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 (H 2 O 2 ) 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-C 3 N 4 ), here, an ultrathin g-C 3 N 4 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-C 3 N 4 . The remarkable H 2 O 2 yield (3177.0 μmolꞏg −1 ꞏh −1 ) of CN-T-1 (by two-step calcination , 1 °Cꞏmin −1 optimal heating rate) was 3.7 times that (858.6 μmolꞏg −1 ꞏh −1 ) of CN-O-1 (by one-step calcination , 1 °Cꞏmin −1 heating rate) and higher than those of pure g-C 3 N 4 in literature. Most of the H 2 O 2 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 ⋅ O 2 - radicals were verified to be the primary active species. A two-step single electron ORR pathway ( O 2 + e - → ⋅ O 2 - → H 2 O 2 ) was confirmed for H 2 O 2 production over CN-T-1. An ultrathin g-C 3 N 4 nanosheet (CN-T-1) with large surface area and enhanced crystallinity by two-step calcination at 1 °C·min -1 exhibited an increased photocatalytic H 2 O 2 production yield of 3177.0 μmol·g ·1 ·h -1 .