Thin-film composite membranes (TFC or TFM) are

semipermeable membrane Semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecul ...

s manufactured principally for use in

water purification Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...

water desalination Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance, as in soil desalination, which is an issue for agriculture. Saltw ...

systems. They also have use in chemical applications such as batteries and

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...

s. A TFC membrane can be considered as a

molecular sieve A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...

constructed in the form of a film from two or more layered materials. TFC membranes are commonly classified as

nanofiltration Nanofiltration is a membrane filtration process used most often to soften and disinfect water. Overview Nanofiltration is a Membrane technology, membrane filtration-based method that uses nanometer sized pores through which particles smaller t ...

(NF) and

reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...

(RO) membranes. Both types are typically made out of a thin

polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made through ...

layer (<200 nm) deposited on top of a

polyethersulfone Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl- SO2-aryl subunit. Due to the high cost of raw material ...

polysulfone Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl- SO2-aryl subunit. Due to the high cost of raw material ...

porous layer (about 50 microns) on top of a

non-woven Nonwoven fabric is a fabric-like material made from staple fibre (short) and long fibres (continuous long), bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing industry to denote fabri ...

fabric support sheet. The three layer configuration gives the desired properties of high rejection of undesired materials (like salts), high filtration rate, and good mechanical strength. The polyamide top layer is responsible for the high rejection and is chosen primarily for its permeability to water and relative impermeability to various dissolved impurities including salt ions and other small, unfilterable

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

History

The first viable reverse osmosis membrane was made from cellulose acetate as an integrally skinned asymmetric semi-permeable membrane. This membrane was made by Loeb and Sourirajan at

UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California St ...

in 1959 and patented in 1960. In 1972, John Cadotte of North Star Technologies (later FilmTec Corporation) developed the first interfacial polyamide (IP) thin-film-composite (TFC) membrane. The current generation of reverse osmosis (RO) membrane materials are based on a composite material patented by FilmTec Corporation in 1970 (now part of

DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...

). Today, most such membranes for reverse osmosis and nanofiltration use a Polyamide active layer.

Structure and materials

As is suggested by the name, TFC membranes are composed of multiple layers. Membranes designed for desalination use an active thin-film layer of

layered with

as a porous support layer. Other materials, usually

zeolites Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These pos ...

, are also used in the manufacture of TFC membranes.

Applications

Thin film composite membranes are used in * Water purification; * as a chemical reaction

buffer Buffer may refer to: Science * Buffer gas, an inert or nonflammable gas * Buffer solution, a solution used to prevent changes in pH * Buffering agent, the weak acid or base in a buffer solution * Lysis buffer, in cell biology * Metal ion buffer * ...

(batteries and fuel cells); * in industrial gas separations.

Limitations

Thin film composites membranes typically suffer from compaction effects under pressure. As the water pressure increases, the polymers are slightly reorganized into a tighter fitting structure that results in a lower porosity, ultimately limiting the efficiency of the system designed to use them. In general, the higher the pressure, the greater the compaction. Surface fouling: Colloidal particulates, bacteria infestation (biofouling). Chemical decomposition and oxidation.

Performance

A filtration membrane's performance is rated by selectivity, chemical resistance, operational pressure differential and the pure water flow rate per unit area. Due to the importance of throughput, a membrane is manufactured as thinly as possible. These thin layers introduce defects that may affect selectivity, so system design usually trades off the desired throughput against both selectivity and operational pressure. In applications other than filtration, parameters such as mechanical strength, temperature stability, and electrical conductivity may dominate.

Active research areas

Nano-composite membranes (TFN). Key points: multiple layers, multiple materials. Mitigation of membrane fouling New materials, synthetic zeolites, etc. to obtain higher performance. NanoH2O Inc. commercialized a membrane in which zeolite nanoparticles were synthesized and embedded within an RO membrane to form a thin-film nanocomposite, or TFN, which has proven to be more than 50-100% more permeable compared to conventional RO membranes while maintaining the same level of salt rejection. Seah MQ, Lau WJ, Goh PS, Tseng HH, Wahab RA, Ismail AF. “Progress of Interfacial Polymerization Techniques for Polyamide Thin Film (Nano)Composite Membrane Fabrication: A Comprehensive Review.” Polymers (Basel). 2020 Nov 27;12(12):2817. doi: 10.3390/polym12122817. PMID: 33261079; PMCID: PMC7760071. Fuel-cells. Batteries.

References

{{reflist Filters Membrane technology Water technology