Graphitic Carbon Nitride Quantum Dots (g-C3N4 QDs): From Chemistry to Applications

Since their emergence in 2014, graphitic carbon nitride quantum dots (g-C3N4 QDs) have attracted much interest from the scientific community due to their distinctive physicochemical features, including structural, morphological, electrochemical, and optoelectronic properties. Owing to their desirable characteristics, such as non-zero band gap, ability to be chemically functionalized or doped, possessing tunable properties, outstanding dispersibility in different media, and biocompatibility, g-C3N4 QDs have shown promise for photocatalysis, energy devices, sensing, bioimaging, solar cells, optoelectronics, among other applications. As these fields are rapidly evolving, it is very strenuous to pinpoint the emerging challenges of the g-C3N4 QDs development and application during the last decade, mainly due to the lack of critical reviews of the innovations in the g-C3N4 QDs synthesis pathways and domains of application. Herein, an extensive survey is conducted on the g-C3N4 QDs synthesis, characterization, and applications. Scenarios for the future development of g-C3N4 QDs and their potential applications are highlighted and discussed in detail. The provided critical section suggests a myriad of opportunities for g-C3N4 QDs, especially for their synthesis and functionalization, where a combination of eco-friendly/single step synthesis and chemical modification may be used to prepare g-C3N4 QDs with, for example, enhanced photoluminescence and production yields.

Insights into engineered graphitic carbon nitride quantum dots for hazardous contaminants degradation in wastewater

Increased environmental pollution is a critical issue that must be addressed. Photocatalytic, adsorption, and membrane filtration methods are suitable in environmental governance because of their high selectivity, low cost, environment-friendly nature, and excellent treatment efficiency. Graphitic carbon nitride (g-C₃N₄) quantum dots (QDs) have been considered as photocatalysts, adsorbents, and membrane materials for wastewater treatments, owing to their stability, adsorption capacity, photochemical properties, and low toxicity and cost. This review summarizes g-C₃N₄ QD synthesis techniques, operating parameters affecting the removal performance in the treatment process, modification effects with other semiconductors, and benefits and drawbacks of g-C₃N₄ QD-based materials. Furthermore, this review discusses the practical applications of g-C₃N₄ QDs as adsorbents, photocatalysts, and membrane materials for organic and inorganic contaminant treatments and their value-added product formation potential. Modified g-C₃N₄ QD-based material adsorbents, photocatalysts, and membranes present potentially applicable effects, such as removal of most waterborne contaminants. Excellent results were obtained for the reduction of methyl orange, bisphenol A, tetracycline, ciprofloxacin, phenol, rhodamine B, E. coli, and Hg. Overall, this paper provides comprehensive background on g-C₃N₄ QD-based materials and their diverse applications in wastewater treatment, and it presents a foundation for the enhancement of similar unique materials in the future.

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

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.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Fabrication of ternary AgBr/BiPO4/g-C3N4 heterostructure with dual Z-scheme and its visible light photocatalytic activity for Reactive Blue 19

A plasmonic photocatalyst of AgBr/BiPO₄/g-C₃N₄ was prepared. X-ray powder diffraction, Scanning electron microscope, Transmission electron microscopy, Fourier infrared spectroscopy, Ultraviolet Visible diffuse reflectance spectroscopy and photoluminescence emission spectra have been employed to determine the structure, morphology and optical property of the as-prepared AgBr/BiPO₄/g-C₃N₄ composite and analysis the reasons for improving photocatalytic efficiency. The optimal doping ratio of AgBr was 10 wt% by degrading 20 mg/L of Reactive Blue 19 (RB19) under visible light (λ > 420 nm), and 10 wt%AgBr/BiPO₄/g-C₃N₄ degraded 20 mg/L of RB19 to 2.59% at 40 min, which is ascribed to synergistic effects at the interface of AgBr, BiPO₄ and g-C₃N₄. The effect of catalyst dosage, initial concentration and initial pH of RB19 solution on photocatalytic efficiency was investigated. Four cycles of experiments were conducted. Finally, through the trapping experiment, we found that the main active factor for degrading RB19 in the photocatalytic process is O₂^-. The possible photocatalytic mechanism of AgBr/BiPO₄/g-C₃N₄ was discussed in connection with the synergistic effect of Ag and active substances at the AgBr/BiPO₄/g-C₃N₄ interface.

In situ fabrication of I-doped Bi2O2CO3/g-C3N4 heterojunctions for enhanced photodegradation activity under visible light

Iodine-doped Bi₂O₂CO₃/g-C₃N₄ heterojunctions consisting of graphitic carbon nitride (g-C₃N₄) and iodine-doped bismutite (Bi₂O₂CO₃) components were successfully in situ synthesized by a one-pot hydrothermal method. Characterizations such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) demonstrated iodine was favorably doped into the Bi₂O₂CO₃ component, of which the {001} facets grew in situ from {002} facets of g-C₃N₄ for the heterostructure construction of I-doped Bi₂O₂CO₃/g-C₃N₄ (IB/CN). The photocatalytic activity of catalysts was evaluated by the degradation efficiency of 1,5-dihydroxynaphthalene under visible light. 1.5-IB/CN with a reasonable iodine doping amount (Bi: I molar ratio = 1.0: 1.5) exhibited the superior photodegradation performance compared to Bi₂O₂CO₃, achieving an 85.5% removal ratio after 100 min illumination. The enhanced activity of 1.5-IB/CN was attributed to both of the heterostructure that promoted the separation of photoinduced carriers and iodine doping that tuned the bandgap for sufficient visible-light harvesting. The degradation intermediates of 1,5-dihydroxynaphthalene in the system were determined and its possible photodegradation pathway was proposed in detail. This study provides a rational approach for enhancing the visible-light catalytic activity of wide-bandgap Bi₂O₂CO₃, and reveals a new perspective on the removal mechanism of organic pollutants.

Metal-free photocatalysts for hydrogen evolution

This article provides a comprehensive review of the latest progress, challenges and recommended future research related to metal-free photocatalysts for hydrogen productionviawater-splitting.

Metal-free C60/CNTs/g-C3N4 ternary heterostructures: synthesis and enhanced visible-light-driven photocatalytic performance

A metal-free C60/CNTs/g-C3N4 nanoheterostructure with excellent visible-light photocatalysis for rhodamine B (Rh B) degradation has been reported. Via a convenient low-temperature solution-phase method, g-C3N4 nanosheets can serve as substrate for dispersion of C60/CNTs. The loading of C60/CNTs onto g-C3N4 nanosheets surfaces significantly enhanced visible-light-driven photocatalytic activity of g-C3N4 catalyst, for oxidation of organic pollutant (Rh B, 100%). Excellent photocatalytic properties of C60/CNTs/g-C3N4 can be predominantly attributed to the intimate interfacial contact among constructing compounds, increased specific surface area and enhanced light adsorption efficiency resulted from C60/CNTs carbon materials. Particularly, the synergistic heterostructure interaction remarkably hinders the electron-hole pairs recombination, giving rise to significantly enhanced photocatalytic performance of C60/CNTs/g-C3N4 in comparison with other counterparts.

Recent Advances of Graphitic Carbon Nitride-Based Structures and Applications in Catalyst, Sensing, Imaging, and LEDs

The graphitic carbon nitride (g-C3N4) which is a two-dimensional conjugated polymer has drawn broad interdisciplinary attention as a low-cost, metal-free, and visible-light-responsive photocatalyst in the area of environmental remediation. The g-C3N4-based materials have excellent electronic band structures, electron-rich properties, basic surface functionalities, high physicochemical stabilities and are "earth-abundant." This review summarizes the latest progress related to the design and construction of g-C3N4-based materials and their applications including catalysis, sensing, imaging, and white-light-emitting diodes. An outlook on possible further developments in g-C3N4-based research for emerging properties and applications is also included.

Synthesis of Monometallic (Au and Pd) and Bimetallic (AuPd) Nanoparticles Using Carbon Nitride (C3N4) Quantum Dots via the Photochemical Route for Nitrophenol Reduction

In this study, we report the synthesis of monometallic (Au and Pd) and bimetallic (AuPd) nanoparticles (NPs) using graphitic carbon nitride (g-C₃N₄) quantum dots (QDs) and photochemical routes. Eliminating the necessity of any extra stabilizer or reducing agent, the photochemical reactions have been carried out using a UV light source of 365 nm where C₃N₄ QD itself functions as a suitable stabilizer as well as a reducing agent. The g-C₃N₄ QDs are excited upon irradiation with UV light and produce photogenerated electrons, which further facilitate the reduction of metal ions. The successful formation of Au, Pd, and AuPd alloy nanoparticles is evidenced by UV-vis, powder X-ray diffraction, X-ray photon spectroscopy, and energy-dispersive spectroscopy techniques. The morphology and distribution of metal nanoparticles over the C₃N₄ QD surface has been systematically investigated by high-resolution transmission electron microscopy (HRTEM) and SAED analysis. To explore the catalytic activity of the as-prepared samples, the reduction reaction of 4-nitrophenol with excellent performance is also investigated. It is noteworthy that the synthesis of both monometallic and bimetallic NPs can be accomplished by using a very small amount of g-C₃N₄, which can be used as a promising photoreducing material as well as a stabilizer for the synthesis of various metal nanoparticles.

Synthesis and characterization of BiPO4/g-C3N4 nanocomposites with significantly enhanced visible-light photocatalytic activity for benzene degradation

BiPO₄/g-C₃N₄ nanocomposites were fabricated by a hydrothermal method including calcination and showed high photocatalytic activity under visible light.

Photoelectrochemical performance of g-C3N4/Au/BiPO4Z-scheme composites to improve the mineralization property under solar light

g-C₃N₄/Au/BiPO₄as a hierarchical Z-scheme system was prepared through three steps at different reaction temperatures, using thiourea as a precursor to synthesize g-C₃N₄.

Quantum dots derived from two-dimensional materials and their applications for catalysis and energy

Equipped with a wide range of extraordinary and tailorable properties, quantum dots derived from two-dimensional materials promise a spectrum of novel applications including catalysis and energy.

A review of BiPO4, a highly efficient oxyacid-type photocatalyst, used for environmental applications

This review presents the recent progress on the oxyacid-type photocatalyst, BiPO₄, which possesses excellent UV-activity for environmental applications.

Enhancing visible light photocatalytic activity of BiOBr/rod-like BiPO4 through a heterojunction by a two-step method

Visible light driven BiOBr/rod-like BiPO₄ composites with different BiOBr to BiPO₄ molar ratios were fabricated via a facile deposition-precipitation method.

AgBr nanoparticles decorated BiPO4 microrod: a novel p–n heterojunction with enhanced photocatalytic activities

AgBr nanoparticles were decorated on the surface of BiPO₄ micro-rod to fabricate a novel p–n heterojunction photocatalyst via a facile deposition–precipitation method.