Direct synthesis of pore-expanded amino-functionalized mesoporous silicas with dimethyldecylamine and the effect of expander dosage on their characterization and decolorization of sulphonated azo dyes

With harmless reagents, a series of pore-expanded amino-functionalized mesoporous silicas (PEAFMS) were directly synthesized under mild alkali condition. During the preparation, dimethyldecylamine (DMDA) served as the expander. The PEAFMS samples (S0, S0.50, S1.00, S1.50 and S2.00), which were prepared using different DMDA/surfactant (cetyltrimethylammonium, abbr. CTAB) molar ratio of 0, 0.50, 1.00, 1.50 and 2.00, were characterized by FTIR spectroscopy, CHN elemental analysis, X-ray diffraction and N2 adsorption measurement. Results demonstrated that the addition of DMDA markedly influenced the porous structures of synthesized samples. Their pore sizes and pore volumes were adjusted in the range from 4.684 to 22.31 nm and from 0.6046 to 1.360 cm3/g, respectively. Subsequently, the adsorption mechanism of sulphonated azo dyes onto obtained PEAFMS samples was analyzed and the optimal pH was determined as pH 2. The synthesized decolorants were then compared for the removal of given dyes (acid mordant dark yellow GG and reactive red violet X-2R) from aqueous solutions and the degressive order of adsorption capacities for two dyes was S1.50 > S2.00 > S1.00 > S0.50 > S0. The experimental results confirmed that the use of DMDA could improve the decolorization performance of functionalized mesoporous silicas. The sample synthesized with DMDA/CTAB molar ratio of 1.50 owned the suitable pore size (19.04 nm) and pore volume (1.360 cm3/g), so it exhibited better decolorization ability than counterparts. The adsorbed amount of acid mordant dark yellow GG and reactive red violet X-2R reached 1.713 and 0.902 mmol/g, respectively.