Fractal-Percolation Structure Architectonics in Sol-Gel Synthesis

Abstract

It was developed a new technique to assess micro- and mesopores with sizes below a few nanometers. The porous materials with hierarchical fractal-percolation structure were obtained with the sol-gel method. The tetraethoxysilane hydrolysis and polycondensation reactions were performed in the presence of salts as the sources of metal oxides. The porous materials were obtained under spinodal decomposition conditions during application of the polymer sol to the substrate surface and thermal treatment of the structures. The model is based on an enhanced Kepler net of the 4612 type with hexagonal cells filled with a quasi-two-dimensional projection of the Jullien fractal after the 2nd iteration. The materials obtained with the sol-gel method were studied using the atomic force microscopy, electron microscopy, thermal desorption, as well as an AutoCAD 2022 computer simulation of the percolation transition in a two-component system using the proposed multimodal model. Based on the results obtained, a new method was suggested to assess micro- and mesopores with sizes below a few nanometrs, which cannot be analyzed using the atomic force microscopy and electron microscopy.

SnO2-Based Porous Nanomaterials: Sol-Gel Formation and Gas-Sensing Application

“…The analysis of gas sensitivity measurements based on PPD and X-ray phase analysis data allowed us to find the optimal temperature for annealing nanocomposites of a three-component system, SiO 2 –SnO 2 –In 2 O 3 (700 °C). Based on complex studies of AFM, the BET technique and on previous research [ 47 , 48 ], a hierarchical model of the formation of two-component and three-component porous nanocomposites was proposed, presented in Figure 20 and Figure 21 (in the inset, the semiconductor and dielectric grains of nanocomposites are indicated in pink and blue), accordingly. According to the AFM data, it was found that two-component porous nanocomposites, SiO 2 –SnO 2 , were macro–meso–microporous (macropore sizes of 170–180 nm and mesopore sizes of 40–50 nm) and three-component porous nanocomposites, SiO 2 –SnO 2 –In 2 O 3 , were meso–microporous (mesopore sizes of 11–15 nm).…”

“…In refs. [ 47 , 48 ], it is shown that the analytical capabilities of atomic force microscopy do not allow for the diagnosis of elements with sizes smaller than the locality of the method; therefore, the micropore system (less than 2 nm in size) cannot be detected. At the same time, the contribution of such pores to the total surface area can be determined by using the BET technique.…”

“…It was found that the surface area of the porous nanocomposites calculated by processing atomic force images differed by 2–3 orders of magnitude from the surface area calculated according to the BET data. This indicated the existence of a micropore system of less than 10 nm, which was not diagnosed using AFM [ 47 , 48 ].…”

Impedance Spectroscopy of Hierarchical Porous Nanomaterials Based on por-Si, por-Si Incorporated by Ni and Metal Oxides for Gas Sensors

“…Design of new material structure is a promising way to solve this problem. The most interesting approach is the development of materials with a fractal structure [17]. Fractal TiO 2 gas sensor has excellent performance in acetone detection, which attributed to the high film porosity and fractal like network structures [18].…”

Step-By-Step Modeling and Demetallation Experimental Study on the Porous Structure in Zeolites

“…A distinction is made among zeolites [ 32 , 33 ] based on micropore size, and the groups range from zeolites with small micropores (0.3–0.45 nm, A), through medium (0.55 nm, pentasils) and large (0.75 nm, faujasites, β—0.64 × 0.76 nm) to extra large (>0.8 nm, mordenites).…”