This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Production of Graphene”.
1. Which of the following is the correct order of chemical vapour deposition for graphene production?
a) Diffusion of by products through boundary layer ➜ Desorption of the by products from the surface ➜ Chemical reaction on the surface ➜ Adsorption of reactants onto substrate surface ➜ Diffusion of gases through boundary layer
b) Diffusion of gases through boundary layer ➜ Adsorption of reactants onto substrate surface ➜ Chemical reaction on the surface ➜ Desorption of the by-products from the surface ➜ Diffusion of by- products through boundary layer
c) Diffusion of gases through boundary layer ➜ Chemical reaction on the surface ➜ Adsorption of reactants onto substrate surface ➜ Diffusion of by products through boundary layer ➜ Desorption of the by products from the surface
d) Adsorption of reactants onto substrate surface ➜ Chemical reaction on the surface ➜ Diffusion of by products through boundary layer ➜ Diffusion of gases through boundary layer ➜ Desorption of the by products from the surface
View Answer
Explanation: CVD is conducted in a reaction chamber under certain temperature and pressure. Here, the carrier gases are combined and deposited on the substrate. Chemical reaction occur on the surface where the material is formed while the waste gases or by products are removed from the surface of the substrate.
2. Which among the given options does not fall under the advantages of bottom-up methods for graphene production?
a) Controlled thickness
b) Formation of unoxidized sheets
c) High quality
d) Low production scale
View Answer
Explanation: Bottom up methods for graphene production has both advantages and disadvantages. Its benefits include controlled thickness, formation of unoxidized high quality sheets and production of large area of pure graphene.
3. What is the role of surfactant in the production of graphene from graphite?
a) Increases surface tension of the solvent
b) Prevents restacking
c) Reduces graphene concentration
d) Prevents sonication
View Answer
Explanation: In the process of obtaining graphene from graphite surfactants are added to the solvent. This is done prior to sonication in order to prevent restacking by adsorbing to the graphene’s surface. The resulting solution has higher graphene concentration.
4. Which of the following is not a method of synthesis for graphene?
a) Blow moulding
b) Exfoliation
c) Epitaxial growth
d) Hummers method
View Answer
Explanation: Graphene method can be synthesized using both top down and bottom up processes. The top down method include mechanical exfoliation, electro-chemical exfoliation, sonication, hummer’s method and hydrothermal reduction of graphene oxide. Bottom up methods involve CVD, epitaxial growth, pyrolysis etc. Blow moulding is a polymer processing technique and is not used for graphene production.
5. Which method of graphene production involves the deposition of reduced graphene oxide onto the substrate at ultrahigh speed?
a) Supersonic spray
b) Hydrothermal reduction of graphene oxide
c) Epitaxial growth of graphene
d) Carbon dioxide reduction
View Answer
Explanation: The supersonic spray method uses a graphene spray gun to deposit one atom thick layer of graphene onto the substrate. The de Laval nozzle is inserted with reduced graphene oxide. These molecules are then converted into fine particles during its exposure to supersonic speed gas stream. These are further transformed into tiny droplets in the air. The graphene droplets evaporate and evenly disperse, while being suspended in air. Upon coming in contact with substrate, the energy of the impact rearranges the carbon atoms into flawless graphene.
6. Hydrothermal self-assembly method of graphene synthesis has many benefits but it is incapable of controlling the thickness of graphene sheets produced.
a) True
b) False
View Answer
Explanation: One of the biggest benefits of using hydrothermal self-assembly method for graphene production is its capability of controlling the thickness of graphene sheets produced. The method is able to control the thickness, ranging from monolayer to multilayers and is referred to as Tang-Lau Method.
7. What is the drawback of the earliest method used for graphene production?
a) Production of corrosive and toxic gases
b) Expensive ionic liquids
c) Highly proficient and skilled experts are required
d) An extremely high temperature process
View Answer
Explanation: Mechanical exfoliation is the earliest method used for graphene production. Though this method is quite simple and safe, yet its use is limited due to various drawbacks. These comprise of low yield, demand for highly skilled experts and poor size of the obtained flakes.
8. Mention the incorrect option with respect to the method of graphene synthesis by hydrothermal reduction of graphene oxide.
a) Environment-friendly process
b) Graphene nanofluids exhibit Newtonian behavior
c) Very expensive method of preparation
d) Viscosity of graphene colloidal suspension is similar to water
View Answer
Explanation: Graphene can be produced by the process of hydrothermal reduction of graphene oxide. This process is industrially applicable, environment friendly and quite economical. The process results in graphene colloidal suspension having graphene nanofluids that exhibit Newtonian behavior. Their viscosity is similar enough to water.
9. How is graphene produced from carbon nanotubes (CNTs)?
a) Centrifugation
b) Etching
c) Combustion
d) Restacking
View Answer
Explanation: Graphene can be produced from carbon nanotubes (CNTs) by cutting or etching them. This method can result in both single layered and multi layered graphene, depending upon the precursor nanotubes. If the starting nanotubes are single walled carbon nanotubes (SWCNT), they result in single layered graphene. While multi-walled carbon nanotubes (MWCNT) result in multi layered graphene upon unzipping CNT.
10. Choose the incorrect statement with respect to CVD for graphene production.
a) Transition metals like Ni, Cu, Pa, and Ir cannot be used as substrates for growth of graphene
b) Temperature dependence plays a vital role and can affect the type of reactions taking place
c) Substrate selection depends upon the feasibility of transferring graphene onto the required material
d) Carrier gases used in the process are usually methane, hydrogen and argon
View Answer
Explanation: CVD is a way of combining and depositing gaseous reactants onto a substrate. The process is conducted in a reaction chamber where carrier gases are combined under a certain temperature and pressure. Temperature plays a pivotal role in the process. The substrate on which the material is formed is usually a transition metal such as Ni, Cu, Pa etc. Here, substrate selection is vital since it depends on the feasibility of transferring graphene on the material.
11. Which of the following does not match with the features of the graphene formed using the Ion implantation method?
a) Wrinkled
b) Tear Free
c) Residue free
d) Wafer scale
View Answer
Explanation: Ion implantation method involves formation of graphene on silicon substrate. This process is carried out to form wafer-scale, wrinkle free, tension free and residue free graphene layer.
12. In electrochemical exfoliation method for graphene synthesis, varying pulsed voltage regulates a number of properties of the graphene sheets. Which of the following properties is not one of them?
a) Flake area
b) Thickness of sheets
c) Number of defects
d) Intercalating ions
View Answer
Explanation: Electrochemical exfoliation is an eco-friendly process producing high quality graphene. By varying a pulsed voltage it is possible to regulate the thickness, flake area and number of defects of the resulting graphene sheets.
13. Which among the following is a top down process for graphene production?
a) Epitaxial Growth
b) Pyrolysis
c) Hydrothermal reduction of graphene oxide
d) Chemical vapour deposition
View Answer
Explanation: Top down process for graphene production is a subtractive method in which materials are removed to produce features of a controlled shape and size. Top down methods involve mechanical exfoliation, sonication, chemical exfoliation, hydrothermal reduction of graphene oxide etc.
14. Which of the following is not an advantage of Hydrothermal self-assembly method of Graphene production?
a) Safe
b) Simple
c) Environment-friendly
d) Low yield
View Answer
Explanation: Hydrothermal self-assembly method of graphene synthesis is a substrate free bottom-up process. It is safer, simpler and more eco-friendly than exfoliation. However, it is a low scale production method.
15. Choose the correct option indicating the sequential order for Graphene production.
a) Sonication ➜ Centrifugation ➜ Use of ionic liquids ➜ Addition of surfactants
b) Use of Ionic liquids ➜ Sonication ➜ Addition of surfactants ➜ Centrifugation
c) Centrifugation ➜ Use of Ionic liquids ➜ Sonication ➜ Addition of surfactant
d) Addition of surfactant ➜ Sonication ➜ Centrifugation ➜ Use of Ionic liquids
View Answer
Explanation: Initially, a surfactant is added to a solvent before conducting sonication in order to prevent restacking. Now, dispersing graphite in a liquid medium can produce graphene by sonication followed by centrifugation. Use of a suitable ionic liquid that behaves as dispersing liquid medium can produce greater concentrations of graphene.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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