Organocatalysis with carbon nitrides

Carbon nitrides, a distinguished class of metal-free catalytic materials, have presented a good potential for chemical transformations and are expected to become prominent materials for organocatalysis. This is largely possible due to their low cost, exceptional thermal and chemical stability, non-toxicity, ease of functionalization, porosity development, etc. Especially, the carbon nitrides with increased porosity and nitrogen contents are more versatile than their bulk counterparts for catalysis. These N-rich carbon nitrides are discussed in the earlier parts of the review. Later, the review highlights the role of such carbon nitride materials for the various organic catalytic reactions including Knoevenagel condensation, oxidation, hydrogenation, esterification, transesterification, cycloaddition, and hydrolysis. The recently emerging concepts in carbon nitride-based organocatalysis have been given special attention. In each of the sections, the structure-property relationship of the materials was discussed and related to their catalysis action. Relevant comparisons with other catalytic materials are also discussed to realize their real potential value. The perspective, challenges, and future directions are also discussed. The overall objective of this review is to provide up-to-date information on new developments in carbon nitride-based organic catalysis reactions that could see them rising as prominent catalytic materials in the future.

Synthesis of g-C3N4 Derived from Different Precursors for Photodegradation of Sulfamethazine under Visible Light

In this study, a series of g-C3N4 nanosheets were prepared by various thermal oxidative etching times from four different precursors (urea, melamine, dicyandiamide and thiourea). The physicochemical properties of these g-C3N4 nanosheets were analyzed in detail using scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence emission spectra, Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis and ultraviolet-visible diffuse reflectance. The results revealed that the g-C3N4 nanosheets obtained a thinner layer thickness and larger specific surface area, with an extension of thermal oxidative etching time. Meanwhile, sulfamethazine (SMZ), one of the most widely used sulfonamides, was used to evaluate the photocatalyst activity of the g-C3N4 nanosheets prepared in this study. Compared to other g-C3N4 nanosheets, urea-derived g-C3N4 nanosheets under 330 min thermal oxidative etching showed the highest photocatalytic activity for SMZ under visible light. In conclusion, our study provides detailed insights into the synthesis and characterization of g-C3N4 nanosheets prepared from various precursors and highlights the importance of thermal oxidative etching time in determining the photocatalytic activity of these materials.

A rod-like melem with high fluorescence quantum yield for sensitive detection of reduced glutathione

A rod-like melem with high fluorescence quantum yield of 71.3 % was prepared in this work to enhance the chemiluminescence (CL) intensity of Na₂SO₃-Ce (Ⅳ) system. The results showed that the CL intensity of Na₂SO₃-Ce (Ⅳ) system could be increased by 350 times based on chemiluminescence resonance energy transfer (CRET) mechanism. Furthermore, a CL sensor based on Na₂SO₃-Ce (Ⅳ)-melem system was designed to detect reduced glutathione (G-SH). It was indicated that the CL sensor exhibited excellent G-SH detection performance with a detection limit of 0.065 nM and a linear range from 0.32 to 650 μM. This study applied melem for CL detection and provided a new way for the detection of G-SH.

Facile Synthesis of g-C3N4/TiO2/Hectorite Z-Scheme Composite and Its Visible Photocatalytic Degradation of Rhodamine B

A novel g-C3N4/TiO2/hectorite Z-scheme composites with oxygen vacancy (Vo) defects and Ti3+ were synthesized by so-gel method and high temperature solid phase reaction. This composite exhibited high visible photo-catalytic degradation of rhodamine B (RhB). The apparent rate constant of g-C3N4/TiO2/hectorite was 0.01705 min-1, which is approximately 5.38 and 4.88 times that of P25 and g-C3N4, respectively. The enhancement of photo-catalytic efficiency of the composites can be attributed to the great light harvesting ability, high specific surface area and effective separation of electrons(e-) and holes(h+). The F element from Hectorite causes the formation of Vo and Ti3+ in TiO2, making it responsive to visible light. The effective separation of e- and h+ mainly results from Z-scheme transfer of photo-produced electrons in g-C3N4/TiO2 interface. The composites can be easily recycled and the degradation rate of the RhB still reached 84% after five cycles, indicating its good reusability.

Metal free alkene hydrogenation by B-doped graphitic carbon nitride

Metal free hydrogenation of styrene under mild conditions employing boron-doped carbon nitride catalysts is reported.

Noble metal-free V2O5/g-C3N4 composites for selective oxidation of olefins using hydrogen peroxide as an oxidant

Vanadium pentoxide modified graphitic carbon nitride (V2O5/g-C3N4) composites were prepared through a method of wet impregnation and calcination. The obtained samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, photoluminescence, electron spin resonance and N2 adsorption/desorption isotherms. Oxidation of olefins was employed to evaluate the catalytic and photocatalytic activities of the prepared V2O5/g-C3N4 composites. Different weight ratios (1%, 2%, 3%, 4% and 5%) of V2O5 loaded composites were prepared and a 3% loaded composite was found to show optimal catalytic performance for the reaction. This noble metal-free catalyst showed excellent performance in the oxidation of styrene to benzaldehyde with high conversion (98.7%) and selectivity (88.4%) under visible light irradiation. A plausible mechanism was proposed for this oxidation reaction with hydrogen peroxide as an oxidant. Other styrene substrates were also selectively transformed to their corresponding aldehydes with high yields (up to 92%), using such a noble metal-free catalytic system.