For the first time, the thermoelectric properties of cement/ single-walled carbon nanotubes (SWCNT) nanocomposites over 3, 7, 14 and 28 days of hydration are reported, while a thermoelectric generator device...

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The low-cost and self-assembled hybrid organic–inorganic semiconductors (HOIS) appear lately to be ideal for novel optoelectronic devices due to their inherent stable excitonic states, even at room temperature. 2D HOIS, superlattices of alternating layers of amines and of corner sharing lead halide octahedra, exhibit dielectrically confined bound excitonic states that are ideal for light emitting diodes (LEDs). HOIS-based deep blue LEDs are rarely reported, in which cases HOIS is usually deposited between electron and hole transport layers. Here, in the quest of suitable 2D HOIS for single layer LEDs (SLLEDs), we report on the synthesis and characterization of (4-fluoro-phenethylamine-H)2PbBr4 and its defect variations (DV), formed by nonstoichiometric synthesis. The DV thin films, deposited on conducting transparent anodes, allow for easy and simple fabrication of SLLEDs, using a Ga/In droplet cathode. The pristine iodine analogue readily provides green SLLEDs, while here only the DVs or pristine material’s mixtures with MoS2 nanosized platelets appear to function. It is suggested that the defects disrupt the long-range planar and insulating nature of the micrometric 2D HOIS crystalline platelets, thus, providing mechanisms for current flow, while the excitonic recombination half times are not affected by the defects. The organic 4-fluoro-phenethylamine enhances the EL functionality of the DVs compared to other amines because of the fluorine repulsion among the amine tails, leading to stable, weakly bound, organically decorated 2D inorganic sheets. It is expected that this work will provide incentive for utilizing HOIS DVs, being compatible with large scale synthesis.

A waste-originated one-part alkali-activated nanocomposite is introduced herein as a novel thermoelectric material. For this purpose, single-walled carbon nanotubes (SWCNTs) were utilized as nanoinclusions to create an electrically conductive network within the investigated alkali-activated construction material. Thermoelectric and microstructure characteristics of SWCNT-alkali-activated nanocomposites were assessed after 28 days. Nanocomposites with 1.0 wt.% SWCNTs exhibited a multifunctional behavior, a combination of structural load-bearing, electrical conductivity, and thermoelectric response. These nanocomposites (1.0 wt.%) achieved the highest thermoelectric performance in terms of power factor (PF), compared to the lower SWCNTs’ incorporations, namely 0.1 and 0.5 wt.%. The measured electrical conductivity (σ) and Seebeck coefficient (S) were 1660 S·m−1 and 15.8 µV·K−1, respectively, which led to a power factor of 0.414 μW·m−1·K−2. Consequently, they have been utilized as the building block of a thermoelectric generator (TEG) device, which demonstrated a maximum power output (Pout) of 0.695 µW, with a power density (PD) of 372 nW·m−2, upon exposure to a temperature gradient of 60 K. The presented SWCNT-alkali-activated nanocomposites could establish the pathway towards waste thermal energy harvesting and future sustainable civil engineering structures.

So far, there is no validated technology for characterizing the dispersion and morphology state of carbon nanotubes (CNTs) aqueous dispersions during sonication. Taking advantage of the conductive nature of CNTs, the main hypothesis of the current study is that Electrochemical Impedance Spectroscopy (EIS) is an appropriate technique for the in-situ monitoring and qualification of the dispersion state of CNTs in aqueous media. To confirm our hypothesis, we monitored the Impedance |Z| during the sonication process as a function of type CNTs/admixtures used for the preparation of the aqueous solutions and of crucial process parameters, such as the applied sonication power and duration (i.e., sonication energy). For dispersions above the percolation threshold, a drop of |Z| by approximately seven orders of magnitude was observed, followed by a linear reduction. The dramatic change in |Z| is regarded as an indication of the formation of a conductive path or destruction of an existing one during sonication and can be used to characterize the dispersion and morphology state of CNTs. The results of the EIS provide, straightforwardly and reliably, the required information to create an optimum dispersion protocol for conductive CNT suspensions. The produced dispersions are part of research focusing on the manufacturing of cement-based composite materials with advanced thermoelectric functionalities for energy harvesting. Such dispersions are not only limited to energy harvesting applications but also to applications where functionalities are introduced through the use of conductive-based suspensions.