Ultratrace Detection of Nickel(II) Ions in Water Samples Using Dimethylglyoxime-Doped GQDs as the Induced Metal Complex Nanoparticles by a Resonance Light Scattering Sensor

Abstract

This study aimed to synthesize dimethylglyoxime (DMG) (N-source)-doped graphene quantum dots (N-GQDs) via simultaneous pyrolysis of citric acid and 1.0% (w/v) DMG. The maximum excitation wavelength (λ_max, ex = 380 nm) of the N-GQD solution (49% quantum yield (QY)) was a red shift with respect to that of bare GQDs (λ_max, ex = 365 nm) (46% QY); at the same maximum emission wavelength (λ_max, em = 460 nm), their resonance light scattering (RLS) intensity peak was observed at λ_max, ex/em = 530/533 nm. FTIR, X-ray photoelectron spectroscopy, XRD, energy-dispersive X-ray spectroscopy, and transmission electron microscopy analyses were performed to examine the synthesized materials. The selective and sensitive detection of Ni²⁺ using the RLS intensity was performed at 533 nm under the optimum conditions consisting of both 25 mg L^-1 N-GQDs and 2.5 mg L^-1 DMG in the ammonium buffer solution of pH 9.0. The linearity of Ni²⁺ was 50.0-200.0 μg L^-1 with a regression line, <i>y</i> = 5.031<i>x</i> - 190.4 (<i>r</i> ² = 0.9948). The limit of detection (LOD) and the limit of quantitation (LOQ) were determined to be 20.0 and 60.0 μg L^-1, respectively. The method precision expressed as % RSDs was 4.90 for intraday (<i>n</i> = 3 × 3) and 7.65 for interday (<i>n</i> = 5 × 3). This developed method afforded good recoveries of Ni²⁺ in a range of 85-108% when spiked with real water samples. Overall, this innovative method illustrated the identification and detection of Ni²⁺ as a DMG complex with N-GQDs, and the detection was highly sensitive and selective.