Construction of g-C3N4/TiO2 nanotube arrays Z-scheme heterojunction to improve visible light catalytic activity

Boosted photocatalytic performance of cobalt ferrite anchored g-C3N4 nanocomposite toward various emerging environmental hazardous pollutants degradation: insights into stability and Z-scheme mechanism

In this study, a highly efficient CoFe2O4-anchored g-C3N4 nanocomposite with Z-scheme photocatalyst was developed by facile calcination and hydrothermal technique. To evaluate the crystalline structure, sample surface morphology, elemental compositions, and charge conductivity of the as-synthesized catalysts by various characterization techniques. The high interfacial contact of CoFe2O4 nanoparticles (NPs) with g-C3N4 nanosheets reduced the optical bandgap from 2.67 to 2.5 eV, which improved the charge carrier separation and transfer. The photo-degradation of methylene blue (MB) and rhodamine B (Rh B) aqueous pollutant suspension under visible-light influence was used to investigate the photocatalytic degradation activity of the efficient CoFe2O4/g-C3N4 composite catalyst. The heterostructured spinel CoFe2O4 anchored g-C3N4 photocatalysts (PCs) with Z-scheme show better photocatalytic degradation performance for both organic dyes. Meanwhile, the efficiency of aqueous MB and Rh B degradation in 120 and 100 min under visible-light could be up to 91.1% and 73.7%, which is greater than pristine g-C3N4 and CoFe2O4 catalysts. The recycling stability test showed no significant changes in the photo-degradation activity after four repeated cycles. Thus, this work provides an efficient tactic for the construction of highly efficient magnetic PCs for the removal of hazardous pollutants in the aquatic environment.

Hydrothermal Synthesis of Heterostructured g-C3N4/Ag-TiO2 Nanocomposites for Enhanced Photocatalytic Degradation of Organic Pollutants

In this study, heterostructured g-C3N4/Ag-TiO2 nanocomposites were successfully fabricated using an easily accessible hydrothermal route. Various analytical tools were employed to investigate the surface morphology, crystal structure, specific surface area, and optical properties of as-synthesized samples. XRD and TEM characterization results provided evidence of the successful fabrication of the ternary g-C3N4/Ag-TiO2 heterostructured nanocomposite. The heterostructured g-C3N4/Ag-TiO2 nanocomposite exhibited the best degradation efficiency of 98.04% against rhodamine B (RhB) within 180 min under visible LED light irradiation. The g-C3N4/Ag-TiO2 nanocomposite exhibited an apparent reaction rate constant 13.16, 4.7, and 1.33 times higher than that of TiO2, Ag-TiO2, and g-C3N4, respectively. The g-C3N4/Ag-TiO2 ternary composite demonstrated higher photocatalytic activity than pristine TiO2 and binary Ag-TiO2 photocatalysts for the degradation of RhB under visible LED light irradiation. The improved photocatalytic performance of the g-C3N4/Ag-TiO2 nanocomposite can be attributed to the formation of an excellent heterostructure between TiO2 and g-C3N4 as well as the incorporation of Ag nanoparticles, which promoted efficient charge carrier separation and transfer and suppressed the rate of recombination. Therefore, this study presents the development of heterostructured g-C3N4/Ag-TiO2 nanocomposites that exhibit excellent photocatalytic performance for the efficient degradation of harmful organic pollutants in wastewater, making them promising candidates for environmental remediation.

Development of Sulfur-Doped Graphitic Carbon Nitride for Hydrogen Evolution under Visible-Light Irradiation

Developing eco-friendly strategies to produce green fuel has attracted continuous and extensive attention. In this study, a novel gas-templating method was developed to prepare 2D porous S-doped g-C₃N₄ photocatalyst through simultaneous pyrolysis of urea (main g-C₃N₄ precursor) and ammonium sulfate (sulfur source and structure promoter). Different content of ammonium sulfate was examined to find the optimal synthesis conditions and to investigate the property-governed activity. The physicochemical properties of the obtained photocatalysts were analyzed by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), scanning transmission electron microscopy (STEM), specific surface area (BET) measurement, ultraviolet-visible light diffuse reflectance spectroscopy (UV/vis DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and reversed double-beam photo-acoustic spectroscopy (RDB-PAS). The as-prepared S-doped g-C₃N₄ photocatalysts were applied for photocatalytic H₂ evolution under vis irradiation. The condition-dependent activity was probed to achieve the best photocatalytic performance. It was demonstrated that ammonium sulfate played a crucial role to achieve concurrently 2D morphology, controlled nanostructure, and S-doping of g-C₃N₄ in a one-pot process. The 2D nanoporous S-doped g-C₃N₄ of crumpled lamellar-like structure with large specific surface area (73.8 m² g^-1) and improved electron-hole separation showed a remarkable H₂ generation rate, which was almost one order in magnitude higher than that of pristine g-C₃N₄. It has been found that though all properties are crucial for the overall photocatalytic performance, efficient doping is probably a key factor for high photocatalytic activity. Moreover, the photocatalysts exhibit significant stability during recycling. Accordingly, a significant potential of S-doped g-C₃N₄ has been revealed for practical use under natural solar radiation.

Photocatalytic Activity of TiO2/g-C3N4 Nanocomposites for Removal of Monochlorophenols from Water

This research employed g-C₃N₄ nanosheets in the hydrothermal synthesis of TiO₂/g-C₃N₄ hybrid photocatalysts. The TiO₂/g-C₃N₄ heterojunctions, well-dispersed TiO₂ nanoparticles on the g-C₃N₄ nanosheets, are effective photocatalysts for the degradation of monochlorophenols (MCPs: 2-CP, 3-CP, and 4-CP) which are prominent water contaminants. The removal efficiency of 2-CP and 4-CP reached 87% and 64%, respectively, after treatment of 25 ppm CP solutions with the photocatalyst (40TiO₂/g-C₃N₄, 1 g/L) and irradiation with UV-Vis light. Treatment of CP solutions with g-C₃N₄ nanosheets or TiO₂ alone in conjunction with irradiation gave removal efficiencies lower than 50%, which suggests the two act synergically to enhance the photocatalytic activity of the 40TiO₂/g-C₃N₄ nanocomposite. Superoxide and hydroxyl radicals are key active species produced during CP photodegradation. In addition, the observed nitrogen and Ti³⁺ defects and oxygen vacancies in the TiO₂/g-C₃N₄ nanocomposites may improve the light-harvesting ability of the composite and assist preventing rapid electron-hole recombination on the surface, enhancing the photocatalytic performance. In addition, interfacial interactions between the MCPs (low polarity) and thermally exfoliated carbon nitride in the TiO₂/g-C₃N₄ nanocomposites may also enhance MCP degradation.

In-situ electrodeposition synthesis of Z-scheme rGO/g-C3N4/TNAs photoelectrodes and its degradation mechanism for oxytetracycline in dual-chamber photoelectrocatalytic system

The dual-chamber photoelectrocatalytic (PEC) system possess advantages in the degradation efficiency and processing cost of organic contaminants. In this study, TiO₂ nanotube arrays modified by rGO and g-C₃N₄ (rGO/g-C₃N₄/TNAs) photoelectrodes were successfully prepared. The surface micromorphology, chemical structure, crystal structure, and basic element composition of rGO/g-C₃N₄/TNAs photoelectrodes were studied by SEM, FTIR, XRD, Raman, and XPS. UV-vis absorption, photoluminescence (PL) spectra, and photoelectrochemical (PECH) tests were used to explore the photoelectrochemical characteristics of rGO/g-C₃N₄/TNAs photoelectrodes. Under simulated sunlight illumination, the dual-chamber PEC system with external bias voltage was used to investigate the degradation of oxytetracycline (OTC) on rGO/g-C₃N₄/TNAs photoelectrodes. The results showed that rGO and g-C₃N₄ were successfully loaded on TNAs, and the separation efficiency of electrons and holes at rGO/g-C₃N₄/TNAs photoelectrodes was improved. The light absorption range of rGO/g-C₃N₄/TNAs photoelectrodes extends to the visible light region and has better light absorption performance. Compared with the photocatalytic process, when 1.2 V bias voltage was applied, the degradation efficiency of OTC in anode and cathode chambers in PEC were increased by 3.28% and 44.01% within 60 min, respectively. In addition, the anode and cathode chambers have different degradation effects on OTC. Both the external bias voltage and initial pH have significant effects in cathode chamber, but have little effect in photoanode chamber. The fluorescence excitation-emission matrix spectra and liquid chromatography-tandem mass spectrometry showed that there were different intermediates in the degradation process of OTC. This study indicated that for the dual-chamber PEC system, rGO/g-C₃N₄/TNAs photoelectrodes exhibited excellent photocatalytic performance and have potential application prospects in water environmental remediation.

Identification of Active Species in Photodegradation of Aqueous Imidacloprid over g-C3N4/TiO2 Nanocomposites

In this work, g-C3N4/TiO2 composites were fabricated through a hydrothermal method for the efficient photocatalytic degradation of imidacloprid (IMI) pesticide. The composites were fabricated at varying loading of sonochemically exfoliated g-C3N4 (denoted as CNS). Complementary characterization results indicate that the heterojunction between the CNS and TiO2 formed. Among the composites, the 0.5CNS/TiO2 material gave the highest photocatalytic activity (93% IMI removal efficiency) under UV-Vis light irradiation, which was 2.2 times over the pristine g-C3N4. The high photocatalytic activity of the g-C3N4/TiO2 composites could be ascribed to the band gap energy reduction and suppression of photo-induced charge carrier recombination on both TiO2 and CNS surfaces. In addition, it was found that the active species involved in the photodegradation process are OH• and holes, and a possible mechanism was proposed. The g-C3N4/TiO2 photocatalysts exhibited stable photocatalytic performance after regeneration, which shows that g-C3N4/TiO2 is a promising material for the photodegradation of imidacloprid pesticide in wastewater.

Construction of a double heterojunction between graphite carbon nitride and anatase TiO2 with co-exposed (101) and (001) faces for enhanced photocatalytic degradation

This study aimed to promote the separation of photogenerated carriers and improve the redox performance of graphite carbon nitride (g-C₃N₄) by synthesizing a double-heterojunction-structure photocatalyst, g-C₃N₄/(101)-(001)-TiO₂, through the solvothermal method. The photocatalyst comprised a Z-system formed from g-C₃N₄ and the (101) plane of TiO₂, as well as a surface heterojunction formed from the (101) and (001) planes of TiO₂. The results showed that g-C₃N₄/(101)-(001)-TiO₂ had strong photocatalytic activity and stable performance in the photodegradation of paracetamol. The active species ·O₂⁻ and ·OH were found to play important roles in the photocatalytic degradation of paracetamol through a radical-quenching experiment. The charge-transfer mechanism was also described in detail. Overall, this work provided a new strategy for the Z-system heterojunction and opened up the application of this structure in the degradation of organic pollutants.

A double-heterojunction-structure photocatalyst g-C₃N₄/(101)-(001)-TiO₂ with Z-system and surface heterojunction, was synthesized, which can effectively promote the separation of photogenerated e⁻–h⁺ pairs and the degradation of organic pollutants.

Biomedical application of graphitic carbon nitrides: tissue depositionin vivo, induction of reactive oxygen species (ROS) and cell viability in tumor cells

The urgency for new materials in oncology is immediate. In this study we have developed the g-C₃N₄, a graphitic-like structure formed by periodically linked tris-s-triazine units. The g-C₃N₄has been synthesized by a simple and fast thermal process. XRD has shown the formation of the crystalline sheet with a compacted structure. The graphite-like structure and the functional groups have been shown by Raman and FTIR spectroscopy. TEM image and AFM revealed the porous composed of five or six C-N layers stacked. DRS and Photoluminescence analyses confirmed the structure with band gap of 2.87 eV and emission band at 448 nm in different wavelengths excitation conditions. The biological results showed inhibitory effect on cancer cell lines and non-toxic effect in normal cell lines. To the best of our knowledge, this is the first work demonstrating the cytotoxic effects of 2D g-C₃N₄in a cancer cell line, without any external or synergistic influence. The biodistribution/tissue accumulation showed that g-C₃N₄present a tendency to accumulation on the lung in the first 2 h, but after 24 h the profile of the biodistribution change and it is found mainly in the liver. Thus, 2D-g-C₃N₄showed great potential for the treatment of several cancer types.

g-C3N4 Sensitized by an Indoline Dye for Photocatalytic H2 Evolution

Protonated g-C3N4 (pCN) formed by treating bulk g-C3N4 with an aqueous HCl solution was modified with D149 dye, i.e., 5-[[4[4-(2,2-diphenylethenyl) phenyl]-1,2,3,3a,4,8b-hexahydrocyclopent[b]indol-7-yl] methylene]-2-(3-ethyl-4-oxo-2-thioxo-5-thiazolidinylidene)-4-oxo-thiazolidin-2-ylidenerhodanine, for photocatalytic water splitting (using Pt as a co-catalyst). The D149/pCN-Pt composite showed a much higher rate (2138.2 µmol·h−1·g−1) of H2 production than pCN-Pt (657.0 µmol·h−1·g−1). Through relevant characterization, the significantly high activity of D149/pCN-Pt was linked to improved absorption of visible light, accelerated electron transfer, and more efficient separation of charge carriers. The presence of both D149 and Pt was found to be important for these factors. A mechanism was proposed.

Photoelectrocatalytic degradation of p-chloronitrobenzene by g-C3N4/TiO2 nanotube arrays photoelectrodes under visible light irradiation

As a typical refractory pollutant, p-chloronitrobenzene (p-CNB) from industrial wastewater poses a serious threat to the aquatic environment safety and human health. The photoelectrocatalytic (PEC) technology is regarded as a promising and cleaner approach for p-CNB removal. Therefore, the graphitic carbon nitride (g-C₃N₄) modified TiO₂ nanotube arrays (g-C₃N₄/TNAs) were prepared as the photoelectrodes for p-CNB degradation. The PEC degradation efficiency for p-CNB by g-C₃N₄/TNAs (0.00484 min^-1) was much higher than that by bare TNAs (0.00135 min^-1) under visible light. The g-C₃N₄/TNAs photoelectrodes exhibited excellent visible-light response, efficient charges separation and high redox potentials of electron/hole, which was favorable for p-CNB degradation. The radical scavenging experiments indicated that both reductive electrons and oxidized species (holes and ·OH) played crucial roles simultaneously during the dechlorination process, whereas the mineralization of p-CNB mainly depended on the photo-generated holes and ·OH. The degradation pathways of p-CNB were proposed through GC/MS spectra. The acute toxicity, bioaccumulation factor and mutagenicity of identified intermediates were reduced after PEC degradation by g-C₃N₄/TNAs photoelectrodes. The Z-scheme g-C₃N₄/TNAs provided an efficient approach for simultaneous dechlorination and mineralization of refractory pollutants.