Study on the ultraviolet absorbing properties of cotton fabric finished with boron and nitrogen co-doped carbon dots

To improve the UV resistance of cotton fabrics, three different carbon dots doped with boron and nitrogen (BN-CDs) were prepared by a one-step hydrothermal synthesis method using citric acid, ammonium citrate and glucose as different carbon sources, and ethylenediamine and borax as nitrogen and boron sources, respectively. Three types of blended aqueous solutions (BN-CDs/WPU) with BN-CDs and water-based polyurethane were sprayed on the surface of cotton fabric, and then the cotton fabric was rolled and dried. The structure and optical properties of BN-CDs were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible spectrophotometry, and fluorescence spectrophotometry. The structure and ultraviolet screening capability of cotton fabrics after finishing with BN-CD/WPU blend solution were characterized. Results showed that the prepared BN-CDs were graphite-like nanocrystals with an approximately 0.3-nm crystal plane spacing. All BN-CDs had rich hydroxyl groups and amine groups on the surface, which made the BN-CDs soluble in water. BN-CDs had a strong absorption peak in the ultraviolet region and emitted bright blue fluorescence independent of excitation wavelengths. Cotton fabrics finished with BN-CDs/WPU all showed a high ultraviolet protection factor (UPF), an excellent level of protection, and good washing durability. In particular, in cotton fabrics treated with BN-CDs prepared using citric acid as a carbon source, the UPF value was still as high as 50.1 even after washing 10 times, and the fabrics maintained good elasticity and morphological characteristics. Results thus showed that BN-CDs can be used as UV absorption agents for finishing cotton fabrics.