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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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Evaluation of photocatalytic characters of CN-M500 sample.(a) Effect of initial MB concentration on the photocatalytic activity of CN-M500 at pristine pH of MB solution with g-C3N4 dosage of 1.0g/L; (b) Effect of photocatalyst dosage on the photocatalytic activity of CN-M500 at pristine pH of MB solution with initial MB concentration of 5mg/L; (c) UV-Vis absorption spectra of MB after different periods of the photocatalytic decomposition over CN-M500 at the pristine pH value of MB solution with g-C3N4 dosage of 1.0g/L and initial MB concentration of 5mg/L (inset: the color change of MB solution during reaction process); and (d) Recycle tests for CN-M500 sample under exactly identical conditions with the solid photocatalyst repeatedly washed by deionized water, centrifuged and dried after used once before.
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pone.0142616.g009: Evaluation of photocatalytic characters of CN-M500 sample.(a) Effect of initial MB concentration on the photocatalytic activity of CN-M500 at pristine pH of MB solution with g-C3N4 dosage of 1.0g/L; (b) Effect of photocatalyst dosage on the photocatalytic activity of CN-M500 at pristine pH of MB solution with initial MB concentration of 5mg/L; (c) UV-Vis absorption spectra of MB after different periods of the photocatalytic decomposition over CN-M500 at the pristine pH value of MB solution with g-C3N4 dosage of 1.0g/L and initial MB concentration of 5mg/L (inset: the color change of MB solution during reaction process); and (d) Recycle tests for CN-M500 sample under exactly identical conditions with the solid photocatalyst repeatedly washed by deionized water, centrifuged and dried after used once before.

Mentions: Afterwards, the photocatalytic activity of CN-M500 was investigated under different conditions of initial MB concentration and photocatalyst dosage, as shown in Fig 9(a) and 9(b), respectively. From Fig 9(a), an obvious decrease in MB discoloration ratio from 100% to 3.2% can be observed with the increase in initial MB concentration from 5 to 30 mg/L, indicating a negative relationship between g-C3N4 photocatalytic activity and initial dye concentration. This phenomenon can be explained by the three following factors: firstly, a higher concentration of dye would reduce the active sites of g-C3N4 surface due to the adsorption of more dye molecules, hampering the formation of active oxidative species (•OH and •O2-); secondly, a higher concentration of dye would produce more intermediates with slow diffusion from catalyst surface, resulting in the deactivation of g-C3N4 photocatalyst; thirdly, a higher concentration of dye would make more light photons adsorbed by the dye itself, leading to a lower light quantum efficiency [55]. From Fig 9(b), it can be obviously found that the increase in g-C3N4 dosage can improve the adsorption capacity and photocatalytic activity for MB discoloration. When g-C3N4 dosage is 2.0g/L, MB molecules with the concentration of 5mg/L can be completely decomposed under visible-light irradiation within 90 min reaction time. This is because, with the increase in catalyst dosage, the active sites on the surface of g-C3N4 catalyst increase and generated active species increase [56]. The UV-Vis absorption spectra of MB solution after different periods of the photocatalytic decomposition are illustrated in Fig 9(c), from which it can be observed that the two main absorption peaks at 292 nm and 665 nm gradually weaken and completely disappear after 120 min reaction time, implying that MB molecules are completely decomposed into water and carbon dioxide at this moment. The inset in Fig 9(c) demonstrates that the MB solution after 120 min reaction time becomes colorless. Moreover, good stability of a photocatalyst has been regarded as another important part for the evaluation of photocatalytic activity [48]. The recyclability of CN-M500 photocatalyst was examined and the results are illustrated in Fig 9(d). After five cycles, there is no apparent decrease in MB discoloration ratio and the photocatalytic activity of g-C3N4 photocatalyst is relatively stable, suggesting that g-C3N4 photocatalyst has good stability.


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)

Evaluation of photocatalytic characters of CN-M500 sample.(a) Effect of initial MB concentration on the photocatalytic activity of CN-M500 at pristine pH of MB solution with g-C3N4 dosage of 1.0g/L; (b) Effect of photocatalyst dosage on the photocatalytic activity of CN-M500 at pristine pH of MB solution with initial MB concentration of 5mg/L; (c) UV-Vis absorption spectra of MB after different periods of the photocatalytic decomposition over CN-M500 at the pristine pH value of MB solution with g-C3N4 dosage of 1.0g/L and initial MB concentration of 5mg/L (inset: the color change of MB solution during reaction process); and (d) Recycle tests for CN-M500 sample under exactly identical conditions with the solid photocatalyst repeatedly washed by deionized water, centrifuged and dried after used once before.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4643995&req=5

pone.0142616.g009: Evaluation of photocatalytic characters of CN-M500 sample.(a) Effect of initial MB concentration on the photocatalytic activity of CN-M500 at pristine pH of MB solution with g-C3N4 dosage of 1.0g/L; (b) Effect of photocatalyst dosage on the photocatalytic activity of CN-M500 at pristine pH of MB solution with initial MB concentration of 5mg/L; (c) UV-Vis absorption spectra of MB after different periods of the photocatalytic decomposition over CN-M500 at the pristine pH value of MB solution with g-C3N4 dosage of 1.0g/L and initial MB concentration of 5mg/L (inset: the color change of MB solution during reaction process); and (d) Recycle tests for CN-M500 sample under exactly identical conditions with the solid photocatalyst repeatedly washed by deionized water, centrifuged and dried after used once before.
Mentions: Afterwards, the photocatalytic activity of CN-M500 was investigated under different conditions of initial MB concentration and photocatalyst dosage, as shown in Fig 9(a) and 9(b), respectively. From Fig 9(a), an obvious decrease in MB discoloration ratio from 100% to 3.2% can be observed with the increase in initial MB concentration from 5 to 30 mg/L, indicating a negative relationship between g-C3N4 photocatalytic activity and initial dye concentration. This phenomenon can be explained by the three following factors: firstly, a higher concentration of dye would reduce the active sites of g-C3N4 surface due to the adsorption of more dye molecules, hampering the formation of active oxidative species (•OH and •O2-); secondly, a higher concentration of dye would produce more intermediates with slow diffusion from catalyst surface, resulting in the deactivation of g-C3N4 photocatalyst; thirdly, a higher concentration of dye would make more light photons adsorbed by the dye itself, leading to a lower light quantum efficiency [55]. From Fig 9(b), it can be obviously found that the increase in g-C3N4 dosage can improve the adsorption capacity and photocatalytic activity for MB discoloration. When g-C3N4 dosage is 2.0g/L, MB molecules with the concentration of 5mg/L can be completely decomposed under visible-light irradiation within 90 min reaction time. This is because, with the increase in catalyst dosage, the active sites on the surface of g-C3N4 catalyst increase and generated active species increase [56]. The UV-Vis absorption spectra of MB solution after different periods of the photocatalytic decomposition are illustrated in Fig 9(c), from which it can be observed that the two main absorption peaks at 292 nm and 665 nm gradually weaken and completely disappear after 120 min reaction time, implying that MB molecules are completely decomposed into water and carbon dioxide at this moment. The inset in Fig 9(c) demonstrates that the MB solution after 120 min reaction time becomes colorless. Moreover, good stability of a photocatalyst has been regarded as another important part for the evaluation of photocatalytic activity [48]. The recyclability of CN-M500 photocatalyst was examined and the results are illustrated in Fig 9(d). After five cycles, there is no apparent decrease in MB discoloration ratio and the photocatalytic activity of g-C3N4 photocatalyst is relatively stable, suggesting that g-C3N4 photocatalyst has good stability.

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
Related in: MedlinePlus