Hydrothermal synthesis of nitrogen-doped carbon dots as a sensitive fluorescent probe for the rapid, selective determination of Hg²⁺

<p>In the present work, a green synthetic method for producing nitrogen-doped carbon dots (NCDs) by using ammonium citrate and urea is introduced. The obtained NCDs were characterised by transmission electron microscopy, Fourier transform infrared spectra, UV–vis absorption and fluorescence spectra. The results showed that the prepared NCDs were spherical with a size of about 3.5 nm, emitting strong and stable blue fluorescence when excited at 352 nm. It was noting that the NCDs enable sensitive and selective determination of Hg²⁺ in tap water with a linear range of 0.01–5 mg L⁻¹ based on a possible charge transfer process. The detection limit was 9.4 µg L⁻¹.</p

Hydrothermal synthesis of fluorescent nitrogen-doped carbon quantum dots from ascorbic acid and valine for selective determination of picric acid in water samples

<p>Nitrogen doped carbon quantum dots (N-CQDs) were synthesised by a hydrothermal method using ascorbic acid and valine as precursors. The as-synthesised N-CQDs were characterised by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV−vis absorption spectra, as well as fluorescence spectrophotometer. The results revealed that the as-prepared N-CQDs were spherical shaped with an average diameter of 4 nm and emitted bright blue photoluminescence with a quantum yield of approximately 4.8 %. Additionally, we found that the fluorescence of the N-CQDs was intensively quenched by the addition of picric acid (PA). The decrease of the fluorescence intensity made it possible to determine PA in the linear range of 0.06–7.81 µg ml^–¹ based on the fluorescence resonance energy transfer between PA and N-CQDs. The detection limit was as low as 11.46 ng ml^–¹. The proposed approach was further successfully applied for the determination of PA in water sample collected from Fenhe river for public safety and security, suggesting its great potential towards water routine analysis.</p

Active Antifogging Property of Monolayer SiO₂ Film with Bioinspired Multiscale Hierarchical Pagoda Structures

Antifogging surfaces with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, a major challenge remains in achieving high-speed antifogging performance and revealing the hydrophilic-based antifogging mechanism of glass or other transparent materials under aggressive fogging conditions. Herein, with inspiration from the fog-free property of the typical Morpho menelaus terrestris butterfly (Butler, 1866) wing scales, a monolayer SiO₂ film with multiscale hierarchical pagoda structures (MHPSs) based on glass substrate was designed and fabricated using an optimized biotemplate-assisted wet chemical method without any post-treatments. The biomimetic monolayer film (BMF) composed of nanoscale SiO₂ 3D networks displayed excellent antifogging properties, which is superior to that of the glass substrate itself. The MHPS-based BMF even kept high transmittance (∼95%) under aggressive fog conditions, and it almost instantaneously recovered to a fog-free state (<5 s). Moreover, the underlying active antifogging strategy gathering initial fog capture and final antifog together was revealed. The fogdrops spontaneously adhered on the BMF surface and rapidly spread along the MHPSs in an anisotropic way, which made the fogdrops evaporate instantaneously to attain an initial fog-free state, leading to an efficient active antifogging performance. These properties mainly benefit from the synergistic effect of both hydrophilic chemical compositions (nanoscale SiO₂) and physical structures (biomimetic MHPSs) of the BMF. High-speed active antifogging performance of the glass materials enabled the retention of a high transmittance property even in humid conditions, heralding reliable optical performance in outdoor practical applications, especially in aggressive foggy environments. More importantly, the investigations in this work offer a promising way to handily design and fabricate quasi-textured surfaces with multiscale hierarchical structures that possess high-performance physicochemical properties

Active Antifogging Property of Monolayer SiO₂ Film with Bioinspired Multiscale Hierarchical Pagoda Structures

Antifogging surfaces with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, a major challenge remains in achieving high-speed antifogging performance and revealing the hydrophilic-based antifogging mechanism of glass or other transparent materials under aggressive fogging conditions. Herein, with inspiration from the fog-free property of the typical Morpho menelaus terrestris butterfly (Butler, 1866) wing scales, a monolayer SiO₂ film with multiscale hierarchical pagoda structures (MHPSs) based on glass substrate was designed and fabricated using an optimized biotemplate-assisted wet chemical method without any post-treatments. The biomimetic monolayer film (BMF) composed of nanoscale SiO₂ 3D networks displayed excellent antifogging properties, which is superior to that of the glass substrate itself. The MHPS-based BMF even kept high transmittance (∼95%) under aggressive fog conditions, and it almost instantaneously recovered to a fog-free state (<5 s). Moreover, the underlying active antifogging strategy gathering initial fog capture and final antifog together was revealed. The fogdrops spontaneously adhered on the BMF surface and rapidly spread along the MHPSs in an anisotropic way, which made the fogdrops evaporate instantaneously to attain an initial fog-free state, leading to an efficient active antifogging performance. These properties mainly benefit from the synergistic effect of both hydrophilic chemical compositions (nanoscale SiO₂) and physical structures (biomimetic MHPSs) of the BMF. High-speed active antifogging performance of the glass materials enabled the retention of a high transmittance property even in humid conditions, heralding reliable optical performance in outdoor practical applications, especially in aggressive foggy environments. More importantly, the investigations in this work offer a promising way to handily design and fabricate quasi-textured surfaces with multiscale hierarchical structures that possess high-performance physicochemical properties

Bioinspired Omnidirectional Self-Stable Reflectors with Multiscale Hierarchical Structures

Structured surfaces, demonstrating various wondrous physicochemical performances, are ubiquitous phenomena in nature. Butterfly wings with impressive structural colors are an interesting example for multiscale hierarchical structures (MHSs). However, most natural structural colors are relatively unstable and highly sensitive to incident angles, which limit their potential practical applications to a certain extent. Here, we reported a bioinspired color reflector with omnidirectional reflective self-stable (ORS) properties, which is inspired by the wing scales of <i>Papilio palinurus</i> butterfly. Through experimental exploration and theoretical analysis, it was found that the vivid colors of such butterfly wings are structure-based and possess novel ORS properties, which attributes to the multiple optical actions between light and the complex structures coupling the inverse opal-like structures (IOSs) and stacked lamellar ridges (SLRs). On the basis of this, we designed and successfully fabricated the SiO₂-based bioinspired color reflectors (BCRs) through a facile and effective biotemplate method. It was confirmed that the MHSs in biotemplate are inherited by the obtained SiO₂-based BCRs. More importantly, the SiO₂-based BCRs also demonstrated the similar ORS properties in a wide wavelength range. We forcefully anticipate that the reported MHS-based ORS performance discovered in butterfly wing scales here could offer new thoughts for scientists to solve unstable reflection issues in particular optical field. The involved biotemplate fabrication method offers a facile and effective strategy for fabricating functional nanomaterials or bioinspired nanodevices with 3D complex nanostructures, such as structured optical devices, displays, and optoelectronic equipment

Degradable Bioinspired Hypersensitive Strain Sensor with High Mechanical Strength Using a Basalt Fiber as a Reinforced Layer

Flexible strain sensors have received extensive attention due to their broad application prospects. However, a majority of present flexible strain sensors may fail to maintain normal sensing performances upon external loads because of their low strength and thus their performances are affected drastically with increasing loads, which severely restricts large-area popularization and application. Scorpions with hypersensitive vibration slit sensilla are coincident with a similar predicament. Herein, it is revealed that scorpions intelligently use risky slits to detect subtle vibrations, and meanwhile, the distinct layered composites of the main body of this organ prevent catastrophic failure of the sensory structure. Furthermore, the extensive use of flexible sensors will generate a mass of electronic waste just as obsoleting silicon-based devices. Considering mechanical properties and environmental issues, a flexible strain sensor based on an elastomer (Ecoflex)-wrapped fabric with the woven structure was designed and fabricated. Note that introducing a “green” basalt fiber (BF) into a degradable elastomer can effectively avoid environmental issues and significantly enhance the mechanical properties of the sensor. As a result, it shows excellent sensitivity (gauge factor (GF) ∼138.10) and high durability (∼40,000 cycles). Moreover, the reduced graphene oxide (RGO)/BF/Ecoflex flexible strain sensor possesses superior mechanical properties (tensile strength ∼20 MPa) and good flexibility. More significantly, the sensor can maintain normal performances under large external tensions, impact loads, and even underwater environments, providing novel design principles for environmentally friendly flexible sensors under extremely harsh environments

Degradable Bioinspired Hypersensitive Strain Sensor with High Mechanical Strength Using a Basalt Fiber as a Reinforced Layer

Flexible strain sensors have received extensive attention due to their broad application prospects. However, a majority of present flexible strain sensors may fail to maintain normal sensing performances upon external loads because of their low strength and thus their performances are affected drastically with increasing loads, which severely restricts large-area popularization and application. Scorpions with hypersensitive vibration slit sensilla are coincident with a similar predicament. Herein, it is revealed that scorpions intelligently use risky slits to detect subtle vibrations, and meanwhile, the distinct layered composites of the main body of this organ prevent catastrophic failure of the sensory structure. Furthermore, the extensive use of flexible sensors will generate a mass of electronic waste just as obsoleting silicon-based devices. Considering mechanical properties and environmental issues, a flexible strain sensor based on an elastomer (Ecoflex)-wrapped fabric with the woven structure was designed and fabricated. Note that introducing a “green” basalt fiber (BF) into a degradable elastomer can effectively avoid environmental issues and significantly enhance the mechanical properties of the sensor. As a result, it shows excellent sensitivity (gauge factor (GF) ∼138.10) and high durability (∼40,000 cycles). Moreover, the reduced graphene oxide (RGO)/BF/Ecoflex flexible strain sensor possesses superior mechanical properties (tensile strength ∼20 MPa) and good flexibility. More significantly, the sensor can maintain normal performances under large external tensions, impact loads, and even underwater environments, providing novel design principles for environmentally friendly flexible sensors under extremely harsh environments

Degradable Bioinspired Hypersensitive Strain Sensor with High Mechanical Strength Using a Basalt Fiber as a Reinforced Layer

Flexible strain sensors have received extensive attention due to their broad application prospects. However, a majority of present flexible strain sensors may fail to maintain normal sensing performances upon external loads because of their low strength and thus their performances are affected drastically with increasing loads, which severely restricts large-area popularization and application. Scorpions with hypersensitive vibration slit sensilla are coincident with a similar predicament. Herein, it is revealed that scorpions intelligently use risky slits to detect subtle vibrations, and meanwhile, the distinct layered composites of the main body of this organ prevent catastrophic failure of the sensory structure. Furthermore, the extensive use of flexible sensors will generate a mass of electronic waste just as obsoleting silicon-based devices. Considering mechanical properties and environmental issues, a flexible strain sensor based on an elastomer (Ecoflex)-wrapped fabric with the woven structure was designed and fabricated. Note that introducing a “green” basalt fiber (BF) into a degradable elastomer can effectively avoid environmental issues and significantly enhance the mechanical properties of the sensor. As a result, it shows excellent sensitivity (gauge factor (GF) ∼138.10) and high durability (∼40,000 cycles). Moreover, the reduced graphene oxide (RGO)/BF/Ecoflex flexible strain sensor possesses superior mechanical properties (tensile strength ∼20 MPa) and good flexibility. More significantly, the sensor can maintain normal performances under large external tensions, impact loads, and even underwater environments, providing novel design principles for environmentally friendly flexible sensors under extremely harsh environments

Atomistic Insight into the Epitaxial Growth Mechanism of Single-Crystal Two-Dimensional Transition-Metal Dichalcogenides on Au(111) Substrate

A mechanistic understanding of interactions between atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) and their growth substrates is important for achieving the unidirectional alignment of nuclei and seamless stitching of 2D TMD domains and thus 2D wafers. In this work, we conduct a cross-sectional scanning transmission electron microscopy (STEM) study to investigate the atomic-scale nucleation and early stage growth behaviors of chemical vapor deposited monolayer (ML-) MoS2 and molecular beam epitaxy ML-MoSe2 on a Au(111) substrate. Statistical analysis reveals the majority of as-grown domains, i.e., ∼88% for MoS2 and 90% for MoSe2, nucleate on surface terraces, with the rest (i.e., ∼12% for MoS2 and 10% for MoSe2) on surface steps. Moreover, within the latter case, step-associated nucleation, ∼64% of them are terminated with a Mo-zigzag edge in connection with the Au surface steps, with the rest (∼36%) being S-zigzag edges. In conjunction with ab initio density functional theory calculations, the results confirm that van der Waals epitaxy, rather than the surface step guided epitaxy, plays deterministic roles for the realization of unidirectional ML-MoS2 (MoSe2) domains on a Au(111) substrate. In contrast, surface steps, particularly their step height, are mainly responsible for the integrity and thickness of MoS2/MoSe2 films. In detail, it is found that the lateral growth of monolayer thick MoS2/MoSe2 domains only proceeds across mono-Au-atom high surface steps (∼2.4 Å), but fail for higher ones (bi-Au atom step and higher) during the growth. Our cross-sectional STEM study also confirms the existence of considerable compressive residual strain that reaches ∼3.0% for ML-MoS2/MoSe2 domains on Au(111). The present study aims to understand the growth mechanism of 2D TMD wafers