Enormous Promotion of Photocatalytic Activity through the Use of Near-Single Layer Covalent Organic Frameworks

Enhancing the charge separation efficiency is highly effective strategy in improving the photocatalytic activity of covalent organic frameworks(COFs)which have the problems of low conductivity and difficult dissociation of excitons.In this work,we report the sevenfold increase in apparent quantum efficiency resulting from the use of a near-single layer COF(SLCOF)in photocatalytic hydrogen evolution compared with bulk COF.Detected by transient absorption spectroscopy characterization,100% of photogenerated long-lived electrons in the near-SLCOF can be extracted and participate in the photocatalytic process.However,the electron extraction efficiency declined to only about 11% when the COFs were increased to eight layers,implying the difficulty of charge migration among COFs interlayers.The near-SLCOF was prepared by deposition of selfexfoliated COFs colloids on SiO_(2),driven by their strong affinity.This work not only sheds light on the significant influence of COF layer thickness on the charge separation efficiency but also provides a new route to prepare and stabilize COF layers for practical applications.