Light-activated porphyrinoid-capped nanoparticles for gas sensing

The coupling of semiconductors with organic molecules results in a class of sensors whose chemoresistive properties are dictated by the nature of dyes. Organic molecules generally reduce conductivity, but in the case of optically active dyes, such as porphyrinoids, the conductivity is restored by illumination with visible light. In this paper, we investigated the gas sensing properties of ZnO nanoparticles coated with porphyrins and corroles. Under light illumination, the resistance of these materials increases with the adsorption of volatile compounds but decreases when these are strong electron donors. The behavior of these sensors can be explicated on the basis of the structural difference between free-base porphyrin and corrole, the influence of coordinated metal, and the corresponding electronic structures. These sensors are promising electronic noses that combine the selectivity to strong electron donors with the broad selectivity toward the other classes of chemicals. An efficient representation of the data of this peculiar array can be obtained by replacing the Euclidean distance with the angular distance. To this end, a recently introduced spherical principal component analysis algorithm is applied for the first time to gas sensor array data. Results show that a minimal gas sensor array (four elements) can produce a sort of chemotopic map, which enables us to cluster a very large class of pure chemical vapors. Furthermore, this map provides information about the composition of complex odor matrices, such as the headspaces of beef meat and their evolution over the time

Tribological Behavior of NiMoAl-Based Self-Lubricating Composites

The present study focused on the development of NiMoAl-based self-lubricating composites using solid lubricants as the second phase by powder metallurgy. For this, Cr2AlC MAX phase, Cr2AlC-Ag, and MoS2 powders were mixed with the NiMoAl-based matrix and subsequently hot pressed to produce bulk composite samples. The average hardness and wear resistance of the matrix were found to be increased with the addition of MoS2, Cr2AlC MAX phase, and Cr2AlC-Ag powder to the NiMoAl matrix. The addition of Cr2AlC to NiMoAl was more effective in improving the wear resistance than MoS2. The addition of Cr2AlC and Cr2AlC-Ag has increased the hardness by about 75% than that with the addition of NiMoAl alloy. A scanning Kelvin probe system was used to study the surface properties of the tribofilm in detail through work function mapping from the edge area to the wear area (groove). Among all the samples, the one with the addition of Cr2AlC-Ag powder to the NiMoAl matrix possesses the best tribo-mechanical properties. Cr2AlC-Ag composite addition to NiMoAl was found to decrease the wear rate by one-third and to reduce the coefficient of friction by one-fourth, compared to the base NiMoAl alloy. This was attributed to the high-sintered density and formation of strong tribofilms consisting of mixed oxides such as Ag2MoO4 and Al2O3, as confirmed by micro Raman spectra

Aggregation behavior in naphthalene-appended diketopyrrolopyrrole derivatives and its gas adsorption impact on surface potential

Diketopyrrolopyrrole derivatives containing phenyl and thiophene units adorned with alkoxynaphthalene (Naph-PDPP and Naph-TDPP) were synthesized by a Suzuki cross-coupling reaction. The effect of the phenyl/thiophene units on the aggregation behavior and detailed photophysical properties were investigated by UV-visible, steady-state, and time-resolved fluorescence spectroscopy. The absorption and fluorescence spectra of Naph-PDPP and Naph-TDPP in the solid-state exhibit red-shifted spectral patterns due to strong intermolecular interactions. The concentration-dependent photophysical properties reveal the formation of J-type aggregates at higher concentrations and in the solid state. The extent of aggregate formation is higher for Naph-TDPP. DFT and TD-DFT studies showed that Naph-TDPP containing a thiophene ring in the backbone adopts a more planar geometry than Naph-PDPP and undergoes strong pi-pi stacking interactions that favor the formation of J-aggregates. Scanning Kelvin probe measurements on the thin films of Naph-PDPP and Naph-TDPP were performed (both in the dark and under visible light) upon exposure to different volatile organic vapors (ethanol and triethylamine). The study reveals that under visible light illumination, the Naph-PDPP thin film has significant gas adsorption towards ethanol vapors and alters its sign of response

Development of Gas Sensor Array based on Phthalocyanines Functionalized TiO₂/ZnO Heterojunction Thin Films

Gas sensing properties of diverse phthalocyanines functionalized TiO2/ZnO heterojunction thin films were investigated respect to a number of volatile organic compounds (VOCs) in both dark and light conditions. These studies showed that influence of heterojunction along with functionalization alter the optical properties and gas sensing of sensors. Results show that each sensor exhibits a different pattern of relative sensitivity, and this feature can be used to discriminate among a wide range of VOCs

A ZIF-67 derived Co 3 O 4 dodecahedron shaped microparticle electrode based extended gate field-effect transistor for non-enzymatic glucose detection towards the diagnosis of diabetes mellitus

The present study focuses on non-enzymatic glucose detection using an extended gate field-effect transistor (EGFET) based on zeolitic imidazole framework-67 (ZIF-67) derived cobalt tetraoxide (Co3O4) dodecahedron shaped microparticles. XRD has confirmed the cubic phase of Co3O4. HR-SEM images have highlighted hollow Co3O4 dodecahedra with an average particle size of 1.72 mu m. A cost-effective single-use ZIF-67 derived Co3O4 electrode has been fabricated that covers the range of glucose concentration from 1.5 mM to 42 mM (linear range: 1.5 to 10.5 mM) and has a fast response time of <4 s. The sensitivity is calculated to be 50 mu A mM(-1) cm(-2). Our prepared electrode has demonstrated a good selective response against other interfering molecules like sucrose, lactose, fructose, uric acid, and ascorbic acid. The concentration of the interfering molecules is maintained similar to the physiological conditions of human blood. As a maiden attempt, the influence of glucose concentration on the surface potential of the sensing electrode has been investigated using a scanning Kelvin probe (SKP). We have found that the work function decreases with the increase of glucose concentration. Overall, EGFET and SKP studies have revealed that the ZIF-67 derived Co3O4 dodecahedron shaped microparticle based electrode is suitable for rapid detection of glucose

Interaction of VOCs with pyrene tetratopic ligands layered on ZnO nanorods under visible light

In this work, the relationship between photosensitivity and chemical sensitivity of zinc oxide (ZnO) nanorods coated with pyrene based tetratopic ligands (PTL) is investigated under visible light. The electrical resistance of ZnO-PTL is affected by adsorption of different volatile organic compounds (VOCs) such as ethanol, n-hexane, trimethylamine, and triethylamine. The illumination strongly affects the response to the VOCs. To elucidate the interaction mechanism between PTL and VOCs, the experimental studies have been complemented by first principles calculations. Both experimental and computational results have shown that the amines are bound to PTL with higher affinity followed by ethanol (alcohol) and n-hexane (alkane). Our results have proved that the COOH functional group at the peripheral site of PTL is not only used for anchoring the molecule onto the ZnO, but it is also the main adsorption site for the VOCs, in particular for amines. In practice, the photo-optical properties of pyrene molecules are complemented by the high affinity of COOH group for amines in order to achieve a photo-activated sensor. The complementary use of optical dyes and chemical ligands can provide an innovative methodology for chemical sensors design. (C) 2016 Elsevier B.V. All rights reserved

Optimization of Process Parameters for Turning Hastelloy X under Different Machining Environments Using Evolutionary Algorithms: A Comparative Study

In this research work, the machinability of turning Hastelloy X with a PVD Ti-Al-N coated insert tool in dry, wet, and cryogenic machining environments is investigated. The machinability indices namely cutting force (CF), surface roughness (SR), and cutting temperature (CT) are studied for the different set of input process parameters such as cutting speed, feed rate, and machining environment, through the experiments conducted as per L27 orthogonal array. Minitab 17 is used to create quadratic Multiple Linear Regression Models (MLRM) based on the association between turning parameters and machineability indices. The Moth-Flame Optimization (MFO) algorithm is proposed in this work to identify the optimal set of turning parameters through the MLRM models, in view of minimizing the machinability indices. Three case studies by considering individual machinability indices, a combination of dual indices, and a combination of all three indices, are performed. The suggested MFO algorithm’s effectiveness is evaluated in comparison to the findings of Genetic, Grass-Hooper, Grey-Wolf, and Particle Swarm Optimization algorithms. From the results, it is identified that the MFO algorithm outperformed the others. In addition, a confirmation experiment is conducted to verify the results of the MFO algorithm’s optimal combination of turning parameters