Tran Van Tam

Synthesis of B-doped graphene quantum dots as a metal-free electrocatalyst for the oxygen reduction reaction

Boron-doped graphene quantum dots (BGQDs) have been synthesized by a one-step, facile and low temperature method through the hydrothermal treatment of glucose as the precursor in the presence of boric acid. The as-obtained BGQDs possess a high B-doping content up to 4.25% of uniform nm-size. Interestingly, the effect of different types of B–C bond species on the ORR catalytic activity has been investigated to clarify the origin of the electrochemical reduction of O2. Further, the composite of the reduced graphene oxide (rGO) and BGQD (G-BGQDs) was also prepared as a metal-free electrocatalyst for the oxygen reduction reaction (ORR). The G-BGQD composites exhibit a significantly enhanced electrocatalytic activity, including a positive onset potential and a high current density with a one step, four-electron pathway toward the ORR, comparable to the commercial Pt/C catalyst. Among various B–C bond structures in BGQDs, the graphite-like BC3 structure is considered to be an important site for the ORR by improving the electric conductivity and electrocatalytic activity of BGQDs, which is also confirmed by a DFT study. In addition, the G-BGQD composites show an outstanding long-term operational stability and high tolerance to the methanol crossover effect, which are comparable to the commercial Pt/C catalyst. These results demonstrate that the synthesized BGQD, as metal-free catalyst materials, may be inexpensive and efficient electrocatalysts for the replacement of Pt-based catalysts toward the ORR and other electrochemical applications.

Facile synthesis of cysteine–functionalized graphene quantum dots for a fluorescence probe for mercury ions

Cystenine–functionalized graphene quantum dots (cys–GQDs) were synthesized by a simple and facile method, which involves chemical bond formation between L-cysteine and the graphene quantum dots (GQDs) prepared by the carbonization of citric acid. The obtained cys–GQDs show a strong green fluorescence and a uniform lateral size distribution with high crystallinity. The cys–GQDs are further demonstrated as highly sensitive and selective fluorescence probes for Hg2+. In the Hg2+ detection process, the cys–GQDs shows significant fluorescence quenching through a charge transfer process within the cys–GQDs and Hg2+ complex.

Facile fabrication of thermally reduced graphene oxide–platinum nanohybrids and their application in catalytic reduction and dye-sensitized solar cells

We report the fast synthesis of thermally reduced graphene oxide:platinum (TRGO:Pt) nanohybrids by simply spraying a GO:Pt4+ solution on a hot plate. X-ray photoelectron spectroscopy and atomic force microscopy analyses are performed to investigate the thermal reduction of GO:Pt4+ and the morphologies of the TRGO:Pt hybrid monolayer, respectively. The catalytic performance of TRGO:Pt is evaluated for the reduction of o-nitroaniline. A significant increase in the reaction rate constant for TRGO:Pt compared with pure Pt is due to facilitated electron transfer at the TRGO:Pt interface and enhanced catalytic active sites. Effective electron transfer from TRGO to Pt and significantly increased catalytic active sites in hybrids suggest that TRGO:Pt is a highly potential counter electrode material in dye-sensitized solar cells (DSSCs). The hybrid provides numerous electrons to I−/I3− electrolyte to reduce the recombination at the interface. As a result, the performance of DSSCs with the TRGO:Pt hybrid electrode is significantly increased by 34% in comparison with a pure Pt electrode.