Piperazine-Linked Metalphthalocyanine Frameworks for Highly Efficient Visible-Light-Driven H2O2 Photosynthesis

Artificial photosynthesis of H2O2 from O2 reduction provides an energy-saving, safe, and green approach. However, it is still critical to develop highly active and selective 2e– oxygen reduction reaction photocatalysts for efficient H2O2 production owing to the unsatisfactory photosynthesis productivity. Herein, two new two-dimensional piperazine-linked CoPc-based covalent organic frameworks (COFs), namely, CoPc-BTM-COF and CoPc-DAB-COF, were afforded from the nucleophilic substitution reaction of hexadecafluorophthalocyaninato cobalt­(II) (CoPcF16) with 1,2,4,5-benzenetetramine (BTM) or 3,3′-diaminobenzidine (DAB). Powder X-ray diffraction analysis in combination with electron microscopy and a series of spectroscopic technologies reveals their crystalline porous framework with a fully conjugated structure and eclipsed π-stacking model. Ultraviolet–visible diffuse reflectance absorption spectra unveil their excellent light absorption capacity in a wide range of 400–1000 nm. This, together with their enhanced photo-induced charge separation and transport efficiency as disclosed by photocurrent response and photoluminescence measurements, endows the as-prepared piperazine-linked CoPc-based COFs with superior photocatalytic activity toward O2-to-H2O2 conversion under visible-light irradiation (λ > 400 nm). In particular, CoPc-BTM-COF exhibits a record-high H2O2 yield of 2096 μmol h–1 g–1 among the COF-based photocatalysts and an impressive apparent quantum yield of 7.2% at 630 nm. The present result should be helpful for fabricating high-performance and low-cost photocatalysts for visible-light-driven H2O2 photosynthesis.