This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nanoclusters”.
1. Choose the incorrect statement from the following.
a) Glutathione is a great stabilizer for the production of gold nanoclusters
b) Luminescence efficiency of nanoclusters is independent of thiol-to-metal molar ratio
c) THPC is a mild reductant used for gold nanoclusters synthesis
d) Thiols can etch larger nanoparticles to form nanoclusters
View Answer
Explanation: Thiols such as tiopronin, thiolate α – cyclodextrin etc. are very common stabilizers used for the production of nanoclusters. Glutathione is an excellent stabilizer for synthesizing gold nanoclusters. Mild reductant tetrakis (hydroxymethyl) phosphonium (THPC) is used to produce gold nanoclusters. Size and the luminescence efficiency of the nanoclusters depend upon the thiol to metal molar ratio. Thiols used for the production of nanoclusters, etch out larger nanoparticles that are stabilized by other capping agents.
2. Select the sequential order of steps occurring in the fabrication of nanoclusters using liquid metal ions.
a) Potential difference is applied ➔ Emission of metal droplets as spray ➔ Evaporative cooling ➔ Fission of smaller clusters
b) Evaporative cooling ➔ Fission of smaller clusters ➔ Emission of metal droplets as spray ➔ Potential difference is applied
c) Emission of metal droplets as spray ➔ Potential difference is applied ➔ Fission of smaller clusters ➔ Evaporative cooling
d) Fission of smaller clusters ➔ Potential difference is applied ➔ Evaporative cooling ➔ Emission of metal droplets as spray
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Explanation: In this method a needle is wetted with the metal under investigation. It is heated above melting point and applied with a potential difference. This causes the emission of small droplets from the tip in the form of a spray. These droplets undergo evaporative cooling and fission to give rise to the desired nanoclusters.
3. Which of the following method is applied for producing large clusters of nanoparticles?
a) Ion Sputtering
b) Liquid – metal ion
c) Gas Aggregation
d) Seeded supersonic nozzle
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Explanation: Gas Aggregation method can be applied for producing large clusters of nanoparticles. In this process the metals are vaporized and mixed with cold noble gas. This results in the supersaturation of the vapour. Moreover, owing to the lower temperature of the gas mixture, clusters form by successive single atom addition.
4. Which of following is not an advantage of the photoreduction method used for nanocluster formation?
a) Faster Synthesis
b) Absence of impurities
c) Controlled reduction
d) Non-zero valent state
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Explanation: Photoreduction is one of the reduction processes used for nanocluster formation. It uses ultraviolet, visible or infrared rays to bring about the reduction. This method has many advantages such as fast synthesis process, absence of impurities and controlled reduction of the metals.
5. How can nanoclusters of low boiling point metals be created?
a) Using pulsed are reactor
b) Using seeded supersonic nozzle
c) Using lasor vaporization
d) Using ultrasonic nozzle
View Answer
Explanation: Nanoclusters can be synthesized using a number of different methods. However, in order to produce metal clusters having low boiling point, seeded supersonic nozzles are mostly used.
6. Why does the fluorescence property of nanoclusters formed using dendrimers change?
a) Owing to surface modification
b) Owing to maximum emission at different wavelengths
c) Owing to absence of PAMAM
d) Owing to narrow visible light spectrum
View Answer
Explanation: The fluorescence properties of the nanoclusters depend strongly on the types of the dendrimers used as the template for the synthesis. The properties tend to change if surface modifications are brought about by the capping agents. For instance, gold nanoclusters embedded in PAMAM, emitting blue colour can be tuned to emit ultraviolet rays.
7. Why is stabilization necessary for the production of metal nanoclusters?
a) To reduce to zero valent state
b) To allow greater interaction between themselves
c) To prevent aggregation of clusters
d) To form intense continuous beam of single ionized cluster of metals
View Answer
Explanation: Metallic nanoclusters can be synthesized in aqueous medium following two steps. First the reduction of metal ions to zero-valent state. Second, the stabilization of the nanoclusters. Stabilization of the clusters becomes important since it prevents the interaction and aggregation of the metal particles to form larger clusters.
8. Identify the method that can produce clusters of various size and polarity.
a) Laser vaporization
b) Ion Sputtering
c) Gas Aggregation
d) Liquid metal ion
View Answer
Explanation: Laser vaporization method is often used to synthesize nanoclusters of various size and polarity. Pulse laser is used to vaporize the metal and this vapour is cooled by mixing it with cold helium gas. This results in cluster formation.
9. Which compound can be added to form red-emitting gold nanoclusters?
a) 3 – mercaptopropionic acid
b) Acetylsalicylic acid
c) Mercaptoundecanoic acid
d) Reduced lipoic acid
View Answer
Explanation: Fluorescence properties of nanoclusters depend on the types of dendrimers used as template for the synthesis. Freshly prepared reduced lipolic acid (DHLA) when added to gold nanoclusters, form red-emitting fluorophores.
10. Choose the correct order of procedure applied in producing nanoclusters using the seeded supersonic nozzle.
a) Mixing vapor with inert gas ➔ Vaporization of metal ➔ Adiabatic cooling of vapor ➔ Production of supersonic molecular beam
b) Adiabatic cooling of vapor ➔ Mixing vapor with inert gas ➔ Production of supersonic molecular beam ➔ Vaporization of metal
c) Production of supersonic molecular beam ➔ Vaporization of metal ➔ Adiabatic cooling of vapor ➔ Mixing vapor with inert gas
d) Vaporization of metal ➔ Mixing vapor with inert gas ➔ Production of supersonic molecular beam ➔ Adiabatic cooling of vapor
View Answer
Explanation: Seeded supersonic nozzles are applied to produce metallic nano-clusters. The method begins with the vaporization of metal in a hot oven followed by its mixing with inert carrier gas. It is then introduced into a vacuum chamber through a small hole, forming a supersonic molecular beam. The mixture expands into the vacuum adiabatically and hence cools the vapour. These condensed metal vapours become supersaturated and aggregate in the cluster form.
More MCQs on Nanoclusters:
Sanfoundry Global Education & Learning Series – Nanotechnology.
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