Remediation of phenol-contaminated water by pristine and functionalized SWCNTs: Ab initio van der Waals DFT investigation

Abstract

Despite known toxic properties of phenol and its derivatives, their man-caused release into nature continues. Their importance as building blocks in polymers, pesticides, pharmaceuticals and other industrial chemicals remains a barrier for reducing their introduction into ecosystems. Hence, a considerable effort has been devoted to these organic contaminates removal from water sources. In the present work, we have employed functionalized (5, 5) carbon nanotubes (f-CNTs) for adsorption and remidiation of phenol pollutant from water. Several binding sites (incloding hydroxyl and phenyl groups) were considered due to their ability in π-π stacking and H-bonding interactions with phenol. The adsorption modes and energies of both water and phenol to these sites are evaluated using a general dispersion-corrected density functional (DFT-D3) method. We showed that both water and phenol molecules are weakly bound (weak physisorption) to the outer surface of pristine CNT while they can be adsorbed stronger on the functionalized CNTs. It was found that phenol bound stronger to the CNT-OH than water molecule which was due to the existence of simultaneous π-π stacking and H-bonding in the system. Also, we have prepared a brief report about the solvent effect in the adsorption nature of the more stable systems.The results show that the absorption energy sequence for the absorbing/carbon nanotube complexes in the aqueous phase is similar to the calculated absorption energy for in the gas phase, but adsorption decreased in the aqueous phase. We have also provided a succinct report about the reactivity, energy gap and polarity of the considered systems for all systems. For comparison, we evaluated the adsorption behavior for zigzag OH-CNT (8, 0).The calculation reveal that difference of the binding energy of phenol and water molecules on a zigzag is alike to the armchair CNT system. The phenol adsorption properties onto CNT-OH system in periodic and cluster SWCNT have compared and we were found that the results predicted by the CNT saturated with hydrogen can be comparable to periodic SWCNT. Furthermore, our first-principles calculations demonstrated the importance of dispersion corrections based on weak intermolecular interactions in designing absorbents. Our study offers molecular level understanding of the interactions between water/phenol molecule and CNTs surface and may be informative for toxicity agent adsorption and remediation from environment.