Molybdenum disulfide is the New Graphene

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Many sustainability technologies that exist, including solar cells, light-emitting diodes, and transistors, could be greatly improved with regards to energy efficiency and productivity through the incorporation of 2D Molybdenum disulfide nanosheets into semiconductor devices. To create 2D Molybdenite nanosheets, samples of MoS2 undergo exfoliation, in which a solid comes apart in layers after exposure to a solution [1].

At the nanoscale, molybdenite offers a variety of advantages over graphene when used in electronics and optoelectronics. Molybdenite exhibits higher conductivity and increased optical properties, in addition to remarkable strength and light-weight. As it is exfoliated into atomically thin sheets, Molybdenite fluoresces. This optical property of MoS2 yields brighter light for the same amount of energy and material due to an increased light intensity resulting from decreased absorbance, meaning the less light an object absorbs, the more light it reflects, hence a greater light intensity [2]. Additionally, Molybdenite possesses a lower thermal conductivity than graphene, which reduces the rate at which heat flows through the material, maximizing light output (as LED’s generally function optimally under ambient temperatures). While this creates a more efficient semiconductor, the increased brightness can pose a hazard to people’s eyes. This detriment is remedied through the use of fiber couplers (optical fibers stretched while heated), which can divert energy output and regulate light intensity [3]. Another advantage of MoS2 is its band gap, an energy range in which no electron states can exist. By applying an electric field to achieve this energy state, transistors utilizing MoS2 can be turned completely off [4]. Molybdenite is holistically superior to graphene as a semiconducting material due to increased productivity (light intensity) as the result of florescent properties and a low thermal conductivity, and also maintains greater energy efficiency due to the band gap. 

Flakes of MoS2 (B) and MoS2 nanosheets (E).

(Source: Hangxun et al., 2012)

References

  1. "Dictionary of Nanotechnology - Delamination." Dictionary of Nanotechnology - Delamination. N.p., n.d. Web. 13 Dec. 2014.
  2. "Molybdenum Disulfide Has Emerged as a Leading Successor to Graphene."Molybdenum Disulfide Has Emerged as a Leading Successor to Graphene. Northwestern University, 13 Nov. 2014. Web. 13 Dec. 2014.
  3. Paschotta, Rüdiger. "Tapered Fibers." Encyclopedia of Laser Physics and Technology. N.p., n.d. Web. 17 Dec. 2014.
  4. Luan, Feng. "2D Molybdenum Disulfide: A Promising New Optical Material for Ultra-fast Photonics." 2D Molybdenum Disulfide: A Promising New Optical Material for Ultra-fast Photonics. N.p., 30 Oct. 2014. Web. 13 Dec. 2014.
  5. Sun, Xu, Jun Dai, Yuqiao Guo, Changzheng Wu, Fanting Hu, Jiyin Zhao, Xiaocheng Zeng, and Yi Xie. "Semimetallic Molybdenum Disulfide Ultrathin Nanosheets as an Efficient Electrocatalyst for Hydrogen Evolution." Nanoscale 6.14 (2014): 8359. Web.
  6. Zhao, Yufei, Shuangqiang Chen, Bing Sun, Dawei Su, Xiaodan Huang, Hao Liu, Yiming Yan, Kening Sun, and Guoxiu Wang. "Graphene-Co3O4 Nanocomposite as Electrocatalyst with High Performance for Oxygen Evolution Reaction." Sci. Rep. Scientific Reports 5 (2015): 7629. Web.
  7. Li, Mingtao, Lipeng Zhang, Quan Xu, Jianbing Niu, and Zhenhai Xia. "N-doped Graphene as Catalysts for Oxygen Reduction and Oxygen Evolution Reactions: Theoretical Considerations." Journal of Catalysis314 (2014): 66-72. Web.
  8. Guardia, Laura, Juan I. Paredes, José M. Munuera, Silvia Villar-Rodil, Miguel Ayán-Varela, Amelia Martínez-Alonso, and Juan M. D. Tascón. "Chemically Exfoliated MoS 2 Nanosheets as an Efficient Catalyst for Reduction Reactions in the Aqueous Phase." ACS Appl. Mater. Interfaces ACS Applied Materials & Interfaces 6.23 (2014): 21702-1710. Web.
  9. Chng, Elaine Lay Khim, Zdeněk Sofer, and Martin Pumera. "MoS 2 Exhibits Stronger Toxicity with Increased Exfoliation." Nanoscale 6.23 (2014): 14412-4418. Web.

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2D Molybdenum disulfide nanosheets possess several properties that make it superior to graphene with regards to application in electronics and optoelectronics. On the nanoscale, MoS2 fluoresces and has a decreased absorbance, meaning more light reflected, creating more effective light-emitting diodes, regulated by a lower thermal conductivity to decrease risk of optical damage. The band gap of MoS2 is another advantageous property that allows for MoS2 transistors to be turned off to conserve energy [5]. 

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In addition to its band gap advantage, the overpotential of MoS2 is 1/4 the overpotential of graphene. This smaller difference between theoretical and actual energy requirements enables significantly reduced energy consumption. MoS2 also uses 100,000 times less energy than traditional Silicon transistors. Band gaps are not easily artificially created, which suggests MoS2 may be used as a permanent substitute for current graphene semiconductors which lack a band gap. Molybdenite is relatively abundant and easy to process, making it economically viable as well as efficient. In nanoparticles, MoS2 could also act as a more effective agent in the catalysis process of removing sulfur from crude oil. This would prevent sulfur from being released into the atmosphere when the oil is burned and as a result, decrease the effects of acid rain [6,7,8]. 

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The effects of Molybdenite nanosheets and nanoparticles have received little attention outside of their applications to electronics and optoelectronics. Studies suggest increased cytotoxicity can be correlated to increased exfoliation, likely due to the higher surface area and reactivity of the nanomaterials [9]. 

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