Highly luminescent N-doped carbon quantum dots from lemon juice with porphyrin-like structures surrounded by graphitic network for sensing applications

Abstract

Here we demonstrate a simple, low cost, and green synthetic approach to synthesizing water-soluble, nitrogen-doped, fluorescent carbon quantum dots (NCQDs) from lemon juice and ammonia by hydrothermal treatment. Chemical characterizations and low temperature photoluminescence and photoconductivity results show interesting structural features of the as-prepared NCQDs. These new NCQDs consist of a ring type moiety (porphyrin/chlorin) in the centre surrounded by the graphitic network and serve as an efficient fluorescent probe for label-free, sensitive, and selective detection of Fe³⁺ with a detection limit of 140 ppb (2.5 μM), which is remarkably lower than the earlier reports on CQDs-based sensing systems. DFT calculations are carried out to optimise the structural aspects for selective detection of Fe³⁺. This extremely low detection limit (140 ppb) arises due to static quenching in addition to dynamic quenching which generally occurs in most cases.