Green Synthesis for MCM-41 and SBA-15 Silica Using the Waste Mother Liquor

In an attempt to synthesize silicas with respect to green chemistry, the synthesis of MCM-41 and SBA-15 silicas by a low-cost approach through the recycling of waste mother liquors was investigated. The addition of the mother liquor in consecutive syntheses was carried out in order to evaluate the different effects on the physical and chemical properties of the silicas. MCM-41 silicas were characterized by X-ray diffraction, which confirmed the formation of the hexagonal phase in the mother liquor used. According to the results of XRD, BET and SEM, SBA-15 silica has a structure that includes mesopores of various levels, crystallites and grains within the original particles. From the analysis of the textural characteristics of the various samples obtained through nitrogen adsorption/desorption studies carried out at -196 °C, the following conclusions can be highlighted: (i) For the synthesis of MCM-41, there was a trend of increase in specific surface areas, reduction in pore diameter and increase in wall thickness; (ii) For the synthesis of SBA-15 there was an increase in the specific surface area, an increase in the pore diameter and a reduction in the wall thickness. It was found that, under the synthesis conditions, the mother liquor user had an influence on the final characteristics of these materials.