As a kind of carbon nanomaterials family, carbon quantum dots (CDs) have attracted much attention because of their superior photoluminescence (Isnaeni, Herbani, & Suliyanti 2018; Mintz, Guerrero, & Leblanc 2018), ease of functionalization (Park, Yoo, Lim, Kwon, & Rhee 2016; Rednic et al. 2015), low toxicity (Niu et al. 2015) and good biocompatibility (Yang, Zhu, Chen, Chen, & Zhou 2018). Moreover, abundant low-cost sources can be utilized to synthesize the CDs for the application in a variety of fields including biomedicine, optoelectronics, sensing, photovoltaics, and photocatalysis (Park et al. 2016). CDs is zero-dimensional nanomaterial showing size less than 10 nm (Deb, Konwar, & Chowdhury 2020), which also performs high aqueous solubility. Thus, CDs are used to combine polymer matrix to endow them with special functionalization (Devadas & Imae 2018; Wu et al. 2020). The 5 nm sized carbon dots were blended into polymethacrylate, polyurethane, and other common polymers (Zhu et al. 2017). The composite coatings not only possessed self-healing properties but also showed superior anticorrosion properties compared to those of the pure polymer coatings.
Among the polymer/CDs composites, the CDs are introduced on the surface of fiber to endow the fabric with anti-ultraviolet (anti-UV) properties (Shuai, Xu, Sun, Zhang, & Zuo 2022; Zuo, Liang, Xu, Chen, & Zhang 2019), selective detection and effective removal of heavy metal (Durairaj, Maruthapandi, Luong, Perelshtein, & Gedanken 2022; Hu et al. 2022; S. Q. Liu, Liu, Chen, Hou, & Yang 2022). For the fabric, other carbon nanomaterials are also imparted for the functionalization of flame retardancy (Xu et al. 2023; Xue et al. 2020), superhydrophobicity (Zhang et al. 2014; Zheng et al. 2019), electromagnetic shielding (Y. Q. Chen et al. 2019; Islam et al. 2019). Wu et al. prepared single-walled carbon nanohorns and ammonium polyphosphate containing coating for flame retardancy of cotton fabrics (Xu et al. 2023). The peak heat release rate of the flame retardant cotton were decreased by 92.22% in the cone calorimeter test. The coating consisting of multiwall carbon nanotubes (MWNTs) and polybenzoxazine was deposited on the ramie fabric through solution-immersion process (Zhang et al. 2014). The resulted ramie fabric showed good superhydrophobic and conductive properties. The graphene oxide and polypyrrole were applied on the fabric to shield the electromagnetic waves (Lan, Zou, Wang, Qiu, & Ma 2021). The shielding effectiveness of the treated fabric could reach 39.1 dB by increasing the amount of interface in the coating. Based on these previous works, we are wondering whether CDs have similar potential applications, such as flame retardancy.
CDs contain abundant carbonyl groups on their surface, which imparts high water solubility. This property makes CDs suit for fabricating the layer-by-layer (LbL) self-assembled coating. To our knowledge, LbL self-assembly method has gradually become a notable technique to modify the surfaces of polymer matrixes, especially for fabrics (X. X. Chen et al. 2016; Pan et al. 2022; Xue et al. 2020). LbL self-assembly method presents lots of advantages of easy and environmentally friendly operation, a wide selection of materials, controllable coating thickness and shape, and multilayer coatings (Q. Y. Liu et al. 2021). In this work, B, N co-doped CDs were utilized to construct a multilayer coating on the cotton fabric by LbL self-assembly method. Firstly, the anti-UV property of the CDs consisting coating with different layers was investigated. Then the thermal stability and flame retardancy of treated cotton fabric were studied to evaluate if CDs had potential applications as flame retardants. Finally, the wash durability of treated cotton fabric was also considered.