Vol 14, No 7-8 (2019)

In last two decades, Half Heusler (HH) alloys proved themselves as a potential candidate for thermoelectric devices. This is not only due to their structural capability for demonstrating and integrating various new concepts to enhance the thermoelectric figure of merit (ZT) but also high thermal stability which is advantageous for thermoelectric devices. However, most of the efficient HH alloys consist of expensive elements which resist their commercial application. This encouraged the development of highly efficient Fe-based Full Heusler (FH) alloys which have almost similar advantages of HH alloys along with the economical benefit. The main challenge in Fe-based FH as efficient thermoelectric as HH alloys is the reduction of lattice thermal conductivity and optimization of carrier concentration. This could be done through the use of concepts like bulk nanostructuring/bulk nanocomposite and more recently introduced Panoscopic approach or all scale hierarchical architecturing engineering and band structure engineering. In this review, we firstly discussed about the current progress on Fe-based FH alloys along with the challenges in enhancing the figure of merits. Herein, we also discussed various approaches adopted in bulk as well as nanostructured FH alloys to circumvent the interdependency of parameters in achieving higher ZT. It ends with discussion of the future trends for Fe-based FH thermoelectric materials for waste heat recovery. Through this review, we not only explain the probability of finding efficient thermoelectric in Fe-based FH alloys but also give a blueprint for enhancing ZT in many other thermoelectric materials.

The search for effective and nontoxic sterilization drugs for plants against common phytopathogenic microorganisms is a major challenge to improve the biotechnology of plant clonal micropropagation. An analysis of 92 studies that describe the potential use of ZnO and TiO₂ nanoparticles as antimicrobial agents in biotechnology showed that their biological effects depend on several factors: photocatalytic activity, particle size, concentration, morphology, and surface modification. The mechanisms of toxicity, among which the primary one is generation of reactive oxygen species leading to oxidative stress, are also due to these factors. The data describing the direct influence of ZnO and TiO₂ nanoparticles on plants, however, are contradictory, which is probably because of the various particle shapes and sizes, their concentrations, and the species characteristics of the plants studied. These studies have confirmed that photocatalytically active ZnO and TiO₂ nanoparticles may be used as bactericidal and fungicidal drugs for sterilization of explants during clonal micropropagation of plants, while taking into account the possible phytotoxicity of these particles.

This article provides an overview of the thermoelectric efficiency data for various materials, such as nanostructured polycrystalline, nanocomposites with second-phase conductive nanoparticles, nanocomposites with dielectric nanoparticles, and nanocomposites with nanoparticles of a second thermoelectric. Attention is paid to the influence of nanostructuring and the creation of bismuth telluride (Bi₂Te₃) and antimony telluride (Sb₂Te₃) nanocomposites with graphite on the thermoelectric properties of specified materials.

In this study, porous network-like α-Fe₂O₃ and α/γ-Fe₂O₃ nanoparticles (NPs) were synthesized by auto-combustion method and their photocatalytic performance was evaluated using methylene blue (MB) as a dye model. Calcination of the synthesized nanoparticles resulted in α/γ-Fe₂O₃ heterophase magnetite material at 450°С and pure α-Fe₂O₃ at 700 and 800°С. The magnetic property of α/γ-Fe₂O₃ makes the photocatalyst to be easily collected from the photocatalytic system and increases its potential in industrial applications. The α/γ-Fe₂O₃ heterophase material showed a photocatalytic performance almost similar to that of the α-Fe₂O₃ NPs calcined at 800°С, but higher than that of the α-Fe₂O₃ NPs calcined at 700°С. The cliff-like band structure between α-Fe₂O₃ and γ-Fe₂O₃ reduced recombination of photoelectrons and photoholes, thereby improving photocatalytic performance of the α/γ-Fe₂O₃ heterophase material.

The main characteristics of memristive elements based on polythiophene made by Langmuir-Schaefer and spin-coating methods have been compared. The stability of the elements for more than 500 cycles of electric rewriting for both methods has been demonstrated. It has been shown that the elements made by spin-coating method have slower switching kinetics, which, presumably, is associated with relatively higher homogeneity of the film surface. This research may be useful for the development of polythiophene memristive devices with reproducible stable characteristics suitable for various applications: from memory elements to wearable and implantable electronics, and neuromorphic computing systems.

The use of gold nanoparticles (GNPs) as carriers for the decrease in the detection limit of a fluorescence polarization (FP) aptamer assay is proposed. The common FP assay is based on the use of polarized exciting light and changes in the polarization of emitted light by the fluorophore–analyte conjugate before and after its binding with a receptor of the target analyte. Aptamers’ application as receptors in such an assay is limited due to their low molecular weight and, consequently, insufficient influence on polarization of emitted light. This limitation can be overcome by the inclusion of aptamers in larger intermolecular complexes. In the present work, the advantages of GNPs as unified, stable, and simply modified carriers for aptamers are demonstrated. The FP aptamer assay is realized with the use of GNPs with average diameter of 8.7 nm and ochratoxin A (OTA) as the target analyte. Finally, the assay is tested for OTA control in spiked white wine. The reached limit of detection is 2.3 µg/kg, which is 25-fold lower as compared to native aptamer. The time of the assay is 15 min. The universality of the proposed approach makes it possible to use aptamers for FP assays of various low-molecular-weight substances.