High Proton Conductivity of MOF-808 Promotes Methane Production in Anaerobic Digestion

Abstract

Metal–organic frameworks (MOFs) are widely used in fuel cells, catalysis, and other fields. However, the influence and mechanism of the excellent properties of MOFs on biomethane production are still unclear. In this paper, MOF-808 was used to study anaerobic digestion (AD) of corn stalk, which increased biogas production and methane content by 11.06–39.82% and 10.15–14.28%, respectively. The optimal effect of biogas production was reached by adding 0.5 g/L MOF-808. The −OH of MOF-808 provided protons through protonation during AD, and then, a continuous hydrogen bond network was formed in the channels of frameworks. The hydrogen bond network led to the appearance of the Grotthuss mechanism, which made the dispersed H+ in the system to rapidly transport to the outside of the methanogen membrane along the inner surface of the sample and the nanopores, and promoted interspecies hydrogen transfer. The formation of a transmembrane proton gradient improved the hydrogen metabolism level of methanogens and promoted the energy synthesis of microorganisms. In addition, MOF-808 had a positive impact on the community and function of the microorganisms. Due to the stable structure of MOF-808, the reflux of anaerobically digested effluent is a potential way of MOF-808 recycling.