Search

Electrical conductors based on carbons have recently attracted a growing interest due to the prospect of replacing metals. Electrical conductors without metals could represent not only an alternative for traditional wiring, but also a step forward in the progress and advancing of technology. This result can be achieved by combining high electrical conductivity with other properties, that are dexterity, light weight, environmental stability, high strength and flexibility. As the best mechanical properties, high electrical/thermal conductivity of the assembled fibers are all generally associated with low concentration of defects in the fiber backbone and in the individual carbon “building blocks”, a special attention is paid to an empirical relationship between morphology/structure/composition and the electrical properties. In this review, starting from the beginning, from the late 19th century, when the carbon filaments became the lights for urban streets, some of the recent developments in the field of “all-carbon” electrical conductors are discussed. Such conductors can be obtained by assembling nanoscale carbons (i.e., carbon nanotubes, graphene) into macroscopic fibers, yarns and ropes (hereafter fibers). In this perspective, the role played by the chemistry in particular by means of the molecular-level control and doping, is emphasized. This contribution elucidates most recent results in the field, and envisages new potential applications.

Functional materials are promising candidates for application in structural health monitoring/self-healing composites, wearable systems (smart textiles), robotics, and next-generation electronics. Any improvement in these topics would be of great relevance to industry, environment, and global needs for energy sustainability. Taking into consideration all these aspects, low-cost fabrication of electrical functionalities on the outer surface of carbon-nanotube/polypropylene composites is presented in this paper. Electrical-responsive regions and conductive tracks, made of an accumulation layer of carbon nanotubes without the use of metals, have been obtained by the laser irradiation process, leading to confined polymer melting/vaporization with consequent local increase of the nanotube concentration over the electrical percolation threshold. Interestingly, by combining different investigation methods, including thermogravimetric analyses (TGA), X-ray diffraction (XRD) measurements, scanning electron and atomic force microscopies (SEM, AFM), and Raman spectroscopy, the electrical properties of multi-walled carbon nanotube/polypropylene (MWCNT/PP) composites have been elucidated to unfold their potentials under static and dynamic conditions. More interestingly, prototypes made of simple components and electronic circuits (resistor, touch-sensitive devices), where conventional components have been substituted by the carbon nanotube networks, are shown. The results contribute to enabling the direct integration of carbon conductive paths in conventional electronics and next-generation platforms for low-power electronics, sensors, and devices.

The in-situ triboluminescent optical fiber (ITOF) sensor has an integrated sensing and transmission component that converts the energy from damage events like impacts and crack propagation into optical signals that are indicative of the magnitude of damage in composite structures like concrete bridges. Utilizing the triboluminescence (TL) property of ZnS:Mn, the ITOF sensor has been successfully integrated into unreinforced cementitious composite beams to create multifunctional smart structures with in-situ failure detection capabilities. The fabricated beams were tested under flexural loading, and real time failure detection was made by monitoring the TL signals generated by the integrated ITOF sensor. Tested beam samples emitted distinctive TL signals at the instance of failure. In addition, we report herein a new and promising approach to damage characterization using TL emission profiles. Analysis of TL emission profiles indicates that the ITOF sensor responds to crack propagation through the beam even when not in contact with the crack. Scanning electron microscopy analysis indicated that fracto-triboluminescence was responsible for the TL signals observed at the instance of beam failure.

Triboluminescent damage sensors comprising highly efficient triboluminescent materials could allow simple, real-time monitoring of both the magnitude and location of damage. The inability to effectively capture and transmit the triboluminescent optical signals generated within opaque composites like concrete has, however, limited their damage monitoring applications. The in situ triboluminescent optical fiber sensor has been developed to enable the detection and transmission of damage-provoked triboluminescent emissions without having to position triboluminescent crystals in the host material. Flexural tests were performed on mortar and reinforced concrete beams having the in situ triboluminescent optical fiber sensor integrated into them. The intrinsic triboluminescent signals generated in the beams under loading were successfully transmitted through the optical fibers to the photomultiplier tube by side coupling. Successful side coupling will make a truly distributed in situ triboluminescent optical fiber sensor possible when the entire length of the sensor is mostly covered with the triboluminescent composite coating. The results show the viability of the in situ triboluminescent optical fiber sensor for the structural health monitoring of cementitious composites. Real-time failure detection was demonstrated in unreinforced mortar beams, while real-time damage (crack) detection was demonstrated in reinforced concrete beams. Preliminary work on reinforced concrete beams showed that the integrated in situ triboluminescent optical fiber sensor was able to detect multiple cracks caused by loading, thereby providing early warning of structural degradation before failure.

Over the past two decades, dye-sensitized solar cell (DSSC) research continues to gain momentum since its low-cost and environmental sustainability provides a good foundation for practical applications. Recently, CNTs have been introduced into DSSCs to take advantage of their lower electrical resistance, flexibility, excellent electrocatalytic activity and mechanical integrity. This paper introduces the principle of carbon-based solar energy conversion and reviews different types of solar cells using incorporated CNTs as electrode materials. This article also reports on CNTs’ outstanding electrocatalytic functions in enhancing wire-shaped solar cells’ photo-energy conversion.

An innovative solid state dye sensitized photovoltaic carbon nanotubes yarn (DSP-CNY) has been developed using thermally-stable and highly conductive carbon nanotubes (CNT) yarns (CNYs). These CNYs are highly inter-aligned, ultrastrong and flexible with excellent electrical conductivity, mechanical integrity and catalytic properties. The CNYs are coated with a dye-incorporated TiO 2 microfilm and intertwined with a second set of CNYs as a counter electrode (CE). The DSP-CNYs were developed without using any metal wires or any expensive transparent conductive oxides (TCOs), liquid electrolytes, or glass or plastic cladding. The maximum photon to current conversion efficiency ( η AM 1.5 ) achieved with prolonged-time stability was 2.57%. The yarn-shaped flexible cells were able to transport photocurrent over a significant distance using a simple cell configuration with a wide range of structural flexibility (30–330°). These cells are capable of efficiently harvesting incident photons regardless of direction and generating photocurrents with high efficiency and long term stability.

Innovative all solid state dye-sensitized photovoltaic micro-wires (DSPMs) have been developed using low-cost, thermally-stable and highly conductive titanium micro-wires and carbon nanotubes yarns (CNYs). Highly inter-aligned, ultrastrong and flexible CNYs with excellent electrical conductivity, mechanical integrity and catalytic property have been successfully used as counter electrodes (CEs). The open circuit voltage and current density of the DSPMs can remarkably be improved through optimizing the numbers of CNYs and CNYs–TiO2 interface. Optimizing the number of CNYs in the CEs yields a photoconversion efficiency of 0.1959% with prolonged-time stability. The DSPMs were made without expensive transparent conductive oxides (TCOs), liquid electrolytes and glass or plastic cladding. The DSPMs are able to transport photocurrent over a significant distance using a simple cell configuration with a wide range of flexibility (10–180°). These cells are capable of efficiently harvesting incident photon from any direction and generate photocurrent with an efficient reproducibility throughout a large number of illumination on–off cycles.

A novel preparation method of solid state photovoltaic carbon nanotubes (CNT) yarns has been successfully developed by depositing and grafting TiO2 thin films on CNT yarn substrates using a simple sol–gel method and designed for use in structural health monitoring (SHM) applications. The interaligned, ultrastrong and flexible CNYs display excellent electrical conductivity, mechanical integrity and their catalytic properties have been successfully used as working and counter electrodes. The TiO2 nanoparticles have been found to form a homogeneous thin film on the yarn surface, which shows efficient photovoltaic properties with remarkable stability when exposed to simulated solar light (AM 1.5). The yarns’ structure is not altered upon sol-gel treatment and light exposure. The TiO2 film is firmly anchored and the photovoltaic performance is retained even after multiple irradiation cycles. This preparation technique can also be applied to CNT yarn reinforced composite for an innovative in-situ and real-time self damage-sensing properties with infused triboluminescent (TL) materials.Copyright © 2012 by ASME

Nanostructured TiO2 has been synthesized using one-step sol–gel method and characterized by different characterization techniques (SEM, EDS, XRD, and UV–vis spectroscopy). The photocatalytic degradation of methylene blue (MB) and Congo red (CR) is studied with the synthesized TiO2. The photocatalytic degradation data has been validated using several kinetic models. The TiO2 showed efficient photocatalytic degradation performance on MB and CR. In addition to this, the effect of pH on the photocatalytic degradation has been investigated. The TiO2 showed enhanced photocatalytic performance in basic media than that in neutral or acidic ones.