Self-Powered Electrochemical Oxidation of 4‑Aminoazobenzene Driven by a Triboelectric Nanogenerator Shuyan Gao,*,† Jingzhen Su,† Xianjun Wei,† Miao Wang,† Miao Tian,† Tao Jiang,‡ and Zhong Lin Wang*,‡,§ †
School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, P.R. China Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China § School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States ‡
S Supporting Information *
ABSTRACT: A rotary disc-structured triboelectric nanogenerator (rd-TENG) on the basis of free-standing electrification has been designed, where the aluminum composite panel has not been tailored to the stator becauseit is commercially available and cost-effective, has good electronic conductivity, and is easily processed. With the rotating speed increasing from 200 to 1000 rpm, the short-circuit current (Isc) is sharply enhanced from 50 μA to 200 μA, while the measured opencircuit voltage (Voc) and transferred charge (Qtr) almost keep constant, 600 V and 0.4 μC, respectively. The matched load for the rd-TENG at a rotating speed of 600 rpm is 2.7 MΩ, generating a maximum power of 19.75 mW, which corresponds to a maximum power density of 2.28 W m−2. Using the electric power generated by such a rd-TENG, highly toxic and carcinogenic 4-aminoazobenzene can be selectively treated to produce CO2 or an oligomer via reasonably controlling electrochemical oxidation potentials. The underlying mechanism is tentatively proposed based on the cyclic voltammogram, gas chromatograph-mass spectrometer, electrochemical impedance spectroscopy, and UV−vis spectra. Here the electrochemical degradation in a single-compartment cell is more valid, preferable, and feasible. The output Voc and rectified current of rd-TENG guarantee its extensive application to self-power electrochemical degradation of other azo compounds, i.e., 2-(4-dimethylaminophenylazo) benzoic acid, to CO2. This work suggests that rd-TENG, sustainable energy, can be feasibly designed to self-power a practical electrochemical treatment of dyeing wastewater by harvesting vibration energy. KEYWORDS: free-standing, rotary disc structure, triboelectric nanogenerator, 4-aminoazobenzene, self-power
A
breakage of the azo linkage to produce the incompletely degradable aryl amine compounds,7 which are usually toxic, carcinogenic, and mutagenic.8 Reported physical and chemical methods to deal with the aromatic amine compounds, such as photocatalysis,9 absorption,10 biological process,11,12 and
zo dyes are the most popular dyestuffs in the textile industry. Along with their wide applications, a large amount of the resultant waste is released into the environment in the form of industrial effluents generated by pharmaceuticals, cosmetics, textiles, and printing industries.1−6 The wastewater containing reactive azo components exhibits poor gas dissolution and light penetration, resulting in the incalculable damage to the aquatic ecosystem. Furthermore, most of the azo dyes are generally vulnerable to reductive © 2017 American Chemical Society
Received: October 25, 2016 Accepted: January 6, 2017 Published: January 6, 2017 770
DOI: 10.1021/acsnano.6b07183 ACS Nano 2017, 11, 770−778
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ACS Nano coagulation,13 even practicable, may be shadowed by limitations of secondary pollutants, sophisticated instruments, high cost, and low efficiency. The advanced treatment technology has certainly been eagerly desirable. Treating azo dyes by electrochemical method is relatively satisfactory because it has an easy manipulability, high efficiency, high removal rate, and good environment compatibility with the resulting products. There are several conventional electrochemical methods for the decontamination of wastewaters containing azo dyes, such as electrocoagulation,14 electrochemical reduction,15 electrochemical oxidation.16 Unfortunately, these conventional electrochemical processes need an external energy supply to power it, which is always provided by fossil fuels and limits its widespread application. Herein, an electrochemical process without the use of the conventional electrochemical setup, i.e., electrochemical station and galvanostat, is believed to a promising candidate to degrade azo dyes to CO2 or directly polymerize it to an oligomer through well-developed electrochemical technology via reasonably controlling electrochemical oxidation potentials driven by self-powered systems, replacing the traditional fossil fuels for electrical energy supplies. It would highlight (i) environmental compatibility, the nontoxic CO2 product, different from the toxic aryl amine products generated by most methods, (ii) good flexibility, controllable products modulated by the oxidation potentials, and (iii) high efficiency, self-powered systems harvesting universally available and renewable mechanical energy as a good substitute of fossil fuels. Among rich energy sources, ubiquitous mechanical energy is considered as one of the most available power sources in our daily life.17−19 Recently, we creatively invented triboelectric nanogenerator (TENG), based on contact electrification electrostatic induction and essentially different from the widely existing power generation technologies, to conveniently convert random mechanical energy into electricity.20 Soon, such technology has been intensively applied to self-power synthesis of polypyrrole,21 detection and removal of heavy metal ions,22 digital clocks,23 and electrochemical reactions,24 oxidation of toxic gases,25 water splitting,26 and removal of organic matter.27−29 To the best of our knowledge, the self-powered electrochemical treatment of azo dyes, especially the reaction mechanism, is rarely studied.30,31 Herein, we first design a freestanding rotary disc-structured triboelectric nanogenerator (rdTENG) and then apply it to a self-powered electrochemical system (SPES) to treat the carcinogenic azo dye of 4aminoazobenzene (AAB) to CO2 or oligomer via reasonably controlling electrochemical oxidation potentials. Here, AAB is selected as the research subject because most of the azo dyes are derivatives of AAB and the investigation into AAB can guide the general treatment of the azo dyes. Systematical study via cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS), gas chromatograph-mass spectrometer (GCMS), and UV−vis spectra indicates that AAB can be indirectly oxidized by HClO/Cl2 generated at the anode interface selfpowered by rd-TENG.32 In single-compartment cell (S-cell), AAB can be self-powered to be degraded to CO2 or polymerized to an oligomer, which takes advantages of (1) the simple setup without the separator film used in a doublecompartment cell (D-cell) and (2) the low cell voltage and resultant high efficiency. The self-power system and selective treatment of AAB to CO2 or an oligomer are the notable highlights. As expected, such SPES can be successfully extended to electrochemically degrade 2-(4-dimethylaminophenylazo)benzoic acid.
RESULTS AND DISCUSSION Harvesting ambient mechanical energy is believed to provide a cost-effective, clean, and sustainable electric energy as an effective supplement to traditional power supplies. TENGs have been recently invented to convert various mechanical energies into electricity as a portable power source due to its prominent advantages of high power density in terms of power per volume as well as power per weight.33−36 Although various structures of TENGs have been intensively developed,37−40 high-performance TENGs that specifically provide a useful amount of output current and power were rarely reported. Herein, we report a rd-TENG on the basis of free-standing electrification of the stator−rotator with arrays of radial sectors (shown in Figure 1a). The rotator, made of an acrylic sheet
Figure 1. (a) Schematic fabrication process of the rd-TENG. (b) An illustration of an electricity-generating process of the rd-TENG, which consists of an initial state, intermediate state, and final state. (c) Finite element simulation via COMSOL and the electric potential distribution as the rotation angle changes.
coated with Kapton film, is a collection of radially arrayed sectors with each sector unit having a central angle of 10°. A commercially available aluminum composite panel is first tailored to the stator, comprising two complementary-patterned electrode networks on the same plane that are disconnected by fine gaps in between (Figure 1a). The radius of the whole device is about 80 mm. Other fabrication details and the corresponding working principle can be easily found in previous work.23,41−44 Here an aluminum composite panel is first utilized because it is commercially available and costeffective, has good electronic conductivity, and is easily processed. With an external vibration source, the planar771
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Figure 2. Short-circuit current (a), open-circuit voltage (b), and transferred charge (c) of rd-TENG at different rotation rates. (d) The output current and power with the resistance of the external load at a rotating speed of 600 rpm. (e) The transformed short-circuit current and (f) open-circuit voltage at a rotating speed of 600 rpm.
ture,23,45 the continuous alternating current (AC) output from the rd-TENG could be modulated by the conventional transformer to effectively boost the output current at the expense of the output voltage. Therefore, the transformed current was enhanced up to nearly 1.2 mA at the rotating speed of 600 rpm, while the voltage was reduced to about 40 V, meaning that the transformed efficiency reaches about 63.9% (Figure 2e,f). As the TENG has just an AC output current, a bridge rectifier is usually utilized to reverse the negative portion to deliver a direct current (DC) output. The rectified current and voltage are shown in Figure S1. Electrochemical treatment of azo benzene dyes has been proven efficient in terms of simple equipment, flexible modulation, moderate temperature operation, and no sludge formation.46−49 As discussed above, the designed rd-TENG has a high performance, especially, the Isc output increases with increased rotating rate but a constant Voc. The output performance of rd-TENG is greatly improved from a Voc of 70 V and Isc of 1.8 mA30 (insufficient for the thorough degradation of azo dye) to Voc of 600 V and Isc of 120 μA, respectively. The maximum power density reaches 2.28 W m−2 at a rotating speed of 600 rpm. Such advantages of rd-TENG,
structured rd-TENG produces a periodically changing triboelectric potential that induces alternating currents between electrodes. A cycle of an electricity generation process and potential distribution by COMSOL are schematically illustrated in Figure 1b,c. A group of electrical measurements with variable rotating speeds were conducted on the rd-TENG and presented in Figure 2. With the rotating speed increasing from 200 to 1000 rpm, the short-circuit current (Isc) is sharply enhanced from 50 μA to 200 μA (Figure 2a), while the measured open-circuit voltage (Voc) and transferred charge (Qtr) almost keep constant, 600 V and 0.4 μC, respectively, as shown in Figure 2b,c. Along with the increasing load resistance, the output current drops (Figure 2d). The matched load for the rd-TENG at a rotating speed of 600 rpm is 2.7 MΩ, generating a maximum power of 19.75 mW, which corresponds to a maximum power density of 2.28 W m−2. To demonstrate the capability of the rd-TENG as a power source, it was directly connected to 250 LED light bulbs in the absence of any storage or power unit. When the rotating rate was set at 600 rpm, these lights were simultaneously lighted up and lasted several hours (Supporting Information Movie S1). According to litera772
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ACS Nano constant Voc and controllable Isc output, are beneficial to efficiently electrochemically treat azo dyes using natural mechanical energy. Herein, we tried the electrochemical treatment of AAB self-powered by rd-TENG in acidic conditions by preconnecting with a rectifier to ensure a constantly positive current and voltage and the electrolytic cell to form a SPES (Scheme 1). Figure 3a,b shows the CV plots in
0−1.2 and 0−1.4 V with the electrochemical progress, the evolution of chlorine at the anode interface weakens greatly, the AAB degradation rate slows down, and the corresponding current decays seriously. This further confirms the electrochemical polymerization of AAB on the anode under the middle potentials. When the potential is higher than 1.4 V, the evolution current of chlorine keeps nearly constant, demonstrating that the evolution of chlorine is dominant and the electrochemical polymerization of AAB is negligible at the anode interface. According to the CVs and EIS’s results, AAB can be selectively treated to produce CO2 or oligomer via reasonably controlling electrochemical oxidation potentials, which is constructive to electrochemically deal with organic pollutants. The characteristic absorption peak intensities in the visible light region decrease with increasing degradation time. The decoloration percentage of AAB is up to 99.9% after 12 min, as shown in Figure 4a. The progressive decoloring and UV−vis absorption fading in the visible region of AAB suggest the loss of chromophoric group −NN−:
Scheme 1. Schematic diagram of the rd-TENG driving the degradation of AAB
anode: 2Cl− → Cl 2 + 2e−
(1)
cathode: 2H+ + 2e− → H 2
(2)
bulk solution: Cl 2 + H 2O → HOCl + H+ + Cl−
(3)
To ascertain the degradation mechanism, the degraded intermediate compounds in the S-cell and D-cell are respectively collected and identified by GC-MS. The results are compiled in Figures 4b, S4, and S5. As shown in Figure 4b, the peak intensity of 1,4-benzoquinone was scaled down to one-tenth of its original intensity to better display the weak peaks. It can be noted that five new peaks (1, 2, 3, 4, 5) appear in GC, indicating that five intermediate compounds were generated during the degradation process of AAB. Combined with the analysis of MS (Figures S6−S10), it could be deduced that the five chemicals correspond to 2,4-dichloroaniline (1), 4chloroaniline (2), phenol (3), 2,4-dichlorophenol (4), and 4dichlorophenol (5), respectively. Table 1 summarizes the analysis results of the degraded intermediates, from which the degradation mechanism is tentatively proposed in Scheme 3.53 HOCl/Cl2 produced at the anode interface promptly attacks the C−N single bonds neighboring −NN− and nucleophilically substitutes the benzene hydrogen at the ortho-position of −NH2, producing intermediates 2,4-dichloroaniline (1), 4chloroaniline (2), and phenol (3) accompanied by the evolution of N 2 . In the presence of HOCl/Cl 2 , the intermediates (1) and (2) may further be oxidized to 2,4dichlorophenol (4) and 4-chlorophenol (5) respectively, which can further react with HOCl/Cl2 and form 1,4-benzoquinone (6). 3 can also further react with HOCl/Cl2 and form 6. It is well-documented that 6 can easily react with HOCl/Cl2, resulting in aromatic ring degradation until it is thoroughly mineralized to CO2 (eq 4).54 For the D-cell, the degraded
the presence and absence of AAB in the different potential ranges of 0−0.6, 0−0.8, 0−1.0, 0−1.2, 0−1.4, 0−1.6, 0−1.8, and 0−2.0 V vs SCE (the CV plots in the different potential ranges of 0−0.6, 0−0.8, and 0−1.0 V vs SCE were redisplayed in Figure S2 to enlarge the signals). In the relatively high potential ranges, i.e., 0−1.4, 0−1.6, 0−1.8, and 0−2.0 V, the CVs feature different characteristics (the reduction peak of chlorine at around 0.9 V in the absence of AAB is much higher than that in the presence of AAB), no AAB-related reduction/ oxidation peaks are observed, and the AAB solution rapidly changes from orange red to colorless (Figure S3). These demonstrate the indirect oxidation degradation of AAB initiated by the HClO/Cl2 generated at the anode interface (eqs 1−3). The GC-MS discussed later can verify that AAB can be completely degraded to CO2 in this case. In the absence of AAB, the CVs seem similar as those in the presence of AAB in the potential ranges of 0−0.6 and 0−0.8 V, and the AAB solution color does not change at all, meaning no degradation or other chemical reaction happens. In the presence of AAB in the potential range of 0−1.0 V, there are two pairs of evident reduction/oxidation peaks at 0.427 V (peak 4) /0.522 V (peak 1) and 0.613 V (peak 3)/0.669 V (peak 2) (Figure 3c), whose currents are all proportional to the scanning rate (Figure 3d,e). This is ascribed to the interface reduction/oxidation progress of the generated oligomer via the electrochemical oxidation of AAB (Scheme 2). The first redox peak at 0.427 V/0.522 V was proposed as the transition from the leucoemeraldine state to the emeraldine oxidation state, and the second redox peak at 0.613 V/0.669 V was attributed to the transition from the emeraldine oxidation state to the pernigraniline oxidation state.50,51 A thin yellow film was nakedly observed on the anode. Furthermore, the charge-transfer resistance, Ret (semicircle diameter in the EIS (Figure 3f)) increases with time during potentiostatic electrolysis at 1.4 V due to the increasing high resistance with the formation of the oligomer of AAB.52 This phenomenon, the formation of oligomers of AAB on a Pt anode is very similar to that reported on gold and silver anodes.51 It should be mentioned that in the potential range of
intermediate compounds produced in anode compartment were similar as those for the S-cell. Considering the low cell voltage and simple setup of the S-cell, the electrochemical treatment of AAB in a S-cell is more valid, preferable, and feasible here. Such a SPES is further extended to degrade similar azo dyes, i.e., 2-(4-dimethylaminophenylazo)benzoic 773
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Figure 3. (a) CVs of 0.5 mol L−1 HCl solution on Pt electrode at scan rate of 100 mV s−1 over different potential ranges. (b) CVs of 0.5 mol L−1 HCl-AAB (saturated) solution on Pt electrode at scan rate of 100 mV s−1 over different potential ranges. (c) CVs of 0.5 mol L−1 HCl and 0.5 mol L−1 HCl-AAB (saturated) solutions on Pt electrode at scan rate of 100 mV s−1 between 0.0 and 1.0 V. (d) CVs of 0.5 mol L−1 HCl and 0.5 mol L−1 HCl-AAB (saturated) solutions on Pt electrode at different scan rates. (e) Relationship between current density and scan rate. (F) EIS spectra of 0.5 mol L−1 HCl-AAB (saturated) solutions electrolyzed at the potential of 1.4 V (vs SCE) on Pt electrode with the size of 3 cm × 4 cm were collected at different reaction intervals.
Scheme 2. An Oligomer Is Generated via the Electrochemical Oxidation of AAB in the Potential Range of 0−1.0 V
acid. The decoloration percentages of 2-(4dimethylaminophenylazo)benzoic acid is up to 98.4% after 600 min (Figure S11).
CONCLUSION In summary, the designed rotary disc structure on the basis of free-standing electrification of the stator−rotator with arrays of radial sectors endows the rd-TENG with a maximum power density of 2.28 W m−2. Such a high performance is successfully tested to drive a SPES of AAB to produce CO2 or an oligomer based on the electrochemical theory, which makes full use of the strongly active chlorine to generate an efficient electrochemical treatment of AAB and is confirmed by the CVs, EIS, and GC-MS. Here, the electrochemical treatment of AAB in Scell is advantageous in terms of the simple setup without the separator film used in a D-cell, the low cell voltage, and resulting high efficiency. More importantly, the electrochemical treatment of AAB can be selectively treated to produce CO2 or 774
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Figure 4. (a) UV−vis spectra of AAB in the acidic electrolyte during its electrochemical degradation driven by rd-TENG at a rotating speed of 600 rpm. (b) GC-MS spectra of degraded intermediates of AAB in acidic electrolyte. 1, 2,4-dichloroaniline; 2, 4-chloroaniline; 3, phenol; 4, 2,4-dichlorophenol; 5, 4-chlorophenol; 6, 1,4-benzoquinone; and 7, 4-aminoazobenzene. The peak intensity of 6 was scaled down to onetenth of its original intensity.
Table 1. Intermediates Tested by GC-MS in a S-Cell After 0, 50, 80, and 300 s of Degradation of AAB
wavelength range at 190−900 nm. CV and EIS were performed on a CHI660E electrochemical workstation. Fabrication of rd-TENG. The rd-TENG was mainly composed of two parts: a stator and a rotator. For the stator, first, a square-shaped aluminum composite panel sheet was tailored as the stator model with a dimension of 170 mm × 170 mm × 3 mm using a machining center. Then five through holes were created in the square-shaped aluminum composite panel, four of them in the corners and another one in the center. After that, fine gaps with complementary patterns on the Al plane were created by a machining center. Finally, two wires were connected to complementary electrodes, respectively. For the rotator, a disc-shaped acrylic sheet was tailored as the substrate with a radius of 80 mm and a thickness of 8 mm by using a laser cutter. A through hole in the center of acrylic sheet and a 2 mm deep groove were created in the disc-shaped acrylic sheet by a machining center, and then the substrate had a collection of radially arrayed sectors with a central angle of 10°. After that, a layer of Kapton (50 μm) film was coated onto the plane with 2 mm deep groove, and then the portion facing the groove was cut with a blade. Lastly, the stator and rotator were put together with a bearing in the center for fabricating the rd-TENG. The rd-TENG was then fixed on a metal platform through the four through
an oligomer via reasonably controlling electrochemical oxidation potentials. Extensive application of such SPES in degrading 2-(4-dimethylaminophenylazo)benzoic acid further suggests that rd-TENG, on the basis of free-standing electrification and sustainable energy, can be reasonably tailored to self-power practical electrochemical processes of wastewater treatment by harvesting vibration energy.
EXPERIMENTAL SECTION General. Kapton films (500HN; thickness, 50 μm) were purchased from DuPont. Hydrochloric acid (HCl), AAB, and 2-(4dimethylaminophenylazo)benzoic acid were purchased from Alfa Aesar. Aluminum composite panels were purchased from Shanghai Huayuan New Composite Materials Co., Ltd. The output voltage signal of the rd-TENG was acquired using a digital oscilloscope from Agilent with 100 MΩ inner impedance, and the output current and charge signals of the rd-TENG were acquired using a 6514 programmable electrometer from Keithley. GC-MS was measured with an Agilent 6890/5973N Trace GC/MS system. UV− vis spectra were obtained on a TU-1810 spectrometer with the 775
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intermediates of AAB in acidic electrolyte in cathode compartment in the D-cell; (Figure S5) GC-MS spectra of degraded intermediates of AAB in acidic electrolyte in an anode compartment in the D-cell; (Figure S6) MS of 2,4-dichloroaniline (1); (Figure S7) MS of 4-chloroaniline (2); (Figure S8) MS of phenol (3); (Figure S9) MS of 2,4-dichlorophenol (4); (Figure S10) The MS of 4dichlorophenol (5); (Figure S11) UV−vis spectra of 2(4-dimethylaminophenylazo)benzoicacid in the acidic electrolyte during its electrochemical degradation driven by rd-TENG at a rotating speed of 600 rpm (PDF) LEDs lighted up by the rd-TENG (AVI)
Scheme 3. Tentatively Proposed Mechanism of Electrochemical Oxidation Degradation of AAB in a D-Cell
AUTHOR INFORMATION Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Zhong Lin Wang: 0000-0002-5530-0380 Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS Research was supported by the National Science Foundation of China (grant nos. 51432005, 5151101243, 51561145021, and 21471048), the National Key Research and Development Program of China, Minister of Science and Technology (2016YFA0202704), the “thousands talents” program for pioneer researcher and his innovation team, China, the Program for New Century Excellent Talents in University of Ministry of Education of China (NCET-11-0944), the Excellent Youth Foundation of Henan Scientific Committee (124100510004), the Research Project of Chinese Ministry of Education (no. 213023A), the Program for Innovative Research Team in University of Henan Province (no. 14IRTSTHN005), and the Program for Innovative Research Team of Henan Scientific Committee.
holes in the corners of stator by screws. The fabrication process of the rd-TENG is shown in Figure 1. Electrochemical Measurements. The electrochemical treatment of AAB self-powered by rd-TENG was performed in a glass beaker on an electrochemical workstation CHI660E (Shanghai Chenhua Co.). The used acidic electrolyte is a AAB solution (1.68 × 10−4 M) in 0.5 mol L−1 HCl and was pretreated with N2 for 30 min before measurement. CVs are tested at a scan rate of 100 mV s−1 in the potential ranges of 0−0.6, 0−0.8, 0−1.0, 0−1.2, 0−1.4, 0−1.6, 0−1.8, and 0−2.0 V with a three-electrode system, in which platinum foils are selected as the working and counter electrodes, while Hg/Hg2Cl2 is the reference electrode. EIS spectra of 0.5 mol L−1 HCl-AAB (saturated) solutions electrolyzed at the potential of 1.4 V (vs SCE) on Pt electrode are collected at different reaction intervals with the same three-electrode system. For the D-cell, anode and cathode are separated by an airtight anion exchange membrane with an electrolyte in each chamber, and the reference electrode is put in an anode chamber. For the S-cell, three electrodes are fixed in a glass beaker. The degraded intermediates are investigated with GC-MS. A reaction solution of 30 mL is collected at a certain time interval. After neutralized with Na2CO3, it is filtered and extracted with CH2Cl2. The obtained organic layer is kept still at room temperature to gain the dried degraded product, which is dissolved in CH2Cl2 for detection by GC-MS.
REFERENCES (1) Neamtu, M.; Siminiceanu, I.; Yediler, A.; Kettrup, A. Kinetics of Decolorization and Mineralization of Reactive Azo Dyes in Aqueous Solution by the UV/H2O2 Oxidation. Dyes Pigm. 2002, 53, 93−99. (2) Pandey, A.; Singh, P.; Iyengar, L. Bacterial Decolorization and Degradation of Azo Dyes. Int. Biodeterior. Biodegrad. 2007, 59, 73−84. (3) Mohammadi, A.; Yazdanbakhsh, M. R.; Farahnak, L. Synthesis and Evaluation of Changes Induced by Solvent and Substituent in Electronic Absorption Spectra of Some Azo Disperse Dyes. Spectrochim. Acta, Part A 2012, 89, 238−242. (4) Almeida, M. R.; Stephani, R.; Dos Santos, H. F.; de Oliveira, L. F. C. Spectroscopic and Theoretical Study of the “Azo”-Dye E124 in Condensate Phase: Evidence of a Dominant Hydrazo Form. J. Phys. Chem. A 2010, 114, 526−534. (5) Charlton, M. H.; Docherty, R.; McGeein, D. J.; Morley, J. O. Theoretical Investigation of the Structure and Spectra of Donor− Acceptor Azobenzenes. J. Chem. Soc., Faraday Trans. 1993, 89, 1671− 1675. (6) Olmsted, J., III; Lawrence, J.; Yee, G. G. Photochemical Storage Potential of Azobenzenes. Sol. Energy 1983, 30, 271−274. (7) Mehta, H. P.; Peters, A. T. Electron Impact-Induced Fragmentation of 4-Aminoazobenzene Dyes and Relationship with Photochemical Stability. Appl. Spectrosc. 1974, 28, 241−243. (8) Pinheiro, H. M.; Touraud, E.; Thomas, O. Aromatic Amines from Azo Dye Reduction: Status Review with Emphasis on Direct UV
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.6b07183. (Figure S1) The short-circuit current and open-circuit voltage after a transformer and rectifier bridge regulated under a fixed rotating speed of 600 rpm; (Figure S2) The CV plots of 0.5 mol L−1 HCl and 0.5 mol L−1 HCl-AAB (saturated) solutions on Pt electrode at a scan rate of 100 mV s−1 in the different potential ranges of 0−0.6, 0−0.8, and 0−1.0 V vs SCE; (Figure S3) The color change of AAB in the acidic electrolyte before and after the selfpowered degradation by SPES at a rotating rate of 600 rpm; (Figure S4) GC-MS spectra of degraded 776
DOI: 10.1021/acsnano.6b07183 ACS Nano 2017, 11, 770−778
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DOI: 10.1021/acsnano.6b07183 ACS Nano 2017, 11, 770−778
