Crystal structure of polymeric carbon nitride and the determination of its process-temperature-induced modifications

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

doi:10.1088/0953-8984/25/39/395402

Cited by 95 publications

(145 citation statements)

References 27 publications

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“…The asprepared PCN sample often has a C/N ratio of around 0.67, and ∼1 wt% H. Therefore, the structure of this carbon nitride is best represented by the melon model. [15][16][17][18][19] . This model has compositional formula C 6 N 9 H 3 .…”

Section: Polymeric Carbon Nitridesmentioning

confidence: 99%

“…1a contains the XRD patterns of samples prepared at temperatures from 500 to 700 • C. These samples show characteristic patterns of melon. 15,17,18 Two main reflections at ∼ 13 • and ∼ 27.5 • are assigned to intralayer periodicity (210) and interlayer periodicity (001), respectively. Transmission Electron Microscopy (TEM) images show that CN700 has a plate-like morphology ( Fig.…”

Section: Structural Featuresmentioning

confidence: 99%

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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: Polymeric Carbon Nitridesmentioning

confidence: 99%

Section: Structural Featuresmentioning

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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“…The XRD powder pattern of CN shows a main peak at 2θ = 27.5 • corresponding to the characteristic interlayer stacking reflection of polymeric melon sheets and a minor peak at 13.2 • from an in-plane structural motif between nitride pores [26] (Figure S2a). Monophasic AIS gives rise to several peaks that can be assigned to the cubic face-centered lattice of this phase with a slight deviation of the unit cell parameters compared to reference [16] (ICDD 01-071-3985: 10.822 Å, found 10.797 Å) ( Figure S2a).…”

Section: Characterization Of As-prepared and Used Catalystsmentioning

confidence: 99%

Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production

et al. 2018

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Solar hydrogen production from water could be a sustainable and environmentally friendly alternative to fossil energy carriers, yet so far photocatalysts active and stable enough for large-scale applications are not available, calling for advanced research efforts. In this work, H 2 evolution rates of up to 1968 and 5188 µmol h −1 g −1 were obtained from aqueous solutions of triethanolamine (TEOA) and oxalic acid (OA), respectively, by irradiating composites of AgIn 5 S 8 (AIS), mesoporous C 3 N 4 (CN, surface area >150 m 2 /g) and ≤2 wt.% in-situ photodeposited Pt nanoparticles (NPs) with UV-vis (≥300 nm) and pure visible light (≥420 nm). Structural properties and electron transport in these materials were analyzed by XRD, STEM-HAADF, XPS, UV-vis-DRS, ATR-IR, photoluminescence and in situ-EPR spectroscopy. Initial H 2 formation rates were highest for Pt/CN, yet with TEOA this catalyst deactivated by inclusion of Pt NPs in the matrix of CN (most pronounced at λ ≥ 300 nm) while it remained active with OA, since in this case Pt NPs were enriched on the outermost surface of CN. In Pt/AIS-CN catalysts, Pt NPs were preferentially deposited on the surface of the AIS phase which prevents them from inclusion in the CN phase but reduces simultaneously the initial H 2 evolution rate. This suggests that AIS hinders transport of separated electrons from the CN conduction band to Pt NPs but retains the latter accessible by protons to produce H 2 .

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“…[18,20,22] and the powder pattern is consistent with a structural model of melon recently proposed. [29] This structure comprises buckled chains of tris-s-triazine moieties idealized as 3 (Fig. 1).…”

Section: Characterisationmentioning

confidence: 99%

“…This can be further condensed to melon, which may have several isomeric forms [27][28][29] such as (3) and, conceptually at least, ultimately to the idealized composition g-C3N4, which contains infinite 2-D sheets. The local and long-range structure can lead to similar analytical data from common methods of characterization, and hence establishing the true composition and structure necessitates application of a broad range of techniques.…”

Section: Introductionmentioning

confidence: 99%

Pore confinement effects and stabilization of carbon nitride oligomers in macroporous silica for photocatalytic hydrogen production

Qiao

Mitchell

Coulson

et al. 2016

Carbon

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An ordered macroporous host (mac-SiO2) has been used to prevent aggregation of layered photocatalysts based on carbon nitride. Using typical carbon nitride synthesis conditions, cyanamide was condensed at 550 o C in the presence and absence of mac-SiO2. Condensation in the absence of mac-SiO2 results in materials with structural characteristics consistent with the carbon nitride, melon, accompanied by ca. 2 wt% carbonization. For mac-SiO2 supported materials, condensation occurs with greater carbonization (ca. 6 wt%). On addition of 3wt% Pt cocatalyst photocatalytic hydrogen production under visible light is found to be up to 10 times greater for the supported composites. Time-resolved photoluminescence spectroscopy shows that excited state relaxation is more rapid for the mac-SiO2 supported materials suggesting faster electron-hole recombination and that supported carbon nitride does not exhibit improved charge separation. CO2 temperature programmed desorption indicates that enhanced photoactivity of supported carbon nitride is attributable to an increased surface area compared to bulk carbon nitride and an increase in the concentration of weakly basic catalytic sites, consistent with carbon nitride oligomers.

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Crystal structure of polymeric carbon nitride and the determination of its process-temperature-induced modifications

Cited by 95 publications

References 27 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

Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production

Pore confinement effects and stabilization of carbon nitride oligomers in macroporous silica for photocatalytic hydrogen production

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