Remarkable Photocatalytic H2O2 Production Efficiency over Ultrathin g-C3N4 Nanosheet with Large Surface Area and Enhanced Crystallinity by Two-Step Calcination
The generation of hydrogen peroxide(H2O2)from water and oxygen redox reaction by photocatalysis has acquired increasing attention owing to its green and clean properties.Aiming at the low intrinsic photocatalytic activity of carbon nitride(g-C3N4),here,an ultrathin g-C3N4 nanosheet photocatalyst with a large surface area and enhanced crystallinity was fabricated by a two-step thermal polymerization technique.The calcination parameters showed a significant impact on the structural properties and catalytic performance of g-C3N4.The remarkable H2O2 yield(3177.0 μmol·g−1·h−1)of CN-T-1(by two-step calcination,1 ℃·min−1 optimal heating rate)was 3.7 times that(858.6 μmol·g−1·h−1)of CN-O-1(by one-step calcination,1 ℃·min−1 heating rate)and higher than those of pure g-C3N4 in literature.Most of the H2O2 yield for CN-T-1 remained after five cycles,showing good stability.The enhanced catalytic performance of CN-T-1 than CN-O-1 is owing to its larger specific surface area,enhanced crystallinity,higher oxygen adsorption ability and photogenerated carrier separation efficiency,longer lifetime of carriers,and slightly larger bandgap(3.07 eV,+0.26 eV bigger than CN-O-1)with more positive valence band position owing to ultrathin layers.The •O2− radicals were verified to be the primary active species.A two-step single electron ORR pathway(O2+e− → •O2− → H2O2)was confirmed for H2O2 production over CN-T-1.
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