A Comprehensive Review on Adsorption, Photocatalytic and Chemical Degradation of Dyes and Nitro-Compounds over Different Kinds of Porous and Composite Materials

Abstract

Dye and nitro-compound pollution has become a significant issue worldwide. The adsorption and degradation of dyes and nitro-compounds have recently become important areas of study. Different methods, such as precipitation, flocculation, ultra-filtration, ion exchange, coagulation, and electro-catalytic degradation have been adopted for the adsorption and degradation of these organic pollutants. Apart from these methods, adsorption, photocatalytic degradation, and chemical degradation are considered the most economical and efficient to control water pollution from dyes and nitro-compounds. In this review, different kinds of dyes and nitro-compounds, and their adverse effects on aquatic organisms and human beings, were summarized in depth. This review article covers the comprehensive analysis of the adsorption of dyes over different materials (porous polymer, carbon-based materials, clay-based materials, layer double hydroxides, metal-organic frameworks, and biosorbents). The mechanism and kinetics of dye adsorption were the central parts of this study. The structures of all the materials mentioned above were discussed, along with their main functional groups responsible for dye adsorption. Removal and degradation methods, such as adsorption, photocatalytic degradation, and chemical degradation of dyes and nitro-compounds were also the main aim of this review article, as well as the materials used for such degradation. The mechanisms of photocatalytic and chemical degradation were also explained comprehensively. Different factors responsible for adsorption, photocatalytic degradation, and chemical degradation were also highlighted. Advantages and disadvantages, as well as economic cost, were also discussed briefly. This review will be beneficial for the reader as it covers all aspects of dye adsorption and the degradation of dyes and nitro-compounds. Future aspects and shortcomings were also part of this review article. There are several review articles on all these topics, but such a comprehensive study has not been performed so far in the literature.

Keywords: biosorbents; carbon materials; composite; layered double hydroxides; metal–organic frameworks; organic pollutants; polymeric materials; porosity.

Figure 1

Graphical representation of adsorption, photocatalytic degradation, and chemical degradation of dyes and nitro-compounds using different materials.

Figure 2

Dye adsorption over different kinds of designed materials.

Figure 3

Magnetic hyperbranched polymer for dye adsorption via different interactions. Reprinted from ref. [2] with permission.

Figure 4

Adsorption of dyes over carbon-based materials via different interactions. Reprinted from ref. [34] with permission.

Figure 5

Proposed mechanism of dye adsorption over carbon-coated clay. Reprinted from ref. [87] with permission.

Figure 6

Schematic diagram of possible interactions in LDH with dye molecules. Reprinted from ref. [90] with permission.

Figure 7

Various interactions of dye molecules during adsorption over MOFs. Reprinted from ref. [108] with permission.

Figure 8

Proposed adsorption mechanism of crystal violet on lemongrass leaf fibers incorporated with cellulose acetate. Reprinted from ref. [130] with permission.

Figure 9

Dye photo-degradation through sensitization route (A); mechanism of photocatalytic treatment of pollutants (B) (Dye* for unstable dye).

Figure 10

The energies of the valence band levels and conduction band level energies of transition-metal-doped TiO₂, pure TiO₂, and non-metal-doped TiO₂.

Figure 11

A sketch of the radical generation through semiconductor-doped GO or rGO binary composite, showing the valance band and conduction band.

Figure 12

The mechanism for photocatalytic degradation of RhB via MOFs. Reprinted from ref. [178] with permission.

Figure 13

Schematic representation of photocatalytic degradation of dyes over LDH-based composite materials.

Figure 14

Molecular structure of several azo dyes (ortho-methyl red, meta-methyl red, para-methyl red, methyl orange, methyl orange I, methyl orange II, alizarin yellow R, and alizarin yellow GG). The gray, red, blue, yellow, and white balls represent carbon, oxygen, nitrogen, sulfur, and hydrogen atoms, respectively. Reprinted from ref. [205] with permission.

Figure 15

The reduction mechanism of p-Nitrophenol using a reducing agent and catalyst. Reprinted from ref. [212] with permission.