Adsorptive removal of nitro- or sulfonate-containing dyes by a functional metal–organic framework: Quantitative contribution of hydrogen bonding

Abstract

The removal of organic dyes from water is important from the perspective of sustainability. In this study, the adsorptive removal of four dyes having nitro or sulfonate groups was performed using highly porous metal–organic frameworks (MOFs, MIL101s) with or without further functionalization. In particular, a melamine-functionalized MOF (MIL101-Mela) was effective in the removal of martius yellow (MY), naphthol yellow S, orange G, and sunset yellow FCF. For example, the adsorbed quantity of MY over MIL101-Mela, even after the fourth recycle, was 6.9 times that over the fresh activated carbon. Moreover, MIL101-Mela showed higher adsorption capacity for the four studied dyes than previously reported any adsorbent. The adsorption results suggest the importance of the number of hydrogen donors and hydrogen acceptors in adsorbents and dyes, respectively, for improved performance in dye removal. Importantly, the mechanism of the dyes adsorption over the functionalized MIL101s is explained by the formation of six-membered rings between the studied MOFs and the dyes via hydrogen bonding. This work will pave the way toward the development of effective adsorbents for organics having high concentration of nitro or sulfonate groups.