Quantum yield optimization of carbon dots using response surface methodology and its application as control of Fe3+ion levels in drinking water

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Abstract
Early detection of heavy metals in drinking water is a fundamental step that must be taken to prevent adverse effects on health. This research aims to develop a heavy metal ion detector by utilizing the fluorescence properties of carbon dots. Cdots were synthesized using the microwave irradiation method based on the central composite design: urea mass 0.31–3.68 gr; reactor power 200–1000 W; synthesis time is 13–46 min, and the response is quantum yield. Material characterization includes PL, TEM, UV-VIS, XRD, and FTIR. The selectivity and sensitivity of Cdots as detectors were tested for Ag+, Bi3+, Ni2+, Al3+, Co2+, Pb2+, Fe3+, Zn2+, Zr4+, and Hg2+ ions at concentrations of 0–10 μM. The results showed that Cdots were successfully synthesized by fluorescent light green at 544 nm. An adequate response model is quadratic with the formulation QY = +58.36 + 10.41X1 + 14.06X2 +13.59X3–5.57X2X3–4.89X1 2−8.60X2 2–5.40X3 2. The best Cdots were obtained in the formulation of R9 (3 g, 800 W, 40 min), which resulted in a QY of 74.39%. The characteristics of Cdots are spherical, diameter 6.6 nm, the bandgap of 2.53 eV, and having an amorphous structure. The surface of Cdots contains various functional groups such as O–H, C–H, C=O, C–N, and C=C. In the heavy metal detection test, Cdots showed specific sensitivity to Fe3+ ions. The addition of Fe3+ concentration and the extinction of Cdots fluorescence intensity formed a linear correlation F0/F = 0.08894[Fe3+]+0.99391 (R2 = 0.99276). The detection ability of Cdots for Fe3+ ions reaches a concentration of 0.016 ppm, much lower than the regulatory threshold limit of SNI, WHO, and IBWA. The detection of Fe3+ ions in drinking water uses a fluorescence technique consistent with the SSA and ICP-OES. Based on these results, the fluorescence technique using Cdots can be an instrument for quality control of the final drinking water product.
Funding Information
  • Universitas Diponegoro (14-04/UN7.P4.3/PP/2020)

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