Facile synthesis of solar active charcoal passivated Ag₃PO₄ and their two-channel mechanisms for H₂O₂ formation in aerated water

This work presents the use of activated charcoal passivated-Ag₃PO₄ (CAgP) and bare Ag₃PO₄(AgP) nanoparticles (NPs) as effective photocatalysts for the generation of hydrogen peroxide (H₂O₂) in air-saturated water containing either formic acid (FA) or silver nitrate (AgNO₃). The synthesized CAgP and pristine AgP were characterized using various state-of-the-art optical and electron microscopy techniques. The CAgP composites showed remarkable photocatalyzed H₂O₂ formation compared to bare AgP NPs. The CAgP photocatalyzed-assisted H₂O₂ formation from O₂-saturated water under sunlight was achieved via two-channel mechanisms. First, in the presence of FA as a hole scavenger, enhanced H₂O₂ formation was facilitated by the decomposition of FA to produce proton (H⁺), followed by a spontaneous reduction of dissolved molecular oxygen by the valence band electrons. The second pathway involves the formation of H₂O₂ in the absence of electrons (using AgNO₃ as an electron scavenger) which occurs via the oxidation of H₂O by photo-induced holes to generate hydroxyl radicals (^•HO) and the combination of ^•HO radicals to produce H₂O₂. The most notable feature of CAgP composite as a photocatalyst is the ease of H₂O₂ formation in O₂/H₂O and O₂/H₂O/FA system, as well as the ability to reuse the recovered CAgP catalyst for a few reaction cycles without losing substantial catalytic activity or mass.