Figure 4.

Proposed mechanistic scheme for the investigated surface properties of HKUST-1. The paddlewheel unit of the pristine MOF is converted to the dehydrated Cu²⁺/Cu²⁺ dimer upon temperature treatment at 160 °C, which in turn undergoes a partial decarboxylation to yield a Cu⁺/Cu²⁺ complex. The surface Cu²⁺/Cu²⁺ dimer is reversibly replenished upon exposure of the Cu⁺ sites to CO₂ in the gas phase.