Facile synthesis of graphitic C3N4 nanoporous-tube with high enhancement of visible-light photocatalytic activity

Synthesis of novel CuNb2O6/g-C3N4 binary photocatalyst towards efficient visible light reduction of Cr (VI) and dyes degradation for environmental remediation

The further development of an efficient and sustainable water treatment requires the development of a very active and controllable photocatalyst. The heterojunction is a promising site where the activity of such a photocatalyst can be enhanced. Organic dyes have become a severe concern in recent years owing to their significant presence in wastewater. Hexavalent Chromium (Cr (VI)) is a potential carcinogen also exhibiting great persistence in wastewater. So, a low-waste, high-performance materials is required to eliminate organic dyes and Cr (VI) from wastewater. In this study, CNO/g-CN (CuNb₂O₆/g-C₃N₄) photocatalyst synthesized via co-precipitation, followed by calcination which were characterized using physiochemical and photo-electrochemical approaches to identify their structural, photochemical and optical traits. The uniqueness of the synthesized photocatalyst is due to both its efficient photo-reduction of Cr (VI) and photo-degradation of Rhodamine B (RhB), Methylene Blue (MB) and Methyl Orange (MO) under visible light. The CNO/g-CN composite with 30% CNO heterojunctions exhibited the highest photocatalytic activity with Cr (VI) 92.80% photoreduction and efficiency degradation for RhB, MB, MO of 99.6%, 98.50%, 99.0%, respectively, with constant rate (k). This efficient photocatalytic activity is attributed to the lower recombination rate of electron-hole pairs. Free radical trapping experiments showed that ^•O₂^- and h⁺ play an important role in the photodegradation. The study, therefore, opens an alternative route in the synthesis of very efficient binary photocatalysts for application in environmental remediation.

Facile synthesis of bimodal macroporous g-C3N4/SnO2 nanohybrids with enhanced photocatalytic activity

It is of vital importance to construct highly interconnected, macroporous photocatalyst to improve its efficiency and applicability in solar energy conversion and environment remediation. Graphitic-like C₃N₄ (g-C₃N₄), as an analogy to two-dimensional (2D) graphene, is highly identified as a visible-light-responsive polymeric semiconductor. Moreover, the feasibility of g-C₃N₄ in making porous structures has been well established. However, the preparation of macroporous g-C₃N₄ with abundant porous networks and exposure surface, still constitutes a difficulty. To solve it, we report a first facile preparation of bimodal macroporous g-C₃N₄ hybrids with abundant in-plane holes, which is simply enabled by in-situ modification through thermally treating the mixture of thiourea and SnCl₄ (pore modifier) after rotary evaporation. For one hand, the formed in-plane macropores endow the g-C₃N₄ system with plentiful active sites and short, cross-plane diffusion channels that can greatly speed up mass transport and transfer. For another, the heterojunctions founded between g-C₃N₄ and SnO₂ consolidate the electron transfer reaction to greatly reduce the recombination probability. As a consequence, the resulted macroporous g-C₃N₄/SnO₂ nanohybrid had a high specific surface area (SSA) of 44.3 m²/g that was quite comparable to most nano/mesoporous g-C₃N₄ reported. The interconnected porous network also rendered a highly intensified light absorption by strengthening the light penetration. Together with the improved mass transport and electron transfer, the macroporous g-C₃N₄/SnO₂ hybrid exhibited about 2.4-fold increment in the photoactivity compared with pure g-C₃N₄. Additionally, the recyclability of such hybrid could be guaranteed after eight successive uses.

Scalable nanohybrids of graphitic carbon nitride and layered NiCo hydroxide for high supercapacitive performance

The limited number of edge nitrogen atoms and low intrinsic electrical conductivity hinder the supercapacitive energy storage applications of the nitrogen-rich graphitic carbon nitride (g-C₃N₄). In this study, a novel graphitic carbon nitride/NiCo-layered double hydroxide (CNLDH), a two-dimensional nanohybrid, is prepared by a simple hydrothermal synthesis. The homogeneous interpolation of g-C₃N₄ nanosheets into NiCo LDH stacked nanosheets effectively increases the overall performances of the g-C₃N₄/NiCo LDH nanohybrid. The improved morphology of the nanohybrid electrode upon the addition of g-C₃N₄ to the NiCo LDH yields a specific capacity of 183.43 mA h g⁻¹ in 6 M KOH at 1 A g⁻¹, higher than those of bare g-C₃N₄ (20.89 mA h g⁻¹) and NiCo LDH (95.92 mA h g⁻¹) electrodes. The excellent supercapacitive performance of the CNLDH nanohybrid is complemented by its low internal resistance, excellent rate capability, and large cycling lifetime. Furthermore, the hybrid supercapacitor is assembled using CNLDH 0.1 as a positive electrode and activated carbon (AC) as a negative electrode. The hybrid supercapacitor device of CNLDH 0.1//AC shows the maximum specific capacity of 37.44 mA h g⁻¹ at 1 A g⁻¹ with remarkable energy density, power density and good cycling performance. This confirms that the CNLDH 0.1 nanohybrid is an excellent electrode material for supercapacitor applications.

A two dimensional CNLDH 0.1 nanohybrid supercapacitor electrode prepared by simple hydrothermal hybridization of g-C₃N₄ and NiCO LDH shows the maximum specific capacity of 183.43 mA h g⁻¹ with remarkable electrochemical performance.

Template-free synthesis of salmon pink tube-shaped structure carbon nitride with enhanced visible light photocatalytic activity

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion. Herein, an effective strategy, hydrothermal-calcination, for synthesizing extremely active carbon nitride (salmon pink) from a low-cost precursor melamine, is reported. The salmon pink carbon nitride with tube-shaped structure significantly enhanced response to visible light, improved efficiency of charge separation and remarkably enhanced efficiency of methyl orange (MO) degradation than bulk g-C₃N₄ (light orange). The M-10-200-24-600 composite possessed the most wonderful ability towards MO degradation irradiated by visible light, which could achieve a highest degradation efficiency of 84% within 120 min. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar-energy conversion.

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion.

A Metal-Free Carbon-Based Catalyst: An Overview and Directions for Future Research

Metal-free carbon porous materials (CPMs) have gained the intensive attention of scientists and technologists because of their potential applications, ranging from catalysis to energy storage. Various simple and facile strategies are proposed for the preparation of CPMs with well-controlled sizes, shapes, and modifications on the surface. The extraordinary tenability of the pore structure, the environmental acceptability, the unique surface and the corrosion resistance properties allow them to be suitable materials for a large panel of catalysis applications. This review briefly outlines the different signs of progresses made towards synthesizing CPMs, and their properties, including catalytic efficiency, stability, and recyclability. Finally, we make a comparison of their catalytic performances with other nanocomposites, and we provide an outlook on the expected developments in the relevant research works.