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 Ni ²⁺ 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 Ni ²⁺ was 50.0–200.0 μg L ^–1 with a regression line, y = 5.031 x – 190.4 ( r 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 ( n = 3 × 3) and 7.65 for interday ( n = 5 × 3). This developed method afforded good recoveries of Ni ²⁺ in a range of 85–108% when spiked with real water samples. Overall, this innovative method illustrated the identification and detection of Ni ²⁺ as a DMG complex with N-GQDs, and the detection was highly sensitive and selective.