Fabrication and visible light photocatalysisof rod-like graphitic carbon nitride
2015
Due to the limited supply of fossile fuel and its harmful effects
on environment, photocatalysis has become a promising method to solve
the energy crisis and environmental problems. It is of great significance
to develop the novel photocatalysts that can be used to degrade the
organic pollutants and split the water to produce hydrogen under visible
and UV light irradiation. Due to its excellent features (including
unique semiconductor energy band of 2.7 eV, excellent chemical stability,
easy preparation and non-toxic), graphite phase carbon nitride (g-C 3 N 4 ) has received great research interests. It has
been regarded as a new kind of visible light catalyst because it does
not contain metal compound commonly used in solar photocatalysis
area. In this article, rod-like g-C 3 N 4 (RCN)
was synthesized via a “top-down” hydrothermal method
using blocky g-C 3 N 4 as the precursor without
using any other template and additive. X-ray diffraction (XRD), transmission
electron microscopy (TEM), scanning electron microscopy (SEM), UV/Vis
diffuse reflectance spectra (DRS), Fourier-transform infrared spectroscopy
(FTIR), photoluminescence spectroscopy (PL) and nitrogen adsorption-desorption
(BET) analysis techniques were used to analyze the RCN. The results
indicated that under the hydrothermal condition, the high temperature
and high pressure provided by the solvent cracked the blocky g-C 3 N 4 into tiny particles, and then, the
tiny particles connected along with the rod axis direction; at 6 h,
a rod-like structure with length of 2.4 μm and diameter of 45
nm was obtained. The RCN improved the BET of g-C 3 N 4 , accelerated the separation of photo-generated electron-hole
pairs and affected the energy band structure. Because of these properties,
the obtained RCN exhibited an enhanced visible light photocatalytic
activity when compared with that of blocky g-C 3 N 4 according to the results of visible-light photocatalytic degradation
of methylene blue and H 2 production from water splitting.
Under the same conditions, the degradation rate of RCN on methylene
blue was much higher than that of bulk g-C 3 N 4 (58.15%), which reached 98.50%, and the RCN exhibited excellent
cycle stability. The hydrogen production efficiency of RCN of 12.83
μmol/h was significantly increased when compared with that of
blocky g-C 3 N 4 (4.35 μmol/h), which was
about three times of g-C 3 N 4 . The possibility
of the improvement of visible light photocatalytic activity might
be due to the synergistic effects that caused by the rod-like structure.
On the one hand, the fluorescence emission peak position of the RCN
had slightly blue shifted compared with the bulk g-C 3 N 4 , indicating the band gap width became larger. On the other
hand, the larger specific surface area of RCN caused by its unique
rod-shaped morphology could provide more active sites, which could
adsorb more reactive molecules and promote the transfer of surface
charge.
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