Cooperative Chemisorption-Induced Physisorption of CO2 Molecules by Metal-Organic Chains

Abstract

Effective CO2 capture and reduction can be achieved through a molecularscale understanding of interaction of CO2 molecules with chemically active sites and thecooperative effects they induce in functional materials. Self-assembled arrays of parallelchains composed of Au adatoms connected by 1,4-phenylene diisocyanide (PDI) linkersdecorating Au surfaces exhibit self-catalyzed CO2 capture leading to large scale surfacerestructuring at 77 K (ACS Nano 2014, 8, 86448652). We explore the cooperativeinteractions among CO2 molecules, Au-PDI chains and Au substrates that are responsiblefor the self-catalyzed capture by low temperature scanning tunneling microscopy (LTSTM),X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy(IRAS), temperature-programmed desorption (TPD), and dispersion corrected densityfunctional theory (DFT). Decorating Au surfaces with Au-PDI chains gives the interfacialmetalorganic polymer characteristics of both a homogeneous and heterogeneouscatalyst. Au-PDI chains activate the normally inert Au surfaces by promoting CO2 chemisorption at the Au adatom sites even at <20 K. The CO2 δ- speciescoordinating Au adatoms in-turn seed physisorption of CO2 molecules in highly ordered two-dimensional (2D) clusters, which grow with increasing dose to a fullmonolayer and, surprisingly, can be imaged withmolecular resolution on Au crystal terraces. The dispersion interactions with the substrate force the monolayerto assume a rhombic structure similar to a high-pressure CO2 crystalline solid rather than the cubic dry ice phase. The Au surface supported Au-PDI chains providea platform for investigating the physical and chemical interactions involved in CO2 capture and reduction.