Chinese Journal of Chemical Physics  2018, Vol. 31 Issue (1): 92-98

#### The article information

Chun-xue Li, Xiu-ying Li, Bo Liu, Xiu-yan Wang, Guang-bo Che, Xue Lin

A Novel Ag3PO4/Ag/Ag2Mo2O7 Nanowire Photocatalyst: Ternary Nanocomposite for Enhanced Photocatalytic Activity

Chinese Journal of Chemical Physics, 2018, 31(1): 92-98

http://dx.doi.org/10.1063/1674-0068/31/cjcp1706127

### Article history

Accepted on: September 24, 2017
A Novel Ag3PO4/Ag/Ag2Mo2O7 Nanowire Photocatalyst: Ternary Nanocomposite for Enhanced Photocatalytic Activity
Chun-xue Li, Xiu-ying Li, Bo Liu, Xiu-yan Wang, Guang-bo Che, Xue Lin
Dated: Received on June 27, 2017; Accepted on September 24, 2017
Key Laboratory of Preparation and Applications of Environmental Friendly Materials, Jilin Normal University, Changchun 130103, China
*Author to whom correspondence should be addressed. Guang-bo Che, E-mail:guangboche@jlnu.edu.cn; Xue Lin, E-mail:jlsdlinxue@126.com
Abstract: Ag3PO4/Ag/Ag2Mo2O7 composite photocatalyst was successfully prepared via an in situ precipitation method. The as-prepared Ag3PO4/Ag/Ag2Mo2O7 nanocomposite included Ag3PO4 nanoparticles (NPs) as well as Ag NPs assembling on the surface of Ag2Mo2O7 nanowires. Under visible light irradiation (λ > 420 nm), the Ag3PO4/Ag/Ag2Mo2O7 composite degraded rhodamine B (Rh B) efficiently and showed much higher photocatalytic efficiency than pure Ag3PO4, Ag2Mo2O7, or Ag3PO4/Ag2Mo2O7. It was elucidated that the excellent photocatalytic performance of Ag3PO4/Ag/Ag2Mo2O7 for the degradation of Rh B under visible light could be ascribed to the high specific surface area, the extended absorption in the visible light region resulting from the Ag3PO4/Ag loading, and the efficient separation of photogenerated electrons and holes through the ternary heterostrucure composed of Ag3PO4, Ag and Ag2Mo2O7.
Key words: Ag3PO4/Ag/Ag2Mo2O7    Heterostructure    Photocatalysis    Visible light
Ⅰ. INTRODUCTION

In recent years, many significant researches have focused on developing heterogeneous photocatalysts for a range of environmental applications such as air cleanup, water disinfection, hazardous waste remediation, and water purification [1-3]. Numerous reports have discussed the design and development of a variety of semiconductor photocatalysts for use in air or water purification applications [4-6]. Primarily, combinations of metal/metal oxide nanostructures (for example Au, Ag, Pt, TiO$_2$, ZnO, SnO$_2$, WO$_3$, Nb$_2$O$_5$, BiVO$_4$, Fe$_2$O$_3$, etc.) have been investigated for the degradation of organic pollutants and carcinogenic materials [7-15]. Recently, with more and more attention has been paid to the mechanism of Ag$_3$PO$_4$-based hybrid photocatalytic systems, the by-product Ag has been found to be a electron transmission bridge in the Ag/Ag$_3$PO$_4$-based systems [16-23]. It has been reported that the Ag/Ag$_3$PO$_4$-based photocatalysts can not only facilitate the charge separation but also retain the high reducibility and oxidability of the remaining electrons and holes for the corresponding photocatalysts [24, 25]. Thus, it is important to search for suitable components that can construct novel Ag/Ag$_3$PO$_4$-based photocatalysts and largely enhance their photocatalytic performances. Silver molybdates, as one kind of metal molybdates, such as Ag$_6$Mo$_{10}$O$_{33}$, Ag$_2$Mo$_2$O$_7$, Ag$_2$Mo$_4$O$_{13}$, Ag$_2$MoO$_4$, and Ag$_2$Mo$_3$O$_{10}$ have attracted much attention, due to their important application in conducting glass and ammonia sensing material [26-29]. Yu and co-workers figured out that the silver trimolybdate can display excellent plasmonic photocatalytic efficiency under visible-light irradiation [29]. Besides, silver nanoparticles (NPs) have an efficient plasmon resonance in the visible region and would enhance the activity of plasmonic photocatalysts [30].

To the best of our knowledge, there are no reports about coupling mode of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$, and the photocatalytic mechanism of the composite photocatalyst remains far from clear. Herein, we report a successful attempt for the fabrication of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanowire photocatalyst via a facile in situ precipitation method, and the photocatalytic activity of the nanoheterostructures was studied by measuring the degradation of rhodamine B (Rh B) or bisphenol A (BPA) under visible light irradiation ($\lambda$$>420 nm). The experimental results showed that the as-prepared Ag_3PO_4/Ag/Ag_2Mo_2O_7 nanoheterostructures displayed excellent photocatalytic efficiency. In addition, the possible photocatalysis mechanism of Ag_3PO_4/Ag/Ag_2Mo_2O_7 under visible light was also discussed in detail. Ⅱ. EXPERIMENTS A. Preparation of photocatalysts All reagents for synthesis and analysis were commercially available and used without further treatments. Ag_2Mo_2O_7 nanowires were synthesized through a facile hydrothermal method. Briefly, a solution of AgNO_3 (0.40 mol/L, 5 mL H_2O) was stirred for 30 min. Then, (NH_4)_6Mo_7O_{24} (0.286 mmol) was added to the suspension, which was stirred magnetically for another 30 min. After carefully adjusting the pH value of 2 using 25 wt% NH_3$$\cdot$H$_2$O and HNO$_3$ (10%) solution, the mixed solution was transferred into a 20 mL Teflon-lined steel autoclave, which was heated in an oven at 140 ℃ for 12 h. Then the system was allowed to cool to room temperature naturally. At last, the obtained samples of Ag$_2$Mo$_2$O$_7$ nanowires were collected and washed with ethanol and distilled water several times, and dried at 70 ℃ for 10 h.

Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite photocatalyst was synthesized through an in situ precipitation method at room temperature. In a typical process, Ag$_2$Mo$_2$O$_7$ nanowires (500 mg) were dispersed in 100 mL deionized water by ultrasound for 30 min, and then 50 mL 0.0075 mol/L AgNO$_3$ aqueous solution was dropped into the Ag$_2$Mo$_2$O$_7$ dispersed solution. After stirring for 15 min, a 50 mL of 0.0025 mol/L Na$_3$PO$_4$ aqueous solution was added to the above solution drop by drop under magnetic stirring. The pH value was adjusted to 3 by adding 1.0 mol/L NaOH. The resulting suspension was stirred in the dark for another 30 min. Then, the suspension was irradiated by a 300 W Xe lamp equipped with an optical cut-off filter ($\lambda$$>420 nm) for 30 min. Finally, the precipitate was washed with deionized water for 3 times and collected by centrifugation, and then dried at 60 ℃ in the vacuum drying oven. Ag_3PO_4/Ag/Ag_2Mo_2O_7 was obtained. The theoretical value of Ag_3PO_4 loading amount was 10 wt%. For comparison, pure Ag_3PO_4 and Ag_3PO_4/Ag_2Mo_2O_7 samples were prepared under the same conditions. B. Characterization of photocatalysts The crystal structures of the samples were characterized by X-ray diffraction (XRD) on a Rigaku (Japan) D/max 2500 X-ray diffractometer (Cu K\alpha radiation, \lambda=0.15418 nm). The morphologies and structure details of the as-synthesized samples were detected using field emission scanning microscopy (SEM, JSM-6510) and transmission electron microscopy (TEM, JEM-2100F). X-ray photoelectron spectroscopy (XPS) analysis was performed with an ESCALa-b220i-XL electron spectrometer (VGScientific, England) using 300 W Al K\alpha radiation. The optical properties were obtained by the photoluminescence (PL) measurement using HR800 LabRam Infinity Spectro photometer excited by a continuous He-Cd laser with a wavelength of 325 nm at a power of 50 mW. The UV-Vis diffuse reflectance spectra (DRS) were recorded using a scan UV-Vis spectrophotometer (UV-2550). C. Photocatalytic activities studies The photocatalytic properties of the as-prepared samples were evaluated using Rh B as a model compound. In experiments, the Rh B (0.01 mmol/L, 100 mL) solution containing 0.02 g of photocatalyst were mixed in a pyrex reaction glass. A 300 W Xe lamp (\lambda$$>$420 nm) was employed to provide visible light irradiation. A 420 nm cut-off filter was inserted between the lamp and the sample to filter out UV light ($\lambda$$<420 nm). Prior to visible light illumination, the suspension was strongly stirred in the dark for 40 min. Then the solution was exposed to visible light irradiation under magnetic stirring. At given time intervals, 4 mL of the suspension was periodically collected and analyzed after centrifugation. The Rh B concentration was analyzed by a UV-2550 spectrometer to record the maximum absorbance (552 nm). D. Active species trapping experiments For detecting the active species during photocatalytic reactivity, some sacrificial agents, such as 2-propanol (IPA), disodium ethylenediamine tetraacetic acid (EDTA-2Na), and 1, 4-benzoquinone (BQ) were employed as the hydroxyl radical (\cdotOH) scavenger, hole (h^+) scavenger and superoxide radical (O_2$$^{\cdot-}$) scavenger, respectively. The method was similar to the former photocatalytic activity test with the addition of 1 mmol of quencher in the presence of Rh B.

Ⅲ. RESULTS AND DISCUSSION

FIG. 1 displays the XRD patterns of the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite photocatalyst, together with that of pure Ag$_2$Mo$_2$O$_7$ sample. All the peaks of the samples can be indexed with pure phase Ag$_2$Mo$_2$O$_7$, which matches well with the standard JCPDS file No.21-1339. It can be seen that no peaks assigned to Ag$^\rm{0}$ were found in the as-prepared Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample, due to its low amount. Moreover, the changes of all diffractions and lattice parameters were not detectable, which showed that Ag related species resided in the lattice sites and had no separate phase [31]. In addition, no obvious peaks of the Ag$_3$PO$_4$ phases were observed in the pattern of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$, due to low weight and small crystal size of loading Ag$_3$PO$_4$ on the surface of the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite [32].

 FIG. 1 XRD patterns of (a) Ag$_2$Mo$_2$O$_7$ and (b) Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$.XRD patterns of (a) Ag$_2$Mo$_2$O$_7$ and (b) Ag$_3$PO$_4$/ Ag/Ag$_2$Mo$_2$O$_7$.

Further evidence of the components of the sample is obtained by the X-ray photon spectroscopy (XPS) measurements, which is an excellent technique for understanding oxidation state and relative composition of a material. The Ag 3d peaks obtained from the nanowires are shown in FIG. 2(a). It can be seen that the Ag 3d peaks of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ have separated as Ag$^+$ peaks and Ag$^0$ peaks. The peaks at 368.4 and 374.6 eV are attributed to Ag$^0$, [24] indicating the existence of metallic Ag on the surface of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample. The peaks at 367.9 and 373.9 eV are assigned to Ag$^+$ of Ag$_2$Mo$_2$O$_7$ [24]. In FIG. 2(b), Mo 3d peaks centered at 231.7 and 234.9 eV are attributed to Mo 3d$_{3/2}$ and Mo 3d$_{5/2}$, respectively [24]. A broad peak in the range of 129-134 eV of the P 2p spectrum (FIG. 2(c)) is observed for the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample which corresponds to the phosphorus of Ag$_3$PO$_4$ [26, 27].

 FIG. 2 XPS spectra of the as-obtained Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample. (a) Ag 3d spectrum, (b) Mo 3d spectrum, (c) P 2p spectrum.

The SEM images of Ag$_2$Mo$_2$O$_7$ and Ag$_3$PO$_4$/Ag/ Ag$_2$Mo$_2$O$_7$ samples are revealed in FIG. 3. The as-prepared Ag$_2$Mo$_2$O$_7$ are composed of nanowires with widths of about 100 nm, and lengths of up to several micrometers (FIG. 3(a)). The Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample shows a similar morphology to pure Ag$_2$Mo$_2$O$_7$ (FIG. 3(b)), revealing that low amount Ag$_3$PO$_4$ and Ag loading did not have any influence on the morphology of Ag$_2$Mo$_2$O$_7$. FIG. 3(c) shows the enlarged SEM image of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanowires. As can be seen, there are some Ag$_3$PO$_4$ NPs loaded on the surface of the nanowires. Moreover, the component and connection of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ were also investigated by TEM, as shown in FIG. 3(c). It can be clearly found that the Ag NPs and Ag$_3$PO$_4$ NPs were loaded on the surface of Ag$_2$Mo$_2$O$_7$ nanowires, further confirming the formation of a novel ternary heterostructure. FIG. 3(d) displays the HRTEM image of the as-fabricated Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample. By measuring the lattice fringes, the resolved interplanar distances are about 0.236, 0.247, and 0.131 nm, which correspond to the (111) plane of Ag, the (211) plane of Ag$_3$PO$_4$, and the (010) plane of Ag$_2$Mo$_2$O$_7$, respectively.

 FIG. 3 SEM images of (a) Ag$_2$Mo$_2$O$_7$, (b, c) Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$, (d, e) TEM and HRTEM images of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$.

The optical absorption properties of the photocatalysts were studied by UV-Vis DRS spectra. As shown in FIG. 4(a), bare Ag$_2$Mo$_2$O$_7$ exhibits strong absorbance in wavelengths shorter than 475 nm, and pure Ag$_3$PO$_4$ shows strong absorbance in wavelengths shorter than 550 nm. The absorption curve of the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ displays distinctly enhanced visible-light absorption compared to the pure Ag$_2$Mo$_2$O$_7$. The band gap energies of semiconductors can be determined by Kubelka-Munk transformation, $\alpha h\nu$=$A$($h\nu$-$E_\rm{g}$)$^{n/2}$, where $\alpha$ represents the absorption coefficient, $\nu$ is the light frequency, $E_\rm{g}$ is the band gap energy, $A$ is a constant and $n$ depends on the characteristics of the transition in a semiconductor ($n$=1 for a direct transition and $n$=4 for an indirect transition). The band gap energies ($E_\rm{g}$) of pure Ag$_3$PO$_4$ and Ag$_2$Mo$_2$O$_7$ are calculated to be 2.14 and 2.62 eV, respectively (FIG. 4(b)).

 FIG. 4 (a) UV-Vis DRS of as-synthesized Ag$_2$Mo$_2$O$_7$, Ag$_3$PO$_4$ and Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ samples. (b) The plots of ($\alpha hv$)$^2$ versus photon energy ($h\nu$) for the band gap energies of Ag$_3$PO$_4$ and Ag$_2$Mo$_2$O$_7$ sample.

The potentials of VB and CB of a semiconductor material can be estimated according to the following empirical equations:

 $E_{\rm{VB}}\hspace{-0.15cm}=\hspace{-0.15cm} X- E^{\rm{e}} + 0.5E_\rm{g}$ (1)
 $E_{\rm{CB}}\hspace{-0.15cm}=\hspace{-0.15cm}E_{\rm{VB}} - E_\rm{g}$ (2)

where $E_{\rm{VB}}$ is the valence band edge potential, $E_{\rm{CB}}$ is the conduction band edge potential, $X$ is the electronegativity of the semiconductor, which is the geometric mean of the electronegativity of the constituent atoms, $E^\rm{e}$ is the energy of free electrons on the hydrogen scale (about 4.50 eV), $E_\rm{g}$ is the band gap energy of the semiconductor. The $E_{\rm{VB}}$ of Ag$_3$PO$_4$ and Ag$_2$Mo$_2$O$_7$ are calculated to be 2.54 and 2.675 eV, respectively. The $E_{\rm{CB}}$ of Ag$_3$PO$_4$ and Ag$_2$Mo$_2$O$_7$ are estimated to be 0.40 and 0.055 eV, respectively.

N$_\rm{2}$ adsorption-desorption isotherms (FIG. 5) of the as-fabricated Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ and Ag$_2$Mo$_2$O$_7$ samples were performed to determine the surface areas of the samples. The BET surface areas of the as-prepared Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ and Ag$_2$Mo$_2$O$_7$ are 35.598 and 21.420 m$^2$/g, respectively. The larger BET surface area can facilitate more efficient contact of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite with organic contaminants, which is beneficial to the enhancement of photocatalytic performance. FIG. 6(a) displays the photocatalytic decolorization of Rh B over different photocatalysts. Before light irradiation, the solution of Rh B and photocatalyst was magnetically stirred in dark for 40 min. It can be clearly seen that the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite displays superior photocatalytic activity compared to the other samples, as shown in FIG. 6(a). Almost 100% of the Rh B molecules were decomposed after 80 min. For Ag$_3$PO$_4$ Ag$_2$Mo$_2$O$_7$, and Ag$_3$PO$_4$/Ag$_2$Mo$_2$O$_7$ samples, only about 24.0%, 54.0%, and 91.0% of the Rh B dye molecules were destroyed under the same conditions within 80 min, respectively. The as-prepared Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite displayed enhanced photocatalytic efficiency than the other Ag$_2$Mo$_2$O$_7$ based photocatalysts reported in previous reports [26, 33]. Coupling Ag$_2$Mo$_2$O$_7$ with Ag$_3$PO$_4$/Ag can significantly improve the photocatalytic performance for the degradation of Rh B molecules. The Ag$_3$PO$_4$/Ag coating can improve the visible light absorption efficiency (FIG. 4(a)), which is beneficial for the composite photocatalyst to photolyze Rh B [34, 35]. In addition, efficient heterostructure interface between two or three components can restrain the recombination of photoinduced charges effectively, thus enhancing the photocatalytic performance of the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$. FIG. 6(b) shows the comparison of PL spectra of the as-prepared samples under the excitation wavelength of 325 nm. It can be seen that the PL peak intensity of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ decreases obviously. This result reveals that the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ contributes to the effective electron-hole pair separation, which may be a reason for the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample showing enhanced photocatalytic activity under visible light irradiation.

 FIG. 5 N$_2$ adsorption-desorption isotherm curves of the as-prepared samples.
 FIG. 6 (a) Photodegradation efficiencies of Rh B as a function of irradiation time for different photocatalysts. (b) Room temperature PL spectra of as-synthesized samples. (c) Cycling runs for the photocatalytic degradation of Rh B over the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample under visible light irradiation.

In view of the practical applications for photocatalysts, the reusability and stability of the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ are of significance. We carried out photocatalytic experiments using the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ for four cycles to degrade the Rh B dye under visible light irradiation, as shown in FIG. 6(c). The photocatalytic degradation efficiency of the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ sample slightly drops from 100% to 91.0% after four cycles (i.e. only reduces by 9.0%), which reveals that the heterostructured Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ plasmonic photocatalyst in this study is quite stable and can be easily re-used in the photocatalytic process, in contrast to previous reports which show that silver-based photocatalysts are generally unstable [36, 37]. Therefore, our Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ photocatalyst could have potential for the degradation of organic pollutants.

Based on the above experiment results, the possible mechanism of the ternary heterostructured Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ composite with enhanced photocatalytic performance is proposed, which can be explained in FIG. 7. Under visible light irradiation, both Ag$_3$PO$_4$ and Ag$_2$Mo$_2$O$_7$ are excited, and the photogenerated holes and electrons are in their conduction and valence band, respectively. The electrons on the CB of Ag$_3$PO$_4$ can easily shift into metal Ag (electron transfer: Ag$_3$PO$_4$ CB$\rightarrow$Ag) through the Schottky barrier because the CB potential of Ag$_3$PO$_4$ (0.40 eV vs. SHE) is more negative than the Fermi level of the loaded metal Ag. Therefore, the electrons in the CB of Ag$_3$PO$_4$ can be stored in the Ag component. In the system of Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanowires, nano-Ag particles were deposited on the surface of Ag$_2$Mo$_2$O$_7$ nanowires and played an important role as an electron-conduction bridge. Meanwhile, the holes on the VB of Ag$_2$Mo$_2$O$_7$ can also migrate to metal Ag (hole transfer Ⅱ: Ag$_2$Mo$_2$O$_7$ VB$\rightarrow$Ag) because the Fermi level of Ag is more negative than the VB of Ag$_2$Mo$_2$O$_7$, and then combine with the electron here [21, 38, 39]. Therefore, these transfers enhance the charge separation of Ag$_3$PO$_4$ and Ag$_2$Mo$_2$O$_7$ and improve the photoactivity.

 FIG. 7 Schematic diagram of the separation and transfer of photogenerated charges in the heterostructured composite under visible light irradiation.

It is important to detect the main oxidative species in the photocatalytic process for revealing the photocatalytic mechanism. The main oxidative species in the Rh B photocatalytic degradation process were detected through the trapping experiments of radicals and holes in the presence of various scavengers including 2-propanol (IPA, hydroxyl radical scavenger), 1, 4-benzoquinone (BQ, superoxide radical scavenger) and disodium ethylenediaminetetra aceticacid (EDTA-2Na, hole scavenger). Under the visible-light irradiation of the as-prepared Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanowires, the photodegradation rate of Rh B had slight decrease after the addition of hydroxyl radical scavenger IPA (64.1%) and hole scavenger EDTA-2Na (57.0%), showing that hydroxyl radicals and holes are not the main active species that are responsible for the degradation of Rh B in current photocatalytic systems. However, the photodegradation rate of Rh B was decelerated significantly after the addition of superoxide radical scavenger BQ (7%). The above results show that the active species O$^{2\cdot-}$ radicals played the major role in the Rh B degradation over the Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanowires under visible light irradiation.

Ⅳ. CONCLUSION

A novel Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanoheterostructure, in which Ag$_2$Mo$_2$O$_7$ nanowires were decorated with Ag$_3$PO$_4$/Ag, has been synthesized by a facile low-temperature solution-phase method. The Ag$_3$PO$_4$/Ag/Ag$_2$Mo$_2$O$_7$ nanowires showed superior photocatalytic performance to bare Ag$_2$Mo$_2$O$_7$, Ag$_3$PO$_4$, and Ag$_3$PO$_4$/Ag$_2$Mo$_2$O$_7$ in degradation of Rh B and BPA under visible light irradiation. This improvement is attributed to the migration efficiency of the photoinduced carriers through the ternary heterostrucure, the high specific surface area, and the enhanced efficiency of photoharvesting owing to the stable deposition of Ag$_3$PO$_4$/Ag.

Ⅴ. ACKNOWLEDGMENTS

This work was supported by the National Natural Science Foundation of China (No.21407059, No.21576112, No.21407064, and No.21607051), the Science Development Project of Jiangsu Province (BK20140527), the Science and Technology Research Project of the Department of Education of Jilin Province (No.2015220), and the Open Subject of the State Key Laboratory of Rare Earth Resource Utilization (RERU2017011).

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