Triangular Nanostructures Research Articles

Morphology engineering of WO3/BiVO4heterojunctions for efficient photocatalytic water oxidation

Four types of nanostructural WO3/BiVO4 heterojunctions were designed by depositing a BiVO4 layer onto WO3 scaffolds with different morphologies and investigated to understand the influence of heterojunction morphology on their photoelectrochemical performances. The architecture of WO3 scaffolds was controlled by adjusting the solvents used in their solvothermal synthesis. The solvent was found to exert a great influence on the architecture of the obtained WO3 scaffolds. Methanol leads to the formation of block-like nanostructures and ethanol facilitates the formation of nanorods, while isopropyl alcohol and ethylene glycol give rise to the formation of triangular nanowalls and 3D hierarchical nanostructures, respectively. Monoclinic WO3 nanostructures were obtained via removal of ammonium or structural water by annealing the samples obtained at 510 °C in air. A BiVO4 layer was then deposited on the monoclinic WO3 scaffolds with different morphologies by spin-coating to form WO3/BiVO4 heterojunction films, which show significantly enhanced photocurrents compared to their corresponding bare WO3 scaffolds. Among these WO3/BiVO4 nanostructure heterojunctions, the one based on a rod-like WO3 nanostructure shows the best photoelectrochemical (PEC) performance, which can be ascribed to its optimal rod-like morphology, for the construction of WO3/BiVO4 heterojunction regarding efficient charge carrier transfer and collection, while the other one based on WO3 nanowalls exhibits better stability and a higher photocurrent in a long-run test, indicating that morphology engineering significantly influences the activity and stability of WO3-based heterojunctions.

Amino acid assisted growth of CuO nanostructures and their potential application in electrochemical sensing of organophosphate pesticide

This work reports a highly sensitive electrochemical sensor for organophosphate pesticide (malathion) based on unique and attractive CuO nanostructures. The discussed nanostructures were synthesized using low temperature hydrothermal growth method utilizing green amino acids such as glycine, serine, threonine and histidine as effective bio-compatible templates. The morphological evaluation demonstrated formation of unique and attractive 1-D nanostructures reflecting the effective growth controlling and directing capabilities of the utilized amino acids. The as-synthesized CuO nanostructures were noted to possess high affinity towards malathion which enabled their application as electrode material for the development of affinity based electrochemical sensor. Although, the as-synthesized morphologies were all sensitive towards malathion but the glycine directed triangular flake-like nanostructures exhibited greater sensitivity compared to other competitors. The electrochemical behaviour of the modified electrodes was studied using cyclic voltammetry (CV) whereas, differential pulse voltammetry (DPV) was utilized for the analytical evaluation of the sensor. The developed sensor demonstrated high reproducibility, stability, wide detection window (1–12nM), and sensitivity to detect malathion up to 0.1nM based on suppressive signal measurement. In addition, the sensor system exhibited high anti-interference capability in the presence of common co-existing pesticides like lindane, carbendazim, and trichlorfon. The developed sensor provides an effective measure for detecting extremely low concentration of malathion with wide applicability in various fields.

Observation of Size-Dependent Electron–Phonon Scattering and Temperature-Dependent Photoluminescence Quenching in Triangular-Shaped Silver Nanoparticles

Research studies on plasmonic properties of triangular-shaped silver nanoparticles might lead to several interesting applications. However, in this work, triangular-shaped silver nanoparticles have been synthesized by simple solvothermal technique and reported the effect of size on the electron–phonon scattering in the synthesized materials by analyzing their temperature-dependent photoluminescence (PL) emission characteristics. It has been observed that total integrated PL emission intensity is quenched by 33 % with the increase in temperature from 278 to 323 K. The observed decrease in PL emission intensity has been ascribed to the increase of electron–phonon scattering rate with the increase in temperature. The values of electron–phonon coupling strength (S) for synthesized samples have been evaluated by theoretical fitting of the experimentally obtained PL emission data. Smaller sized triangular nanoparticle has been found to exhibit stronger temperature dependence in PL emission, which strongly suggests that smaller sized triangular silver nanostructures have better electron–phonon coupling.

Bismuth nanoparticles integration into heavy metal electrochemical stripping sensor.

Between their many applications bismuth nanoparticles (BiNPs) are showing interest as pre-concentrators in heavy metals detection while being applied as working electrode modifiers used in electrochemical stripping analysis. From the different reported methods to synthesize BiNPs we are focused on the typical polyol method, largely used in these types of metallic and semi-metallic nanoparticles. This study presents the strategy for an easy control of the shape and size of BiNPs including nanocubes, nanosferes and triangular nanostructures. To improve the BiNP size and shape, different reducing agents (ethylene glycol or sodium hypophosphite) and stabilizers (polyvinyl pyrrolidone, PVP, in different amounts) have been studied. The efficiency of BiNPs for heavy metals analysis in terms of detection sensitivity while being used as modifiers of screen-printed carbon electrodes including the applicability of the developed device in real sea water samples is shown. A parallel study between the obtained nanoparticles and their performance in heavy metal sensing has been described in this communication.

Application of triangular silver nanoplates for colorimetric detection of H2O2

In this study, a simple and highly sensitive colorimetric assay of H2O2 using triangular Ag nanoplates has been carried out. In the presence of H2O2, the Ag nanoplates are etched from triangle to round, which leads to the vanishment of the surface plasmon resonance (SPR) absorption at 400nm and significant decrease the absorbance of the band at 670nm. The color change of the reaction system from the initial blue to mauve can be observed. This proposed method can determine H2O2 with a dynamic range of 50nM to 1μM and a low detection limit of 1.36nM. The high sensitivity of the triangular nanoplates can be ascribed to highly reactive edges/tips, and strongly tip sharpness and aspect ratio dependent SPR absorption of the triangular nanostructure. This sensing system is further extended to the detection of glucose by H2O2 generated from the enzymatic oxidation of glucose, and thus holds great promises in clinical applications.

Model of Meniscus Shape and Disjoining Pressure of Thin Liquid Films on Nanostructured Surfaces with Electrostatic Interactions

The effect of electrostatic interactions on the stability of thin liquid films on nanostructured surfaces is important in lubrication, wetting, and phase change but is poorly understood. In this study, a general, closed-form model is developed to account for both the effects of electrostatic and van der Waals interactions on meniscus shape and disjoining pressure for thin liquid films on nanostructured surfaces based on the minimization of free energy, the Derjaguin approximation, and the disjoining pressure theory for flat surfaces. The model is verified using the molecular dynamics (MD) simulations for a water–alumina system with both triangular and square nanostructures of varying depth and film thickness. Good agreement is obtained between MD results and model predictions, demonstrating the robustness of the analytical model. The results show that the electrostatic interactions enhance the disjoining pressure, thereby making the meniscus more conformal to the nanostructured surfaces. In addition, the electrostatic disjoining pressure is shown to increase with the nanostructure depth but decrease with the thin film thickness.

Enhancement of surface enhanced raman scattering from arrays of hybrid Au–Ag nanoparticles via localised surface plasmon resonance

The enhancement of surface enhanced raman scattering of the hybrid Au–Ag triangular nanostructure arrays via localised surface plasmon resonance is systematically investigated. The hybrid nanostructure can prevent the pure silver nanoparticles from oxidation and the stability of Au–Ag nanoparticles compared with non-coated Ag nanoparticles has been verified. Discrete dipole approximation calculated results show the size of the nanoparticle has an important effect on localised surface plasmon resonance of the hybrid nanostructure. Nanosphere lithography is used to fabricate the hybrid nanoparticle arrays with different sizes of nanoparticle. Both theoretical calculations and experimental results show that with an increase in size of the nanoparticle, positions of localised surface plasmon resonance peak are less strongly redshifted and peak of the surface enhanced Raman scattering of the arrays is obviously strengthened. A maximum intensity of the surface enhanced raman scattering can be achieved when the localised surface plasmon resonance wavelength of the hybrid Au–Ag nanoparticle arrays well match the laser excitation wavelength.

A novel and greener approach for shape controlled synthesis of gold and gold–silver core shell nanostructure and their application in optical coatings

Green and facile synthetic methods have gained marvellous fame for the production of polyhedral, anisotropic and spherical gold, and gold–silver bimetallic nanostructures. The useful pivotal characteristics of a green procedure are the usage of environment benign solvent medium, reducing and stabilising agents, and shorter reaction time. We describe here a novel, and greener method for the production of gold and gold–silver core shell nanostructures using aqueous fish scales extract of the Labeo rohita. The effect of various reaction parameters, such as temperature and concentration for the synthesis of the nanostructures were studied. Results indicated that triangular and decahedron gold nanostructures were formed at a lower temperature (40°C) and concentration (10%). While, icosahedral and spherical gold nanostructures were produced at a comparatively higher temperature (100°C) and concentration (40%). The study also revealed that the core–shell bimetallic nanostructures with different morphologies (spherical and oval-shape) were formed at different ratios of chloroaurate and silver nitrate solution. Thus, the present study indicated a simple shape controlled synthesis of gold and gold silver core–shell nanostructures. The synthesised gold nanotriangles were coated over the glass substrate and found to be highly efficient in absorbing infra-red radiations for potential architectural applications. Therefore, the study demonstrated the facile usage of gold nanotriangles for optical coatings. The present strategy depicted the dual functional ability of the fish scale extract as reducing and stabilising agents. This strategy also eliminates the usage of hazardous chemicals, toxic solvents and harsh reducing and stabilizing agents.

Synthetic RNA technologies to control functions of mammalian cells

We recently succeeded in producing nanostructures made of RNA-protein (RNP) complexes. We show that RNA and the ribosomal protein L7Ae can form a triangular-like nanostructure that consists of three L7Ae proteins, which form the apices of the triangle, bound to one RNA scaffold. This shape is created through a 60° kink introduced into the RNA structure on L7Ae binding. By varying the size of the RNA scaffold we could in turn alter the overall size of the triangular nanostructure. Several functions can be added to this nanostructure by the introduction of effector proteins fused to L7Ae. The design and construction of functional RNP nanostructures that detect specific cancer cells are discussed herein. In parallel, we developed synthetic RNP translational switches to control production levels of particular proteins depending on certain input(s) within the intracellular environment. The RNP-binding module was successfully incorporated into mRNA to generate functional RNP switches. The designed ON/OFF translational switches detect expression of the trigger factor and repress or activate expression of a desired protein (e.g., apoptosis regulator) in target mammalian cells. Taken together, RNP-binding module could be employed for constructing designer genetic switches and functional nanostructures to regulate cellular processes.

The Effects of Gold Seeds Stabilizing Agent on Gold Nanostructures Morphologies

The synthesis of gold (Au) nanostructures was successfully achieved through a three-step heterogeneous nucleation process. Two different types of Au seeds were prepared using citrate and cetyltrimethylammonium (CTAB) as stabilisers. Citrate and CTAB stabilized seeds were used to grow Au nanostructures separately. The CTAB stabilized seeds produced larger particles, of various shapes, with an average particle size >120nm with a wide size distribution (50–200nm). The triangular Au nanostructures present in the mixture had a 3 dimensional morphology (i.e. pyramid shape) as confirmed by Atomic Force Microscopy (AFM). The citrate stabilized seeds were monodisperse and yielded well dispersed Au nanostructures with uniform morphology. These seeds had an average particle size of 50nm with a narrow particle size distribution (45 – 55nm).

Effect of nanostructures on the meniscus shape and disjoining pressure of ultrathin liquid film.

The stability of thin liquid films on nanostructured surfaces is important but poorly understood. Here, we develop a general model of the meniscus shape and disjoining pressure for thin liquid films on nanostructured surfaces based on the minimization of the free energy and the Derjaguin approximation. This model is then compared with molecular dynamics simulations for a water-gold system with triangular and square nanostructures of varying depth and film thickness, demonstrating the robustness of the analytical model.

Structural and magnetic properties of cobalt nanostructures on SiO2/Si(1 1 1) substrates

2D architectures of cobalt onto silicon (111) surfaces were elaborated by patterning of magnetic cobalt in the nanometer scale. A continuous cobalt layer of 1, 3 and 10nm thickness, respectively, was first deposited by means of thermoionic vacuum arc technique and then, thermally annealed in vacuum at temperatures ranging from 450 to 800°C. Surface structure was analyzed by atomic force and field emission-scanning electron microscopies. Above 750°C, regular triangular shape cobalt nanostructures are formed with pattern dimensions varying between 10 and 200nm. Good control of shape and packing density could be achieved by adjusting the initial thickness and the thermal and hydrogen plasma treatments. Magnetic properties were investigated using vibrating sample magnetometer technique. The evolution of the coercive field versus packing density and dimensions of the nanostructures was studied and compared to micromagnetic calculations. The observed nanostructures have been modeled by a series of shapes tending to a fractal curve.

Kinetically Controlled Growth of Gold Nanoplates and Nanorods via a One-Step Seed-Mediated Method

In this research, we further developed the one-step seed mediated method to synthesize gold nanoparticles (GNPs) and control their resulting shapes to obtain hexagonal, triangular, rod-shaped, and spherical gold nanostructures. Our method reveals that the reaction kinetics of formation of GNPs with different shapes can be controlled by the rate of addition of ascorbic acid, because this is the critical factor that dictates the energy barrier that needs to be overcome. This in turn affects the growth mechanism process, which involves the adsorption of growth species to gold nanoseeds. There were also observable trends in the dimensions of the GNPs according to different rates of addition of ascorbic acid. We performed further analyses to investigate and confirm the characteristics of the synthesized GNPs.

New Insights into the Side-Face Structure, Growth Aspects, and Reactivity of Agn Nanoprisms

We report an improved synthesis of colloidal Ag(n) nanoprisms using carboxyl compounds (citrate or succinate) and long chain macromolecules (polyvinylpyrrolidone (PVP)). The side-facet structure of the triangular nanostructure was determined in detail using electron tomography in scanning transmission mode (3D STEM) and HRTEM. It has been found that they are built up by {100} facets with a single parallel twin plane. The best conditions for producing uniform Ag nanoprisms with tunable sizes and high yields in the presence of carboxyl compounds additive system are described, and a growth mechanism is proposed. This approach provides also a route to synthesize Ag nanodisks and Au-Ag alloyed nanoprisms.

Electrodeposition of Triangular Pd Rod Nanostructures and Their Electrocatalytic and SERS Activities

We report a simple one-step electrodeposition of triangular Pd rod nanostructures on clean Au substrates without additives. Scanning electron microscopy, transmission electron microscopy, and electrochemical techniques were utilized to characterize the structural features of the triangular Pd rod nanostructures. The regulation of the electrodeposition rate by optimizing the electrolyte concentration and applied potential was critical for the anisotropic growth of Pd in the vertical direction. The triangular Pd rod structures exhibited electrocatalytic activities for oxygen reduction and methanol oxidation reactions. These surfaces could be effectively utilized as reproducible surface-enhanced Raman scattering (SERS) active substrates to produce stable SERS signals under electrochemical systems. A simple preparation of well-defined triangular Pd rod structures would allow new opportunities in various areas utilizing Pd-based nanostructured surfaces.

Lithography-free synthesis of nanostructured cobalt on Si (111) surfaces: structural and magnetic properties

We illustrate the concept of lithography-free synthesis and patterning of magnetic cobalt in the nanometric scale. Our elaboration method allows fabricating 2D architectures of cobalt and cobalt silicide onto silicon (111) surfaces. A continuous cobalt layer of 1, 3 and 10 nm thickness was first deposited by using thermoionic vacuum arc (TVA) technology and then, thermally annealed on vacuum at temperatures from 450° C to 800° C. Surface structure was analyzed by atomic force and field emission-scanning electron microscopies. Above 750° C, regular triangular shape cobalt nanostructures are formed with pattern dimensions varying between 10 and 200 nm. Good control of shape and packing density could be achieved by adjusting the initial thickness and the substrate temperature. Magnetic properties were investigated by means of vibrating sample magnetometer (VSM) technique. The evolution of the coercive field versus packing density and dimensions of the nanostructures was studied and compared to micromagnetic calculations. The observed nanostructures have been modelled by a series of shapes tending to a fractal curve.

Synthesis and Characterization of Silver and Gold Nanoparticles Using Aqueous Extract of Seaweed,Turbinaria conoides,and Their Antimicrofouling Activity

Silver and gold nanoparticles were synthesized using an aqueous extract of the seaweed Turbinaria conoides and their antibiofilm activity against marine biofilm forming bacteria is reported here. The UV-Vis spectra showed the characteristics SPR absorption band for Ag NPs at 421 and for Au NPs at 538 nm. Further, the synthesized nanoparticles were characterized using FT-IR, XRD, FESEM, EDX, and HRTEM analysis. Spherical and triangular nanostructures of the Ag and Au nanoparticles were observed between the size ranges of 2–17 nm and 2–19 nm, respectively. The synthesized Ag NPs are efficient in controlling the bacterial biofilm formation; however, Au NPs did not show any remarkable antibiofilm activity. The maximum zone of inhibition was recorded against E. coli (17.6 ± 0.42 mm), followed by Salmonella sp., S. liquefaciens, and A. hydrophila. The macrotube dilution method inferred the MIC (20–40 µL mL−1) and MBC (40–60 µL mL−1) of Ag NPs. The CLSM images clearly showed the weak adherence and disintegrating biofilm formation of marine biofilm bacterial strains treated with Ag NPs. The Artemia cytotoxicity assay recorded the LC50 value of 88.914 ± 5.04 µL mL−1. Thus the present study proved the efficiency of Ag NPs as a potent antimicrofouling agent and became the future perspective for the possible usage in the biofouling related issues in the aquaculture installations and other marine systems.

A facile photochemical route for the synthesis of triangular Ag nanoplates and colorimetric sensing of H2O2

We describe a facile photochemical route for the synthesis of triangular Ag nanoplates using NADH model compound, N-benzyl-1,4-dihydronicotinamide (BNAH) and the shape-dependent colorimetric sensing of H2O2. Synthesis of Ag nanoplates involves the irradiation of an aqueous mixture of Ag(I) and BNAH in the presence of trisodium citrate with sunlight for 30 min. The photoexcited BNAH reduces Ag(I) to Ag(0) and quasi-spherical nanoparticles were obtained at the initial stage of the reaction. The spherical nanoparticles undergo shape transformation by light and yield nanoparticles of different shapes. The spherical nanoparticles first undergo light-induced transformation to hexagonal nanoplates (∼50 nm) and then to triangular nanoplates (40 nm) in 30 min of irradiation. The triangular nanoplates exhibit two main bands corresponding to the quadrupole and dipole in-plane plasmon resonance at 407 and 620 nm, respectively, along with a shoulder band ∼335 nm corresponding to out-of-plane quadrupole resonance. The Ag nanostructure of different shapes has been used for the colorimetric sensing of H2O2. The thermodynamically favorable oxidative etching of triangular Ag nanoplates by H2O2 turns the initial green color of Ag nanostructures to gray. In the presence of H2O2, the surface plasmon band at 407 nm completely vanishes and the absorbance of the band at 620 nm significantly decreases. The oxidative etching transforms the triangular nanoplates into nanodisc with an average size of 15 nm in 1 min. The shape transformation-induced visible color change was used for the quantification of H2O2. Interestingly, the oxidative etching reaction depends on the shape of the nanoparticles. The shape of the Ag nanoparticles actually controls the redox reaction. The triangular Ag nanoplates are highly sensitive toward H2O2 and it could detect H2O2 at sub-micro molar level without any interference from coexisting other analytes. The high reactivity of the triangular nanoplates can be ascribed to the existence of coordinatively unsaturated reactive atoms at the corners of the triangular nanostructure.

Graphene-layered steps and their fields visualized by 4D electron microscopy

Enhanced image contrast has been seen at graphene-layered steps a few nanometers in height by means of photon-induced near-field electron microscopy (PINEM) using synchronous femtosecond pulses of light and electrons. The observed steps are formed by the edges of graphene strips lying on the surface of a graphene substrate, where the strips are hundreds of nanometers in width and many micrometers in length. PINEM measurements reflect the interaction of imaging electrons and induced (near) electric fields at the steps, and this leads to a much higher contrast than that achieved in bright-field transmission electron microscopy imaging of the same strips. Theory and numerical simulations support the experimental PINEM findings and elucidate the nature of the electric field at the steps formed by the graphene layers. These results extend the range of applications of the experimental PINEM methodology, which has previously been demonstrated for spherical, cylindrical, and triangular nanostructures, to shapes of high aspect ratio (rectangular strips), as well as into the regime of atomic layer thicknesses.

Effect of morphology and solvent on two-photon absorption of nano zinc oxide

In this paper, we report the effect of morphology and solvent on the two-photon absorption of nano zinc oxide. Zinc oxide nanoparticles in two different morphologies like nanospheres and triangular nanostructures are synthesized by novel precipitation technique and their two-photon absorption coefficient is measured using open aperture Z-scan technique. Experimental results show that the zinc oxide nanospheres exhibit higher two-photon absorption coefficient than the zinc oxide triangular nanostructures. The zinc oxide nanospheres dispersed in water exhibit higher two-photon absorption coefficient than that of its dispersion in 2-propanol. The zinc oxide nanospheres dispersed in water shows a decrease in two-photon absorption coefficient with an increase in on-axis irradiance. The result confirms the dependence of shape and solvent on the two-photon absorption of nano zinc oxide.