Robust MOF film of self-rearranged UiO-66-NO2 anchored on gelatin hydrogel via simple thermal-treatment for efficient Pb(II) removal in water and apple juice

Abstract

Pb(II), a highly toxic heavy metals that targets the human nervous system, has contaminated water and food in recent years. The nanomaterial of Metal–organic frameworks (MOFs) possesses superior removal performances. However, their practical application is limited by their nature of fine powdery. Herein, we developed robust MOFs film without the adding of polymer in MOFs ink and the modification of the substrate, which was achieved by choosing appropriate substrate of gelatin hydrogel with functional groups and simple thermal-treatment after coating UiO-66-NO 2 onto gelatin hydrogel. The volatilization of the UiO-66-NO 2 dispersant ethyl acetate promotes the rearrangement and dense accumulation of UiO-66-NO 2 crystals to form a dense UiO-66-NO 2 film. During the following thermal-treatment process, –COOH of UiO-66-NO 2 and –NH 2 of gelatin chemically reacted to establish the stable composites of UiO-66-NO 2 film and gelatin hydrogel. The results of batch adsorption experiments demonstrate that adsorption behaviors of the as-synthesized gelatin/UiO-66-NO 2 film composite hydrogels can be explained by the pseudo-second-order kinetic model and the Langmuir isotherm model, stating that this adsorption process involves with a chemical monolayer adsorption. Besides, gelatin/UiO-66-NO 2 film composite hydrogels own satisfactory removal efficiency for Pb(II) in apple juice, and the adsorption process has little impairment on the quality of apple juice. These results suggest that MOFs film is suitable for water decontamination and food safety control fields. • Developing uniform UiO-66-NO 2 film grown on gelatin hydrogel substrate. • UiO-66-NO 2 crystals rearranged during the volatilization of ethyl acetate. • –COOH of UiO-66-NO 2 reacted with –NH 2 of gelatin during drying process. • Pb(II) chelates with –COOH and –NH 2 of as-synthesized adsorbent. • Adsorption process has little effect on the quality of apple juice.