Adsorption of pharmaceutical products from aqueous solutions on functionalized carbon nanotubes by conventional and green methods: A critical review

Removal of emerging contaminants from aqueous media is a research topic that has become increasingly relevant. These contaminants include pharmaceutical compounds which are frequently found in the environment and, even at low concentrations, they may cause a series of adverse effects in humans and animals. The effective removal of pharmaceutical compounds requires advanced treatments, such as adsorption. Carbon nanotubes (CNTs) have been highlighted as excellent nano-adsorbents for drug removal, while functionalization is often performed on carbon nanotubes to add certain properties to the material and improve its adsorptive capacity. There is a growing interest in performing green route synthesis and functionalization of CNTs, as this can significantly reduce the cost of the entire process. This review presents an overview of studies related to the removal of pharmaceutical compounds, focusing on adsorption systems using conventional and green carbon nanotubes published in between 2011 and May/2022. The adsorptive performance of nanotubes functionalized by green routes and by conventional methods was evaluated by the kinetic, equilibrium and thermodynamic results of recent works. The removal of pharmaceutical compounds using nanotubes functionalized by green routes proved to be comparable to the performance of CNTs obtained by conventional processes, confirming the great potential of green CNTs, since they have the advantages of being ecologically friendly and of potentially reducing the process costs. It was found that, in general, the processes of pharmaceuticals adsorption by carbon nanotubes (conventional or green) are exothermic, spontaneous, and have physisorption as their main mechanism. The Langmuir and PSO models best describe the isotherms and adsorption kinetics, respectively. Parameters such as temperature, pH, concentration, adsorbent dosage, and type of functionalization significantly influenced the uptake behavior and the contaminant removal efficiency. There was a lack of studies on adsorption of PHCs by nanotubes synthesized using green routes, as well as few studies on dynamic systems or focusing on the regeneration of CNTs. Therefore, future research may focus on in-depth investigations of the pharmaceuticals adsorption process using nanotubes obtained by green routes, further development of studies in dynamic systems, as well as effective techniques for the desorption/reuse of CNTs.

Automated summary

The removal of emerging contaminants from aqueous media is an important research topic, and carbon nanotubes are considered excellent nano-adsorbents for drug removal. Green synthesis and functionalization of carbon nanotubes can reduce the cost of the process. Both conventional and green carbon nanotubes have shown effective removal of pharmaceutical compounds through exothermic and physisorption processes.