ISSN / EISSN : 0957-4484 / 1361-6528
Published by: IOP Publishing (10.1088)
Total articles ≅ 20,521
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Understanding underlying processes behind the simple and easily scalable graphene synthesis methods enables their large-scale deployment in the emerging energy storage and printable device applications. Microwave plasma decomposition of organic precursors forms a high-temperature environment, above 3000 K, where the process of catalyst-free dehydrogenation and consequent formation of C2 molecules leads to nucleation and growth of high-quality few-layer graphene (FLG). In this work, we show experimental evidence that a high-temperature environment with a gas mixture of H2 and acetylene, C2H2, leads to a transition from amorphous to highly crystalline material proving the suggested dehydrogenation mechanism. The overall conversion efficiency of carbon to FLG reached up to 47 %, three times as much as for methane or ethanol, and increased with increasing microwave power (i.e. with the size of the high-temperature zone) and hydrocarbon flow rate. The yield decreased with decreasing C:H ratio while the best quality FLG (low D/G - 0.5 and high 2D/G - 1.5 Raman band ratio) was achieved for C:H ratio of 1:3. The structures contained less than 1 at% of oxygen. No additional hydrogen was necessary for the synthesis of FLG from higher alcohols having the same stoichiometry, 1-propanol and isopropanol, but the yield was lower, 15 %, and dependent on the atom arrangement of the precursor. The prepared FLG nanopowder was analyzed by scanning electron microscopy, Raman, X-ray photoelectron spectroscopy, and thermogravimetry. Microwave plasma was monitored by optical emission spectroscopy.
Nanotechnology, Volume 32; https://doi.org/10.1088/1361-6528/ac189e
The COVID-19 outbreak is creating severe impressions on all facets of the global community. Despite strong measures worldwide to try and re-achieve normalcy, the ability of SARS-Cov-2 to survive sturdy ecological settings may contribute to its rapid spread. Scientists from different aspects of life are working together to develop effective treatment strategies against SARS-Cov-2. Apart from using clinical devices for patient recovery, the key focus is on the development of antiviral drugs and vaccines. Given the physical size of the SARS-CoV-2 pathogen and with the vaccine delivery platform currently undergoing clinical trials, the link between nanotechnology is clear, and previous antiviral research using nanomaterials confirms this link. Nanotechnology-based products can effectively suppress various pathogens, including viruses, regardless of drug resistance, biological structure, or physiology. Thus, nanotechnology is opening up new dimensions for developing new strategies regarding diagnosis, prevention, and treatment of COVID-19 and other viral ailments. This article describes the application of nanotechnology against the COVID-19 virus in terms of therapeutic purposes and vaccine development through the invention of nanomaterial-based substances such as sanitizers (hand washing agents and surface disinfectants), masks and gowns, amongst other personal protective equipment (PPE), diagnostic tools, and nanocarrier systems, as well as the drawbacks and challenges of nanotechnology that need to be addressed.
Nanotechnology, Volume 32; https://doi.org/10.1088/1361-6528/ac1753
Owing to their unique structural and electronic properties such as layered structure with tuneable bandgap and high electron mobility, 2D materials have emerged as promising candidates for photocatalysis. Recently, bismuth oxyselenide (Bi2O2Se), a member of bismuth oxychalcogenide's family has shown great potential in high-speed field-effect transistors, infrared photodetectors, ferroelectric devices, and electrochemical sensors. However, the potential of Bi2O2Se in photocatalysis has not yet been explored. In the current work, Bi2O2Se nanosheets with an average size of ~170 nm and a lattice strain of 0.01 were synthesized at room temperature using a facile solution-processed method and the as-synthesized material was investigated with various characterization techniques such as XRD, FE-SEM, UV-Vis spectroscopy. The bandgap for the indirect transition in Bi2O2Se nanosheets was estimated to be 1.19 eV. Further, the visible-light-driven photocatalytic degradation of methylene blue (MB) dye using Bi2O2Se as a photocatalyst is presented. The photocatalytic experiments demonstrate the promising photocatalytic ability of Bi2O2Se as it leads to 25.06% degradation of MB within 80 min of light illumination. The effect of active species trapping agents (carrier and radical scavengers) on photocatalytic activity is also presented and discussed.
Spinel NiFe2O4 nanoparticles have been synthesized via hydrothermal route using Mangifera Indica flower extract (MIFE) as a green surfactant and reducing agent. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to determine the structure and morphology. The formation of single-phase, monodisperse NiFe2O4 with mixed morphology, the predominant shape being of equiaxed nanoparticles having an average particle size ~45 nm, is observed. The thermal magnetization of as-synthesized NiFe2O4 nanoparticles shows ferromagnetic to paramagnetic phase transition at Tc~825K. These nanoparticles show a very high saturation magnetization (Ms) value of 55 emu/g close to the bulk material and amongst the highest reported values for green synthesized NiFe2O4. This material has a coercivity (Hc) of 0.15 kOe and remanent magnetization (Mr) of 8.5 emu/g. The as-synthesized NiFe2O4 nanoparticles show bandgap energy of 2.02 eV, derived from UV-Vis absorption measurement, which is suitable for effective solar photocatalytic reactions. When exposed to sunlight in the presence of as-synthesized NiFe2O4 nanoparticles, 93% of MB-dye degradation is measured in 80 minutes, indicating excellent photocatalytic properties. Based on the as-synthesized NiFe2O4 nanoparticles' observed properties, the effectiveness of MIFE as an environmentally friendly surfactant, and the low-cost dye-degradation prospects of green synthetic NiFe2O4 are affirmed.
Photocatalytic conversion of CO2 to produce fuel is considered a promising approach to reduce CO2 emissions and tackle energy crisis. GaN-based materials have been studied for CO2 reduction because of their excellent optical properties and band structure. However, low photocatalytic activity and severe photocorrosion of GaN-based photoelectrode greatly limits their applications. In this work, photocatalytic activity was improved by adopting InGaN quantum dots (QDs) combined with C3N4 nano-sheets as photoanode, and thus the efficiency of CO2 reduction and the selectivity of hydrogen production were increased significantly. In addition, the photoelectron-chemical corrosion of photoelectrodes has been apparently controlled. InGaN QDs/C3N4 has the highest CO and H2 productions rates of 14.69 μmol/mol/h and 140 μmol/mol/h which were 2.2 times and 14.5 times than that of InGaN film photoelectrode, respectively. The enhancement of photocatalytic activity is attributed to C3N4 modification and a large electric dipole forming on the surface of InGaN QDs, which facilitate the separation and transfer of photo-generated carriers and thus promotes CO2 reduction reaction. This work provides a promising strategy for the development of GaN-based photoanodes with superior stability and efficiency.
An unusually broad bell-shaped component (BSC) has been previously observed in surface electron diffraction on different types of 2D systems. It was suggested to be an indicator of uniformity of epitaxial graphene (Gr) and hexagonal boron nitride (hBN). In the current study we use low-energy electron microscopy and micro-diffraction to directly relate the BSC to the crystal quality of the diffracting 2D material. Specially designed lateral heterostructures were used to map the spatial evolution of the diffraction profile across different 2D materials, namely pure hBN, BCN alloy and pure Gr, where the alloy region exhibits deteriorated structural coherency. The presented results show that the BSC intensity has a minimum in the alloyed region, consequently showing that BSC is sensitive to the lateral domain size and homogeneity of the material under examination. This is further confirmed by the presence of a larger number of sharp moiré spots when the BSC is most pronounced in the pure hBN and Gr regions. Consequently, it is proposed that the BSC can be used as a diagnostics tool for determining the quality of the 2D materials.
In this work, the growth and stability towards O2 exposure of two dimensional (2D) TaS2 on a Cu(111) substrate is investigated. Large area (~1cm2) crystalline 2D-TaS2 films with a metallic character are prepared on a single crystal Cu(111) substrate via a multistep approach based on physical vapor deposition. Analytical techniques such as Auger electron spectroscopy, low energy electron diffraction, and photoemission spectroscopy are used to characterize the composition, crystallinity, and electronic structure of the surface. At coverages below one monolayer equivalent (ML), misoriented TaS2 domains are formed, which are rotated up to ±13^o relative to the Cu(111) crystallographic directions. The TaS2 domains misorientation decreases as the film thickness approaches 1 ML, at which the crystallographic directions of TaS2 and Cu(111) are aligned. The TaS2 film is found to grow epitaxially on Cu(111). As revealed by low energy electron diffraction in conjunction with an atomic model simulation, the (3 × 3) unit cells of TaS2 match the (4 × 4) supercell of Cu(111). Furthermore, the exposure of TaS2 to O2, does not lead to the formation of a robust tantalum oxide film, only minor amounts of stable oxides being detected on the surface. Instead, the exposure of TaS2 films to O2 leads predominantly to a reduction of the film thickness, evidenced by a decrease in the content of both Ta and S atoms of the film. This is attributed to the formation of oxide species that are unstable and mainly desorb from the surface below room temperature. Temperature programmed desorption spectroscopy confirms the formation of SO2, which desorbs form the surface between 100 K and 500 K. These results provide new insights into the oxidative degradation of 2D-TaS2 on Cu(111).
The shift of a magnetization loop along the magnetic field axis for a ferromagnetic (FM)/anti-ferromagnetic (AFM) system when it is cooled through Néel temperature of AFM layer is called exchange anisotropy or exchange bias. Here, using micromagnetic simulations we propose that spin transfer torque (STT) mechanism would indeed be helpful in realizing the shift of the magnetization loop along magnetic field axis through domain wall resistance for an infinitely long FM nanowire without having AFM layer, which we call as spin transfer torque bias (STTB). Essentially, STTB is realized on both positive and negative magnetic field axis by varying the angle between spin polarized current and Zeeman field from 0º to 180º respectively and the origin is attributed to helical motion of the domain wall (DW). However, we do not see STTB at 90º due to coherent rotation of domain. We also ascertain that STTB is also a function of magnetic anisotropy, current density, polarization strength and non-adiabatic spin transfer torque term. Variation in STTB for different FM systems such as Fe2CoSi, Ni80Fe20 and Fe is attributed to a change in domain wall width. We believe that present results would lead to a new dimension in the field of spintronics.
Mercury is highly toxic and increasing attention has been paid to explore effective detection of Hg2+. Here, we report a sensitive Hg2+ sensor based on single-stranded DNA (ssDNA) modified two-dimensional (2D) MOF nanosheets by a ratiometric fluorescent method. The chosen 2D MOF nanosheets possess intrinsic peroxidase-like catalytic ability, ssDNA adsorption and fluorescence quenching. We demonstrate that the adsorption of ssDNA can significantly improve the peroxidase mimetic activity of 2D MOF nanosheets, enhancing the fluorescence of substrate Amplex Red. Taking advantages of the favorable characteristics above, we fabricate an efficient Hg2+ sensor. In the presence of Hg2+, the ssDNA is released from 2D MOF nanosheets, which results in a decreasing of peroxidase mimetic activity of 2D MOF nanosheets and a fluorescence enhancement of attached fluorophore. A linear relationship between ratiometric fluorescence of substrate and fluorophore and Hg2+ concentrations is obtained. The detection limit is 5 nM, which is much lower than the maximal contamination level in drinking water (30 nM) by Word Health Organization. These findings show 2D MOF based ratiometric fluorescent sensor is a convenient and efficient strategy to detect Hg2+.
Telomerase plays an important role in maintaining the length of telomere during cell division and is recognized as a new kind of biomarkers for cancer diagnosis. In this work, we present a brand new telomerase detection strategy based on a DNA-PAINT (DNA points accumulation for imaging in nanoscale topography) like strategy. With an extraordinary spatial resolution (~ 10 nm), the DNA-PAINT based strategy offers several advantages. First, it avoids complicated polymerase chain reaction (PCR) and electrophoresis procedures. Second, it enables super resolution imaging of the reaction products with a high signal-to-noise ratio and facilitates the location of telomeric elongation sites on the single particle level, which results in a high sensitivity. Third, the detection scheme of the DNA-PAINT strategy allows direct in-situ visualization of the telomeric elongation process. All these advantages make the DNA-PAINT telomerase detection strategy significant for dynamic investigation of telomerase related physiological processes as well as cancer diagnosis.