Electronic Supplementary Material
Solvothermal synthesis of oxygen/nitrogen functionalized graphene-like materials with diversified morphology from different carbon sources and their fluorescence properties
Feng Yang,a Meilian Zhao,a Hongyun Ji,b Duhong He,a Li Wu, c Baozhan Zheng, a Dan Xiaoa, b* and Yong Guoa*
a College of Chemistry, Sichuan University, Chengdu, 610064, P. R. China.
bCollege of Chemical Engineering, Sichuan University, Chengdu 610064, P. R. China.
c Analytical & Testing Center, Sichuan University, Chengdu, 610064, P. R. China.
1 The research on synthesis procedure
1.1 Fluorescent glassy carbon
The effect of temperature, treatment time and oxidative system on the fluorescence of glassy carbon has been investigated.
Fig. S1 Fluorescence spectra of fluorescent glassy carbon (FGC) which were treated in mixture acids (HNO3/H2SO4 1/3) system at 90, 100, 120, 130 and 140 ℃, respectively
According to experiments, the reaction rate can be affected by the temperature of mixture acids system. Fig. S1 clearly showed that the fluorescence intensity can be affected by the temperature and the emission peaks did not obviously shift at the 100 ~ 120 ℃, but the emission shifted blue and fluorescence intensity gradually weakened when the temperature was higher than 120 ℃. Hence, we took 120 ℃ as the reaction temperature in the later experiments.
Fig. S2 (a) The photograph of fluorescent glassy carbon (FGC) solutions (without purification treatment) irradiated by ambient light (top) and 365 nm UV light (bottom), which photographed after 24 h; (b) The fluorescence spectra of FGC (Insert: the corresponding normalized fluorescence spectra of FGC). The FGCs were treated with the indicated time at 120 ℃ in H2SO4/HNO3 (3/1 v/v) system
Fig. S3 The high-resolution XPS spectra of (a) glassy carbon and (b) treated glassy carbon in at concentrated H2SO4 system at 120 ℃ for 12 h. Insert: the photographs of 5 mg/mL of glassy carbon, which were treated in concentrated sulfuric acid at 120 ℃ for 5 and 12 h, dissolved in deionized water. After 12 h, the treated glassy carbon already precipitates out
The oxidizing agent for oxidation on GC was selected through compared experiments. It is well known that concentrated H2SO4 and H2SO4/HNO3 mixture acids are strong oxidizing agents. Glassy carbon mixture (5 mg/mL) was treated in concentrated H2SO4 system without HNO3 at 120 ℃ for 5 and 12 h. As shown in Fig. S3, the components of GC do not obviously change after treatment. And the dispersity of glassy carbon is not obviously improved with the treated time prolonging (the insert of Fig. S3). It formed noticeable precipitation making with as-treated glassy carbon after several hours. It indicated that the concentrated H2SO4 could not oxidize glassy carbon effectively. Indeed, experiment provided evidence that HNO3 is irreplaceable in the oxidation reaction system. Hence, the mixture acids system was used in the later experiments.
1.2 Fluorescent graphite
Fig. S4 (a) Aqueous solution (without purification treatment) of the chemically treated graphite, which were treated with the indicated time and photographed directly; (b) The normalized fluorescence spectra of FGT which were treated in mixture acids system (HNO3/H2SO4 1/3) for 0.5, 5.0, 6.0 and 12.0 h, respectively
The influence of the treatment times on the fluorescence emission of FGT was studied (Fig. S4). Compared to sample treated for 0.5 h, the emission peak of the sample treated for more than 5 h shifted red. With prolonging the treatment time (≥ 5 h), the emission peaks did not obviously shift. Therefore, 120 ℃ and 5 h were used in the later graphite experiments.
1.3 Fluorescent graphene oxide
Fig. S5 The fluorescence emission spectra of the FGO aqueous dispersion. Insert: the corresponding normalized fluorescence spectra of fluorescent graphene oxide
The influence of the treatment times on the fluorescence intensity of FGO was studied (Fig. S5). With prolonging the treated-time, the intensity of FGO gradually increased. The phenomena may be attributed to the fact that treatment time affects the defects, doping and oxidation degree of graphene oxide sheets. The easiest way to covalently attach chemical functional groups is by oxidation. Indeed, oxidation reactions in air or nitric (HNO3) and sulfuric (H2SO4) acids create defective sites in the material surface, and form carboxyl, carbonyl groups or other functional groups on the surface of the materials. Thus, the treatment time was 12 h being used in the later experiments.
2 Structural characterization of fluorescent glassy carbon
Fig. S6 TEM images of FGC0.5 (a), FGC5 (b) and FGC6 (c). The insets of (a) show the magnification TEM images of the corresponding section
3 XPS analysis of fluorescent specimens
Fig. S7 The XPS spectra of FGT (black line), FGO (wine line), FGC (olive line)
4 Spectral characteristics of fluorescent specimens
Fig. S8 The effect of the solution pH value on FGT (a), FGO (b), FGC (c) fluorescence spectra; the plots of the values of normalized intensity of the fluorescent nano-carbon particles (black line: FGT; olive line: FGO; wine line: FGC)
Fig. S9 The fluorescence stability of FGT (black line), FGO (red line) and FGC (blue line)
Fig. S10 The selectivity of the FGC for heavy metal cations (10-4 M) in pH = 1.00 HNO3 media (a), 0.1 M NaNO3 media (b) and 0.1 M KNO3 media (c). The excitation wavelength was 340 nm
As shown in Fig. S10, FGC have different responses to metal cations in different medium. Compared to NaNO3 and KNO3 media, FGC has no obvious response to Cu2+ and Pb2+ in acid media. That could be explained as follows: at low pH values, a relatively high concentration of H+, which strongly competed with Cu2+ and Pb2+ for the active sites. It would protonate the oxygen/nitrogen-containing groups (-COO-, -OH, -NO2) of the graphene-like materials surfaces to form -COOH, -OH2+, -NOOH+. Furthermore, the protonation of functional groups lead to electrostatic repulsion, which restricts Cu2+ and Pb2+ to contact with the surface-active groups. With pH value increasing, the functional groups dissociate and form active functional groups, which might enhance the electrostatic attraction between the materials surface and the cationic ions. The number of H+ also decreased at higher pH values, the competition between H+ and cationic ion (Cu2+ and Pb2+) became less significant. As a result, nano-carbon materials have well response to Cu2+ and Pb2+ in neutral medium.
Fig. S11 (a) Fluorescence emission of FGC (black line), the system in the presence of 10-4 M Pb2+ without any chelator (wine line) and with 2 × 10-4 M EDTANa2 (olive line); (b) fluorescence emission of FGC (black line), the sysem in the presence of 10-4 M Cu2+ without any chelator (wine line) and with 2 × 10-4 M EDTANa2 (olive line)