Chemical Cutting of Network Nodes in Polymeric Carbon Nitride for Enhanced Visible-Light Photocatalytic Hydrogen Generation

Abstract

Polymeric carbon nitride (C3N4) has been arising as an important semiconductor photocatalyst for photocatalytic hydrogen evolution and pollutant removal for solving the ever-pressing energy crisis and environmental issues. The crystallinity, degree of polymerization, and defect formation of the C3N4 molecular structure exhibit a profound effect on its photocatalytic performance. Herein, a facile method was proposed to introduce a certain amount of nitrogen vacancies in C3N4 by calcining trithiocyanuric acid and melamine at different temperatures. An optimal photocatalytic hydrogen evolution rate of 65.1 μmol·h–1 is achieved for catalyst SCN600, about 54 times that of pristine C3N4 (CN). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) observations showed that the introduction of nitrogen defects in polymeric carbon nitride molecules by cutting the network nodes is the main factor for enhancing the photocatalytic performance, in addition to the crystallinity and polymerization degree. Nitrogen defects induce the midgap energy level, increasing light utilization and facilitating charge transfer and separation. Density functional theory (DFT) simulations verified that cutting the network nodes increased the localized highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) states in polymeric carbon nitride, thus inhibiting electron–hole recombinations.

Nitrogen defect-containing polymeric carbon nitride for efficient photocatalytic H2 evolution and RhB degradation under visible light irradiation

“…39,40 The Urbach tail is attributed to the electronic states located within the band gap, known as midgap states. 18 According to the Kubelka–Munk function plot shown in Fig. 5(b), the intrinsic band gap value is 2.75 eV for all samples.…”

“…The percentage of the bridging tertiary N atoms (N2, N-[C] 3 ) decrease, indicating some tertiary N atoms are missing to form nitrogen defects located at the tertiary nitrogen lattice sites. 18 The inner N-bridge vacancies are related to the N defects, and formation of edge N-bridge vacancies induces the additional NH x group. That explains why 2SCN has highest content of N defects observed in EPR spectra.…”

“…Our recent study revealed that nitrogen defects in polymeric carbon nitride molecules by cutting the network nodes is the main factor to enhance the photocatalytic performance, besides the crystallinity and polymerization degree. 18 Some literature reported that nanostructured and S-doping g-C 3 N 4 catalysts were prepared with similar co-polymerization method by calcining melamine and trithiocyanuric acid, and ascribed the enhanced photocatalytic performance to synergetic effect of extended light absorption and more catalytic sites. [19][20][21] However, the detailed molecular structure of g-C 3 N 4 remained unexplored.…”

Preparation and Characterization of ZnTiO3/g‐C3N4 Heterojunction Composite Catalyst with Highly Enhanced Photocatalytic CO2 Reduction Performance

“…As shown in the N 1 s spectrum in Figure 7c, we can see three peaks at 398.7, 400.5, and 404.4 eV. The peak at 398.7 eV corresponds to the sp 2 CNC bond in the triazine ring, the peak at 400.5 eV is attributed to the N(C) 3 group, and the peak at 404.4 eV is related to the CNH group, [ 46 ] where the O 1 s region shows a peak (Figure 7d) with a binding energy of 531.2 eV, which is attributed to the TiO bond and the Zn–O bond. The binding energies at 1020.9 and 1,044.1 eV in Figure 7e correspond to Zn 2 p 3/2 and Zn 2 p 1/2 , respectively.…”

Controlling Electronic Properties of Carbon Nitride Nanotubes by Carbon Doping for Photocatalytic H2 Production

“…Among numerous existing materials, graphitic carbon nitride stands out owing to its excellent physical and chemical stability, narrow band gap, and facile fabrication. − The above features enable carbon nitride to be applied in water splitting. Nevertheless, the disadvantages of carbon nitride cause limited photocatalytic ability, including a small surface area and insufficient visible-light-harvesting ability. − Much effort has been devoted to overcoming the above defects to boost its photocatalytic performance, such as metal and nonmetal atom doping, morphology control, creating heterojunction with other materials, and introducing vacancies. − Among these strategies, the introduction of metal and nonmetal atoms (B, F, S, O, Fe, Mo) is prospective for promoting the catalytic ability of carbon nitride. − Long et al prepared O-doped carbon nitride by a one-step annealing way . The O-doped carbon nitride with a modified texture exhibited improved photocatalytic activity.…”