Synthesis of Hierarchical Porous Silica by Sol‐Gel of Sodium Silicate and Nanoemulsion Templating: Effective Combination Conditions

• Published in: ChemistrySelect (Weinheim) Vol. 6; no. 7; pp. 1440 - 1447
• Main Authors: Hessien, Manal, Prouzet, Eric
• Format: Journal Article
• Language: English
• Published: 17.02.2021
• Subjects: Hierarchical Porous Silica; Macropores; Nanoemulsion Templating; Sol-Gel of Sodium Silicate
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202003836

Hierarchical porous materials have attracted a considerable attention owing to the increased interest in their applications. Hierarchical Porous Silica (HPS) was synthesized by combining the sol‐gel of sodium silicate (SS) and oil in water nanoemulsion (O/W‐NE) templating. The oil droplets of NE acted as pore forming agent and the sol‐gel built the silica framework. The O/W‐NE was prepared by a low energy method, i. e., the phase inversion composition (PIC) method. The influence of pH of SS and NE on HPS was studied. The volume of ammonia, used to induce gelling, was studied as a factor influencing the HPS. The calcined samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), FTIR, N2 adsorption and small‐angel X‐ray scattering (SAXS). The results show that the microstructure is highly affected by pH and can be; macropores inserted in a dense matrix; a blend of a dense and a porous structure; or fully hierarchical porous silica. HPS has a specific surface area of 240 m2/g and a large pore volume (1.5 cm3/g) and a surface roughness of 2.95. In nanoemulsion templating, the pH of nanoemulsion and silica precursor affects sodium silicate hydrolysis and condensation around the oil droplets resulting in various microstructure. The interaction between the silica particles and the template is highly affected by the pH as it changes the electrostatic surface charges of particles. Starting from the same pH (HSSS‐ACNE) allowed us to obtain better control over the reaction as we could induce the silica condensation “on‐demand”, instead of as a result of a complete or partial spontaneous reaction.