AgxH3âxPMo12O40 Nanowires with Enhanced Visible-Light

Subscriber access provided by Fudan University

Article

Ag/AgxH3-xPMo12O40 nanowires with enhanced visible light-driven photocatalytic performance Hong-Fei Shi, Gang Yan, Yi Zhang, Hua-Qiao Tan, Wen-Zhe Zhou, Yuan-Yuan Ma, Yang-Guang Li, Weilin Chen, and En-Bo Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b13009 • Publication Date (Web): 14 Dec 2016 Downloaded from http://pubs.acs.org on December 22, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Ag/AgxH3-xPMo12O40 nanowires with enhanced visible light-driven photocatalytic performance Hong-Fei Shi, Gang Yan, Yi Zhang, Hua-Qiao Tan,* Wen-Zhe Zhou, Yuan-Yuan Ma, YangGuang Li,* Weilin Chen and En-Bo Wang* Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun, 130024 (P.R. China) KEYWORDS: Polyoxometalates, Ag, nanowires, photodegradation, photoreduction

ABSTRACT: Photocatalysis, a promising technology platform to address the environmental problems, has been attracted considerable attentions. In this paper, Ag/AgxH3-xPMo12O40 (simplified as Ag/AgHPMo12) nanowires have been synthesized by a facile solid reaction route and in-situ photo-deposited method. The results of SEM and TEM indicate that the diameters of AgHPMo12 nanowires are about 45±10 nm. And Ag nanoparticles (NPs) with diameters in the range of 5-15 nm are uniformly anchored on the surface of AgHPMo12 nanowires. The Ag content in the Ag/AgHPMo12 composite was manipulated by the light irradiation time (Ag/AgHPMo12-x; x stands for the irradiation time; x = 2, 4, 6, 8 h, respectively). With increasing irradiation time, the light absorption of as-synthesized samples in the visible region was gradually enhanced. The Ag/AgHPMo12-4 exhibits the best photocatalytic performance for the degradation of methyl orange and reduction of Cr2O72- under visible light (λ > 420 nm)

1 Environment ACS Paragon Plus


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

irradiation. The study of photocatalytic mechanism reveals that both Ag and AgHPMo12 can be excited by visible light. The photoinduced electrons were transferred from AgHPMo12 to metallic Ag, and combined with the Ag plasmonic holes. The Ag plasmonic electrons were trapped by O2 to form •O2-, or directly reduced Cr2O72- to Cr3+. Meanwhile, the •O2- species and the photogenerated holes of AgHPMo12 were used to oxidize MO or i-PrOH, thus they showed highly efficient and recyclable photocatalytic performance for removing the organic and inorganic pollutants. 1. INTRODUCTION Nowadays, the environmental problems have become one of the top and challenging issues for humanity. Among various kinds of technologies for environmental remediation, semiconductor photocatalysis has been proved to be one of the most promising technologies because it provides a facile way to utilize the inexhaustible light energy for the highly efficient and green removal of environmental pollutants.1-6 In recent years, productive efforts have been made to synthesize Agbased photocatalysts because of their considerably good photocatalytic response, such as Ag/AgX (X=Cl, Br, I),7-10 Ag3PO4,11 AgVO3,12 Ag/(BiO)2CO3,13 Ag/SnNb2O6,14 Ag/TiO2,15-18 Au/CeO2 19,20 and so on. However, most of these Ag-based photocatalysts have a relatively low capability to separate photogenerated charge carriers. Moreover, the anions of these Ag-based composites have neither light response nor redox. Therefore, these Ag-based photocatalysts are light instability, which might be gradually depleted under visible light (λ > 420 nm) irradiation, thus resulting in the deactivation of catalysts in the photocatalysis. Polyoxometalates (POMs) are a fascinating class of typical transition metal-oxygen clusters, which have plenty of compositions, structures, and functionalities.21,22 They possess reversible


Page 2 of 30

Page 3 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


redox properties, which can undergo a stepwise multi-electron redox without any significant structural alteration.23,24 They can serve as photocatalysts, and possess many advantages such as optical and chemical stability, adjustable oxidizability and photochemical activity.25,26 Therefore, they have been successfully utilized in photocatalysis, including water splitting and degradation of pollutants.22, 26-28 However, most of POMs have good water solubility, which are usually used as the homogenous catalysts, thus resulting in difficult separation of catalysts. The photocatalytic performance of POMs is originated from the photoexcitation of the oxygen-to-metal charge transfer of POMs to photogenerate the charge carriers (e--h+). The fast recombination of photogenerated e--h+ pairs in POMs causes the low photocatalytic efficiency. Moreover, most previous works related to POMs-based photocatalyst are limited to UV light (λ < 380 nm), which is only about 4% of the solar spectra.29-32 After thoroughly literature survey, we noticed that reports on the high efficacy of POMs-based photocatalysts under visible-light irradiation by heterogeneous catalytic reaction are rare. Therefore, to design a suitable POM-based photocatalyst with enhanced visible-light driven photocatalytic activity is still a challenging task. One effective way to construct heterogeneous POMs-based catalyst is to couple POMs with the large counter cations. Ag+ with the ionic radius about 0.115 nm has been proved as one of the large cations that can be used to regulate the solubility of POMs. A few Ag+-POMs compounds have been prepared and exhibit good photocatalytic performance.33-37 More importantly, these compounds are usually composed of wide band gap polyoxoanions, such as [PW12O40]3- and [SiW12O40]4-, possessing irregular morphology. Its formation mechanism, the photocatalytic process and mechanism are still not exactly known. Moreover, the enhancement of photocatalytic performance and the further control of such kind of catalysts are scarcely investigated.34



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

In this paper, we successfully fabricated Ag/AgxH3-xPMo12O40 (simplified as Ag/AgHPMo12) nanowires composites through a facile solid reaction route and in-situ photoreduction method. H3PMo12O40 with the band gap of 2.4 eV, which possesses obvious visible light absorption in the range of 400-516 nm, were selected to react with AgNO3 by ball-milling to form insoluble AgPMo12 nanowires. The diameters of AgPMo12 nanowires are about 45±10 nm. After irradiation under UV-Vis light, part of Ag+ in AgPMo12 nanowires were in-situ photoreduced to Ag NPs forming Ag/AgHPMo12 composites. Ag NPs exhibit surface plasmon resonance (SPR) absorption, thus enhancing the visible light absorption of Ag/AgHPMo12. And in addition, it also causes intense local electromagnetic fields by SPR, which accelerates the charge separation of photogenerated e- and h+ in Ag/AgHPMo12. Moreover, the relative narrow band gap and strong reversible redox properties of polyoxoanion [PMo12O40]3- ensure the photochemical stability of the composites. Therefore, the as-synthesized Ag/AgHPMo12 exhibits highly efficient and recyclable photocatalytic performance for the degradation of MO and reduction of Cr2O72- under visible light (λ > 420 nm) irradiation. 2. EXPERIMENTAL SECTIONS 2.1. Chemicals and Reagents. Phosphomolybdic acid (H3PMo12O40), Silver nitrate (AgNO3), Sodium sulfate (Na2SO4), ethanol (CH3CH2OH), Isopropanol (C3H7OH), 4-Hydroxy-TEMPO, Triethanolamine (C6H15NO3), Methyl orange (MO), K4[Fe(CN)6], KCl, Barium sulfate (BaSO4), K3[Fe(CN)6], K2Cr2O7 were purchased from Aladdin Chemical Co., Ltd., China. All chemicals were used without any further purification. 2.2. The Preparation of Ag/AgHPMo12 Nanowires. The phosphomolybdic acid was dried at 150oC for 12h to remove the crystallization water. 5g phosphomolybdic acid and 5g silver


Page 4 of 30

Page 5 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


nitrate were ball-milled at the rate of 400 rpm for 5 h on the QM-QX04 planetary ball mill (Nanjing NanDa Instrument Plant). The obtained samples were washed successively by deionized water for three times and then dried in air. Afterwards, the dry samples were illuminated under 300 W (CEL-HXF300, AULIGHT) Xe lamp for different time to form Ag/AgHPMo12-x composite (x stands for the irradiation time; x = 2, 4, 6, 8 h, respectively). The obtained samples were again washed with deionized water and dried in air. By this method, Ag/AgHPMo12 nanowires with different contents of Ag have been fabricated. For comparison, a series of samples with different stoichiometric ratio of Ag substituted H3PMo12O40 have been prepared according to reference38 by traditional liquid reaction (abbreviated as Ag3PMo12(L), Ag2HPMo12(L) and AgH2PMo12(L), respectively). 2.3. Characterization Methods. The surface morphology of the photocatalysts has been characterized using a JEOL JSM 4800F SEM. Transmission electron microscopy (TEM) and HRTEM images were performed on a JEM-2100F microscope at an acceleration voltage of 200 kV. X-Ray diffraction data were collected on a Bruker AXS D8 Focus by filtered Cu Ka radiation (λ= 1.54056 Å). X-ray photoelectron spectra were performed using an ESCALABMKII spectrometer with an Al-Kα achromatic X-ray source. The UV-Vis diffuse reflectance spectra (DRS) measurements were carried out on a UV-2600 UV-Vis spectrophotometer (Shimadzu), and BaSO4 was employed as a reference. The PL spectra were measured on a Hitachi F-7000 spectrophotometer with the excitation wavelength of 400 nm. 2.4. Photoelectrochemical Measurements. Photocurrent measurements were conducted on a CHI660E Electrochemical Workstation in a conventional three-electrode configuration including a counter electrode, reference electrode and working electrode in a quartz cell. The working electrode prepared with the sample has an active area of ca. 3cm2. A Pt foil and Hg/Hg2Cl2 5 Environment ACS Paragon Plus


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

electrode were used as the counter electrode and reference electrode, respectively. A 300 W (CEL-HXF300, AULIGHT) Xe lamp was applied as the light source. The electrolyte was 0.5 M Na2SO4 aqueous solution. Typically, the working electrodes were prepared as follows: 40 mg of as-prepared samples were suspended in 5ml ethanol with sonication for 30 minutes to obtain slurry. Next, 1 mL solution was uniformly dropped onto a 1×5 cm2 FTO glass substrate. At last, the prepared electrodes were dried at room temperature to obtain the working electrodes. 2.5. Electrochemical Impedance Spectroscopy (EIS) Measurements. EIS was performed using a Model CS350 (Wuhan CorrTest Instrument Corporation) electrochemistry station in 0.1 M KCl solution containing 5 mM Fe(CN)63−/4− with a frequency range from 0.01 Hz to 10 kHz at 0.2 V. The EIS data were recorded using a conventional three-electrode system, where samples on FTO glass with an active area of ca. 1.0 cm2 were prepared as the working electrode, Pt wire as a counter electrode, and Ag/AgCl as a reference electrode, respectively. 2.6. Photocatalytic Tests.

The photocatalytic activities of the as-obtained products were

evaluated by the photodegradation of MO and photoreduction of K2Cr2O7. A glass vessel with a water-cooling jacket was applied as reactor and a 300 W Xe lamp with a 420 nm cut-off filter was employed as illuminant, respectively. The distance between the lamp and the mixture solution was about 12 cm. In a typical process, 20 mg of samples was dispersed into a solution containing 20 mL of MO solution (20 mg·L-1; pH=1) or 40 mL of K2Cr2O7 (80 mg·L-1; VH2O: Visopropanol =1). Before irradiation, the mixture solution was stirred in darkness for a period of time to attain absorption-desorption equilibrium. Afterwards, the above suspension was continually stirred and exposed to the visible-light irradiation. And then a certain amount of suspension was taken out and centrifuged to separate solid particles at given time intervals. The remaining concentration of MO and K2Cr2O7 were determined by a Shimadzu UV-2600 UV-Vis 6 Environment ACS Paragon Plus

Page 6 of 30

Page 7 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


spectrophotometer. For comparison, the photodegradation reactions were also evaluated in the absence of any catalyst. The degradation efficiency was calculated by C/C0, where C is the concentration of remaining MO or K2Cr2O7 solution at each irradiated time, and C0 is the initial concentration. 2.7. Active Species Trapping Experiment. To explore the major active species in the photocatalytic degradation process of MO, we conducted the radical-trapping experiments. The triethanolamine (TEOA), 4-Hydroxy-TEMPO and isopropanol (IPA) were employed as hole (h+) scavenger, superoxide radical (·O2-) scavenger and hydroxyl radical (·OH) scavenger, respectively. Typically, 20 mg of photocatalyst together with different scavenger was dispersed in 20 mL (20 ppm) MO aqueous solution, and the following process was similar to the MO degradation test. 3. RESULTS AND DISCUSSION 3.1. Compositional and Structural Characterization. The surface morphology of the AgPMo12 and Ag/AgHPMo12 samples were visualized by SEM and TEM images. As Figure 1a shows, the AgPMo12 samples are comprised of nanowires with uniform shape and size. The average diameter of the nanowires is about 45 ± 10 nm, and its length is as long as several micrometers in size. After irradiation under UV-Vis light, Ag/AgHPMo12 has been formed. As shown in Figure 1b and 1c, it could be seen that many small Ag nanoparticles are in-situ deposited, which are uniformly anchored on the surface of AgHPMo12 nanowires. The size of Ag NPs ranges from 5 to 15 nm. And the morphology of AgHPMo12 nanowires is well maintained after irradiation. In Figure 1d, the HRTEM image reveals that two independent crystal lattices, Ag and AgHPMo12 are co-existed. The lattice fringe corresponding to the interplanar distance of



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

0.243 nm is assigned to the lattice spacing of Ag (101) plane (JCPDS NO. 41-1402), and the other lattice diffraction fringe with the lattice plane distance 0.292 nm can be ascribed to AgHPMo12, which confirm that Ag nanoparticles have been successfully deposited on the surface of AgHPMo12. The corresponding elemental mapping of Ag/AgHPMo12 is illustrated in Figure 1e-1h, which demonstrates that the Ag, P, Mo elements are well-arranged over the Ag/AgHPMo12 nanowires (Figure S1).

Figure 1. (a) Scanning electron microscopy (SEM) image of AgPMo12 nanowires; (b) SEM, (c) TEM (Insert: the particle size distribution of Ag NPs.) and (d) HRTEM photographs of


Page 8 of 30

Page 9 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ag/AgHPMo12-4; (e) TEM-EDS elemental mapping of Ag/AgHPMo12-4, the corresponding elemental mappings of (f) P, (g) Mo, and (h) Ag elements. Figure 2a displays the XRD patterns of the as-synthesized AgPMo12 and Ag/AgHPMo12 samples. The XRD pattern of AgPMo12 (b) is different from that of pure HPMo12 (a), because H+ cations in H3PMo12O40 have been completely replaced by Ag+ cations forming Ag3PMo12O40 (abbreviated as AgPMo12) compared to XRD patterns of AgxH3-xPMo12 (x=1; 2; 3) samples prepared by liquid reaction (Figure S2). The peaks of 17.80o, 27.10o, 28.51o, 30.56o, 32.50o, 35.12o, 47.91o, 56.32o (marked with *) can be assigned to the diffraction peaks of AgPMo12. After Ag was in-situ photoreduced, part of Ag+ in or adsorbed on AgPMo12 nanowires could be deposited. And in view of the charge balance, the obtained samples can be expressed as Ag/AgxH3-xPMo12O40 (abbreviated as Ag/AgHPMo12). The XRD patterns of Ag/AgHPMo12 show slight changes compared with that of AgPMo12 (Figure S3). Especially, in Ag/AgHPMo128, a series of characteristic diffraction peaks of metal silver have been observed (Figure S4). The peaks at 37.0o, 45.3o, 64.5o, 76.8o，82.3o ( marked with #), can be assigned to the diffraction planes of Ag (JCPDS NO. 41-1402) (101), (103), (110), (201) and (203), respectively.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 30

Figure 2. Left: (a) The XRD patterns of as-obtained samples; pure HPMo12 (a); AgPMo12 (b); Ag/AgHPMo12-2(c); Ag/AgHPMo12-4(d); Ag/AgHPMo12-6(e); Ag/AgHPMo12-8(f), respectively. Right: (b) The DRS of pure HPMo12, AgPMo12, Ag/AgHPMo12 samples. Insets are optical images of pure HPMo12 (c); AgPMo12 (d); Ag/AgHPMo12-4 (e) from top to bottom. The optical properties of the as-prepared samples were investigated by UV-Vis diffuse reflectance spectra in the range of 200-800 nm. As shown in Figure 2b, HPMo12 exhibits a spectrum absorption onset at 516 nm, which is consistent with the band gap of HPMo12 (2.4 eV). As H+ cations were exchanged with Ag+, the absorption band (440 nm) of AgPMo12 nanowires shows an obvious blue shift in comparison with that of HPMo12, which indicates the counter cations of POMs have a significant influence on the band gap of POMs-based photocatalysts. After Ag was photoreduced, the absorption of Ag/AgHPMo12 composites in the visible light region has been greatly enhanced. A wide absorption peak at about 480 nm has been clearly observed, which can be attributed to the surface plasmon resonance (SPR) absorption of Ag NPs.39-41 With the increase of irradiation time, the absorbance of composites in visible light region was also gradually enhanced. It means the amount of Ag NPs gradually increased. As shown in Figure 2d and 2e, the colour of samples changed from Kelly green (HPMo12) via palegreen (AgPMo12) to gray (Ag/AgHPMo12). The band gap energies of AgPMo12 and Ag/AgHPMo12 could be estimated from the Tauc plot42 (Figure S5). It shows that the energy gap for AgPMo12 and Ag/AgHPMo12-x (x=2, 4, 6, 8) is 2.87, 2.82, 2.75, 2.73, 2.72 eV, respectively. The band gap of Ag/AgHPMo12 shows a slight shift compared to AgPMo12. That might be caused by the partial reduction of Ag+ ions, thus leading to the substitution of Ag+ ions with H+ ions in AgHPMo12 nanowires. And according to previous studies, 43, 44 it also might be related to


Page 11 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the Ag metallic clusters that introduce localized energy levels into the AgHPMo12 band gap, thus reducing the energy gap of AgHPMo12 nanowires in Ag/AgHPMo12. To further verify the elemental compositions and chemical states of the as-synthesized samples, X-ray photoelectron spectra (XPS) and the energy dispersive X-ray analysis (EDX) of AgPMo12 and Ag/AgHPMo12-4 were measured. As illustrated in Figure 3a, the Ag 3d, Mo 3p, Mo 3d, C 1s, P 3s and O1s signals are clearly shown in the full scan survey XPS spectra. Figure 3b shows the Mo 3d XPS spectra, the Mo 3d5/2 (231.93eV) and Mo 3d3/2 (235.15eV) peaks of AgHPMo12 can be split into four peaks at 231.84 eV, 232.38 eV and 235.00 eV, 235.50 eV, respectively. The doublet peaks at 231.84 eV (Mo 3d5/2) and 235.00 eV (Mo 3d3/2) can be attributed to Mo(V) species, while the peaks at 232.38 eV (Mo 3d5/2) and 235.50 eV(Mo 3d3/2) are assigned to Mo(VI) species.45 It is well known that HPMo12 has strong reversible redox properties, which can be easily reduced in the air, thus exhibiting low valence molybdenum. In Ag/AgHPMo12-4, the chemical states of Mo also show +5 and +6 states. Figure 3c shows the Ag 3d XPS spectra. In AgPMo12, the peaks at 367.43 eV and 373.45 eV can be attributed to the Ag 3d5/2 and Ag 3d3/2 of Ag (I).46 However, in Ag/AgHPMo12-4, the Ag 3d5/2 and Ag 3d3/2 peaks can be split into two pairs of peaks: one located at 373.4 eV and 367.38 eV can be assigned to Ag+ species; the other peaks located at 374.23 eV and 368.2 eV can be attributed to metallic Ag (0). And the 6.0 eV difference between the binding energy of Ag 3d3/2 and 3d5/2 is also the characteristic of the metallic Ag 3d state.47 As illustrated in Figure 3d and Figure S6, EDX reveal that Mo, O, P and Ag are co-existed in Ag/AgHPMo12 samples.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. XPS spectra of AgPMo12 and Ag/AgHPMo12-4: (a) the full survey; (b) Mo 3d; (c) Ag 3d; (d) EDX of Ag/AgHPMo12-4. 3.2. Photocatalytic Tests. The photocatalytic degradation of MO was selected as the model to assess the photocatalytic performance of Ag/AgHPMo12 samples. Figure 4a shows the time profiles of the degradation of MO using the as-prepared Ag/AgHPMo12 as photocatalysts under visible light irradiation (λ> 420 nm). Obviously, MO shows negligible self-photodegradation without any catalysts in solution under visible light irradiation. At the same condition, about 45.08% of 20mL 20ppm MO can be degraded in 140 min as AgPMo12 nanowires was applied. When part of Ag+ has been photoreduced, the photocatalytic activities of Ag/AgHPMo12 for the degradation of MO were largely enhanced. As shown in Figure 4a, 20mL 20ppm MO can be 12 Environment ACS Paragon Plus

Page 12 of 30

Page 13 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


completely degraded in 110 min for 20mg of Ag/AgHPMo12-2 sample. The Ag content plays an important role in the photocatalytic activity of Ag/AgHPMo12. As the results of XRD, DRS and XPS, with the increase of irradiation time, more metallic Ag has been photoreduced. And in proportion, the photocatalytic performances of Ag/AgHPMo12 were increased first and then decreased. The Ag/AgHPMo12-4 shows the best photocatalytic performance. 20mL 20ppm of MO can be almost 100 % photodegraded by 20mg of Ag/AgHPMo12-4 in 60 min (Figure S7a), which is much faster than that of the samples prepared by traditional liquid reaction (Figure S8 and S9) and the previous work using Ag+-POMs as catalysts.33,35 As further prolonged the irradiation time, the photocatalytic efficiency of Ag/AgHPMo12-6 and Ag/AgHPMo12-8 were obviously reduced. To completely degrade the MO, about 80 min and 140 min should be needed using Ag/AgHPMo12-6 and Ag/AgHPMo12-8 as catalysts, respectively. Their decreased catalytic performances might be caused by the excessive loading of Ag. As exhibited in Figure S10, with the increase of irradiation time, the photoreduced Ag NPs aggregated and grew gradually, thus leading to the reduce of specific surface area of Ag. Meanwhile, as more Ag+ cations have been photoreduced to metallic Ag NPs, the morphology of AgHPMo12 nanowires was also destroyed gradually, especially for Ag/AgHPMo12-8. Both the above two factors are responsible for the decreased photocatalytic performance of Ag/AgHPMo12-6 and Ag/AgHPMo12-8. In addition, the degradation rate of MO shows a significant growth during the photocatalytic process of Ag/AgHPMo12 composites. That might be caused by the photoreduction of polyoxoanion [PMo12O40]3-. In the process of photocatalysis, the polyoxoanions [PMo12O40]3- of Ag/AgHPMo12 composites were gradually photoreduced to heteropoly blue, which obviously enhanced the visible light absorption of Ag/AgHPMo12 composites (as illustrated in Figure S11 and S12).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 30

Therefore, the photocatalytic performances of Ag/AgHPMo12 have been enhanced, thus resulting in the increase of the degradation rate of MO.

Figure 4. The profiles of (a) photodegradation of MO and (b) photoreduction of Cr(VI) by different samples under visible-light irradiation (λ>420 nm); Recycle experiments of (c) photodegradation of MO and (d) photoreduction of Cr(VI) by Ag/AgHPMo12-4 photocatalyst (λ> 420 nm). The Ag/AgHPMo12 composites also show good photocatalytic performance for the reduction of Cr(VI) under the visible light irradiation (λ> 420 nm). As shown in Figure 4b, only 11.65% of Cr(VI) was photoreduced in the absence of the catalysts. Using AgPMo12 nanowires as photocatalysts, about 57.27% of Cr(VI) (40mL 80ppm of Cr2O72-, 20mg photocatalysts) was


Page 15 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reduced into Cr(III) in 40 min. After Ag NPs were photo-deposited, the photocatalytic activities of Ag/AgHPMo12 were obviously enhanced. About 68.82%, 75.33%, 73.87%, 66.67% of Cr(VI) could be photoreduced using Ag/AgHPMo12-x (x= 2, 4, 6, 8 h) as catalysts in 40 min under visible light irradiation. Among these composites, Ag/AgHPMo12-4 exhibits the best photoreduction activity. About 75.33% of 40mL 80mg·L-1 Cr(VI) could be photoreduced by 20mg of Ag/AgHPMo12-4 in 40 min under the visible light irradiation (Figure S7b). The result is consistent with the photodegradation of MO, which indicates Ag/AgHPMo12 composites are efficient visible-light photocatalysts for the degradation of organic dyes and reduction of inorganic ions. Figure 4c and 4d show the recycle experiments of the degradation of MO and reduction of Cr (VI) using Ag/AgHPMo12-4 as the photocatalyst under visible light irradiation (λ> 420 nm). As shown in Figure 4c, after four run cycles, the photocatalytic performance of Ag/AgHPMo12-4 for the degradation of MO did not show any decrease. And it is worth noting that the degradation rate of MO in the second cycle is obviously faster than that in the first run, which may be attributed to the strong reversible redox properties of [PMo12O40]3- polyoxoanion. Under visible light irradiation, [PMo12O40]3- was photoreduced to heteropoly blue, which enhanced the visible light absorption of Ag/AgHPMo12 composites, thus increasing the degradation efficiency of MO in the first cycle (Figure S11 and S12). And in the following recycles, this light activation process is omitted. And thus the increased degradation rate of MO was observed in the following recycles. Figure 4d displays the recycle experiments of the photoreduction of Cr(VI) with Ag/AgHPMo12-4. The reduction efficiency of Cr(VI) exhibits only a slight decrease after four recycles. This decrease might be related to the loss of catalysts in the process of recycle. These



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 30

results reveal that Ag/AgHPMo12 are highly efficient and stable photocatalysts for removing of organic and inorganic pollutants. 3.3. The Reaction Mechanism Study. To confirm the efficient separation of photogenerated charge carriers and the enhanced photocatalytic activity of as-prepared catalysts, the photoluminescence spectra and transient photocurrent responses have been measured. The PL spectra of as-prepared samples were measured with an excitation wavelength of 400 nm. All of the samples show similar peaks centered at about 425 nm, as illustrated in Figure 5a. The peak intensity of PL spectra for Ag/AgHPMo12 catalysts show an obvious decrease in comparison to that of AgPMo12, showing that the recombination of the photogenerated charge carrier is effectively inhibited. The Ag/AgHPMo12-4 catalyst has the lowest peak intensity, indicating a lower recombination of charge carriers and a better photocatalytic performance than the other samples. Figure 5b shows the transient photocurrent responses of AgPMo12, Ag/AgHPMo12-4 under visible light irradiation (λ> 420 nm) (Figure S13). The generated photocurrents are stable and reproducible when the light was switched on and off during three cycles. Under visible-light irradiation, the photocurrent density of Ag/AgHPMo12-4 is 3.7×10-4 mA·cm-2, which is 3.7 times than that of AgPMo12 (1.0×10-4 mA·cm-2). That means an improvement of the charge separation in Ag/AgHPMo12-4. This result is consistent with the PL analysis, which illustrates that the charge separation rate has been improved as metallic Ag NPs were photoreduced on the surface of AgHPMo12 nanowires.


Page 17 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) The PL spectra for HPMo12, AgPMo12, Ag/AgHPMo12 samples, respectively; (b) Transient photocurrent responses of AgPMo12, Ag/AgHPMo12-4 in 0.5 M Na2SO4 aqueous solution at 0.38V vs. Hg/Hg2Cl2 under visible-light irradiation (λ> 420 nm); (c) The EIS Nyquist plots of AgPMo12 and Ag/AgHPMo12-4; (d) The effects of various scavengers on photocatalytic activity of Ag/AgHPMo12-4 photocatalyst. Electrochemical impedance spectroscopy (EIS) measurements were also carried out to investigate the separation efficiency of the photogenerated electrons and holes. The Nyquist plots of different electrodes were shown in Figure 5c and Figure S14. Generally, the small arc radius on the EIS Nyquist plot corresponds to the low charge transfer resistance (Rct). Obviously, the Rct of the Ag/AgHPMo12-4 is much smaller than that of AgPMo12, implying an effective



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 30

separation of photogenerated charge carriers and fast interfacial charge transfer, which is beneficial for the enhanced photocatalytic activity.48 To further understand the mechanism of photodegradation of MO, the free radicals and hole trapping experiments were conducted. In this investigation, triethanolamine (TEOA, h+ quencher), 49 4-Hydroxy-TEMPO (•O2- quencher) 50 and isopropanol (IPA, •OH quencher) 51 are applied to find which reactive species play the main role in the process of MO degradation for Ag/AgHPMo12 catalysts. As Figure 5d shows, the degradation efficiency of MO is not decreased upon addition of IPA, implying •OH species contributing a slight role in the degradation of MO. Nevertheless, the decrease in the degradation rate is obviously observed when TEOA or 4Hydroxy-TEMPO (or N2, Figure S15) was introduced into the photocatalytic reaction system. Therefore, the •O2- radicals and h+ radicals are the two main active species during photodegradation process of MO using Ag/AgHPMo12 nanowires as catalysts under visible light irradiation. On the basis of the above results, the possible mechanisms of the photodegradation of MO and photoreduction of Cr(VI) for Ag/AgHPMo12 nanowires have been proposed. The band gap Eg of AgHPMo12 is estimated to be 2.87 eV by UV-Vis diffuse reflectance spectra of AgPMo12 (Figure S5). The CB value of AgHPMo12 could be estimated according to the Mott-Schottky test result of AgPMo12, which is about 0.54 eV (Figure S16). Therefore, the VB value of AgHPMo12 is 3.41 eV (E(VB) = E(CB) + Eg). The mechanism of photodegradation of MO is illustrated in Figure 6a. As Ag/AgHPMo12 was irradiated with visible light, both AgHPMo12 and Ag NPs can be excited. Ag NPs show surface plasmon resonance (SPR) absorption. And it causes intense local electromagnetic fields by SPR (inset), which accelerates the charge separation of photogenerated e- and h+ in Ag/AgHPMo12. The electrons can be excited from the VB of AgHPMo12 to its CB, 18 Environment ACS Paragon Plus

Page 19 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and leaving holes in its VB. The photo-excited holes of AgHPMo12 directly oxidized MO molecules in the aqueous solution. However, the superoxide radical (•O2-) cannot be formed on AgHPMo12 surface because the CB of AgHPMo12 is more positive than that of the O2/•O2potential (−0.046 V vs. NHE). Simultaneously, a great number of electron-hole pairs was photogenerated because of the plasmonic absorbance of metallic Ag NPs.52 Because the CB edge potential of AgHPMo12 (0.54 V vs. NHE) is more negative than the potential of Ag+/Ag (+0.799 V vs. NHE), therefore we suggest that the photogenerated electrons were transferred from the CB of AgHPMo12 to Ag NPs, and recombined with the plasmonic holes of metallic Ag.51,53,54 Subsequently, the plasmonic electrons on the Ag NPs could be trapped by the absorbed O2 to form •O2- reactive species, which can oxidize MO molecules directly to the degraded products. And thus MO molecules were photodegraded efficiently by the h+ and •O2- active species. The mechanism for the photoreduction of Cr(VI) is similar to that of photodegradation of MO, except the photo-excited holes of AgHPMo12 nanowires were used to oxidize i-PrOH, and the plasmonic electrons of Ag NPs were used to reduce Cr2O72- to Cr3+ directly. As exhibited in Figure 6b, Cr(VI) was efficiently photoreduced by Ag/AgHPMo12 composites under visible-light irradiation.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

Figure 6. The possible photocatalytic reaction mechanism of (a) photodegradation of MO and (b) photoreduction of Cr(VI) for the Ag/AgHPMo12 photocatalysts under visible-light irradiation (λ > 420 nm). Insert: the surface plasmon resonance (SPR) effect of Ag. 4. CONCLUSION In summary, we have developed a simple and facile route to synthesize the heterogeneous Ag/AgHPMo12

nanowires

photocatalysts.

These

compounds

exhibit

highly

efficient

photocatalytic activities for the degradation of methyl orange (MO) and the reduction of Cr(VI) with good reusability and photostability under visible light irradiation (λ > 420 nm). The outstanding photocatalytic performances are ascribed to the enhancement of optical absorption of [PMo12O40]3- and Ag surface plasmon resonance (SPR) in visible light region, and the effective charge separation of Ag/AgHPMo12 composites. In addition, the reasonable mechanisms of these composites working under visible light irradiation have been proposed according to the results of PL spectra, transient photocurrent responses, electrochemical impedance spectroscopy and radical trapping experiments, which might provide some new ideas for the design and


Page 21 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


preparation of new highly efficient heterogeneous POMs-based photocatalysts. Some related explorations are under way in our group. ASSOCIATED CONTENT Supporting Information. SEM-EDS elemental mapping of Ag/AgHPMo12-4, the XRD patterns of AgxH3-xPMo12 (x=1; 2; 3) samples prepared by liquid phase reaction, the XRD patterns of AgPMo12 and Ag/AgHPMo128 samples, band gap energy calculation for AgPMo12 and Ag/AgHPMo12-x (x=2, 4, 6, 8), EDX data and SEM images for Ag/AgHPMo12-x (x=2, 4, 8), photodegradation profiles of MO and Cr(VI) for Ag/AgHPMo12-4, the DRS and the profiles of MO photodegradation for AgxH3xPMo12

(x=1; 2; 3) prepared by liquid phase reaction after 4h light irradiation, optical images and

DRS data for fresh and recovered Ag/AgHPMo12-4 sample, the transient photocurrent responses and EIS Nyquist plots of different samples, Mott-Schottky plot for AgPMo12, VB and CB calculation of AgxH3-xPMo12O40, The HOMO and LOMO calculation of H3PMo12O40. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]; [email protected]; [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 30

The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge the financial support from the National Natural Science Foundation of China (grant no, 21271039, 21401131 and 21301166), the Fundamental Research Funds for the Central Universities (grant no. 2412016KJ018) and Opening Project of Key Laboratory of Polyoxometalate Science of the Ministry of Education (grant no. 130014556).

REFERENCES (1) Chen, X.; Mao, S. Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications. Chem. Rev. 2007, 107, 2891-2959. (2) Tong, H.; Ouyang, S.; Bi, Y.; Umezawa, N.; Oshikiri, M.; Ye, J. Nano-Photocatalytic Materials: Possibilities and Challenges. Adv. Mater. 2012, 24, 229-251. (3) Chen, X.; Shen, S.; Guo, L.; Mao, S. Semiconductor-Based Photocatalytic Hydrogen Generation. Chem. Rev. 2010, 110, 6503-6570. (4) Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A Metal-Free Polymeric Photocatalyst for Hydrogen Production from Water under Visible Light. Nat. Mater. 2009, 8, 76-80. (5) Li, C.; Wang, F.; Yu, J. C. Semiconductor/Biomolecular Composites for Solar Energy Applications. Energy Environ. Sci. 2011, 4, 100-113.


Page 23 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Ariga, K.; Ishihara, S.; Abe, H.; Li, M.; Hill, J. P. Materials Nanoarchitectonics for Environmental Remediation and Sensing. J. Mater. Chem. 2012, 22, 2369-2377. (7) Daupor, H.; Wongnawa, S. Urchinlike Ag/AgCl Photocatalyst: Synthesis, Characterization, and Activity. Appl. Catal., A 2014, 473, 59-69. (8) Huang, Z.; Wen, M.; Wu, D.; Wu, Q. A Special Ag/AgCl Network-Nanostructure for Selective Catalytic Degradation of Refractory Chlorophenol Contaminants. RSC Adv. 2015, 5, 12261-122673. (9) Wu, S.; Shen, X.; Ji, Z.; Zhu, G.; Chen, C.; Chen, K.; Bu, R.; Yang, L. Synthesis of AgCl Hollow Cubes and Their Application in Photocatalytic Degradation of Organic Pollutants. CrystEngComm 2015, 17, 2517-2522. (10) Wang, D.; Duan, Y.; Luo, Q.; Li, X.; Bao, L. Visible Light Photocatalytic Activities of Plasmonic Ag/AgBr Particles Synthesized by a Double Jet Method. Desalination 2011, 270, 174-180. (11) Wan, J.; Liu, E.; Fan, J.; Hu, X.; Sun, L.; Tang, C.; Yin, Y.; Li, H.; Hu, Y. In-Situ Synthesis of Plasmonic Ag/Ag3PO4 Tetrahedron with Exposed{111} Facets for High VisibleLight Photocatalytic Activity and Stability. Ceram. Int. 2015, 41, 6933-6940. (12) Zhao, W.; Guo, Y.; Faiz, Y.; Yuan, W.-T.; Sun, C.; Wang, S.-M.; Deng, Y.-H.; Zhuang, Y.; Li, Y.; Wang, X.-M.; He, H.; Yang, S.-G. Facile In-Suit Synthesis of Ag/AgVO3 Onedimensional Hybrid Nanoribbons with Enhanced Performance of Plasmonic Visible-Light Photocatalysis. Appl. Catal., B 2015, 163, 288-297.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 30

(13) Dong, F.; Li, Q.; Zhou, Y.; Sun, Y.; Zhang, H.; Wu, Z. In Situ Decoration of Plasmonic Ag Nanocrystals on the Surface of (BiO)2CO3 Hierarchical Microspheres for Enhanced Visible Light Photocatalysis. Dalton Trans. 2014, 43, 9468-9480. (14) Xun, S.; Zhang, Z.; Wang, T.; Jiang, D.; Li, H. Synthesis of Novel Metal Nanoparitcles/SnNb2O6 Nanosheets Plasmonic Nanocomposite Photocatalysts with Enhanced Visible-Light Photocatalytic Activity and Mechanism Insight. J. Alloys Compd. 2016, 685, 647-655. (15) Leong, K. H.; Gan, B. L.; Ibrahim, S.; Saravanan, P. Synthesis of Surface Plasmon Resonance (SPR) Triggered Ag/TiO2 Photocatalyst for Degradation of Endocrine Disturbing Compounds. Appl. Surf. Sci. 2014, 319, 128-135. (16) Pugazhenthiran, N.; Murugesan, S.; Anandan, S. High Surface Area Ag-TiO2 Nanotubes for Solar/Visible-Light Photocatalytic Degradation of Ceftiofur Sodium. J. Hazard. Mater. 2013, 263, 541- 549. (17) Choi, Y.; Kim, H.I.; Moon, G.H.; Jo, S.; Choi, W. Boosting up the Low Catalytic Activity of Silver for H2 Production on Ag/TiO2 Photocatalyst: Thiocyanate as a Selective Modifier. ACS Catal. 2016, 6, 821-828. (18) Jia, C.Y.; Zhang, G.Z.; Zhong, W.H.; Jiang, J. A First-Principle Study of Synergized O2 Activation and CO Oxidation by Ag Nanoparticles on TiO2 (101) Support. ACS Appl. Mater. Interfaces 2016, 8, 10315-10323. (19) Lei, W.Y.; Zhang, T.T.; Gu, L.; Liu, P.; Rodriguez, J.A.; Liu, G.; Liu, M.H. SurfaceStructure Sensitivity of CeO2 Nanocrystals in Photocatalysis and Enhancing the Reactivity with Nanogold. ACS Catal. 2015, 5, 4385-4393.


Page 25 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20) Jiang, D.; Wang, W.Z.; Sun, S.M.; Zhang, L.; Zheng, Y.L. Equilibrating the Plasmonic and Catalytic Roles of Metallic Nanostructures in Photocatalytic Oxidation over Au-Modified CeO2. ACS Catal. 2015, 5, 613-621. (21) Du, D.-Y.; Qin, J.-S.; Li, S.-L.; Su, Z.-M.; Lan, Y.-Q. Recent Advances in Porous Polyoxometalate-Based Metal–Organic Framework Materials. Chem. Soc. Rev. 2014, 43, 46154632. (22) Dolbecq, A.; Dumas, E.; Mayer, C. R.; Mialane, P. Hybrid Organic-Inorganic Polyoxometalate Compounds: From Structural Diversity to Applications. Chem. Rev. 2010, 110, 6009-6048. (23) Sadakane, M.; Steckhan, E. Electrochemical Properties of Polyoxometalates as Electrocatalysts. Chem. Rev. 1998, 98, 219-237. (24) Li, J.-S.; Sang, X.-J.; Chen, W.-L.; Zhang, L.-C.; Zhu, Z.-M.; Ma, T.-Y.; Su, Z.-M.; Wang, E. B. Enhanced Visible Photovoltaic Response of

TiO2 Thin Film with an All-Inorganic

Donor−Acceptor Type Polyoxometalate. ACS Appl. Mater. Interfaces 2015, 7, 13714-13721. (25) Hiskia, A.; Mylonas, A.; Papaconstantinou, E. Comparison of the Photoredox Properties of Polyoxometallates and Semiconducting Particles. Chem. Soc. Rev. 2001, 30, 62-69. (26) Sivakumar, R.; Thomas, J.; Yoon, M. Polyoxometalate-Based Molecular/Nano Composites: Advances in Environmental Remediation by Photocatalysis and Biomimetic Approaches to Solar Energy Conversion. J. Photochem. Photobiol., C 2012, 13, 277-298. (27) Weinstock, I. A. Homogeneous-Phase Electron-Transfer Reactions of Polyoxometalates. Chem. Rev. 1998, 98, 113-170.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 30

(28) Dolbecq, A.; Mialane, P.; Keita, B.; Nadjo, L. Polyoxometalate-Based Materials for Efficient Solar and Visible Light Harvesting: Application to the Photocatalytic Degradation of Azo Dyes. J. Mater. Chem. 2012, 22, 24509-24521. (29) Yue, B.; Zhou, Y.; Xu, J.; Wu, Z.; Zhang, X.; Zou, Y.; Jin, S. Photocatalytic Degradation of Aqueous 4-Chlorophenol by Silica-Immobilized Polyoxometalates. Environ. Sci. Technol. 2002, 36, 1325-1329. (30) Guo, Y.; Wang, Y.; Hu, C.; Wang, Y.; Wang, E.; Zhou, Y.; Feng, S. Microporous Polyoxometalates POMs/SiO2: Synthesis and Photocatalytic Degradation of Aqueous Organocholorine Pesticides. Chem. Mater. 2000, 12, 3501-3508. (31) Ozer, R. R.; Ferry, J. L. Photocatalytic Oxidation of Aqueous 1,2-Dichlorobenzene by Polyoxometalates Supported on the NaY Zeolite. J. Phys. Chem. B 2002, 106, 4336-4342. (32) Zhang, D.; Li, X.; Tan, H.; Zhang, G.; Zhao, Z.; Shi, H.; Zhang, L.; Yu, W.; Sun, Z. Photocatalytic Reduction of Cr(VI) by Polyoxometalates-TiO2 Electrospun Nanofiber Composites. RSC Adv. 2014, 4, 44322-44326. (33) Zhou, W.; Li, N.; Cao, M.; Hu, C. Three-dimensional Ag/POM/Cu2O Tricomponent Nanohybrids with Enhanced Visible-Light Photocatalytic Activity. Mater. Lett. 2013, 99, 68-71. (34) Huang, H.; Li, X.; Kang, Z.; Liu, Y.; Li, H.; He, X.; Lian, S.; Liu, J.; Lee, S.-T. Tuning Metal@Metal Salt Photocatalytic Abilities by Different Charged Anions. Dalton Trans. 2010, 39, 10593-10597.


Page 27 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Zhou, W.; Cao, M.; Li, N.; Su, S.; Zhao, X.; Wang, J.; Li, X.; Hu, C. Ag@AgHPW as a Plasmonic Catalyst for Visible-Light Photocatalytic Degradation of Environmentally Harmful Organic Pollutants. Mater. Res. Bull. 2013, 48, 2308-2316. (36) Chen, C.; Wang, Q.; Lei, P.; Song, W.; Ma, W.; Zhao, J. Photodegradation of Dye Pollutants Catalyzed by Porous K3PW12O40 under Visible Irradiation. Environ. Sci. Technol. 2006, 40, 3965-3970. (37) Zhou, W.; Cao, M.; Su, S.; Li, N.; Zhao, X.; Wang, J.; Li, X.; Hu, C. A Newly-Designed Polyoxometalate-Based Plasmonic Visible-Light Catalyst for the Photodegradation of Methyl Blue. J. Mol. Catal. A: Chem. 2013, 371, 70-76. (38) Borghèse, S.; Blanc, A.; Pale P.; Louis B. Brønsted Acid Sites in Metal-containing Solid Acids: From Quantification to Molecular Design of New Catalysts/silver(I)-polyoxometalates. Dalton Trans., 2011, 40, 1220-1223. (39) Wang, X.; Liow, C.; Bisht, A.; Liu, X.; Sum, T. C.; Chen, X.; Li, S. Engineering Interfacial Photo-Induced Charge Transfer Based on Nanobamboo Array Architecture for Efficient Solar-to-Chemical Energy Conversion. Adv. Mater. 2015, 27, 2207-2214. (40) Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-Metal Nanostructures for Efficient Conversion of Solar to Chemical Energy. Nat. Mater. 2011, 10, 911-921. (41) Zhang, Z.; Huang, Y.; Liu, K.; Guo, L.; Yuan, Q.; Dong, B. Multichannel-Improved Charge-Carrier Dynamics in Well-Designed Hetero-nanostructural Plasmonic Photocatalysts toward Highly Efficient Solar-to-Fuels Conversion. Adv. Mater. 2015, 27, 5906-5914.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 30

(42) Murphy, A. B. Band-gap Determination from Diffuse Reflectance Measurements of Semiconductor Films, and Application to Photoelectrochemical Water-Splitting. Sol. Energy Mater. Sol. Cell, 2007, 91, 1326-1337. (43) Wang, D.; Xue, G.; Zhen, Y.; Fu, F.; Li, D. Monodispersed Ag Nanoparticles Loaded on the Surface of Spherical Bi2WO6 Nanoarchitectures with Enhanced Photocatalytic Activities. J. Mater. Chem. 2012, 22, 4751-4758. (44) Cui, C.; Wang, Y.; Liang, D.; Cui, W.; Hu, H.; Lu, B.; Xu, S.; Li, X.; Wang, C.; Yang, Y. Photo-Assisted Synthesis of Ag3PO4/Reduced Graphene Oxide/Ag Heterostructure Photocatalyst with Enhanced Photocatalytic Activity and Stability under Visible Light. Appl. Catal., B 2014, 158-159, 150-160. (45) Liang, R.; Chen, R.; Jing, F.; Qin, N.; Wu, L. Multifunctional Polyoxometalates Encapsulated in MIL-100(Fe): Highly Efficient Photocatalysts for Selective Transformation Under Visible Light. Dalton Trans. 2015, 44,18227-18236. (46) Zhang, H.; Wang, G.; Chen, D.; Lv, X.; Li, J. Tuning Photoelectrochemical Performances of Ag-TiO2 Nanocomposites via Reduction/Oxidation of Ag. Chem. Mater. 2008, 20, 6543-6549. (47) Chen, Z.; Fang, L.; Dong, W.; Zheng, F.; Shen, M.; Wang, J. Inverse Opal Structured Ag/TiO2 Plasmonic Photocatalyst Prepared by Pulsed Current Deposition and Its Enhanced Visible Light Photocatalytic Activity. J. Mater. Chem. A 2014, 2, 824-832. (48) Leng, W. H.; Zhang, Z.; Zhang, J. Q.; Cao, C. N. Investigation of the Kinetics of a TiO2 Photoelectrocatalytic Reaction Involving Charge Transfer and Recombination through Surface States by Electrochemical Impedance Spectroscopy. J. Phys. Chem. B 2005, 109, 15008-15023.


Page 29 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(49) Chen, Y.; Lu, A.; Li, Y.; Zhang, L.; Yip, H. Y.; Zhao, H.; An, T.; Wong, P.-K. Naturally Occurring Sphalerite as a Novel Cost-Effective Photocatalyst for Bacterial Disinfection under Visible Light. Environ. Sci. Technol. 2011, 45, 5689-5695. (50) Feng, Y.; Shen, J.; Cai, Q.; Yang H.; Shen, Q. The Preparation and Properties of a gC3N4/AgBr Nanocomposite Photocatalyst Based on Protonation Pretreatment. New J. Chem. 2015, 39, 1132-1138. (51) Luo, B.; Xu, D.; Li, D.; Wu, G.; Wu, M.; Shi, W.; Chen, M. Fabrication of a Ag/Bi3TaO7 Plasmonic Photocatalyst with Enhanced Photocatalytic Activity for Degradation of Tetracycline. ACS Appl. Mater. Interfaces 2015, 7, 17061-17069. (52) Guo, Y.; Chen, L.; Ma, F.; Zhang, S.; Yang, Y.; Yuan, X.; Guo, Y. Efficient Degradation of Tetrabromobisphenol A by Heterostructured Ag/Bi5Nb3O15 Material under the Simulated Sunlight Irradiation. J. Hazard. Mater. 2011, 189, 614-618. (53) Yan, X.; Wang, X.; Gu, W.; Wu, M.; Yan, Y.; Hu, B.; Che, G.; Han, D.; Yang, J.; Fan, W.; Shi, W. Single-Crystalline AgIn(MoO4)2 Nanosheets Grafted Ag/AgBr Composites with Enhanced Plasmonic Photocatalytic Activity for Degradation of Tetracycline under Visible Light. Appl. Catal., B 2015, 164, 297-304. (54) Tang, Y.; Jiang, Z.; Deng, J.; Gong, D.; Lai, Y.; Tay, H. T.; Joo, I. T. K.; Lau, T. H.; Dong, Z.; Chen, Z. Synthesis of Nanostructured Silver/Silver Halides on Titanate Surfaces and Their Visible-Light Photocatalytic Performance. ACS Appl. Mater. Interfaces 2012, 4, 438-446.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC Graphic


Page 30 of 30

AgxH3âxPMo12O40 Nanowires with Enhanced Visible-Light

Recommend Documents

AgxH3âxPMo12O40 Nanowires with Enhanced Visible-Light