Papers by Keyword: Controlled Growth

Abstract: Scale deposits in geothermal power plants are well-known potential sources of minerals. Extensive research in mineral recovery is crucial due to the considerable variability in scale composition and geochemistry based on location. Geothermal scales from Batangas, Philippines, were used to synthesize size-modified amorphous silica (SiO₂) via sol-gel method. Initial analyses employing x-ray fluorescence spectroscopy (XRF), total dissolved solids (TDS), electrical conductivity (EC), and pH measurements confirmed that the scale is rich in silica and salts at neutral pH. Then, the effect of varying scale concentration, precipitation pH, and aging time on the particle size distribution of recovered amorphous silica were investigated. Dynamic light scattering (DLS) for particle size analysis (PSA) revealed that the sample with 2.5% (w/v) scale precursor in NaOH and precipitated until pH 10 had the lowest average cumulant diameter (1.66 μm). Moreover, the synergy of precipitation pH and aging time was found to significantly affect the polydispersity index and cumulative diameter of precipitated SiO₂ based on 2³ factorial ANOVA at 0.05 significance level. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed that the precipitates were amorphous SiO₂ with spherical morphology. This study proves the viability of utilizing geothermal scales from Batangas, Philippines for the synthesis of amorphous SiO₂ with controlled particle size, which is a potential filler for composite materials.

Abstract: Single-walled carbon nanotubes (SWCNTs) as a promising candidate in a wide range of applications have shown great potentials in optical, electronic, magnetic and mechanical fields. Precisely due to their excellent characteristics and performances, it has attracted widespread attention, and much progress has been made during recent decades. However, due to the huge challenge in controlled synthesis and purification, obtaining SWCNTs with consistent chirality has seriously limited their high-end industrial applications. In this article, we will review the approaches recently developed in chirality-controlled preparation of SWCNTs. Among them, we will introduce the mechanism of templated growth of SWCNTs from chiral affinities, including cloning and seeds designing strategies. The preparation of SWCNTs catalyzed by noble metal and assisted with weak oxidant have been illustrated as well. Meanwhile, we will also discuss some chirality-selective separation approaches, which pay more attention to post-processing strategies by purifying the chiral SWCNTs with functional reagents. We expect that these strategies in controlling the chirality of CNTs will shed more light on the mechanism and process for atomic structural control of CNTs, and may also be applicable in the controlled synthesis of other nanomaterials.

Abstract: Nanostructured ZnO with versatile morphologies has great potential applications in many fields. In this work, ZnO materials with different morphologies were deposited on Zn foils by a simple aqueous solution method, and the shape of ZnO can be controlled by the concentration of Cl ions in the solution. Rods, spheres and platelets were obtained respectively with the concentration of Cl ions increase. The competition between Cl ions and growth units in the solution results the formation of ZnO materials with different morphologies. At the same time, the preferential orientation of the crystal plane is also changed by the concentration of Cl ions. The different morphologies of ZnO grown form this kind of solution method was also explained.

Abstract: The growth of microarc oxidation (MAO) coatings on aluminum substrates was controlled by different mono-component solutions, involving (NaPO₃)₆, Na₃PO₄, Na₂SiO₃ and Na₂MoO₄ aqueous electrolyte. The results show that (NaPO₃)₆ solution can accelerate the growth of MAO coating, revealed by the maximum coating thickness of 12.1 μm; and meanwhile, Na₂SiO₃ solution favors the doping of solute elements during MAO, suggested by 10.75 at.% Si in coating. Furthermore, the variety of mono-component solution also affects the porous structure of MAO coating. It is assumed that the property of coating/solution interface is influenced by solution variety, while the interfacial property determines the solidification of ceramic particles and the adsorption of solute anion during microarc discharge, thus realizing controlled growth of MAO coating.

Abstract: A low temperature sol-gel approach was demonstrated to prepare ZnO nanoparticles with controlled morphologies. By changing the concentration of NH₄OH, the ZnO nanoparticles evolves from sphere-like, star-like and sheet-like structures. No peak of additional phase was observed in the XRD patterns except the diffraction peaks of ZnO. The estimated crystallite size of ZnO nanoparticles decreases with the increase of NH₄OH. It is also found that the morphology of nanoparticles affects the optical bandgap of ZnO. The optical bandgap of sphere-like,star-like, and sheet-like ZnO nanoparticles are 3.55 eV, 3.48 eV and 3.45 eV, respectively. The growth mechanism of ZnO nanoparticles was discussed.

Abstract: Low-pressure chemical vapor deposition (LP-CVD) technique has been utilized for controlled growth of carbon nanotube (CNT) arrays on silicon wafers. The tube-diameters of CNTs and the number of graphene layers are controlled by varying the thickness of catalyst films. The catalyst particle density and the growth conditions such as the ambient gas and the local environment are all crucial for the formation of vertically aligned CNT arrays. The length of CNT arrays can be controlled by altering the growth time. In addition, the supercapacitive properties of CNT arrays with various morphologies growing on different current collectors have been investigated using a less corrosive 0.5 M Na₂SO₄ aqueous solution as the electrolyte. Vertically aligned CNT arrays on Ti-Si substrate produce a higher capacitance compared to randomly oriented CNTs on the same current collector. Furthermore, Ni foam enables better utilization of active materials than Ti-Si substrate. CNT arrays electrodes fabricated by this simple, low cost approach demonstrate stable and consistent capacitor behaviors for a wide range of scan rates. Moreover, CNT arrays electrodes provide better platform for further integration with transitional metal oxide, via simple sputtering or electrodeposition technique, to enhance the supercapacitive performance.

Abstract: SnO2 nanocrystals with various morphologies were synthesized via a hydrothermal method assisting by the surfactant CTAB. The morphologies of the products were significantly dependent on the synthesis conditions. The products were characterized by X-ray diffraction (XRD) and field scanning electron microscopy (FESEM).The results showed products SnO2 nanoparticles and spheres like structure assembled with nanocones were obtained by varying the dosage of CTAB and the concentration of NaOH. The forming process of SnO2 sphere like structure was discussed and the proposed mechanism was put forward in this work.