Nanostructured Materials for Water Purification: Adsorption of Heavy Metal Ions and Organic Dyes

Abstract

Chemical water pollution poses a threat to human beings and ecological systems. The purification of water to remove toxic organic and inorganic pollutants is essential for a safe society and a clean environment. Adsorption-based water treatment is considered one of the most effective and economic technologies designed to remove toxic substances. In this article, we review the recent progress in the field of nanostructured materials used for water purification, particularly those used for the adsorption of heavy metal ions and organic dyes. This review includes a range of nanostructured materials such as metal-based nanoparticles, polymer-based nanomaterials, carbon nanomaterials, bio-mass materials, and other types of nanostructured materials. Finally, the current challenges in the fields of adsorption of toxic materials using nanostructured materials are briefly discussed.

Keywords: heavy metal adsorption; nanostructured materials; organic dye adsorption; wastewater treatment.

Figure 1

Various water pollutants and nanostructured materials used for the removal of pollutants.

Figure 2

(Left) SEM image of hierarchical structured IO@CaCO₃ adsorbent consisting of magnetic iron oxide nanoneedles. (Right) As(V), Cr(VI) and Pb(II) heavy metal ion removal efficiencies of IO@CaCO₃ adsorbents. Reproduced with permission from [84]. Copyright 2017 Elsevier.

Figure 3

(Left) FE-SEM images of samples MgO-GO. (Right) Schematic illustration of the adsorption mechanism between MgO-GO composite and Congo red, which involves electrostatic and π–π interactions. Reproduced with permission from [90]. Copyright 2018 Elsevier.

Figure 4

(Left) Effect of pH on removal of malachite green dye using rGO as an adsorbent. (Right) High-resolution TEM images of rGO demonstrating the holes area (encircled by red color), defect sites (indicated by white arrows), and a schematic illustration of rGO lamella consisting of holes and residual oxygen functionalities. Reproduced with permission from [131]. Copyright 2017 Elsevier.

Figure 5

Schematic illustration of the process for fabricating the 3D graphene-CNTs hybrid structures. Reproduced with permission from [147]. Copyright 2015 Royal Society of Chemistry.

Figure 6

(Left) (a) Synthetic scheme of a 3D GO sponge. (b) Flexibility test of a GO sponge. (c) Low-magnification of SEM image for the GO sponge surface and (d) high-magnification of SEM image for the inner part of the 3D GO sponge. (Right) Chemical structures of methylene blue, methyl violet, and GO. Digital images of the original MB dye solution, the pale color solution with precipitated MB adsorbed GO sponges. Reproduced with permission from [159]. Copyright 2012 American Chemical Society.

Figure 7

Hierarchical structures of cellulose, chitin, silk fibroin, and collagen in wood, shrimp shell, silkworm cocoon, and bovine tendon. Reproduced with permission from [163]. Copyright 2021 John Wiley and Sons.

Figure 8

Schematic illustration for the adsorption of direct red-80 and methylene blue by the prepared nanocomposite bead, the digital image of the nanocomposite bead (Gel-CNT-MNPs) immersed in the dyes solutions in the presence of magnet. Reproduced from [193] with permission. Copyright 2017 Elsevier.

Figure 9

(Left) Schematic illustration for the fabrication of melamine formaldehyde (MF) sponge composites. The PAM and PAA brushes were grafted by the “grafting-from” method, and PEI was grafted by the “grafting-to” method. (Right) Image of a glass of water containing a low concentration of each heavy metal ion (Cu²⁺: 0.368 mg/L or Pb²⁺: 0.250 mg/L) after submerging a PEI-coated sponge (upper image). Images of various polymer brush-grafted sponge. Reproduced from [222] with permission. Copyright 2016 Elsevier.