g-C3N4 Samples Research Articles

Enhanced visible-light-driven photocatalytic performance of porous graphitic carbon nitride

In this study, a series of porous graphitic carbon nitride (g-C3N4) materials were fabricated through a direct pyrolysis of protonated melamine by nitric acid solution. These as-prepared porous samples were characterized by a collection of analytical techniques. It was found that a proper concentration of nitric acid solution involved facilitated to generate samples in tube-like morphology with numerous pores, identified with X-ray diffraction patterns, FT-IR spectra, SEM, TEM, and BET measurements. These g-C3N4 samples were subjected to photocatalytic degradation of dye Rhodamine B (RhB) in aqueous under visible-light irradiation. Under identical conditions, those porous g-C3N4 samples showed significantly improved catalytic performance in comparison with the sample prepared without the introduction of nitric acid. In particularly, the best candidate, sample M1:1, showed an apparent reaction rate nearly 6.2 times that of the unmodified counterpart. The enhancement of photocatalytic performance could be attributed to the favorable porous structure with the enlarged specific surface area and the suitable electronic structure as well. In addition, ESR measurements were conducted for the sake of proposing a photocatalytic degradation mechanism.

In Situ Co-Crystallization for Fabrication of g-C3N4/Bi5O7I Heterojunction for Enhanced Visible-Light Photocatalysis

We developed for the first time an in situ co-crystallization route for fabrication of a heterojunctional photocatalyst g-C3N4/Bi5O7I by adopting melamine and BiOI as coprecursors. This synthetic method enables intimate interfacial interaction with chemical bonding between g-C3N4 and Bi5O7I, which is beneficial for charge transfer at the interface. The photocatalysis properties of g-C3N4/Bi5O7I composites were studied by photodegradation of Rhodamine B (RhB) and phenol and generation of transient photocurrent with illumination of visible-light (λ > 420 nm), The results revealed that the g-C3N4/Bi5O7I composite shows enhanced photocatalytic reactivity compared to the pristine g-C3N4 and Bi5O7I samples. Investigations on the behaviors of charge carriers via electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra suggests that the g-C3N4/Bi5O7I heterojunctional structure constructed of the in situ co-thermolysis approach is responsible for the efficient separation and transfer of photogenerated electrons (e–) and holes (h+), thus giving rise to the higher photocatalytic activity. The present work opens a new avenue for manipulation of high-performance semiconductor heterojunction for photocatalytic and photoelectrochemical application.

Enhanced visible-light-driven photocatalytic removal of NO: Effect on layer distortion on g-C3N4 by H2 heating

We report a simple strategy for realizing the tunable structure distortion of graphitic carbon nitride (g-C3N4) layers by H2 post calcination to improve the intrinsic electronic structure and the photocatalytic performances of g-C3N4 samples. In comparison with the O2 or N2 post treatment, the H2-modified g-C3N4 develops new optical absorption above 460nm and enhances photocatalytic activity for NO removal. The combined characterization results reveal that H2 heating induced the structure distortion of g-C3N4 layers is originated from the creation of amino groups within the structure and generation of the strong hydrogen bonding interactions between layers. The distorted structure allows n–π* electron transitions in g-C3N4 to increase visible-light absorption. The structure distortion also enables more electrons to be available for initiating the photocatalytic reaction and the separation of photogenerated charge carriers in g-C3N4. This work provides a simple strategy for realizing the tunable structure distortion of g-C3N4 layers to adjust its electronic structure and photocatalysis.

Improvement in photocatalytic H2 evolution over g-C3N4 prepared from protonated melamine

Porous g-C3N4 (pm-g-C3N4) samples were prepared by sintering protonated melamine. Photocatalytic activities for H2 production over the g-C3N4 samples were evaluated under visible-light irradiation. Specific surface areas and condensation degree of the g-C3N4 samples prepared from protonated melamine turn larger as the calcination temperatures increase (400°C, 450°C, 500°C, 550°C, and 580°C for 1h). Also, their bandgaps are narrowed and PL peak red shifts, and thus their photocatalytic activities are enhanced. Compared with the reference g-C3N4 samples synthesized by sintering melamine without any protonation (m-g-C3N4), the pm-g-C3N4 samples exhibit better photocatalytic performances, owing to larger specific surface area, less recombination of photogenerated carriers and higher degree of condensation. By optimizing the preparation parameters and the amount of Pt cocatalyst, the highest hydrogen evolution rate of 417μmolh−1g−1 was achieved over the pm-g-C3N4 samples synthesized at 550°C for 2h, when irradiated by 300-W Xe lamp with a cutoff filter (λ≥420nm).

Complete oxidation of acetaldehyde over a composite photocatalyst of graphitic carbon nitride and tungsten(VI) oxide under visible-light irradiation

Graphitic carbon nitride (g-C3N4) was prepared by heating melamine and then its specific surface area was enlarged by hydrothermal treatment in aqueous sodium hydroxide solution. The g-C3N4 samples were blended with tungsten(VI) oxide (WO3) using a planetary mill in order to improve photocatalytic activity. The composite photocatalyst with optimized amounts of these contents showed higher photocatalytic activity for decomposition of acetaldehyde under visible-light irradiation than did original samples. From the results, we concluded that the composite photocatalyst utilizes both high oxidation ability of WO3 and high reduction ability of g-C3N4 by Z-scheme charge transfer.

Controllable synthesis of nanotube-type graphitic C3N4 and their visible-light photocatalytic and fluorescent properties

This paper describes a facile and generally feasible method to synthesize nanotube-type graphitic carbon nitride (g-C3N4) by directly heating melamine packed in an appropriate compact degree which plays a crucial role in the formation process of g-C3N4. This approach has several advantages: (i) no templates or extra organics are involved; (ii) high industrial feasibility; (iii) low cost; and (iv) general applicability. The as-synthesized g-C3N4 samples show intense fluorescence with a photoluminescent (PL) peak at 460 nm indicating their potential applications as a blue light fluorescence material. They also exhibit excellent visible-light photocatalytic activity compared to a reference P25 photocatalyst. The method reported may open up new opportunities for further studies as well as practical applications of g-C3N4 nanotubes in fields such as light-emitting devices, gas storage and photocatalysis.

In Situ Construction of g-C3N4/g-C3N4 Metal-Free Heterojunction for Enhanced Visible-Light Photocatalysis

The photocatalytic performance of the star photocatalyst g-C3N4 was restricted by the low efficiency because of the fast charge recombination. The present work developed a facile in situ method to construct g-C3N4/g-C3N4 metal-free isotype heterojunction with molecular composite precursors with the aim to greatly promote the charge separation. Considering the fact that g-C3N4 samples prepared from urea and thiourea separately have different band structure, the molecular composite precursors of urea and thiourea were treated simultaneously under the same thermal conditions, in situ creating a novel layered g-C3N4/g-C3N4 metal-free heterojunction (g-g CN heterojunction). This synthesis method is facile, economic, and environmentally benign using easily available earth-abundant green precursors. The confirmation of isotype g-g CN heterojunction was based on XRD, HRTEM, valence band XPS, ns-level PL, photocurrent, and EIS measurement. Upon visible-light irradiation, the photogenerated electrons transfer from g-C3N4 (thiourea) to g-C3N4 (urea) driven by the conduction band offset of 0.10 eV, whereas the photogenerated holes transfer from g-C3N4 (urea) to g-C3N4 (thiourea) driven by the valence band offset of 0.40 eV. The potential difference between the two g-C3N4 components in the heterojunction is the main driving force for efficient charge separation and transfer. For the removal of NO in air, the g-g CN heterojunction exhibited significantly enhanced visible light photocatalytic activity over g-C3N4 alone and physical mixture of g-C3N4 samples. The enhanced photocatalytic performance of g-g CN isotype heterojunction can be directly ascribed to efficient charge separation and transfer across the heterojunction interface as well as prolonged lifetime of charge carriers. This work demonstrated that rational design and construction of isotype heterojunction could open up a new avenue for the development of new efficient visible-light photocatalysts.

Tailoring the Mesoporous Texture of Graphitic Carbon Nitride

Recently, graphitic carbon nitride (g-C3N4) materials have received a great attention from many researchers due to their various roles as a visible light harvesting photocatalyst, metal-free catalyst, reactive template, nitrogen source of nitridation reaction, etc. g-C3N4 could be prepared by temperature-induced polymerization of cyanamide or melamine. In this study, we report a preparation of mesoporous graphitic carbon nitrides with tailored porous texture including pore size, and specific surface area from cyanamide and colloidal silica nanoparticles (Ludox). At first, cyanamide-silica nanocomposites were prepared by mixing colloidal silica with different size in the range of 7-22 nm and cyanamide, followed by evaporating the solvent in the resulting mixture. Mesoporous g-C3N4 samples were prepared by calcining cyanamide-silica nanocomposite at 550 degrees C for 4 hrs and removing the silica nanoparticles by using ammonium hydrogen fluoride. The formation of g-C3N4 was confirmed by the sharp (002) peak (d = 3.25 A) of graphitic interlayer stacking, and the broad (100) peak (d = 6.86 A) of in-plane repeating unit in the X-ray diffraction patterns. According to N2 adsorption-desorption analysis, the pore size of mesoporous carbon nitrides was similar to the size of colloidal silica used as hard template (7-22 nm). The specific surface area of mesoporous g-C3N4 could be tailored in the range of 189 m2/g-288 m2/g.

Engineering the nanoarchitecture and texture of polymeric carbon nitride semiconductor for enhanced visible light photocatalytic activity

In order to develop g-C3N4 for better visible light photocatalysis, g-C3N4 nanoarchitectures was synthesized by direct pyrolysis of cheap urea at 550°C and engineered through the variation of pyrolysis time. By prolonging the pyrolysis time, the crystallinity of the resulted sample was enhanced, the thickness and size of the layers were reduced, the surface area and pore volume were significantly enlarged, and the band structure was modified. Especially for urea treated for 4h, the obtained g-C3N4 nanosheets possessed high surface area (288m2/g) due to the reduced layer thickness and the improved porous structure. A layer exfoliation and splitting mechanism was proposed to explain the gradual reduction of layer thickness and size of g-C3N4 nanoarchitectures with increased pyrolysis time. The as-synthesized g-C3N4 samples were applied for photocatalytic removal of gaseous NO and aqueous RhB under visible light irradiation. It was found that the activity of g-C3N4 was gradually improved as the pyrolysis time was prolonged from 0min to 240min. The enhanced crystallinity, reduced layer thickness, high surface area, large pore volume, enlarged band gap, and reduced number of defects were responsible for the activity enhancement of g-C3N4 sample treated for a longer time. As the precursor urea is very cheap and the synthesis method is facile template-free, the as-synthesized g-C3N4 nanoscale sheets could provide an efficient visible light driven photocatalyst for large-scale applications.

A new and environmentally benign precursor for the synthesis of mesoporous g-C3N4 with tunable surface area

An environmentally benign and widely available precursor, guanidinium chloride, has been employed, for the first time, for the synthesis of mesoporous g-C3N4 materials via a nanocasting method using 12 nm colloid silica as a hard template. A series of mesoporous g-C3N4 (C3N4-G-r) samples with bimodal pore systems (1.8 and 13.4 nm), and high surface areas (146-215 m(2) g(-1)) along with large pore volumes (0.57-0.84 m(3) g(-1)), depending on the amount of templates, have been successfully prepared. Several techniques including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and CHN elemental analysis have confirmed the formation of graphitic structures and extremely high nitrogen content of the synthesized C3N4-G-r materials. In Friedel-Crafts acylation reaction between hexanoyl chloride and benzene, C3N4-G-r samples, especially C3N4-G-1.0 with a large surface area of 215 m(2) g(-1), have demonstrated high catalytic conversions, affording a maximum yield of 86% of n-hexanophenone in 4 h at 80 °C.