The world of two-dimensional carbides and nitrides (MXenes).

Flexible and ultrathin GO@MXene sandwich-type multilayered film toward superior electromagnetic interference shielding in a wide gigahertz range of 3.95–18.0 GHz

Cost-effective, rapid, and accurate virus detection technologies play key roles in reducing viral transmission. Prompt and accurate virus detection enables timely treatment and effective quarantine of virus carrier, and therefore effectively reduces the possibility of large-scale spread. However, conventional virus detection techniques often suffer from slow response, high cost or sophisticated procedures. Recently, two-dimensional (2D) materials have been used as promising sensing platforms for the high-performance detection of a variety of chemical and biological substances. The unique properties of 2D materials, such as large specific area, active surface interaction with biomolecules and facile surface functionalization, provide advantages in developing novel virus detection technologies with fast response and high sensitivity. Furthermore, 2D materials possess versatile and tunable electronic, electrochemical and optical properties, making them ideal platforms to demonstrate conceptual sensing techniques and explore complex sensing mechanisms in next-generation biosensors. In this review, we first briefly summarize the virus detection techniques with an emphasis on the current efforts in fighting again COVID-19. Then, we introduce the preparation methods and properties of 2D materials utilized in biosensors, including graphene, transition metal dichalcogenides (TMDs) and other 2D materials. Furthermore, we discuss the working principles of various virus detection technologies based on emerging 2D materials, such as field-effect transistor-based virus detection, electrochemical virus detection, optical virus detection and other virus detection techniques. Then, we elaborate on the essential works in 2D material-based high-performance virus detection. Finally, our perspective on the challenges and future research direction in this field is discussed.

The family of 2D transition metal carbides, nitrides, and carbonitrides (MXenes) has attracted an enormous amount of attention due to their tunable optical, electronic, electrochemical, and mechanical properties. Recently, a new branch of MXenes materials research has emerged that is exploring and engineering the intrinsic optical response of MXenes, resulting in compact nonlinear optical (NLO) devices. As a novel 2D materials system, MXenes not only exhibit common advantages of classical 2D materials for NLO applications but also demonstrate their unique superiority, such as high yield and scalable synthesis, good stability, switchable NLO response, etc. Here, a fundamental overview of MXenes nonlinear optics is provided, covering everything from MXenes synthesis to linear and NLO properties and NLO applications. The synthesis method and its influence on the MXenes structures and morphology are discussed, which dominated the linear optics of MXenes. Then, the third‐order NLO properties and carrier dynamics of MXenes, from basic theory to experimental results, are elaborated. Their NLO applications, including ultrashort laser pulse, single‐frequency laser generation, all‐optical phase modulation, wavelength modulation, and passive photonic diodes, are also highlighted. Finally, the current challenges and an outlook for future MXenes NLO research are proposed.

Two dimensional (2D) materials such as graphene and transition metal dichalcogenide (TMDC) like MoS2, WTe2 have brought widespread attention as their novel 2D confined properties and applications in nano devices. Among them, the up to date multilayer PtSe2 has been reported to be high mobility, air stable and possess novel phenomenon like Dirac fermions but to date have little study as the tunable electronic properties via structural control. Here we use the first principle calculations based on density functional theory (DFT) to study the tunable structure and electronic properties of monolayer and multilayer PtSe2 by the method of strain. We find that when apply compress strain on monolayer PtSe2 at -3% or more, the photoluminescence will enhance due to a larger density of states at conductance band minimum (CBM). With the increase of layer number, the band gap become small rapidly. The band gap change from 1.3 eV for monolayer to 0.4 eV for bilayer. With three layers, the band gap becomes 0.1 eV. Begin at four layer, the PtSe2 multilayer become a negative band gap semimetal. The DOS under VBM is small for multilayers due to the large splitting between the first valence band with the second valence band. This indicate the possible low photoluminescence strength for these multilayers. Our results can pave a way for the experiment electronic and optical properties tuning in multilayer PtSe2 and possible in the similar TMDCs.

2D transition metal carbides, carbonitrides, and nitrides, known as MXenes, are a rapidly growing family of 2D materials with close to 30 members experimentally synthesized, and dozens more studied theoretically. They exhibit outstanding electronic, optical, mechanical, and thermal properties with versatile transition metal and surface chemistries. They have shown promise in many applications, such as energy storage, electromagnetic interference shielding, transparent electrodes, sensors, catalysis, photothermal therapy, etc. The high electronic conductivity and wide range of optical absorption properties of MXenes are the key to their success in the aforementioned applications. However, relatively little is currently known about their fundamental electronic and optical properties, limiting their use to their full potential. Here, MXenes' electronic and optical properties from both theoretical and experimental perspectives, as well as applications related to those properties, are discussed, providing a guide for researchers who are exploring those properties of MXenes.

Chapter 14 - 2D materials and van der Waals heterostructures platforms for advanced sensing of COVID-19

The electromagnetic interference (EMI) shielding of Sm-containing magnesium alloys in the 30–1500 MHz testing frequency range was investigated by coaxial cable method. The results demonstrated that Mg–3Zn alloys displayed the best electromagnetic shielding property. When 0.5 wt% of Zr was added for crystal grain refinement, the shielding effectiveness (SE) was apparently reduced. The addition of the rare earth element Sm in ZK magnesium alloys can improve the electromagnetic interference shielding of magnesium alloys. The main reason for the differences in electromagnetic interference shielding of magnesium alloys was the change in conductivity. The addition of Zr in Mg–Zn alloys can refine the grains and consequently improve the grain boundary area significantly. Therefore, the number of irregularly arranged atoms at the grain boundaries increased, decreasing the conductivity of magnesium alloys and leading to a decrease in the electromagnetic interference shielding. Following the Sm addition, the Mg–Zn–Sm phase was precipitated at the grain boundaries and in cores. The precipitation of Sm-containing rare earth phases could consume the solid-soluted Zn atoms within the Mg, resulting in an increase in electrical conductivity and electromagnetic interference shielding improvement.

Potentially the largest family of 2D materials, known as transition metal carbides and/or nitrides (MXenes), have a chemical formula of Mn+1XnTx, where M represents a transition metal (Ti, Mo, Nb, V, Cr, etc.), X is either carbon and/or nitrogen, and Tx represents surface terminations. The diversity in composition offers a plethora of structures and chemistries to investigate. The first discovered MXene, titanium carbide, has shown unique light-matter interactions enabling applications such as electromagnetic interference shielding, wireless communication, photothermal therapy, and as a transparent conducting electrode. Combining the optical properties with ease in processing, high electronic conductivity and mechanical strength, MXenes have the characteristics necessary to develop as optical materials, however the solution processing routes to achieve controlled nanoparticle dispersions and quality thin films are not optimized and only a few compositions have been explored. This dissertation focuses on the development of colloidal solution processing approaches, including size selection, and stability control, of carbide MXenes in various solvents, fabrication of MXene films of optical quality, and characterization of the optical properties of MXenes in the colloidal and solid state. Control of the MXene dispersion allowed for the preparation of a range of MXene compositions, varying M and n, exhibiting an unusually broad and visually striking color spectrum. The origin of the color variation, spectroscopic information from the ultraviolet to the near infrared, and a relationship between the optical spectra and the electronic properties is examined. Under the assumption that it is possible to change the optical features, optical property tuning is explored by the change in surface chemistry, modification of the composition by alloying, and the application of an electric charge through electrochemical charge injection. Using the spectroscopic details provided throughout this dissertation, a few optoelectronic applications of MXenes are demonstrated, expanding the opportunities for research on this family of optically active materials.

Heterogeneous films assembled from Ti3C2Tx MXene and porous double-layered carbon nanosheets for high-performance electromagnetic interference shielding

Carbon fiber-reinforced plastic (CFRP) composites, owing to their lightweight and strength-weight ratio, are being used in many applications to replace traditional metallic materials and their alloys. The combination of polymeric composites with metallic materials can provide a significant impact in engineering applications. This paper evaluates electromagnetic interference shielding of bimetal-carbon prepreg fibers textile composite materials. Prepreg carbon fibers and metal wire mesh are used to make electromagnetic interference shielding samples. The material samples consist of making plain weaves of metal wire mesh and carbon prepreg and stack them with prepreg carbon fiber layers. In order to produce plain woven fabrics, wefts were made of prepreg carbon fibers and warps were made of wire meshes. In each woven fabric, two yarns of different metal wire meshes were alternated one after another. The combination of conductive wire meshes such as stainless steel-copper, stainless steel-nickel, and copper-nickel in a woven fabric was considered. The electromagnetic shielding effectiveness was evaluated for each textile composite material based on ASTM 4935-99. Results showed a possible application of these materials for electromagnetic interference shielding with higher absorption. The best electromagnetic interference shielding performance was obtained for a combination of stainless steel-copper-CFRP with a shielding effectiveness of 131.6 dB. The absorption losses for all samples were about 82% of electromagnetic interference shielding effectiveness. The mechanical properties and scanning electron image of fabricated samples were also investigated.

Responsive polymer thin films

Environmentally tolerant conductive organohydrogel toward superior electromagnetic interference shielding and human motion detection

Two-dimensional (2D) materials have attracted increasing research interest because of the abundant choice of materials with diverse and tunable electronic, optical, and chemical properties. Moreover, 2D material based heterostructures combining several individual 2D materials provide unique platforms to create an almost infinite number of materials and show exotic physical phenomena as well as new properties and applications. To achieve these high expectations, methods for the scalable preparation of 2D materials and 2D heterostructures of high quality and low cost must be developed. Chemical vapor deposition (CVD) is a powerful method which may meet the above requirements, and has been extensively used to grow 2D materials and their heterostructures in recent years, despite several challenges remaining. In this review of the challenges in the CVD growth of 2D materials, we highlight recent advances in the controlled growth of single crystal 2D materials, with an emphasis on semiconducting transition metal dichalcogenides. We provide insight into the growth mechanisms of single crystal 2D domains and the key technologies used to realize wafer-scale growth of continuous and homogeneous 2D films which are important for practical applications. Meanwhile, strategies to design and grow various kinds of 2D material based heterostructures are thoroughly discussed. The applications of CVD-grown 2D materials and their heterostructures in electronics, optoelectronics, sensors, flexible devices, and electrocatalysis are also discussed. Finally, we suggest solutions to these challenges and ideas concerning future developments in this emerging field.

Structural complexity and wide application of two-dimensional S/O type antimonene

Injectable self-healing hydrogels, as implanted materials, have received great attention over the past decades. The tunable optical and mechanical properties as well as the ability to lower the risk of inflammatory responses are essential considerations for their applications in diverse bioengineering processes. In this work, we report a novel injectable self-healing hydrogel with tunable optical, mechanical, and antimicrobial properties, fabricated by a multifunctional ABA triblock copolymer gelator, poly{(4-formylphenyl methacrylate)-co-[[2-(methacryloyloxy)ethyl] trimethylammonium chloride]}-b-poly(N-isopropylacrylamide)-b-poly{(4-formylphenyl methacrylate)-co-[[2-(methacryloyloxy)ethyl] trimethylammonium chloride]} and polyethylenimine. The self-healing capability of the hydrogel was demonstrated by rheology tests, and quantitative force measurements using a surface forces apparatus (SFA) provided molecular insights into the self-healing mechanism of Schiff base reaction. Additionally, the optical and mechanical properties of the hydrogel can be fine-tuned in a sensitive temperature-responsive manner because of the local nano-hydrophobic domains formed through the phase transition of the ABA triblock copolymer gelator. The hydrogel also demonstrated multiple sol–gel transitions subjected to pH change. Moreover, the hydrogel can also effectively inhibit the growth of both Gram-negative and Gram-positive bacteria (Escherichia coli and Staphylococcus aureus), while showing low cytotoxicity to both fibroblast and cancer cells (MRC-5 and HeLa). The novel multifunctional injectable self-healing hydrogel with tunable optical, mechanical, and excellent antimicrobial properties shows great potential in various bioengineering applications.