Optimized Synthesis Temperature and Time to Obtain Crystalline Carbon Nitride with Enhanced Photocatalytic Activity for Phenol Degradation

Abstract

In this work, the crystalline carbon nitride photocatalysts were synthesized by an ionothermal technique with varied synthesis temperature of 500, 550, and 600 °C, and synthesis time of 2, 4, and 6 h. Fourier transform infrared spectra showed the successful formation of the prepared carbon nitrides from their characteristic vibration peaks. X-ray diffraction patterns suggested that the same phase of poly(triazine imide) and heptazine could be observed, but with different crystallinity. The optical properties showed that different temperatures and synthesis time resulted in the different band gap energy (2.72–3.02 eV) as well as the specific surface area (24–73 m2 g–1). The transmission electron microscopy image revealed that the crystalline carbon nitride has a near-hexagonal prismatic crystallite size of about 50 nm. Analysis by high-performance liquid chromatography showed that the best photocatalytic activity for phenol degradation under solar light simulator was obtained on the crystalline carbon nitride prepared at the 550 °C for 4 h, which would be due to the high crystallinity, suitable low band gap energy (2.82 eV), and large specific surface area (73 m2 g–1). Controlling both the temperature and synthesis time is shown to be important to obtain the best physicochemical properties leading to high activity.

Crystalline C3N4/CeO2composites as photocatalyst for hydrogen production in visible light

“…The adsorption band at 887-889 cm -1 observed in g-C3N4 and g-C3N4/CeO2 was corresponded to the deformation mode of heptazine deformation [51], [52]. The absorption bands appeared at 1200-1650 cm -1 assigned to the typical characteristic of aromatic C-N heterocyclic [37], [45], [46], [49], [50]. The peaks at 1203-1357 cm -1 are attributed to the aromatic C-N stretching vibration.…”

“…With the addition of CeO2, the peaks gained increase intensity compared to bulk g-C3N4. The small band observed at 2128 cm -1 was due to the dissociated CN network, forming both C≡N and N=C=N bonds, formed by broken aromatic unit of C3N4 [49].…”

“…The broad adsorption band at 3000-3250 cm -1 is attributed to the stretching vibration of N-H (primary and secondary amine), which indicates that uncondensed amino functional group is present in the sample [22], [37], [49], [52]. A highly intense peak attributes to higher number of -NH/-NH2 groups were observed on g-C3N4 and CeO/g-C3N4, which indicates a larger number of particles are presence as smaller polymer contained fewer heptazine units [53].…”

“…The N-H stretching bands were disappeared on C-C3N4 and CeO/C-C3N4, which implied crystallisation in the presence of ionic salt removed defects. The broad peak 3250-3313 cm 1 is attributed to the vibration of intermolecular O-H hydrogen bonds or hydroxyl groups from the absorption of water in CN [22], [49]- [51].…”