Functionalized Halloysite Nanotubes for Enhanced Removal of Hg²⁺ Ions From Aqueous Solutions

Abstract

Water is essential for humans, animals, and plants; pollutants, usually derived from anthropogenic activities, can have a serious effect on its quality. Heavy metals are significant pollutants and are often highly toxic to living organisms, even at very low concentrations. Among the numerous removal techniques proposed, adsorption onto suitable adsorbent materials is considered to be one of the most promising. The objective of the current study was to determine the effectiveness of halloysite nanotubes (HNT) functionalized with organic amino or thiol groups as adsorbent materials to decontaminate polluted waters, using the removal of Hg2+ ions, one of the most dangerous heavy metals, as the test case. The effects of pH, ionic strength (I), and temperature of the metal ion solution on the adsorption ability and affinity of both materials were evaluated. To this end, adsorption experiments were carried out with no ionic medium and in NaNO3 and NaCl at I = 0.1 mol L−1, in the pH range 3–5 and in the temperature range 283.15–313.15 K. Kinetic and thermodynamic aspects of adsorption were considered by measuring the metal ion concentrations in aqueous solution. Various equations were used to fit experimental data, and the results obtained were explained on the basis of both the adsorbent’s characterization and the Hg2+ speciation under the given experimental conditions. Thiol and amino groups enhanced the adsorption capability of halloysite for Hg2+ ions in the pH range 3–5. The pH, the ionic medium, and the ionic strength of aqueous solution all play an important role in the adsorption process. A physical adsorption mechanism enhanced by ion exchange is proposed for both functionalized materials.

Halloysite Nanotubes: Smart Nanomaterials in Catalysis

“…The modification of the inner and/or outer surfaces opens different strategies to introduce new properties on HNTs expanding their application fields. It has been indeed proposed the use of HNTs as fillers in polymeric matrices [9][10][11][12][13], flame retardants [14], nanoadsorbents for environmental remediation [15][16][17][18][19][20][21][22], and due to their biocompatibility, as drug carrier and delivery systems [23][24][25][26][27][28][29][30][31][32][33]. Furthermore, suitable modifications confer to HNTs additional properties such as luminescence [34] or fluorescence tracking ability [35], which of course allow us to utilize the obtained nanosystems for bioimaging.…”

Modification of halloysite nanotubes by hydroxyl terminated triazine‐based dendritic polymer for efficient adsorptive removal of Cd (II) from aqueous media

“…[34] According to the literature, using organosilanes for the HNTs modification has been proved to be an effective method of improving the surface characteristics to load adaptable guests. [35][36][37][38][39] The HNTs capability of selective surface alteration using covalent grafting amineterminated dendritic groups, for example, polymer to load or eliminate pollutants via host-guest structure has attracted considerable attention among various modification methods. [40][41][42][43] Generally, pristine HNTs can remove heavy metal ions from aqueous media through the mechanisms of site geometry, physical and/or chemisorption, and so on.…”