碳量子点阳离子表面活性剂的多功能性

碳量子点以其多彩的荧光及廉价而丰富的制备原料引起人们的广泛兴趣。至今，已有大量关于碳量子点制备及其荧光性能直接利用的文献报道。若采用恰当的方法对碳量子点进行化学修饰，则可以将其转化为实用的精细化学品，从而拓展碳量子点的应用领域。本文报道了一种碳量子点阳离子表面活性剂的制备方法。首先，乙二胺四乙酸、二乙胺及双氧水的混合水溶液经水热处理，获得碳量子点(以OX-CQDs表示)，再以氯代正构十二烷对其进行季铵化修饰，获得新型碳量子点阳离子表面活性剂(以OX-CQDs-C₁₂H₂₅表示)。OX-CQDs-C₁₂H₂₅具有良好的降低水的表面张力和减小水接触角的能力，水的界面张力能降低至26.7 mN∙m⁻¹，其性能超过了一些新型的Gemini型阳离子表面活性剂；季铵化的修饰也大大提高了OX-CQDs对大肠杆菌的抑菌能力，低至0.41 mg∙mL⁻¹的OX-CQDs-C₁₂H₂₅溶液其抑菌率接近100%。表面活性剂，抑菌性和荧光性能赋予了OX-CQDs-C₁₂H₂₅的多种功能性。

Versatile Performance of a Cationic Surfactant Derived from Carbon Quantum Dots

Carbon quantum dots (CQDs) have attracted extensive interest due to their strong fluorescence as well as inexpensive and plentiful resources for manufacture. There are numerous published reports on the preparation of CQDs and direct applications based on their photoluminescence. Successive chemical modification of CQDs in an appropriate manner might expand the application scope of CQDs and transform them into practical fine chemicals. The various functional groups on the surface of CQDs allow for efficient chemical modification while imparting them with hydrophilicity. Covalent linking of hydrophobic hydrocarbon chains to CQDs would lead to the formation of novel surfactants. Here, a technique for preparing CQD-based cationic surfactants is depicted in detail. This was rare to be reported according to recent publishes. First, a mixture of ethylenediamine tetraacetic acid and ethylenediamine in the presence of hydrogen peroxide in an aqueous medium was pyrolyzed at 180 ℃ for 60 min. The resulting CQDs are represented as OX-CQDs. Then, the OX-CQDs were subjected to quaternization with 1-chlorododecane for obtaining the cationic surfactant (OX-CQDs-C₁₂H₂₅). The OX-CQDs-C₁₂H₂₅ surfactant effectively decreased the surface tension of water from 72.0 to 26.7 mN∙m⁻¹ at the critical micelle concentration of 5.0 mg∙mL⁻¹, thus demonstrating superior performance over several new Gemini cationic surfactants. The OX-CQDs-C₁₂H₂₅ surfactant also decreased the contact angles of water considerably. However, when longer alkyl chains such as －C₁₄H₂₉ or －C₁₆H₃₃ were attached to the CQDs, the corresponding surfactant was less effective in decreasing the surface tension of water. Calculations based on the Gibbs absorption isothermal equation revealed that two more －C₁₂H₂₅ chains were bonded with a carbon quantum dot averagely, implying that the as-prepared CQD-cationic surfactant belonged to the category of Gemini surfactants. Quaternization with 1-chlorododecane also led to a notable enhancement in the antibacterial activity for Escherichia coli as compared with that of unmodified CQDs. The antibacterial percentage approached 100% even the solution was diluted to 0.41 mg∙mL⁻¹, which was much lower than the critical micelle concentration. The fluorescence quantum yield of OX-CQDs-C₁₂H₂₅ reached 6.44%. Experimental results revealed that hydrogen peroxide played a positive role in improving the surface activity and fluorescence quantum yield of OX-CQDs-C₁₂H₂₅. The surface activity, antibiosis, and fluorescence endowed the versatilities of OX-CQDs-C₁₂H₂₅. This novel, economical technique for synthesizing cationic surfactants eliminates the need for introducing hydrophilic groups. The hydrothermal approach for preparing CQDs satisfies the demand for green chemical synthesis. From this aspect, our technique provides efficient access to synthesizing cationic surfactants.