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Synergic Effect between Adsorption and Photocatalysis of Metal-Free g-C3N4 Derived from Different Precursors.

Xu HY, Wu LC, Zhao H, Jin LG, Qi SY - PLoS ONE (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin, P. R. China.

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.

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XRD patterns of g-C3N4 samples derived from different precursors at different temperatures.(a) Dicyandiamide. (b) Melamine.
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pone.0142616.g001: XRD patterns of g-C3N4 samples derived from different precursors at different temperatures.(a) Dicyandiamide. (b) Melamine.

Mentions: XRD patterns of g-C3N4 samples derived from different precursors at different temperatures are presented in Fig 1(a) and 1(b), respectively, where it can be seen that there exist two distinct diffraction peaks for all the obtained samples. For g-C3N4 samples derived from dicyandiamide, these two diffraction peaks occur at 13.16° and 27.28°, respectively (Fig 1(a)). And, for the samples derived from melamine, the both peaks center at 13.05° and 27.59°, respectively (Fig 1(b)). Therefore, there is no difference in the position of XRD peaks for g-C3N4 samples prepared from different precursors, suggesting that all the samples possess the same crystal structure of g-C3N4. For the both peaks, 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 also can be seen from the 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. Moreover, it should be noted that, at the same condition of temperature, g-C3N4 sample derived from melamine exhibits sharper XRD peaks than that from dicyandiamide, implying that the former has better crystallinity with less defects and disturbances in the graphitic structure. According to XRD results, the crystal size of g-C3N4 was computed by Scherrer formula D = Kλ/βcosθ, where D is the crystallite size (nm), K the Scherrer constant (about 0.9), λ the wavelength of Cu-Kα radiation (0.15418nm), and β the full width of (002) diffraction peak at half maximum [43]. The calculated crystallite sizes of all g-C3N4 samples are listed in Table 1. On the whole, at the same pyrolysis temperature, the crystallite size of g-C3N4 sample obtained from dicyandiamide is smaller than that from melamine. The possible explanation for this tendency might be that the polycondensation route for dicyandiamide to form g-C3N4 is different to that for melamine. According to previous reports [27, 44], these two routes are illustrated in Fig 2. The precursor melamine can be directly pyrolyzed and polymerized to form g-C3N4, nevertheless, dicyandiamide must be firstly condensed into melamine and then pyrolyzed and polymerized to form g-C3N4. The redundant step for dicyandiamide to form g-C3N4 encumbers the nucleation and growth of g-C3N4, thus it is not hard to understand that the crystallite size of g-C3N4 derived from dicyandiamide is smaller within the same pyrolysis time. Furthermore, for the same precursor, the crystallite size increases with the pyrolysis temperature increasing, suggesting that higher temperature favors the nucleation and growth of g-C3N4.


Synergic Effect between Adsorption and Photocatalysis of Metal-Free g-C3N4 Derived from Different Precursors.

Xu HY, Wu LC, Zhao H, Jin LG, Qi SY - PLoS ONE (2015)

XRD patterns of g-C3N4 samples derived from different precursors at different temperatures.(a) Dicyandiamide. (b) Melamine.
© Copyright Policy
Related In: Results  -  Collection

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pone.0142616.g001: XRD patterns of g-C3N4 samples derived from different precursors at different temperatures.(a) Dicyandiamide. (b) Melamine.
Mentions: XRD patterns of g-C3N4 samples derived from different precursors at different temperatures are presented in Fig 1(a) and 1(b), respectively, where it can be seen that there exist two distinct diffraction peaks for all the obtained samples. For g-C3N4 samples derived from dicyandiamide, these two diffraction peaks occur at 13.16° and 27.28°, respectively (Fig 1(a)). And, for the samples derived from melamine, the both peaks center at 13.05° and 27.59°, respectively (Fig 1(b)). Therefore, there is no difference in the position of XRD peaks for g-C3N4 samples prepared from different precursors, suggesting that all the samples possess the same crystal structure of g-C3N4. For the both peaks, 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 also can be seen from the 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. Moreover, it should be noted that, at the same condition of temperature, g-C3N4 sample derived from melamine exhibits sharper XRD peaks than that from dicyandiamide, implying that the former has better crystallinity with less defects and disturbances in the graphitic structure. According to XRD results, the crystal size of g-C3N4 was computed by Scherrer formula D = Kλ/βcosθ, where D is the crystallite size (nm), K the Scherrer constant (about 0.9), λ the wavelength of Cu-Kα radiation (0.15418nm), and β the full width of (002) diffraction peak at half maximum [43]. The calculated crystallite sizes of all g-C3N4 samples are listed in Table 1. On the whole, at the same pyrolysis temperature, the crystallite size of g-C3N4 sample obtained from dicyandiamide is smaller than that from melamine. The possible explanation for this tendency might be that the polycondensation route for dicyandiamide to form g-C3N4 is different to that for melamine. According to previous reports [27, 44], these two routes are illustrated in Fig 2. The precursor melamine can be directly pyrolyzed and polymerized to form g-C3N4, nevertheless, dicyandiamide must be firstly condensed into melamine and then pyrolyzed and polymerized to form g-C3N4. The redundant step for dicyandiamide to form g-C3N4 encumbers the nucleation and growth of g-C3N4, thus it is not hard to understand that the crystallite size of g-C3N4 derived from dicyandiamide is smaller within the same pyrolysis time. Furthermore, for the same precursor, the crystallite size increases with the pyrolysis temperature increasing, suggesting that higher temperature favors the nucleation and growth of g-C3N4.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin, P. R. China.

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.

Show MeSH