This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Meso Porous Materials”.
1. What are the interactions involved in the formation of M41S mesoporous materials?
a) Polymers and positively charged silica species
b) Positive surfactants and negative inorganic salts
c) Neutral interaction (S0I0)
d) Silica or alumina interconnected tetrahedrally by oxygen atoms
View Answer
Explanation: The formation of M41S type of mesoporous materials involves the interactions between positively charged species of surfactants (S+) in the micelles and negatively charged inorganic silica (I–) species that forms electrostatic interactions (S+I–). There are few other mechanisms suggested for the formation of mesoporous materials, which are called liquid crystal templating (LCT), self – assembly and cooperative self-assembly.
2. Which of these effects is not observed in mesoporous materials that have undergone calcinations?
a) Accessible channels of mesoporous materials
b) Collapse in silica lamellae
c) Condensation of silica structure
d) Disconnected mesoporous channels in SBA-15
View Answer
Explanation: Calcination of mesoporous materials have made the channels accessible in these substancesby removing the surfactants. It further promotes additional condensation of the silica structure. Calcined SBA – 15 has micropores that connect mesoporous channels due to the PEO chains of Pluronic – 123 within the silica walls. In case of MCM-50, calcination of the surfactant results in the collapse of silica lamellae.
3. Select the correct order of steps followed in the synthesis of mesoporous materials of type M41S.
a) Increase in temperature ➔ Hydrolysis and pre – condensation ➔ Direct condensation of silica ➔ Rigorous stirring of solution ➔ Dissolution of organic surfactant in the solvent ➔ Addition of silica source
b) Rigorous stirring of solution ➔ Dissolution of organic surfactant in the solvent ➔ Increase in temperature ➔ Addition of silica source ➔ Direct condensation of silica ➔ Hydrolysis and pre – condensation
c) Dissolution of organic surfactant in the solvent ➔ Addition of silica source ➔ Rigorous stirring of solution ➔ Hydrolysis and pre – condensation ➔ Increase in temperature ➔ Direct condensation of silica
d) Addition of silica source ➔ Direct condensation of silica ➔ Hydrolysis and pre – condensation ➔ Rigorous stirring of solution ➔ Dissolution of organic surfactant in the solvent ➔ Increase in temperature
View Answer
Explanation: The synthesis of M41S type of mesoporous materials begins with the dissolution of organic surfactant in the solvent. This is followed by the addition of a silica source. The mixture is stirred enough and the temperature is increased. The rise in temperature is carried out from a certain point where hydrolysis and pre-condensation can occur. This results in a hydrothermal step inside the autoclaves that initiate the direct condensation of silica.
4. Which material can have both mesoporosity and microporosity?
a) Tantalum oxide
b) Activated carbon
c) SBA – 16
d) Polypropylene oxide
View Answer
Explanation: Activated carbon is a very popular mesoporous material due to its multifarious applications. It is a carbon framework processed to have small, low volume pores that increase its surface area. It exhibits both microporosity and mesoporosity depending on the conditions under which it was synthesized.
5. Find out the correct pair of mesoporous materials majorly used for the treatment of wastewater.
a) MCM-41 and SBA-1
b) SBA-15 and MSU-X
c) MCM-48 and SBA-16
d) KIT–6 and MCM-50
View Answer
Explanation: Mesoporous materials of the type MCM-41, SBA-15 and SBA-1 are mostly used for wastewater treatment. MCM-41 and magnetic SBA-15 when functionalized with thiol groups can be used effectively in removing Hg2+ from wastewater (about 97%). SBA-1 and MCM-41 when modified with amino groups prove to be efficient in removing arsenate and chromate ions. MCM-41 can also eliminate Rhodamine B and Yellow Dye from water.
6. What makes mesoporous materials preferable to zeolites when used as catalysts in reactions involving large molecules?
a) Hydrothermal stability
b) Larger pore size
c) Moderate acidity
d) Greater surface area
View Answer
Explanation: The moderate acidity of mesoporous materials offers advantages over zeolites when used as catalysts in reactions involving large molecules. E.g.: – Pyrolysis of biomass. These materials possess high surface area which facilitates their usage as catalyst supports of metals (such as Au, Pd, Au-Pd) for the oxidation of volatile organic compounds.
7. Mesoporous materials act as solid ligands to remove actinides from liquid effluents.
a) True
b) False
View Answer
Explanation: Mesoporous materials such as MCM-41 functionalized with thiol groups are effective in removing radioactive elements such as 137Cs, 90Sr and 60Co. They can also eliminate actinides from liquid effluents. These materials also serve the purpose of detecting any radiation defects.
8. Choose the incorrect statement from the following.
a) Synthetic methods easily allow for the control of the quality of secondary level porosity
b) Lattice units are limited in crystalline inorganic materials
c) Mesoporous materials can be used in catalysis, sorption, gas sensing and ion exchange
d) Stöber process can be used to form mesoporous materials
View Answer
Explanation: Crystalline inorganic mesoporous materials have limited number of lattice units and this significantly changes the solid-state chemistry. Stöber process can be used to produce mesoporous substances. The synthetic methods initially used for mesoporous material production couldn’t control the quality of the secondary level of porosity generated. The mesoporous materials have varied applications including catalysis, ion exchange, optics, sorption etc.
9. What is the use of mesoporous materials in the medical field?
a) Tissue engineering
b) Controlled drug delivery
c) Artificial kidneys
d) Dressing component
View Answer
Explanation: Mesoporous materials are excellent substances for use in medical field. They can be used for enzyme immobilization, DNA adsorption, gene transfer and controlled drug delivery. SBA-15 functionalized with amino groups are used for controlled release of an anticancer drug, Gemcitabine. MCM-41 can be used for delivering drugs such as Ibuprofen and Captopril.
10. What type of interactions are found in mesoporous materials of type SBA-15?
a) Positive surfactants and negative inorganic salts
b) Neutral interaction (S0I0)
c) Polymers and positively charged silica species
d) Silica or alumina interconnected tetrahedrally by oxygen atoms
View Answer
Explanation: The mesoporous materials of type SBA-15 includes an interaction which is the result of an indirect reaction between the polymer and the positively charged silica species in an acidic medium [(S0H+)(X–I+)]. X– represents the counter ion which is in strongly acidic conditions.
11. Pick out the odd one from the following.
a) MCM-41
b) Titanium oxide
c) Activated carbon
d) Zeolites
View Answer
Explanation: Mesoporous materials include some kind of silica and alumina that have similarly sized pores. MCM-41 (hexagonal) is a mesoporous material made from silica. Some mesoporous materials include oxides of niobium, tantalum, titanium, zirconium, cerium and tin. Mesoporous carbon and activated carbon are among other well-known mesoporous materials.
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