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In this communication a novel concept for pH sensing is introduced which is specifically adapted to monitor carbonation induced corrosion in concrete structures. The method is based on a ratiometric measurement principle, exploiting the pH sensitive colour switching of thymol blue in the basic pH regime and the emissive properties of two different (Zn)CdSe/ZnS core shell quantum dots. The transition point of thymol blue in a Hydrogel D4 matrix was determined to be at around pH 11.6, which fits ideally to the intended application. Next to the fundamental spectroscopic characterization of the ratiometric response, a new design for a sensor head, suitable for the incorporation into concrete matrices is presented. Toward this, a manufacturing process was developed which includes the preparation of a double layer of polymers containing either thymol blue or a quantum dot mixture inside a porous ceramic tube. Results of a proof-of-priciple performance test of the sensor head in solutions of different pH and in cement specimens are presented, with encouraging results paving the way for future field tests in concrete.
Different from negatively charged CuInS2 (CIS) based quantum dots (QDs), positively charged QDs are difficult to obtain in good optical quality, but are desirable for certain applications. We herein present a general synthesis strategy that allows for a universal surface modification of ternary CIS based QDs with thiol containing ligands.
The idea behind the synthesis design is, to apply a ZnS shell first for passivating and protecting the core QDs, and then add a second ZnS shell for the functionalization via ligand exchange. Whereby easy ligand exchange with thiolated molecules is systematically set up, by using a weak bonding amine ligand for the second shell. Molecules with various terminal groups were used to functionalize the nanoparticles and stabilize them in different media making any surface charge and polarity accessible. Surface defect chemistry seemed to play an important role in our synthesis strategy, therefore to gain a deeper understanding how these defect sites can alter the electronic structure of core/shell nanoparticles theoretical calculations based on density functional theory were performed, whilst structural, colloidal and optical properties were characterized experimentally (by dynamic light scattering, x-ray diffraction, infrared spectroscopy, zeta potential, absorption- and (time resolved) photoluminescence
measurements).
A new approach to determine the elements carbon, hydrogen, nitrogen and oxygen (CHNO) in polymers by wavelength-dispersive X-ray fluorescence analysis (WDXRF) in combination with partial least squares (PLS) regression was explored. The quantification of CHNO was achieved by using the Rayleigh and Compton scattering spectra of an Rh X-ray tube from 84 different polymers. Concealed differences of the corresponding scattering spectra could be utilized to quantify CHNO in a multivariate manner. It was shown that the developed model was capable of determining these commonly non-measurable matrix elements in polymers using WDXRF. Furthermore, the influence of spectral resolution, which is given by the collimator and the crystal, on the prediction of CHNO was explored in this study. It was found that minimal spectral resolution led to the most accurate CHNO predictions. Information about matrix composition could be used to improve so-called semi-quantitative XRF methods based on fundamental parameters (FP) for the analysis of plastics, soil or other samples with high organic content.
Cathodoluminescence and Photoluminescence of YPO4:Pr3+, Y2SiO5:Pr3+, YBO3:Pr3+, and YPO4:Bi3+
(2017)
This study investigated the ability of electrically conductive carbon rovings to detect cracks in textile-reinforced concrete (TRC) structures. The key innovation lies in the integration of carbon rovings into the reinforcing textile, which not only contributes to the mechanical properties of the concrete structure but also eliminates the need for an additional sensory system, such as strain gauges, to monitor the structural health. Carbon rovings are integrated into a grid-like textile reinforcement that differs in binding type and dispersion concentration of the styrene butadiene rubber (SBR) coating. Ninety final samples were subjected to a four-point bending test in which the electrical changes of the carbon rovings were measured simultaneously to capture the strain. The mechanical results show that the SBR50-coated TRC samples with circular and elliptical cross-sectional shape achieved, with 1.55 kN, the highest bending tensile strength, which is also captured with a value of 0.65 Ω by the electrical impedance monitoring. The elongation and fracture of the rovings have a significant effect on the impedance mainly due to electrical resistance change. A correlation was found between the impedance change, binding type and coating. This suggests that the elongation and fracture mechanisms are affected by the number of outer and inner filaments, as well as the coating.
The Effect of Ionic Defect Interactions on the Hydration of Yttrium-Doped Barium Zirconate, Phys
(2021)
Production of Singlet Oxygen for Water Purification via NIR-LED Radiation Sources and Porphyrin
(2016)