Microstructure-Controlled Aerosol–Gel Synthesis of ZnO Quantum Dots Dispersed in SiO₂ Nanospheres

Abstract

ZnO quantum dots dispersed in a silica matrix were synthesized from a TEOS:Zn(NO(3))(2) solution by a one-step aerosol-gel method. It was demonstrated that the molar concentration ratio of Zn to Si (Zn/Si) in the aqueous solution was an efficient parameter with which to control the size, the degree of agglomeration, and the microstructure of ZnO quantum dots (QDs) in the SiO(2) matrix. When Zn/Si ≤ 0.5, unaggregated quantum dots as small as 2 nm were distributed preferentially inside SiO(2) spheres. When Zn/Si ≥ 1.0, however, ZnO QDs of ∼7 nm were agglomerated and reached the SiO(2) surface. When decreasing the ratio of the Zn/Si, a blue shift in the band gap of ZnO was observed from the UV/Visible absorption spectra, representing the quantum size effect. The photoluminescence emission spectra at room temperature denoted two wide peaks of deep-level defect-related emissions at 2.2-2.8 eV. When decreasing Zn/Si, the first peak at ∼2.3 eV was blue-shifted in keeping with the decrease in the size of the QDs. Interestingly, the second visible peak at 2.8 eV disappeared in the surface-exposed ZnO QDs when Zn/Si ≥ 1.0.

Thermal decomposition of alkane hydrocarbons inside a porous Ni anode for fuel supply of direct carbon fuel cell: Effects of morphology and crystallinity of carbon

“…In addition, the crystallinity of the carbon particles was analyzed by Raman spectroscopy (inVia Raman microscope, Renishaw) using a 514 nm Ar laser light, and X-ray diffraction (XRD, D/max 2400, Rigaku). More details of characterization experiments are available elsewhere [25,26]. …”

Pt Catalyst over SiO2 and Al2O3 Supports Synthesized by Aerosol Method for HC-SCR DeNOx Application

“…Assynthesized catalysts nanoparticles were collected by a glass membrane filter with 1 µm pores (Milipore). More details about experimental setup are available elsewhere (Lee et al, 2007;Firmansyah et al, 2009Firmansyah et al, , 2012.…”

“…The larger size of Pt dots when supported by Al 2 O 3 is likely attributed to higher furnace temperature, which might facilitate to sinter Pt particles into larger dots. Additionally, it can be postulated that, in the absence of sol-gel reactions which can form a matrix structure to anchor the Pt particles (Firmansyah et al, 2012), coproduced Pt dots may have a better chance to move and sinter on the surface of alumina spheres. Of particular interest is understanding the formation mechanism of Pt dots on the surface of the metal oxide spheres, in view of size and hetero-structure of Pt particles; when a droplet evaporates during the spray-pyrolysis process, the dissolved solutes are locally concentrated near the droplet surface, and diffuse toward the center of the droplet in response to the concentration gradient, while the solvent diffuses toward the outermost region, and evaporates.…”

“…, where R g is the gas constant, F is the Faraday constant, ν + and ν -are respectively the valences of the cation and anion, and λ 0 is the limiting ionic conductance (Reid et al, 1987;Firmansyah et al, 2009Firmansyah et al, , 2012 (Reid et al, 1987;Firmansyah et al, 2009Firmansyah et al, , 2012 , η B is the solvent viscosity in cP, V A is the molar volume of solute A at its normal boiling temperature in cm 3 mol -1 , and ϕ is the association factor. As a result, the diffusion coefficient of Pt(acac) 2 in ethanol is estimated to be 4.1 × 10 -6 cm 2 s -1 and the diffusion coefficient of TEOS in water is estimated at 8.0 × 10 -6 cm 2 s -1 .…”

“…Combining the sol-gel method with the aerosol spray-pyrolysis method (called the aerosol-gel method hereafter), we may take the unique benefits of each method (Lee et al, 2007;Firmansyah et al, 2009Firmansyah et al, , 2012, together with the advantage of costeffective production of microstructure-controlled particles (Lee et al, 1997;Santiago et al, 2011). Better understanding the process, one can extend this method to the synthesis of binary hetero-structured catalysts.…”