Nitrogen-doped graphene as metal free basic catalyst for coupling reactions

From grape bagasse to graphene-like porous carbon nanosheets for CO2 capture

Graphene-based materials have increasingly attracted attention in recent years. It is a material is recognized worldwide due to its numerous applications in several sectors. However, graphene production involves several challenges: scalability, high costs, and high-quality production. This study synthesized graphene-like porous carbon nanosheets (GPCNs) through a thermochemical process under a nitrogen atmosphere using grape bagasse as a precursor. Three temperatures (700, 800, and 900 ºC) of the pyrolysis process were studied. Chemical graphitization and activation were used to form high-specific surface area materials: FeCl3.6H2O(aq) and ZnCl2(s) in a simultaneous activation-graphitization (SAG) method. The materials obtained (GPCN700, GPCN800, and GPCN900) were compared to previously produced chars (C700, C800, and C900). A high specific surface area and total pore volume were obtained for GPCN materials, and GPCN900 presented the highest values: 1062.7 m2g-1 and 0.635 cm3 g-1, respectively. The GPCN and char materials were classified as mesoporous and applied as adsorbents for CO2(g). The GPCN800 presented the best CO2(g) adsorbent, with a CO2(g) adsorption capacity of 168.71 mg g-1.

Facile preparation of graphene nitride by irradiating MHz ultrasound

The present study aimed at developing a simple sonochemical method to prepare graphene nitride from the mixture of graphite and aqueous ammonia solution. Ultrasound of 1.6 MHz was irradiated to the sample in a fabricated sonoreactor at predetermined ultrasonic power and duration. The one-pot method succeeded in the preparation of graphene nitride. The generation was proven by XPS analysis in finding N1S peak in the spectrum. Detail analysis of N1s peak suggested that the major nitrogen species was pyrrolic type. Furthermore, the presence of CO bond proved the oxidation by OH radical. The reaction product had the value of N/C as high as 0.08, which is comparable to reported values for ultrasonic preparation of graphene nitride. The fact indicates that the significance of chemical effects of MHz range ultrasound, and the finding of the simple preparation method will accelerate practical application of graphene nitride.

High C2-C4 selectivity in CO2 hydrogenation by particle size control of Co-Fe alloy nanoparticles wrapped on N-doped graphitic carbon

A catalyst based on first-row Fe and Co with a record of 51% selectivity to C₂-C₄ hydrocarbons at 36% CO₂ conversion is disclosed. The factors responsible for the C₂₊ selectivity are a narrow Co-Fe particle size distribution of about 10 nm and embedment in N-doped graphitic matrix. These hydrogenation catalysts convert CO₂ into C₂-C₄ hydrocarbons, including ethane, propane, n-butane, ethylene and propylene together with methane, CO. Selectivity varies depending on the catalyst, CO₂ conversion, and the operation conditions. Operating with an H₂/CO₂ ratio of 4 at 300°C and pressure on 5 bar, a remarkable combined 30% of ethylene and propylene at 34% CO₂ conversion was achieved. The present results open the way to develop an economically attractive process for CO₂ reduction leading to products of higher added value and longer life cycles with a substantial selectivity.

•

Co-Fe nanoparticles wrapped on N-doped graphitic carbon catalyzes CO₂ hydrogenation

•

Co-Fe@(N)Carbon affords 51% selectivity to C₂-C₄ hydrocarbons at 36% CO₂ conversion

•

At H₂/CO₂ 4, 300°C and 5 bar, a combined 30% of CH₂ = CH₂ and MeCH = CH₂ is achieved

•

Particle size (10 nm) and N-doping are crucial to achieve high C₂₊ selectivity

Recent advances in metal-free heteroatom-doped carbon heterogonous catalysts

The development of cost-effective, efficient, and novel catalytic systems is always an important topic for heterogeneous catalysis from academia and industrial points of view. Heteroatom-doped carbon materials have gained more and more attention as effective heterogeneous catalysts to replace metal-based catalysts, because of their excellent physicochemical properties, outstanding structure characteristics, environmental compatibility, low cost, inexhaustible resources, and low energy consumption. Doping of heteroatoms can tailor the properties of carbons for different utilizations of interest. In comparison to pure carbon catalysts, these catalysts demonstrate superior catalytic activity in many organic reactions. This review highlights the most recent progress in synthetic strategies to fabricate metal-free heteroatom-doped carbon catalysts including single and multiple heteroatom-doped carbons and the catalytic applications of these fascinating materials in various organic transformations such as oxidation, hydrogenation, hydrochlorination, dehydrogenation, etc.

Recent advances in metal-free heteroatom-doped carbon heterogeneous catalysts including the preparation methods and their catalytic applications in various organic reactions have been reported.

Porous Graphitic Carbons Containing Nitrogen by Structuration of Chitosan with Pluronic P123

Using Pluronic P123 as a structure-directing agent and chitosan as a carbon precursor, different porous carbons with remarkable morphologies such as orthohedra or spheres with diametrically opposite holes are obtained. These particles of micrometric size are constituted by the stacking of thin sheets (60 nm) that become increasingly bent in the opposite sense, concave in the upper and convex in the bottom hemispheres, as the chitosan proportion increases. TEM images, after dispersion of the particles by sonication, show that besides micrometric graphene sheets, the material is constituted by nanometric onion-like carbons. The morphology and structure of these porous carbons can be explained based on the ability of Pluronic P123 to undergo self-assembly in aqueous solution due to its amphoteric nature and the filmogenic properties of chitosan to coat Pluronic P123 nanoobjects undergoing structuration and becoming transformed into nitrogen-doped graphitic carbons. XPS analysis reveals the presence of nitrogen in their composition. These porous carbons exhibit a significant CO2 adsorption capacity of above 3 mmol g-1 under 100 kPa at 273 K attributable to their large specific surface area, ultraporosity, and the presence of basic N sites. In addition, the presence of dopant elements in the graphitic carbons opening the gap is responsible for the photocatalytic activity for H2 generation in the presence of sacrificial electron donors, reaching a H2 production of 63 μmol g-1 in 24 h.

Design, Fabrication, and Mechanism of Nitrogen-Doped Graphene-Based Photocatalyst

Solving energy and environmental problems through solar-driven photocatalysis is an attractive and challenging topic. Hence, various types of photocatalysts have been developed successively to address the demands of photocatalysis. Graphene-based materials have elicited considerable attention since the discovery of graphene. As a derivative of graphene, nitrogen-doped graphene (NG) particularly stands out. Nitrogen atoms can break the undifferentiated structure of graphene and open the bandgap while endowing graphene with an uneven electron density distribution. Therefore, NG retains nearly all the advantages of original graphene and is equipped with several novel properties, ensuring infinite possibilities for NG-based photocatalysis. This review introduces the atomic and band structures of NG, summarizes in situ and ex situ synthesis methods, highlights the mechanism and advantages of NG in photocatalysis, and outlines its applications in different photocatalysis directions (primarily hydrogen production, CO₂ reduction, pollutant degradation, and as photoactive ingredient). Lastly, the central challenges and possible improvements of NG-based photocatalysis in the future are presented. This study is expected to learn from the past and achieve progress toward the future for NG-based photocatalysis.

Guanine-Derived Porous Carbonaceous Materials: Towards C1 N1

Herein, the basic nature of noble covalent, sp2-conjugated materials prepared via direct condensation of guanine in the presence of an inorganic salt melt as structure directing agent was studied. At temperatures below 700 °C stable and more basic addition products with at C/N ratio of 1 (C1 N1 adducts) and with rather uniform micropore sizes were formed. Carbonization at higher temperatures broke the structural motif, and N-doped carbons with 11 wt % and surface areas of 1900 m2  g-1 were obtained. The capability for CO2 sorption and catalytic activity of the materials depended of both their basicity and their pore morphology. The optimization of the synthetic parameters led to very active (100 % conversion) and highly selective (99 % selectivity) heterogeneous base catalysts, as exemplified with the model Knoevenagel condensation of benzaldehyde with malononitrile. The high stability upon oxidation of these covalent materials and their basicity open new perspectives in heterogeneous organocatalysis.

Graphene-based carbocatalysts for carbon-carbon bond formation

Organic transformations are usually catalyzed by metal-based catalysts. In contrast, metal-free catalysts have attracted considerable attention from the viewpoint of sustainability and safety. Among the studies in metal-free catalysis, graphene-based materials have been introduced in the reactions that are usually catalyzed by transition metal catalysts. This review covers the literature (up to the beginning of April 2020) on the use of graphene and its derivatives as carbocatalysts for C-C bond-forming reactions, which are one of the fundamental reactions in organic syntheses. Besides, mechanistic studies are included for the rational understanding of the catalysis. Graphene has significant potential in the field of metal-free catalysis because of the fine-tunable potential of the structure, high stability and durability, and no metal contamination, making it a next-generation candidate material in catalysis.