Search Results (33)

Sarin is an extremely toxic and fast-acting chemical warfare nerve agent that poses a serious threat to human health, necessitating the development of appropriate sensing technologies. Dimethyl methylphosphonate (DMMP), which has a chemical structure similar to that of sarin but is non-toxic, is often used as a simulation agent in related research. Among promising gas-sensing materials, CuFe₂O₄ exhibits suitable thermal stability. It is easily produced and has low toxicity. Its performance can be enhanced using heterogeneous ion doping to increase the number of surface defects and content of adsorbed oxygen. Therefore, a solvothermal method was adopted in this study to prepare CuFe₂O₄ hollow microspheres that were subsequently doped with different ratios of Sn⁴⁺ or Sn²⁺. Detailed characterizations of the obtained materials were conducted, and the corresponding CuFe₂O₄-based gas sensors were fabricated. Their gas-sensing performance against DMMP was studied to analyze and discuss the gas-sensing and sensitization mechanisms associated with Sn⁴⁺ and Sn²⁺ doping. The CuFe₂O₄-based sensor doped with 2 mol% Sn²⁺ exhibited excellent gas-sensing performance in response to a 1 ppm concentration of DMMP, with response and recovery times of 12 and 63 s, respectively. Notably, its response to 1 ppm DMMP (16.27) was 3.3-fold higher than that to 1 ppm 2-CEES (4.98). The doped CuFe₂O₄ sensor exhibited superior response–recovery characteristics and enhanced moisture resistance compared to the undoped sensor. Full article

Metamaterials enable the modulation of elastic waves or acoustic waves in unprecedented ways and have a wide range of potential applications. This paper achieves the simultaneous manipulation of surface elastic waves (SEWs) and surface acoustic waves (SAWs) using two-dimensional acousto-elastic metamaterials (AEMMs). The proposed AEMMs are composed of periodic hollow cylinders on the surface of a semi-infinite substrate. The band diagrams and the frequency responses of the AEMMs are numerically calculated through the finite element approach. The band diagrams exhibit simultaneous bandgaps for the SEWs and SAWs, which can also be effectively tuned by the modification of AEMM geometry. Furthermore, we construct the AEMM waveguide by the introduction of a line defect and hence demonstrate its ability to guide the SEWs and SAWs simultaneously. We expect that the proposed AEMMs will contribute to the development of multi-functional wave devices, such as filters for dual waves in microelectronics or liquid sensors that detect more than one physical property. Full article

Infrared detection is more and more widely used in the field of non-destructive testing of buildings to detect whether there is a defect on the surface of the building facade. In many cases, it is necessary to obtain more information about the defect, such as the depth of the defect, so as to evaluate the severity of the defect and repair. The theoretical formula of hollowing defect depths was derived in this paper based on the heat transfer characteristics of the intact and defective areas on the building facade, and the influence of defects with different shapes, sizes and cavity thicknesses on the temperature distribution of the building facade was summarized quantitatively. Firstly, the theoretical formula of the hollowing defect depth and the factors affecting the distribution of the temperature gradient on the building facade excited by external thermal source was derived and restricted by the boundary condition. Secondly, three sets of physical building facade models that contained hollowing defects with different shapes, sizes and cavity thicknesses were fabricated and designed, and the experimental platform was built. The infrared thermograms and the temperature characteristic curves of the hollowing defect in a natural light environment were obtained and fitted according to the temperature differences of the defective area, while analyzing the influence of the size, shape and cavity thicknesses on surface temperature distribution. Finally, the theoretical formula of the defect depth that is applicable to the building façade was validated through the experimental simulation of 14 forms of hollowing. The experimental results demonstrated that the revised formula of defect depth is consistent with the actual defect depth, and the three-dimensional positioning of the hollowing defect of the building facade can be effectively carried out and combined with the defect size taken from the obtained infrared thermal image. Full article

Under the influence of material defects, structural grooving, environmental corrosion, and other factors in engineering, concrete-filled steel tubes incur local defects on their external surfaces that affect their structural integrity and service life. This work conducts axial compression tests on 10 grooving-damaged square hollow concrete-filled steel tube (SHCFST) columns to investigate the effect of grooving damage on their axial compressive ultimate bearing capacity and the effect of steel tubes on concrete confinement. It explores the effects of three parameters, namely, the length of grooves, presence of slots in internal and external steel tubes, and orientation of grooves, on structural static performance. This study analyzes the loading, failure mechanisms, and axial compressive ultimate bearing capacity of grooving-damaged SHCFST columns. Results indicate that grooving weakens the steel tube’s confinement effect on the concrete core, reducing the axial compressive ultimate bearing capacity of specimens. On the basis of this experimental research, a method for calculating the axial compressive ultimate bearing capacity and axial compressive stiffness of grooving-damaged SHCFST columns is proposed. The calculation results closely align with experimental outcomes, providing valuable insights for related scientific research and engineering applications. Full article

A unique method for synthesizing a surface modifier for metallic hydrogen permeable membranes based on non-classic bimetallic pentagonally structured Pd-Pt nanoparticles was developed. It was found that nanoparticles had unique hollow structures. This significantly reduced the cost of their production due to the economical use of metal. According to the results of electrochemical studies, a synthesized bimetallic Pd-Pt/Pd-Ag modifier showed excellent catalytic activity (up to 60.72 mA cm⁻²), long-term stability, and resistance to CO_ads poisoning in the alkaline oxidation reaction of methanol. The membrane with the pentagonally structured Pd-Pt/Pd-Ag modifier showed the highest hydrogen permeation flux density, up to 27.3 mmol s⁻¹ m⁻². The obtained hydrogen flux density was two times higher than that for membranes with a classic Pd_black/Pd-Ag modifier and an order of magnitude higher than that for an unmodified membrane. Since the rate of transcrystalline hydrogen transfer through a membrane increased, while the speed of transfer through defects remained unchanged, a one and a half times rise in selectivity of the developed Pd-Pt/Pd-Ag membranes was recorded, and it amounted to 3514. The achieved results were due to both the synergistic effect of the combination of Pd and Pt metals in the modifier composition and the large number of available catalytically active centers, which were present as a result of non-classic morphology with high-index facets. The specific faceting, defect structure, and unusual properties provide great opportunities for the application of nanoparticles in the areas of membrane reactors, electrocatalysis, and the petrochemical and hydrogen industries. Full article

SiC devices have been typically subjected to extreme environments and complex stresses during operation, such as intense radiation and large diurnal amplitude differences on the lunar surface. Radiation displacement damage may lead to degradation or failure of the performance of semiconductor devices. In this paper, the effects of temperature and incidence angle on the irradiation cascade effect of 6H-SiC were investigated separately using the principles of molecular dynamics. Temperatures were set to 100 K, 150 K, 200 K, 250 K, 300 K, 350 K, 400 K and 450 K. The incidence direction was parallel to the specified crystal plane, with angles of 8°, 15°, 30°, 45°, 60° and 75° to the negative direction of the Z-axis. In this paper, the six types of defects were counted, and the microscopic distribution images and trajectories of each type of defect were extracted. The results show a linear relationship between the peak of the Frenkel pair and temperature. The recombination rate of Frenkel pairs depends on the local temperature and degree of aggregation at the center of the cascade collision. Increasing the angle of incidence first inhibits and then promotes the production of total defects and Frenkel pairs. The lowest number of total defects, Frenkel pairs and antisite defects are produced at a 45° incident angle. At an incidence angle of 75°, larger size hollow clusters and anti-clusters are more likely to appear in the 6H-SiC. Full article

Wastewater contaminated with antibiotics is a major environmental challenge. The oxidation process is one of the most common and effective ways to remove these pollutants. The use of metal-free, green, and inexpensive catalysts can be a good alternative to metal-containing photocatalysts in environmental applications. We developed here the green synthesis of bio-graphenes by using natural precursors (Xanthan, Chitosan, Boswellia, Tragacanth). The use of these precursors can act as templates to create 3D doped graphene structures with special morphology. Also, this method is a simple method for in situ synthesis of doped graphenes. The elements present in the natural biopolymers (N) and other elements in the natural composition (P, S) are easily placed in the graphene structure and improve the catalytic activity due to the structural defects, surface charges, increased electron transfers, and high absorption. The results have shown that the hollow cubic Chitosan-derived graphene has shown the best performance due to the doping of N, S, and P. The Boswellia-derived graphene shows the highest surface area but a lower catalytic performance, which indicates the more effective role of doping in the catalytic activity. In this mechanism, O₂ dissolved in water absorbs onto the positively charged C adjacent to N dopants to create oxygenated radicals, which enables the degradation of antibiotic molecules. Light irradiation increases the amount of radicals and rate of antibiotic removal. Full article

Glycine (Gly), as one of the fundamental components of biomolecules, plays a crucial role in functional biomolecular coatings. The presence of structural defects and hydroxyl-containing functional groups in magnesium (Mg) materials, which are commonly used as biomedical materials, significantly affects their biocompatibility and corrosion resistance performance. This study computationally investigates the influence of vacancy defects and hydroxyl groups on the adsorption behavior of Gly on Mg(0001) surfaces. All potential adsorption configurations are considered through first-principles calculations. The findings indicate that stronger chemisorption occurs when Gly is positioned at the edge of the groove, where the surface has a vacancy defect concentration of 1/3. Among the four adsorption locations, the fcc-hollow site is determined to be the most favorable adsorption site for hydroxyl. The adsorption energy of Gly on the Mg(0001) surface containing the hydroxyl (−1.11 eV) is 0.05 eV more than that of on the Mg(0001) surface (−1.16 eV). The adsorption energies, electronic properties, charge transfer, and stable configurations are calculated to evaluate the interaction mechanism between Gly and defective surfaces. Calculated results provide a comprehensive understanding of the interaction mechanism of biomolecules on defective Mg surfaces and also indicate the directions for future experimental research. Full article

In sand casting, gas porosity is a common defect that can result in decreased strength, leakage, rough surfaces, or other problems. Although the forming mechanism is very complicated, gas release from sand cores is often a significant contributor to the formation of gas porosity defects. Therefore, studying the gas release behavior of sand cores is crucial to solving this problem. Current research on the gas release behavior of sand cores mainly focuses on parameters such as gas permeability and gas generation properties, through experimental measurement and numerical simulation methods. However, accurately reflecting the gas generation situation in the actual casting process is difficult, and there are certain limitations. To achieve the actual casting condition, a sand core was designed and enclosed inside a casting. The core print was extended to the sand mold surface, with two types of core prints: hollow and dense. Pressure and airflow speed sensors were installed on the exposed surface of the core print to investigate the burn-off of the binder of the 3D-printed furan resin quartz sand cores. The experimental results showed that the gas generation rate was high in the initial stage of the burn-off process. The gas pressure quickly reached its peak in the initial stage and then decreased rapidly. The exhaust speed of the dense type of core print was 1 m/s, lasting for 500 s. The pressure peak of the hollow-type sand core was 1.09 kPa, and the exhaust speed peak was 1.89 m/s. The binder can be sufficiently burned off for the location surrounding the casting and the crack-affected area, so the burnt sand appears white, while the burnt core appears black due to insufficient burning of the binder because of isolation from the air. The gas generated by the burnt resin sand in contact with air was 30.7% less than that generated by the burnt resin sand insulated from the air. Full article

In this study, we report the use of a radiofrequency plasma-assisted chemical vapor deposition (RF-CVD) system with a hollow cathode geometry to hydrogenate anatase TiO₂ thin films. The goal was to create black TiO₂ films with improved light absorption capabilities. The initial TiO₂ was developed through magnetron sputtering, and this study specifically investigated the impact of hollow cathode hydrogen plasma (HCHP) treatment duration on the crucial characteristics of the resulting black TiO₂ films. The HCHP treatment effectively created in-bandgap states in the TiO₂ structure, leading to enhanced light absorption and improved conductivity. Morphological analysis showed a 24% surface area increase after 15 min of treatment. Wettability and surface energy results displayed nonlinear behavior, highlighting the influence of morphology on hydrophilicity improvement. The anatase TiO₂ phase remained consistent, as confirmed by diffractograms. Raman analysis revealed structural alterations and induced lattice defects. Treated samples exhibited outstanding photodegradation performance, removing over 45% of methylene blue dye compared to ~25% by the pristine TiO₂ film. The study emphasized the significant impact of 15-min hydrogenation on the HCHP treatment. The research provided valuable insights into the role of hydrogenation time using the HCHP treatment route on anatase TiO₂ thin films and demonstrated the potential of the produced black TiO₂ thin films for photocatalytic applications. Full article

Although water splitting is a promising method to produce clean hydrogen energy, it requires efficient and low-cost catalysts for the oxygen evolution reaction (OER). This study focused on plasma treatment’s significance of surface oxygen vacancies in improving OER electrocatalytic activity. For this, we directly grew hollow NiCoPBA nanocages using a Prussian blue analogue (PBA) on nickel foam (NF). The material was treated with N plasma, followed by a thermal reduction process for inducing oxygen vacancies and N doping on the structure of NiCoPBA. These oxygen defects were found to play an essential role as a catalyst center for the OER in enhancing the charge transfer efficiency of NiCoPBA. The N-doped hollow NiCoPBA/NF showed excellent OER performance in an alkaline medium, with a low overpotential of 289 mV at 10 mA cm⁻² and a high stability for 24 h. The catalyst also outperformed a commercial RuO₂ (350 mV). We believe that using plasma-induced oxygen vacancies with simultaneous N doping will provide a novel insight into the design of low-priced NiCoPBA electrocatalysts. Full article

Cu-doped manganese oxide (Cu–Mn₂O₄) prepared using aerosol decomposition was used as a CO oxidation catalyst. Cu was successfully doped into Mn₂O₄ due to their nitrate precursors having closed thermal decomposition properties, which ensured the atomic ratio of Cu/(Cu + Mn) in Cu–Mn₂O₄ close to that in their nitrate precursors. The 0.5Cu–Mn₂O₄ catalyst of 0.48 Cu/(Cu + Mn) atomic ratio had the best CO oxidation performance, with T₅₀ and T₉₀ as low as 48 and 69 °C, respectively. The 0.5Cu–Mn₂O₄ catalyst also had (1) a hollow sphere morphology, where the sphere wall was composed of a large number of nanospheres (about 10 nm), (2) the largest specific surface area and defects on the interfacing of the nanospheres, and (3) the highest Mn³⁺, Cu⁺, and Oads ratios, which facilitated oxygen vacancy formation, CO adsorption, and CO oxidation, respectively, yielding a synergetic effect on CO oxidation. DRIFTS-MS analysis results showed that terminal-type oxygen (M=O) and bridge-type oxygen (M-O-M) on 0.5Cu–Mn₂O₄ were reactive at a low temperature, resulting in-good low-temperature CO oxidation performance. Water could adsorb on 0.5Cu–Mn₂O₄ and inhibited M=O and M-O-M reaction with CO. Water could not inhibit O₂ decomposition to M=O and M-O-M. The 0.5Cu–Mn₂O₄ catalyst had excellent water resistance at 150 °C, at which the influence of water (up to 5%) on CO oxidation could be completely eliminated. Full article

Prefabricated concrete hollow slab bridges are widely used in short- and medium-span highway bridges in China due to the advantages of high production quality, installation convenience, and low construction cost. Field investigation shows that severe hinge joint damage occurred during the service life, and mechanical performance of the bridges also deteriorated with the weakened joints. It is important to accurately evaluate the performance of hollow slab bridges to ensure the safety of the highway system. In this paper, transverse connectivity and durability of the concrete hollow slab bridges are investigated in a field test using the surface damage and neural networks. Hollow slab bridges in the Wu-He highway system were taken as the background bridge. Surface damage was visually checked and statistically analyzed. Static load test was conducted to evaluate the transverse connectivity of the hinge joints based on the girder responses. The hollow slab bridges were then demolished, and a total of 75 concrete girder segments were cut off. Durability of the girders was evaluated based on the conditions of concrete and rebars, and the analytic hierarchy process along with the fuzzy comprehensive evaluation method was employed. Results showed that there were two main types of the defects in the hollow slab bridges, i.e., the transverse cracks on the bottom plates of the girders and the longitudinal cracks in the hinge joints. The distribution of the deflection of each girder was non-uniform due to the weakening of the transverse connectivity, and the girders in the background bridges were within the moderate deterioration condition after 25 years’ service life. An evaluation method of the hollow slab girders using the neural networks and surface damage was verified by the field test data. The maximum crack width at different locations of the bridges was used in the input layer of the neural network, and the hinge joint damage or the durability was considered as the output results. The prediction error of the method in the test set was within 15.0% for the hinge joint damage and within 40% for the durability result of the girder, indicating the feasibility of the evaluation method. Full article

In order to solve the problems of low detection efficiency and safety of artificial surface defects in hot-state cross wedge rolling shaft production line, a machine vision-based method for detecting surface hollow defect of hot-state shafts is proposed. Firstly, by analyzing the high reflective properties of the metal shaft surface, the best lighting method was obtained. And by analyzing the image contrast between image foreground and image background, the most suitable optical filter type in image acquisition was determined. Then, Fourier Gaussian low-pass filtering method is used to remove the interference noise of rolled shafts surface in frequency domain, such as high-light, oxide skin and surface texture. Finally, by analyzing the characteristics of the surface hollow defect area, a defect identification method combining the Otsu threshold method and the adaptive threshold method is proposed to realize the effective extraction of surface hollow defect of rolled shafts. The test results show that the average recognition rate of the method based on machine vision is 95.7%. The results of this paper provide technical support to meet the production requirements of high quality and high performance of cross wedge rolling. Full article

Transition metal sulfides have been explored as electrode materials for non-enzymatic detection. In this work, we investigated the effects of phosphorus doping on the electrochemical performances of NiCo₂S₄ electrodes (P-NiCo₂S₄) towards glucose oxidation. The fabricated non-enzymatic biosensor displayed better sensing performances than pristine NiCo₂S₄, with a good sensitivity of 250 µA mM⁻¹ cm⁻², a low detection limit (LOD) of 0.46 µM (S/N = 3), a wide linear range of 0.001 to 5.2 mM, and high selectivity. Moreover, P-NiCo₂S₄ demonstrated its feasibility for glucose determination for practical sample testing. This is due to the fact that the synergetic effects between Ni and Co species, and the partial substitution of S vacancies with P can help to increase electronic conductivity, enrich binary electroactive sites, and facilitate surface electroactivity. Thus, it is found that the incorporation of dopants into NiCo₂S₄ is an effective strategy to improve the electrochemical activity of host materials. Full article