Formation Of Hierarchical Nanostructures Research Articles

Surfactant‐Mediated Electrochemical Precipitation of ZnO Nanospheres for Adsorption of Eosin Yellow & Rhodamine B Dyes

AbstractA simple electrochemical technique was used to synthesise zinc oxide (ZO) nanospheres and their in‐situ modification by a two‐step route of electrochemical precipitation with subsequent calcination. The ZO sample has been employed as an adsorbent for the removal of toxic dyes from their solutions. The electrochemical precipitation of zinc hydroxide (ZH) was carried out in a zinc nitrate bath at ~pH 4. The optimised concentration of 40 g dm−3 is used for the synthesis of modified zinc oxide (MZO) in the presence of the surfactant TEAB. XRD analysis confirms the formation of the heterostructure ZO. The field‐emission scanning electron microscopy (FESEM) images support the formation of hierarchical nanostructures with interconnected nanospheres in the presence of surfactant TEAB, which was confirmed by a high‐resolution transmission electron microscopy (HRTEM) study. The porous nature of ZO and MZO was established by the N2 adsorption‐desorption studies. The MZO sample showed ~99 % adsorption efficiency at an optimum dose of 0.09 g/20 mL of the 100 mg dm−3 Eosin Yellow dye solution within 120 min. However, the same sample showed 96 % adsorption efficiency at an optimum dose of 0.05 g/20 mL of the 100 mg dm−3 Rhodamine‐B dye solution within 120 min.

Highly Active and Stable NiCuMo Electrocatalyst Supported on 304 Stainless Steel Porous Transport Layer for Hydrogen Evolution in Alkaline Water Electrolyzer

AbstractSeveral functionalized porous transport layers with Pt‐free electrocatalysts for hydrogen evolution reaction in alkaline conditions, based on Ni, Cu, and Mo, are prepared through electrodeposition onto a 304 stainless steel mesh. Morphological characterization confirms the fabrication of electrodes with high electrochemical surface active area due to the formation of hierarchical nanostructures. Mo presence into the electrocatalysts increases the activity toward the hydrogen evolution reaction. The optimization of electrodeposition process leads to the preparation of highly active NiCuMo electrocatalyst that exhibits near zero onset overpotential and overpotentials of 15 and 113 mV at 10 and 100 mA cm−2, respectively, in 1 m KOH electrolyte. Moreover, this electrocatalyst shows superior stability with respect to other Pt‐free electrocatalysts, reaching 100 h of durability with low overpotentials value demonstrating the successful preparation of very promising functionalized porous transport layers for future‐generation alkaline electrolyzers.

Distinctive Optical Properties of Hierarchically Ordered Nanostructures Self-Assembled from Multiblock Copolymer/Nanoparticle Mixtures.

Hybrid materials with hierarchical nanostructures are of great interest for their advanced functions. However, the effect of the formation of hierarchical nanostructures on properties is not well understood. Here, through combining dissipative particle dynamics simulation and the finite-difference time-domain method, the optical properties of hierarchically ordered nanostructures formed by mixtures of A(BC)n multiblock copolymers and nanoparticles (NPs) are investigated. A series of hierarchically ordered nanostructures with multiple small-length-scale hybrid domains are obtained from the self-assembly of A(BC)n /NP. An increase and blueshift in optical absorption are observed when the number of small-length-scale hybrid domains increases. The small-length-scale hybrid domains enhance light scattering, which consequently contributes to the improved optical performance. These findings can yield guidelines for designing hierarchically ordered functional nanocomposites with light-harvesting characteristics.

Exploring the self-assembly of dumbbell-shaped polyoxometalate hybrids, from molecular building units to nanostructured soft materials.

The formation of hierarchical nanostructures using preformed dumbbell-like species made of covalent organic–inorganic polyoxometalate (POM)-based hybrids is herein described. In this system, the presence of charged subunits (POM, metal linkers, and counter ions) in the complex molecular architecture can drive their aggregation, which results from a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. We show that the nature of the POM and the charge of the metal linker are key parameters for the hierarchical nanoorganization. The experimental findings were corroborated with a computational investigation combining DFT and molecular dynamics simulation methods, which outlines the importance of solvation of the counter ion and POM/counter ion association in the aggregation process. The dumbbell-like species can also form gels, in the presence of a poorer solvent, displaying similar nanoorganization of the aggregates. We show that starting from the designed molecular building units whose internal charges can be controlled by redox trigger we can achieve their implementation into soft nanostructured materials through the control of their supramolecular organization.

Nanoscale Block Copolymer Self‐Assembly and Microscale Polymer Film Dewetting: Progress in Understanding the Role of Interfacial Energies in the Formation of Hierarchical Nanostructures

AbstractBlock copolymer (BCP) self‐assembly (SA) can be exploited for next‐generation lithography for the advanced nanopatterning of surfaces with versatile nanoscale features. To render BCP‐SA suitable for the creation of tailored surface patterns, a fundamental understanding of interfacial interactions is crucial. This progress report gives an overview on the interplay of BCP microscale film thickness modulation and nanoscale microphase separation during BCP‐SA. Light is shed on the role of interfacial energies in both events. Microscale processes determining the topography of BCP films, i.e., hole/island formation and dewetting into droplets, are presented. Nanoscale microphase separation into energetically favorable pattern orientations in dependency on the polymer film thickness and influenced by surface polarities are discussed critically. Finally, examples are shown in which the combination of microscale dewetting and nanoscale microphase separation are exploited to create hierarchical nanostructures from BCPs. An outlook is given presenting successful applications of both mechanisms on prepatterned surfaces in order to control position and morphology of the hierarchical nanostructures. This approach is particularly promising for the creation of advanced surface architectures.

Control of the hierarchical self-assembly of polyoxometalate-based metallomacrocycles by redox trigger and solvent composition

Discrete metallomacrocycles are attractive scaffolds for the formation of complex supramolecular architectures with emergent properties. We herein describe the formation of hierarchical nanostructures using preformed metallomacrocycles by coordination-driven self-assembly of a covalent organic-inorganic polyoxometalate (POM)-based hybrid. In this system, we take advantage of the presence of charged subunits (POM, metal linker, and counterions) within the metallomacrocycles, which drive their aggregation through intermolecular electrostatic interactions. We show that the solvent composition and the charge of the metal linker are key parameters that steer the supramolecular organization. Different types of hierarchical self-assemblies, zero-dimensional (0D) dense nanoparticles, and 1D worm-like nanoobjects, can be selectively formed owing to different aggregation modes of the metallomacrocycles. Finally, we report that the worm-like structures drastically enhance the solubility in water of a pyrene derivative and can act as molecular carriers.

Fabrication of hierarchical CoP nanosheet@microwire arrays via space-confined phosphidation toward high-efficiency water oxidation electrocatalysis under alkaline conditions.

In spite of recent advances in the synthesis of transition metal phosphide nanostructures, the simple fabrication of hierarchical arrays with more accessible active sites still remains a great challenge. In this Communication, we report a space-confined phosphidation strategy toward developing hierarchical CoP nanosheet@microwire arrays on nickel foam (CoP NS@MW/NF) using a Co(H2PO4)2·2H3PO4 microwire array as the precursor. The thermally stable nature of the anion in the precursor is key to hierarchical nanostructure formation. When used as a 3D electrode for water oxidation electrocatalysis, such CoP NS@MW/NF needs an overpotential as low as 296 mV to drive a geometrical catalytic current density of 100 mA cm-2 in 1.0 M KOH, outperforming all reported Co phosphide catalysts in alkaline media. This catalyst also shows superior long-term electrochemical durability, maintaining its activity for at least 65 h. This study offers us a general method for facile preparation of hierarchical arrays for applications.

Strain-Mediated Interfacial Dynamics during Au-PbS Core-Shell Nanostructure Formation.

An understanding of the hierarchical nanostructure formation is of significant importance for the design of advanced functional materials. Here, we report the in situ study of lead sulfide (PbS) growth on gold (Au) nanorod seeds using liquid cell transmission electron microscopy (TEM). By tracking the formation dynamics of Au-PbS core-shell nanoparticles, we found the preferential heterogeneous nucleation of PbS on the ends of a Au nanorod prior to the development of a complete PdS shell. During PbS shell growth, drastic sulfidation of Au nanorod was observed, leading to large volume shrinkage (up to 50%) of the initial Au nanorod seed. We also captured intriguing wavy interfacial behavior, which can be explained by our DFT calculation results that the local strain gradient at the core-shell interface facilitates the mass transport and mediates reversible phase transitions of Au ↔ Au2S during the PbS shell growth.

A kinetic model for the formation of hierarchical nanostructures during the evaporation of phase-forming compound solutions

A kinetic model for the precipitation of a dispersed compound from solutions is formulated, based on a description of the evolution in the function of its particle distribution according to its states during precipitation. A boundary problem about the precipitation of a compound during the evaporation of a solvent from a solution under conditions in which the rate of aggregate formation is high is considered. The solution to this boundary problem can be used to describe the formation of a film of polystyrene during the evaporation of its solution in toluene and o-xylene deposited onto a substrate.

Facile synthesis of Zn doped CuO hierarchical nanostructures: Structural, optical and antibacterial properties

ZnxCu1−xO (where x= 0, 0.01, 0.03, 0.05, 0.07 and 0.1 mol%) hierarchical nanostructures have been prepared via soft chemical route. X-ray diffraction (XRD) results of the synthesized samples reveal the monoclinic structure of CuO without any impurity related phases. The micro-structural parameters such as crystallite size and microstrain have been strongly influenced by Zn doping. Scanning electron microscope (SEM) analyses depict the formation of hierarchical nanostructures having average particle size in the range of 26-43 nm. The surface area of CuO nanostructures has been reduced systematically with the increase in Zn content which is linked with the variations in particle size. An obvious decrease in the optical band gap energy of the synthesized CuO hierarchical nanostructures has been observed with Zn doping which is assigned to the formation of shallow levels in the band gap of CuO and combined transition from oxygen 2p states to d sates of Cu and Zn ions. The bactericidal potency of the CuO hierarchical nanostructures have been found to be enhanced remarkably with Zn doping.

Hierarchical nanostructures of tunable shapes through self-aggregation of POSS end-functional polymer and poly(ionic liquid) hybrids

Herein, the synthesis of polyhedral oligomeric silsesquioxanes (POSS) end-functional poly(1-vinyl imidazole) (POSS-PVim) hybrid using thiolated POSS in combination with AIBN as the radical initiator is described. Owing to its amphiphilic nature, such a hybrid could self-aggregate into primary micelles with PVim corona and a core containing POSS crystalline aggregates in water. POSS-PVim hybrid molecules also self-assemble to form micelles in DMF. These primary micelles further associate into compound micelles (nanospheres) through secondary ionic interactions in water (pH 6) and in DMF as established by FESEM and DLS. Interestingly, the formation of hierarchical nanostructures of different shapes such as cube, pyramid and chain-like morphology is observed due to different mode of aggregation of primary micelles upon tuning the pH of the medium. The addition of Zn(II) ion also induces aggregation of primary micelles into dendritic nanostructures. The formation of crystalline POSS aggregates is confirmed from XRD and HRTEM. Zeta-potential measurement reveals ionic interactions among PVim chain of micelles that lead to the formation of anisotropic hybrid nanostructures. POSS-poly(ionic liquid) (POSS-PIL) hybrid can be easily prepared from POSS-PVim hybrid via post-grafting modification of pendent imidazole group with 1-bromoalkanes of different alkyl chain length, which again undergoes self-aggregation into cube-shaped nanostructures in water.

Nanoscale tin dioxide films and zinc oxide hierarchical nanostructures for gas sensing applications

Nanoscale tin dioxide (SnO2) and zinc oxide (ZnO) layers are considered as promising candidates for preparation of sensing elements for metal oxide semiconductor gas sensors. Tin dioxide films deposited by direct current magnetron sputtering are investigated. The influence of deposition temperature and annealing on the structure and electrical properties of the tin dioxide films are considered. The development of design and technological solution of active layer with high gas sensitivity, reproducibility and stability is offered. Studies of effects of the pulse electrodeposition regimes on structural and substructural parameters and on morphology of zinc oxide arrays made it possible to identify modes that are optimal for formation of hierarchical nanostructures with large specific surface area suitable for gas sensing applications.

Controllable synthesis of branched ZnO/Si nanowire arrays with hierarchical structure.

A rational approach for creating branched ZnO/Si nanowire arrays with hierarchical structure was developed based on a combination of three simple and cost-effective synthesis pathways. The crucial procedure included growth of crystalline Si nanowire arrays as backbones by chemical etching of Si substrates, deposition of ZnO thin film as a seed layer by magnetron sputtering, and fabrication of ZnO nanowire arrays as branches by hydrothermal growth. The successful synthesis of ZnO/Si heterogeneous nanostructures was confirmed by morphologic, structural, and optical characterizations. The roles of key experimental parameters, such as the etchant solution, the substrate direction, and the seed layer on the hierarchical nanostructure formation, were systematically investigated. It was demonstrated that an etchant solution with an appropriate redox potential of the oxidant was crucial for a moderate etching speed to achieve a well-aligned Si nanowire array with solid and round surface. Meanwhile, the presence of gravity gradient was a key issue for the growth of branched ZnO nanowire arrays. The substrate should be placed vertically or facedown in contrast to the solution surface during the hydrothermal growth. Otherwise, only the condensation of the ZnO nanoparticles took place in a form of film on the substrate surface. The seed layer played another important role in the growth of ZnO nanowire arrays, as it provided nucleation sites and determined the growing direction and density of the nanowire arrays for reducing the thermodynamic barrier. The results of this study might provide insight on the synthesis of hierarchical three-dimensional nanostructure materials and offer an approach for the development of complex devices and advanced applications.

Doughnut-shaped hierarchical Cu2ZnSnS4 microparticles synthesized by cyclic microwave irradiation

For the first time, hierarchical doughnut-shaped Cu2ZnSnS4 (CZTS) microparticles were synthesized by microwave-assisted solution method. N,N-dimethylformamide and polyvinylpyrrolidone (PVP) were used as solvent and stabilizing agent respectively, and the results showed that PVP played an important role in the formation of hierarchical nanostructures. Structural analysis by X-ray diffraction and Raman studies confirmed the formation of single phase kesterite CZTS. Morphological analysis by scanning electron microscope showed doughnut-shaped CZTS microparticles composed of large number of interpenetrating nanoplates. Optical analysis by UV–Vis diffused reflectance spectra showed strong absorption in the visible region with an optical band gap of 1.54eV. Asymmetric broad emission bands around 1.55eV and 1.30eV were observed in the photoluminescence spectrum. A possible formation mechanism for doughnut-shaped CZTS microparticles was put forward and discussed briefly.

Hydrothermal synthesis and characterization of hierarchically nanostructured La2(MoO4)3

In this study, we report a hydrothermal method for the preparation of La2(MoO4)3 with a hierarchical nanostructure consisted of nanosheets. The influences of heating times on the products were also investigated. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The potassium sodium tartrate plays a key role in the formation of hierarchical nanostructures. The potassium sodium tartrate was used as a chelating ligand and a template molecule in the synthesis and self-assembly of nanosheets. In view of experimental results, a possible formation mechanism of these hierarchical nanostructures in the growth processes was proposed. This synthetic strategy was also successfully applied to fabricate KNd(MoO4)2 with the hierarchical nanostructure.

Using Thiol–Gold Bond Formation To Bridge Surfaces with a Polymer Brush: SFA Experiments and MD Simulations

Complementary interactions between functionalized surfaces are challenging to quantify, as both kinetics and thermodynamics are important. Optimal reaction parameters are key to the efficient formation of hierarchical nanostructures. Here, we report both surface forces apparatus (SFA) studies and molecular dynamics (MD) simulations of the controlled binding of thiol functionalized polymer brushes to complementary gold surfaces. Polymer brush–brush, brush–mica, and brush–gold experiments were performed in toluene. These comparative studies reveal the subtle balance of nonspecific and specific contributions to the measured interactions. Importantly, the physical phenomena responsible for the measured force profile in the selective binding system, including the formation of thiol–gold bonds, the resulting adhesion between the surfaces, the work to separate the surfaces, and the anchor strength of the polymer brush can be extracted. Corroborating MD simulations demonstrate that hysteresis in the approach and separation of these selectively bound surfaces is not the result of kinetic effects, but rather is due to the polydispersity of the brush itself and the resulting thiolated chain end distribution. We relate our findings to observations made in the formation of hierarchical particle aggregates.

Cysteine-functionalized zwitterionic ZnO quantum dots

Abstract

Preparation and optic properties of 3D ZnSe hierarchical nanostructure

Abstract ZnSe hierarchical nanostructures with high crystallinity were prepared via a solvothermal reaction at the water–oil interface without the help of templates or surfactants. X-ray diffraction, transmission electron microscope, absorption spectrum and photoluminescence spectrum were used to characterize the products. Meanwhile, a possible mechanism for the formation of the ZnSe hierarchical nanostructures is discussed. The experimental results indicate that the ZnSe hierarchical nanostructures adopt spherical flower-like morphology assembled from nanosheets and possess high crystallinity. The oil–water interface plays an important role in the formation of hierarchical nanostructures. Moreover, the ZnSe hierarchical nanostructures exhibit a narrow emission with full width at half maximum (FWHM) of approximate 13 nm.

Rational designing of nanoporous nanopattern arrays of Au, Pt and SiO2: synthesis using lithography, sputtering and selective dissolution

Nanoporous materials are of great importance in a variety of applications such as heterogeneous catalysts because of their large specific surface area and tuneable porosity. Herein, we proposed an approach for rationally designing nanoporous materials on a substrate by lithography, co-sputtering and selective dissolution. The physical processes (i.e., lithography and sputtering) were used to design shapes and arrangements of nanostructures, and the chemical dissolution process was used to form nanopores inside the nano-patterns. In order to investigate the compatibility of the sputtering and selective etching with the lithography process, we formed patterned nanoporous Au by co-sputtering of AuCu followed by selective dissolution of Cu with acid. Interestingly, using this process, dish-shaped Au nanostructure arrays formed through lithography processes were successfully decorated with nanoporous Au, resulting in the enhancement of SERS intensity by 10 times. Then, in order to show the versatility of our approach, we synthesized nanoporous SiO2 patterns. In this case, nanoporous SiO2 was synthesized by co-sputtering of SiO2 with Cu followed by selective dissolution of Cu with acid. Because of removal of the thermal process, this SiO2 synthesis appears to be compatible with a variety of nanofabrication procedures. Finally, in order to investigate further merits of the use of sputtering, we demonstrated the synthesis of dendritic Pt nanoporous particle arrays by co-sputtering and acid treatment. Interestingly, nanoporous particle arrays, i.e., hierarchical structure, were formed from PtCu crystal grains without coagulation, showing a possibility that crystal grains can play a role in the formation of hierarchical nanostructures.

Hierarchical metallic and ceramic nanostructures from laser interference ablation and block copolymer phase separation

We report on the formation of hierarchical nanostructures of Au, PtOx, FexOy and PdOx using a hybrid technique by combining laser interference ablation (LIA) and block copolymer phase separation (BCPS). Different types of hierarchical arrays can be obtained including square, triangular, linear and circular arrays by varying the loading time of the block co-polymer with metallic salts, and the laser interference technique. The primary ordering of the as-generated nanoarrays (30-100 nm) is tunable by changing either the composition of the block copolymer spun from solution or by changing other parameters that affect the phase separation kinetics of the block copolymer, while the secondary ordering of the features can be tuned from 200 nm to 2 μm, by changing the angle of convergence of the laser beams on the patterned substrate. Such a robust method can be applied to the fabrication of other metallic and ceramic materials including Ag, Co, and Ni (O) and has potential use in the large scale fabrication of hierarchical arrays of catalysts that can be used to grow germanium, silicon nanowires using the vapour-liquid-solid growth (VLS) technique. The as-generated arrays can also find use in optical as well as sensor applications for biodetection and biosensing.