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Synthesis, Characterization and Photoelectrochemical Application of two Dimensional MoS2 and WS2 Nanosheets

Zirak, Mohammad | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49335 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Zaker Moshfegh, AliReza; Moradlou, Omran
  7. Abstract:
  8. In this research, Synthesis, characterization and photoelectrochemical application of two dimensional MoS2 and WS2 nanosheets have been carefully investigated. And finally, based on theoritical and experimental analysis results, the mechanisms of the observed photoelectrochemical (PEC) activities were suggested.The ab initio density functional calculations about Mo1-xWxS2 monolayer deposited over a TiO2 (110) substrate revealed a shift in band position of the Mo1-xWxS2 in favor of photoelectrochemical water splitting. Moreover, increase of W concentration in Mo1-xWxS2 could improve the charge separation and increase the effective mass ratio leading to an extension of the electron–hole pair.Single layer of MoS2 and WS2 were obtained by using solvothermal Li intercalation method with lateral sizes of 170 ± 13 and 200 ± 30 nm, respectively. 2D-MoS2 and 2D-WS2 few layer nanosheets were also synthesized by using sonication-exfoliation conditions in mixed water-ethanol solution. Using the optimized parameters, the MoS2 nanosheets with thickness of 6 ± 1 nm and lateral dimension of 60 ± 8 nm and WS2 nanosheets with thickness of 5 ± 1 nm and lateral dimension of 200 ± 15 nm were synthesized.CdS nanoparticles (with average diameter of 10 nm) were grown on MoS2(t)/ITO and WS2(t)/ITO electrodes. the highest photo-current density of 350 µA/cm2 was measured for the CdS/WS2(30 s)/ITO sample which was about 2.8 times higher than the value obtained for bare CdS/ITO (125 µA/cm2). The highest scaling exponent (β) value was measured for the CdS/WS2(30 s)/ITO (β= 0.91 ± 0.01) which it was 0.88 ± 0.01 for the bare CdS/ITO electrode, indicating that the recombination of charge carriers is minimized in CdS/WS2(30s)/ITO sample. Photocatalytic activity enhancement as well as providing good photo-stability makes MoS2 and WS2 nanosheets promising candidates for solar energy conversion applications
  9. Keywords:
  10. Stochastic Analysis ; Optical Stability ; photoelectrocatalytic Activity ; Density Functional Theory (DFT) ; Statistical Physics ; Two Dimentional Nanosheets ; Single-layer Synthesis

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