g-C3N4 Based Photocatalyst for the Efficient Photodegradation of Toxic Methyl Orange Dye: Recent Modifications and Future Perspectives

Abstract

Industrial effluents containing dyes are the dominant pollutants, making the drinking water unfit. Among the dyes, methylene orange (MO) dye is mutagenic, carcinogenic and toxic to aquatic organisms. Therefore, its removal from water bodies through effective and economical approach is gaining increased attention in the last decades. Photocatalytic degradation has the ability to convert economically complex dye molecules into non-toxic and smaller species via redox reactions, by using photocatalysts. g-C₃N₄ is a metal-free n-type semiconductor, typical nonmetallic and non-toxici polymeric photocatalyst. It widely used in photocatalytic materials, due to its easy and simple synthesis, fascinating electronic band structure, high stability and abundant availability. As a photocatalyst, its major drawbacks are its limited efficiency in separating photo-excited electron-hole pairs, high separated charge recombination, low specific surface area, and low absorption coefficient. In this review, we report the recent modification strategies adopted for g-C₃N₄ for the efficient photodegradation of MO dye. The different modification approaches, such as nanocomposites and heterojunctions, as well as doping and defect introductions, are briefly discussed. The mechanism of the photodegradation of MO dye by g-C₃N₄ and future perspectives are discussed. This review paper will predict strategies for the fabrication of an efficient g-C₃N₄-based photocatalyst for the photodegradation of MO dye.

Keywords: g-C3N4; methyl orange; modifications; photocatalyst; photodegradation.

Figure 1

(a) Chemical structure of Methyl orange; (b) the optimized MO molecular structure created using Gaussian 03 software package on the basis of the HF/6-31G method. Reprinted/adapted with permission from [19], 2023, Elsevier (License Number 5507170462000).

Figure 2

(a) Triazine and (b) tri-striazine (heptazine) structures of g-C₃N₄ (blue, gray and white balls are nitrogen, carbon and hydrogen, respectively) [60].

Figure 3

Annual article frequency published extracted from the Scopus database on 13 March 2023 (Searched with the keyword ‘g-C₃N₄ for methyl orange degradation’).

Figure 4

The possible proposed photocatalytic mechanism for MO dye degradation (path 1), showing the BiOI/AgI/g−C₃N₄ composites’ irradiation under visible−light. Reprinted/adapted with permission from [115], 2023, Springer Nature (License Number 5507180161444).

Figure 5

(a) PL spectra, (b) EIS Nyquist spectra, and (c) transient photocurrent response of BCN, SCN, and F-SCN. Reprinted/adapted with permission from [118], 2023, Elsevier (License Number 5507180566714).

Figure 6

Schematic diagram for the formation of p-C₃N₄ [129].