Review on heavy metal adsorption processes by carbon nanotubes

The most important and indispensable substance for life on earth is water. Regrettably, the growths of civilization, population, and industrssialization have led to a steady deterioration in the quality of available water resources. Heavy metals are a particular problem because of their high toxicity. This work highlights up-to-date methods for the removal of heavy metals from water using the technique of adsorption. After a comprehensive review of the range of materials used as adsorbents to remove heavy metals, the paper focuses on one particular technique, involving carbon nanotubes (CNTs). Tests have confirmed that CNTs are highly efficient, but have also revealed some drawbacks. Further adjustments and refinements are therefore required to improve their ability to remove heavy metals. This study shows that using deep eutectic solvents (DESs) as a functionalization agent to replace ionic liquids (ILs) has a number of advantages, including lower costs, easier availability of materials and environmentally friendliness. In sum, it suggests that the most efficient adsorption process is to use functionalized CNTs with DESs as an adsorbent. The critical analysis and conclusions emerging from this study should be of benefit to engineers, environmental scientists and chemists interested in the use of carbon nanotubes for use in environmental remediation. Published by Elsevier Ltd.