Membrane filters, also known as microporous filters, are thin, semi-permeable membranes that are used for filtering and purifying fluids or gases. They are made from a variety of materials such as cellulose, nitrocellulose, nylon, or PTFE (polytetrafluoroethylene).

The membrane filter's pore size can vary depending on the specific application, ranging from a few nanometers to several micrometers in diameter. This pore size can be tailored to filter out specific particles or molecules, such as bacteria, viruses, or large proteins.

Membrane filters work through a process called size exclusion, where particles that are larger than the pore size of the filter are physically blocked and cannot pass through, while smaller particles can pass through the filter. This allows for the separation and purification of a variety of materials, such as biological samples, chemicals, or industrial solutions.

There are several types of membrane filters, including:

Microfiltration: used for separating and purifying larger particles, such as bacteria or suspended solids.

Ultrafiltration: used for separating and purifying smaller particles, such as proteins or viruses.

Nanofiltration: used for separating and purifying very small particles, such as organic molecules or ions.

Reverse Osmosis: a type of nanofiltration that is used for purifying water by removing dissolved salts and other impurities.

Overall, membrane filters are widely used in various industries, including biotechnology, pharmaceuticals, food and beverage, water treatment, and environmental monitoring, for their ability to efficiently and selectively filter out particles and molecules from fluids or gases.