Confined crystallization of microporous metal-organic framework within mesoporous silica with enhanced hydrostability: Ultrafast removal of organic dyes from aqueous solutions by MIL-68(Al)@SBA-15 composite

In this study, MIL-68(Al), a metal-organic framework, and SBA-15 (Santa Barbara Amorphous-15), a well-known silica material, were chosen for fabrication of composite material 1 by reflux method. The composite 1 named MIL-68(Al)@SBA-15 was characterized fully. TEM images and BET results confirmed the crystallization of MIL-68(Al) inside SBA-15 channels. Interestingly the BET surface area increased from 797 m2 g−1 for SBA-15 to 947 m2 g−1 for composite 1. Herein for the first time, we synthesized and used composite 1 for the adsorption of dye pollutants from water. The adsorption ability of composite 1 was investigated towards different dye solutions and was compared with the ability of bare MIL-68(Al) and SBA-15. The results revealed that the composite 1 adsorbed 100 % of MB solution in 0.5 min with a maximum adsorption capacity of 68.93 mg g−1. Furthermore, the composite 1 was used for adsorption of binary, ternary, and quaternary mixed dye solutions and showed high adsorption efficiency for removal of all the mixed dye solutions in short time. The kinetics of the adsorption process follows the pseudo-second-order model, and the Langmuir isotherm model provides the best fitting for the adsorption of MB onto composite 1. Also, for investigation of the effect of synthesis route on the prepared composite material, the composite 2 named MIL-68(Al)/SBA-15 was synthesized by solid-state grinding and its adsorption ability toward dye solutions was compared with composite 1.