Influence of annealing temperature on physical properties and photocatalytic ability of g-C3N4 nanosheets synthesized through urea polymerization in Ar atmosphere

Abstract

The influences of annealing temperature on structure, morphology, vibration, optical properties and photocatalytic ability of g-C3N4 nanosheets synthesized from urea in Ar atmosphere were investigated in detail by using x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR), UV–vis absorption, and photoluminescence (PL). It was found that the preparation temperature had a great effect on structure and physical properties of g-C3N4. As the processing temperature increased from 450°C to 650°C, the interlayer stacking distance of g-C3N4 decreased from 3.281Å to 3.217Å and the lattice parameter a decreased from 5.010Å to 4.934Å. This indicated a denser packing fashion of g-C3N4 at high annealing temperature. Moreover, the FTIR spectra and SEM images revealed a large fraction of small polymer segments containing only a few heptazine units as annealing temperature increased. BET result indicated an increasing specific surface area as preparation temperature increased. UV–vis absorption spectra showed a decrease of the band gap energy with increasing calcination temperature which agrees well with the measured PL spectra. It was demonstrated that samples annealed at 550°C exhibited the strongest photocatalytic activity. A decomposition of 80% and 100% of rhodamine B was obtained within respectively 1h and 2h under Xenon lamp irradiation. Photocatalytic result could be adequately explained based on evidences of specific surface area, average pore volume and pore size, and recombination rate of photoinduced electron-hole pairs.