Formation of mesoporous silicates using Triton XN surfactants in the presence of concentrated mineral acids

Mesoporous silicates have been prepared from synthesis mixtures with different acid contents using Triton XN surfactants with short poly(ethylene oxide) (PEO) chains. At very high acid contents, even Triton X45 (n(EO) = 5.0) with a very low cloud point, gives mesoporous solids. Triton X114 (n(EO) = 8.0) and Triton X100 (n(EO) = 10.0) give high quality (HQ) products within a well-defined range of acid contents. HQ products give sharper XRD peaks and narrower pore size distributions than low quality (LQ) products. We attribute the formation of the HQ products to the altered organisation of the surfactant and the formation of hydrogen-bonded adducts with the PEO chains. The N₂ adsorption-desorption parameters of the solids obtained by calcining silica-Triton XN mesophases are governed by the hydrophilicity of the surfactant, which in turn depends on the length of the PEO chains and on the acid content. Increased hydrophilicity leads to a decrease in the surface area, pore volume and pore diameter of the products.