Transforming an Insulating Metal–Organic Framework (MOF) into Semiconducting MOF/Gold Nanoparticle (AuNP) and MOF/Polymer/AuNP Composites to Gain Electrical Conductivity

Abstract

Transforming permanently porous but electrically insulating metal–organic frameworks (MOFs) into electrically conducting materials is key to expanding their utility beyond traditional guest storage, separation, and delivery applications into the realms of modern electronics and energy technologies. To this end, herein, we have converted a highly porous but intrinsically insulating NU-1000 MOF into semiconducting NU-1000/gold nanoparticle (AuNP) and NU-1000/polydopamine/AuNP composites via MOF- and polymer-induced reduction of infiltrated Au3+ ions into metallic AuNPs. The NU-1000/AuNP and NU-1000/PDA/AuNP composites not only gained significant room temperature electrical conductivity (∼10–7 S/cm), which was ca. 104 times greater than any MOF/metal nanoparticle (MNP) composites exhibited thus far under the same conditions, i.e., without photoinduction and thermal induction, but also retained sizable porosity and surface areas (1527 and 715 m2/g, respectively), which were also larger than most intrinsically conducting 3D MOFs developed to date. The markedly higher conductivities of the NU-1000/AuNP and NU-1000/PDA/AuNP composites can be attributed to more efficient charge hopping or tunneling through well-dispersed AuNPs embedded inside the crystalline MOF matrix, which pristine NU-1000 lacked. Thus, this work presented an effective new strategy to transform porous but nonconducting MOFs into electrically conducting MOF/MNP composites with considerable porosity, which could be useful in future electronics, electrocatalysis, and energy storage devices.