All Organic S-Scheme Heterojunction PDI-Ala/S-C₃N₄ Photocatalyst with Enhanced Photocatalytic Performance

Abstract

Organic photocatalysts have attracted attention owing to their suitable redox band positions, low cost, high chemical stability, and good tunability of their framework and electronic structure. As a novel organic photocatalyst, PDI-Ala (N,N'-bis(propionic acid)-perylene-3,4,9,10tetracarboxylic diimide) has strong visible-light response, low valence band position, and strong oxidation ability. However, the low photogenerated charge transfer rate and high carrier recombination rate limit its application. Due to the aromatic heterocyclic structure of g-C3N4 and large delocalized π bond in the planar structure of PDI-Ala, g-C3N4 and PDI-Ala can be tightly combined through π-π interactions and N-C bond. The band structure of sulfur-doped g-C3N4 (S-C3N4) matched well with PDI-Ala than that with g-C3N4. The electron delocalization effect, internal electric field, and newly formed chemical bond jointly promote the separation and migration of photogenerated carriers between PDI-Ala and S-C3N4. To this end, a novel step-scheme (Sscheme) heterojunction photocatalyst comprising organic semiconductor PDI-Ala and S-C3N4 was prepared by an in situ self-assembly strategy. Meanwhile, PDI-Ala was self-assembled by transverse hydrogen bonding and longitudinal π-π stacking. The crystal structure, morphology, valency, optical properties, stability, and energy band structure of the PDI-Ala/S-C3N4 photocatalysts were systematically analyzed and studied by various characterization methods such as X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, ultraviolet visible diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, and Mott-Schottky curve. The work functions and interface coupling characteristics were determined using density functional theory. The photocatalytic activities of the synthesized photocatalyst for H2O2 production and the degradation of tetracycline (TC) and p-nitrophenol (PNP) under visible-light irradiation are discussed. The PDI-Ala/S-C3N4 S-scheme heterojunction with band matching and tight interface bonding accelerates the intermolecular electron transfer and broadens the visible-light response range of the heterojunction. In addition, in the processes of the PDI-Ala/S-C3N4 photocatalytic degradation reaction, a variety of active species (h + , •O2 − , and H2O2) were produced and accumulated. Therefore, the PDI-Ala/S-C3N4 heterojunction exhibited enhanced photocatalytic performance in the degradation of TC, PNP, and H2O2 production. Under visible-light irradiation, the optimum 30%PDI-Ala/S-C3N4 removed 90% of TC within 90 min. In addition, 30%PDI-Ala/S-C3N4 displayed the highest H2O2 evolution rate of 28.3 μmol•h −1 •g −1 , which was 2.9 and 1.6 times higher than those of PDI-Ala and S-C3N4,

P-Doped g-C₃N₄ Nanosheets with Highly Dispersed Co_0.2Ni_1.6Fe_0.2P Cocatalyst for Efficient Photocatalytic Hydrogen Evolution

“…8A). In general, lower PL intensity means efficient charge separation, indicating higher photocatalytic performance [63][64][65] . Since PL intensity of PCNS-CoNiFeP and PCNS is lower than that of CNS, indicating that P doping of CNS and loading of highly dispersed CoNiFeP decrease the recombination of photogenerated electron-hole pairs, due to the improved charge trapping by the introduced P and CoNiFeP cocatalysts as the electron traps.…”

Engineering Schottky-like and heterojunction materials for enhanced photocatalysis performance – a review

“…Direct Z-scheme heterojunctions are also termed as S-scheme heterojunctions 80 . A direct Z-scheme heterojunction consists of staggered band alignment, with charge transfer mechanism completely different from type II heterojunction 79,81…”

“…80 A direct Z-scheme heterojunction consists of staggered band alignment, with charge transfer mechanism completely different from that of a type II heterojunction. 79,81 The photo-generated electrons in the conduction band of the semiconducting material with a high reduction potential (semiconductor B) and holes in the valence band of the semiconducting material with a high oxidation potential (semiconductor A) are reserved for photocatalytic reactions. 79 When two semiconductors come in close contact, initially the diffusion of electrons occur from semiconductor B possessing a high reduction potential to semiconductor A with a high oxidation potential.…”

g‐C3N4‐Based 2D/2D Composite Heterojunction Photocatalyst

“…Photocatalysis technology holds enormous potential in addressing environment and energy issues because it converts inexhaustible solar energy into storable chemical energy. [1,2] Specifically, under light irradiation, some redox reactions can occur on the surface of photocatalysts; these reactions include water splitting to hydrogen and oxygen, [3,4] CO 2 reduction to organic fuels, [5][6][7][8] NO removal, [9,10] N 2 fixation, [11][12][13] contaminant degradation, [14,15] bacteria disinfection, [16] and so on. The most common photocatalysts are semiconductors, such as TiO 2 , [17] CdS, [18,19] and graphitic carbon nitride (g-C 3 N 4 ).…”