Rational design of plasmonic Ag@CoFe<inf>2</inf>O<inf>4</inf>/g-C<inf>3</inf>N<inf>4</inf> p-n heterojunction photocatalysts for efficient overall water splitting

Highly efficient and direct photocatalytic H2 evolution from water via water splitting without using sacrificial reagents is a challenging approach to convert solar energy into renewable and storable chemical energy. Herein, by amalgamating the architecture recommendations and energy band engineering principles into the design formulation, a novel Ag@CoFe2O4/g-C3N4 plasmonic p-n heterojunction photocatalytic system is designed and constructed for the first time. The Ag@CoFe2O4/g-C3N4 photocatalyst so designed, under the illumination of the visible-light (λ > 420 nm), produced H2 and O2 in 2:1 stoichiometric amount at the rates of 335 μmol h−1 and 186 μmol h−1, respectively, with an apparent quantum yield reaching 3.35% at 420 nm, demonstrating that Ag@CoFe2O4 dimer colloids are responsible for oxidation and g-C3N4 for reduction. Moreover, in the presence of triethanolamine, the apparent quantum yield achieved by Ag@CoFe2O4/g-C3N4 is 16.47% with hydrogen produced at the rate 3.5 times higher than the CoFe2O4/g-C3N4 heterojunction photocatalyst with AQY of 5.49%. The combination of Ag plasmonic effect and internal electric field established at the interface of p-type CoFe2O4 and n-type g-C3N4 boosts the separation efficiency of photoexcitons from CoFe2O4 to g-C3N4, extending the visible-light absorption capacity of the systems. The generation of optimum amount of defects like oxygen vacancies at the p-n heterojunction interface due to the structural distortion of CoFe2O4 also plays a prominent photocatalytic enhancement by providing active sites for the adsorption of water molecules for the light driven catalytic reactions. Our work introduces a potential avenue to design efficient photocatalysts by constructing several other suitable p-n heterojunction semiconductor photocatalysts toward practical application in solar energy conversion.