Novel pH-responsive swing gate system for adsorption and controlled release of BTB and MG dyes using amine functionalized mesoporous SBA-15 silica

Adsorption of anionic bromothymol blue (BTB) and cationic malachite green (MG) dyes on mono-, di- and triamine/ammonium functionalized mesoporous SBA-15 silica was investigated. The adsorbents were prepared via a post-synthesis grafting method of SBA-15 material using 3-aminopropyltrimethoxysilane, [1-(2-aminoethyl)-3aminopropyl]trimethoxysilane and 1-[3-(trimethoxysilyl)-propyl]-diethylenetriamine, followed by acidification in HCl solution to convert the attached surface amine groups to positively charged ammonium moieties. The release of BTB and MG species from free amine or ammonium functionalized adsorbents was controlled by adjusting the pH of solution. This system is proposed to be used as delivery modulation design system in which an ionically controlled molecular gate is created by using free amine/ammonium functionalized mesoporous materials with pH-responsive groups at the pore outlets. Results showed that the functionalized amine/ammonium SBA-15 materials act as a swing gate system and allow controlled selective adsorption–release of BTB and MG adsorbents and resulted in clean separation between them. Graphical Abstract