Oligomer‐Incorporated Polymeric Layer Framework of Graphitic Carbon Nitride for Effective Photocatalytic Hydrogen Evolution

Abstract

Developing a structural design of g-CN to enhance absorption in the solar spectrum, [11] facilitate separation of photogenerated charges, [12] and expose the active sites for charge transfer [13] is a major challenge for improving the applicability of g-CN.The structure of g-CN comprises 2D layers that are constituted by H-bondingconnected melon strains (Scheme 1). [14] The layers are linked through van der Waals attraction to form a 3D framework. Scheme 1 elucidates that the melon strain is produced through polymerization of 1,3,4,6,7,9,9b-Heptaazaphenalene-2,5,8-triamine (melem) molecules along with NH 3 removal; its structure comprises heptazine units connected by NH bridges. This g-CN framework results in an electronic structure exhibiting a bandgap straddling the redox potentials for H 2 and O 2 evolutions from water splitting and a gap width of ≈2.7 eV, [4] which enables g-CN to capture a considerable amount of solar irradiation.Previous studies have reported that crystalline graphite-like CN (i.e., g-C 3 N 4 ) exhibited negligible activity in photocatalysis, whereas g-CN, which is partially condensed and contains amino groups, was active in H 2 evolution under illumination. [15] Lotsch and co-workers reported that low-molecular-weight melon, a type of melem oligomer, exhibited a higher efficiency than melon in H 2 evolution under illumination at λ ≈ 420 nm. This was because of the increase in kinetics even though the energy gap of the melem oligomer was larger than that of melon. [16] Theoretical calculations have indicated that the lowest unoccupied molecular orbital of melem oligomers is contributed by hybrid systems comprising edged carbon and nitrogen atoms, central nitrogen atoms, and bridging amino groups, and by localized terminal primary amines. [16,17] Experimental studies on dendrimers and metal-organic frameworks have revealed that photodeposition of metallic platinum in H 2 PtCl 6 solution preferentially occurred at the amino groups. [18] These findings imply that the amino groups of melem oligomers acted as the electron-donating sites for photocatalytic H 2 evolution and their robust interaction with the deposited metallic platinum facilitated the transfer of excited electrons from the amino sites to the solution phase for H 2 evolution. [19] A framework comprising melem oligomers for providing amino sites can enable the production of g-CN materials with high photocatalytic activity. [13,20] However, melem oligomers are wide-bandgap This paper presents a structural design of graphitic carbon nitride (CN) for use as an active photocatalyst in H 2 evolution reactions. The active photocatalyst is synthesized by subjecting a CN sample to consecutive annealing and ammonia treatments. The CN sample is produced through urea condensation. The annealing treatment destroys the polymeric CN to form a defective polymeric layer framework incorporating 1,3,4,6,7,9,9b-Heptaazaphenalene-2,5,8-triamine (melem) oligomers. The annealed CN exhibits a wide absorption range in visible light because the distorted ...

Sugarcane juice derived carbon dot–graphitic carbon nitride composites for bisphenol A degradation under sunlight irradiation

“…It is well-known that the organic semiconductor g-C 3 N 4 possesses visible light harvesting properties due to its narrow band gap energy (≈2.7 eV) [15]. Thus g-C 3 N 4 has emerged as a promising polymeric semiconductor for photocatalytic reduction of carbon dioxide (CO 2 ) [16–20], hydrogen evolution [21–25], oxidation of NO [26–27], and degradation of pollutants [28–30]. However, the photocatalytic performance of bulk g-C 3 N 4 remains unsatisfactory because of the fast recombination rate of electron pairs and narrower light absorption range over the entire solar spectrum.…”

Recent Developments in Graphitic Carbon Nitride Based Hydrogels as Photocatalysts

“…Extensive studies and reviews have investigated the synthesis, structural engineering, doping, heterocomposites, and pre‐ and post‐treatments of g‐C 3 N 4 ‐based compounds for photocatalytic applications . Generally, bulk g‐C 3 N 4 can be synthesized through the thermal condensation of various precursors with R‐C‐NH 2 units, including melamine, cyanamide, dicyandiamide, thiourea, urea, and mixtures thereof .…”

Co2P Nanorods as an Efficient Cocatalyst Decorated Porous g‐C3N4 Nanosheets for Photocatalytic Hydrogen Production under Visible Light Irradiation

“…[2] Nevertheless, pure g-C 3 N 4 demonstrates intrinsically high recombination rate of photogenerated charge carriers, which severely hampers the photocatalytic reaction process for H 2 production. [3] Stemming from this bottleneck, the incorporation of cocatalysts into the g-C 3 N 4 system could conspicuously accelerate the charge separation and www.advancedsciencenews.com www.particle-journal.com thus facilitating exploitable opportunities on the efficient hybrid photocatalysts for solar energy conversion and storage. The morphology of pure g-C 3 N 4 , Co 2 P, and Co 2 P/g-C 3 N 4 are assessed via transmission electron microscopy (TEM).…”