Table 2.

The GQDs-based optical sensor for ferric ion detection.

Type of GQDs	Synthesis Method	Starting Materials	Optical Method	Linear Range	LOD 1 (nM)	References
P-GQDs	carbonization/hydrothermal	pyrene/hydrazine hydrate	Fluorescent probe	-	5	[22]
N-GQDs	pyrolysis/hydrothermal	citric acid/hydrazine	Fluorescent probe	1–1945 µM	90	[23]
BMIM+-GQDs	electrochemical cutting	3D graphene	Fluorescent sensor	0–80 µM	7220	[19]
N-GQDs	acid vapor cutting	MOF-derived carbon	Fluorescent probe	1–70 µM	80	[24]
N-GQDs	carbonization/hydrothermal	citric acid/ammonia	Fluorescent probe	1–500 µM	1000	[25]
S-GQDs	electrolysis	graphite/sodium p-toluensulfonate	Fluorescent probe	0–0.7 µM	4.2	[26]
NA-GQDs	thermolysis	glycine	Fluorescent sensor	0.5–500 µM	100	[27]
GQDs	acid vapor cutting	SiO2(SBA-15)	Fluorescent probe	3–60 µM	300	[28]
GQDs	pyrolysis	citric acid	Dual-channel fluorescent probe	10–200 µM	10 000	[29]
RBD-GQDs	electrochemical exfoliation/acidic oxidation	graphite rod/rhodamine B	Fluorescent sensor	0–1 µM	20	[30]
GQDs	microwave/pyrolysis	aspartic acid/NH4HCO3	Fluorescent probe	0–50 µM	260	[31]
SL/GQDs	pyrolysis/hydrothermal	citric acid/SL/NaOH	Fluorescent sensor	0.005–500 µM	0.5	[32]
GQDs/PS-AER	acid oxidation/absorption	graphite/PS-AER	Fluorescent sensor	1–7 µM	650	[33]
DA-GQDs	pyrolysis/covalent conjugation	citric acid/dopamine	Fluorescent probe	0.02–2 µM	7.6	[34]
AL-GQDs	Solution chemistry/amidation	GO/amino acid	Fluorescent probe	0.05–200 µM	50	[35]
DPA-GQDs	pyrolysis	citric acid/D-penicillamine	Fluorescent probe	0.004–1.8 mM	1200	[36]
BGQDs	electrolysis	graphite rod/borax solution	Fluorescent probe	0.01–100 µM	5	[21]
N-GQDs	hydrothermal	glutathione/Ag+	Fluorescent probe	50–2000 µM	70	[37]
N, S-GQDs	hydrothermal	1,3,6-trinitropyrene/thiourea/DMF/sodium hydroxide	Fluorescent probe	0.01–25.0 µM	8	[38]
N, S-GQDs	dehydration	citric acid/L-cysteine	Fluorescent probe	0.01–3 μM	3.3	[39]
GQDs	oxidation	carbon black/nitric acid	Fluorescent probe	0–60 μM	450	[40]
RH-GQDs	hydrothermal	rice husk	Fluorescent sensor	0–1 mM	5.8	[41]
N, Fe-GQDs	hydrothermal	ammonium iron (III) citrate	Fluorometric and Colorimetric dual-mode sensor	10–110 μM 0–450 μM	3210 1340	[42]
af-GQDs	chemical oxidation/hydrothermal	high-softening point asphalt/ammonia	Fluorescent probe	0–50 µM	0.51	[43]

¹ where LOD is limit of detection. af: amino-functionalized, AL: l-analine, B: boron, DA: dopamine, DMF: dimethylformamide, DPA: D-penicillamine, GO: graphene oxide, MOF: metal-organic framework, N: nitrogen, NA: nitrogen and amino acid, P: photoluminescent, PS-AER: polystyrenic anion-exchange resin, RBD: rhodamine B derivative, RH: rice husk, S: sulfur, SL: ligninsulfonate.