Síntese e caracterização de carbon dots derivados de resíduos carbonáceos de diferentes cidades de Alagoas para aplicação como sonda fluorescente de Cr(VI)

Abstract

The search for more efficient and sustainable methods to detect chromium ((Cr (VI)) in various environmental and industrial compartments is of great relevance, since this species can cause serious harm to human health and the environment. The development of fluorescent probes for Cr (VI) detection has been a promising alternative. Among the fluorescent probes, carbon dots (CDs) have stood out due to their numerous unique properties, such as photostability, low toxicity, high water solubility, biocompatibility, and low cost. Given the above, in this work the bagasse of the peels of Citrus latifolia (tahiti lemon) from different cities of Alagoas (Coruripe (C-Dots_AC), Rio Largo (C-Dots_AR) and Maceió (C-Dots_AM)) were used as precursors to synthesize carbon dots (CDs) via hydrothermal method. Furthermore, under optimized conditions C-Dots_AM was applied for the detection of Cr (VI) in aqueous solution. The CDs from the studied cities showed similar structural and photophysical properties. Thus, the CDots_AC, C-Dots_AR and C-Dots_AM exhibited higher frequency sizes below 10 nm, characteristic absorptions of π - π* (230 nm) and n - π* (286 nm) transitions and vibrational stretching of oxygenated groups and amines. The C-Dots showed excitation wavelengthdependent emission (λexc), with maximum emission at 445 nm when excited at 350 nm. All CDots in a preliminary study exhibited similar analytical response towards Cr (VI) sensitivity compared to other species, and thus, C-Dots_AM was chosen for a more detailed Cr (VI) detection study. Optimization of the analytical parameters was performed in which the best response of the method was at pH 7, tris buffer and 50 mM concentration. The ionic strength did not interfere with sensitivity as it did not show significant signal change over a concentration range of 0-150 mM. The reaction dwell time for analysis was 20 min and both Cdot_L and Cdot_L + Cr (VI) showed photostability for up to 60 min with continuous radiation exposure. Under the optimized conditions, the system showed a linear range from 0.05 to 10.0 mg L-1. Furthermore, in the evaluation of the detection mechanism of Cr (VI) by Cdot_L it was found that the interaction process between Cdot_L and Cr (VI) is associated with the internal filter effect and static quenching. Finally, the results obtained indicate that Cdot_L presents itself as a low cost and promising probe for Cr (VI) detection.