Photoinduced Enhancement of Uranium Extraction from Seawater by MOF/Black Phosphorus Quantum Dots Heterojunction Anchored on Cellulose Nanofiber Aerogel

UiO-66-NH2/black phosphorus quantum dots (MOF/BPQDs) heterojunctions are anchored on the carboxyl cellulose nanofiber (CNF) aerogel with high porosity (>98%) to fabricate high-efficiency uranium adsorbents (BP@CNF-MOF). CNF aerogels possess abundant carboxyl groups, which can serve as nucleation centers to in situ synthesize UiO-66-NH2 with smaller crystal size, high mass loading, and good adhesion. BP@CNF-MOF demonstrates good mechanical flexibility and minimal MOF loss from the CNF aerogel, both of which result from the mutual physical interactions and entanglements of CNFs as well as strong binding interactions between MOF crystals and CNF aerogel. Owing to the excellent heterogeneous photocatalytic activity of MOF/BPQDs, on one hand, marine bacteria can be effectively destroyed by reactive oxygen species (ROS). On the other hand, the photocatalytic U(VI) reduction to insoluble U(IV) could be facilitated, thereby allowing more binding sites on the MOF crystals for further U(VI) adsorption. Consequently, compared with dark conditions, the adsorption efficiency of the light irradiated BP@CNF-MOF increases by 55.3%, reaching up to 6.77 mg-U per g-Ads after 6 weeks of exposure to natural seawater. The intrinsic instability of BPQDs can be overcome by MOF coating layer simultaneously. The strategy applied in this work could also be applicable to other superior MOF crystals.

Automated summary

The BP@CNF-MOF high-efficiency uranium adsorbents are fabricated by anchoring UiO-66-NH2/black phosphorus quantum dots heterojunctions on carboxyl cellulose nanofiber aerogel. The adsorbents demonstrate good mechanical flexibility and enhanced adsorption efficiency under light irradiation due to the excellent heterogeneous photocatalytic activity of MOF/BPQDs. The strategy could potentially be applied to enhance adsorption efficiency of other superior MOF crystals as well.