Zirconium carbide (ZrC) ceramics have a high melting point, low neutron absorption cross section, and excellent resistance to the impact of fission products and are considered to be one of the best candidate materials for fourth-generation nuclear energy systems. ZrC ceramics with a high relative density of 99.1% were successfully prepared via pressureless sintering using a small amount of MoSi2 as an additive. The influence of the MoSi2 content on the densification behavior, microstructure, mechanical properties, and thermal properties of ZrC ceramics was systematically investigated. The results show that the densification of ZrC was significantly enhanced by the introduction of MoSi2 due to the formation of a liquid phase during sintering. In addition, the ZrC grains were refined due to the pinning effect of the generated silicon carbide. The flexural strength and Vickers hardness of ZrC ceramics with 2.5 vol% MoSi2 sintered at 1850 °C were 408 ± 12 MPa and 17.1 GPa, respectively, which were approximately 30% and 10% higher compared to the samples without the addition of MoSi2. The improved mechanical properties were mainly attributed to the high relative density (99.1%) and refined microstructure.
The effects of Ti doping on the microstructure and properties of SiCp/Al composites fabricated by pressureless infiltration were comprehensively investigated using first-principles calculations and experimental analyses. First-principles calculations revealed that the interface wetting and bonding strength in an Al/SiC system could be significantly enhanced by Ti doping. Subsequently, the Ti element was incorporated into SiC preforms in the form of TiO2 and TiC to verify the influence of Ti doping on the pressureless infiltration performance of SiCp/Al composites. The experimental results demonstrated that the pressureless infiltration of molten Al into SiC preforms was promoted by adding TiC or TiO2 due to the improved wettability. However, incorporating TiO2 leads to the growth of AlN whiskers under a N2 atmosphere, thereby hindering the complete densification of the composites. On the other hand, TiC doping can improve wettability and interface strength without deleterious reactions. As a consequence, the TiC-doped SiCp/Al composites exhibited excellent properties, including a high relative density of 99.4%, a bending strength of 287 ± 18 MPa, and a thermal conductivity of 142 W·m-1·K-1.
Motivated by the desire for more sensitivity and stable surface-enhanced Raman scattering (SERS) substrates to trace detect chloramphenicol due to its high toxicity and ubiquity, MXene has attracted increasing attention and is encountering the high-priority task of further observably improving detection sensitivity. Herein, a universal SERS optimization strategy that incorporates NH4VO3 to induce few-layer MXenes assembling into multiporous nanosheet stacking structures was innovatively proposed. The synthesized Nb2C-based multiporous nanosheet stacking structure can achieve a low limit of detection of 10-10 M and a high enhancement factor of 2.6 × 109 for MeB molecules, whose detection sensitivity is improved by 3 orders of magnitude relative to few-layer Nb2C MXenes. Such remarkably enhanced SERS sensitivity mainly originates from the multiple synergistic contributions of the developed physical adsorption, the chemical enhancement, and the conspicuously improved electromagnetic enhancement arising from the intersecting MXenes. Furthermore, the improved SERS sensitivity endows Nb2C-based multiporous structures with the capability to achieve ultrasensitive detection of chloramphenicol with a wide linear range from 100 µg/mL to 1 ng/mL. We believe it is of great significance in conspicuously developing the SERS sensitivity of other MXenes with surficial negative charges and has a great promising perspective for the trace detection of other antibiotics in microsystems.
Lateral flow immunoassay (LFIA) has been widely used for the early diagnosis of diseases. However, conventional colorimetric LFIA possesses limited sensitivity, and the single-mode readout signal is easily affected by the external environment, leading to insufficient accuracy. Herein, multifunctional Fe3O4@MoS2@Pt nanotags with a unique "pompon mum"-like structure were triumphantly prepared, exhibiting excellent peroxidase (POD)-like activity, photothermal properties, and magnetic separation capability. Furthermore, the Fe3O4@MoS2@Pt nanotags were used to establish dual-mode LFIA (dLFIA) for the first time, enabling the catalytic colorimetric and photothermal dual-mode detection of severe acute respiratory syndrome coronavirus 2 nucleocapsid protein (SARS-CoV-2 NP) and influenza A (H1N1). The calculated limits of detection (cLODs) of SARS-CoV-2 NP and H1N1 were 80 and 20 ng/mL in catalytic colorimetric mode and 10 and 8 ng/mL in photothermal mode, respectively, demonstrating about 100 times more sensitive than the commercial colloidal Au-LFIA strips (1 ng/mL for SARS-CoV-2 NP; 1 µg/mL for H1N1). The recovery rates of dLFIA in simulated nose swab samples were 95.2-103.8% with a coefficient of variance of 2.3-10.1%. These results indicated that the proposed dLFIA platform showed great potential for the rapid diagnosis of respiratory viruses.
Influenza A Virus, H1N1 Subtype , Metal Nanoparticles , Molybdenum , Catalysis , Colorimetry , Immunoassay , Gold
In the present work, the recent advancements in additive manufacturing (AM) techniques for fabricating nanocomposite parts with complex shaped structures are explained, along with defect non-destructive testing (NDT) methods. A brief overview of the AM processes for nanocomposites is presented, grouped by the type of feedstock used in each technology. This work also reviews the defects in nanocomposites that can affect the quality of the final product. Additionally, a detailed description of X-CT, ultrasonic phased array technology, and infrared thermography is provided, highlighting their potential application in non-destructive inspection of nanocomposites in the future. Lastly, it concludes by offering recommendations for the development of NDT methods specifically tailored for nanocomposites, emphasizing the need to utilize NDT methods for optimizing nano-additive manufacturing process parameters, developing new NDT techniques, and enhancing the resolution of existing NDT methods.
Polyaluminocarbosilane (PACS) is an important precursor for silicon carbide (SiC) fibers and ceramics. The structure of PACS and the oxidative curing, thermal pyrolysis, and sintering effect of Al have already been substantially studied. However, the structural evolution of polyaluminocarbosilane itself during the polymer-ceramic conversion process, especially the changes in the structure forms of Al, are still pending questions. In this study, PACS with a higher Al content is synthesized and the above questions are elaborately investigated by FTIR, NMR, Raman, XPS, XRD, and TEM analyses. It is found that up to 800-900 °C the amorphous SiOxCy, AlOxSiy, and free carbon phases are initially formed. With increasing temperature, the SiOxCy phase partially separates into SiO2 then reacts with free carbon. The AlOxSiy phase changes into Al3C4 and Al2O3 by reaction with free carbon at around 1100 °C. The complicated reactions between Al3C4, Al2O3, and free carbon occur, leading to the formation of the Al4O4C and Al2OC phases at around 1600 °C, which then react with the SiC and free carbon, resulting in the formation of the Al4SiC4 phase at 1800 °C. The amorphous carbon phase grows with the increasing temperature, which then turns into a crystalline graphitic structure at around 1600 °C. The growth of ß-SiC is inhibited by the existence of the Al4O4C, Al2OC, and Al4SiC4 phases, which also favor the formation of α-SiC at 1600-1800 °C.
Surface-Enhanced Raman Scattering (SERS) technology, as a powerful tool to identify molecular species by collecting molecular spectral signals at the single-molecule level, has achieved substantial progresses in the fields of environmental science, medical diagnosis, food safety, and biological analysis. As deepening research is delved into SERS sensing, more and more high-performance or multifunctional SERS substrate materials emerge, which are expected to push Raman sensing into more application fields. Especially in the field of biological analysis, intrinsic and extrinsic SERS sensing schemes have been widely used and explored due to their fast, sensitive and reliable advantages. Herein, recent developments of SERS substrates and their applications in biomolecular detection (SARS-CoV-2 virus, tumor etc.), biological imaging and pesticide detection are summarized. The SERS concepts (including its basic theory and sensing mechanism) and the important strategies (extending from nanomaterials with tunable shapes and nanostructures to surface bio-functionalization by modifying affinity groups or specific biomolecules) for improving SERS biosensing performance are comprehensively discussed. For data analysis and identification, the applications of machine learning methods and software acquisition sources in SERS biosensing and diagnosing are discussed in detail. In conclusion, the challenges and perspectives of SERS biosensing in the future are presented.
Biosensing Techniques , COVID-19 , Nanostructures , Humans , Spectrum Analysis, Raman/methods , SARS-CoV-2 , Nanostructures/chemistry , Nanotechnology , Biosensing Techniques/methods
Dense SiC-based composite ceramics were fabricated by means of the ex situ addition of TaC using solid-state spark plasma sintering (SPS). Commercially available ß-SiC and TaC powders were chosen as raw materials. Electron backscattered diffraction (EBSD) analysis was conducted to investigate the grain boundary mapping of SiC-TaC composite ceramics. With the increase in TaC, the misorientation angles of the α-SiC phase shifted to a relatively small range. It was deduced that the ex situ pinning stress from TaC greatly suppressed the growth of α-SiC grains. The low ßâα transformability of the specimen with the composition of SiC-20 vol.% TaC (ST-4) implied that a possible microstructure of newly nucleated α-SiC embedded within metastable ß-SiC grains, which could have been responsible for the improvement in strength and fracture toughness. The as-sintered SiC-20 vol.% TaC (ST-4) composite ceramic had a relative density of 98.0%, a bending strength of 708.8 ± 28.7 MPa, a fracture toughness of 8.3 ± 0.8 MPa·m1/2, an elastic modulus of 384.9 ± 28.3 GPa and a Vickers hardness of 17.5 ± 0.4 GPa.
Mesocarbon microbead-silicon carbide (MCMB-SiC) composites were prepared by hot-press sintering (2100 °C/40 MPa/1 h) with two different graphitized MCMBs as the second phase, which exhibited good self-lubricating properties. The effects of the graphitization degree of the MCMBs on the microstructure and properties of the composites were investigated contrastively. The results showed that the composites that added raw MCMBs with a low degree of graphitization had excellent self-sintering properties, higher densities, and better mechanical properties; by comparison, the composites that added mature MCMBs with a high degree of graphitization, which has regular and orderly lamellar structures, not only had good mechanical properties but also exhibited a lower and more stable dry friction coefficient (0.35), despite the higher wear rate (2.66 × 10-6 mm3·N-1·m-1). Large amounts of mature MCMBs were peeled off during the friction process to form a uniform and flat graphite lubricating film, which was the main reason for reducing the dry friction coefficient of the self-lubricating composites and making the friction coefficient more stable.
In this study, different reaction-bonded boron carbide (RBBC) composites with a free carbon addition from 0 to 15 wt% were prepared, and the effect of the carbon content on the mechanical properties was discussed. With the free carbon addition increase from 0 to 15 wt%, the residual silicon content in the RBBC composite decreased first and then increased. Meanwhile, the strength of the RBBC composite improved first and then worsened. In the RBBC composite without free carbon, the B4C grains are obviously dissolved, the grains become facet-shape, and the grain boundary becomes straight. The microstructure of the composite was tested by SEM, and the phase composition of the composite was tested by XRD. The RBBC composite with the addition of 10 wt% free carbon has the highest flexural strength (444 MPa) and elastic modulus (329 GPa). In the composite with a 10 wt% carbon addition, the phase distribution is uniform and the structure is compact.
In this study, the joining of silicon carbide (SiC) ceramics was achieved via a Si-C reaction bonding method using the phenolic resin (PF)-MgCl2 system as the carbon precursor. Specifically, by adding MgCl2 to the phenolic resin mixture, the average pore size of the product of carbonization of the PF resin mixture increased from 14 ± 5 nm to 524 ± 21 nm, which was beneficial for the infiltration of molten silicon at high temperature. The microstructure of the joined specimens and the effect of the inert filler on the joint strength were investigated. It was demonstrated that SiC-SiC joints with strong interfacial bonding and high flexural strength could be obtained by the Si-C reaction bonding method using a phenol formaldehyde resin/alcohol sol-gel system as the carbon precursor. The flexural strength of the joined specimens reached the highest value, i.e., 308 ± 27 MPa when the solid loading of the inert filler was 26%. Overall, stable joining of silicon carbide ceramics was achieved by the proposed method, which has significance for realizing the preparation of complex-shaped or large silicon carbide ceramic parts.
The tissue inhibitor of metalloproteinases-1 (TIMP-1) protein can regulate the expression of certain proteases and microRNAs in cancer cells, and it is highly possible to diagnose cancers through analyzing the expression of TIMP-1 on exosomes. However, it is still a great challenge to obtain reliable physiological information on TIMP-1 by label-free method from exosomes in plasma. Here, we designed a porous-plasmonic SERS chip functionalized with synthesized CP05 polypeptide, which can specifically capture and distinguish exosomes from diverse origins. The SERS chip can accurately locate the plasmon in TIMP-1 protein to analyze the discrepancy of related fingerprint peaks of different exosomes. Based on the designed SERS chip, we successfully distinguished the lung and colon cancer cell-derived exosomes from normal exosomes at the single vesicle level by unique Raman spectroscopy and machine learning methods. This work not only provides a practical SERS chip for the application of Raman technology in human tumor monitoring and prognosis, but also provides a new idea for analyzing the feature of exosomes at the spectral level.
Biosensing Techniques , Colonic Neoplasms , Exosomes , Lung Neoplasms , Cell Line, Tumor , Colonic Neoplasms/diagnosis , Exosomes/chemistry , Humans , Lung , Lung Neoplasms/metabolism , Spectrum Analysis, Raman/methods , Tissue Inhibitor of Metalloproteinase-1/analysis , Tissue Inhibitor of Metalloproteinase-1/metabolism
The current COVID-19 pandemic urges us to develop ultra-sensitive surface-enhanced Raman scattering (SERS) substrates to identify the infectiousness of SARS-CoV-2 virions in actual environments. Here, a micrometer-sized spherical SnS2 structure with the hierarchical nanostructure of "nano-canyon" morphology was developed as semiconductor-based SERS substrate, and it exhibited an extremely low limit of detection of 10-13 M for methylene blue, which is one of the highest sensitivities among the reported pure semiconductor-based SERS substrates. Such ultra-high SERS sensitivity originated from the synergistic enhancements of the molecular enrichment caused by capillary effect and the charge transfer chemical enhancement boosted by the lattice strain and sulfur vacancies. The novel two-step SERS diagnostic route based on the ultra-sensitive SnS2 substrate was presented to diagnose the infectiousness of SARS-CoV-2 through the identification standard of SERS signals for SARS-CoV-2 S protein and RNA, which could accurately identify non-infectious lysed SARS-CoV-2 virions in actual environments, whereas the current PCR methods cannot.
MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage. Here, we report the preparation of V2SnC MAX phase by the molten salt method. V2SnC is investigated as a lithium storage anode, showing a high gravimetric capacity of 490 mAh g-1 and volumetric capacity of 570 mAh cm-3 as well as superior rate performance of 95 mAh g-1 (110 mAh cm-3) at 50 C, surpassing the ever-reported performance of MAX phase anodes. Supported by operando X-ray diffraction and density functional theory, a charge storage mechanism with dual redox reaction is proposed with a Sn-Li (de)alloying reaction that occurs at the edge sites of V2SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V2C layers with Li. This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.
Titanium oxide is widely applied as a photocatalyst. However, its low efficiency and narrow light absorption range are two main disadvantages that severely impede its practical application. In this work, black TiOx films with different chemical compositions were fabricated by tuning target voltage and controlling O2 flow during reactive DC magnetron sputtering. The optimized TiOx films with mixed phases (TiO, Ti2O3, Ti3O5, and TiO2) exhibited fantastic photothermal and photocatalytic activity by combining high light-absorptive Ti2O3 and Ti3O5 phases with the photocatalytic TiO2 phase. The sample prepared with oxygen flow at 5.6 ± 0.2 sccm and target voltage near 400 V exhibited excellent optical absorbance of 89.29% under visible light, which could improve surface temperature to 114 °C under sunlight. This film could degrade Rhodamine-B up to 74% after 150 min of UV irradiation. In a word, this work provides a guideline for fabricating black TiOx films with photothermal-assisted photocatalytic activity by reactive DC magnetron sputtering, which could avoid the usage of hydrogen and is convenient for quantity preparation.
The current COVID-19 pandemic urges the extremely sensitive and prompt detection of SARS-CoV-2 virus. Here, we present a Human Angiotensin-converting-enzyme 2 (ACE2)-functionalized gold "virus traps" nanostructure as an extremely sensitive SERS biosensor, to selectively capture and rapidly detect S-protein expressed coronavirus, such as the current SARS-CoV-2 in the contaminated water, down to the single-virus level. Such a SERS sensor features extraordinary 106-fold virus enrichment originating from high-affinity of ACE2 with S protein as well as "virus-traps" composed of oblique gold nanoneedles, and 109-fold enhancement of Raman signals originating from multi-component SERS effects. Furthermore, the identification standard of virus signals is established by machine-learning and identification techniques, resulting in an especially low detection limit of 80 copies mL-1 for the simulated contaminated water by SARS-CoV-2 virus with complex circumstance as short as 5 min, which is of great significance for achieving real-time monitoring and early warning of coronavirus. Moreover, here-developed method can be used to establish the identification standard for future unknown coronavirus, and immediately enable extremely sensitive and rapid detection of novel virus. Supplementary Information: The online version contains supplementary material available at 10.1007/s40820-021-00620-8.
Boron carbide (B4C) ceramics were synthesized by spark plasma sintering at a temperature between 1600 and 2050 °C without employing any sintering additives. The effect of sintering process parameters, such as temperature, holding time, pressure, hearting rate, and pulsed electric current, and the particle size of the raw powder on the densification behavior and mechanical properties of B4C ceramics, were comprehensively and systematically investigated. Hardness and fracture toughness of B4C that has a density close to the theoretical value were found to be 33.5 ± 0.2 GPa and 3.21 ± 0.13 MPa·m1/2, respectively. Electron backscatter diffraction (EBSD) analysis revealed no abnormal growth of grains due to an increase in holding time and pressure. Twin structures present in ceramics are beneficial for their mechanical performance.
Laser additive manufacturing is a promising technique for the preparation of complex-shaped SiC composites. High-quality powders are critical for high-precision laser printing. In this work, core-shell Cf @phenolic resin (PR) composites for selective laser sintering of carbon fiber reinforced silicon carbide (Cf/SiC) composites were fabricated by surface modification using 3-aminopropyltriethoxy silane coupling agent (KH550) in combination with planetary ball milling. PR coated uniformly on the fiber surface to form a core-shell structure. The effects of PR on the morphology, elemental composition, interfacial interactions, and laser absorption of the core-shell composite powder were investigated in detail. Results indicated that the composite powder exhibited good laser absorption within the infrared band.
Ceramics including oxides, carbides, nitrides, borides, carbonitrides, silicates, and MAX phases have wide applications in electrode materials, high-temperature structural materials, and anticorrosive materials for harsh environments. However, the difficulty in processing ceramics with complex shapes from green powders has been restricting applications in emerging areas. Herein, polymer-derived ceramics (PDCs) were used to assist the pressureless processing of MAX phase particles. The processing temperature could be lowered by 400 to 600 °C, which is favorable for both industrialization and engineering applications. The good processability of MAX-preceramic polymer mixtures and high accuracy of replica from preceramic polymer make it possible to fabricate artificial objects with complex shapes and fine texture. This method provides a method to fabricate MAX phase ceramics/composites, as well as some other ceramics.
