Graphene, nanotubes and carbon nanostructures for water remediation and environmental applications
The diffusion in groundwater and surface water bodies of conventional and emerging organic contaminants (EOCs), such as dyes, pesticides, pharmaceutical, personal care products, induced a rapid decline of the quality of water. Conventional wastewater treatment plants (WWTP) are not able to remove completely these substances and need therefore to be upgraded with additional treatment steps. Among the techniques reported to achieve this goal, adsorption (usually on activated carbon) was found to be the most promising due to its low cost, operational simplicity, easy regeneration, sludge-free operation, and no involvement of toxic intermediate.
Carbon NanoStructures (CNS) include, among others, carbon nanotubes (CNT), in particular multi walled carbon nanotubes (MWCNT), and graphene-based materials (GBM) are promising adsorbents for pollutant removal from wastewater also due to their possible surface functionalization that, in principle, can increase the adsorption rate and provide regeneration. Nevertheless, literature works on adsorption of pollutants by means of CNTs and GBM are not that many, compared to other application fields, and they often highlight critical issues that have limited, so far, perspectives for a practical application.
Among the problems and open questions for the use of CNSs in water remediation, we focus on the following:
• actual effectiveness of pristine CNSs in general and effect of different structures on adsorption
• possible contribution of functionalization
• problems related to functionalization (solvents, residues, scalability)
• possible dispersion of CNSs in water
Objective of this research is to provide hints for the solution of, or at least to answer, the aforementioned issues. We focus on the study of the adsorption of pollutants and how it is affected by chemical modification of CNSs. From one side, our investigations will be not aiming to a direct short time application, but to the understanding of fundamental questions. On the other hand, we provide the bases for follow-up proposals aiming to the removal of pollutants through adsorption, and they will also allow to design future strategies for different applications, like photocatalytical transformation of pollutants into fuels and selective analytical methods for the detection of pollutants or biomarkers.
The team involves Prof. Ester Marotta, with expertise on the analysis of pollutants.
We synthesized and characterized through IR, TGA, TEM, XPS and DLS measurements a multi-walled carbon nanotube (MWCNT) derivative bearing benzenesulfonate groups (MWCNT-S). The obtained material demonstrated to have good dispersibility in water and better capability to adsorb methylene blue dye (MB) compared to the pristine MWCNT adsorbent. Adsorption kinetic studies showed a faster process with respect not only to that of the unfunctionalized MWCNT adsorbent but also to those of widely used activated carbons.
The adsorption capacity of MWCNT-S is more than doubled with respect to that of the insoluble pristine MWCNT adsorbent.
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he ability to regenerate the adsorbent through ionic exchange with NaCl was shown in a preliminary test, offering a sustainable and cost-effective solution for water treatment, allowing not only for the reuse of the adsorbent material but also for the recovery of the pollutant.