Hydrogen Peroxide Involved Anodic Charge Transfer and

Aug 22, 2017 - Gergely F. Samu , Rebecca A. Scheidt , Prashant V. Kamat , and Csaba Janáky. Chemistry of Materials 2017 Article ASAP. Abstract | Full...
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Hydrogen Peroxide Involved Anodic Charge Transfer and Electrochemiluminescence of All-Inorganic Halide Perovskite CsPbBr3 Nanocrystals in an Aqueous Medium Yan Huang,†,§ Xiaoyan Long,‡,§ Dazhong Shen,⊥ Guizheng Zou,*,‡ Bin Zhang,‡ and Huaisheng Wang*,† †

Department of Chemistry, Liaocheng University, Liaocheng 252059, China School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China ⊥ College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan 250014, China ‡

S Supporting Information *

ABSTRACT: Reactive oxygen species (ROS) involved anodic charge transfer and electrochemiluminescence (ECL) of all-inorganic halide perovskite CsPbBr3 nanocrystals (NCs) were investigated in an aqueous medium with hydrogen peroxide (H2O2) as the model. CsPbBr3 NCs could be electrochemically oxidized to positively charged states by injecting holes onto the highest occupied molecular orbitals and could be chemically reduced to negatively charged states by injecting electrons onto the lowest unoccupied molecular orbitals by ROS. The charge transfer between CsPbBr3 NCs of oxidative and reductive states could bring out monochromatic ECL with onset around +0.8 V, maximum emission around 519 nm, and a full width at half-maximum around 20 nm. H2O2 could selectively enhance the anodic ECL of CsPbBr3 NCs, which not only opened a way to design a bioprocessinvolved photovoltaic device with CsPbBr3 NCs but also was promising for color-selective ECL biosensing.

Figure 1. UV−vis absorption and PL (λex = 400 nm) spectra of CsPbBr3 NCs. Insets: (A) Fluorescence decay curve of CsPbBr3 NCs. SEM patterns of (B) a GCE and (C) CsPbBr3 NCs|GCE.

T

induced electrochemiluminescence (ECL) of CsPbBr3 NCs in an organic medium.15 ECL is a powerful technique to explore the charged state and charge transfer of various NCs16,17 and especially to design novel ECL strategies with NCs as emitters.18 Although many NCs, such as CdSe,19 CdTe,20 ZnSe,21 and CdInS,22 have been designed as promising electrochemiluminophores because of their ECL in an aqueous medium, few investigations on the charge transfer and ECL of all-inorganic perovskite NCs in an aqueous medium have been carried out until now.23,24 Because the insolubility of CsPbBr3 NCs prohibits NC release from CsPbBr3 NCs|GCE into an aqueous medium, which is favorable for the improved stability of CsPbBr3 NCs, herein we explored the anodic charge transfer and ECL of allinorganic perovskite NCs in an aqueous medium with CsPbBr3 NCs|GCE and found that some reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), participated in the anodic redox and ECL of CsPbBr3 NCs. H2O2 was involved in many bioprocesses25 and was crucial to the image function of biomolecules under a stimulated environment. These results

he earlier researches on all-inorganic halide perovskite (CsPbX3, X = Cl, Br, and I) mainly focused on bulk crystals or thin films. Since Protesescu and co-workers proposed a convenient method to prepare CsPbX3 nanocrystals (NCs),1 CsPbX3 NCs have become promising materials for photovoltaic and optoelectronic devices.2−5 CsPbX3 NCs not only displayed outstanding optical performances,5−7 such as tunable photoluminescence (PL), high quantum yields, and excellent color purity,1,6,8−10 but also were promising for various expanded applications because PL and electroluminescence of CsPbBr3 NCs were intrinsically different from those of traditional colloidal NCs (Figure 1).7,11,12 Although an exchange reaction between CsPbBr3 NCs and organohalides has been used to determine ions,13 only a few fluorescent strategies have been proposed with CsPbBr3 NCs as lumiphores;14 because perovskite NCs are unstable in polar solvents,14 they decompose and lose PL quickly in strong polar solvents such as water or ethanol. Recently, our group demonstrated that CsPbBr3 NCs, prepared by the method proposed by Protesescu and coworkers,1 could form a perovskite NC film on a glassy carbon electrode (GCE), i.e., CsPbBr3 NCs|GCE,15 and CsPbBr3 NCs| GCE could be utilized to explore the electrochemical redox© 2017 American Chemical Society

Received: June 15, 2017 Published: August 22, 2017 10135

DOI: 10.1021/acs.inorgchem.7b01515 Inorg. Chem. 2017, 56, 10135−10138

Communication

Inorganic Chemistry

spectrum was almost identical with the PL spectrum of CsPbBr3 NCs, which not only confirmed that the anodic ECL originated from CsPbBr3 NCs but also indicated that there were no surface defects or traps on CsPbBr3 NCs of highly crystallized structures15 because the surface defects or traps on unpassivated NCs might result in an obvious red-shifted or broadened ECL spectrum.29−31 The color purity of ECL from CsPbBr3 NCs| GCE in an aqueous medium was almost the same to those in an organic medium15 and was much higher than those from both the traditional chemical ECL emitters and the promising dualstabilizer-capped CdSe NCs.32 ECL of CsPbBr3 NCs|GCE might be of the highest color purity for all of the reported ECL systems in an aqueous medium to the best of our knowledge.15 Previous research has demonstrated that the anodic ECL of CsPbBr3 NCs|GCE in an organic medium could only be achieved with the presence of tri-n-propylamine,15 while no anodic ECL was achieved on CsPbBr3 NCs|GCE in the same organic medium without coreactant.15 The anodic ECL of CsPbBr3 NCs|GCE in a bare PB might be associated with some electrochemically generated chemicals (or radicals) at the GCE surface, which could chemically reduce CsPbBr3 NCs to negatively charged states (R−) by injecting electrons onto the lowest unoccupied molecular orbitals (LUMOs). It was previously demonstrated that ROS, such as O2•− or HO2−, could be electrochemically generated at the anode and react with ECL chemicals for anodic ECL in an aqueous medium.33 Herein, CsPbBr3 NCs|GCE did demonstrate both an enhanced oxidative current (Figure 2B) and obviously enhanced ECL with an onset of around +0.8 V and a maximum emission of around +1.25 V (Figure 2A) by introducing 0.10 μM H2O2 into the aforementioned bare PB. The ECL spectrum of CsPbBr3 NCs|GCE in PB containing 0.10 μM H2O2 was also almost the same to the PL spectrum, indicating that H2O2 participated in the anodic charge transfer for the anodic ECL of CsPbBr3 NCs without altering the excited states. Actually, ECL of CsPbBr3 NCs|GCE in both bare PB and PB containing 0.10 μM H2O2 displayed similar onset potentials, while CsPbBr3 NCs|GCE displayed an enhanced DPV response in PB containing 0.10 μM H2O2 over that in blank PB, indicating that the electrochemical oxidation of H2O2 on CsPbBr3 NCs| GCE did produce some radicals of strong reducing ability, which could reduce CsPbBr3 NCs to negatively charged states (R−) by injecting electrons onto the LUMOs. The enhanced ECL with the presence of H2O2 not only confirmed that H2O2 could participate in the redox and ECL of perovskite CsPbBr3 NCs but also manifested that CsPbBr3 NCs have the ability to store charges, which could subsequently lead to ECL upon hole and/ or electron transfer.17 Along with the monochromatic ECL of CsPbBr3 NCs|GCE in an organic medium,15 ECL of CsPbBr3 NCs|GCE in an aqueous medium further confirmed that CsPbBr3 NCs|GCE could preserve the highly passivated surface states of NCs in both organic and aqueous media and bring out ECL of the same excited states. The mechanism for ECL of CsPbBr3 NCs|GCE in PB was embodied by eqs 1−6.

are important to the design of a biorelated optoelectronic device and a novel biorelated ECL strategy.19,26,27 The as-prepared CsPbBr3 NCs displayed a distinct first electronic absorption peak at 509 nm and a symmetric PL peak at 516 nm with a full width at half-maximum (fwhm) of 19 nm, which was consistent with previously reported results.15 A PL decay curve of CsbBr3 NCs was well-fitted with a triexponential decay model (Table S1), and the PL lifetime was determined to be of 95.9 ns (inset A). X-ray diffraction (XRD) and transmission electron microscopy (TEM) patterns proved that CsPbBr3 NCs were of perfect cubic crystal structure (Figures S1 and S2).15 Scanning electron microscopy (SEM) patterns (insets B and C) proved that CsPbBr3 NCs were uniformly dispersed on the GCE surface.15 No obvious electrochemical and ECL responses were detected with a bare GCE in 0.10 M phosphate buffer (PB) containing 0.0 or 0.10 μM H2O2 (Figure S3) because no obvious charge transfer occurred on a bare GCE in PB without the presence of CsPbBr3 NCs (curves a and b, inset A of Figure 2). The slightly enhanced

Figure 2. (A) ECL and (B) cyclic voltammetry of CsPbBr3 NCs|GCE in 0.10 M pH 7.4 PB containing (a) 0.0 and (b) 0.1 μM H2O2 at 50 mV/s. Inset: (A) DPV profiles of (a and b) a bare GCE and (c and d) CsPbBr3 NCs|GCE in 0.10 M pH 7.4 PB containing (a and c) 0.0 and (b and d) 0.1 μM H2O2 at 50 mV/s. (B) ECL spectra of CsPbBr3 NCs|GCE in 0.10 M pH 7.4 PB containing (a) 0.0 and (b) 0.1 μM H2O2 at 50 mV/s.

current of a GCE in PB containing H2O2 than the same GCE in bare PB is probably due the anodic oxidation of H2O2. The obvious oxidative peak on the differential pulse voltammetry (DPV) profile of CsPbBr3 NCs|GCE in a bare PB (curve c, inset A of Figure 2) manifested that CsPbBr3 NCs could be electrochemically oxidized to positively charged states (R+) by injecting holes onto highest occupied molecular orbitals (HOMOs).15,17 Although CsPbBr3 NCs|GCE displayed much lower electrochemical response than the GCE in a bare PB (Figures 2B and S3B), obvious anodic ECL with an onset potential of around +0.8 V and maximum emission of around +1.12 V was also achieved on CsPbBr3 NCs|GCE in a bare PB without any traditional coreactant (curve a, Figure 2A). Despite the poor stability of perovskite NCs in polar solvents,28 herein the anodic ECL might indicate that CsPbBr3 NCs|GCE is stable enough for the electrochemical redox and ECL in an aqueous medium. Importantly, the ECL spectrum displayed a single and symmetric peak around 518 nm (2.39 eV) with a fwhm of 20 nm. The ECL

3OH− − 2e → HO2− + H 2O

(1)

H 2O2 + OH− → HO2− + H 2O → O2−

(2)

O2− + R → R−

(3)

R − e → R+

(4)

or

10136

DOI: 10.1021/acs.inorgchem.7b01515 Inorg. Chem. 2017, 56, 10135−10138

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Inorganic Chemistry R− + R+ → R*

(5)

R* → R + hν

(6)

even the mixture of these compounds also demonstrated negligible interference with H2O2 at the 0.1 μM level. The monochromatic and H2O2-involved ECL might eventually enable promising applications of perovskite NCs beyond optoelectronic and photovoltaic devices.4,5 In conclusion, the charge-transfer-related anodic redox and ECL of all-inorganic perovskite CsPbBr3 NCs was investigated in an aqueous medium for the first time. CsPbBr3 NCs could be electrochemically oxidized to the oxidative states at anodes, while some ROS could chemically reduce CsPbBr3 NCs to reductive states. The charge transfer of CsPbBr3 NCs between oxidative and reductive states could bring out monochromatic ECL in an aqueous medium, which might present a way to design a ECL strategy of high color selectivity with highly crystallized NCs. A small biomolecule, such as H2O2, could selectively enhance the anodic ECL without changing its spectral features. The promising redox and ECL nature of CsPbBr3 NCs in an aqueous medium not only opened the way to design biochemical-involved optoelectronic and photovoltaic devices but also indicated that polar solvents could also be used to investigate the redox nature of CsPbBr3 NCs under given conditions.

ECL of CsPbBr3 NCs|GCE increased gradually with the increased concentration of H2O2 in PB (Figure 3). A linear

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01515. Experimental section, XRD, TEM, and PL lifetime characterizations of the CsPbBr3 NCs, and ECL control testing (PDF)

Figure 3. ECL of CsPbBr3 NCs|GCE in 0.10 M pH 7.4 PB containing (a) 0.0, (b) 0.020, (c) 0.030, (d) 0.050, (e) 0.10, (f) 0.50, and (g) 1.0 μM H2O2 at 50 mV/s. Inset: Calibration curve for H2O2 detection.

relationship between the maximum ECL intensity and the logarithm of the H2O2 concentration was obtained from 0.030 to 1.0 μM (the inset of Figure 3), and the limit of detection was 0.020 μM (S/N = 3). The performance of CsPbBr3 NCs|GCEbased ECL for determining H2O2 was superior to some nonenzymatic ECL, amperometric, and colorimetric strategies (Table S2).34−37 Importantly, the anodic ECL of CsPbBr3 NCs|GCE was highly selective toward H2O2 (Figure 4). Common interfering substances for determining H2O2, such as ascorbic acid (AA), uric acid (UA), dopamine (DA), and glucose, displayed negligible ECL response on CsPbBr3 NCs|GCE in blank PB;

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Guizheng Zou: 0000-0002-3295-3848 Bin Zhang: 0000-0002-1529-6356 Author Contributions §

Y.H. and X.L. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This project was supported by the National Natural Science Foundation of China (Grants 21427808, 21375077, and 21375055) and the Fundamental Research Foundation of Shandong University (Grant 2015JC037).

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Figure 4. Response specificity for ECL of CsPbBr3 NCs|GCE toward H2O2. The bars represented the ECL intensity of CsPbBr3 NCs|GCE in 0.10 M pH 7.4 PB containing (a) 0.0 μM H2O2, (b) 1.0 μM AA, (c) 1.0 μM UA, (d) 1.0 μM DA, (e) 1.0 μM glucose, (f) 0.1 μM H2O2, and (g) a mixture of 1.0 μM AA, UA, DA, glucose and 0.1 μM H2O2. 10137

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