nanofilters

Nanofilters are filtration membranes or devices that use nanoscale pore structures or nanostructured materials to separate components in fluids. They operate by selective passage based on size, and sometimes charge, allowing water and small neutral solutes to pass while retaining larger solutes, ions, or molecules. This makes them useful for purifying water and concentrating or removing specific solutes in liquids.

Pore sizes in nanofiltration are typically around 1 nanometer, with a molecular weight cutoff in the range of a few hundred to a few thousand daltons. Nanofiltration sits between ultrafiltration and reverse osmosis in terms of ion rejection and required pressure. It tends to reject multivalent ions more effectively than monovalent ions and can remove certain organic molecules and colorants, while permitting many monovalent salts to pass under operating conditions.

Most nanofiltration membranes are polymeric, such as thin-film composite polyamide or other polymers, though ceramic versions also exist. Filtration occurs under pressure, with energy needs generally lower than those of reverse osmosis for similar throughput. Practical performance is influenced by fouling, which can be caused by organic matter, scaling, or biofilms; pre-treatment and cleaning protocols are important for sustained operation.

Common applications include drinking and municipal water treatment, brackish water desalination, dairy and food processing (such as demineralization of sugar solutions and whey processing), and pharmaceutical purification. In addition to traditional membranes, ongoing research explores fouling-resistant coatings, advanced nanocomposite or graphene-based membranes, and tailored nanofilter configurations for analytical and industrial uses.