This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nanorods”.
1. What is the role of silver ions introduced in the seed – mediated growth method for gold nanorod synthesis?
a) Encourages growth of unwanted crystal facets
b) Acts as a strong stabilizers and surfactant
c) Increases aspect ratio to 10
d) Growth of rods in 1 dimension
View Answer
Explanation: Silver ions when introduced to the growth solution results in the nanorods of aspect ratio less than five in majority of the yield. Silver plate is used in the solution to allow for one direction growth and rod formation. It can also determine the length of the nanorods formed.
2. What is the role of hexadecyltrimethylammonium bromide in the electrochemical fabrication method of gold nanorods?
a) Reducing agent
b) Cationic surfactant
c) Oxidizing agent
d) Destabilizer
View Answer
Explanation: Hexadecyltrimethylammonium bromide is used as a cationic surfactant in the electrolytic solution. It can also function as a supporting electrolyte and stabilizer to prevent the aggregation of nanorods. It induces the formation of the rods.
3. How does the temperature influence the crystallite size of iron oxide nanorods formed using the hydrothermal method?
a) Strictly increases
b) Remain unaffected
c) Strictly decreases
d) Increases and then decreases
View Answer
Explanation: In hydrothermal process for nanorods synthesis, the crystallite and particle size of iron oxide vary with temperature. It rises significantly when temperature is changed from 250 to 350°C. This is due to the initiation of the nucleation process when the monomer concentration reaches the saturation point. However, the size doesn’t increase indefinitely with temperature. Once it exceeds 380°C which is the critical temperature the particle size starts to reduce. This occurs because of the low solvent power of supercritical water but an extremely high hydrolysis rate of iron salt in supercritical water.
4. Select the sequential order of the procedure for ZnO nanorod synthesis using the CVD method.
a) Temperature increased above 450°C ➔ Au droplets supersaturated with Zn vapour ➔ Quartz vial filled with Zn vapour ➔ ZnO nucleation ➔ Metallic zinc placed on alumina
b) Au droplets supersaturated with Zn vapour ➔ Metallic zinc placed on alumina ➔ ZnO nucleation ➔ Quartz vial filled with Zn vapour ➔ Temperature increased above 450°C
c) Quartz vial filled with Zn vapour ➔ ZnO nucleation ➔ Metallic zinc placed on alumina ➔ Temperature increased above 450°C ➔ Au droplets supersaturated with Zn vapour
d) Metallic zinc placed on alumina ➔ Temperature increased above 450°C ➔ Quartz vial filled with Zn vapour ➔ Au droplets supersaturated with Zn vapour ➔ ZnO nucleation
View Answer
Explanation: Granulated zinc of high purity is placed on alumina and kept inside a quartz ampoule sealed at one end. The entire setup is inside a quartz tube that is rapidly heated in a thermal furnace. Gold is used as a catalyst in this process. As soon as the temperature goes beyond the melting point of zinc (420°C), it vaporizes to fill the quartz vial. Catalyst forms liquid droplets to supersaturate the zinc vapours. ZnO nucleation growth is initiated upon the introduction of oxygen gas. Thus, ZnO precipitates when the droplets reach a critical radius. Finally, desired ZnO nanorods are obtained.
5. Which of the following is not an advantage of the cation exchange method used for the synthesis of nanorods?
a) Shape conserving
b) Kinetically unfavorable
c) Fast process
d) Heterostructure formation
View Answer
Explanation: Cation exchange is a promising technique for the synthesis of nanorods. This is due to the several advantages it has which include shape conserving and kinetically favorable properties. It is also faster in comparison to the bulk crystal systems due to high surface area of the existing nanorods used as templates in this method. Moreover, nanorod heterostructures can be created by adding complexity via partial transformation.
6. What is the most common method for single crystalline ZnO nanorod synthesis?
a) Solvothermal method
b) Chemical reduction
c) Vapour – liquid – solid method
d) Electrochemical method
View Answer
Explanation: The vapour liquid solid (VLS) process is used to synthesize single crystalline ZnO nanorods. It involves vaporization of zinc at above 900°C to mix it with catalytic droplets in order to form alloy droplets. Reaction of the zinc vapours and a mixture of CO/CO2 at the catalyst-substrate interface is followed by nucleation and growth of ZnO nanorods.
7. What is the process involved in the formation of water dispersible hollow iron oxide nanocapsules?
a) Thermal decomposition
b) Electrochemical process
c) Wrap-bake-peal method
d) Co-precipitation method
View Answer
Explanation: Wrap-bake-peel process is used for the synthesis of water dispersible hollow iron oxide nano-capsules using β-FeOOH nanoparticles. The process involves silica coating, heat treatment and removal of silica layer. This results in the transformation of phases and structures of β-FeOOH nanorods to form the water dispersible hollow nanocapsules.
8. What are the conditions for the growth of ZnO layers on the p-type silicon wafer in MBE technique for nanorod synthesis?
a) Substrate temperature = 1200-1500°C
b) Purity of Zn = 12-20%
c) Chamber pressure ⁓ (1-4) × 10-4 mbar
d) Temperature of Zn – Knudsen cell = 50°C – 100°C
View Answer
Explanation: The molecular beam epitaxy (MBE) system can be used to grow the ZnO layers on the p-type silicon wafer under certain conditions. These are – substrate temperature ranging between (300-430)°C, temperature of the Zn-Knudsen cell of about 300°C, pressure of the chamber, during growth, in the range of (1-4) × 10-4 mbar, purity of the Zn beads of about 99.999%.
9. Hydrothermal method can be used to produce branched and urchin – shaped morphologies of the ZnO nanorods.
a) True
b) False
View Answer
Explanation: ZnO nanorods can be prepared via hydrothermal method using zinc nitrate [Zn(NO3)26H2O] and hexamethylenetetramine (HMT) (C6H12N4). The mixture of zinc nitrate and HMT is heated to (60 – 95)°C. This leads to ZnO nanorods that assemble into branched and urchin-shaped morphologies. The nanorods grow larger with thick branches when the temperature is reduced to 75 and 60°C.
10. How can large iron oxide nanorods be synthesized in thermal decomposition method?
a) Annealing by high temperature
b) Using suitable catalysts
c) Employing non-toxic capping agents
d) Applying polyethylene glycol to solution
View Answer
Explanation: Thermal decomposition involves the breaking of chemical bonds of metal organic compounds at high temperature. The nanorods produced using this method ranges within a size of 50 – 100nm. The large length of the nanorods obtained is due to the annealing by high temperature.
11. Additives worsen the growth of gold nanorods.
a) True
b) False
View Answer
Explanation: Aromatic additives such as CTAB has been known to increase yield and produce highly uniform gold nanorods via the seed – mediated growth method. Sodium salicylate acting as an additive can increase the length of the nanorods.
12. Find out a top – down process used for the fabrication of gold nanorods.
a) Lithography
b) Solvothermal
c) Photochemical reduction
d) Sonochemical
View Answer
Explanation: Top-down methods used for gold nanorod production include ion beam or etching through the removal of gold from pre-deposited gold films. Lithography is also employed to create masks that are ultimately needed for gold nanorod synthesis. Physical methods such as sputtering and electron beam evaporation are utilized to cover the substrate, deposited with gold, by the mask.
13. Hydrothermal method is not a suitable technique for ZnO nanorod synthesis.
a) True
b) False
View Answer
Explanation: Hydrothermal method is one of the most advantageous processes of ZnO nanorod preparation. It is a simple, well controlled process that generates high yield, operates at low temperature ranging between (60-100)°C. It produces ZnO nanorods that have excellent morphology with well-defined structures.
14. How can the length be determined for gold nanorods synthesized by the electrochemical process?
a) Catalytic activity of acids
b) Amount of electrolyte
c) Stabilizing activity of CTAB
d) Concentration of silver ions
View Answer
Explanation: The length of gold nanorods can be determined by the presence of the silver plate in the solution. The silver present reacts with the ions of gold that are formed by the dissolution of the anode. The dissolved silver and the concentration of gold ions in the solution helps to determine the length of these nanorods formed.
15. Pick out the odd one from the following.
a) Lysergic acid
b) Polyethylene glycol
c) Ascorbic acid
d) Cetyltrimethylammonium bromide
View Answer
Explanation: Ascorbic acid, cetyltrimethylammonium bromide (CTAB) and polyethylene glycol are important compounds used in seed mediated growth process of synthesis of gold nanorods. Ascorbic acid acts as a reducing agent while CTAB is employed as a surfactant in the process. Polyethylene glycol is used to drive out the CTAB from the surface of the nanorods, while maintaining its stability, to prevent their toxicity.
More MCQs on Nanorods:
Sanfoundry Global Education & Learning Series – Nanotechnology.
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