A review on g-C3N4-based photocatalysts

and Applications of Fullerenes, Carbon Dots, Nanotubes, Graphene, Nanodiamonds, and Combined Superstructures Vasilios Georgakilas,† Jason A. Perman,‡ Jiri Tucek,‡ and Radek Zboril*,‡ †Material Science Department, University of Patras, 26504 Rio Patras, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University in Olomouc, 17 listopadu 1192/12, 771 46 Olomouc, Czech Republic

Broad family of carbon nanoallotropes: classification, chemistry, and applications of fullerenes, carbon dots, nanotubes, graphene, nanodiamonds, and combined superstructures.

Graphene-based materials exhibit remarkable electronic, optical, and mechanical properties, which has resulted in both high scientific interest and huge potential for a variety of applications. Furthermore, the family of graphene-based materials is growing because of developments in preparation methods. Raman spectroscopy is a versatile tool to identify and characterize the chemical and physical properties of these materials, both at the laboratory and mass-production scale. This technique is so important that most of the papers published concerning these materials contain at least one Raman spectrum. Thus, here, we systematically review the developments in Raman spectroscopy of graphene-based materials from both fundamental research and practical (i.e., device applications) perspectives. We describe the essential Raman scattering processes of the entire first- and second-order modes in intrinsic graphene. Furthermore, the shear, layer-breathing, G and 2D modes of multilayer graphene with different stacking orders are discussed. Techniques to determine the number of graphene layers, to probe resonance Raman spectra of monolayer and multilayer graphenes and to obtain Raman images of graphene-based materials are also presented. The extensive capabilities of Raman spectroscopy for the investigation of the fundamental properties of graphene under external perturbations are described, which have also been extended to other graphene-based materials, such as graphene quantum dots, carbon dots, graphene oxide, nanoribbons, chemical vapor deposition-grown and SiC epitaxially grown graphene flakes, composites, and graphene-based van der Waals heterostructures. These fundamental properties have been used to probe the states, effects, and mechanisms of graphene materials present in the related heterostructures and devices. We hope that this review will be beneficial in all the aspects of graphene investigations, from basic research to material synthesis and device applications.

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Raman spectroscopy of graphene-based materials and its applications in related devices.

Rational design and facile preparation of non-noble trifunctional electrocatalysts with high performance, low cost and strong durability for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are highly demanded, but remain as a big challenge. Herein, we report a spontaneous gas-foaming method to prepare nitrogen doped ultrathin carbon nanosheets (NCNs) by simply pyrolysing a mixture of citric acid and NH4Cl. Under the optimized pyrolysis temperature (carbonized at 1000 °C) and mass ratio of precursors (1 : 1), the synthesized NCN-1000-5 sample possesses an ultrathin sheet structure, an ultrahigh specific surface area (1793 m2 g−1), and rich edge defects, and exhibits low overpotential and robust stability for the ORR, OER and HER. By means of density functional theory (DFT) computations, we revealed that the intrinsic active sites for the ORR, OER and HER are the carbon atoms located at the armchair edge and adjacent to the graphitic N dopants. When practically used as a catalyst in rechargeable Zn–air batteries, a high energy density (806 W h kg−1), a low charge/discharge voltage gap (0.77 V) and an ultralong cycle life (over 330 h) were obtained at 10 mA cm−2 for NCN-1000-5. This work not only presents a versatile strategy to develop advanced carbon materials with ultrahigh specific surface area and abundant edge defects, but also provides useful guidance for designing and developing multifunctional metal-free catalysts for various energy-related electrocatalytic reactions.

https://par.nsf.gov/servlets/purl/10106996

Defect-rich and ultrathin N doped carbon nanosheets as advanced trifunctional metal-free electrocatalysts for the ORR, OER and HER

Carbon dots (CDs) are one of the advancing fluorescent materials, which draw increasing attention in both theoretical research and practical applications. However, the clear chemical structure and photoluminescence (PL) mechanism of CDs is still an open debate, which limits the development of CDs. Because of the diversity of CDs, it is highly important to clarify this issue for specific CDs models. Herein, a type of CDs, made from citric acid with extremely high quantum yield, is investigated. Through the separation of the CDs, a type of bright blue fluorophore (IPCA) was discovered. IPCA and its derivatives were investigated and they were proven to contribute to the molecular state PL. Other components in the CDs were related to the carbon core state PL, which included polymer clusters and nanosized carbon cores. We conclude that this type of CDs contained complex components and multiple PL centers and that an independent fluorophore strongly affects the PL properties of the CDs. These two conclusions can potentially be true for similar CDs.

Investigation from chemical structure to photoluminescent mechanism: a type of carbon dots from the pyrolysis of citric acid and an amine

The synthesis of water-soluble nitrogen-doped carbon dots has received great attention, due to their wide applications in oxygen reduction reaction, cell imaging, sensors, and drug delivery. Herein, nitrogen-doped, carbon-rich, highly photoluminescent carbon dots have been synthesized for the first time from ammonium citrate under hydrothermal conditions. The obtained nitrogen-doped carbon dots possess bright blue luminescence, short fluorescence lifetime, pH-sensitivity and excellent stability at a high salt concentration. They have potential to be used for pH sensors, cell imaging, solar cells, and photocatalysis.

http://yfzhang.sjtu.edu.cn/en/publications/2014/1.pdf

Nitrogen-doped, carbon-rich, highly photoluminescent carbon dots from ammonium citrate

Method for synthesizing nitrogen doped carbon quantum dot based on one-step monocomponent hydro-thermal synthesis

http://yfzhang.sjtu.edu.cn/en/publications/2014/6.pdf

Synthesis of carbon nanotubes on graphene quantum dot surface by catalyst free chemical vapor deposition

The invention discloses a graphene quantum dot based method for synthesis of a carbon nanotube by chemical vapor deposition. The method includes: adding a well prepared graphene quantum dot solution on a silicon slice surface dropwisely, conducting drying, then sending the silicon slice into a chemical vapor deposition reaction furnace, introducing acetylene, ethylene, methane, propylene, butane and the like as a carbon source, adjusting the temperature to a proper reaction temperature, and synthesizing the carbon nanotube under certain pressure condition. The invention does not involve any catalyst, and only uses acetylene, ethylene, methane, propylene, butane and the like and the graphene quantum dot respectively as the carbon source and the substrate to prepare the carbon nanotube. Compared with the prior art, the method does not use any catalyst, and takes the graphene quantum dot as the substrate for the first time, and the steps are simple and are easy to operate, so that the method is suitable for industrial production.

Graphene quantum dot based method for synthesis of carbon nanotube by chemical vapor deposition

The invention discloses a method for hydrothermally synthesizing carbon quantum dots on basis of tartaric acid and organic amine. The method comprises the steps of: adding tartaric acid into water, then adding organic amine, evenly mixing the solution, adding in a hydrothermal reaction kettle, reacting at 150-220 DEG C for 18-36 hours, conducting dialysis treatment to obtain impurity-free carbon quantum dots. The invention provides a new method for synthesizing carbon quantum dots, and the carbon quantum dots which are good in controllability and uniform in particle size can be synthesized.

Liu Yun

Papers

Nitrogen-doped, carbon-rich, highly photoluminescent carbon dots from ammonium citrate

Method for synthesizing nitrogen doped carbon quantum dot based on one-step monocomponent hydro-thermal synthesis

Synthesis of carbon nanotubes on graphene quantum dot surface by catalyst free chemical vapor deposition

Graphene quantum dot based method for synthesis of carbon nanotube by chemical vapor deposition

Method for hydrothermally synthesizing carbon quantum dots on basis of tartaric acid and organic amine