag nanoparticle-functionalized ZnO:Ag nanocolumnar films. The highest responses to VOCs, in particular to (CH3)2CHOH, were obtained at a low operating temperature (250 °C) for the samples synergistically enhanced with dopants and nanoparticles simultaneously. In addition, the response times, particularly the recovery times, are greatly reduced for the fully modified nanocolumnar thin films for a wide range of operating temperatures. The adsorption of propanol, acetone, methane, and hydrogen at various surface sites of the Ag-doped Ag8/ZnO(0001) surface has been examined with the density functional theory (DFT) calculations to understand the preference for organic compounds and to confirm experimental results. The response of the synergistically enhanced sensors to gas molecules containing certain functional groups is in excellent agreement with density functional theory calculations performed in this work too. This new fabrication strategy can underpin the next generation of advanced materials for gas sensing applications and prevent VOC levels that are hazardous to human health and can cause environmental damages

Strategies for the transition to CAD based 3D design education

In the proposed paper, our experience in managing the transition from traditional design education to CAD based design as a case study for comparison is documented. Use of CAD technologies on both undergraduate and Master level is also discussed

Nanostructure investigation of the layered ternary compound Ni3–xSn1–yTe2

The structure of Ni3-xSn1-yTe2 is characterized by layered structural motifs related to an average NiAs/Ni2In-type. Order/disorder phenomena were analyzed via a detailed nanostructure investigation including electron diffraction and high resolution transmission electron microscopy (HRTEM) in conjunction with image simulation. Dependent on the stoichiometry, commensurate and incommensurate satellite reflections with respect to the parent NiAs structure were observed in Fourier transform and electron diffraction pattern as a result of occupational modulation of Te and Sn atoms. For the commensurate case a triplication of the c-lattice parameter is evident as a result of Sn-Te-Te stacking. Further, HRTEM micrographs indicate additional ordering phenomena along the c* direction depending on Ni/vacancy ordering which was rationalized by an alternating filling of van der Waals gaps with Ni. Also morphological defects in bright field images were observed. HRTEM investigations prove that these morphological defects are of structural nature, i.e. they are based on domains shifted relative to each other (antiphase boundaries)

Does a Low Amount of Substituents Improve the Thermoelectric Properties of Cr2-xMxS3 (M = Ti, V, Sn)?

The effects of low-level partial cation substitution in Cr2−xMxS3 with M = Ti, V or Sn and x = 0.05 and 0.1 have been investigated regarding the long- and short-range crystal structures and thermoelectric properties. All substituted compounds crystallized in the equilibrium phase of Cr2S3, adopting the space group R. Electron beam irradiation led to a phase transformation from space group R to P1c with a subsequent appearance of diffuse scattering, indicating short-range ordering of cations in the partially occupied cation layers. Substitution of Cr by V led to a reduction in electrical conductivity and subsequently to a lower thermoelectric performance in comparison to the pristine material. In contrast, substitution with Ti yielded an improvement of the performance due to a higher electrical conductivity and a reasonably high Seebeck coefficient. Both Sn-substituted compounds contained only traces of Sn. Surprisingly, a significant improvement of the electrical conductivities could be observed in comparison to the pristine material as well as the other Cr2−xMxS3 materials

Temperature and magnetic field dependent raman study of electron-phonon interactions in thin films of bi2se3 and bi2te3 nanoflakes

We have investigated two-dimensional nanostructures of the topological insulators Bi2Se3 and Bi2Te3 by means of temperature and magnetic field dependent Raman spectroscopy. The surface contribution of our samples was increased by using thin films of dropcasted nanoflakes with the aim of enhancing their topological properties. Raman spectroscopy provides a contact-free method to investigate the behavior of topological properties with temperature and magnetic fields at lower dimensions. The temperature dependent Raman study reveals anharmonic phonon behavior for Bi2Te3 indicative of a two-phonon relaxation mechanism in this material. Contrary to this, Bi2Se3 shows clear deviations from a two-phonon anharmonic decay model at temperatures below 120 K exhibiting a hardening and broadening, especially of the A1g2 mode. Similarly, the magnetic field dependent self-energy effects are only observed for the A1g2 mode of Bi2Se3, showing a broadening and hardening with increasing field. We interpret our results in terms of corrections to the phonon self-energy for Bi2Se3 at temperatures below 120 K and magnetic fields above 4 T due to electron-hole pair excitations associated with the conducting surface states. The phonon renormalization with increasing magnetic field is explained by a gap opening in the Dirac cone that enables phonon coupling to the changing electric susceptibility

Surface functionalization of ZnO:Ag columnar thin films with AgAu and AgPt bimetallic alloy nanoparticles as an efficient pathway for highly sensitive gas discrimination and early hazard detection in batteries

For a fast and reliable monitoring of hazardous environments, the discrimination and detection of volatile organic compounds (VOCs) in the low ppm range is highly demanded and requires the development of new chemical sensors. We report herein, a novel approach to tailor the selectivity of nanocomposite thin film sensors by investigating systematically the effect of surface decoration of Ag-doped ZnO (ZnO:Ag) columnar thin films. We have used AgPt and AgAu noble bimetallic alloy nanoparticles (NPs) to decorate the surfaces of ZnO:Ag and measured the resulting gas sensing properties towards VOC vapors and hydrogen gas. The gas response of the nanocomposite containing AgAu NPs to 100 ppm of ethanol, acetone, n-butanol, 2-propanol and methanol vapors was increased on average by a factor of 4 compared to the pristine ZnO:Ag columnar films. However, decoration with AgPt NPs led to a considerable reduction of the gas response to all VOC vapors and an increase of the response to H2 by roughly one order of magnitude, indicating a possibile route to tailor the selectivity by surface decoration. For this reason, the reported NPs decorated ZnO:Ag thin film sensors are suitable for the detection of H2 in Li-ion batteries, which is an early indication of the thermal runaway that leads to complete battery failure and possible explosion. To understand the impact of NP surface decoration on the gas sensing properties of ZnO:Ag thin films, we employed density functional theory calculations with on-site Coulomb corrections and long-range dispersion interactions (DFT+U−D3-(BJ)) and investigated the adsorption of various VOC molecules and hydrogen onto the Ag-doped and NP decorated (101 @#x0305;0) surface of zinc oxide ZnO. The calculated surface free energies indicate that Ag5Au5/ZnO(101 @#x0305;0):Ag is the most favourable system for the detection of VOCs, which is also the most reactive towards them based on its work function. Our calculated adsorption energies show that Ag9Pt/ZnO(101 @#x0305;0):Ag has the largest preference for H2 and the lowest preference for the organic asdorbates, which is in line with the high selectivity of AgPt/ZnO:Ag sensors towards the former molecule observed in our experiments