Visible-Light-Driven g-C₃N₄/TiO₂ Based Heterojunction Nanocomposites for Photocatalytic Degradation of Organic Dyes in Wastewater: A Review

Abstract

Water pollution by organic contaminants is one of the most severe issues confronting the world today as a result of the rapid increase of industrialization, urbanization, human population growth, and advances in agricultural technologies. Several attempts have been made to address global water pollution issues by utilizing conventional wastewater treatment technologies. However, conventional wastewater treatment methods have several limitations such as low efficiency, high operation costs, generation of secondary waste, require additional chemicals as oxidants and extra energy. Therefore, Heterogeneous photocatalysis has gained a lot of attention in the degradation of persistent organic pollutants because it combines high efficiency, environmental friendliness, cheap cost, and safety. Subsequently, the designing of novel nanocomposite photocatalysts with strong visible light-harvesting ability, efficient charge separation and transportation, and superb stability is imminently desired for wastewater treatment. Recently, the notion of combining g-C3N4 with TiO2 to design high photocatalytic performance heterojunction photoactive nanocomposites for organic pollutant degradation has received a lot of attention. Meanwhile, the construction of g-C3N4/TiO2-based heterojunction nanocomposites may enhance the ability of harvesting visible light, boost charge separation and transfer efficiency, and robust photocatalytic activity. Firstly, this review concisely explained the main sources of water pollution, as well as potential treatment approaches and the fundamental mechanism of heterogeneous photocatalysis. Subsequently, the details of properties, synthesis techniques, photoactivity modification strategies, and photocatalytic applications of g-C3N4, TiO2, and g-C3N4/TiO2 heterojunction photocatalysts are presented. Following that, the recent advances aimed at improving the photocatalytic performance of various types of visible-light-driven g-C3N4/TiO2 heterojunction photocatalysts for organic pollutant degradation in wastewater are presented in detail. Finally, some concluding remarks and perspectives on the challenges and opportunities for constructing different types of g-C3N4/TiO2-based heterostructured photocatalysts are presented.

Single-Step Synthesis of Graphitic Carbon Nitride Nanomaterials by Directly Calcining the Mixture of Urea and Thiourea: Application for Rhodamine B (RhB) Dye Degradation

“…The major causes of water pollution are the release of untreated industrial effluents and uncontrolled anthropogenic activities [ 3 , 4 , 5 ]. Meanwhile, various hazardous pollutants including antibiotics, phenols, pesticides, pharmaceuticals, and dyes from textile industries are causes of major water pollution [ 6 ]. Among them, dyes from textile industries generate a large amount of industrial wastewater due to the huge water demand and frequent discharge into the environment [ 6 , 7 ].…”

“…Meanwhile, various hazardous pollutants including antibiotics, phenols, pesticides, pharmaceuticals, and dyes from textile industries are causes of major water pollution [ 6 ]. Among them, dyes from textile industries generate a large amount of industrial wastewater due to the huge water demand and frequent discharge into the environment [ 6 , 7 ]. In addition, approximately 10–20% of total dyes from textile industries in the world are dissipated as effluent into the environment throughout the production process [ 2 , 8 , 9 ].…”

Microwave Synthesis of Visible-Light-Activated g-C3N4/TiO2 Photocatalysts

“…At the same time, the electrons on the CB of g-C 3 N 4 could be captured by O 2 to form ·O 2 − radical species due to the more cathodic CB potential (−1 V vs. NHE) compared to the redox potential of O 2 /·O 2 − (−0.33 V vs. NHE) radicals [ 137 , 138 ]. These hydroxyl and superoxide radical species (OH − and ·O 2 − , respectively) will further reduce and oxidize MO dye to H 2 O and CO 2 , with a major contribution from the superoxide radicals, as observed in the photodegradation experiments with ROS ( Figure 11 b) [ 139 , 140 ]. In this case, the good coupling between TiO 2 and g-C 3 N 4 leads to a stronger reduction and oxidation abilities, which will confer improved efficiency to the heterostructure for MO photocatalytic degradation under sunlight.…”

A pragmatic review on photocatalytic degradation of methyl orange dye pollutant using greenly biofunctionalized nanometallic materials: A focus on aquatic body

“…In recent times, several reviews 2,8,32,75–125 have been published on the photocatalytic degradation of various dye pollutants in an aquatic medium using different nanomaterials. However, only a few 2–4,77,81,82,86,91,96,102,123,124 focus on the biosynthesized NPs for the dye photodegradation application.…”