Carbon Nanotubes in Water Purification

 

Water pollutants have huge impacts on the entire living systems including terrestrial, aquatic, and aerial flora and fauna. In addition to conventional priority, and newly emerging micro/nano-pollutants, increasing global warming and consequent climate changes are posing major threats to the fresh water availability. Global warming and climate change are constantly increasing the salinity level of both land and sea water, dwindling the availability of existing fresh water for household, agriculture and industry. This has made it urgent to invent an appropriate water treatment technology that not only removes macro-, micro- and nano-pollutants but also desalinates water to a significant extent. Tip-functionalized nonpolar interior home of carbon nanotubes (CNTs) provides strong invitation to polar water molecules and rejects salts and pollutants. Low energy consumption, antifouling and self-cleaning functions have made CNT membranes extraordinary over the conventional ones. We comprehensively reviewed here molecular modeling and experimental aspects of CNT-membrane fabrication and functionalization for the desalination of both sea and brackish water.

Carbon nanotubes (CNTs) have emerged as the foremost nanomaterial (NM) for water       purification. It can remove almost all three types of pollutants, i.e. organic, inorganic and biological pollutants. This is because of their large surface area, high aspect ratio and greater chemical reactivity along with lower cost and energy. An ample literature study suggests that the frivolous use of CNTs as adsorbents, composites or catalysts, sensors, membranes and engineered NMs is the main reason that 6.0 and 5.5% of CNTs leak from waste water treatment plants (WWTPs) and waste incineration plants, respectively. Alternatively, CNTs could be lost to soil (14.8%) and air (1.4%) from the disposal phase, which might ultimately escape to fresh water bodies. 

Carbon nanotubes (CNTs) are fibrous materials formed from honeycomb crystal lattice layers of graphite wrapped into a tube shape either as a single layer or as multiple layers. Precise structural arrangement and order give them a variety of beneficial properties such as ultra-lightweight, high surface tension and high aspect ratio. Single-wall carbon nanotubes (SWCNTs) consist of the cylindrical shape of a single shell of graphene whereas multi-walled carbon nanotubes (MWCNTs) are composed of multiple layers of graphene sheets . Both types of CNTs have been used for direct water desalination and indirect removal of pollutants that complicate the desalination process.

It is important to understand that not all CNTs are toxic in which altering shape, size and composition would modify the nanotoxicity of CNTs. CNT with the length of long fibres (> 20 μm) which exceeds the macrophage length cannot be engulfed by macrophage leading to inefficient phagocytosis, and this prevents their clearance from the system, causing harmful effects. Generally, a number of studies have indicated that longer length and larger diameter possess greater toxicity than smaller ones. Furthermore, the length and diameter of CNTs which can be controlled during CNT synthesis are another major factors that determine the life cycle and toxicity.

AKNOWLEDGEMENT : This content is taken from the research paper of Carbon nanotube membranes for water purification: A bright future in water desalination

 => https://www.sciencedirect.com/science/article/abs/pii/S0011916413006127   

 and also from the research paper of The Toxic Truth About Carbon Nanotubes in Water Purification: a Perspective View

=> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6005998/#:~:text=Carbon%20nanotubes%20(CNTs)%20have%20emerged,and%20biological%20pollutants%20%5B2%5D.