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Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H2 production under visible light.

Wang G, Huang B, Li Z, Lou Z, Wang Z, Dai Y, Whangbo MH - Sci Rep (2015)

Bottom Line: Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent.This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value.Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, People's Republic of China.

ABSTRACT
Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H2 production under visible light were evaluated by gas chromatograph, and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations. Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH4 in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H2 production under visible-light irradiation without loading noble metal. This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value. Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

No MeSH data available.


Photocatalytic reactions results.(A) Photocatalytic production of H2 by the ZnS sample (0.5 g) obtained using 0.01 mol NaBH4 as a function of the visible-light irradiation time. (B) Hydrogen production rate by ZnS samples obtained using different amounts of NaBH4 (a = 0 mol, b = 0.003 mol, c = 0.005 mol, d = 0.01 mol, e = 0.02 mol, and f = 0.03 mol).
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f6: Photocatalytic reactions results.(A) Photocatalytic production of H2 by the ZnS sample (0.5 g) obtained using 0.01 mol NaBH4 as a function of the visible-light irradiation time. (B) Hydrogen production rate by ZnS samples obtained using different amounts of NaBH4 (a = 0 mol, b = 0.003 mol, c = 0.005 mol, d = 0.01 mol, e = 0.02 mol, and f = 0.03 mol).

Mentions: The ability of the ZnS samples (0.5 g) for photocatalytic hydrogen generations under visible light (λ > 420 nm) irradiation was evaluated by using 100 mL aqueous solution containing Na2S (0.25 M) and Na2SO3 (0.5 M) as sacrificial agents. The H2 production of the ZnS sample (obtained with 0.01 mol of NaBH4) as a function of the irradiation time is presented in Fig. 6A, which shows that the activity of the sample has no decrease after 7 h irradiation (The XPS results of this sample, before and after photocatalytic reaction, were also show in Fig S4, ESI†). The hydrogen production rates of the ZnS samples synthesized using different amounts of NaBH4 (0–0.03 mol), displayed in Fig. 6B, show that the production rate increases until the amount of NaBH4 reaches 0.01 mol but drops abruptly when it is beyond 0.01 mol. This means that the S vacancies enhance the visible light absorption resulting in an enhanced high photocatalytic activity. However, when present in excess amount, vacancies act as recombination centers for photogenerated carriers decreasing the photocatalytic activity. With increasing the amount of NaBH4 to 0.02 and 0.03 mol, lots of hierarchical microspheres are broken, which can also contribute to the precipitous decline of the H2 production rate. Cycling photocatalytic experiments of ZnS were also done for evaluating the stability of the ZnS samples (Fig S8, ESI†), which exhibited good stability after 3 times photocatalytic reactions.


Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H2 production under visible light.

Wang G, Huang B, Li Z, Lou Z, Wang Z, Dai Y, Whangbo MH - Sci Rep (2015)

Photocatalytic reactions results.(A) Photocatalytic production of H2 by the ZnS sample (0.5 g) obtained using 0.01 mol NaBH4 as a function of the visible-light irradiation time. (B) Hydrogen production rate by ZnS samples obtained using different amounts of NaBH4 (a = 0 mol, b = 0.003 mol, c = 0.005 mol, d = 0.01 mol, e = 0.02 mol, and f = 0.03 mol).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4339798&req=5

f6: Photocatalytic reactions results.(A) Photocatalytic production of H2 by the ZnS sample (0.5 g) obtained using 0.01 mol NaBH4 as a function of the visible-light irradiation time. (B) Hydrogen production rate by ZnS samples obtained using different amounts of NaBH4 (a = 0 mol, b = 0.003 mol, c = 0.005 mol, d = 0.01 mol, e = 0.02 mol, and f = 0.03 mol).
Mentions: The ability of the ZnS samples (0.5 g) for photocatalytic hydrogen generations under visible light (λ > 420 nm) irradiation was evaluated by using 100 mL aqueous solution containing Na2S (0.25 M) and Na2SO3 (0.5 M) as sacrificial agents. The H2 production of the ZnS sample (obtained with 0.01 mol of NaBH4) as a function of the irradiation time is presented in Fig. 6A, which shows that the activity of the sample has no decrease after 7 h irradiation (The XPS results of this sample, before and after photocatalytic reaction, were also show in Fig S4, ESI†). The hydrogen production rates of the ZnS samples synthesized using different amounts of NaBH4 (0–0.03 mol), displayed in Fig. 6B, show that the production rate increases until the amount of NaBH4 reaches 0.01 mol but drops abruptly when it is beyond 0.01 mol. This means that the S vacancies enhance the visible light absorption resulting in an enhanced high photocatalytic activity. However, when present in excess amount, vacancies act as recombination centers for photogenerated carriers decreasing the photocatalytic activity. With increasing the amount of NaBH4 to 0.02 and 0.03 mol, lots of hierarchical microspheres are broken, which can also contribute to the precipitous decline of the H2 production rate. Cycling photocatalytic experiments of ZnS were also done for evaluating the stability of the ZnS samples (Fig S8, ESI†), which exhibited good stability after 3 times photocatalytic reactions.

Bottom Line: Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent.This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value.Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, People's Republic of China.

ABSTRACT
Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H2 production under visible light were evaluated by gas chromatograph, and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations. Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH4 in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H2 production under visible-light irradiation without loading noble metal. This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value. Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

No MeSH data available.