Hydrogen-bond-stabilized high density catechol monolayer on magnetite Fe3O4(111)

Catecholic anchor groups are widely used to immobilize functional molecules on various substrates. In this work, the structure and stability of catechol adsorbed on single-crystalline magnetite Fe3O4(111) surfaces have been studied experimentally with temperature programmed desorption, X-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy in combination with periodic density functional theory calculations. The experimental results show that the adsorbed catechol monolayer is thermally stable up to 600 K. At higher temperature, complete combustion with involvement of lattice oxygen occurs. A high-coverage adsorption phase, which contains two catechol molecules per Fe3O4(111) unit cell (2cc/u.c.), is identified at low temperature, which transforms into a regular adsorption phase with one catechol molecule per unit cell (1cc/u.c.) at and above room temperature. Calculations show that the monodentate catechol-iron complex is favored over the bidentate catechol-iron complex for the 1cc/u.c. phase. Remarkably, intermolecular hydrogen bonds, as well as molecule-surface H-bond interaction trigger known cooperativity effects to stabilize the high-coverage, 2cc/u.c. phase.