Abstract
Graphitic carbon nitride (g-C3N4) used in this work was obtained by heating dicyandiamide and melamine, respectively, at different temperatures. The differences of g-C3N4 derived from different precursors in phase composition, functional group, surface morphology, microstructure, surface property, band gap and specific surface area were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-visible diffuse reflection spectroscopy and BET surface area analyzer, respectively. The photocatalytic discoloration of an active cationic dye, Methylene Blue (MB) under visible-light irradiation indicated that g-C3N4 derived from melamine at 500°C (CN-M500) had higher adsorption capacity and better photocatalytic activity than that from dicyandiamide at 500°C (CN-D500), which was attributed to the larger surface area of CN-M500. MB discoloration ratio over CN-M500 was affected by initial MB concentration and photocatalyst dosage. After 120 min reaction time, the blue color of MB solution disappeared completely. Subsequently, based on the measurement of the surface Zeta potentials of CN-M500 at different pHs, an active anionic dye, Methyl Orange (MO) was selected as the contrastive target pollutant with MB to reveal the synergic effect between adsorption and photocatalysis. Finally, the photocatalytic mechanism was discussed.
Highlights
The global crises of environmental pollution and energy shortage have driven most scientists to research and develop novel techniques to both eliminate environmental pollution and utilize solar energy
The stronger one is generated by the stacking of the conjugated aromatic ring, indexed as the (002) crystal plane for graphite-like materials [41]; while, the weaker one is attributed to the in-plane ordering of tri-s-triazine units, assigned as the (100) crystal plane [42]. It can be seen from the X-ray diffraction (XRD) patterns that, at the pyrolytic temperature of 460°C, two unknown impurity peaks occur near 11° and 25° for g-C3N4 samples derived from both dicyandiamide and melamine, which might be attributed to the incomplete polycondensation of precursors
At the same pyrolysis temperature, the crystallite size of g-C3N4 sample obtained from dicyandiamide was smaller than that from melamine
Summary
The global crises of environmental pollution and energy shortage have driven most scientists to research and develop novel techniques to both eliminate environmental pollution and utilize solar energy. Photocatalysis has emerged from these techniques because of its utilization of solar energy for both organic contaminations degradation and hydrogen production [1]. Titanium dioxide (TiO2) has been regarded as one of the most prominent photocatalysts due to its non-toxicity, good stability and high activity [2]. As a semiconductor with wider band gap (3.0–3.2 eV), single phase TiO2 photocatalyst, such as anatase or rutile, can be excited only by the light in UV region [3], restricting the full use of solar resource.
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