Abstract
This work reports a new technique called “Suspension Impregnation Method” (SiM) as an alternative to the “Incipient Impregnation Method” (IiM) for the synthesis of noble metal (Au) nanoparticles. The SiM was used to synthesize gold nanoparticles supported by titanium oxide and compared with those of IiM. The reactor for the SiM technique was based on the principles of mixing, heat, and mass transfer of the suspension reactors and the metal particle synthesis was processed in situ under the oxidation reduction potentials. Three different conditions were established to observe the effect of pH on the size of the metal particles: acid (HCl), neutral (water) and alkaline (urea). The samples were characterized by nitrogen adsorption, X-Ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA), Transmission Electron Microscopy (TEM) and CO2 adsorption. The surface area was slightly modified, and the average pore diameter was reduced in all materials. The structure of the titanium oxide was not altered. A deposit of organic material was detected in samples synthesized in alkaline medium for both methods. The pH influenced the formation of conglomerates in IiM and resulted in large particle sizes (3–9 nm). In contrast, an in situ reduction in the species in SiM resulted in smaller particle sizes than IiM (2–3 nm).
Highlights
Nanoparticles (NP) are solid particles at the atomic or molecular scale, synthesized to take advantage of the properties presented by materials at this level and are usually larger than bulk solids
Valden et al [11] studied the activity of gold nanoparticles (AuNP), and they argue that AuNPs with a diameter of 3 nm have the highest activity for CO oxidation; this can be attributed to the effect of the quantum size of the nanosized particles and the effect of load transfer with the carrier
When the TiO2 is impregnated with Au, using the impregnation or suspension method, the isotherms show a displacement to the left, meaning a decrease in pore diameter
Summary
Nanoparticles (NP) are solid particles at the atomic or molecular scale, synthesized to take advantage of the properties presented by materials at this level and are usually larger than bulk solids. Each stage considers various parameters that, in turn, affect the size of the metal particles and the efficiency of the charge, such as: type of support [23], precursor [24], concentration of the precursor [25], deposition time [26,27], temperature [27] and pH [27,28]. The deposition precipitation (DP) method involves the addition of a precipitating agent into the solution of a support and a metal precursor [26]. In addition to pH and temperature, there are other parameters which affect the metal particle size and metal loading efficiency, such as reaction time [26], support [26], precipitation agent, etc.
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