ZnCr2O4@ZnO/g‐C3N4: A Triple‐Junction Nanostructured Material for Effective Hydrogen and Oxygen Evolution under Visible Light

A triple‐junction nanostructured material consisting of porous exfoliated graphitic carbon nitride (g‐C3N4) nanosheets, ZnO, and ZnCr2O4is prepared by a one‐pot synthesis method through the calcination of a mixture of urea, thiourea, and Zn–Cr layered double hydroxide (LDH) at 450 °C. The structural, morphological, and optical properties of the prepared nanocomposites are characterized by various physicochemical techniques. This synthesis process simultaneously makes the material porous, produces exfoliated sheets of g‐C3N4, and disperses mixed metal oxides on the surface of g‐C3N4owing to the slow evolution of significant amount of gases such as H2O, CO2, NH3, and H2S. The dispersion of ZnO and ZnCr2O4on the surface of the g‐C3N4exfoliated nanosheets results in a preferable resolution for visible‐light‐induced photocatalytic H2and O2evolution. An optimal g‐C3N4content (60 %) in the ZnCr2O4@ZnO/g‐C3N4nanostructured composite results in maximum H2(847 μmol in 2 h) and O2(455 μmol in 2 h) production in the presence of CH3OH and AgNO3, respectively, as sacrificial reagents. The apparent conversion efficiencies for H2and O2evolution are 28.01 and 15.0 %, respectively. The increased photocatalytic activity is attributed to the proper alignment of the band structure, synergistic effects owing to the good coordination between g‐C3N4(Lewis base) and ZnIIions (Lewis acid), and the suppression of electron–hole recombination owing to the formation of g‐C3N4nanosheets.