Effective and Green Treatment of Cyanide-Containing Wastewater over Two-Dimensional Conjugated Metal–Organic Frameworks: A Combined Density Functional Theory and Descriptor Study

The removal of cyanide from industrial wastewater is urgent, as conventional biological, physical, or chemical methods are not highly efficient and often require harsh conditions. Therefore, we conduct density functional theory to identify two-dimensional (2D) conjugated metal-organic frameworks (c-MOFs) of 3d transition metals linked by triphenylene (TM-HHTP, where TM = Sc-Zn). All possible reaction pathways are considered for two cyanide adsorption modes: C-terminal and N-terminal. The results indicate that the primary final products for the energetically most favorable routes are a blend of NH₃ and CH₄ gases via the C- terminal adsorption modes and a gaseous mixture of CH₃NH₂, NH₃ and CH₄ via the N-terminal adsorption modes. Moreover, the composition of the CNRR product is dependent on the applied voltage. The electrocatalytic performances of various TM-HHTP materials are analyzed using seven interpretable intrinsic descriptors. Among the ten investigated c-MOFs, Ti-, V-, Mn-, Ni-, and Cu-HHTP monolayers stand out as promising CNRR electrocatalysts with high electrochemical stability, low limiting potential, and high selectivity against the hydrogen evolution reaction. This work offers a new wastewater resource utilization method and provides theoretical guidance for the design of electrode materials for effluent treatment.