Time-dependent Morphology Evolution Research Articles

Evolution of CuO bundles of nanowires by room temperature surface oxidation of electroplated Cu for high-performing energy storage device

In the present work, copper oxide bundles of nanowires (CuO BNWs) were synthesized by room-temperature surface oxidation of an electroplated Cu layer in an alkaline bath. The time-dependent morphological evolution of CuO BNWs is systematically achieved by varying surface oxidation times. The CuO BNWs provide a high surface area (19.12 m2/g) and have shown excellent supercapacitive performance with a specific capacitance of 509 F/g at 1 A/g current density owing to fast electron transfer paths offered by BNWs. The all-solid-state hybrid supercapacitor device (SS//Cu//CuO-BNWs//KOH-PVA//rGO) demonstrates a specific capacitance of 77.3 F/g and energy density of 22.57 Wh/kg at a power density of 1.29 kW/kg.

Temperature and time dependent morphological evolution of solution phase synthesized copper oxide nanostructures

Temperature and time dependent morphological evolution of solution phase synthesized copper oxide nanostructures

Surface etching evolution of mechanically polished single crystal diamond with subsurface cleavage in microwave hydrogen plasma: Topography, state and electrical properties

Surface etching of single-crystal diamond (SCD) in hydrogen plasma plays a decisive role for high-quality homoepitaxy and surface conduction of diamond. The complexity of surface/subsurface condition such as defects would give rise to the distinct morphology features and even further result in the unpredictable properties. Correspondingly, the evolutionary relationship between the morphology and electrical properties of mechanically polished SCDs which have typical cleavage damage in microns depth after hydrogen plasma treatment still needs to be further completed. In this work, the chemical vapor deposited (CVD) SCDs with uniform polishing-caused subsurface cleavage were immersed in microwave hydrogen plasma for variable duration. Time-dependent morphological evolution, multi-mode etched pits (EPs) (resulting from local defects/cracks and dislocations) and associated etching mechanism were comprehensively studied. At the early stage of plasma treatment before 60 min, owing to the obvious surface roughing generated by preferential etching (with the rate of >400 nm/h) of severe mechanically damaged regions, the hole mobility was significantly deteriorated, also accompanying with the apparent drop of sheet concentration. Concurrently, the deposited surface sp2 amorphous carbon (a-C) nanodots on diamond surface and non-sp3 hydrogen bonds reconstruction, which arising from defect-etching produced local abundant carbon-containing radicals or possible exfoliation generated by hydrogen penetration of massive defective regions, also would play an adverse role for the conduction associated with (100) C–H surface. However, the surface roughness was reduced from the maximum 13.2 nm–4.2 nm by prolonging etching, resulting from the smoothing effect of small-angle crystal misorientation on waved height difference related to the uniform (111) cleavage and the removal of dense irregular EPs associated with polishing-induced local defects as well as the vanishing of surface a-C nanodots. In this case, the improvement of surface electrical properties together with the negative correlation of the mobility and sheet concentration were appeared by the gradual formation of (100) diamond surface and the building of uniform (100) C–H bonds.

In Situ One-Pot Synthesis of C-Decorated and Cl-Doped Sea-Urchin-like Rutile Titanium Dioxide with Highly Efficient Visible-Light Photocatalytic Activity

Titanium dioxide (TiO2) that offers high light-harvesting capacity and efficient charge separation holds great promise in photocatalysis. In this work, an in situ one-pot hydrothermal synthesis was explored to prepare a C-decorated and Cl-doped sea-urchin-like rutile TiO2 (Cl-TiO2/C). The growth of sea-urchin-like 3D hierarchical nanostructures was governed by a mechanism of nucleation and nuclei growth-dissolution-recrystallization growth from time-dependent morphology evolution. The crystal morphology and the content of Cl and C could be controlled by the volume ratio of HCl to TBOT. Systematic studies indicated that the 0.4Cl-TiO2/C sample (the volume ratio of HCl to TBOT was 0.4) exhibited the highest visible-light photocatalytic activity for the degradation of rhodamine B, with kinetic rate constant (k) of 0.0221 min-1, being 6.5 and 3.75 times higher than that of TiO2 and Cl-TiO2. The enhanced photocatalytic performance could be attributed to the high charge separation and transfer efficiency induced by Cl-doping and C decoration and the excellent light-harvesting capacity caused by its sea-urchin-like nanostructure. Moreover, the 0.4Cl-TiO2/C sample exhibited good reusability and excellent structural stability for five cycles. This facile one-pot approach provides new insight for the preparation of a TiO2-based photocatalyst with excellent photocatalytic performance for potential application in practical wastewater treatment.

Hyperbranched hierarchical nanoarchitectures of ZnOHF: synthesis, characterization, growth mechanism and their gas sensing property

The growth and design of hyperbranched hierarchical nanoarchitectures attract considerable current research enthusiasm in various scientific and technological fields, in which high porosity, large surface area and strong coupling between the sub-branches, are expected. In this paper, the growth of hierarchical ZnOHF nanoarchitectures via a hydrothermal strategy is demonstrated. A variety of controllable morphologies with tunable degrees of branching, such as nanoparticles, nanorods, polypods, sheaf- and spherulite-like prickly hierarchical nanoarchitectures, can be obtained with the controlled regulation of the synthetic parameters including temperature, reaction time and solvent component. For the formation of ZnOHF hierarchical nanoarchitectures, the crystal splitting growth mechanism plays the dominant role, which is evidenced by the time-dependent morphological evolution. It is shown that the gas sensing properties of ZnOHF hyperbranched hierarchical nanoarchitectures may be closely correlated with their branching degrees. The half-sheaf-shaped ZnOHF nanoarchitecture exhibits the highest response for ethanol among some common hazardous volatile compounds.

Comparison of carrier dynamic behavior and photocatalytic molecular oxygen activation of optimized MAPbX3 (X = I, Br)

Abstract Understanding carrier dynamic behavior including carrier lifetime and concentration, electrochemical behavior and band structure of the MAPbX3 (X = I, Br) with high crystal quality are important for improving photocatalytic applications. Herein, a facile isopropanol-assisted solvothermal strategy was demonstrated for highly yielding synthesis MAPbX3 (X = I, Br) cubic microcrystals with high crystallinity for degrading water insoluble dyes in an organic solvent system. Supported by time-dependent morphology evolution experimental evidence, a high temperature gradient inside the solution leads to natural convection which can induce the screw dislocation in microcrystals. The XRD, IR, steady-state photoluminescence (PL) spectra, fluorescence lifetimes UV–vis spectra and electrochemical tests were investigated to found a direct correlation between crystal quality (crystallinity and defects) and optical properties (PL intensity and bandgap). Importantly, MAPbBr3 displayed almost an order of magnitude more efficient photocatalytic degradation of malachite green (MG) dye in isopropanol solvent relative to those of MAPbI3, which was ascribed to good stability and superior photoinduced electron transfer for molecular oxygen activation.

Precursor- and Time-Dependent Morphological Evolution of ZnO Nanostructures for Comparative Photocatalytic Activity and Adsorption Dynamics with Methylene Blue Dye.

Diverse ZnO nanostructures were successfully fabricated at 700 °C by direct annealing of 1D Zn(II) coordination polymer precursors, namely, [Zn2(bpma)2(adc)2]n, [Zn2(bpea)2(adc)2]n, and {[Zn2(bpta)2(adc)2]·2H2O}n. The effect of sacrificial ligands present in the precursors as well as a variation in the retention time (6–24 h) during their synthesis resulted in 0D nanospheres, 1D microrods, and 3D polyhedra (with a diamond-like structure) of ZnO. The as-synthesized ZnO nanostructures were characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, diffuse reflectance spectroscopy, and Raman spectroscopy. The hexagonal crystal structure was confirmed for all the ZnO samples. A lattice spacing of 0.22 nm has been observed for nanospheres, whereas a lattice spacing of 0.26 nm has been observed for the polyhedra. Their Raman spectra confirm the wurtzite phase of ZnO. UV–vis spectra of ZnO nanostructures exhibit broad peaks in the range of 350–370 nm, and the band gap energies are found to be in the range of 3.02–3.20 eV. Based on the photoluminescence spectra photocatalytic activities of the as-synthesized ZnO nanostructures calcined for 12 h were tested with methylene blue (MB) as a contaminant in an aqueous solution. These results demonstrate that the photocatalytic efficiency of polyhedra is higher than those of nanospheres and microrods. The adsorption kinetics of MB dye by these nanostructures were studied by three different kinetic models—Elovich’s, intraparticle, and pseudo-second-order. The maximum rate of adsorption was observed with the intraparticle diffusion model.

Efficient antimony removal by self-assembled core-shell nanocomposite of Co3O4@rGO and the analysis of its adsorption mechanism

Co3O4@rGO were facilely prepared by template free self-assemble in this study. The morphology of Co3O4@rGO was actiniaria-like core-shell structural nanocomposites. The formation mechanism of Co3O4@rGO core-shell nanocomposite was discussed according to its significant time-dependent morphology evolution course. To evaluate the application potential of Co3O4@rGO, its adsorption performance toward highly toxic antimony ions were studied. The Co3O4@rGO nanocomposite exhibit high anti-interference ability and high adsorption ability. The maximum adsorption capacities towards Sb(III) and Sb(V) are 151.04 and 165.51 mg/g, respectively. River water samples containing antimony violating the limit were used to evaluate the practical application of Co3O4@rGO, and high performance was achieved. The EU and China limits for antimony in drinking water can be met by using mesoporous Co3O4@rGO treating the actual river water samples with original antimony concentration lower than 50 μg/L. Adsorption isotherm, adsorption kinetics, pH and co-existing ions effects were also studied in details. The results indicate that mesoporous Co3O4@rGO is an excellent adsorbent for antimony removal. Mesoporous Co3O4@rGO nanocomposite is a potential candidate for antimony removal from waste water.

Controlled synthesis and panchromatic printing of highly luminescent NaYF4:Ln3+ upconversion hollow microtubes for information encryption on various packaging substrates

Lanthanide-ion doped β-NaYF4 crystals with bright and tunable upconversion luminescence are urgently demanded in anti-counterfeiting printing. Herein, novel highly luminescent hexagonal NaYF4:Ln3+ upconversion hollow microtubes (UCHMs) were controlled synthesized by a one-pot hydrothermal method employing poly(ethylene imine) (PEI) as ligand. The surface of the synthesized UCHMs was decorated by water-soluble polymer of PEI, rendering the hydrophilic nature of UCHMs. Besides, the synthesized UCHMs exhibited bright upconversion luminescence under the irradiation of a 980 nm laser due to the unique structure and morphology. Time-dependent morphology evolution showed that the formation of UCHMs experience a morphology change from nanoparticles to hexahedron to microprisms, and ultimately to microtubes via a dissolution-reconstruction formation mechanism. Furthermore, the resulting UCHMs were used as pigments for preparation of luminescent inks and their application in anti-counterfeiting printing was explored. To realize panchromatic printing, we prepared three-primary-color (RGB) UCHMs by rational tailoring the doping pairs and molar ratio of the lanthanide ions in UCHMs. Based on the superposition principle of the red-green-blue as three primary colors, a wide array of luminescent inks with panchromatic luminescent colors were prepared. The successful creation of securely light-responsive smart encryption patterns on various packaging substrates such as art paper, aluminum sheet, polyethylene terephthalate (PET) film and cardboard by screen printing was demonstrated. Our strategy provides a new route for controlled synthesis of hydrophilic UCHMs and the as-prepared UCHMs have great potential in application of packaging anti-counterfeiting.

Facile synthesis of hierarchical hexagonal flower-like WO3·0.33H2O nanostructures with enhanced visible-light-driven photocatalytic activity

Novel hierarchical hexagonal flower-like WO3·0.33H2O nanostructures (HHFWNs) have been successfully synthesized by hydrothermal method. We found that the hierarchical architectures of WO3·0.33H2O are self-assembled by a number of regular-shaped nanosheets of size 10–20 nm, which are cross-linked in the interior of the micro-hexagonal-flower. According to the time-dependent morphology evolution process, a possible formation mechanism is put forward. The effects of PEG-400 and H2O2 on the product are also studied. Furthermore, the photocatalytic activity of the obtained HHFWNs was investigated for the degradation of RhB under visible light illumination. The product exhibits excellent photocatalytic activity and has good stability and reproducibility. We believe that the present work will provide some ideas for further fabrication of other novel nanostructures and exploration of their applications.

Effect of growth time on solvothermal synthesis of vanadium dioxide for electrochemical supercapacitor application

In this work, we report the time-dependent morphological evolution of the as-prepared vanadium dioxide (VO2) and its electrochemical performance for supercapacitor applications. VO2 with different morphologies (microspheres and nanosheets) were successfully synthesised by solvothermal method for time growth ranging from 2 h 30min to 12 h at a temperature of 200 °C. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), gas adsorption/desorption analysis and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure, morphology, composition and the oxidation state of the as-prepared samples. The electrochemical behaviour of the as-prepared VO2 samples were analysed in a three-electrode cell configuration using 6 M KOH aqueous electrolyte. The VO2 samples revealed monoclinic crystal structure (with VO2 (B) monoclinic phase for the samples prepared for 4 h and 6 h and VO2 (A) monoclinic phase for the samples grown for 2 h 30min and 12 h). The VO2 samples grown for 4 h and 6 h displayed nanoflakes and nanosheets-like morphology, respectively, whereas VO2 samples grown for 2 h 30min and 12 h revealed nanorods-like morphology. The 6 h grown sample also showed more porous structure leading to much higher specific surface area, pore volume and enhanced electrochemical performance with highest specific discharge capacity of 49.28 mA h g−1 at current density of 0.5 A g−1 and the corresponding specific capacitance of 663 F g−1 at a scan rate of 5 mV s−1 with excellent cycling stability as compared to others samples. Accordingly, the 6 h is considered to be optimal growth time for VO2 nanosheets for considerable potential as an electrode material for supercapacitor applications.

Preparation, Growth Mechanism, Upconversion, and Near-Infrared Photoluminescence Properties of Convex-Lens-like NaYF4 Microcrystals Doped with Various Rare Earth Ions Excited at 808 nm

Preparation of rare earth ions doped photoluminescence materials with controlled morphology was desired to fulfill the requirement of different applications. In the work, the convex-lens like NaYF4 microcrystals doped with various rare earth ions were prepared by adjusting preparation parameters including the reaction time, reaction temperature, NaOH concentration, ratio of oleic acid to 1-octadecene and types of doping ions. Possible growth mechanism of convex-lens like NaYF4 microcrystals is proposed based on reaction time and temperature dependent morphology evolution. The formation of micro convex-lens includes the three processes of NaYF4 nanoparticles self-assemble, dissolution–nucleation and regrowth. Doping-ions dependent near infrared and upconversion luminescence properties of convex-lens like NaYF4 microcrystals were investigated excited at the 808 nm. The visible upconversion luminescence was observed in the Er3+, Yb3+/Er3+, Nd3+/Er3+, Nd3+/Yb3+/Er3+ doped convex-lens like NaYF4 microcrystals,...

Nanocluster-Mediated Synthesis of Diverse ZnTe Nanostructures: from Nanocrystals to 1D Nanobelts.

Liquid phase one-pot synthesis of semiconductor nanocrystals, by direct nucleation-growth crystallization, is unsuccessful for synthesis of some kinds of semiconductors. Using ZnTe as an example here, highly disperse ZnTe nanoclusters with diameters of 2-3 nm were first synthesized by a facile solvothermal method. Then the ZnTe nanoclusters were chosen as starting crystallization seeds to mediate the synthesis of flexible semiconductor nanostructures. Three-dimensional (3D) oriented assembly of ZnTe nanoclusters to monodisperse dendrimer-like nanocrystals (DLNCs), and one-dimensional (1D) ZnTe nanobelts with cubic phase, have been achieved successfully. Supported by TEM characterization of time-dependent morphology evolution, the oriented attachment assisted seed growth, based on ZnTe nanoclusters, enabled the 1D flexible ZnTe nanobelts formation, which could reach to ≈10 micrometers length.

Formation of urchin-like ZnO nanostructures by sol-gel electrophoretic deposition for photocatalytic application

Currently, more attentions have been paid to the design and synthesis of three dimensional nanostructures. ZnO urchin-like shapes assembled by nanoparticles are grown on FTO glass substrates by sol-gel electrophoretic deposition of a colloidal sol containing zinc acetate (ZAD), triethylamine (TeA), and methanol. Based on observations from a time-dependent morphology evolution process, a three-step sequential growth model is recommended. The formation of urchin-like ZnO nanostructures depends on the type of media, sol concentration, and molar ratio of TeA/ZAD. Importantly, strong structure-induced photocatalytic performance enhancement for the degradation of methylene blue is obtained by these ZnO nanostructures compared to traditional ZnO film. The large specific surface area (48.4 m2 g−1), strong light absorption ability, and nanoparticle shape affect the charge separation and transfer of urchin-like particles and hence enormously enhance the performance of photocatalyst. This work helps better understanding of the urchin-like shapes formed during sol-gel electrophoretic deposition and introduces an efficient way to enhance the photocatalytic efficiency of ZnO by changing the morphology.

Controllable Synthesis of Polyhedral Fe₃O₄ Hollow Spheres Using Hexamethylenetetramine as Structure-Directing Agent.

Polyhedral Fe₃O₄ hollow spheres were synthesized using hexamethylenetetramine as structure-directing agent and the effect of hexamethylenetetramine on the morphology was investigated in detailed. The comparison for samples prepared with and without hexamethylenetetramine indicated that hexamethylenetetramine played a vital role in the formation process of the hollow polyhedral structure. The formation process and growth mechanism of Fe₃O₄ spheres with hollow polyhedral morphology were preliminarily explored according to a detailed time-dependent morphology and structure evolution. It was deduced that the hollow polyhedral structure can be ascribed to the cooperation of oriented aggregation and Ostwald ripening mechanisms. The as-prepared Fe₃O₄ hollow spheres with polyhedral structures which possess high magnetization saturation value (73 emu/g) at room temperature, large cavity and huge specific surface area (57.12 m2·g–1) are expected to have wide potential applications, for example in the drug delivery process, magnetic separation and waste treatment in the future.

3D hierarchical golden wattle-like TiO2 microspheres: polar acetone-based solvothermal synthesis and enhanced water purification performance

3D hierarchical TiO2 microsphere structures self-assembled from 1D nanostructures have attracted considerable research attention due to their unique microstructures and properties, and non-polar solvent-based solvothermal methods have been proved to be effective techniques to synthesize such structures. However, to the best of our knowledge, no successful products have been reported based on polar solvents in the available literature. Herein, for the first time, uniform and sophisticated golden wattle (Acacia pycnantha)-like TiO2 microsphere structures, self-assembled from highly crystallized and radially grown 1D rutile nanorods, were successfully synthesized via a template-free solvothermal reaction using only polar acetone as the solvent in the presence of hydrochloric acid (HCl). The obtained samples showed good water purification performance, even superior to Degussa P25, owing to their unique 1D nanorod building block structure, fast electron transfer rate, excellent light harvesting capability and good crystallinity. In addition, a three-step growth mechanism of the golden wattle-like TiO2 microspheres was proposed based on a time-dependent morphology and crystal form evolution process. The synthetic strategy for the golden wattle-like TiO2 microspheres employed in this study provides new insights into the design of 3D hierarchical TiO2 structures for practical environmental purification applications.

Self-assembly synthesis of LaPO4 hierarchical hollow spheres with enhanced photocatalytic CO2-reduction performance

Urchin-like LaPO4 hollow spheres were successfully synthesized by a facile solution route using citric acid (CA) as a structure-directing agent. The size of the three-dimensional (3D) hollow spheres was tuned by changing the concentration of CA. The formation mechanism of the 3D LaPO4 hollow spheres was revealed by studying the time-dependent morphology evolution process. Importantly, compared with monodispersed one-dimensional (1D) LaPO4 nanorods, the 3D LaPO4 hollow spheres self-assembled from nanorods showed a 6.8-fold enhancement in photocatalytic activity for CO2 reduction, which is attributed to the synergistic effect of their hierarchical hollow structure, higher light-harvesting capacity, and faster electron transfer. Our findings provide not only a simple, facile method for the synthesis of hierarchical hollow micro/nanoarchitectures but also an efficient route for enhancing the photocatalytic performance.

Morphology dependence of electrochemical properties on palladium nanocrystals

In recent years, shape control has received the most attention in the exploration of Pd nanocrystals (NCs). However, exploring an efficient approach for the systematic production of Pd NCs under similar reaction conditions still presents a significant challenge, which is significantly important to clearly explain the effectiveness of morphology on the catalytic activity of Pd NCs. We designed and accomplished a facile strategy for the morphology transformation between Pd nanosheets and Pd nanotetrahedra by simply controlling the reaction temperature. A growth mechanism was proposed based on TEM images of the time-dependent morphology evolution. The Pd nanosheets and Pd nanotetrahedra exhibit higher activity for the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) compared with the benchmark Pd/C catalysts, and their activities are dependent on the morphology. In particular, Pd nanosheets show an increased activity by 3.81 (MOR) and 2.86 (ORR) times due to their large specific surface area and exposed facets.

Controlled synthesis of CeO2 microstructures from 1D rod-like to 3D lotus-like and their morphology-dependent properties

Monodisperse 3D lotus-like CeO2 microstructures have been successfully synthesized via controlling the morphology of CeCO3OH precursors under hydrothermal condition as well as subsequent calcination. The reaction time was systematically investigated. XRD, FT-IR, SEM, TEM, XPS, Raman scattering and Photoluminescence (PL) spectra were employed to characterize the samples. The lotus-like CeO2 hierarchical structures with an average of 4–6 μm are composed of many nanoplates of 100–200 nm in thickness as the petals stacking together to form open flowers and have a fluorite cubic structure. Based on the time-dependent morphology evolution evidences, a nucleation-dissolution-recrystallization mechanism has been proposed to explain the transformation from rod-like structures to lotus-like CeO2 hierarchical structures with the increase of reaction time. It is found that there are Ce3+ ions and oxygen vacancies in surface of samples. The magnetic and photoluminescence measurements indicated that all CeO2 samples exhibit excellent ferromagnetism and optical properties at room temperature, and while increasing the reaction time, the ferromagnetism and optical properties increase more, which can be reasonably explained for the influences of the different morphology of the particles and the concentration of oxygen vacancies and Ce3+ ions.

Hollow cauliflower-like WO3 nanostructures: Hydrothermal synthesis and their CO sensing properties

Hollow cauliflower-like WO3 nanostructures have been successfully synthesized via a facile hydrothermal process. The 3D novel structure is assembled by lots of non-uniform hexagonal WO3 nanorods, which shows the porosity surface and the hollow interiors. According to the time-dependent morphology evolution process, a possible formation mechanism was proposed. Gas sensing investigations reveal that the sample sensor exhibits excellent CO sensing properties at 270°C, which may substantially benefit from the (001) reactive surfaces of hexagonal phase and the hollow porous structure.