UiO-66-COOH introduces free carboxylic acid functionality into the UiO-66 family, giving the framework more polar and coordinating binding sites. This makes it particularly interesting for selective adsorption of polar compounds, metal ions and other species where hydrogen bonding, electrostatic interactions or coordination can be important. It can be useful in water-treatment research, adsorptive purification, functional membrane development and as a platform for further chemical modification.