Theoretical Study And Green Preparation Of Carbon Quantum Dots

As a rising star, carbon quantum dots (CQDs) are mostly prepared by oxidation, thus it is key points to investigate the interaction between CQDs and oxygen atom. So far, the chemical oxidation method is the most common method for the preparation of CQDs, and strong acids will be used in the synthesis process. That will not only damage the environment, but restrict commercial process of CQDs. Therefore, it is of vital significance to discover an environmental friendly method to prepare CQDs at lower cost and larger-scale of production.Firstly, according to the density function theory (DFT) method, the interaction between CQDs and oxygen atom was simulated by the B3LYP functional with the 6-31G basis set. In this study, a large graphene sheet (C54H18, D6h) was used as the original configuration. Due to the symmetry of graphene, a representative patch was put forward to simplify the description. Based on the representative patch on the surface, the single point energy was discussed to make the potential energy surface (PES) at a reasonable interaction distance. By the calculation of PES on the representative patch, four possible stable isomers of the C54H18-O radical can be obtained. Meanwhile, the structures and energies of the four stable radical were further investigated thermodynamically, kinetically and chemically. Moreover, the transition states at different key points of the representative patch were given to explain the possible reaction mechanism between CQDs and oxygen atom. It is shows that the oxygen atom is easy to absorb to form epoxy bonds above the bond center and hard to absorb above the center of the six membered rings.Secondly, CQDs with different functional groups for anode catalysts of the PEMFC were explored by DFT. In this study, a large graphene sheet (C54H18) was used as the original configuration. And the electron affinity and the combination between the graphene and hydrogen atom were calculated at the B3LYP with the 6-31G (d, p). Based on the calculation, metal-free anode catalysts of the PEMFC were screened. The calculation results show that the metal-free graphene materials with CHO functional groups have better catalytic properties theoretically. Thirdly, a green synthesis strategy has been developed for producing CQDs from a kind of Chinese sulfonated coal. After separated and purified by column chromatography, the structure of CQDs was roughly identified by IR, UV, NMR, MS and element analysis. The results show that CQDs is uniformly distributed by scanning electron microscopy. More than 95% of the particle size is 5.021 nm and the band width is 0.1382 nm. Furthermore, this CQDs can be a novel sensitive sensor to detect water formaldehyde species, and the detection limit can reach 0.2 ppm level.