Electronic Supplementary Material
Chemiluminescence reaction of glucose-derived graphene quantum dots with hypochlorite, and its application to the determination of free chlorine
Tooba Hallaj, Mohammad Amjadi*, Jamshid L. Manzoori and Roghayeh Shokri
Possible reaction pathways for CL reaction of GQDs-ClO-
Hypochlorite may be able to oxidize the surface carboxylate ions of the GQDs to produce peroxyacids, which then decompose to yield singlet oxygen [1]. This can lead to the production of excited dimolsinglet oxygen, (1O2)2*, followed by the transfer of energy to the GQDs:
GQD-CO2- + ClO- → GQD-CO3- + Cl-
GQD-CO3- + ClO-→ GQD-CO2- + 1O2 + Cl-
1O2 + 1O2 → (1O2)2*
(1O2)2* + GQD → GQD*
GQD* → GQD + hν (∼ 510 nm)
Furthermore, the excited GQDs may result from annihilation of electron-injected and hole-injected GQDs produced by a series of possible reactions. It is reported that peroxyacids in aqueous solution may be hydrolyzed to hydrogen peroxide (H2O2) [2]. Then, hydroxyl radical can be produced in the reaction between ClO- and H2O2 [3]. At the same time, H2O2 may react with •OH to form HO2• which is unstable and decomposes to intermediate radical O2•−[4]. These radicals can further react with GQDs to produce GQDs+ and GQDs- by the processes of hole and electron injection. The subsequent relaxation of chemically generated exciton by electron-hole recombination produces CL emission:
GQD-CO3H + H2O → GQD-CO2- + H2O2
H2O2 + ClO- → ClO• + •OH + OH-
H2O2 + •OH → HO2• + H2O
HO2• → O2•− + H+
GQD + O2•− → GQD•− + O2
GQD + •OH → GQD•+
GQD•+ + GQD•− → GQD*
GQD* → GQD + hν (∼ 510 nm)
To confirm this pathway, the effect of some radical scavengers on the CL intensity of GQD/ClO- /CTAB system was investigated (Table S1). NaN3 , as a well-known scavenger for singlet oxygen [5], quenched the CL of the system which provided an evidence for contribution of 1O2 to the observed CL. The generation of •OH in the examined system was confirmed with the observed quenching effect upon the addition of thiourea, as a radical scavenger for •OH [6]. Moreover, quercetin which is known to be a scavenger for superoxide [7] had a negative effect on the CL intensity. Thus it was assumed that O2•− is generated in the examined system. Finally, ascorbic acid as a common oxygen free radical scavenger [8] had a remarkable negative effect on the CL signal, which further confirms the generation of free radicals in the CL reaction.
Table S1. Effects of radical scavengers on GQDs/ ClO- /CTAB CL system
Radical scavengers / Concentration (M) / Quenching percent (%)NaN3 / 3 × 10-2 / 35
Thiourea / 1 × 10-2 / 88
Quercetin / 1 × 10-4 / 30
Ascorbic acid / 1 × 10-3 / 83
Optimization of chemical conditions
Fig. S1. Optimization of the CL reaction conditions: (a) Effect of pH value. Conditions: GQD (200 µL), phosphate buffer (0.01 M), CTAB (0.025 M) and ClO- (10−3 M); (b) Effect of phosphate buffer concentration. Conditions: (pH=8), other conditions are as in a; (c) Effect of CTAB concentration. Conditions: phosphate buffer (0.01 M), other conditions are as in b; (d) Effect of GQD solution volume. Conditions: CTAB (0.025 M), other conditions are as in c.
Fig. S1a.
Fig. S1b.
Fig. S1c.
Fig. S1d.
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