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Highly efficient photocatalytic H₂ evolution from water using visible light and structure-controlled graphitic carbon nitride.

Martin DJ, Qiu K, Shevlin SA, Handoko AD, Chen X, Guo Z, Tang J - Angew. Chem. Int. Ed. Engl. (2014)

Bottom Line: Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported.The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5% under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts.Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.

View Article: PubMed Central - PubMed

Affiliation: Solar Energy Group, Department of Chemical Engineering, UCL, Torrington Place, London, WC1E 7JE (UK).

No MeSH data available.


a) Quantum yield of urea-based g-C3N4, as measured by usingband-pass filters at specific wavelengths (absorbance is shown by the black dashed line, internalquantum yield by circles with crosses). b) Stability test of the urea-derivedg-C3N4 under irradiation with visible light(λ≥395 nm).
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fig04: a) Quantum yield of urea-based g-C3N4, as measured by usingband-pass filters at specific wavelengths (absorbance is shown by the black dashed line, internalquantum yield by circles with crosses). b) Stability test of the urea-derivedg-C3N4 under irradiation with visible light(λ≥395 nm).

Mentions: As mentioned previously, apart from the need for a photocatalyst to be cheap and robust, it mustexhibit a high quantum yield for hydrogen production from water if it is to be consideredcommercially viable. Compounds that traditionally exhibit high efficiencies either suffer frominstability (e.g. sulfides13) or are made of relativelyexpensive metals (e.g. GaAs–GaInP214). Thecheap and stable urea-derived g-C3N4 in this study has a peak internal quantumyield of 28.4 % at 365 nm (Figure 4 a). Even under irradiation with visible light atλ=400 nm, the quantum yield is 26.5 %, nearly anorder of magnitude greater than the highest reported (3.75 % at 420 nm,7f obtained by liquid exfoliation). To ensure the reliability ofour measurement, we examined as a reference a benchmark cyanamide-derivedg-C3N4, which showed comparable activity (Table 2; the small difference is due to the use of a 395 nm long-pass filterinstead of a 420 nm filter). As proposed previously, the huge enhancement inhydrogen-evolution rate of our urea-derived sample (3327.5 vs.142.3 μmol h−1 g−1) can beattributed to a lower protonation status and the condensation state. Recently, a facile syntheticmethod for three-dimensional porous g-C3N4 was introduced by using aggregatesof melamine and cyanuric acid (MCA) co-crystals in dimethyl sulfoxide (DMSO, sample denotedMCA_DMSO) as precursors.12 It was reported that the quantumyield of g-C3N4_MCA_DMSO at λ=420 nm was2.3 % (Table 2), much higher than thatof melamine-derived bulk g-C3N4 (0.26 %) under the sameconditions. We repeated this study and observed very similar morphologies and optical properties tothose reported (see Figure S14). Correspondingly, a similar quantum yield of3.1 % at λ=400 nm was obtained(Table 2; the difference is due to the wavelength ofthe band-pass filter). Since MCA_DMSO is another oxygen-containing precursor, the rise in thequantum yield as compared to that of a melamine sample further supports our proposed protonationmechanism. Furthermore, the reason why our optimized urea-derived g-C3N4 ismore than 10 times more efficient than MCA_DMSO g-C3N4, in terms ofquantum yield at 400 nm, given the very similar specific surface area of these two samples,is because of the much higher oxygen concentration in the urea precursor, which helps to passivateprotonation sites and polymerize g-C3N4 without structuralinstability/buckling.


Highly efficient photocatalytic H₂ evolution from water using visible light and structure-controlled graphitic carbon nitride.

Martin DJ, Qiu K, Shevlin SA, Handoko AD, Chen X, Guo Z, Tang J - Angew. Chem. Int. Ed. Engl. (2014)

a) Quantum yield of urea-based g-C3N4, as measured by usingband-pass filters at specific wavelengths (absorbance is shown by the black dashed line, internalquantum yield by circles with crosses). b) Stability test of the urea-derivedg-C3N4 under irradiation with visible light(λ≥395 nm).
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Related In: Results  -  Collection

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fig04: a) Quantum yield of urea-based g-C3N4, as measured by usingband-pass filters at specific wavelengths (absorbance is shown by the black dashed line, internalquantum yield by circles with crosses). b) Stability test of the urea-derivedg-C3N4 under irradiation with visible light(λ≥395 nm).
Mentions: As mentioned previously, apart from the need for a photocatalyst to be cheap and robust, it mustexhibit a high quantum yield for hydrogen production from water if it is to be consideredcommercially viable. Compounds that traditionally exhibit high efficiencies either suffer frominstability (e.g. sulfides13) or are made of relativelyexpensive metals (e.g. GaAs–GaInP214). Thecheap and stable urea-derived g-C3N4 in this study has a peak internal quantumyield of 28.4 % at 365 nm (Figure 4 a). Even under irradiation with visible light atλ=400 nm, the quantum yield is 26.5 %, nearly anorder of magnitude greater than the highest reported (3.75 % at 420 nm,7f obtained by liquid exfoliation). To ensure the reliability ofour measurement, we examined as a reference a benchmark cyanamide-derivedg-C3N4, which showed comparable activity (Table 2; the small difference is due to the use of a 395 nm long-pass filterinstead of a 420 nm filter). As proposed previously, the huge enhancement inhydrogen-evolution rate of our urea-derived sample (3327.5 vs.142.3 μmol h−1 g−1) can beattributed to a lower protonation status and the condensation state. Recently, a facile syntheticmethod for three-dimensional porous g-C3N4 was introduced by using aggregatesof melamine and cyanuric acid (MCA) co-crystals in dimethyl sulfoxide (DMSO, sample denotedMCA_DMSO) as precursors.12 It was reported that the quantumyield of g-C3N4_MCA_DMSO at λ=420 nm was2.3 % (Table 2), much higher than thatof melamine-derived bulk g-C3N4 (0.26 %) under the sameconditions. We repeated this study and observed very similar morphologies and optical properties tothose reported (see Figure S14). Correspondingly, a similar quantum yield of3.1 % at λ=400 nm was obtained(Table 2; the difference is due to the wavelength ofthe band-pass filter). Since MCA_DMSO is another oxygen-containing precursor, the rise in thequantum yield as compared to that of a melamine sample further supports our proposed protonationmechanism. Furthermore, the reason why our optimized urea-derived g-C3N4 ismore than 10 times more efficient than MCA_DMSO g-C3N4, in terms ofquantum yield at 400 nm, given the very similar specific surface area of these two samples,is because of the much higher oxygen concentration in the urea precursor, which helps to passivateprotonation sites and polymerize g-C3N4 without structuralinstability/buckling.

Bottom Line: Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported.The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5% under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts.Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.

View Article: PubMed Central - PubMed

Affiliation: Solar Energy Group, Department of Chemical Engineering, UCL, Torrington Place, London, WC1E 7JE (UK).

No MeSH data available.