Promoting exciton dissociation in crystalline carbon nitride via cation-anion synergy for hydrogen peroxide photosynthesis

doi:10.1016/S1872-2067(25)64896-0

Abstract

Abstract:

Enhancing the carrier separation efficiency and charge transport properties of polymeric carbon nitride (PCN) has been a major focus of research. Extensive interest has been directed toward its modification and functionalization. In this study, a molten-salt approach was employed to simultaneously introduce cationic (K⁺) and anionic (-C≡N) species, enabling the one-step synthesis of highly crystalline PCN with significantly improved carrier separation and charge transport efficiencies. Comprehensive experimental characterization and theoretical calculations reveal that the coupling interaction between the cations and anions substantially increased the localized charge distribution, thereby facilitating exciton dissociation. Moreover, the incorporation of -C≡N and K⁺ ion pairs enhanced the adsorption and activation of O₂, driving the two-electron oxygen reduction reaction (2e^- ORR) to produce H₂O₂, exhibiting a remarkable 46.6-fold increase over unmodified PCN. This work provided valuable insights into the critical role of cation-anion pairs in enhancing exciton dissociation, paving the cost-effective way for photocatalysts toward efficient solar energy conversion and high-value-added chemicals artificial photosynthesis.

Key words: Polymeric carbon nitride, Cation-anion ion pairs, Molten salt approach, Exciton dissociation, H₂O₂ photosynthesis

Junqing Li, Kelin He, Ying Tao, Chao Chen, Linfu Xie, Yunfei Ma, Junpeng Wang, Changwen Xu, Yang Li, Qitao Zhang. Promoting exciton dissociation in crystalline carbon nitride via cation-anion synergy for hydrogen peroxide photosynthesis[J]. Chinese Journal of Catalysis, 2026, 82: 174-186.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(25)64896-0

https://www.cjcatal.com/EN/Y2026/V82/I3/174

Figures/Tables 6

Fig. 1. Synthesis processes and morphology of M-KPCN. (a) Schematic diagram of the synthesis procedures of M-KPCN. (b,c) HR-TEM images of the M-KPCN sample. HAADF-STEM image (d) and distribution of element mapping images (e,f) of M-KPCN sample.

Fig. 2. Structural characterization of M-KPCN. XRD patterns (a), FT-IR spectra (b), and ESR spectra (c) of U-PCN, M-PCN, U-KPCN and M-KPCN. C 1s (d) and N 1s (e) XPS spectra of U-PCN and M-KPCN. (f) Solid-state 13C MAS NMR spectra of original U-PCN and M-KPCN. UV-vis diffuse reflection spectra (g) and Tauc plot (h) of U-PCN, M-PCN, U-KPCN and M-KPCN. (i) Schematic illustration of band structures of U-PCN, M-PCN, U-KPCN and M-KPCN.

Fig. 3. Characterization of exciton dissociation and charge transport. (a) Transient photocurrent response under visible light illumination. EIS spectra (b), PL spectra (c), and Time-resolved PL spectra (d) of as-formed samples. Temperature-dependent PL spectra of M-PCN (e) and M-KPCN (f). Calculated charge density distribution of VBM and CBM in U-PCN (g,h) and M-KPCN (i,j). The charge difference density of O2 adsorbed on U-PCN (k) and M-KPCN (l). The yellow represents the electron accumulation area, and the light blue represents the electron dissipation area. The blue, gray, white, and red spheres represent N, C, H, and O atoms, respectively. (m) Quantitative charge transfer (ΔQ) from photocatalyst to adsorbed O2.

Fig. 4. 2D mapping fs-TA spectra of U-PCN (a) and M-KPCN (d). TA spectra of U-PCN (b) and M-KPCN (e). Corresponding TA kinetic traces of U-PCN (c) and M-KPCN (f). C 1s (g), N 1s (h), and K 2p (i) spectra of M-KPCN in dark and light.

Fig. 5. Photocatalytic performance of M-KPCN in the photosynthesis of H2O2 and high-value-added chemicals. (a) Photocatalytic H2O2 generation rates of as-prepared samples. (b) Photocatalytic H2O2 generation rates and associated AQY under photoirradiation (wavelengths of 365, 420, 450, 500, and 600 nm). (c) Repeated runs of photocatalytic H2O2 production over M-KPCN for 5 times under visible light irradiation (3 h for each cycle). Yield and conversion rate of benzyl alcohol (d), methylbenzyl alcohol (e), and 4-methoxybenzyl alcohol (f) using M-KPCN photocatalyst under visible light irradiation.

Fig. 6. Produced free radicals and proposed mechanism study. (a) Koutecky-Levich plots of U-PCN, M-PCN and M-KPCN measured by RDE. (b) Photocatalytic H2O2 generation by M-KPCN with the addition of AgNO3, BQ, and TBA sacrificial reagents. (c) Photocatalytic H2O2 generation by M-KPCN with different atmosphere conditions. In-situ EPR signals of ?O2- (d) and ?OOH (e) over M-KPCN in the presence of DMPO. (f) EPR signals of 1O2 was tested in the presence of TEMP. (h) Calculated Gibbs free energy variation during H2O2 production process for each intermediate species using U-PCN and M-KPCN.

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