Carbon Nitride Grafted Cobalt Complex (Co@npg-C3 N4 ) for Visible Light−Assisted Esterification of Aldehydes

Synergistic effect of novel Co-modified micro/nano geopolymers in a photo-PDS system

Persulfate activation is an efficient advanced oxidation process for water treatment. However, many catalyst materials make their preparation methods and raw materials very complicated and expensive while pursuing high-efficiency catalytic effects. In this research, a novel Co-modified micro/nano geopolymer (Co-MNG) material was prepared from solid waste using a mechanochemical method. The whole preparation process of Co-MNG is simple and time-saving, and most of its raw materials are solid waste. In addition, it has few adverse effects on the environment during preparation and use and has a good effect on PDS activation. Under dark conditions, 1 mg L^-1 of unloaded Co metal MNG material could degrade 20 mg L^-1 Rhodamine B solution by 79% in 60 min with 15 mM PDS, but the application of visible light could not enhance its effect. However, after adding 4 wt% of different Co-containing compounds, the prepared Co-MNG materials could improve their degradation effect under the same conditions, and it is more obvious under the condition of applying visible light. Among them, MNG-Co(NO₃)₂ could completely degrade RhB within 40 min under the application of visible light. ESR (electron spin resonance) tests showed that the MNG-Co(NO₃)₂ material could generate a variety of active radicals in a photo-PDS system, such as h⁺, ·OH, ·O₂^- and SO₄^-. Mechanistic research experiments showed that both visible light and Co-MNG materials can activate PDS to a certain extent, but when both exist at the same time, the material could effectively couple visible light and Co activation of PDS in a photo-PDS activation system to achieve synergistic degradation of pollutants in water.

Photocatalyzed oxidative cleavage of CC bond to carbonyl compounds by a recyclable homogeneous carbon nitride semiconductor/aqueous system

The development of methods based on direct oxidative cleavage of alkynes to carbonyls is an extremely challenging task. In this work, we describe a UV light-driven, potassium/sodium poly(heptazine imide) (K,Na-PHI)-catalyzed protocol for the selective oxidative cleavage of alkynes to acids under an O₂ atmosphere using water as a solvent. Various aromatic alkynes can be selectively cleaved to afford aromatic acids in good to high yield under clean, mild conditions. Mechanistic investigation indicates that the photogenerated hydroxyl radicals in situ act as green oxidation active species. Moreover, this protocol could be further developed as a sequential oxidative cleavage/esterification process for the preparation of aryl esters. Notably, the KNaPHI-II/water catalyst system could be used several times without significant loss of activity.

Photocatalytic activation and utilization of CO2 for N-formylation of amines promoted by a zinc(ii) phthalocyanine grafted on g-carbon nitride hybrid

Photochemical conversion of various amines to N-formamides using CO2 under ambient conditions with a hybrid photocatalyst composed of zinc phthalocyanine grafted to g-carbon nitride in high to excellent yields has been described.

Photochemical Activation of Aromatic Aldehydes: Synthesis of Amides, Hydroxamic Acids and Esters

A cheap, facile and metal-free photochemical protocol for the activation of aromatic aldehydes has been developed. Utilizing thioxanthen-9-one as the photocatalyst and cheap household lamps as the light source, a variety of aromatic aldehydes have been activated and subsequently converted in a one-pot reaction into amides, hydroxamic acids and esters in good to high yields. The applicability of this method was highlighted in the synthesis of Moclobemide, a drug against depression and social anxiety. Extended and detailed mechanistic studies have been conducted, in order to determine a plausible mechanism for the reaction.

Direct access to α-acyloxycarbonyl compounds and esters via oxidative esterification of aldehydes under visible light

An efficient synthesis of α-acyloxycarbonyl compounds and esters from aldehydes and α-bromocarbonyl compounds/benzyl bromide derivatives via photoredox catalysis has been developed.

Highly efficient conversion of the nitroarenes to amines at the interface of a ternary hybrid containing silver nanoparticles doped reduced graphene oxide/ graphitic carbon nitride under visible light

In this report, a ternary Ag-rGO/g-C₃N₄ hybrid was synthesized by a simple hydrothermal approach for the photocatalytic reduction of nitroarene compounds into their corresponding amines under visible light. Importantly, the present method did not require reducing agents, like hydrazine hydrate; instead methanol has been used as a source of electrons and protons for the photoreduction process. After grafting of Ag NPs, a significant enhancement in the efficiency of the rGO/g-C₃N₄ for the reduction of nitrobenzenes was observed. Under optimized experimental conditions, the conversion of nitrobenzene and yield of aniline were determined to be 99% and 98%, respectively under visible light illumination for 4 h. The nitrobenzene compounds bearing both electron donating and withdrawing groups were selectively converted into their corresponding aniline products without altering the functionality. The enhanced performance of the developed photocatalyst attributed to the effective separation of photoexcited electrons on the photocatalyst surface and their subsequent transfer for the reduction of nitrobenzene molecules.

C3N4-Photocatalyzed aerobic oxidative cleavage of CC bonds in alkynes with diazonium salts leading to two different aldehydes or esters in one pot

C₃N₄-Photocatalyzed oxidative cleavage of CC bonds in alkynes with diazonium salts to obtain two different aldehydes or esters.

Artificial Photosynthesis with Polymeric Carbon Nitride: When Meeting Metal Nanoparticles, Single Atoms, and Molecular Complexes

Artificial photosynthesis for solar water splitting and CO₂ reduction to produce hydrogen and hydrocarbon fuels has been considered as one of the most promising ways to solve increasingly serious energy and environmental problems. As a well-documented metal-free semiconductor, polymeric carbon nitride (PCN) has been widely used and intensively investigated for photocatalytic water splitting and CO₂ reduction, owing to its physicochemical stability, visible-light response, and facile synthesis. However, PCN as a photocatalyst still suffers from the fast recombination of electron-hole pairs and poor water redox reaction kinetics, greatly restricting its activity for artificial photosynthesis. Among the various modification approaches developed so far, decorating PCN with metals in different existences of nanoparticles, single atoms and molecular complexes, has been evidently very effective to overcome these limitations to improve photocatalytic performances. In this Review article, a systematic introduction to the state-of-the-art metal/PCN photocatalyst systems is given, with metals in versatility of nanoparticles, single atoms, and molecular complexes. Then, the recent processes of the metal/PCN photocatalyst systems in the applications of artificial photosynthesis, e.g., water splitting and CO₂ reduction, are reviewed. Finally, the remaining challenges and opportunities for the development of high efficiency metal/PCN photocatalyst systems are presented and prospected.

Noble Metal-Free Photocatalysts Consisting of Graphitic Carbon Nitride, Nickel Complex, and Nickel Oxide Nanoparticles for Efficient Hydrogen Generation

A facile and simple synthetic route is developed to prepare earth-abundant and noble metal-free hybrid photocatalysts, which are composed of graphitic carbon nitride (CN), nickel complex, and NiO _x nanoparticles. Bimolecular nucleophilic substitution reaction was employed to attach a nickel complex onto a graphitic CN framework through covalent bonds to support its high loading and dispersion. NiO _x nanoparticles were further incorporated into the catalysts to serve as a hole-transporting medium to improve the separation of photogenerated carriers for higher photocatalytic activity. Both yNiL/CN and yNiL/NiO _x/CN exhibit superb H₂ evolution activity. The optimum H₂ evolution rate of the binary photocatalysts yNiL/CN reaches 303.3 μmol·h^-1·g^-1, whereas that of the ternary photocatalysts yNiL/NiO _x/CN reaches 524.1 μmol·h^-1·g^-1, and the apparent quantum efficiency reaches 1.46% at 450 nm. This finding reveals that coordination of a nickel complex is significant in promoting photocatalytic performance, and the incorporation of NiO _x nanoparticles as a hole-transporting medium is beneficial for separation of the photogenerated charge carriers. The novel hybrid system offers a new horizon for designing transition-metal complex-modified graphitic CN as noble metal-free and highly active photocatalysts for efficient visible light-driven hydrogen generation.

Visible light-induced transformation of aldehydes to esters, carboxylic anhydrides and amides

A transition metal- and organophotocatalyst free synthesis of esters, carboxylic anhydrides and amides from aldehydes induced by visible-light has been reported.