Effect of processing temperature on structure and photocatalytic properties of g-C3N4

Highly nitrogen-enriched mesoporous carbon nitride materials with 2-dimensional (2-D) (2D-meso-CN) and 3-dimensional (3-D) mesostructures (3D-meso-CN) were synthesized using mesoporous silica as a hard template and cyanamide as a precursor via the incipient wetness process without using any solvent. The materials were characterized by small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) for the mesostructure analysis, N2 adsorption–desorption isotherms for surface area and pore size distribution, and X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FT-IR) spectroscopy for the composition analysis of frameworks. The mesoporous carbon nitride replicas have graphitic-like stacking of carbon nitride sheets in mesopore walls. The N/C ratio of the mesoporous carbon nitride replicas is 1.13 after the carbonization at 550 °C for 3 h. 2D-meso-CN and 3D-meso-CN have the BET surface area of 361 and 343 m2 g−1, large pore volume of 0.50 and 0.67 cm3 g−1, and pore diameter of 27.8 A (for 2D-meso-CN), 24.5 and 80.3 A (for 3D-meso-CN), respectively. It was found that the 3D-meso-CN has higher capacity of hydrogen uptake of 0.25 wt% than the pure mesoporous carbon FDU-15 (0.16 wt%) at 50 bar under room temperature (298 K).

Facile synthesis of mesoporous carbon nitrides using the incipient wetness method and the application as hydrogen adsorbent

Synthesis and characterization of microporous carbon nitride

Graphitic carbon nitride (g-C3N4) has emerged as one of the most promising visible light active photocatalysts for NOx removal. Due to its low efficiency in bulk form though, many methods have been applied in order to improve the optical properties and photocatalytic activity. Among them, exfoliation via chemical and thermal treatment appears to be very effective and easy to perform. In this work, g-C3N4 was exfoliated by high-yield chemical and thermal treatment. A thorough comparative investigation was performed, revealing successful exfoliation of g-C3N4 and significantly enhanced visible light photocatalytic activity. Both methods led to high pore volume and specific surface area. It was established that chemical exfoliation resulted in wider band gap with more positive VB edge in comparison to thermal exfoliation. Furthermore, increased superoxide radical formation and reactivity of photogenerated electrons was demonstrated by EPR measurements in the case of chemical exfoliation. The chemically exfoliated g-C3N4 showed superior photocatalytic performance in NOx removal under visible light irradiation. This outcome was ascribed to the increased superoxide radical formation, the favorable band gap edges and porosity of the materials.

Chemical vs thermal exfoliation of g-C3N4 for NOx removal under visible light irradiation

Conventional synthesis methods of functional materials are usually time- and energy consuming and contribute to the accumulation of waste solvents. An alternative solution is the use of environmentally friendly recipes such as mechanochemical synthesis, which may be employed for large-scale production of materials. Mechanochemistry has been applied in various areas, such as metallurgy, mineral processing, construction and synthesis of organic compounds, and currently it is experiencing a renaissance because of its successful implementation for the synthesis of diverse organic, inorganic and organic–inorganic hybrid nanomaterials. Here mechanochemical synthesis of highly porous materials is reviewed with special emphasis on novel sorbents. Mechanochemically-assisted methods are well suited for the preparation of highly porous carbons (such as lignin- or tannin-derived carbons), metal–organic frameworks (e.g., MOF-5, MIL-101 and U-67) or covalent organic frameworks with specific surface areas up to 3500 m2 g−1. Recently, ball milling was also utilized for the synthesis of ordered coordination polymers and perfectly ordered mesoporous carbons. Nowadays, mechanochemistry has become a powerful and quite universal method for the preparation of various materials. Hence, there is a need for a review summarizing the current accomplishments in this field. Most of the mechanochemically obtained porous materials reported so far have been designed for adsorption, catalysis and energy storage related applications.

Mechanochemical synthesis of highly porous materials

Under the conditions of high-energy ball milling, the reaction of C 3 N 3 Cl 3 and Li 3 N has progressed in a high-efficient way. Carbon nitride with the atomic ratio of 1.23–1.30 for N to C that is very similar to the stoichiometry of C 3 N 4 has been obtained. Moreover, XRD reveals that with the prolonging of the milling time, the products can be soon transformed to comparatively well-crystallized graphitic carbon nitride (g-C 3 N 4 ). SEM investigations show the products have the glassy morphology with different dimension from micron to nano scales. The XPS analysis shows the products have the presumable element compositions and the chemical bond state.

Chengchang Jia

Papers

A facile mechanochemical way to prepare g-C3N4

WITHDRAWN: A facile mechanochemical way to prepare g-C3N4