Synthesis of pH-responsive fluorescent carbon dots using waste leather scrap for anti-counterfeiting

The fabrication of carbon dots (CDs) with biomass materials has become one of the research hot spots. Waste leather scrap (WLS) has been proven to be practicable for the preparation of CDs with simple fluorescence properties for anti-counterfeiting because of their cheap and environmentally responsible characteristics. For a more complex and harder imitation of anti-counterfeiting, stimuli-responsive CDs with WLS as raw material are urgently needed. Herein, acid-responsive fluorescent carbon dots (L-CDs) and alkaline-responsive fluorescent carbon dots (H-CDs) were prepared from WLS via a simple one-step solvothermal/hydrothermal method with emission wavelengths of 457 nm and 549 nm, respectively. When decreasing or increasing the pH value, their emission wavelengths change to 633 nm and 424 nm, respectively. The CDs are highly fluorescence reversible (20 times) in a broad pH region. The detailed results indicated that CDs have the structure of graphite carbon and possess wealthy chemical groups, like C--O, -OH, C-N, etc. These are the main reasons for the change of emission wavelength. Due to the stable pH-responsiveness, the CDs were employed as fingerprint, ink, and figure code in anti-counterfeiting. The pH-responsive fluorescent CDs using WLS for anti-counterfeiting enrich the process of solid waste with a sustainable, cost-effective method for practical applications.