Postsynthetic acid modification of amino-tagged metal-organic frameworks:Structure-function relationship for catalytic 5-hydroxymethylfurfural synthesis

Developing an efficient and selective catalyst for the dehydration of fructose to 5-hydroxymethylfurfural(HMF)is significant for biomass conversion.Herein,a metal-organic framework(MOF)with acidity and strong hydrophobicity is first reported by the condensation of amino-tagged MOFs with mercapto carboxylic acids and subsequent oxidation.The hydrophobic acidic MOFs possess acid densities ranging from 0.2-1.0 mmol·g^(-1),H_(2)O contact angles of 114°-125°,and specific surface areas above260 m^(2)·g^(-1).Compared to the methyl sulfo-functionalized MOF,the benzene sulfo-functionalized MOF with a strong hydrophobicity shows much higher activity and selectivity for the conversion of fructose to 5-hydroxymethylfurfural.In particular,2.99%(mass)UiO-PhSO_(3)H shows the best catalytic performance with a 90.4%HMF yield due to its suitable hydrophobicity and abundant acidic sites.Moreover,the catalyst shows great stability after recycling for 5 runs.This work provides an interesting design strategy for the preparation of hydrophobic acidic MOFs and shows the powerful synergistic effect of acidity and hydrophobicity.