Significant Enhancement of Visible-Light-Driven Hydrogen Evolution by Structure Regulation of Carbon Nitrides

Abstract

Photocatalytic water splitting for hydrogen evolution by utilizing solar energy has a great significance for high-density solar energy storage and environmental sustainability. Here, a defect-rich amorphous carbon nitride (DACN) photocatalyst has been synthesized by simply direct calcination of the rationally size-reduced urea crystals. The introduction of nitrogen vacancies combined with disordered structure cause a broad visible-light-reponsive range, countless lateral edge/exposed surface bonding sites, and quenched radiative recombination, suggesting that this DACN enhances photocatalytic activity for hydrogen production. A record high hydrogen evolution rate of 37,680 μmol h g under visible-light irradiation and an extraordinary apparent quantum efficiency of 34.4% at 400 nm were achieved, higher than most of the existing graphitic carbon nitride-based photocatalysts.

Formation of g‐C3N4 Nanotubes towards Superior Photocatalysis Performance

“…The XRD patterns of samples pure 650 CN, pure R‐650 CN and Fe 3+ R‐650 CN are contrasted in detail and these results are shown in Figure c, d, and e. It is noted that the difference among three samples is that the peak around 27° belonging to Fe 3+ R‐650 CN greatly decreased in intensity (Figure c). This is attributed to rich −NH x leading to the disturbance of interlayers and the formation of tubular structure in Fe 3+ R‐650 CN . For another, when enlarged the spectra around 12.8 and 27.1° in detail (Figure d & e), the peak at around 12.64° related to (001) facet for pure 650 CN was red‐shifted about 0.164 to 12.80° for Fe 3+ R‐650 CN.…”

“…This is attributed to rich À NH x leading to the disturbance of interlayers and the formation of tubular structure in Fe 3 + R-650 CN. [37] For another, when enlarged the spectra around 12.8 and 27.1°in detail (Figure 5d & e), the peak at around 12.64°related to (001) facet for pure 650 CN was red-shifted about 0.164 to 12.80°for Fe 3 + R-650 CN. This is attributed to the morphology changing from sheet-like to tubular structure leads to lattice distortion in certain degree.…”

“…This feature benefited to superior photogenerated carrier separation from photoexcited electron‐hole pairs. Furthermore, the electron paramagnetic resonance spectra (EPR) of samples indicates one single Lorentzian line with a g value of 2.0032 induced by the unpaired electrons on the nitride atoms of the heptazine rings as shown in Figure d . The signal of Fe 3+ R‐650 CN presents a relatively high intensity compared with pure 650 CN.…”

“…Furthermore, the electron paramagnetic resonance spectra (EPR) of samples indicates one single Lorentzian line with a g value of 2.0032 induced by the unpaired electrons on the nitride atoms of the heptazine rings as shown in Figure 8d. [37] The signal of Fe 3 + R-650 CN presents a relatively high intensity compared with pure 650 CN. This means a high concentration of lone pair electrons contained in sample and the photocatalytic property of the sample may be improved.…”

Enhanced Light‐Driven Hydrogen‐Production Activity Induced by Accelerated Interfacial Charge Transfer in Donor–Acceptor Conjugated Polymers/TiO2 Hybrid

“…[11] Given that organic semiconductor polymeric g-C 3 N 4 was found to act as ap hotocatalyst for hydrogen evolution, [6] av ariety of modified g-C 3 N 4 composites have been explored with high photocatalyticactivity. [12][13][14][15][16][17][18][19][20] Ta ken the typical TiO 2 as an example, g-C 3 N 4 /TiO 2 -based composites exhibited excellent photocatalytic performance. [21][22][23][24][25] Very recently,m edium-band gap conjugated polymers composedo fa lternating electron donor( D) and electron acceptor (A) have emerged as promising photocatalysts.…”