Sunlight-driven water-splitting using two-dimensional carbon based semiconductors
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The document discusses sunlight-driven water-splitting technology using two-dimensional carbon-based semiconductors, detailing mechanisms for charge generation and separation. It explores various photocatalysts, including composites that utilize Z-scheme processes and reduced graphene oxide for improved electron transfer. The structural stability and band gap positions of different carbon nitride derivatives and their roles in photocatalytic efficiency are also highlighted.
![Schematic illustration of the synthesis of HMP-3 polymer by copolymerization of
cyameluric chloride and 4,4’-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dianiline
(BTDADA). Adapted with permission from ref.335](https://image.slidesharecdn.com/reviewpresentation-180919193757/85/Sunlight-driven-water-splitting-using-two-dimensional-carbon-based-semiconductors-16-320.jpg)
Sunlight-driven water-splitting using two-dimensional carbon based semiconductors
- 1. Published in: J. Mater. Chem. A, 2018,6, 12876-12931 Sunlight-driven water-splitting using two-dimensional carbon based semiconductors Pawan Kumar, Rabah Boukherroub and Karthik Shankar
- 2. Band gap and band edge positions of a range of semiconductors vs NHE at pH 7 representing redox potential of water splitting.
- 3. (a) Schematic illustration of the charge generation, separation, recombination and conversion processes in photocatalysts, (b) Facilitation of charge separation by electron and hole capturing agents.
- 4. Mechanistic representation of direct and Z-scheme of photocatalysis on two different band gap semiconductors for overall water splitting
- 5. Schematics of visible light driven electron-hole pair generation in CdS and their efficient separation on reduced graphene oxide in CdS/rGO nanocomposite. The photogenerated electrons in the conduction band of CdS are transferred to Pt and rGO sheets, which facilitate better charge separation and electrons are more easily accessible to protons to generate H2.
- 6. Two photon Z-scheme overall water splitting on BiVO4- Ru-SrTiO3:Rh photocatalyst. BiVO4 can oxidize water to O2 by photogenerated holes due to positive valence band, but cannot reduce protons. While Ru-SrTiO3:Rh composite can reduce protons due to negative conduction band, but cannot oxidize water. Composite of BiVO4 and Ru-SrTiO3:Rh photocatalyst can sustain overall water splitting by two photons. BiVO4, after photoexcitation, transfers electrons to the valence band of Ru-SrTiO3:Rh, which upon second excitation reach to conduction band of Ru-SrTiO3:Rh. Reduced graphene oxide serves as a solid-state redox mediator by facilitating electron transfer from conduction band of BiVO4 to valence band of Ru- SrTiO3:Rh.
- 7. Band diagram of GO showing the conduction band (CB) and valence band (VB) positions relative to proton reduction and water oxidation. The CB of GO has high overpotential than the level of H2 generation and photogenerated electrons are transferred to solution phase for proton reduction. The holes in VB of GO are annihilated by hole scavenger (methanol) instead of O2 generation from water oxidation due to higher reduction potential of methanol than water. The top-of-valence energy level was obtained using density functional theory for GO with 12.5% O coverage, and the levels for H2 and O2 generation were obtained from the literature.
- 8. Structure of N-doped graphene showing various types of N atoms according to bonding configuration.
- 9. Structure of graphitic carbon nitride based on (a) s-heptazine (gh- C3N4) and (b) s-triazine units (gt-C3N4). The s-heptazine network gh- C3N4 is about 30 kJ mol-1 more stable than gt-C3N4
- 10. Band structure diagram of g-C3N4 showing positions of conduction and valence bands and relative oxidation and reduction potentials of water
- 11. Schematic illustration of solvent-assisted exfoliation of bulk g-C3N4 to ultrathin nanosheets.
- 12. Plausible mechanism of electron transfer between K-g-C3N4 nanosheets having different thicknesses and band structures. Adapted with permission from Ref. 293
- 13. Chemical structure of MgPc and carbon nitride and immobilization of MgPc on mpg-C3N4 through π-π interaction. Adapted with permission from ref.301
- 14. Basic structure of some carbon nitride precursors and their relevant molecular structures
- 15. Sketch of band structure of g-C3N4 and polyimide polymer depicting the shifting of band position of carbon nitride by introducing PMDA units. Adapted with permission from ref.320.
- 16. Schematic illustration of the synthesis of HMP-3 polymer by copolymerization of cyameluric chloride and 4,4’-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dianiline (BTDADA). Adapted with permission from ref.335
- 17. (a) Generation of electron-hole pairs in g-C3N4/C2N nanocomposite by three possible routes (Adapted from ref.114); b) The comparative optical absorption coefficients of g-C3N4/C2N nanocomposite and g-C3N4. Reproduced with permission from ref.114 Copyright 2016 Wiley-VCH.