Developments in the Application of Nanomaterials for Water Treatment and Their Impact on the Environment

Abstract

Nanotechnology is an uppermost priority area of research in several nations presently because of its enormous capability and financial impact. One of the most promising environmental utilizations of nanotechnology has been in water treatment and remediation where various nanomaterials can purify water by means of several mechanisms inclusive of the adsorption of dyes, heavy metals, and other pollutants, inactivation and removal of pathogens, and conversion of harmful materials into less harmful compounds. To achieve this, nanomaterials have been generated in several shapes, integrated to form different composites and functionalized with active components. Additionally, the nanomaterials have been added to membranes that can assist to improve the water treatment efficiency. In this paper, we have discussed the advantages of nanomaterials in applications such as adsorbents (removal of dyes, heavy metals, pharmaceuticals, and organic contaminants from water), membrane materials, catalytic utilization, and microbial decontamination. We discuss the different carbon-based nanomaterials (carbon nanotubes, graphene, graphene oxide, fullerenes, etc.), and metal and metal-oxide based nanomaterials (zinc-oxide, titanium dioxide, nano zerovalent iron, etc.) for the water treatment application. It can be noted that the nanomaterials have the ability for improving the environmental remediation system. The examination of different studies confirmed that out of the various nanomaterials, graphene and its derivatives (e.g., reduced graphene oxide, graphene oxide, graphene-based metals, and graphene-based metal oxides) with huge surface area and increased purity, outstanding environmental compatibility and selectivity, display high absorption capability as they trap electrons, avoiding their recombination. Additionally, we discussed the negative impacts of nanomaterials such as membrane damage and cell damage to the living beings in the aqueous environment. Acknowledgment of the possible benefits and inadvertent hazards of nanomaterials to the environment is important for pursuing their future advancement.

Keywords: adsorbents; environment; membranes; nanomaterials; toxicity; water pollution.

Figure 1

Different classification as well as the extensive range of applications of some of the nanomaterials.

Figure 2

Impact of nanomaterials on the water environment.

Figure 3

TEM images of magnetic-modified multiwalled carbon nanotubes (CNTs). Reproduced from Ref [61], with permission from Elsevier, 2011.

Figure 4

Schematic representation of the non-covalent interactions between graphene oxide, 1-OA, and malachite green (MG). Reproduced from [64], with permission from Elsevier, 2018.

Figure 5

The XRD pattern of the synthesized titanium dioxide nanoparticle. Reproduced from ref [58], with permission from Elsevier, 2009.

Figure 6

Chemical modifications of carbon nanotubes (CNTs). Reproduced from Reference [78], with permission from Elsevier, 2018.

Figure 7

Sulfonated multiwalled carbon nanotube (MWCNT) assisted thin-film nanocomposite (TFN) membrane. (a) Representation of the mechanism of membrane separation. (b) The separation efficiency of the 0.01% TFN membrane for various salts and dyes at 0.6 MPa and 25 °C. (c) Comparing the work results with other sulfonated TFC membranes or the CNT–polymer composite membranes. Reproduced from [109], with permission from Elsevier, 2017.

Figure 8

(a–c) Degradation of 5 diverse dyes (solo-chrome black (SB), thymol blue (TB), cresol red (CR), methyl blue (MB), and methyl orange (MO)) utilizing titanium dioxide (TiO₂), hafnium oxide (HfO₂)/TiO₂, and hydrogenated HfO₂ doped TiO₂ (H-HfO₂/TiO₂) at pH 7. (d–f) The degradation of MB dye at various pH employing the H-HfO₂/TiO₂. Reproduced from reference [120], with permission from Elsevier, 2018.

Figure 9

Diagrammatic portrayal of photocatalytic oxidation of the methylene blue (MB) dye at the aminosilicate sol–gel supported silver nanoparticles. Reproduced from reference [123], with permission from Elsevier, 2018.

Figure 10

Diagrammatic representation for the suggested mechanism of photocatalytic dye degradation by biogenic silver nanoparticles and correspondingly explaining the activation energy role. Reproduced from Reference [124], with permission from Elsevier, 2019.

Figure 11

Toxicity effects (oxidative stress and membrane damage) of GO on R. subcapitata green alga; evaluated by flow cytometer. Values are mean +SD (N = 3). * statistically significant difference from control (p < 0.05). Reproduced from reference [178], with permission from Elsevier, 2015.

Figure 12

Deformity of zebrafish embryos when exposed to graphene quantum dots of concentration 200 μg/mL, scale bar = 0.5 mm. (A) Standard larvae and (B–D) abnormal larvae. Deformities are specified by red arrows. BT, bent tail; BS, bent spine; VC, vitelline cyst; and PE, pericardial edema. Reproduced from reference [185], with permission from Elsevier, 2015.