technology plays a vital role in waste-water treatment and air purification. One class of filtration techniques is based on the use of membranes with suitable hole sizes, whereby the liquid is pressed through the membrane. Nanoporous membranes are suitable for a mechanical filtration with extremely small pores smaller than 10 nm (“nanofiltration”) and may be composed of nanotubes. Nanofiltration is mainly used for the removal of ions or the separation of different fluids. On a larger scale, the membrane filtration technique is named ultrafiltration, which works down to between 10 and 100 nm. One important field of application for ultrafiltration is for medical purposes as can be found in renal dialysis. Magnetic nanoparticles offer an effective and reliable method to remove heavy metal contaminants from waste water by making use of magnetic separation techniques. Using nanoscale particles increases the efficiency to absorb the contaminants and is comparatively inexpensive compared to traditional precipitation and filtration methods. Treatment and remediation techniques also can be greatly improved through nanotechnology. The potential exists to develop inexpensive remediation and treatment technologies that enable the rapid and effective cleanup of recalcitrant compounds, especially those located in inaccessible areas to remove toxic contaminants from the environment. Researchers have developed a coating process to make a sponge-like silica to latch onto toxic metals in water. Self-Assembled Monolayers on Mesoporous supports easily capture such metals as lead and mercury, which are then recovered for reuse or contained in-place forever.