Preparation of Carbon Quantum Dots from Corn Straw and their Application in Cu2+ Detection

Water-soluble carbon quantum dots were hydrothermally produced using corn straw as the starting material and nitric acid solution as solvent, then they were introduced as fluorescent probes for the detection of Cu2+. High-resolution transmission electron microscopy and X-ray diffraction showed that the carbon quantum dots were spherical amorphous particles with a diameter of 5 nm. The surface functional groups of carbon quantum dots were observed via Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. A new approach for Cu2+ detection was designed using carbon quantum dots based on fluorescence quenching. Linear relationships between the fluorescence variation and the Cu2+ level (1 mg.L-1 to 20 mg.L-1 and 20 mg.L-1 to 500 mg.L-1) were obtained, with coefficients of determination of 0.9960 and 0.9923, respectively. The Cu2+ detection limit was 4.26 mg.L-1. The probable quenching principle between Cu2+ and the carbon quantum dots was attributed to charge transfer.