Facile Synthesis of Solar Active Charcoal Passivated Ag3/PO4 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 decomposition of FA to produce proton (H⁺), followed by a spontaneous reduction of dissolved molecular oxygen by the photo-excited electrons. The second photocatalytic pathway involves the formation of H₂O₂ in the absence of electrons (using AgNO₃ as an electron scavenger) which occurred via oxidation of H₂O by photo-induced holes to generate hydroxyl radicals ( ● HO) and the combination of photogenerated ● HO 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.