“Ship-in-a-bottle” entrapment of biomolecules in MOF-based xerogel monoliths for high-performance electrochemical hydrogen evolution

Abstract

The “ship-in-a-bottle” entrapment of bioactive molecules in metal–organic framework (MOF)-based xerogel monoliths based on a controlled mesopore architecture was reported. In this method, varying the nanoparticle sizes of MOFs yielded xerogel monoliths with controlled mesopores for enhancing the adsorption of biomolecules, followed by the removal of solvents with high surface tension to narrow the mesopore size for permanent entrapment of guests. The obtained UiO-66 xerogel monoliths have Brunauer–Emmett–Teller surface areas > 1000 m² g⁻¹ with mesopore sizes ranging from 8.2 to 21 nm. The xerogel monoliths with the optimum mesopore size exhibited ∼9-fold enhancement of vitamin B12 (VB) uptake over UiO-66 powder. The removal of water from the VB-containing xerogel monoliths resulted in the permanent entrapment of VB with a negligible leak rate of ∼0.05 wt% h⁻¹ in water. The excellent supporting environment of the obtained xerogel monoliths for maximizing catalytic performance through biomolecule entrapment was demonstrated in the electrochemical hydrogen evolution reaction (HER) with high performance, catalytic durability for at least 24 h, a low overpotential/Tafel slope of 21 mV/47 mV dec⁻¹, and turnover frequencies of 1.8 and 9.3 s⁻¹ at 100 and 200 mV, respectively. These results are comparable to those of the best-performing MOF-based and cobalt-based catalysts for the HER. Owing to the advantages of MOF-based xerogel monoliths over traditional gel-based materials, particularly, the possibility for controlling micro/mesopore size and polarity, our strategy realizes a powerful tool for coupling various substances of unique properties within the tunable chemical surface and pore size of MOF-based xerogel monoliths to provide supporting environments for enhancing catalytic performance.