Extending the π-Conjugation of g-C₃N₄ by Incorporating Aromatic Carbon for Photocatalytic H₂ Evolution from Aqueous Solution

Abstract

This study details the synthesis of high-activity g-C3N4 catalysts for H2 generation from a triethanolamine aqueous solution under visible light. We anneal a mixture of urea and NH4Cl to obtain g-C3N4 nanosheets, which are subsequently solvated with ethanol molecules and annealed to form aromatic carbon-doped g-C3N4. The results of analyses conducted using X-ray photoelectron, Fourier-transform infrared, and carbon-13 nuclear magnetic resonance spectroscopies demonstrated that annealing the ethanol molecules leads to the grafting of aromatic heterocycles on the g-C3N4 nanosheets and substitution of nitrogen with carbon. The grafted aromatic heterocycles and doped carbon atoms extend the π-conjugation system in g-C3N4 to reduce the band gap and facilitate the separation of photogenerated charges. The carbon-incorporating also preserve the crystallinity of g-C3N4 during high-temperature annealing, which facilitates the suppression of the recombination of photogenerated charges at defect sites. The developed aromatic carbon-doped g-C3N4 effectively catalyzes H2 generation from the aqueous solution, achieving apparent quantum yields of 14% and 2.2% under 420 and 550 nm monochromatic irradiation, respectively, whereas urea-derived g-C3N4 reached only 3.4% and 0.1%. The proposed strategy of extending the π-conjugation system is promising for promoting the activity of carbon-nitride photocatalysts.

Intramolecular Charge Transfer and Extended Conjugate Effects in Donor–π–Acceptor‐Type Mesoporous Carbon Nitride for Photocatalytic Hydrogen Evolution

“…It is clear that the extended conjugation effect enlarges the range of motion of electrons.T he introductiono faconjugated structure can enhance the electron delocalization to reduce the recombination of photoelectron-hole for improved photocatalytic activity. [43] Li and Zhang designed ag -C 3 N 4 -based D-p-A-p-D structured catalystt hat displayed enhanced photocatalytic hydrogen evolution. [44] However, the complex synthesis ands tability of the core structure could limit the use of the catalyst.…”

Organosilica Nanotube Templates: One‐Pot Synthesis of Carbon‐Modified Polymeric Carbon Nitride Nanorods for Photocatalysis

“…In addition, the formation of heterojunctions by fabricating PCN composites with graphene, carbon, TiO 2 , etc., has been demonstrated to improve the photocatalytic performance through the enhanced charge separation at the heterojunctions . Grafting of aromatic moieties to C 3 N 4 could also realize the enhancement of visible‐light photocatalytic hydrogen generation from water . However, this is frequently a multistep procedure, involving grafting onto pre‐prepared C 3 N 4 .…”

Influence of Thermal and Photochemical Treatments on Structure and Optical Properties of Single‐Layer Carbon Nitride

“…An XPS study of the GCN samples showed them to have the same atomic C/N ratio of 0.68 in a broad range of T p (ESI, Table S1, Supporting Information). This value is lower than expected for the stoichiometric C 3 N 4 , 0.75, indicating an excess of nitrogen atoms, most probable in the form of primary and secondary amino groups that survived the polycondensation. An analysis of the high‐resolution XPS spectra, presented in details elsewhere, showed that nitrogen is present in three states – pyridinic CNC, pyrrolic C 3 N and bound into C 2 NH fragments.…”

“…The formation of peroxide species can be clearly observed by FTIR spectroscopy. The IR spectra of bulk GCN reveal a “fingerprint” band at 810 cm −1 (Figure a) as well as a set of vibrational peaks in the range of 1200–1700 cm −1 characteristic for triazines/heptazines . A neighboring peak at 890 cm −1 observed in the spectrum of the GCN sample produced at 600 °C can be assigned to the valence OO vibration in peroxides/hydroperoxides .…”

“…This aim can also be achieved by doping GCN with “alien” atoms, such as O, S, P, B, etc. as well as by introducing additional aromatic species into the polyheptazine sheets by adding corresponding precursors on the stage of polycondensation . The most popular dopant of GCN is probably oxygen that can be introduced by a partial GCN oxidation both during the synthesis and in post‐synthesis treatments …”