Visible-Light Induced Self-Powered Sensing Platform Based on a

Letter pubs.acs.org/ac

Visible-Light Induced Self-Powered Sensing Platform Based on a Photofuel Cell Kai Yan, Yaohua Yang, Otieno Kevin Okoth, Ling Cheng, and Jingdong Zhang* Key Laboratory of Material Chemistry for Energy Conversion and Storage (Ministry of Education), School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, P. R. China S Supporting Information *

ABSTRACT: A self-powered sensing system possesses the capacity of harvesting energy from the environment and has no requirement for external electrical power supply during the chemical sensing of analytes. Herein, we design an enzyme-free selfpowered sensing platform based on a photofuel cell (PFC) driven by visible-light, using glucose as a model analyte. The fabricated PFC consists of a Ni(OH)2/CdS/TiO2 photoanode and a hemin-graphene (HG) nanocomposite coated cathode in separated chambers. Under visible-light irradiation, glucose in the anodic chamber is facilely oxidized on Ni(OH)2/CdS/TiO2 while H2O2 in the cathodic chamber is catalytically reduced by HG, which generates a certain cell output sensitive to the variation of glucose concentration. Thus, a PFC based self-powered sensor is realized for glucose detection. Compared to the existing enzymatic self-powered glucose sensors, our proposed PFC based strategy exhibits much lower detection concentration. Moreover, it avoids the limitation of conventional enzyme immobilized electrodes and has the potential to develop high-performance self-powered sensors with broader analyte species.

S

plays a crucial role in construction of PFC. To efficiently utilize solar irradiation and promote the performance of PFC, photoanode is usually prepared or modified with narrow band gap semiconductors that have a strong ability to absorb visible light.23,24 Additionally, for cathode, suitable electrocatalysts employed can accelerate the reduction process and promote the cell performance.25 Although much effort has been devoted to the development of high-performance PFCs, it is still a challenge to explore the application of the relatively weak electrical output of PFCs. In the present work, we proposed the first PFC based selfpowered sensor. The PFC consisted of a Ni(OH)2/CdS/TiO2 photoanode and a hemin-graphene (HG) modified cathode in separated chambers. Glucose, the most intensively studied fuel in enzymatic self-powered sensors, was used as the model analyte to evaluate the performance of the proposed sensing platform. Considering that narrow band gap semiconductor CdS quantum dots (QDs) could serve as photosensitizer to promote the visible-light photocatalytic activity of TiO2,26,27 we fabricated the photoanode by coupling CdS QDs with TiO2. Moreover, Ni(OH)2, which has been extensively explored as an efficient electrocatalyst toward glucose oxidation in developing nonenzymatic glucose sensors,28,29 was deposited on CdS/ TiO2 to further enhance the photoelectrocatalytic activity of photoanode. The proposed PFC was based on the photo-

elf-powered sensors for biological and chemical sensing have attracted considerable interest due to their potential application in batteryless devices.1,2 Unlike traditional electrochemical devices using an external electrical power supply, selfpowered sensors are generally operated on the basis of energy transformation such as in a fuel cell3 and triboelectric nanogenerator4 which can drive the sensing progress. So far, enzymatic fuel cells have dominated self-powered sensors because of their simple configuration and unique capabilities to provide sustainable energy from renewable environment sources under mild conditions.5−7 Various enzymes such as glucose oxidase,8,9 cholesterol oxidase,10 glucose dehydrogenase,11 and alcohol dehydrogenase12,13 have been successfully employed for construction of self-powered sensors. Nevertheless, the enzymatic biofuel cells based self-powered sensors have suffered from the lack of stability originating from the intrinsic nature of enzymes and limited zymolytes.14,15 Since Fujishima and Honda described the first photocatalytic water splitting system using a semiconductor electrode in 1972,16 photocatalytic processes have been extensively studied in pollutant degradation, hydrogen production, solar cells, and CO2 reduction.17,18 In recent years, photofuel cells (PFCs), which can convert solar irradiation to electricity during the photocatalytic oxidation process of organic compounds, have emerged as attractive devices for effective utilization of organic pollutants as fuel.19−22 The typical PFC can be readily fabricated using a photoanode for oxidation of fuel and a cathode for reduction of electron acceptor. The concomitant processes of oxidation on photoanode and reduction on cathode can generate electrical power. Generally, photoanode © XXXX American Chemical Society

Received: April 22, 2016 Accepted: May 29, 2016

A

DOI: 10.1021/acs.analchem.6b01600 Anal. Chem. XXXX, XXX, XXX−XXX

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Analytical Chemistry electrocatalytic oxidation of glucose on photoanode and reduction of H2O2 on cathode, which could generate enough output as electrical signal for glucose sensing. Scheme 1 illustrates the proposed self-powered sensing mechanism and the reaction of analyte on the photoanode. Scheme 1. Schematic Illustration for (A) the Proposed PFC Based Self-Powered Sensor and (B) Photoelectrocatalytic Reaction of Glucose on Ni(OH)2/CdS/TiO2 Photoanode

Figure 1. (A) Scanning electron microscopy (SEM) of Ni(OH)2/ CdS/TiO2 photoanode. (B) UV−visible diffuse reflectance spectra of photoanode. (C) EDS of Ni(OH)2/CdS/TiO2 photoanode. (D) Smoothed XPS spectrum of Ni 2p of photoanode. The suffix (s) represents the corresponding satellite peaks of Ni 2p.

electrode surface is further revealed by the variation of electron transfer resistance. The photoelectrocatalytic activity of photoanode for oxidation of fuel plays a crucial role in achieving a highperformance PFC. In the present PFC, glucose served as the fuel. Thus, we studied the electrochemical behavior of glucose on CdS/TiO2 and Ni(OH)2/CdS/TiO2 electrodes in 0.1 M NaOH by cyclic voltammetry (CV). It was observed that the CdS/TiO2 electrode did not show any electrochemical response toward glucose (curve a in Figure 2A). While the Ni(OH)2/CdS/TiO2 electrode was employed, an oxidation peak at 0.47 V appeared in the CV curve recorded in 0.1 M NaOH (curve b in Figure 2A), attributed to the oxidation of Ni(OH)2 to NiOOH in alkaline electrolyte.34 When 2 mM glucose was added into the electrolyte, the oxidation peak of Ni(OH)2/CdS/TiO2 was obviously increased (curve c in Figure 2A), confirming the well-known catalysis of Ni2+/Ni3+ redox couple toward the oxidation of glucose according to the following reactions:29

In such a PFC, the Ni(OH)2/CdS/TiO2 photoanode was prepared by a three-step route consisting of liquid phase deposition of TiO2 film on fluoride doped tin oxide (FTO) substrate, layer-by-layer assembly of CdS QDs, and electrochemical deposition of Ni(OH)2. The experimental details are provided in the Supporting Information. As illustrated in Figure S1, many TiO2 nanoparticles with a size of ca. 30 nm were uniformly deposited on the electrode surface. After CdS QDs were assembled on TiO2 electrode, the surface was covered by a compact film of CdS and the absorption in the visible region was obviously improved due to the excellent optical properties of CdS QDs. Furthermore, after Ni(OH)2 was deposited, the as-prepared Ni(OH)2/CdS/TiO2 photoanode showed a porous and rough surface structure (Figure 1A) but no significant change was observed in the light absorption (Figure 1B). Energy dispersive spectroscopy (EDS, Figure 1C) and X-ray photoelectron spectra (XPS, Figure S2) confirmed the presence of elements (Ni, O, Cd, S, and Ti) in the photoanode. Narrow scanning of XPS of Ni 2p (Figure 1D) displayed two major peaks of Ni 2p3/2 and Ni 2p1/2 located at 855.8 and 873.5 eV, respectively. The spin-energy separation of 17.7 eV confirmed the existence of Ni(OH)2 phase on the photoanode.30,31 Additionally, there appeared satellite peaks close to two major peaks of Ni 2p, assigned to the shakeup process of ejected electrons during the XPS analysis.32,33 The EDS mapping results (Figure S3) indicated that the CdS quantum dots and Ni(OH)2 were deposited uniformly across the entire TiO2 film surface. Moreover, considering that TiO2, CdS, and Ni(OH)2 had different electron transfer abilities, we studied the interfacial properties of various electrodes by electrochemical impedance spectroscopy (EIS). As can be seen from Figure S4, the effective immobilization of TiO2, CdS, and Ni(OH)2 on the

Ni(OH)2 + OH− → NiOOH + H 2O + e−

(1)

NiOOH + Glucose → Ni(OH)2 + Glucolactone

(2)

Interestingly, when the Ni(OH)2/CdS/TiO2 electrode was irradiated under visible light, the CV curve for glucose became sigmoidal in shape, accompanied by dramatic enhancement in the oxidation peak current (curve d in Figure 2A), similar to our previous observation on the photoelectrocatalytic oxidation of p-phenylenediamine on a CdS QDs-graphene hybrid film coated electrode.35 This demonstrates the high photoelectrocatalytic activity of Ni(OH)2/CdS/TiO2 for glucose oxidation, which can be attributed to the participation of photogenerated electrons on CdS in the catalytic oxidation process of glucose. Moreover, an increased CV background was also observed, due to the photo-oxidation of water.16,36 On the other hand, the cathode used in the PFC was prepared by modifying FTO substrate with HG composites which were prepared through a hydrothermal method as described in the Supporting Information. In order to enhance B

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The construction of PFCs was facilely done by combining the proposed photoanode and cathode in two chambers separated by a Nafion membrane. We investigated the dependence of output voltage (V−I curves, Figure 3A) or

Figure 2. (A) CV curves of (a) CdS/TiO2 in the presence of 100 μM glucose, (b) Ni(OH)2/CdS/TiO2 in absence of glucose, (c) Ni(OH)2/CdS/TiO2 in the presence of 100 μM glucose, and (d) Ni(OH)2/CdS/TiO2 under irradiation in the presence of 100 μM glucose. The CV curves were recorded in 0.1 M NaOH at a scan rate of 50 mV/s. (B) CV curves of bare FTO (a, c) and HG/FTO (b, d) in the absence (a, b) and presence (c, d) of 5 mM H2O2. The CV curves were recorded in 0.1 M PBS (pH 7.4) saturated with N2 at a scan rate of 50 mV/s. (C) Polarization curves of photoanode recorded in 0.1 M NaOH without (a) and with (b) 50 μM glucose under visible light irradiation at a scan rate of 2.0 mV/s. (D) Polarization curves of cathode recorded in 0.1 M PBS (pH 7.4) without (a) and with (b) 5 mM H2O2 saturated with N2 at a scan rate of 2.0 mV/s.

Figure 3. (A) V−I curves and (B) P−I curves of PFC using HG/FTO as cathode in 5 mM H2O2 and different electrodes: (a) TiO2, (b) CdS/TiO2, and (c, d) Ni(OH)2/CdS/TiO2 as photoanode in the presence (a, b, c) and absence (d) of 50 μM glucose in anolyte. (C) V−I curves and (D) P−I curves of PFC using Ni(OH)2/CdS/TiO2 as photoanode in 50 μM glucose and different electrodes: (a) bare FTO and (b) HG/FTO as cathode in 5 mM H2O2.

power density (P−I curves, Figure 3B) on the cell current using different photoanodes. The maximum output power (PMax) of the PFC for 50 μM glucose was increased by ten times when CdS/TiO2 was used instead of TiO2 photoanode, attributed to the enhanced visible-light photocatalytic activity of TiO2 by CdS QDs. The PMax was further increased by nearly two times when a Ni(OH)2/CdS/TiO2 photoanode was used, showing the contribution of Ni(OH)2 to glucose oxidation. Thus, the Ni(OH)2/CdS/TiO2 based PFC exhibited the best output performance with an open circuit potential (OCP) of 1.21 V and a PMax value of 10.5 μW·cm−2 as compared with the PFCs using TiO2 and CdS/TiO2 as photoanodes. Moreover, to achieve the highest cell performance, the effects of the amounts of CdS and Ni(OH)2 on the PMax response of PFC toward 50 μM glucose were optimized, as depicted in Figures S5 and S6. Therefore, such a high performance PFC is attributed to the synergy of the excellent photocatalytic activity of CdS quantum dots and high electrocatalytic activity of Ni(OH)2 for glucose oxidation. Meanwhile, we also compared the output performances of PFCs using different cathodes. As seen in Figure 3C,D, the PFC based on HG/FTO cathode obviously exhibited higher output performance in terms of OCP and PMax than the FTO based one owing to the electrocatalysis of HG toward H2O2 reduction. Interestingly, the OCP of 1.21 V for the constructed PFC employing Ni(OH)2/CdS/TiO2 as photoanode and HG/ FTO as cathode is obviously higher than the theoretical value estimated from the onset potentials of photoanode and cathode (Figure 2C,D). This can be explained by the chemical bias applied between the photoanode and cathode, which is induced by different pH values of anolyte and catholyte.41

the fuel cell efficiency, we added 5 mM H2O2 acting as electron scavenger in the catholyte. For bare FTO electrode, only low cathodic current for H2O2 was observed. While a HG/FTO electrode was used instead of bare FTO, a high catalytic cathodic current was observed due to the high electrocatalytic activity of hemin in HG composites for H2O2 reduction:37−39 Hemin

H 2O2 + 2e− + 2H+ ⎯⎯⎯⎯⎯⎯→ 2H 2O

(3)

To examine the thermodynamic feasibility of the proposed PFC using Ni(OH)2/CdS/TiO2 photoanode and HG/FTO cathode, the polarization curves for the two electrodes recorded in their corresponding electrolytes with and without substrates (glucose for photoanode or H2O2 for cathode) were analyzed. On the Ni(OH)2/CdS/TiO2 photoanode, an onset anodic potential appeared at ca. −700 mV in the presence of glucose (Figure 2C), which was obviously induced by the photoelectrocatalytic oxidation of glucose. In comparison, an anodic current without glucose on the photoanode under irradiation started at ca. −600 mV, attributed to the oxidation of Ni(OH)2. For the HG/FTO cathode, the reduction of H2O2 started at ca. 200 mV and reached a plateau of 40 μA at ca. −100 mV. Accordingly, the Ni(OH)2/CdS/TiO2 photoanode oxidizes glucose promptly at a low potential while the HG based cathode catalyzes the reduction of H2O2 efficiently at a high potential, demonstrating that the proposed PFC is thermodynamically available.40 Moreover, the kinetics at the photoanode is the limiting factor since the catalytic current on the photoanode is smaller than that on the cathode, and thus, controlling the photoanode reaction would influence the cell performance.10 C

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photoanode and cathode were stored at 4 °C before the test. The results showed that the PFC still maintained at least 94.5% of the initial response in the continuous tests (Figure 4D), suggesting that the sensor had high stability. Additionally, the stability of the sensor was studied by exposing the photoanode under visible light irradiation. As shown in Figure S8, the proposed sensor only exhibited a small decline of ca. 7% in PMax response after a 30 min irradiation, showing an acceptable light stability. Moreover, the reproducibility of the developed selfpowered sensor was evaluated by checking the responses of six independently prepared PFC toward 50 μM glucose. A relative standard deviation value of 3.5% was obtained, showing a good reproducibility. In summary, this work has introduced a novel concept of PFC based self-powered sensing platform driven by visible light. Since the PFCs are based on highly active and stable photocatalysts that allow many organic compounds to act as fuel, some problems in enzyme based biofuel cell sensors can be avoided and a potential of broader analyte species may be provided. Moreover, the visible light-driven devices are favorable to the effective utilization of solar light. Naturally, the selectivity of the PFC based self-powered sensor can be improved when specific reorganization techniques such as antibodies, molecularly imprinted polymers, and aptamers are incorporated. The present self-powered sensing platform based on PFC paves a way to the development of new highperformance sensors without using external electrical power supply.

The developed PFC was explored for self-powered sensing of glucose. The P−I curves (Figure 4A) and V−I curves (Figure

Figure 4. (A) P−I curves of PFC for glucose at different concentrations: (a) 0 μM, (b) 10 μM, (c) 50 μM, (d) 100 μM, (e) 200 μM, (f) 300 μM, and (g) 500 μM. Other conditions are the same as those in curve c of Figure 3A. (B) Linear relationship between PMax of sensor and glucose concentration. (C) Histogram for PMax obtained on PFC for 100 μM glucose solution containing 5 μM ascorbic acid (AA), uric acid (UA), and dopamine (DA). (D) Stability of the developed self-powered sensor toward 50 μM glucose. Error bars were derived from the standard deviation of three measurements.

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ASSOCIATED CONTENT

S Supporting Information *

S7) of the PFC for glucose at different concentrations were analyzed. It was found that both OCP and PMax of the PFC increased linearly with the glucose concentration from 10 to 500 μM. The linear regression equations can be expressed as PMax/μW·cm−2 = 0.0385c/μM + 7.75 (correlation coefficient R = 0.998) and OCP/V = 0.000266c/μM + 1.18 (R = 0.995). The existence of OCP and PMax in the absence of glucose could be induced by (1) the chemical bias owing to the pH difference between anolyte and catholyte and (2) photo-oxidation of water on photoanode under visible-light irradiation. Considering the analytical sensitivity of the self-powered sensor, we adopted PMax as the output signal for glucose sensing in such a PFC. The detection limit (3S/N) was estimated to be 5.3 μM. Compared with previously reported self-powered glucose sensors (Table S1), the proposed PFC based sensor exhibits much lower detection concentration, due to the efficient photoelectrocatalytic oxidation of glucose on the Ni(OH)2/ CdS/TiO2 photoanode. Moreover, the high electrocatalytic activity of HG modified cathode toward the reduction of H2O2 is advantageous to promote the output performance of PFC for self-powered sensing. The interference studies were carried out in 100 μM glucose solution under the optimum conditions by adding 5 μM of the potential coexisting species, considering that the normal physiological level of glucose is at least 30 times of the interfering species such as ascorbic acid, uric acid, and dopamine.14,42 As shown in Figure 4C, all these species did not show obvious interference in the determination of glucose, confirming an acceptable selectivity toward the detection of glucose. The long-term stability of the sensor was also investigated by checking the PMax response of the fabricated PFC toward 50 μM glucose every 10 days. Both the

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.analchem.6b01600. Additional experimental details, figures showing characterization of the photoanode and performance of the photofuel cell, a table showing a comparison of different self-powered sensors for glucose determination (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-27-87543032. Fax: +86-27-87543632. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant No. 61571198). We also thank the Analytical and Testing Center of Huazhong University of Science and Technology for the use of the SEM and XPS instruments.

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REFERENCES

(1) Katz, E.; Bückmann, A. F.; Willner, I. J. Am. Chem. Soc. 2001, 123, 10752−10753. (2) Zhou, M.; Dong, S. Acc. Chem. Res. 2011, 44, 1232−1243. (3) Zhou, M. Electroanalysis 2015, 27, 1786−1810. (4) Wang, Z. L. ACS Nano 2013, 7, 9533−9557. (5) Germain, M. N.; Arechederra, R. L.; Minteer, S. D. J. Am. Chem. Soc. 2008, 130, 15272−15273. D

DOI: 10.1021/acs.analchem.6b01600 Anal. Chem. XXXX, XXX, XXX−XXX

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Analytical Chemistry (6) Arechederra, R. L.; Minteer, S. D. Anal. Bioanal. Chem. 2011, 400, 1605−1611. (7) Zhou, M.; Wang, J. Electroanalysis 2012, 24, 197−209. (8) Meredith, M. T.; Minteer, S. D. Anal. Chem. 2011, 83, 5436− 5441. (9) Hou, C.; Fan, S.; Lang, Q.; Liu, A. Anal. Chem. 2015, 87, 3382− 3387. (10) Sekretaryova, A. N.; Beni, V.; Eriksson, M.; Karyakin, A. A.; Turner, A. P. F.; Vagin, M. Y. Anal. Chem. 2014, 86, 9540−9547. (11) Bai, L.; Jin, L.; Han, L.; Dong, S. Energy Environ. Sci. 2013, 6, 3015−3021. (12) Zhang, L.; Zhou, M.; Dong, S. Anal. Chem. 2012, 84, 10345− 10349. (13) Wen, D.; Deng, L.; Guo, S.; Dong, S. Anal. Chem. 2011, 83, 3968−3972. (14) Meng, L.; Jin, J.; Yang, G.; Lu, T.; Zhang, H.; Cai, C. Anal. Chem. 2009, 81, 7271−7280. (15) Kim, J.; Jia, H.; Wang, P. Biotechnol. Adv. 2006, 24, 296−308. (16) Fujishima, A.; Honda, K. Nature 1972, 238, 37−38. (17) Ma, Y.; Wang, X.; Jia, Y.; Chen, X.; Han, H.; Li, C. Chem. Rev. 2014, 114, 9987−10043. (18) Ravelli, D.; Dondi, D.; Fagnoni, M.; Albini, A. Chem. Soc. Rev. 2009, 38, 1999−2011. (19) Antoniadou, M.; Lianos, P. Appl. Catal., B 2010, 99, 307−313. (20) Fujishima, Y.; Okamoto, S.; Yoshiba, M.; Itoi, T.; Kawamura, S.; Yoshida, Y.; Ogura, Y.; Izumi, Y. J. Mater. Chem. A 2015, 3, 8389− 8404. (21) Roy, P.; Berger, S.; Schmuki, P. Angew. Chem., Int. Ed. 2011, 50, 2904−2939. (22) Liu, Y.; Li, J.; Zhou, B.; Chen, H.; Wang, Z.; Cai, W. Chem. Commun. 2011, 47, 10314−10316. (23) Yu, X.-Y.; Lei, B.-X.; Kuang, D.-B.; Su, C.-Y. Chem. Sci. 2011, 2, 1396−1400. (24) Tada, H.; Fujishima, M.; Kobayashi, H. Chem. Soc. Rev. 2011, 40, 4232−4243. (25) Winther-Jensen, B.; MacFarlane, D. R. Energy Environ. Sci. 2011, 4, 2790−2798. (26) Zhang, H.; Chen, G.; Bahnemann, D. W. J. Mater. Chem. 2009, 19, 5089−5121. (27) Sun, W.-T.; Yu, Y.; Pan, H.-Y.; Gao, X.-F.; Chen, Q.; Peng, L.M. J. Am. Chem. Soc. 2008, 130, 1124−1125. (28) Zhang, Y.; Xu, F.; Sun, Y.; Shi, Y.; Wen, Z.; Li, Z. J. Mater. Chem. 2011, 21, 16949−16954. (29) Safavi, A.; Maleki, N.; Farjami, E. Biosens. Bioelectron. 2009, 24, 1655−1660. (30) Zhang, F.; Zhu, D.; Chen, X.; Xu, X.; Yang, Z.; Zou, C.; Yang, K.; Huang, S. Phys. Chem. Chem. Phys. 2014, 16, 4186−4192. (31) Yan, J.; Fan, Z.; Sun, W.; Ning, G.; Wei, T.; Zhang, Q.; Zhang, R.; Zhi, L.; Wei, F. Adv. Funct. Mater. 2012, 22, 2632−2641. (32) McIntyre, N. S.; Cook, M. G. Anal. Chem. 1975, 47, 2208− 2213. (33) Marchetti, L.; Miserque, F.; Perrin, S.; Pijolat, M. Surf. Interface Anal. 2015, 47, 632−642. (34) Cibrev, D.; Jankulovska, M.; Lana-Villarreal, T.; Gómez, R. ACS Appl. Mater. Interfaces 2014, 6, 10304−10312. (35) Zhu, Y.; Yan, K.; Liu, Y.; Zhang, J. Anal. Chim. Acta 2015, 884, 29−36. (36) Ogura, Y.; Okamoto, S.; Itoi, T.; Fujishima, Y.; Yoshida, Y.; Izumi, Y. Chem. Commun. 2014, 50, 3067−3070. (37) Lin, Y.; Wu, L.; Huang, Y.; Ren, J.; Qu, X. Chem. Sci. 2015, 6, 1272−1276. (38) Guo, Y.; Deng, L.; Li, J.; Guo, S.; Wang, E.; Dong, S. ACS Nano 2011, 5, 1282−1290. (39) Guo, Y.; Li, J.; Dong, S. Sens. Actuators, B 2011, 160, 295−300. (40) Yan, Y.; Fang, J.; Yang, Z.; Qiao, J.; Wang, Z.; Yu, Q.; Sun, K. Chem. Commun. 2013, 49, 8632−8634. (41) Lianos, P. J. Hazard. Mater. 2011, 185, 575−590. (42) Wang, C.; Yin, L.; Zhang, L.; Gao, R. J. Phys. Chem. C 2010, 114, 4408−4413. E

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