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Review

Recent Advances in Graphitic Carbon Nitride-Based Materials in the Photocatalytic Degradation of Emerging Contaminants

1
School of Environmental and Chemical Engineering, Foshan University, Foshan 528200, China
2
College of Light Chemical Industry and Materials Engineering, Shunde Polytechnic University, Foshan 528333, China
3
Foshan Water Group, Foshan 528000, China
*
Authors to whom correspondence should be addressed.
Inorganics 2025, 13(10), 319; https://doi.org/10.3390/inorganics13100319
Submission received: 19 August 2025 / Revised: 17 September 2025 / Accepted: 22 September 2025 / Published: 26 September 2025
(This article belongs to the Special Issue Novel Photo(electro)catalytic Degradation)

Abstract

The increasing presence of emerging contaminants (ECs) has attracted considerable attention due to their potential harm to human health and ecosystems. Graphitic carbon nitride (g-C3N4), a semiconductor devoid of metals, stands out due to its distinctive optical properties and strong resistance to chemical degradation, which holds significant promise in the photocatalytic degradation of ECs. However, the inherent limitations of g-C3N4, such as its reduced specific surface area and the swift recombination of photogenerated electron-hole pairs, have prompted extensive research on modification strategies to enhance its photocatalytic performance. Current research on g-C3N4-based materials is often constrained in scope, with most reviews focusing solely on modification strategies or its application in degrading a single category of emerging contaminants (ECs). In this review, a systematic overview of synthesis methods and advanced modification strategies for g-C3N4-based materials is discussed, highlighting their recent advances in the photocatalytic degradation of various ECs using g-C3N4-based materials, which underscores their potential for environmental remediation. Moreover, this article critically examines the current challenges and outlines future research directions, with particular emphasis on integrating artificial intelligence and machine learning to accelerate the development of g-C3N4-based photocatalysts and optimize degradation processes, thereby promoting their efficient application in the photocatalytic degradation of ECs.

1. Introduction

In recent years, the accelerated growth of global industry and the extensive usage of chemicals have resulted in a continuous increase in residual emerging contaminants (ECs) in the environment, which has garnered extensive attention from the international community [1]. The United Nations Environment Programme (UNEP) defines ECs as all pollutants stemming from human activities that are detectable in the environment but not fully regulated by laws, regulations, and standards, thus posing potential risks to human life and the ecological environment, which are recognized as issues demanding urgent global cooperation. These contaminants mainly originate from industrial effluents, domestic waste, agricultural runoff, and hospital discharges, and are generally classified into four groups: persistent organic pollutants (POPs), endocrine disrupting chemicals (EDCs), antibiotics, and microplastics (MPs) [2].
Conventional wastewater treatment methods (such as physical and biological methods) exhibit limitations in effectively removing ECs [3]. As an important component of advanced oxidation processes (AOPs), photocatalytic oxidation technology is widely recognized as an effective strategy for treating organic pollutants [4]. Owing to its advantages such as high solar energy utilization efficiency, no secondary pollution, and strong environmental applicability, this technology has shown broad prospects in the field of organic pollutant degradation, opening up a new approach for the treatment of ECs [5].
In recent years, g-C3N4 has garnered significant attention in photocatalysis due to its abundant availability, non-toxicity, chemical stability, and narrow bandgap (2.7 eV), allowing effective visible light harvesting [6]. Since its photocatalytic characteristics were first reported by Wang et al. in 2009 [7], research on g-C3N4 as a photocatalyst has rapidly expanded. It is extensively used across diverse fields, including water splitting, CO2 reduction, and organic pollutant degradation. This characteristic arises from the sp2 hybridization of carbon and nitrogen atoms in g-C3N4, creating a π-conjugated electronic system [8], and is based on the tri-s-triazine ring as fundamental structural unit and is composed solely of C and N atoms. It demonstrates high thermal stability (up to 600 °C), facile synthesis, and low production cost, making it a practical photocatalyst [9]. Furthermore, g-C3N4 has a suitable band structure (conduction band at −1.3 V and valence band at +1.4 V vs. normal hydrogen electrode (NHE)), which enables photocatalytic activity under visible light and provides strong reducibility.
However, g-C3N4 has intrinsic limitations, including a small specific surface area [10], low visible-light utilization efficiency, and rapid recombination of photogenerated electron–hole pairs [11]. Despite its intrinsic limitations, its tunable structure allows its performance to be improved through strategies including morphological control, elemental doping, defect creation, and heterojunction construction. Modified g-C3N4 demonstrates significantly enhanced photocatalytic degradation efficiency for emerging contaminants, with notable advantages particularly in broadening the spectral response range, strengthening reactive oxygen species (ROS) generation efficiency, and augmenting specific adsorption capacity.
To elucidate recent progress in g-C3N4 synthesis and modification strategies, this review systematically examines the development of high-performance, cost-effective g-C3N4-Based Materials (CNMBs) for the remediation of ECs (Figure 1). This review also evaluates the challenges associated with g-C3N4-based photocatalytic technology and explores its potential in solar-driven applications. Finally, recommendations are provided to improve ECs removal and to maximize its practical efficiency, offering theoretical support for advancing environmental governance.

2. Synthesis of g-C3N4-Based Materials

g-C3N4 can be readily synthesized through condensation and addition polymerization at various temperatures, employing organic precursors like melamine, thiourea, and urea, which contain carbon, nitrogen, and sulfur. Common approaches for synthesizing g-C3N4 encompass thermal polymerization, hydrothermal synthesis, sol–gel processing, chemical vapor deposition, and microwave-assisted synthesis, providing multiple pathways for material preparation. By adjusting precursors and reaction conditions, these methods enable precise modulation of the structural and functional properties of g-C3N4 to suit specific application requirements. A detailed comparison and summary of these preparation methods are provided in Table 1.

2.1. Thermal Polymerization (TP)

Thermal polymerization is the dominant method for synthesizing g-C3N4, where carbon-, nitrogen-, sulfur-rich organic precursors such as melamine [12], cyanamide [13], dicyandiamide [14], urea [15] and thiourea [16] undergo polycondensation reactions under thermal treatment (Figure 2a). The chemical properties of the precursors directly influence the polymerization pathway, morphology, and porosity of g-C3N4. For instance, melamine tends to form dense layers with small surface area [12], and urea [15] leads to the creation of porous structures that enhance surface area and charge separation, while thiourea [17] and dicyandiamide [18] introduce defects that extend visible light response. Moreover, the polymerization temperature significantly influences the crystallinity, defect formation, and electronic band structure, thereby enabling controlled tuning of g-C3N4 morphology (Figure 2b). Gu et al. obtained bulk-like, lamellar, nanotubular, and nanodot structures of g-C3N4 through temperature control [19], whereas Mo et al. [20] prepared nanosheets and bulk forms using urea as the precursor. Reaction atmosphere (e.g., N2 or Ar) [21] influences doping and defects, inhibiting oxidation, maintaining stoichiometry, and potentially introducing carbon vacancies that modify energy bands, light absorption, and charge separation.

2.2. Hydrothermal Method (HT Method)

Hydrothermal synthesis of g-C3N4 occurs at relatively low temperatures and pressures, allowing precise control over morphology, defects, and surface properties by adjusting solvents, precursors, temperature, and reaction time [23]. Hydrothermal synthesis, aided by solvents or templates, produces nanosheets, quantum dots, and porous structures, and facilitates the incorporation of heteroatoms or composites in the liquid phase. Additionally, the hydrothermal environment also promotes hydroxyl and amino groups, enhancing hydrophilicity and chemical reactivity [23]. Zhang et al. [24] synthesized C-doped g-C3N4 through hydrothermal synthesis, to optimize electron transport and photocatalytic performance. Carbon doping reduced the bandgap from 2.6 eV to 2.0 eV, red-shifting the UV-vis absorption edge to expand visible light response, prolonged photogenerated carrier lifetime, and enhanced separation efficiency and visible-light photocurrent, and thereby boosted the degradation efficiency of 4-nitrophenol

2.3. Sol–Gel Method (Sol–Gel)

The sol–gel method enables precise control over the structural, optical, and morphological characteristics of g-C3N4 during its preparation, which is crucial for enhancing photocatalytic efficiency and achieving sustainable environmental reactions [25]. This method is favored for its high purity, excellent uniformity, low cost, and room-temperature processing capability, making it one of the effective approaches for fabricating g-C3N4 and its nanocomposites. In the sol–gel method, precursors like metal alkoxides and salts experience hydrolysis and polycondensation, forming a sol that transitions into a 3D gel structure. Two fundamental reaction mechanisms, hydrolysis and condensation, enable precise control over M-OH-M and M-O-M (oxygen-based bonding) [26]. Developing g-C3N4 photocatalysts with controllable structural, optical, and morphological properties through this method will enable efficient photocatalysis for sustainable reaction environments. Kailasam et al. [27] synthesized mesoporous carbon nitride with uniform 12 nm spherical pores via this method, achieving 3.2 times higher photocatalytic hydrogen evolution than bulk graphitic carbon nitride. Hollmann et al. [28] produced SG-CN photocatalysts with 20 times higher hydrogen evolution rate than bulk CN, attributed to porous framework, partial crystallographic disorder, and extensive surface area enabling rapid electron transport and proton adsorption.

2.4. Microwave-Assisted Synthesis (MAWA)

Microwave-assisted synthesis (MAWA) for g-C3N4, valued for rapidity and efficiency, uses microwave dielectric heating of precursors to quickly construct composites, producing highly crystalline g-C3N4 in minutes—greatly boosting preparation efficiency versus traditional high-temperature, long-duration methods. Chen et al. [29] applied it to dope phosphorus into g-C3N4 and optimized catalyst dosage via ion exchange, with advantages like instantaneous volumetric heating, faster reactions, and higher precision. Liu et al. [30] developed a microwave-enhanced molten salt technique, using melamine to fabricate isotype heterojunctions from triazine-heptazine derivatives in g-C3N4 which achieved a visible-light photocatalytic hydrogen evolution rate of 1480 μmol g−1 h−1, outperforming er-ms-g-C3N4 by 5 times, er-g-C3N4 by 15 times, and mw-g-C3N4 by 23 times. Integrating microwave heating with molten salt polycondensation efficiently and versatilely enables rapid synthesis of g-C3N4-derived photocatalysts, enhancing productivity and consistency for large-scale photocatalytic applications.

2.5. Chemical Vapor Deposition (CVD)

Chemical vapor deposition (CVD) is highly effective in synthesizing carbon nitride composite photocatalysts. This method involves nitrogen-containing precursors (e.g., NH3, N2), carbon sources (e.g., C2H2, CH3OH), and carrier gases (e.g., Ar, N2). These substances undergo pretreatment (such as high-temperature gas infusion) and then undergo controlled decomposition at high temperatures in a reaction chamber. High temperatures and appropriate reaction times are beneficial for improving the yield and purity of the products. Wang et al. [31] prepared irregular mesoporous g-C3N4 nanotubes (MCN) via vapor deposition using a modified halloysite template. Compared with traditional bulk g-C3N4, these nanotubes have smaller sizes, denser stacking of structural units, and larger specific surface areas. This reduces light-induced electron-hole recombination, enhances photon-capturing ability, and increases the visible light-induced photocatalytic hydrogen production efficiency by 14.3 times.
Table 1. Comparison and Summary of g-C3N4 Preparation Methods.
Table 1. Comparison and Summary of g-C3N4 Preparation Methods.
Preparation MethodAdvantagesDisadvantagesProduct
Morphologies
ApplicationRef.
Thermal polymerizationCost-efficient equipment, mature scalable process, high-purity product outputsevere aggregation, low specific surface area, crystallinity, poor charge transfer efficiency, inadequate morphology control, high energyBulk/granular morphologiesphotocatalysts, electrodes, catalyst supports[32]
Hydrothermal methodLow-temperature synthesis (<200 °C): well-crystallized products with tunable morphologiesprolonged reaction duration; solvent/impurity residuesNanosheets,
nanorods,
hollow spheres
photocatalytic water splitting, CO2 reduction, biosensing apps[33,34]
Sol–gel methodLow-temp synthesis (<200 °C), mesoporous/porous architectures, homogeneous doping, precise structural control, compositional homogeneityIntricate multi-step process, drying-shrinkage cracking, scalability challenges, high precursor costsMesoporous,
Porous particles
Composite coatings, thin films fabrication, sensors, anticorrosive apps, flexible electronics[35]
Microwave-assisted synthesisRapid reaction kinetics, low energy consumption, well-dispersed productsElusive process parameter optimizationNanoparticles,
Porous architectures
pollutant degradation, energy storage, high-throughput lab studies[36]
Chemical vapor depositionHigh-purity dense films: precise thickness, composition control, large-area fabricationCostly vacuum equipment, excessive energy use, low yieldsThinfilms, Coatings, NanoarraysHigh-quality thin films fabrication, electronic devices, optical coatings, semiconductor heterojunctions[37]

3. Modification Strategies for g-C3N4-Based Materials

Enhancement of g-C3N4 photocatalytic activity requires effective light harvesting, efficient separation and migration of charge carriers, increased surface area, and abundant active sites. Morphology control, elemental doping, defect engineering, and heterostructure formation are key strategies to modulate its electronic and physicochemical properties and improve photocatalytic efficiency.

3.1. Morphology Control

Photocatalytic activity correlates with catalyst dimensions, surface morphology, and structure, enhanced by increasing surface area and accessible active sites. This promotes light reflection/scattering, shortens charge carrier travel distance, and boosts efficiency [38]. Soft and hard templating and exfoliation regulate g-C3N4 morphology, producing 0D–3D structures that aid charge transport and improve properties (Figure 3) [39]. Wang et al. [13] used silica templates for mesoporous g-C3N4 (HCNS), enhancing visible-light hydrogen evolution via optimized band structure and light harvesting. Supramolecular approaches with triazine address hollow structure collapse, yielding larger surface area, better light harvesting, and more reactive sites, with internal reflection boosting charge generation. Dong et al. [40] prepared ultra-thin nanosheets via HCl-assisted exfoliation, where protonation dissociates bulk material and etching induces defects to improve charge separation. Gu et al. [41] created hierarchical nanoporous microspheres via template-free solvothermal treatment and calcination, achieving broader light absorption and better carrier transport to enhance hydrogen production.

3.2. Elemental Doping

Metal or non-metal doping enhances g-C3N4 photocatalytic performance by modifying electronic and band configurations, boosting light harvesting, and optimizing charge separation. Metal doping narrows the bandgap via donor and acceptor states to broaden light absorption. Cation doping includes hole doping (e.g., Mn2+ coordinating with nitrogen) (Figure 4a) and interlayer doping (e.g., K+ bridging layers) (Figure 4b), which enhance the carrier mobility, charge transport, and visible light capture [43]. Xiong et al. [44] showed K doping narrows the bandgap and improves oxidation strength.
Non-metal doping, differing from metal doping, forms covalent bonds and alters electron distribution via charge polarization, dispersing π-electrons, reducing recombination, and expanding light absorption. As illustrated in Figure 4c, specific dopants such as P [45], O [46], N [47], B [48], S [49] and C [50] along with halogens [51] showed improved activity, particularly in hydrogen generation and pollutant breakdown [52].
Dual or multi-element co-doping extends visible-light absorption and promotes charge separation. Chen et al. [53] synthesized porous g-C3N4 with Rh-P modification, achieving 33 times higher hydrogen yield than unaltered g-C3N4, significantly boosting activity.
Figure 4. (a) Potential dopant candidate locations within the monolayer of g-C3N4: Metal ion cave doping, color scheme: C, red; N, yellow. (Adapted with permission from Ref. [54]). (b) Metal ion interlayer doping. (reproduced with permission from Ref. [44], copyright 2016 ACS Publications). (c) Possible substitution sites for non-metal doping. (Adapted with permission from Ref. [55]).
Figure 4. (a) Potential dopant candidate locations within the monolayer of g-C3N4: Metal ion cave doping, color scheme: C, red; N, yellow. (Adapted with permission from Ref. [54]). (b) Metal ion interlayer doping. (reproduced with permission from Ref. [44], copyright 2016 ACS Publications). (c) Possible substitution sites for non-metal doping. (Adapted with permission from Ref. [55]).
Inorganics 13 00319 g004

3.3. Defect Engineering

Defect engineering, by introducing specific types of defects, can change the periodicity of the g-C3N4 crystal structure. These defects act as trapping centers, modify the band structure, reduce electron-hole recombination, and enhance charge separation. They create new electronic states in the bandgap, broadening photon harvesting range. Typical defects include amino defects, cyano groups (−C≡N), carbon vacancies (CVs), and nitrogen vacancies (NVs) (Figure 5a–d) [56]. To accurately analyze the content of these defects, X-ray Photoelectron Spectroscopy (XPS) is the most widely used for amino defects and cyano groups. For instance, the presence of cyano groups can be identified by a characteristic peak at approximately 284.8 eV in the C 1 s spectrum, while amino defects correspond to a signal at around 399.8 eV in the N 1 s spectrum [21]. Carbon vacancies (CVs) and nitrogen vacancies (NVs) both exhibit typical paramagnetism due to the presence of unpaired electrons resulting from unsaturated electron orbitals. In this case, Electron Paramagnetic Resonance (EPR) spectroscopy serves as an effective complement to XPS for the quantitative analysis of vacancy defects. Such vacancies produce a characteristic signal in EPR measurements, and the absolute concentration of CVs or NVs can be determined [57].
Lin et al. [58] synthesized dual vacancy carbon nitride (DACN) with N and O vacancies via thermal polymerization, generating more unpaired electrons in aromatic heterocycles, to reduce electron-hole recombination and enhance visible light absorption. Visible light photocatalysis improves 11.7 times vs. pure g-C3N4. Liao et al. [59] prepared p-n homojunction g-C3N4 with abundant nitrogen vacancies via hydrothermal-calcination, reducing electron-hole recombination and enhancing photon harvesting, boosting visible light photocatalysis 8.7 times vs. conventional g-C3N4, due to the expanded visible response, large surface areas, and p-n homojunction. Yang et al. [60] made nitrogen vacancy-containing CN (NVs-PCN), where nitrogen vacancies regulate electronic structure, promote charge separation, and prolong carrier lifetime, leading to CO2 photocatalytic reduction 279 times that of pristine PCN. Chang et al. [61] prepared AT-CN with carbon and nitrogen vacancies via thermal polymerization, where nitrogen vacancies act as active adsorption sites by extending light absorption, reducing charge recombination, and increasing surface area. Carbon vacancies dissociate C-N bonds in tri-s-triazine by generating unsaturated nitrogen coordination, capturing electrons to reduce recombination, and enhancing hydrophilicity, thus improving visible light photocatalysis.

3.4. Heterostructure Construction

To design high-performance g-C3N4-based composite photocatalysts, materials need a narrow bandgap for visible light harvesting and suitable band positions for redox reactions. Single semiconductors struggled to meet these requirements, while heterojunctions addressed these by leveraging band structure and width differences to promote electron-hole migration and separation at the interface [62], with types including Type-II, Z-scheme, S-scheme, and Schottky heterojunctions [63].
Type II heterojunctions achieve band matching by combining two semiconductors with staggered band structures (designated as PS1 (right) and PS2 (left)) [64]. In this system, the CB position of PS1 is higher than that of PS2, while the VB position of PS2 is deeper than that of PS1, causing electrons to accumulate in the CB of PS2 for reduction reactions, and holes to gather in the VB of PS1 for oxidation reactions (Figure 6a). However, Type II heterojunctions have inherent defects such as difficult coordination of charge transfer impedance and weakening of redox capabilities.
Z-scheme heterojunctions enhance system redox capability by integrating two photocatalytic systems: materials with negative CB potentials (e.g., g-C3N4, Cu2O, etc.) as reduction sites (photosystem I) and those with positive VB potentials (e.g., BiVO4, WO3, etc.) as oxidation sites (photosystem II). They form a unique electron transfer pathway via mediators (Figure 6b), maintaining strong redox capacity of photogenerated electrons and holes, an advantage over Type II heterojunctions. Wisal Muhammad et al. [65] synthesized a 2D/2D NiFe2O4/g-C3N4 Z-scheme heterojunction in the optimized 6NFO/CN, electrons from NFO CB and holes from CN VB are effectively separated via direct Z-scheme transfer, suppressing recombination, significantly enhancing organic pollutant degradation efficiency under visible light, and outperforming pure g-C3N4.
In 2020, Prof. Yu’s team [66] pioneered the S-scheme charge transfer mechanism, derived from Type II heterojunctions and Z-scheme systems. Its core involves staggered band alignment between reducible (PS1) and oxidizing (PS2) photocatalysts (Figure 6c): PS1 band structure (Fermi level, CB, VB) is higher than PS2, driving electron migration to PS2. Contact forms a built-in electric field (IEF) from PS1 to PS2, inducing band bending. Photoexcitation makes PS2 CB electrons transfer to PS1 VB for recombination, with some jumping to PS1 high CB to enhance reduction. Regulated by IEF, band gradient, and interfacial interactions, this retains high-activity carriers, balancing redox driving force and charge separation efficiency. Zhang et al. [67] engineered S-scheme ZIS/CPCN via calcination and hydrothermal methods, using crystalline carbon nitride. It removes quinolones efficiently via internal electric field and low-energy charge recombination, degrading 86% of levofloxacin in 3 h. Chahkandi et al. [68] synthesized HAp@Bi2S3 core–shell structures, loading them onto g-C3N4 to form dual S-scheme HAp@Bi2S3/g-C3N4. This improves charge separation/transfer, extends carrier lifetime, and enhances activity, degrading 98.2% of metformin in 60 min.
g-C3N4 can host noble metal nanoparticles (NPs) to form Schottky junctions, with the surface plasmon resonance (SPR) effect enhancing interfacial localized electric fields [69]. The combination generates a Mott-Schottky barrier due to work function differences, enabling photoexcited electrons to migrate from g-C3N4 CB to the metal Fermi level to reduce electron-hole recombination. Additionally, the photothermal effect enhances light-to-energy conversion and charge carrier utilization (Figure 6d), improving light uptake and photo-generated charge separation to maximize photocatalytic performance.

4. Applications of g-C3N4-Based Materials in the Control of ECs

Persistent organic pollutants (POPs), endocrine-disrupting chemicals (EDCs), antibiotics, and microplastics (MPs) are four major ECs of global concern with significant environmental and ecological risks. g-C3N4-based photocatalysts have demonstrated exceptional potential for their remediation, where photoinduced ROS (•OH, •O2) mineralize ECs into benign CO2 and H2O through advanced oxidation processes, providing an environmentally sustainable solution. Table 2 summarizes the ROS in the photocatalytic degradation process of g-C3N4-based materials, the corresponding ROS detection methods, and the associated possible pollutant degradation pathways.

4.1. POPs Degradation

POPs have garnered widespread international attention due to their environmental persistence, bioaccumulation potential, long-range transport capabilities, and posing threats to human health and ecosystems [75]. POPs include precursors such as dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), dioxins, and per-and polyfluoroalkyl substances (PFAS). Owing to their inherent chemical stability, POPs exhibit remarkable resistance to conventional degradation methods, including chemical oxidation and biological treatment. g-C3N4-based photocatalysts can mineralize these pollutants by harnessing the power of light by using electrons and holes to drive oxidation-reduction reactions to effectively break down POPs. This eco-friendly approach is widely regarded as a sustainable solution for eliminating POPs from our surroundings.
Li et al. [76] achieved efficient degradation of perfluorooctanoic acid (PFOA) under visible light by combining g-C3N4 with Fe3+. This system achieved 80% degradation of PFOA within 20 h under visible light irradiation. Research indicated that PFOA degradation efficiency correlates with the quantity of g-C3N4, and the g-C3N4/Fe3+ system persistently produces strong oxidative •OH radicals to degrade PFOA (Figure 7a), improving photocatalytic efficiency. Wang et al. [77] synthesized a magnetic Fe3O4@β-CD/g-C3N4 nanocomposite photocatalyst for efficient removal of PCBs from wastewater. Fe3O4@β-CD/g-C3N4 managed to degrade six PCBs with efficiencies ranging from 77% to 98% within 55 min and kept its good stability even after six degradation cycles (Figure 7b). Wang et al. [78] developed an innovative photocatalyst with a porous core–shell design, consisting of magnetic β-cyclodextrin integrated with g-C3N4 (Mβ-CD/GCN). This advanced material was specifically tailored for harnessing solar energy to break down PCBs through photocatalytic degradation. Specifically, Fe2+ and Fe3+ in Fe3O4 react with H2O2 and water to generate •OH, while Fe2+ reacts with O2 to produce •O2 and Fe3+. The reversible Fe(III)/Fe(II) redox cycle minimizes iron loss and enhances radical generation. With the synergistic effects of h+, •O2, and •OH, PCB180 was degraded by 93% in 135 min under light, exhibiting a first-order reaction rate constant 3.23 times higher than that of GCN. PCB180 was ultimately mineralized or transformed into degradation intermediates (Figure 7c,d). Sathish Kumar et al. [79] engineered a nanocomposite by integrating polydopamine (pDA) into g-C3N4 (g-C3N4/pDA) using a hydrothermal synthesis technique. This innovative material was designed to enhance the photocatalytic breakdown of the organophosphorus pesticide profenofos (PF) when exposed to UV light. The pDA establishes a stable bond with the g-C3N4 surface via covalent linkages and π-π interactions. Specifically, the catechol groups in pDA have a strong affinity for the NH2 groups on g-C3N4. By forming strong covalent bonds, a continuous polymer layer is created. π-π interactions with pDA on the g-C3N4 surface significantly reduce electron-hole recombination and enhance the transport of photoexcited charge carriers. This process leads to an impressive photocatalytic degradation rate, reaching 96.4% efficiency for PF in just 25 min (Figure 7e). Su et al. [80] synthesized photocatalytic nanosheets with a high specific surface area through morphology control and developed amphiphilic groups for surface modification, endowing the photocatalyst with Pickering particle functionality (LC-g-C3N4-2AC) (Figure 7f). The engineered photocatalyst firmly anchors itself at the micron-scale interface of the oil-water emulsion, dramatically boosting mass transfer efficiency within the biphasic system. Moreover, the electron-hole recombination in g-C3N4-2AC, which is synthesized by exfoliating bulk g-C3N4, is markedly reduced. This suppression enhances the generation of ROS at the surface reaction sites, thereby improving photodegradation performance, which degrades oily wastewater into various organic acids and aldehydes, eventually oxidizing them into CO2, H2O, and other small molecules. Employing this straightforward PE photocatalytic system, the degradation rate of n-hexane model oily wastewater attained 97.2%. By combining photocatalytic and polyethylene catalytic technologies, researchers developed a stable polyethylene photocatalytic system to degrade organic pollutants in oily wastewater, offering a novel approach for developing efficient g-C3N4-based photocatalysts with potential applications in degrading persistent organic pollutants in aquatic environments. The performance of these various g-C3N4-based photocatalysts for the elimination of POPs is comprehensively summarized in Table 3.

4.2. EDCs Degradation

EDCs are external chemical agents, which are capable in disrupting the normal operations of the endocrine system in living beings. These chemicals can lead to genetic mutations, cellular alterations, and increase the risk of various cancers, including breast and prostate cancer. These precursors may also result in abnormal reproductive system development, behavioral changes, reduced reproductive capacity, and even species extinction [92]. EDCs mainly consist of synthetic phenolic compounds like BPA, nonylphenol, and octylphenol, commonly found in consumer goods. By the end of 2022, worldwide demand for BPA surged to a staggering of 10.6 million tons [93]. This uptick in both production and usage has exacerbated the contamination of aquatic ecosystems by endocrine-disrupting chemicals, posing a growing environmental threat.
BPA, a prevalent EDC, can be efficiently degraded through g-C3N4 photocatalysis, an eco-friendly and economical approach. Mu et al. [94] effectively fabricated a 2D/3D S-scheme heterostructure (g-C3N4/BiO1.2I0.6) through calcination of g-C3N4 nanosheets and BiOI with a floral morphology. The 2D/3D structure ensures close heterojunction interaction, promoting swift electron transfer and boosting photocatalytic efficiency (Figure 8a). The degradation rate of BPA by 0.2 g-C3N4/BiO1.2I0.6 is 3.2 times higher than that of g-C3N4. Guo et al. [95] engineered the g-C3N4 structure with Co and S (pg-C3N4/Co3O4/CoS) to achieve photocatalytic-PMS oxidation-coupled degradation of Bisphenol F(BPF). The addition of Co markedly improved the activation performance of g-C3N4 and peroxymonosulfate (PMS), while the sulfidation treatment increased the active sites for PMS activation. The incorporation of Co and S expanded the interlayer spacing of g-C3N4 and enhanced its visible-light harvesting efficiency (Figure 8b). DFT calculations (Figure 8c) reveal that electron transfer from carbon nitride to CoS enhances Co3+/Co2+ regeneration. The formation of CoS on Co3O4 shifts the Fermi level towards the CB in g-C3N4, improving its conductivity and facilitating photogenerated charge transfer. The pg-C3N4/Co3O4/CoS system exhibits a degradation rate 4 times higher than the pure PMS system, achieves a 90% TOC removal rate, and retains excellent catalytic activity after 5 cycles. Yu et al. [96] synthesized a cobalt-oxygen co-doped nitrogen-deficient g-C3N4 (Co-O-CNV) charge-transfer complex through thermal polycondensation, employing oxalic acid as a dual-functional precursor serving as both oxygen donor and chelating agent. During copolymerization, cobalt atoms were uniformly distributed and integrated into the OCNVN conjugated framework, establishing “metal-ligand” guest interactions. This structure optimized the optical bandgap of Co-OCNVN and significantly enhanced its light harvesting efficiency ability. The cobalt atoms, serving as separation hubs, greatly enhanced charge carrier separation efficiency. The degradation rate of 0.78% Co-OCNVN was 13 times that of the bulk g-C3N4. And Co-OCNVN could achieve the complete degradation of BPA within 3 h (Figure 8d). Ming et al. [97] hybridized carbon nitride nanosheets with CQDs (PCNC) through thermal polymerization. The Carbon Quantum Dots (CQDs) effectively captured photogenerated electrons, enhancing charge separation and transfer, and activated PMS (PMS/PCNC), resulting in a 95% BPA removal rate (Figure 8e). This study provides an example for developing efficient metal-free photocatalysts for PMS activation and offers a case for removing BPA from wastewater. Luo et al. [98] constructed a porous g-C3N4 sheet/reduced graphene oxide (RGO)/BiOI nanosheet (CRB) catalyst (Figure 8f). RGO, positioned between BiOI nanosheets and porous g-C3N4 nanosheets, acted as an electron shuttle, significantly enhancing carrier separation. Under visible light, CRB activated persulfate (PS). With 0.25 g/L CRB and 0.5 mM PS, 6 mg/L of 17α-ethinylestradiol (EE2) was completely removed within 2 min, with a degradation rate as high as 1.6557 min−1. Xu et al. [99] synthesized an efficient MIL-100(Fe)/ZnFe2O4/porous carbon nitride (MIL/ZC) ternary catalyst. The synergistic interplay between porous carbon nitride (PCN) and complementary catalysts significantly boosted the dissociation of photogenerated electron-hole, thanks to an optimized dual charge transfer mechanism. This advancement led to an impressive 99.84% degradation rate of nonylphenol (NP) when using the 30MIL/ZC2 composite, which showcases its remarkable efficiency in environmental remediation. Bi et al. [100] synthesized phosphorus-doped g-C3N4 (PCN) photocatalysts through thermal polymerization for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under visible light. Phosphorus doping developed impurity bands into g-C3N4, narrowing the bandgap and boosting visible light harvesting efficiency, leading to a PCN degradation rate constant nearly quadruple that of CN (Figure 8g). DFT calculations were used to study the density of states (DOS) and band structures of 4-PCN and CN. The analysis revealed that the doping process preserved the overall trend in the band structure, though the introduction of impurity bands in 4-PCN resulted in a noticeable narrowing of the bandgap. Specifically, the VB edge of CN is dominated by nitrogen orbitals, whereas the CB edge arises from a combined contribution of both nitrogen and carbon orbitals. Phosphorus doping led to interactions between P atoms in 4-PCN and neighboring carbon and nitrogen atoms, giving rise to impurity states. These impurity states formed impurity bands in the band structure, further reducing the bandgap (Figure 8h). Phosphorus doping represents an effective strategy for enhancing the photocatalytic performance of g-C3N4. The performance of these various g-C3N4-based photocatalysts for the elimination of EDCs is comprehensively summarized in Table 4.

4.3. Antibiotics Degradation

Antibiotics, as antimicrobial compounds, are extensively utilized in human and veterinary medicine for infection treatment and prevention, as well as growth promotion in aquaculture. Following the discovery of penicillin, multiple antibiotic classes, including sulfonamides, quinolones, tetracyclines, and macrolides, have become pervasive environmental contaminants, detected in surface waters and drinking water systems worldwide [110]. The process of photocatalytic degradation of antibiotics has garnered widespread attention and practical application, thanks to its affordability, remarkable effectiveness, and absence of harmful byproducts, positioning it as a reliable solution for eliminating antibiotics.
Dou et al. [111] synthesized mesoporous g-C3N4 (MCN) through morphology control, achieving degradation rates of amoxicillin (AMX) and cefotaxime (CFX) under visible light irradiation that were 2.5 and 4 times higher than those of BCN, respectively. The improved photocatalytic activity of MCN is primarily attributed to the formation of a porous structure (Figure 9a). Phoon et al. [112] synthesized I-doped mesoporous g-C3N4 (GCN-I) via thermal polymerization, and found that with the increase in the amount of I dopant, carbon vacancies appeared, leading to a decrease in the C/N ratio. This phenomenon allows more electrons to delocalize in the GCN structure, promoting the generation of more radicals and enhancing photodegradation performance (Figure 9b). Under visible light, GCN-I0.50 achieved a 99.8% removal rate of tetracycline within 180 min. Constructing heterojunctions and doping with carbon quantum dots can significantly enhance the photocatalytic activity of g-C3N4, thereby improving the removal efficiency of organic pollutants. Wu et al. [113] effectively produced a photocatalyst of hollow porous carbon nitride nanospheres modified with carbon quantum dots (HCNS/CDs), which effectively degrades multiple antibiotics under visible and natural light. The hollow nanosphere structure of HCNS/CDs provides abundant reactive sites, and optical harvesting efficiency is enhanced due to internal light reflection. Carbon quantum dots can convert long-wavelength visible and near-infrared light into short-wavelength light, thereby enhancing the photocatalytic degradation efficiency of HCNS/CDs (Figure 9c). Wu et al. [114] created a Z-scheme highly photoactive graphene layer and TiO2/g-C3N4 (GTOCN) composite photocatalyst for the degradation of antibiotics such as tetracycline and ciprofloxacin. In this ternary structure, electrons from the CB of TiO2 are rapidly captured by graphene and transferred to the VB of g-C3N4, promoting efficient charge transport and improving the division of photoinduced electron-hole pairs. GTOCN3 achieved an 83.5% removal rate of tetracycline within 80 min, with a total organic carbon removal rate of 66.3%, demonstrating significant degradation and mineralization effects on antibiotics under visible light (Figure 9d–f). Liu et al. [115] developed ultrathin carbon nitride nanosheets featuring atomic porosity and carbon vacancies (Cv-CNNs) through a two-step thermal method. Carbon vacancies led to the conversion of exposed nitrogen atoms into -NH2 groups, serving as hole stabilizers to extend the excited state lifetime of the photocatalyst and improve the dispersibility of CN sheets in water. Quantum mechanical simulations have shown that the presence of carbon vacancies in CN sheets actually modifies their two-dimensional structure. This adjustment enhances charge separation, narrows the gap for charge to travel to the surface, and cuts down on the likelihood of charge carrier recombination. The CvCNNs exhibited significantly enhanced sulfadiazine (SDZ) adsorption capacity. The introduction of carbon vacancies conversely has modulated the band energy levels in carbon nitride photocatalysts, enhancing their redox potentials and consequently promoting both photocatalytic water splitting for hydrogen evolution and SDZ degradation (Figure 9g–i). Experimental results showed that SDZ on Cv-CNNs was completely degraded within 90 min under visible light irradiation, and the material maintained 95% stability over five cycles. Hassanzadeh et al. [116] developed a Z-scheme g-C3N4/NiFe2O4/Ag nanocomposite by anchoring NiFe2O4/Ag nanoparticles onto g-C3N4. This cutting-edge approach substantially reduced the recombination of electron-hole, resulting in a remarkable improvement in the material’s photocatalytic efficiency and redox capabilities under visible light exposure. The nanocomposite exhibited a 92.1% degradation efficiency for tetracycline (TC) in 120 min. Zhou et al. [117] prepared nitrogen-deficient carbon nitride (FCN-5) through formic acid-aided pyrolysis. The inclusion of formic acid did not just bring about nitrogen defects and boost active sites, but also emitted gases during pyrolysis. This resulted in a porous framework, increased surface area, and reduced electron-hole recombination. As a result, the photoresponse performance was enhanced. In fact, FCN-5 managed to achieve a degradation efficiency of 95.1% for TC within 60 min. The performance of these various g-C3N4-based photocatalysts for the elimination of antibiotics is comprehensively summarized in Table 5.

4.4. MPs Degradation

MPs are plastic particles less than 5 mm in size. They mainly result from the fragmentation of larger plastic debris. Due to their persistence, MPs have emerged as a major environmental pollutant, now infiltrating our water bodies, food sources, air, and even bodily tissues such as blood and lungs. This MP contamination mainly arises from airborne and aquatic microplastics, significantly harming marine ecosystems [128]. Globally, 19–23 million tons of plastic debris are discharged annually. By 2030, this quantity is expected to soar to 53 million tons annually, with around 10 million tons ultimately reaching the oceans. Despite the growing buildup of plastic waste, merely 11% undergoes recycling [129].
Photocatalysis offers an energy-efficient solution to reduce MPs pollution by converting them into CO2 and H2O. Moreover, MPs act as inexpensive sacrificial precursors. Their polymer chains are degraded and converted into valuable chemicals and fuels. Nguyen et al. [130] employed hydrothermal and microwave methods to integrate g-C3N4 with FeNi-BTC (benzene-1,3,5-tricarboxylic acid) and CQDs, resulting in the formation of (g-C3N4/CQD/FeNi-BTC). The fabricated photocatalytic composite boasted a substantial pore volume of 1.192 cm3 g−1, a high specific surface area of 1090 m2 g−1, a 40–60 nm particle size, and visible-light harvesting efficiency in the range of 2.27–2.52 eV (Figure 10a). With a concentration of 1200 mg/L, the material showed remarkable adsorption efficiency for microplastics like polystyrene (PS) and polyethylene terephthalate (PET), reaching almost 100% adsorption in 45 min. Moreover, after 3 days of visible-light irradiation, the degradation rate of MPs with a concentration of 2500 mg/L reached 82.16% (Figure 10b). Wang et al. [131] developed a Z-scheme heterojunction by integrating WO3 with g-C3N4 (WO3/g-C3N4) through a hydrothermal synthesis process. This novel technique significantly enhanced the separation efficiency of photogenerated electron-hole pairs. Notably, the 30%WO3/g-C3N4 composite demonstrated exceptional performance in this regard. The 30%WO3/g-C3N4 composite increased the hydrogen evolution rate from PET degradation to 14.21 mM. This study opens new pathways for sustainable energy generation. Liu et al. [132] developed −C≡N and C-OH groups into PCN by terminating the polymerization reaction with iodide ions (I) (Figure 10c), which led to the production of a series of hydrophilic fragmented homogeneous carbon nitride (TP-PCN) (Figure 10d). I acted as an inhibitor during the exfoliation process by disrupting π-π bonds, reducing the stacking of ultrathin layers in PCN, thereby increasing the specific surface area of TP-PCN and significantly shortening the electron transfer path to the surface. Additionally, it enhanced in-plane electron migration, diminished energy dissipation caused by electron-hole recombination, and effectively promoted PET degradation and hydrogen production (Figure 10e). The photocatalytic conversion of PET to H2 by TP-PCN reached 600.3 μmol g−1 h−1. Liang et al. [127] synthesized porous carbon nitride nanoparticles with N3c vacancies (NCN0.48) through morphology control (Figure 10f). Specifically, the N3c vacancies acted as capture sites for photogenerated charges, effectively reducing carrier recombination. They also improved O2 adsorption and activation via strong C-O interactions, boosting •O2 production (Figure 10g,h). Meanwhile, the large specific surface area and highly porous structure of NCN0.48 provided abundant reactive sites, enhancing pollutant adsorption capacity and facilitating superior photocatalytic performance. Within 150 h, the photocatalytic degradation efficiency of NCN0.48 for PET is 43.1%, much higher than that of CN at 13.6%. The performance of these various g-C3N4-based photocatalysts for the elimination of MPs is comprehensively summarized in Table 6.

4.5. Application of Carbon Nitride-Based Materials in Degrading ECs in Actual Water Bodies

Currently, extensive research has been conducted on g-C3N4-based materials in the field of photocatalytic degradation of emerging contaminants in real wastewater, and these materials have demonstrated remarkable application potential. Endowed with excellent chemical stability, visible-light response capability, and environmental benignity, g-C3N4-based materials enable efficient degradation of typical ECs present in real wastewater. Bi et al. [100] investigated the photocatalytic performance of 4-PCN for 2,4-D degradation using actual water samples from the rivers and reservoirs of Harbin. Results showed its degradation efficiency was lower than in ultrapure water, attributed to inhibition by dissolved organic matter (DOM) and ions (e.g., Cl, HCO3) [136]. Nevertheless, 4-PCN still removed 60~70% of 2,4-D. After 20 min of irradiation, about 45% total organic carbon (TOC) reduction indicated the mineralization of 2,4-D. Additionally, five recycling tests revealed no significant activity loss, and XRD, FTIR, TEM, SEM and XRD analyses confirmed unchanged crystal structure and functional groups of 4-PCN, verifying its good reusability and stability. Considering the complexity of real water matrices, where antibiotics may coexist with inorganic ions and other substances, the influence of common aqueous anions (Cl, HCO3, NO3, SO42−, HPO42−) on the photodegradation of OFX was investigated. Feng et al. [126] prepared nitrogen-deficient, oxygen-doped porous g-C3N4 with a wider bandgap (denoted as RCN-2h), which achieved 100% degradation of ofloxacin (OFX) within 15 min. The results revealed that Cl, NO3, and SO42− had negligible effects, whereas HCO3 and HPO42− exhibited inhibitory effects. This inhibition was attributed to the Coulombic repulsion under alkaline conditions between these anions and OFX, as well as their ability to capture photogenerated holes (h+), leading to the formation of weakly oxidative species. The degradation rate constant of RCN-2h was 15.4 times higher than that of bulk g-C3N4 (BCN).
Zhang et al. [137] successfully prepared a Z-scheme heterojunction (5% Ag2V4O11/TCN) composed of silver vanadate quantum dots and tubular carbon nitride. This catalyst achieved a photocatalytic degradation efficiency of 86.25% for TC within 120 min. Four cyclic experiments showed that the degradation efficiency of TC remained at 80% after four cycles, confirming the strong stability of 5% Ag2V4O11/TCN. Furthermore, the study employed liquid chromatography-mass spectrometry (LC-MS) to analyze the intermediates generated during the degradation of TC and investigated their toxic effects as well as their interactions with free radicals. The degradation pathways of TC involved reactions such as hydroxylation, demethylation, and deamidation, yielding various intermediates. These intermediates were further converted into small molecular products through ring-opening and bond-cleavage processes, ultimately mineralizing into CO2 and H2O, accompanied by a significant reduction in toxicity. Quenching experiments and ESR results demonstrated that free radicals (·OH, ·O2, h+, and 1O2) played crucial roles in the degradation process, with·O2 contributing the most significantly. Highly reactive free radicals attacked TC molecules and their intermediates, thereby promoting the cleavage of C–C, C–N, and C–O bonds as well as structural ring-opening, which accelerated the decomposition and detoxification of toxic intermediates.
In summary, g-C3N4-based materials exhibit notable potential for photocatalytic degradation of ECs in real wastewater. Though their efficiency is inhibited by DOM and ions in real water, they still achieve effective EC removal. Recycling tests and XRD/FTIR confirm their stability, while TOC and LC-MS verify extensive EC mineralization, thereby reducing the risk of hazardous byproducts. Mechanistic studies, including proposed degradation pathways and identification of intermediate products via techniques such as LC-MS, further deepen the understanding of reaction processes and confirm the environmental compatibility of the degradation products. and the degradation performance, cyclic stability, and potential metal leaching risks of g-C3N4-based catalysts for ECs are summarized in Table 7.

5. Conclusions and Perspectives

g-C3N4-based materials show promise in environmental applications but have limited pristine performance. Research thus focuses on high-performance g-C3N4 via key modifications (morphology control, defect engineering, doping, and heterojunction construction) to expand light response and boost carrier separation. For doping: Metal doping needs to tackle active species agglomeration and enhance stability; non-metal doping requires precise content control; co-doping faces challenges of unclear synergies and complex structural regulation. In heterojunction construction: Despite their performance benefits, the structure-activity relationship between fine structures and catalytic activity remains unclear. Core issues include interface charge transfer, energy band matching, and long-term stability. Notably, the structural evolution of g-C3N4 during modification merits attention.
g-C3N4-based materials have been applied in the removal of various ECs. Modifications are typically necessary to enhance their activity and stability to meet the degradation requirements for different types of ECs. AI and ML play critical roles in advancing this process by analyzing large datasets of modification parameters and forecasting EC degradation performance, which can rapidly establish correlations to guide the rational design of high-efficiency modified g-C3N4, avoiding the inefficiency of traditional trial-and-error. However, systematic studies on the correlation between modification methods and specific ECs remain scarce. Furthermore, given that one of the primary applications of g-C3N4 is the remediation of contaminated water environments, the potential environmental impacts of modified g-C3N4 also warrant careful consideration. AI and ML can further support the optimization of g-C3N4-based water treatment processes, they can integrate data on photocatalyst stability and ecological toxicity with reaction conditions to predict both degradation efficiency and secondary pollution risks, promoting the translation of g-C3N4-based technologies from lab-scale to practical applications.
In summary, g-C3N4-based materials exhibit promising prospects for application in the degradation of emerging pollutants. To facilitate their practical implementation, the following recommendations are proposed for future study.
(i).
Presently, the charge transfer mechanisms in g-C3N4-based materials are not fully understood, and further studies are required to explore this process to improve their photocatalytic efficiency. Combining DFT calculations and experimental characterization methods to verify and optimize the charge transfer process in g-C3N4-based materials will provide a theoretical foundation for developing more efficient photocatalysts and precisely controlling photocatalytic reaction pathways.
(ii).
A thorough investigation into the thermodynamics and kinetics of surface reactions in g-C3N4-based materials is essential for refining material design, boosting charge separation efficiency, and accelerating photocatalytic reactions. AI-assisted analysis, particularly ML-driven kinetic modeling, has emerged as a powerful tool to unravel microscopic mechanisms. It can also reduce trial-and-error costs by summarizing experimental experience: studies have shown that ML algorithms predict surface reaction barriers and charge separation efficiencies by correlating experimental thermodynamic data with structural descriptors of g-C3N4-based materials, which not only deepens mechanism understanding but also enhances the selectivity of pollutant degradation by optimizing active species generation.
(iii).
Recent research indicates that g-C3N4-based photocatalytic materials exhibit low efficiency in the removal of POPs and may generate intermediate products with higher toxicity. Therefore, particular heed must be paid to the mineralization degree of emerging pollutants and the toxicity risks of intermediate products during the photocatalytic degradation by g-C3N4-based materials. Additionally, for g-C3N4 composites modified with metals, the potential leaching of metal ions should be monitored, as it helps further reduce the environmental risk of the final degradation system.
(iv).
While g-C3N4-based photocatalysts demonstrate remarkable pollutant degradation performance under laboratory conditions, their applications remain restricted to small-scale experiments. Moreover, the inherent powder morphology of g-C3N4 materials complicates recovery processes, thereby limiting their practical engineering applications. Consequently, future research should prioritize enhancing the stability and reusability of g-C3N4-based materials to facilitate their transition from laboratory research to scaled-up environmental engineering applications.
(v).
Currently, g-C3N4-based photocatalytic materials primarily rely on photoexcitation to generate strongly oxidative radicals for organic pollutant degradation, whose activity ceases without illumination. To address this limitation, integrating g-C3N4 with piezoelectric materials enables persistent radical generation via the piezoelectric effect even in dark conditions for emerging contaminant degradation. Simultaneously, the built-in electric field from piezoelectric coupling facilitates photogenerated charge separation and reduces recombination, thereby enhancing photocatalytic efficiency.

Author Contributions

Conceptualization, D.X. and D.L.; methodology, D.X. and D.L.; software, H.C., D.L. and X.C.; validation, S.H., F.C. and D.X.; formal analysis, D.X., Z.L., Z.H., Z.C., J.H., W.H., X.T., Y.W. and Y.F.; investigation, H.C. and S.H.; resources, H.C. and S.H.; data curation, D.X. and D.L.; writing—original draft preparation, D.X. and D.L.; writing—review and editing, D.L. and S.H.; supervision, D.L., H.C. and S.H.; project administration, H.C.; funding acquisition, H.C., D.L. and X.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Guangdong Provincial Program for Young Innovative Talents in General Higher Education Institutions (2024KQNCX169), the National Natural Science Foundation of China (42477220), and the Foshan City Self-Funded Science and Technology Innovation Project Incubation Program (2420001003624).

Data Availability Statement

No new data were created or analyzed in this study.

Conflicts of Interest

Author Chen Feng is employed by Foshan Water Group. The authors declare that this study was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest. Affiliated companies did not participate in the study design, data collection, analysis, interpretation, writing of this manuscript, or the decision to submit it for publication.

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Figure 1. Synthesis, modification, and application of carbon nitride-based materials.
Figure 1. Synthesis, modification, and application of carbon nitride-based materials.
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Figure 2. (a) A schematic diagram visually represents the thermal polymerization process employed to synthesize g-C3N4 at different temperatures (C, N, H atoms denoted with green, blue and orange balls), (It is adapted from Ref. [22]). (b) SEM and TEM images of bulk g-C3N4, g-C3N4-470, g-C3N4-500, g- g-C3N4-520, and g- g-C3N4-540, respectively [19]. (reproduced with permission from Ref. [19], copyright 2015 RSC Advances).
Figure 2. (a) A schematic diagram visually represents the thermal polymerization process employed to synthesize g-C3N4 at different temperatures (C, N, H atoms denoted with green, blue and orange balls), (It is adapted from Ref. [22]). (b) SEM and TEM images of bulk g-C3N4, g-C3N4-470, g-C3N4-500, g- g-C3N4-520, and g- g-C3N4-540, respectively [19]. (reproduced with permission from Ref. [19], copyright 2015 RSC Advances).
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Figure 3. The applications of g-C3N4-based materials with different dimensions (from 0D to 3D). (Adapted with permission from Ref [42]).
Figure 3. The applications of g-C3N4-based materials with different dimensions (from 0D to 3D). (Adapted with permission from Ref [42]).
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Figure 5. Typical positions of the (a) amino defects, (b) cyano defects, (c) C vacancies and (d) N vacancies in g-C3N4. (reproduced with permission from Ref. [56], copyright 2021 Elsevier).
Figure 5. Typical positions of the (a) amino defects, (b) cyano defects, (c) C vacancies and (d) N vacancies in g-C3N4. (reproduced with permission from Ref. [56], copyright 2021 Elsevier).
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Figure 6. Processes of charge carrier separation in diverse heterojunctions under light exposure: (a) Type-II; (b) Z-scheme; (c) S-scheme; (d) Schottky heterojunction. (It is adapted from Ref. [63]).
Figure 6. Processes of charge carrier separation in diverse heterojunctions under light exposure: (a) Type-II; (b) Z-scheme; (c) S-scheme; (d) Schottky heterojunction. (It is adapted from Ref. [63]).
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Figure 7. (a) Schematic of PFOA breakdown in the CN/Fe-Vis process. (reproduced with permission from Ref. [76], copyright 2024 Elsevier). (b) The breakdown process of Fe3O4@β-CD/g-C3N4 for PCB180 degradation. (reproduced with permission from Ref. [77], copyright 2022 Elsevier). (c) Photocatalytic breakdown process of PCB180 using Mβ-CD/GCN composite. (d) Degradation dynamics of PCB180 using dual catalysts, and kinetic rate constant analysis. (reproduced with permission from Ref. [78], copyright 2022 Elsevier). (e) Synthesis process of g-C3N4/pDA nanocomposites and their use in PF photocatalytic degradation. (reproduced with permission from Ref. [79], copyright 2024 Elsevier). (f) Preparation of LC-g-C3N4-2AC photocatalytic materials. (reproduced with permission from Ref. [80], copyright 2023 Elsevier).
Figure 7. (a) Schematic of PFOA breakdown in the CN/Fe-Vis process. (reproduced with permission from Ref. [76], copyright 2024 Elsevier). (b) The breakdown process of Fe3O4@β-CD/g-C3N4 for PCB180 degradation. (reproduced with permission from Ref. [77], copyright 2022 Elsevier). (c) Photocatalytic breakdown process of PCB180 using Mβ-CD/GCN composite. (d) Degradation dynamics of PCB180 using dual catalysts, and kinetic rate constant analysis. (reproduced with permission from Ref. [78], copyright 2022 Elsevier). (e) Synthesis process of g-C3N4/pDA nanocomposites and their use in PF photocatalytic degradation. (reproduced with permission from Ref. [79], copyright 2024 Elsevier). (f) Preparation of LC-g-C3N4-2AC photocatalytic materials. (reproduced with permission from Ref. [80], copyright 2023 Elsevier).
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Figure 8. (a) Schematic of the construction process of 2D/3D g-C3N4/BiO1.2I0.6S-scheme heterojunctions (TEM image of 0.2-C3N4/BiO1.2I0.6 is presented in the illustration). (reproduced with permission from Ref. [94], copyright 2022 Elsevier). (b) Diagram of pg-C3N4/Co3O4/CoS synthesis process. (c) The corresponding geometry structures of (I) pg-C3N4/Co3O4, (II) pg-C3N4/Co3O4/CoS; The charge density variation maps for the adsorption structures of (III) PMS and (IV) BPF. (reproduced with permission from Ref. [95], copyright 2021 Elsevier). (d) Schematic of potential photocatalytic process for Co-OCNVN (Degradation performance of g-CN, OCNVN, x Co-OCNVN, and Co-CN). (The right illustration shows the degradation efficiency of g-CN, OCNVN, x Co-OCNVN, and Co-CN, as well as the corresponding apparent pseudo first order rate constant (k1)). (reproduced with permission from Ref. [96], copyright 2020 Elsevier). (e) Photocatalytic activation and degradation mechanism of PMS/PCNC. (reproduced with permission from Ref. [97], copyright 2021 Elsevier). (f) Preparation route of CRB catalyst and degradation mechanism of EE2 in the 0.1CRB-10/PS/Vis system. (reproduced with permission from Ref. [98], copyright 2024 Elsevier). (g) UV-Vis diffuse reflectance spectra and bandgap energies of CN and 4-PCN. (h) Bandgap Modification through Impurity Band Formation via P Doping. (reproduced with permission from Ref. [100], copyright 2023 Elsevier).
Figure 8. (a) Schematic of the construction process of 2D/3D g-C3N4/BiO1.2I0.6S-scheme heterojunctions (TEM image of 0.2-C3N4/BiO1.2I0.6 is presented in the illustration). (reproduced with permission from Ref. [94], copyright 2022 Elsevier). (b) Diagram of pg-C3N4/Co3O4/CoS synthesis process. (c) The corresponding geometry structures of (I) pg-C3N4/Co3O4, (II) pg-C3N4/Co3O4/CoS; The charge density variation maps for the adsorption structures of (III) PMS and (IV) BPF. (reproduced with permission from Ref. [95], copyright 2021 Elsevier). (d) Schematic of potential photocatalytic process for Co-OCNVN (Degradation performance of g-CN, OCNVN, x Co-OCNVN, and Co-CN). (The right illustration shows the degradation efficiency of g-CN, OCNVN, x Co-OCNVN, and Co-CN, as well as the corresponding apparent pseudo first order rate constant (k1)). (reproduced with permission from Ref. [96], copyright 2020 Elsevier). (e) Photocatalytic activation and degradation mechanism of PMS/PCNC. (reproduced with permission from Ref. [97], copyright 2021 Elsevier). (f) Preparation route of CRB catalyst and degradation mechanism of EE2 in the 0.1CRB-10/PS/Vis system. (reproduced with permission from Ref. [98], copyright 2024 Elsevier). (g) UV-Vis diffuse reflectance spectra and bandgap energies of CN and 4-PCN. (h) Bandgap Modification through Impurity Band Formation via P Doping. (reproduced with permission from Ref. [100], copyright 2023 Elsevier).
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Figure 9. (a) The N2 adsorption–desorption isotherms and corresponding BJH pore size distribution plots (inset) were analyzed for both BCN and MCN samples. A comparative pore volume analysis (inset) was also conducted at a fixed mass (m = 1 g). Furthermore, the morphological characteristics of BCN and MCN were examined via scanning electron microscopy (SEM). (reproduced with permission from Ref. [111], copyright 2020 Elsevier). (b) The possible structure of I-doped GCN. (reproduced with permission from Ref. [112], copyright 2024 Elsevier). (c) Illustration of the photocatalytic mechanism of HCNS/CD when exposed to broad-spectrum light. (reproduced with permission from Ref. [113], copyright 2020 Elsevier). (d) Visible-light-driven photocatalytic breakdown of organic contaminants using GTOCN3. (e) Photocatalytic degradation performance of GTOCN3 towards TC. (f) Electrochemical impedance spectroscopy of GTOCN3. (reproduced with permission from Ref. [114], copyright 2020 Elsevier). (g) Schematic diagram of the synthesis of Cv-CNNs. (h) Valence and CB potential calculations of CN, CNN, and Cv-CNN. (i) Development of CN layers for SDZ uptake and their corresponding adsorption energies (1–5 denote CNNsa, Cv-CNNsa1, Cv-CNNsa2, CNNsb, and Cv-CNNsb, respectively). (Reproduced with permission from Ref. [115], copyright 2020 Elsevier).
Figure 9. (a) The N2 adsorption–desorption isotherms and corresponding BJH pore size distribution plots (inset) were analyzed for both BCN and MCN samples. A comparative pore volume analysis (inset) was also conducted at a fixed mass (m = 1 g). Furthermore, the morphological characteristics of BCN and MCN were examined via scanning electron microscopy (SEM). (reproduced with permission from Ref. [111], copyright 2020 Elsevier). (b) The possible structure of I-doped GCN. (reproduced with permission from Ref. [112], copyright 2024 Elsevier). (c) Illustration of the photocatalytic mechanism of HCNS/CD when exposed to broad-spectrum light. (reproduced with permission from Ref. [113], copyright 2020 Elsevier). (d) Visible-light-driven photocatalytic breakdown of organic contaminants using GTOCN3. (e) Photocatalytic degradation performance of GTOCN3 towards TC. (f) Electrochemical impedance spectroscopy of GTOCN3. (reproduced with permission from Ref. [114], copyright 2020 Elsevier). (g) Schematic diagram of the synthesis of Cv-CNNs. (h) Valence and CB potential calculations of CN, CNN, and Cv-CNN. (i) Development of CN layers for SDZ uptake and their corresponding adsorption energies (1–5 denote CNNsa, Cv-CNNsa1, Cv-CNNsa2, CNNsb, and Cv-CNNsb, respectively). (Reproduced with permission from Ref. [115], copyright 2020 Elsevier).
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Figure 10. (a) Microwave hydrothermal synthesis of g-C3N4/CQD/FeNi-BTC. (b) Microplastic elimination performance of g-C3N4/CQD/Fe-BTC versus g-C3N4/CQD/FeNi-BTC. (reproduced with permission from Ref. [130], copyright 2024 Elsevier). (c) Solid-state13C NMR spectra of PCN and TP-PCN (KI 75%). (d) Contact angle test visuals for the synthesized samples in digital format. (e) Schematic illustration of the reaction mechanism for microplastic degradation and hydrogen evolution by hydrophilic TP-PCN photocatalyst. (reproduced with permission from Ref. [132], copyright 2023 Elsevier). (f) Photocatalytic mechanism of microplastic degradation by NCN0.48 under light irradiation. (g) Optimized configurations of O2 adsorption on g-C3N4 surfaces and carbon atoms in N3c-deficient g-C3N4. (h) Gibbs free energy profile for O2 adsorption on g-C3N4 surfaces and g-C3N4 with N3c vacancies. (Reproduced with permission from Ref. [127], copyright 2024 Elsevier).
Figure 10. (a) Microwave hydrothermal synthesis of g-C3N4/CQD/FeNi-BTC. (b) Microplastic elimination performance of g-C3N4/CQD/Fe-BTC versus g-C3N4/CQD/FeNi-BTC. (reproduced with permission from Ref. [130], copyright 2024 Elsevier). (c) Solid-state13C NMR spectra of PCN and TP-PCN (KI 75%). (d) Contact angle test visuals for the synthesized samples in digital format. (e) Schematic illustration of the reaction mechanism for microplastic degradation and hydrogen evolution by hydrophilic TP-PCN photocatalyst. (reproduced with permission from Ref. [132], copyright 2023 Elsevier). (f) Photocatalytic mechanism of microplastic degradation by NCN0.48 under light irradiation. (g) Optimized configurations of O2 adsorption on g-C3N4 surfaces and carbon atoms in N3c-deficient g-C3N4. (h) Gibbs free energy profile for O2 adsorption on g-C3N4 surfaces and g-C3N4 with N3c vacancies. (Reproduced with permission from Ref. [127], copyright 2024 Elsevier).
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Table 2. Photocatalytic Degradation of g-C3N4-Based Materials: ROS, Detection Methods, and Degradation Pathways.
Table 2. Photocatalytic Degradation of g-C3N4-Based Materials: ROS, Detection Methods, and Degradation Pathways.
ROS TypeSpecific SpeciesQuencherTesting
Method
Degradation Pathway
(Radical Attack Sites)
Ref.
Radical species•O2Benzoquinone (BQ)Electron Paramagnetic Resonance (EPR): DMPO trappingElectron-rich groups (e.g., phenolic hydroxyl, amino groups); reduce nitro (-NO2) and azo (-N = N-) unsaturated bonds, disrupting conjugated systems.[70]
•OHTertiary
butanol (TBA)
EPR: DMPO or PBN trappingNon-selective attack, preferentially abstracting hydrogen atoms from C-H bonds; oxidizing aromatic rings, alkenes, amines and most organic pollutants, initiating chain degradation.[71]
1O2Sodium azide (NaN3), L-histidine, β-caroteneEPR: TEMP trappingSelectively attacking unsaturated bonds (e.g., C=C, C=O) and aromatic conjugated structures.[72]
Non-radical speciesh+Disodium edetate (EDTA-2Na), MethanolQuenching experiment:
Transient photocurrent response
Directly oxidizing electron-dense sites of adsorbed pollutants (e.g., phenolic hydroxyl, amino groups); or indirectly generating •OH by oxidizing surface OH/H2O.[73]
Surface charge transfer/Electrochemical Impedance Spectroscopy (EIS)Electron transfer attacking the lowest unoccupied molecular orbital (LUMO) of pollutants; selectively degrading pollutants that form coordination bonds with catalyst surfaces (e.g., carboxyl/hydroxyl-containing organics).[74]
Table 3. Summary of the g-C3N4-based photocatalysts for the removal of POPs.
Table 3. Summary of the g-C3N4-based photocatalysts for the removal of POPs.
CatalystsLight SourceCategory of PollutantPollutant ConcentrationCatalyst DosageDegradation
Efficiency (%)
Ref.
g-C3N4-Ni
nanocomposite
UV/SunlightPAHs6 mg/L4 mg/LUV:77% in 5 h
Sunlight: 55% in 5 h
[81]
g-C3N4-Ag-Cu-Ni nanocompositeUV/SunlightPAHs2 mg/L2 mg/LUV: 67% in 5 h
Sunlight: 57% in 5 h
[82]
Fe/g-C3N4350 W Xe lamp (λ > 420 nm)Phenol20 mg/L1 g/L (H2O2  =  8.0 mM)100% in 50 min[83]
ZnNbO/g-CN500 W Xe lamp2,4-DCP10 mg/L0.4 g/L95.7% in 180 min[84]
AD-CQDs/g-C3N4sunlight2,4-DCP10 mg/L0.05 g/L100% in 90 min[85]
g-CN/CoFeO@GOSonocatalytic (50 W)Pyrene5 mg/L, 10 mg/L0.04 g/L92.3% and 86.7% in 120 min[86]
P-CN-NB300 W Xe lamp (420 nm cut-off filter)HBA1 mg/L0.5 g/L77.3% in 120 min[87]
Pd/FA-PCN300 W Xe lamp
(400 nm cut-off filter)
PCBs1 mg/L0.5 g/L100% in 140 min[88]
TEA-CN-30300 W Xe lamp (400 nm cut-off filter)Atrazine1 mg/L0.3 g/L90% in 60 min[89]
AgCl@pg-C3N4300 W Xe lamp (λ > 420 nm)Atrazine100 mg/L0.8 g/L99% in 60 min[90]
4NrGO/g−g PSCNVisible light4-NP15 mg/L1 g/L70.55% in 60 min[91]
Table 4. Summary of the g-C3N4 -based photocatalysts for the removal of EDCs.
Table 4. Summary of the g-C3N4 -based photocatalysts for the removal of EDCs.
CatalystsLight SourceCategory of PollutantPollutant
Concentration
Catalyst DosageDegradation
Efficiency (%)
Ref.
CN-BP300 W Xe lamp
(420 nm cut-off filter)
BPA0.3 g/L1 g/L100% in 35 min[101]
CN-S300 W Xe lamp
(400 and 800 nm filters)
BPA/DBP5 mg/L1 g/L96%/58% in 120 min[102]
OPCN300 W Xe lamp (420 nm ≤ λ  ≤  780 nm).BPA20 mg/L1 g/L99% in 55 min[103]
MoS2/g-C3N4500 W Xe lamp
(λ ≥ 420 nm)
BPA10 mg/L0.5 g/L96% in 150 min[104]
Bt-OA-CN300 W Xe lamp
(UV cut-off filter)
BPA10 mg/L0.6 g/L100% in 150 min[105]
AgCl/Ag3PO4/
g-C3N4
300 W metal-halide lamp
(UV cut-off filter, λ < 400 nm)
Methylparaben 20 mg/L0.5/L100% in 30 min[106]
GCN-500LED (λex max = 417 nm)Paraben4.68 mg/L1 g/L100% in 20 min[107]
O3+/g-C3N4UV(365 nm, TL 6 W BLB)Paraben1 mg/L0.5 g/L95% in 15 min[108]
O-MCN500 W Xe lamp
(λ > 400 nm cut-off filter)
BPA10 mg/L40 mg/L97% in 180 min[109]
Table 5. Summary of the g-C3N4-based photocatalysts for the removal of antibiotics.
Table 5. Summary of the g-C3N4-based photocatalysts for the removal of antibiotics.
CatalystsLight SourceCategory of PollutantPollutant
Concentration
Catalyst DosageDegradation
Efficiency (%)
Ref.
NC MCN300 W Xe lamp
(400 < λ < 800 nm)
TC15 mg/L1 g/L100% in 30 min[118]
BiOCl/g-C3N4300 W Xe lampTC20 mg/L0.1 g/L97.1% in 60 min[119]
LaFeO3/g-C3N4/BiFeO3300 W-Xe arc lamp
with filter
CIP10 mg/L0.4 g/L98.6% in 60 min[120]
Co-pCNVisible lightOTC20 mg/L0.3 g/L75.7% in 40 min[121]
g-C3N4/TiO2150 W tungsten lampCIP10 mg/L1 mg/L95% in 60 min[122]
RGO@ g-C3N4/BiVO4500 W halogen lampCIP/AMX10 mg/L1 g/L84.3% and 91.9% in 3 h[123]
O-gCNPMSOTC5 mg/L0.5 g/L63.7% in 60 min[124]
(Nv, Os)-CNVisible lightSZO20 mg/L0.2 g/L75% in 90 min[73]
g-C3N4@Ser-PMO100 W white lampOFL20 mg/L1 g/L99% in 90 min[125]
RCN300 W X lamp
(λ ≥ 420 nm)
OFX10 mg/L1 g/L100% in 35 min[126]
NCN300 W Xe lampENR20 mg/L1 g/L97.1% in 4 h[127]
Table 6. Summary of the g-C3N4-based photocatalysts for the removal of MPs.
Table 6. Summary of the g-C3N4-based photocatalysts for the removal of MPs.
CatalystsLight SourceCategory of PollutantPollutant ConcentrationCatalyst DosageDegradation
Efficiency (%)
Ref.
MC-70Two 50 W UV lampsPolyaniline100 mg/L1 g/L97% in 7 d[133]
OSCNxenon lamp (68.0 mW∙cm2) PE/PLA300 μm0.04 g/L44.1% ± 3.59 and 53.3% ± 3.93% in 8 d[134]
NCN0.48UV (365 nm, TL 6 W BLB)Paraben750 mg/L1 g/L43.1% in 150 h[127]
30%WO3/g-C3N4300 W xenon lamp (cutoff filter at 420 nm)PET500 mg/L2 g/LH2 evolution (14.21 mM)[131]
2 wt%CoP/CN300 W xenon lamp (cutoff filter at 420 nm)PET5000 mg/L0.48 g/LH2 evolution (1.3 mmol/g)[135]
Table 7. Summary of the degradation performance, cyclic stability, and metal leaching risks of g-C3N4-based catalysts for ECs.
Table 7. Summary of the degradation performance, cyclic stability, and metal leaching risks of g-C3N4-based catalysts for ECs.
CatalystsCategory of PollutantNumber of CyclesDegradation
Efficiency (Before)
Degradation
Efficiency (After)
Metal Leaching
Risk
Ref.
Fe/g-C3N4Phenol598%88%Fe[83]
ZnNbO/g-CN2,4-DCP495.7%83.3%Zn and Nb[84]
g-CN/CoFeO@GOPyrene486.7%78%Co and Fe[86]
P-CN-NBHBA477.3%Stable/[87]
OPCNBPA499%Stable/[103]
MoS2/g-C3N4BPA496%StableMo[104]
BiOCl/g-C3N4TC497.1%87.6%Bi[119]
g-C3N4@Ser-PMOOFL499%80%/[125]
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Xu, D.; Cai, H.; Li, D.; Chen, F.; Han, S.; Chen, X.; Li, Z.; He, Z.; Chen, Z.; He, J.; et al. Recent Advances in Graphitic Carbon Nitride-Based Materials in the Photocatalytic Degradation of Emerging Contaminants. Inorganics 2025, 13, 319. https://doi.org/10.3390/inorganics13100319

AMA Style

Xu D, Cai H, Li D, Chen F, Han S, Chen X, Li Z, He Z, Chen Z, He J, et al. Recent Advances in Graphitic Carbon Nitride-Based Materials in the Photocatalytic Degradation of Emerging Contaminants. Inorganics. 2025; 13(10):319. https://doi.org/10.3390/inorganics13100319

Chicago/Turabian Style

Xu, Dan, Heshan Cai, Daguang Li, Feng Chen, Shuwen Han, Xiaojuan Chen, Zhenyi Li, Zebang He, Zhuhong Chen, Jiabao He, and et al. 2025. "Recent Advances in Graphitic Carbon Nitride-Based Materials in the Photocatalytic Degradation of Emerging Contaminants" Inorganics 13, no. 10: 319. https://doi.org/10.3390/inorganics13100319

APA Style

Xu, D., Cai, H., Li, D., Chen, F., Han, S., Chen, X., Li, Z., He, Z., Chen, Z., He, J., Huang, W., Tang, X., Wen, Y., & Feng, Y. (2025). Recent Advances in Graphitic Carbon Nitride-Based Materials in the Photocatalytic Degradation of Emerging Contaminants. Inorganics, 13(10), 319. https://doi.org/10.3390/inorganics13100319

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