Photocatalytic Cr(VI) reduction on an ultrathin TPA-COF/UiO-66-NH₂ heterostructure with enhanced pollutant enrichment and interfacial charge separation

Constructing well-defined MOF/COF heterostructures that integrate pollutant enrichment with efficient interfacial charge separation remains challenging, as intimate interfacial contact may compromise framework integrity. Herein, an ultrathin TPA-COF/UiO-66-NH₂ heterostructure is fabricated via interfacial self-assembly of exfoliated TPA-COF nanosheets, forming a conformal COF coating while preserving the crystallinity and microporosity of UiO-66-NH₂. Microscopic, thermogravimetric, and nitrogen sorption analyses reveal a continuous ultrathin COF layer with a low yet quantifiable loading (~1.5 wt%) and a BET surface area comparable to that of the pristine MOF. Compared with the individual components and their physical mixture, the assembled heterostructure exhibits markedly enhanced photocatalytic Cr(VI) reduction, highlighting the importance of controlled interfacial integration. Comparative adsorption studies, kinetic modeling, and pH-dependent experiments indicate that Cr(VI) enrichment is closely associated with surface-charge-mediated interactions of the amine-functionalized framework. Suppressed photoluminescence, enhanced photocurrent response, and radical scavenging experiments are consistent with improved interfacial charge separation, with photogenerated electrons serving as the dominant reductive species. Band-edge analysis further suggests a staggered energy alignment that is energetically favorable for interfacial carrier transfer. These findings illustrate how combining functional-group-mediated enrichment with controlled interfacial assembly can cooperatively influence adsorption and charge-transfer processes in MOF/COF heterostructures.