Multi-Color Fluorescent Carbon Dots: Graphitized sp2 Conjugated Domains and Surface State Energy Level Co-Modulate Band Gap Rather Than Size Effects.,Chemistry - A European Journal

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Multi-Color Fluorescent Carbon Dots: Graphitized sp2 Conjugated Domains and Surface State Energy Level Co-Modulate Band Gap Rather Than Size Effects.
Chemistry - A European Journal ( IF 3.9 ) Pub Date : 2020-03-26 , DOI: 10.1002/chem.202000763
Siqi Wei ₁ , Xinghang Yin ₁ , Haoyi Li ₁ , Xiaoyu Du ₁ , Limei Zhang ₁ , Qiang Yang ₁ , Rui Yang ₁

Affiliation

Four types of carbon dots (CDs) with various color (blue, green, yellow, and red) emissions have been synthesized under solvent‐free conditions from citric acid and different nitrogen sources (DMF, urea, ethanamide, and formamide). By detailed characterization and comparison, it is confirmed that the graphitized sp² conjugated domain and surface functional groups such as C−O and C=N play synergetic roles in adjusting the fluorescence properties. Notably, the size effect is not the dominant mechanism to achieve multi‐color fluorescence emissions in this work. The structural configuration of the carbon dots further influences the energy band structure, as demonstrated in simplified energy level diagrams. An absorption peak at approximately 560 nm appears in the visible light region for red‐emitting CDs, assigned to an n→π* transition of the aromatic structure, thus introducing a new surface state energy level, resulting in a reduction in the energy of electron transition and the expansion into the visible region of the UV/Vis spectrum. Taking advantage of the diverse absorption and emission properties, different CDs/TiO₂ binary composites are obtained for photocatalytic degradation of organic dyes, and it is found that the absorption range in terms of visible light and the band gap of the carbon dots make a difference to the photocatalytic performance of the composites.

中文翻译：

多色荧光碳点：石墨化的sp2共轭域和表面态能级共同调节带隙而不是尺寸效应。

在无溶剂条件下，由柠檬酸和不同的氮源（DMF，尿素，乙酰胺和甲酰胺）合成了四种颜色（蓝色，绿色，黄色和红色）的碳点（CD）。通过详细的表征和比较，证实了石墨化的sp ²共轭结构域和表面官能团（例如C-O和C = N）在调节荧光特性中起协同作用。值得注意的是，在这项工作中，尺寸效应并不是实现多色荧光发射的主要机制。碳点的结构配置进一步影响能带结构，如简化的能级图所示。对于发出红色光的CD，在可见光区域出现一个大约560 nm的吸收峰，该峰对应于芳族结构的n→π*跃迁，从而引入了新的表面态能级，从而降低了电子的能量过渡并扩展到UV / Vis光谱的可见区域。利用各种吸收和发射特性，可以使用不同的CD / TiO ₂ 获得了用于有机染料的光催化降解的二元复合材料，发现可见光的吸收范围和碳点的带隙对复合材料的光催化性能产生了影响。

更新日期：2020-03-26

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