Large-scale direct pyrolysis synthesis of excitation-independent carbon dots and analysis of ferric (III) ion sensing mechanism

A one-step direct pyrolysis method without any post-treatment steps and a mass yield of up to 69% was realized for preparing N-doped carbon dots (NCDs). The NCDs exhibit excellent excitation-independent blue fluorescence with quantum yield (QY) of 65.5%, and their luminescence mechanism was explored based on optical properties and structural composition, which mainly originates from surface state photoluminescence (PL). The NCDs display highly selective and sensitive detection of Fe 3+ in tris-HCl buffer system, a good linear relationship between PL intensity ratios and Fe 3+ concentrations was obtained in concentration range of 0 to 400 μM with a low LOD of 0.703 μM. The formation of ferric hydroxide colloid is the main reason for the specific recognition of Fe 3+ by NCDs, and buffer solution plays a key role in the formation of ferric hydroxide colloid and selective detection of Fe 3+ . The sensing mechanism is a dynamic quenching electron transfer process in the action of hydrogen bonding and colloidal adsorption. Three real water samples were applied to evaluate actual application of NCDs probe, satisfactory recoveries (93.5%–105.6%) indicate that NCDs has great practical potential for detection of metal ions in environmental water assays.