Efficient and selective removal of congo red by mesoporous amino-modified MIL-101(Cr) nanoadsorbents

Extending applications of the mesoporous MOFs in the efficient removal of organic dyes have being concentrated on. In this paper, a nanoscale, mesoporous and amino-functionalized NH2-MIL-101(Cr) sized in 50 nm with uniform mesopores of 3.93 nm has been synthesized, the isoelectric point of which is at pH 8.5. The adsorption activities of NH2-MIL-101(Cr) toward the organic dyes including congo red (CR), methyl orange, direct blue 80, acid blue 1, rhodamine B and methyl blue have been studied. Comparatively, NH2-MIL-101(Cr) nanoadsorbents present the highest adsorption activity toward CR, which value is higher than most previously reported adsorption results of CR on other solid adsorbents. The CR adsorption is featured Langmuir monolayer adsorption, endothermic, increase entropy and spontaneous process with a negative ΔG°. The best adsorption selectivity for CR is attributed to the hydrogen bonding formed between CR and NH2-MIL-101(Cr), the matched molecular size and the electrostatic attraction. [Display omitted] •High removal efficiency for CR by mesoporous, nanosized NH2-MIL-101(Cr).•Best adsorption selectivity is observed for CR over other organic dyes.•The enhanced adsorption of CR is owing to the formation of hydrogen bond.•The consistency between pore size and molecular size of CR play important roles.