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As a new class of fluorescent carbon materials, graphene quantum dots (GQDs) have attracted tremendous attention due to their outstanding properties and potential applications in biological, optoelectronic, and energy-related fields. Herein, top-down and bottom-up strategies for the fabrication of GQDs, mainly containing oxidative cleavage, the hydrothermal or solvothermal method, the ultrasonic-assisted or microwave-assisted process, electrochemical oxidation, controllable synthesis, and carbonization from small molecules or polymers, are discussed. Different methods are presented in order to study their characteristics and their influence on the final properties of the GQDs. The respective advantages and disadvantages of the methods are introduced. With regard to some important or novel methods, the mechanisms are proposed for reference. Moreover, recent exciting progresses on the applications of GQD, such as sensors, bio-imaging, drug carriers, and solar cells are highlighted. Finally, a brief outlook is given, pointing out the issues still to be settled for further development. We believe that new preparation methods and properties of GQDs will be found, and GQDs will play more important roles in novel devices and various applications.

Utilizing the low‐cost catalysts with excellent catalytic activities to replace the expensive ones for H2 evolution still faces great challenges. It is significant to design the new catalysts with the synergistic effect to improve the activities and decrease the cost of the applications. Herein, the novel nanocatalyst of graphene quantum dots loaded bimetallic nanoparticles (Pt‐Co/GQDs) has been synthesized for the H2 evolution from hydrolysis of amine borane (AB) for the first time. The result indicates that the Pt‐Co/GQDs nanocatalyst holds the better catalytic activities than Pt/GQDs, exhibiting the bimetallic synergies in the hydrolysis process. The synthesized catalyst has been characterized by various measurements, such as TEM, XPS, EDS, UV–Vis, and PL spectra. The effect of the catalyst on the hydrolysis of AB is investigated. It is demonstrated that the value of total turnover frequencies (TOFs) can arrive to 520 molH2·molPt−1·min−1 via the catalyst designing, which is very high in comparison with other reported catalysts. This work has developed an effective nanocatalyst with a lower cost which is never reported in the hydrolysis of AB, possessing both great significance and huge potential in the H2 evolution by hydrolysis of the hydrogen storage materials. [ABSTRACT FROM AUTHOR]

Utilization of nonprecious metals to replace precious metals in the catalytic hydrolysis of hydrogen storage materials causes wide attention. Herein, nonprecious bimetallic nanoparticles loaded on N-doped graphene quantum dots (Co-Ni/N-GQDs) have been synthesized and applied in the hydrolysis of NH3BH3 for the first time. It is demonstrated that Co-Ni/N-GQDs exhibit the obvious bimetallic synergies in the hydrolysis of NH3BH3, and the total turnover frequency (TOF) value reaches 19.94 mol H2 ⋅ mol Cat − 1 ⋅ min − 1 via the optimized design. This work first explored the catalytic performance for the nonprecious bimetallic nanoparticles loaded on N-GQDs in the hydrolysis of NH3BH3, greatly facilitating the development of both nonprecious metals and N-GQDs in the hydrogen evolution. Nonprecious bimetallic nanoparticles loaded on N-doped graphene quantum dots (Co-Ni/N-GQDs) were developed in the hydrolysis of NH3BH3 for the first time. It is demonstrated that Co-Ni/N-GQDs exhibit excellent catalytic performances in the hydrolysis of NH3BH3, and the total turnover frequency (TOF) value can reach 19.94 molH2⋅molCat–1⋅min–1. [ABSTRACT FROM AUTHOR]

A facile and effective route to synthesize graphene quantum dots for cell imaging and as a deoxidizer by using glucan as a precursor is developed. AuNPs are successfully synthesized by mixing of graphene quantum dots and Au(III) salts without any additional reductants. The reducing driving force of these graphene quantum dots is much weaker than that of strong reducing agents such as NaBH4. The sizes of the as-synthesized AuNPs are much larger, with an average size of 15 nm. Notably, this size range is specifically useful and optimal for the application of AuNPs in biomedical applications. In addition, the as-synthesized graphene quantum dots are also successfully applied in cell imaging. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) have aroused widespread attention because of their remarkable properties and potential applications. Herein, we discuss both the top-down and bottom-up strategies for the synthesis of GQDs. Different processes are presented to study their characteristics and the influence on the final properties of GQDs. The respective advantages and disadvantages of these methods are summarized. With regard to some important or novel ones, mechanisms are proposed for reference. In addition, the application of GQDs in biosensors is highlighted in detail. At last, we put forward some problems to be solved and give a brief prospect in their future developments. This review is very useful for quickly gaining knowledge and experience for synthesizing GQDs and designing the related novel biosensors. The latest progresses on the synthesis of GQDs are reviewed. The top-down and bottom-up strategies are discussed comprehensively. The potential application of GQDs in biosensors and their design solution are introduced. A brief outlook and further development for the GQDs are pointed out. This review not only provides a useful guide on the synthesis of GQDs, but also facilitates designing the novel biosensor devices for researchers. [ABSTRACT FROM AUTHOR]

Recently, effective hydrogen (H 2) evolution upon hydrolysis of different hydrogen storage materials has received much attention. Herein, graphene quantum dots-transition metal nanoparticles (GQDs-TMNPs), with high dispersibility and activity, have been successfully applied in the hydrolysis of both NH 3 BH 3 (AB) and NaBH 4 for the first time. GQDs-RhNPs, GQDs-RuNPs, and GQDs-PtNPs are very effective in the hydrolysis of AB and the turnover frequencies (TOFs) can achieve to as high as 656, 384, and 281 mol H2 ·mol cat −1 min−1, respectively. Moreover, the synergistic effect between GQDs and TMNPs is explored, and the mechanisms of catalytic hydrolysis of AB and NaBH 4 by GQDs-TMNPs are proposed. This work not only paves the way for the development of GQDs-TMNPs nanocatalysts for the different hydrogen storage materials, but also further advances the understanding of the synergistic effects between GQDs and TMNPs. Image 1 • GQDs-TMNPs have been firstly applied in the hydrolysis of both AB and NaBH 4. • RhNPs, PtNPs and RuNPs are very efficient for H 2 evolution upon hydrolysis of AB and NaBH 4. • GQDs-TMNPs have been successfully recycled 5 times without significant decrease. [ABSTRACT FROM AUTHOR]

Fabrication of graphene quantum dots (GQDs) often requires strong acids or organic solvents, and their green synthesises on sustainable routes still face challenges. Herein, an eco‐friendly synthetic process has been developed, in which the natural polymer cellulose has been utilized as a new precursor for the first time. The reaction system is only composed of cellulose and water, in absence of any other chemical reagents. Moreover, the products contain only GQDs, carbide precipitates, and water, leading to easy separation and avoiding complicated post‐processes. In addition, the synthetic mechanism is presented that the formation process of GQDs consists of the first hydrolyzation and the following cyclic condensation. With highly photoluminescent (PL) properties, favourable hydrophilicity, low cytotoxicity and excellent biocompatability, the as‐synthesized GQDs have been successfully applied in bioimaging. This work not only develops a sustainable route for the green synthesis of GQDs, but also finds a renewable resource as the raw material, which significantly facilitates the extensive applications of GQDs in biological fields. An eco‐friendly process for the synthesis of graphene quantum dots (GQDs) has been developed, in which the natural polymer cellulose was utilized as a new precursor for the first time. The synthetic mechanism is presented and the GQDs with high PL emission have been successfully applied in bioimaging. This work not only develops a sustainable route for the green synthesis of GQDs, but also finds a renewable resource as the raw material, significantly facilitating the extensive applications of GQDs in the biological fields. [ABSTRACT FROM AUTHOR]