The adsorption behavior and mechanism of Cr(VI) on facile synthesized mesoporous NH-SiO.

An efficient Cr(VI) adsorbent, mesoporous amine-functionalized silica (NH-SiO), was successfully synthesized within 2 h by a facile one-step route under room temperature and aqueous solution. The structure properties of the obtained materials were characterized by N adsorption-desorption isotherm, XRD, TEM, and FT-IR. The Cr(VI) removal performance was investigated by batch experiment. It was found that Cr(VI) removal performance was dependent on solution pH, and the removal efficiency is above 90% for initial pH in the range of 1.0-4.0. The adsorption process was obeyed by pseudo-second-order model, and the equilibrium adsorption data were fitted well by Langmuir model. The maximum monolayer adsorption capacity was 205.76 mg/g at pH 2.0, which was larger than that of traditional two-step tri-amine-functionalized MCM-41. Additionally, high selectivity was exhibited in NH-SiO for removal Cr(VI) from co-presence anions Cl, NO, PO, SO, and SiO. Furthermore, the spent NH-SiO could be regenerated by 0.005 M NaOH, and Cr(VI) removal is above 92% after NH-SiO recycled four. From the analyzed results of adsorption energy, FT-IR, and XPS, the electrostatic attraction between protonated amine group and HCrO was the mainly adsorption mechanism. And then some adsorbed Cr(VI) was reduced to low toxicity Cr(III) on the adsorbent surface by electron transfer from nitrogen in -NBr group to Cr(VI).