Potassium‐Ion‐Assisted Regeneration of Active Cyano Groups in Carbon Nitride Nanoribbons: Visible‐Light‐Driven Photocatalytic Nitrogen Reduction

Abstract

As a metal‐free nitrogen reduction reaction (NRR) photocatalyst, g‐C3N4 is available from a scalable synthesis at low cost. Importantly, it can be readily functionalized to enhance photocatalytic activities. However, the use of g‐C3N4‐based photocatalysts for the NRR has been questioned because of the elusive mechanism and the involvement of N defects. This work reports the synthesis of a g‐C3N4 photocatalyst modified with cyano groups and intercalated K+ (mCNN), possessing extended visible‐light harvesting capacity and superior photocatalytic NRR activity (NH3 yield: 3.42 mmol g−1 h−1). Experimental and theoretical studies suggest that the ‐C≡N in mCNN can be regenerated through a pathway analogous to Mars van Krevelen process with the aid of the intercalated K+. The results confirm that the regeneration of the cyano group not only enhances photocatalytic activity and sustains the catalytic cycle, but also stabilizes the photocatalyst.

Laser direct writing derived robust carbon nitride films with efficient photon‐to‐electron conversion for multifunctional photoelectrical applications

“…To gain an insight into the PEC enhancement of LCN and M‐LCN, the related optical properties were explored by UV‐vis DRS (Figure 3C). The light absorption in the UV region for all samples can be ascribed to the overlapped electron transitions of π → π* in the sp 2 ‐hybridized in the conjugated aromatic rings 56 . Compared to BCN, the DRS spectra of LCN and M‐LCN are both red‐shifted with an obvious threshold near 690 nm, resulting from the n → π* electron transition of the lone pairs of electrons around the nitrogen atom in the heptazine units 56 .…”

Elucidating Effects of Orbital Delocalization on Electrochemiluminescent Efficiency for Carbon Nitrides

“…As shown in Figure 1c, the FT-IR spectra of all CNMWT showed the peak at around 800 and 1100-1700 cm -1 , typically attributing to triazine or heptazine ring out of plane bending and the C-N heterocycles stretching vibrations, respectively. [31][32] Notably, characteristic vibrations for ν(−NH2) at 3457/3325 cm -1 and C≡N at 2205 cm -1 were observed for CNMW400, [33][34] suggesting an incomplete polymerization; at the higher temperature, these terminal groups gradually disappeared. To disclose more precise evolution of molecular structures, especially for the exact type of repeating units, during the condensation synthesis of CNMWT, the matrix-free laser desorption/ionization time-of-flight (LDI-TOF) mass spectra of CNMW400, CNMW500, CNMW580 (Figure 1d) and the control bulk CN550 (Figure S8) were further measured.…”

Atomic-level insights into the activation of nitrogen via hydrogen-bond interaction toward nitrogen photofixation

“…To further verify the origin of generated NH 3 , an isotope labeling test was performed using P-15 N 2 as the nitrogen source. 1 H NMR spectra clearly displayed the doublets for 15 S2, entry 3). Besides, the O 2 production rate was also measured during N 2 photofixation over 3%-S/Cu (Figures S15 and S16).…”

“…The reduction of nitrogen (N 2 ) molecules into ammonia (NH 3 ) under mild reaction conditions has attracted tremendous attention to meet current energy and environmental demands. 1,2 Considering the extremely high stability of a N 2 molecule with a bond length of 107.8 pm and a bond dissociation energy of 945 KJ/mol, the activation of N 2 molecules is generally regarded as the bottleneck in N 2 reduction. 3,4 Thanks to a variety of efforts, the transformation of electrons to the antibonding orbitals of N 2 molecules has been proved to be crucial step during the activation of N 2 molecules from both theoretical and experimental perspectives.…”