Recent advances in graphitic carbon nitride as a catalyst for heterogeneous Fenton-like reactions

Graphitic carbon nitride (g-C₃N₄), an appealing metal-free polymer, has featured in extensive research in heterogeneous Fenton-like reactions owing to its advantages of stable chemical and thermal properties, ease of structural regulation and unique redox ability. However, there are still some gaps in the understanding of the mechanism and fate of g-C₃N₄ and its derivatives in heterogeneous Fenton reaction degradation of contaminants. This paper gives systematic emphasis to the development and progress of g-C₃N₄ and its composites as catalysts in heterogeneous Fenton-like reactions. The main synthesis strategies of g-C₃N₄ composites are discussed, including calcination, hydrothermal method and self-assembly method. Then, the key catalytic properties of g-C₃N₄ in Fenton-like applications, including anchoring nanoparticles, increasing specific surface area and exposed active surface sites, as well as regulating charge transfer reactions, are highlighted. Special emphasis is placed on its multifunctional role in heterogeneous Fenton-like reactions and the mechanisms involved in the activation of hydrogen peroxide, persulfates, and photocatalytic activation of persulfate. Lastly, the existing challenges and possible development direction of g-C₃N₄-coupling Fenton reactions are proposed. It is believed that this paper will bring useful information for the development of graphitic carbon nitride in both laboratory studies and practical applications.

Cu-doped g-C3N4 catalyst with stable Cu0 and Cu+ for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH

The development of new heterogeneous Cu-based solid catalysts for hydroxyl radical (∙OH) generation plays a crucial role in degradation of pollutants at neutral pH circumstance. In this work, a Cu-doped graphitic carbon nitride (g-C₃N₄) complex was synthesized in one-step pyrolysis process using copper chloride dihydrate and dicyandiamide as precursors. The results reveal that after Cu doping, the bulk structure of g-C₃N₄ was destroyed with fragmentary morphology formation. Besides, Cu⁰ and Cu⁺ were successfully embedded in g-C₃N₄ sheet. Moreover, amoxicillin (AMX) removal by heterogeneous electro-Fenton process was performed to evaluate the catalytic activity of the Cu-doped g-C₃N₄. 99.1% AMX removal efficiency was obtained after 60 min electrolysis under neutral pH condition when the current density was 12 mA cm² and the catalyst dosage was 0.3 g L^-1. Both Cu⁰ and Cu⁺ were stably retained in the Cu-doped g-C₃N₄ catalyst and AMX removal efficiency reached 91.1%, even after 5 cycles, manifesting the remarkable stability of Cu-doped g-C₃N₄. Also, Cu-doped g-C₃N₄ possessed excellent catalytic activities for AMX removal in various waterbodies. According to the catalytic mechanism analysis, the ∙OH was proved to be the primary reactive species for AMX removal in heterogeneous electro-Fenton process. Based on the identification of sixteen different intermediate products, the possible degradation pathways were proposed. This work provides a simple method to synthesize a Cu-based solid catalyst containing stable Cu⁰ and Cu ⁺ for degradation of pollutants in wastewater.

Construction of a novel Cu2(OH)3F/g-C3N4 heterojunction as a high-activity Fenton-like catalyst driven by visible light

Inhibiting the competitive effect of O₂ in copper-based Fenton reagents and improving the photogenerated electron–hole pair separation of g-C₃N₄ are the focus of current research.

Three-Dimensional CuO/TiO2 Hybrid Nanorod Arrays Prepared by Electrodeposition in AAO Membranes as an Excellent Fenton-Like Photocatalyst for Dye Degradation

Three-dimensional (3D) CuO/TiO₂ hybrid heterostructure nanorod arrays (NRs) with noble-metal-free composition, fabricated by template-assisted low-cost processes, were used as the photo-Fenton-like catalyst for dye degradation. Here, CuO NRs were deposited into anodic aluminum oxide templates by electrodeposition method annealed at various temperatures, followed by deposition of TiO₂ thin films through E-gun evaporation, resulting in the formation of CuO/TiO₂ p-n heterojunction. The distribution of elements and compositions of the CuO/TiO₂ p-n heterojunction were analyzed by EDS mapping and EELS profiles, respectively. In the presence of H₂O₂, CuO/TiO₂ hybrid structure performed more efficiently than CuO NRs for Rhodamine B degradation under the irradiation of 500-W mercury-xenon arc lamp. This study demonstrated the effect of length of CuO NRs, on the photo-degradation performance of CuO NRs as well as CuO/TiO₂ heterostructure. The optimized CuO/TiO₂ hybrid NR array structure exhibited the highest photo-degradation activity, and the mechanism and role of photo-Fenton acting as the catalyst in photo-degradation of dye was also investigated.

Sonochemical-assisted route for synthesis of spherical shaped holmium vanadate nanocatalyst for polluted waste water treatment

Solar photocatalytic process has been shown to be an energy effective and eco-friendly degradation of unwanted pollutants present in the industrial wastewater. The present study introduces the preparation and characterization of novel holmium vanadate (HoVO₄₎ nanostructures that fully used in the photodegradation efficiency of anionic and cationic organic pollutants. HoVO₄ synthesized via a sonochemical-assisted route and triethylenetetramine (TETA) was used as a capping and precipitation agent. The experiments were carried out under a probe as sonication source, and its power was adjusted in 30 W (9 kHz), 50 W (15 kHz) and 80 W (24 kHz) for different samples. The obtained nanostructures were characterized by surface analytical and spectral techniques includes XRD, FT-IR, SEM, TEM and UV-visible spectra measurements. The HR-SEM images reveal that HoVO₄ exists as a spindle-shape with spherical morphology together. HR-TEM images reveal that prepared catalyst has a spherical structure with uniform particle size. The results outline 67.6% elimination of methyl violet dye within 90 min under UV light in the presence of the optimal nano-sized formulation of 24.5 nm size. The prepared photocatalyst possesses high stability and reusability without appreciable loss of catalytic activity up to three runs.

Tumor Microenvironment-Responsive Cu2(OH)PO4 Nanocrystals for Selective and Controllable Radiosentization via the X-ray-Triggered Fenton-like Reaction

Traditional radiotherapy can induce injury to the normal tissue around the tumor, so the development of novel radiosensitizer with high selectivity and controllability that can lead to more effective and reliable radiotherapy is highly desirable. Herein, a new smart radiosensitizer based on Cu₂(OH)PO₄ nanocrystals that can simultaneously respond to endogenous stimulus (H₂O₂) and exogenous stimulus (X-ray) is reported. First, Cu₂(OH)PO₄ nanocrystals can generate Cu^I sites under X-ray irradiation through X-ray-induced photoelectron transfer process. Then, X-ray-triggered Cu^I sites serve as a catalyst for efficiently decomposing overexpressed H₂O₂ in the tumor microenvironment into highly toxic hydroxyl radical through the Fenton-like reaction, finally inducing apoptosis and necrosis of cancer cells. Meanwhile, this nonspontaneous Fenton-like reaction is greatly limited within normal tissues because of its oxygen-rich condition and insufficient H₂O₂ relative to tumor tissues. Thus, this strategy can ensure that the process of radiosentization can only be executed within hypoxic tumors but not in normal cells, resulting in the minimum damages to surrounding healthy tissues. As a result, the X-ray-triggered Fenton-like reaction via introducing nontoxic Cu₂(OH)PO₄ nanocrystals under the dual stimuli provides a more controllable and reliable activation approach to simultaneously enhance the radiotherapeutic efficacy and reduce side effects.

One-step in situ synthesis of BiOCl/(BiO)2CO3 composite photocatalysts with exposed high-energy {001} facets

BiOCl/(BiO)₂CO₃ composites with reactive exposed {001} facets have been synthesized by a one-step in situ solvothermal method. The synergistic effect of type-II band alignment and exposed high-energy facets enhances photocatalytic activity.

Cu2(OH)PO4/reduced graphene oxide nanocomposites for enhanced photocatalytic degradation of 2,4-dichlorophenol under infrared light irradiation

Sparked by the growing environmental crises, photocatalytic degradation of chlorophenols with inexhaustible solar energy is expected to be converted into actual applications. Here, we report the preparation of the nanocomposite of Cu₂(OH)PO₄ and reduced graphene oxide (Cu₂(OH)PO₄/rGO) through a one-step hydrothermal method and examined its infrared-light photocatalytic activity in the degradation of 2,4-dichlorophenol (2,4-DCP). As evidenced by the absorption spectra and the degradation of 2,4-DCP, Cu₂(OH)PO₄/rGO exhibited enhanced infrared light-driven photocatalytic activity compared to pure Cu₂(OH)PO₄ and was very stable even after repeated cycling. More importantly, the introduction of hydrogen peroxide (H₂O₂) could combine the photocatalytic and photo-Fenton effects into one reaction system and maximize the infrared light photocatalytic efficiency. Typically, the rate constant of Cu₂(OH)PO₄/rGO and H₂O₂ was more than 6.25 times higher than that of only Cu₂(OH)PO₄/rGO, and almost 10 times greater than the value for pure Cu₂(OH)PO₄. Further, a plausible mechanism for the enhanced photocatalytic properties of Cu₂(OH)PO₄/rGO has been discussed. These findings may help the development of novel hybrid photocatalysts with enhanced infrared light photocatalytic activity for applications in the treatment of chlorophenol-contaminated wastewater.

Nanocomposites of Cu₂(OH)PO₄ and rGO exhibit the maximized infrared light photocatalytic activity for the degradation of 2,4-DCP due to the combination of the photocatalytic and photo-Fenton effects into one reaction system.

Influence of precursor pH on the structure and photo-Fenton performance of Fe/hydrochar

Fe/hydrochar exhibited high visible light photo-Fenton activity because hydrochar accelerated the Fe³⁺/Fe²⁺ cycle at the catalyst/water interface.

One-pot preparation of Bi/Bi2WO6/reduced graphene oxide as a plasmonic photocatalyst with improved activity under visible light

The Bi/Bi₂WO₆/rGO nanocomposite for simultaneous RhB adsorption and photocatalysis was synthesized by a one-pot hydrothermal method.