M.J. Uddin

Getting light through cementitious composites with in situ triboluminescent damage sensor

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.

Structure and Redox Activity of Copper Sites Isolated in a Nanoporous P4VP Polymeric Matrix

In the recent years, metal-containing polymers have become very attractive owing to their possible applications as catalysts for organic synthesis. Several examples can be found of functionalized microporous polystyrenes (PSs) characterized by very low surface areas, whereby the reactive sites are accessible to the reactants only upon swelling by the solvent. Swelling usually does not occur for gaseous species and this property usually prevents the use of polymer-based catalysts for gas-phase synthesis. This restriction can, however, be overcome by the use of macroporous polymeric matrices, for which a permanent open texture is obtained by 20–40 % levels of cross-linking. The development of easy methods to immobilize organometallic species into these polymers while maintaining their porous structure will allow their application to catalytic reactions also in the absence of a swellable solvent. An example of this class of systems is the nitrogencontaining polymers, such as poly(4-vinylpyridine) (P4VP), which play important roles as basic catalysts and are used extensively to generate metal complexes with transition metals. P4VP has been used as a good support for immobilization of CuCl2 [5] in the oxidative carbonylation of methanol to dimethylcarbonate (DMC), the oxidative coupling of 2,6dimethylphenol, and the oxidation of tetralin. In these processes, all conducted in the liquid phase, Cu is reduced to Cu and HCl is released. Even though it is usually accepted that the basic N atoms of the pyridine (Py) rings act as preferential sites for Cu grafting and several models have been proposed, 8] there is no direct proof of the structure of the active species during the redox process. In this work, CuCl2 was molecularly immobilized inside a highly crosslinked P4VP matrix characterized by permanent porosity (Figure S1 in the Supporting Information); this system allowed catalysis also in the gas phase, and has been investigated in detail by in situ spectroscopy. The grafting procedure and the redox processes involving the Cu sites were investigated by means of several complementary in situ techniques (FTIR, UV/Vis, XANES, and EXAFS spectroscopy), allowing the determination of the structure of the system at each step. The determination of the structure surrounding Cu sites has to be considered a nontrivial result because of the amorphous nature of the host matrix. Detailed knowledge of the structural changes upon redox reaction is necessary for understanding more complex catalytic processes. CuCl2 coordination to the N atoms of the Py rings in P4VP matrices was demonstrated by IR spectroscopy (Figure 1): the

Tailoring the photocatalytic reaction rate of a nanostructured TiO2 matrix using additional gas phase oxygen

Nanostructured TiO2 was synthesized by the sol–gel method. The titania was supported on nanoporous poly(styrene-co-divinylbenzene) (PS). The samples were characterized by several techniques (scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy). Three types of TiO2 samples were prepared using various temperatures and were studied for the photocatalytic degradation of methylene blue. The photocatalytic efficiency of TiO2 was observed to increase by activating the TiO2 surface using nanoporous PS. The photocatalytic performance of the synthesized samples showed a higher performance using molecular O2, which was purged through the reactor.

Triboluminesence multifunctional cementitious composites with in situ damage sensing capability

Structural health monitoring of civil infrastructure systems like concrete bridges and dams has become critical because of the aging and overloading of these CIS. Most of the available SHM methods are not in-situ and can be very expensive. The triboluminescence multifunctional cementitious composites (TMCC) have in-built crack detection mechanism that can enable bridge engineers to monitor and detect abnormal crack formation in concrete structures so that timely corrective action can be taken to prevent costly or catastrophic failures. This article reports the fabrication process and test result of the flexural characterization of the TMCC. Accelerated durability test indicated that the 0.5 ZnS:Mn/Epoxy weight fraction ITOF sensor configuration to be more desirable in terms of durability. The alkaline environment at the highest temperature investigated (45 °C) resulted in significant reduction in the mean glass transition and storage moduli of the tested ITOF thin films. Further work is ongoing to correlate the TL response of the TMCC with damage, particularly crack opening.

Solid-State Dye Sensitized Optoelectronic Carbon Nanotube-Wires: An Energy Harvesting Damage Sensor With Nanotechnology Approach

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

EFFECT OF AG AND AU DOPING ON THE PHOTOCATALYTIC ACTIVITY OF TIO2 SUPPORTED ON TEXTILE FIBRES

A simple method to develop TiO 2 , Ag or Au-doped TiO 2 thin films on cotton textiles for advanced applications, is reported. The homogeneous TiO2 thin films have been deposited on cotton textiles by using sol-gel method at low temperature (100° C), whereas Ag and Au nanoparticles were then deposited on the pre-existent TiO 2 films by photoreduction. The Ag/TiO2 covered cotton fibres show multichromic behaviour (grey colour under visible light and brown colour upon ultraviolet light exposure) as well as photoactivity. The Au-TiO2 film coated the cotton textile produces a purple colour with excellent self cleaning properties. The original and treated fibres have been characterized by several techniques (SEM, HRTEM, FTIR, Raman, UV–vis spectroscopy and XRD).