Photophysics of polymeric carbon nitride: An optical quasimonomer

Merschjann, Christoph; Tyborski, Tobias; Orthmann, Steven; Yang, F.; Schwarzburg, Klaus; Lublow, Michael; Lux‐Steiner, Martha Ch.; Schedel‐Niedrig, Th.

doi:10.1103/physrevb.87.205204

Cited by 126 publications

(165 citation statements)

References 31 publications

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“…The notion that PCNs' optical properties are largely local is supported in the literature. Recently, Merschjann et al 28 advanced experimental evidence for this notion, and Butchosa et al 29 contributed insights from theory. Disagreement exists as to what extent the optical nature of PCNs can be described in terms of a classical semiconductor's, and to what extent it should be considered as an oligomeric aromatic moiety embedded in a molecular solid.…”

Section: Refining the Methodologymentioning

confidence: 99%

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Melissen

Bahers

et al. 2018

Chem. Mater.

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Polymeric carbon nitride (PCN)-based materials have opened new research avenues in the photocatalytic field. The understanding of parameters underlying the optical properties of PCNs is critical to improve their performance. Herein, the optical properties of PCNs are investigated with a combination of Time-Dependent Density Functional Theory (TD-DFT) calculations and laboratory characterizations, including Variable Temperature (VT)-XRD, VT-UV-Vis and VT-IR techniques, on samples prepared using a broad range of synthesis temperatures. Upon increasing the synthesis temperature from 390 to 600°C, the optical gap E opt g (eV) narrows from 2.92 to 2.67, and on further increasing the synthesis temperature to 700°C, widens to 3.03 and another absorption at ∼2.2 eV is observed. The TD-DFT calculations show that E opt g of PCNs converges rapidly with heptazine oligomer size, indicating localized photophysics behavior and justifying a molecular approach. Calculations exploring geometrical variations upon increasing the temperature at which the optical properties were determined revealed that the net effect of these variations were limited, suggesting a vibrational origin of the observed decrease in the gap. The absorption at ∼2.2 eV is tentatively attributed to fully polymerized graphitic PCN oligomers as suggested by the excitation wavelength-dependent photoluminescence emission behavior. The results provide novel insights into the optical properties of PCNs, providing directions for the development of the next generation of PCN-based photocatalysts with optimal light harvesting abilities.

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Section: Refining the Methodologymentioning

confidence: 99%

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Melissen

Bahers

et al. 2018

Chem. Mater.

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“…17 Modication of the g-C 3 N 4 bulk geometry toward the nano-scale is therefore required to remedy these limitations.…”

Section: -10mentioning

confidence: 99%

“…There is, however, a large difference of the respective conduction band edges of about 1.4 eV (E C of Si is located at 4.05 eV, while E C of g-C 3 N 4 is located between 2.6 and 3.0 eV). 8,14,15,17 Such a band discontinuity represents an additional energy barrier which can necessitate a corresponding high overpotential unless there is an interfacial dipole that lowers this barrier. In fact, the band alignment between silicon and the g-C 3 N 4 nanostructures appears to occur without pronounced discontinuity at the conduction band edges.…”

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confidence: 99%

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Graphitic carbon nitride nano-emitters on silicon: a photoelectrochemical heterojunction composed of earth-abundant materials for enhanced evolution of hydrogen

et al. 2014

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Graphitic carbon nitride is a promising heterogeneous catalyst for light-induced generation of hydrogen. Here, we report the successful formation of nano-scaled carbon nitride structures on silicon, mitigating the known limitations of charge transport within bulky C-N networks. An efficient photoelectrochemical heterojunction is thereby realized, developed from earth-abundant materials only.The conversion of solar energy to chemical energy is one of the principal routes to establish a green global economy.1 Particularly, hydrogen as a product of solar water splitting may assume a decisive role upon transition from fossil to renewable energy resources.2 For realization of the solar-to-hydrogen conversion process by photoelectrochemical water splitting, suitable photoelectrodes still have to be developed and to meet important demands such as efficiency and durability. Most critical, electrode fabrication has to rely on cost-saving material consumption, and the use of earth-abundant materials appears inevitable for novel device architectures. In this respect, the combination of silicon and polymeric graphitic carbon nitride (g-C 3 N 4 ) represents a highly attractive heterostructure, integrating a state-of-the-art photoabsorber and a promising photocatalyst. Silicon-based photoelectrodes on the one hand, already reached near-record efficiencies in light-induced evolution of hydrogen but had to be activated by noble-metal catalysts.3,4 On the other hand, g-C 3 N 4 is an established candidate for photocatalytic hydrogen production since the report of Wang et al. in 2008 (ref. 5) which boosted almost instantaneously the interest in this material due to the prospect of solar fuel generation without use of noble metal catalysts. 6-10

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“…50,51 Transient photoluminescence studies on g-C 3 N 4 revealed recently an estimated value of the charge carrier lifetimes of the order of 3 ns due to charge localization and native defects. 52 Therefore, the polymeric carbon nitride structure is characterized by short minority carrier diffusion lengths (<2 nm) that prevent efficient charge transfer in thick lms. The thickness of the g-C 3 N 4 lm is therefore the key issue in designing an efficient heterostructured photocathode.…”

Section: -49mentioning

confidence: 99%

Solar hydrogen evolution using metal-free photocatalytic polymeric carbon nitride/CuInS2 composites as photocathodes

et al. 2013

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a Polymeric carbon nitride (g-C 3 N 4 ) films were synthesized on polycrystalline semiconductor CuInS 2 chalcopyrite thin film electrodes by thermal polycondensation and were investigated as photocathodes for the hydrogen evolution reaction (HER) under photoelectrochemical conditions. The composite photocathode materials were compared to g-C 3 N 4 powders and were characterized with grazing incidence X-ray diffraction and X-ray photoemission spectroscopy as well as Fourier transform infrared and Raman spectroscopies. Surface modification of polycrystalline CuInS 2 semiconducting thin films with photocatalytically active g-C 3 N 4 films revealed structural and chemical properties corresponding to the properties of g-C 3 N 4 powders. The g-C 3 N 4 /CuInS 2 composite photocathode material generates a cathodic photocurrent at potentials up to +0.36 V vs. RHE in 0.1 M H 2 SO 4 aqueous solution (pH 1), which corresponds to a +0.15 V higher onset potential of cathodic photocurrent than the unmodified CuInS 2 semiconducting thin film photocathodes. The cathodic photocurrent for the modified composite photocathode materials was reduced by almost 60% at the hydrogen redox potential. However, the photocurrent generated from the g-C 3 N 4 /CuInS 2 composite electrode was stable for 22 h. Therefore, the presence of the polymeric g-C 3 N 4 films composed of a network of nanoporous crystallites strongly protects the CuInS 2 semiconducting substrate from degradation and photocorrosion under acidic conditions. Conversion of visible light to hydrogen by photoelectrochemical water splitting can thus be successfully achieved by g-C 3 N 4 films synthesized on polycrystalline CuInS 2 chalcopyrite electrodes.

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Photophysics of polymeric carbon nitride: An optical quasimonomer

Cited by 126 publications

References 31 publications

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Graphitic carbon nitride nano-emitters on silicon: a photoelectrochemical heterojunction composed of earth-abundant materials for enhanced evolution of hydrogen

Solar hydrogen evolution using metal-free photocatalytic polymeric carbon nitride/CuInS2 composites as photocathodes

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