Electronic Supplementary Material
A europium (III) based nano-flake MOF film for efficient fluorescent sensing of picric acid
Feng Zhang, Gaowei Zhang, Hua Yao, Yi Wang, Tianshu Chu, Yangyi Yang*
School of Chemistry & School of Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510275, P. R. China
*Corresponding Author: E-mail: ; Tel: +86-20-84112977
General procedure for fluorescence measurements
The sensing experiments were carried out by monitoring the fluorescence quenching behavior of the Eu-NDC thin films directly immersed in the corresponding diluted NAEs aqueous solution, and the luminescence intensity was monitored from 500 to 750 nm with the excitation wavelength fixed at 355 nm. Each concentration detecting was repeated at least three times and consistent results are reported. Then the used film was washed with water for detecting the next concentration. All samples were measured at room temperature.
Optimization of experimental conditions
As described in main paper, we try to explore the possibility that fabricating a perfect thin film in a seconds level deposition time. Herein, the relationship between the current density and deposition time was investigated in detail on the condition that NH4NO3 was selected as the support electrolyte and all the reactant concentrations were fixed.
The process of thin films electrodeposited at different current densities of 0.1~ 0.6 mA cm−2 was carefully observed. When the current density was 0.1 mA cm−2, only a very small part of the surface of the FTO substrate was covered by the MOF of Eu-NDC within 3 minutes. It took about 10 minutes that the whole surface of the FTO was covered with white thin film. When the current density was 0.2 and 0.3 mA cm−2, the whole surface of the FTO was covered need about 2 and 1minute, respectively. When the current density was increased to 0.4 mA cm−2, a smooth and uniform white film was formed only take about 30 seconds, and it exhibited bright red luminescence under a UV lamp. When the current density was 0.5 mA cm−2, as expected, it only spent about 20 seconds obtaining a compact and uniform thin film. However, increasing the current density to 0.6 mA cm−2, it still need at least 20 seconds. This phenomenon may be because it takes a certain time of the chemical reaction on the interface of electrode to achieve the film-forming condition. Therefore, the condition of J = 0.5 mA cm−2 and t = 20 seconds were used to prepare a deposited MOF thin film for subsequent experiments.
Fig. S1 Powder X-ray diffraction patterns of electrodeposited thin film, peaks of SnO2 were found (SnO2, JCPDS file no. 46-1088), which belong to the FTO substrate.
Fig. S2 FT-IR spectra of H2NDC ligand and Eu-NDC thin film.
As shown in Fig. S2, there is distinct difference between the ligand and Eu-NDC thin film. When the Eu3+ coordinating to the carboxy group of H2NDC, the O-H of carboxy group stretching vibrations at the general range of 3300-2500 cm-1 were disappeared and the carbonyl stretching vibration was suppressed. The IR of Eu-NDC thin film shows bands at 3517, 3405, 1662, 1608, 1548, 1491, 1409, 1361, 1200, 928, 792, 567 and 484 cm-1. The bands at 3405 cm−1 is due to the stretching vibrations of O-H of water, and 1662 cm−1 is due to the stretching vibrations of C=O. The rest of bands are almost coincides with the original reported data of Eu-NDC MOFs crystal (3508, 1602, 1547, 1491, 1412, 1353, 1199, 927, 795, 564 and 492 cm-1)[1]. The FT-IR spectra clearly demonstrate the formation of Eu-NDC thin film.
Fig. S3 Excitation and emission spectra of the Eu-NDC film in water.
The excitation spectrum shows a broad band in the range of 300–385 nm, which is ascribed to the π–π* electron transition of the organic ligands. When excited at 355 nm, emission bands centered at 579, 591, 614, 650 and 696 nm can be found. These can be attributed to 5D0 → 7FJ ( J = 0, 1, 2, 3, 4) transitions of Eu3+, respectively. The most prominent characteristic emission peak of the Eu-NDC thin film owes to the highly conjugated structure of the organic linkers, which commonly known as “antenna effect” and greatly enhances the optical performance of the Eu3+ ions.
Fig. S4 Time-dependent 5D0→7F2 normalized intensities of Eu-NDC film in water.
Fig. S5 Photographs of Eu-NDC thin films under visible light (a) and UV lamp excited at 365 nm in the absence and presence of 80 μM PA (b).
Detection Limit and Quantitation Limit for PA with Eu-NDC thin film in aqueous phase
Detection Limit = 3σ/slope = 3 * 1.94/8.73 = 0.67 μM
Quantitation Limit = 10 σ/slope = 10 * 1.94/8.73 = 2.22 μM
Multiple number of PL spectra (n = 13) were recorded for the Eu-NDC thin film immersed in deionized water. Sample standard deviation σ for the blank sensor, without the addition of PA was calculated to be 1.94.
Fig. S6 Relation of fluorescence intensity against PA of Eu-NDC thin film.
Fig. S7 (a) Concentration-dependent fluorescence quenching of the Eu-NDC thin film upon the addition of different concentrations of PA in the Pearl River water. (b) Stern–Volmer plot for the response to PA. Inset shows the Stern–Volmer plot in the PA concentration range of 0∼60 μM at room temperature.
Fig. S8 The quenching efficiency of Eu-NDC thin films toward PA, DNP and NP.
Fig. S9 (a) Concentration-dependent fluorescence quenching of the Eu-NDC thin film upon the addition of different concentrations of PA in the solutions of the Tris-HCl buffer (pH = 7.4). (b) Stern–Volmer plot for the response to PA. Inset shows the Stern–Volmer plot in the PA concentration range of 0∼75 μM at room temperature.
Table S1. HOMO and LUMO energy levels of selected analytes calculated by density functional theory (DFT) at B3LYP/6-31G* accuracy level using Gaussian 09 package of programs [2].
Analytes / HOMO (eV) / LUMO (eV) / Band Gap (eV)H2NDC
PA / -6.4135
-8.2374 / -2.187
-3.898 / 4.2265
4.3394
TNT / -8.4793 / -3.479 / 5.0003
NT / -7.3626 / -2.3171 / 5.0455
DNT / -8.1131 / -2.9769 / 5.1362
DNB / -8.4129 / -3.135 / 5.2779
NB / -7.5917 / -2.4294 / 5.1623
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