Photocatalytic hydrogen peroxide production by anthraquinone-augmented polymeric carbon nitride

We describe the exploitation of the selective catalytic property of anthraquinone (AQ) for solar photocatalytic synthesis of hydrogen peroxide (H2O2) as a green, sustainable alternative to organic-solvent-based and energy-intensive industry-benchmark processes that also rely on AQ catalysis. We accomplished this by anchoring AQ onto polymeric carbon nitride (C3N4), a metal-free visible light photocatalyst (band gap energy = 2.7 eV), that has been previously demonstrated for selective H2O2 synthesis. A net H2O2 production rate of 361 μmol g−1 h−1 and an apparent quantum yield (AQY) of 19.5% at 380 nm excitation were achieved using AQ-augmented C3N4 under simulated 1-sun illumination in the presence of an organic electron donor (2-propanol); these results were 4.4-fold and 8.3-fold higher than those reported for bare C3N4, respectively. A suite of experimental analyses confirmed the unique roles of AQ co-catalysis in (i) capturing electrons from the conduction band of C3N4, thereby reducing futile exciton recombination, which is otherwise prevalent in bare C3N4; (ii) effectively mediating electron transfer to drive hydrogenation reaction to form anthrahydroquinone (AQH2) from AQ; and (iii) catalyzing oxygen reduction to H2O2 through the dehydrogenation of AQH2 back to AQ, resulting in the facile and selective formation of H2O2. In addition, the reduced decomposition of produced H2O2 by the C3N4/AQ composite photocatalysts, when compared to bare C3N4 or C3N4 composited with common metallic co-catalysts such as Pt and Ag, was found to contribute to the significant enhancement in H2O2 production through the oxidation of both organic and water.