Efficient simultaneous removal of Cu(II) and Cr2O72− from aqueous solution by a renewable amphoteric functionalized mesoporous silica

A renewable, amphoteric functionalized mesoporous silica (AG-SBA-15) was synthesized with a two-steps process: firstly, aluminum atoms was incorporated into the framework of SBA-15 and then melamine-based dendrimers groups were anchored onto the Al-substituted SBA-15. The amphoteric AG-SBA-15 kept an ordered hexagonal mesostructure after the functionalization and regeneration processes and exhibited an excellent performance for simultaneous removal of Cu(II) cations and Cr2O72− metalloid anions from aqueous solution, with the maximum adsorption capacity of 2.216 mmol/g Cu(II) and 3.305 mmol/g Cr2O72−, respectively. Batch adsorption experiments results indicated that the optimized pH value for simultaneous removal of Cu(II) and Cr2O72− was 5.0. The adsorption rate was extremely fast and the equilibrium reached within 30 min. The adsorption of Cu(II) and Cr2O72− by AG-SBA-15 were fitted better to Langmuir than Freundlich Model and thermodynamic parameters revealed the spontaneous and exothermic nature of the adsorption. Reusability studies of AG-SBA-15 were carried out by 5 repeated adsorption-desorption cycles and the results confirmed that AG-SBA-15 could be easily reused with little loss in removal efficiency. Furthermore, simultaneous removal mechanism of Cu(II) and Cr2O72− by AG-SBA-15 was proposed by X-ray photoelectron spectroscope analysis (XPS), which revealed that Cu(II) was adsorbed by a combination of electrostatic interaction, while Cr(VI) could be immobilized by reduction.