Urea‐Modified Carbon Nitrides: Enhancing Photocatalytic Hydrogen Evolution by Rational Defect Engineering

Lau, Vincent Wing‐hei; Yu, Victor; Ehrat, Florian; Botari, Tiago; Moudrakovski, Igor L.; Simon, Thomas; Düppel, Viola; Medina, Elise; Stolarczyk, Jacek K.; Feldmann, Jochen; Blüm, Volker; Lotsch, Bettina V.

doi:10.1002/aenm.201602251

Cited by 268 publications

(223 citation statements)

References 81 publications

Supporting

Mentioning

204

Contrasting

Unclassified

Order By: Relevance

“…The authors underline that the notion of certain defects in the carbon nitride structure enhancing the photocatalytic activity -which a redshift of the bandgap would certainly do -is well described in the literature. 8,52 This conclusion is supported by the results of a white-color PCN with nanosheet morphology (Carbon nitride nanosheets (CNNS)), 10 which shows similar composition and structure to those of other PCN samples (Fig. S1, S5-6 and Table S1).…”

Section: Discussionsupporting

confidence: 70%

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

Melissen

Bahers

et al. 2018

Chem. Mater.

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionsupporting

confidence: 70%

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

Melissen

Bahers

et al. 2018

Chem. Mater.

View full text Add to dashboard Cite

show abstract

“…The XPS spectrum in Figure S7 in the Supporting Information confirms the existence of C, N, and P in the BP/CN heterostructure. [38,39] The high-resolution N 1s spectrum is composed of three peaks with energies of 398.3, 399.6, and 400.7 eV corresponding to sp 2 bonded N (CNC) in the triazine rings, tertiary nitrogen groups (NC 3 ) in the skeleton, and surface uncondensed CNH amino groups, respectively (Figure 2d). [38,39] The high-resolution N 1s spectrum is composed of three peaks with energies of 398.3, 399.6, and 400.7 eV corresponding to sp 2 bonded N (CNC) in the triazine rings, tertiary nitrogen groups (NC 3 ) in the skeleton, and surface uncondensed CNH amino groups, respectively (Figure 2d).…”

Section: Tem (Hr-tem) Image Is Displayed Inmentioning

confidence: 99%

A Low‐Cost Metal‐Free Photocatalyst Based on Black Phosphorus

et al. 2018

View full text Add to dashboard Cite

An efficient metal‐free photocatalyst composed of black phosphorus (BP) and graphitic carbon nitride (CN) is prepared on a large scale by ball milling. Using economical urea and red phosphorus (RP) as the raw materials, the estimated materials cost of BP/CN is 0.235 Euro per gram. The BP/CN heterostructure shows efficient charge separation and possesses abundant active sites, giving rise to excellent photocatalytic H2 evolution and rhodamine B (RhB) degradation efficiency. Without using a co‐catalyst, the metal‐free BP/CN emits H2 consistently at a rate as large as 786 µmol h−1 g−1 and RhB is decomposed in merely 25 min during visible‐light irradiation. The corresponding electron/hole transfer and catalytic mechanisms are analyzed and described. The efficient metal‐free catalyst is promising in visible‐light photocatalysis and the simple ball‐milling synthetic method can be readily scaled up.

show abstract

“…4a) than PCN synthesized from urea at 550°C according to Chen's report [39], and the corresponding apparent quantum efficiency (QE) of supramolecular NS at 420 ± 10 nm reaches 1.2%. However, it is much lower than the stateof-art results from PCN [40][41][42]. The recycling measurements for H 2 production are shown in Fig.…”

mentioning

confidence: 70%

Fluorescein supramolecular nanosheets: A novel organic photocatalyst for visible-light-driven H2 evolution from water

Zhang

2018

Sci. China Mater.

View full text Add to dashboard Cite

Photocatalytic water splitting for hydrogen evolution is one of the most promising approaches to address energy and environmental issues [1][2][3][4]. Metal-free photocatalysts, usually containing low cost and earth-abundant C, N and O elements, are more advantageous than the traditional metal-based photocatalysts and have attracted considerable interest for many years [5][6][7][8][9][10]. In the reported metal-free photocatalysts, polymer carbon nitride (PCN) is extensively studied, but the relatively large band gap (~2.7 eV) and the low activity limit its photocatalytic applications [11][12][13][14][15][16][17]. Therefore, to develop a novel wide light range and high-efficiency metal-free photocatalysts for H 2 production is very essential.Supramolecule usually refers to the molecular aggregates assembled by intermolecular interactions (hydrogen bonds) or constructed with other hybrid structures and has been used directly for energy harvesting and transformation, such as water splitting, pollutant degradation and sensor [18][19][20]. The supramolecules withflexible skeletal structure through the different molecular self-assembly patterns have larger conjugated structure, more efficient charge transfer and separation, and broader absorption range than single molecule and polymer [21,22]. Among very few supramolecular photocatalysts, although the widely reported metal-contained porphyrin hybrids have good photocatalytic performance for H 2 production, metal-free porphyrin systems present a relatively poor activity, the metal composition confines their further applications due to high cost, metals toxicity and complicated preparation process [23,24]. Recently, Zhu and co-workers [25] reported a non-covalent selfassembled perylene-3,4,9,10-tetracarboxylic diimide (PDINH) supramolecular composed of metal-free organic molecules, working as a visible-light photocatalyst for O 2 production and photodegradation. However, the conduction band (CB) of PDINH supra-molecular is (−0.049 V versus normal hydrogen electrode (NHE)); thus crippled in the application of H 2 production from water. Therefore, it is very significant to develop the easy obtained and novel metal-free supramolecular photocatalysts for H 2 production from water. The fluorescein, first synthesized in 1871, has been widely used in labelling and sensing biomolecules, as well as ophthalmology because of its high absorption in the visible region and low toxicity [26][27][28][29]. Herein, we demonstrate that the fluorescein supramolecular crystal self-assembled by single molecule is highly efficient for H 2 production from water under visible light. The morphology can be easily selfassembled into nanosheets via a simple dissolution-recrystallization process. To date, this is the first report on H 2 production under visible light over fluorescein supramolecular crystal, which extends the family of organic supramolecular photocatalytic materials. This study may open up new insights into the search of other metal-free and organic photocatalysts.We applied Gaussia...

show abstract

Urea‐Modified Carbon Nitrides: Enhancing Photocatalytic Hydrogen Evolution by Rational Defect Engineering

Cited by 268 publications

References 81 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

A Low‐Cost Metal‐Free Photocatalyst Based on Black Phosphorus

Fluorescein supramolecular nanosheets: A novel organic photocatalyst for visible-light-driven H2 evolution from water

Contact Info

Product

Resources

About