Synthesis, Characterization, and Gas Permeation Properties

General Introduction
requisition. At present, a variety of novel membrane materials are employed for
specific functions including the separation of small molecules like gases and vapors as
well as relatively larger entities such as colloids and insoluble matter, the resolution of
optical isomers, ions, or biological matter, and in catalytic membrane reactors and
sensor systems, hence finding a multitude of potential applications in the domains of
biomaterial, chemical, medicinal, and catalysis sciences. 22
“Membrane” serves as an interphase between two adjacent phases acting as a
selective barrier, administering the transport of substances between two compartments
under the influence of the potential gradient in concentration or pressure, or the
electrical imbalance across the selective integument. 23
Regardless of the architectural diversities, the porous or non-porous nature and
the pore size of the membrane are of vital significance in determining the transport and
separation mechanisms. Therefore the membrane-based separation processes can be
broadly classified as strainer filtration, microfiltration, ultrafiltration, nanofiltration,
dialysis, reverse osmosis, pervaporation, and gas separation. Strainer filtration
involves membranes possessing the pore-size of ≥ 5 μm and is used for the separation
of large particulate matter in laboratories. The microfiltration (MF) and ultrafiltration
(UF) techniques rely on molecular sieving through the pores; the former makes use of
membranes of 0.1–5 μm pore-size to filter fine particles and bacteria from water while
the latter with the membrane pore-diameter of 2–50 nm is employed for concentration,
fractionation, or purification processes to separate water and microsolutes from
colloids. 24 The pore-size of nanofiltration (NF) membranes (≤ 2 nm) is somewhat
intermediate of those of the ultrafiltration and reverse osmosis membranes. On the
other hand, electrodialysis (ED), reverse osmosis (RO), and pervaporation (PV)
membranes make use of both the polymer segmental gaps (~ 0.3–0.5 nm) and the
micropores (≤ 1 nm). RO, employed for sea-water desalination for drinking and
process applications, and fine purification for medical and microelectronics
industries, 25 is based on the solution-diffusion model; ED utilizes ion exchange
membranes to effect separation and obeys the Donnan effect while PV follows the
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