Plasmonic-Enhanced Near-Infrared Photocatalytic Activity of F Doped

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Plasmonic-Enhanced Near-Infrared Photocatalytic Activity of F Doped (NH4)0.33WO3 Nanorods Yi Kang, Xiaomei Wu, and Qiang Gao ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05880 • Publication Date (Web): 28 Jan 2019 Downloaded from http://pubs.acs.org on January 29, 2019

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ACS Sustainable Chemistry & Engineering

Plasmonic-Enhanced Near-Infrared Photocatalytic Activity of F Doped (NH4)0.33WO3 Nanorods Yi Kang, Xiaomei Wu, Qiang Gao* School of Materials Science and engineering, South China University of Technology, Guangzhou, 510641, People’s Republic of China

* Corresponding author: Email: [email protected], [email protected]. Tel: +86-020-87114243

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Abstract: To achieve efficient utilization of solar power for environmental remediation, search for suitable materials as efficient solar light driven photocatalysts is one of the most challenging missions. In this work, F doped (NH4)0.33WO3 was first synthesized as a novel near-infrared (NIR) photocatalyst with enhanced photocatalytic activity. Compared to that of pure ammonium tungsten bronze, a blue shift of the NIR plasmon band and an enhanced NIR absorbance of F doped (NH4)0.33WO3 could be observed. 83% of rhodamine B (RhB) was degraded by F doped (NH4)0.33WO3 under NIR irradiation within 180 min. The NIR photodegradation rate of the optimal F doped (NH4)0.33WO3 for RhB was 0.0102 min−1, about 8.5 times as high as that of (NH4)0.33WO3. The enhanced NIR photocatalytic performance of F doped (NH4)0.33WO3 can be attributed to the remarkable enhanced generation and separation of NIR localized surface plasomon resonance induced electron–hole pairs. Moreover, the F doped (NH4)0.33WO3 nanorods could also degrade 36% of RhB and 93% of RhB when exposed to the UV light and visible light, respectively. This work develops a promising photocatalyst with a full solar light response for future environmental pollutants cleaning up. Key words: Photocatalytic; Localized surface plasomon resonance (LSPR); Near infrared (NIR); Tungsten bronzes; Full solar spectrum

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Introduction As a green power, solar energy has been widely used to solve environmental and energy problems. 1 Among all kinds of solar-power applications, photocatalytic technologies for environmental remediation have attracted extensive attention. 2-8 TiO2, as a most promising semiconductor photocatalyst, is widely studied in photodegration of organic pollutants. 9-11 However, the photoactivity of TiO2 is limited in the ultraviolet (UV) light (＜420nm) range. 12 Thus, several studies have been focused on widening the photoabsorption to visible region, which accounts for 42% of the solar energy. 13-14 Besides doped TiO2, 15 a lot of novel photocatalysts such as Ag3PO4, 16 BiVO4, 17-18 C3N4, 19-25 CdS, 26-27 SrTiO3, 28-29 BiOX (X=Cl, Br, I) etc., 30-32

were investigated. However, near-infrared light (NIR, 760-2500nm), which

accounts for 52% of the solar energy, have not yet fully utilized in photocatalytic field. 33-34 Up to now, only a few NIR photocatalysts, such as up-conversion materials, 35-39

Cu2(OH)PO4, 40 Bi2WO6, 1, 41-42 metal sulfide, 43-46 and metal oxide 47-52 have been

reported. Therefore, the development of novel NIR photocatalysts with high photocatalytic efficiency and chemical stability is of great value. Recently, nanostructured tungsten bronzes ((MxWO3, M= Li+, Na+, K+, and NH4+, etc.) with excellent NIR absorption properties have drawn increasing attentions. 53-56 The strong NIR absorption of tungsten bronzes can be ascribed to localized surface plasmonic resonance (LSPR). 55 As a novel NIR absorption material, nanosized tungsten bronze based smart window coatings have been widely used for solar shielding of buildings. 57-58 In order to further utilization of the absorbed NIR, the NIR 3



photocatalytic performance of tungsten bronzes have been investigated. 59 However, pure tungsten bronze have very low NIR photocatalytic efficiencies. Liu et al. prepared CsxWO3 nanorods photocatalyts, which only removed 37% of MB under NIR irradiation after 6 hours. 59 Liu et al. prepared P25/(NH4)xWO3 hybrid photocatalyts, which only degrade 68% of RhB under NIR irradiation for 12 h. 60 The poor NIR photocatalytic performance of tungsten bronze limits their practical applications. Therefore, enhance of the NIR photocatalytic activity of tungsten bronze is of great importance. Several studies reported the improvement of NIR photocatalytic performance of tungsten bronze by semiconductor technology. 49, 61-62 However, the improvement of the NIR photocatalytic performance of tungsten bronze by anion doping have not been reported. In this study, NIR photocatalytic activity of F doped (NH4)0.33WO3 was reported for the first time. The NIR photocatalytic performance of (NH4)0.33WO3 was greatly improved by the doping of F ions. The phase composition, morphology, optical property, NIR photocatalytic performance and photocatalytic mechanism of as obtained F doped (NH4)0.33WO3 nanostructures were investigated.

Experimental Synthesis of F doped (NH4)0.33WO3 The preparation of pure (NH4)0.33WO3 was carried out as follows. 0.6 g of tungsten hexachloride and 0.6 g of ammonium acetate was dissolved into 100 mL of npropanol under violently stirring. After the mixture become homogeneous, the obtained yellow solution was put into an autoclave. After that, the autoclave was 4


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heated at 190℃ for 24 h. Finally, the products were collected, wash thoroughly, and dried at 60℃ for 4h. The obtained sample was named as F0. Doped samples were prepared using a procedure that was similar to that described for undoped (NH4)0.33WO3. However, one important feature of this process was that certain amounts of hydrofluoric acid was added into the mix solution of WCl6 and CH3COONH4. The usage of HF were 0.25 mL, 0.5 mL, and 0.75 mL, respectively. The final products were named as F0.25, F0.5, and F0.75, respectively. Characterization The phase composition of the samples were carried out on an X'Pert Pro X-ray diffractometer. Morphological observations of the samples were identified by a NanoSEM 430 scanning electron microscope. A transmission electron microscope (TEM, JEM 2100) was also used to characterize the nanostructures of the catalysts. A Thermo Fisher X-ray Photoelectron Spectroscopy spectrometer was used to investigate the surface chemical composition of the samples. The optical spectra were performed with a Lambda950 spectrophotometer. The photoluminescence (PL) spectra were recorded with an Fls920 fluorescence spectrophotometer. The ESR signals with an irradiated source of 780 nm were measured by a Bruker A300 spectrometer. Electrochemical impedance spectroscopy (EIS) of the samples were recorded using a Metrohm PGSTAT 204. Photocatalytic test The photoactivities of the F doped (NH4)0.33WO3 were evaluated by the decompositon of rhodamine B (RhB). During the test, it was found that (NH4)0.33WO3 exhibited high adsorption abilities of RhB, which was consistent with previous report. 5



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To avoid the influence of absorption, 0.05g tungsten bronze powders was pre-

treated in 50 mL of RhB solution (50 mg/L) for 5h to reach a absorption–desorption equilibrium. After that, the particles was centrifuged and transferred to a 50 mL of RhB solution (20 mg/L), which was subsequently stirred for about 0.5 h to attain adsorption equilibrium before irradiation. Then the solution was illuminated by a 375 W infrared lamp where the wavelengths below 760 nm were shielded, a 300 W xenon lamp where the wavelengths below 420 nm were filtered out as visible light source, and a 500 W mercury lamp as UV light source. To eliminate the thermal effect, a thermostatic water circulation equipment was used. An Agilent Cary 60 UV-VIS spectrophotometer was used to investigate the concentration of RhB solution.

Results and discussion Structure and morphology

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Fig.1 XRD patterns of pure (NH4)0.33WO3 and F doped (NH4)0.33WO3: (a) pure (NH4)0.33WO3 (F0), (b) F0.25, (c) F0.5, (d) F0.75. Fig.1 shows the XRD patterns of as prepared ammonium tungsten bronze with different usage of HF. The XRD profiles of (NH4)xWO3 and F doped (NH4)xWO3 samples can be regarded as the hexagonal (NH4)0.33WO3 (JCPDS NO. 42-0452) . The XRD peaks with 2θ values of 13.8°, 23.7°, 27.9°, 34.1°, 36.9° , and 49.3° correspond to (100), (002), (200), (112), (202), and (220) planes of hexagonal (NH4)0.33WO3, respectively. After doping of F ions, new diffraction peaks corresponding to (111) and (102) planes of hexagonal (NH4)0.33WO3 also appear. Although the crystal phase is not influenced by fluorine doping, the relative peak intensity of ratio of (100), (002), and (200) planes changes dramatically. Compared to those of pure ammonium tungsten bronze, the peak intensity ration of (100) / (200) of F doped ammonium tungsten bronze increases significantly, suggesting the preferential growth of F doped ammonium tungsten bronze along (100) direction. This preferential growth could be attributed to the selective adsorption of F− on certain facet of (NH4)0.33WO3. More interestingly, the peak position of F doped (NH4)0.33WO3 shifts to a lower 2θ direction, suggesting an enlargement of the lattice parameters. Thus, the shift of the diffraction peak can be ascribed to the replacement of lattice oxygen atom in WO6 octahedron by fluorine atom, which is consistent with previous reports. 63-64

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Fig.2 SEM images of (NH4)0.33WO3 (F0) (a) and F doped (NH4)0.33WO3 (F0.75) (b). Fig. 2 shows the morphology of as-prepared ammonium tungsten bronze. As for undoped (NH4)0.33WO3, agglomerated nanoparticles and some rod-like structures can be observed (Fig.2a). However, the surface morphology changes remarkably for F doped (NH4)0.33WO3. Large numbers of nanorods can be observed for F doped (NH4)0.33WO3.

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Fig.3 (a) TEM image of (NH4)0.33WO3 nanostructures (F0), (b) HRTEM image of a (NH4)0.33WO3 nanorod (F0), (c) TEM image of F doped (NH4)0.33WO3 nanostructures (F0.75), (d) HRTEM image of an individual F doped (NH4)0.33WO3 nanorod (F0.75), (e) Elemental mapping of an individual nanorod (F0.75). 9



Later, the more detailed nanostructure characters of ammonium tungsten bronze sample were examined by TEM and HRTEM technique. The (NH4)0.33WO3 nanorods with a diameter of 15–100 nm and a length of 40–500 nm can be seen from Fig.3a. The preferential growth of (NH4)0.33WO3 along the c axis is confirmed by the HRTEM image (Fig.3b). The crystal lattice constant perpendicular to the nanorod is 0.375 nm, which is identified as the (002) plane of (NH4)0.33WO3. As for F doped (NH4)0.33WO3, nanorods with a length of 200-900 nm and a diameter of 80-300nm can be observed (Fig.3c). The fringe spacing of 0.390 nm can be indexed to the interplanar distance of (002) plane of (NH4)0.33WO3. In comparison to that of pure (NH4)0.33WO3, the enlarged (002) interplanar distance of F doped (NH4)0.33WO3 further confirms the doping of F ions in the crystal structure of ammonium tungsten bronze (Fig.3d). The elemental mapping image of an F doped (NH4)0.33WO3 nanorod is shown in Fig.3e. It is revealed that W, O, F, and N are uniformly distributed throughout the nanorod which further confirms the chemistry composition of the prepared F doped ammonium tungsten bronze. Moreover, the atomic percent of N, O, W, and F by EDS is 16.9%, 46.4%, 21.5%, and 15.2%, respectively.

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Chemical composition

Fig.4 XPS spectra of the samples: (a) wide spectra of F doped (NH4)0.33WO3, (b) W 4f of the samples, (c) O 1s of the samples, (d) F 1s of F doped (NH4)0.33WO3, (e) N 1s of the samples. Figure 4a shows the appearance of N, W, O, and F elements. As shown in Fig.4b, the W 4f5/2 and W 4f7/2 peaks shift to higher binding energy direction after F doping, which can be attributed to the high electron-attracting eﬀect from the neighboring F 11



occupy oxygen sites in the lattice. 65 The W4f spectra could be fitted into four peaks (Fig. 4b). The peaks at 37.8 eV and 35.6 eV are assigned to W6+, while the peaks at 36.6 eV and 34.2 eV may attribute to W5+. Interestingly, as shown in Fig. 4b, the F doped (NH4)0.33WO3 exhibits higher ratio of W5+/W6+ (about 0.26) than that of undoped (NH4)0.33WO3 (about 0.14). Thus, much more W5+ ions exist in F doped (NH4)0.33WO3 crystals. The increased W5+ ion in the F-(NH4)0.33WO3 may be attributed to the reduction of W6+ ions by electrons after F doping. As shown in Fig.4c, two peaks can be observed from the fitted curve of O1s. The peaks at 530.5 eV and 531.5 eV can be assigned to the lattice oxygen and surface hydroxyl group, respectively. The hydroxyl content (%) can be calculated by the area ratio of the 531.5 eV peak to the O1s. The hydroxyl contents of F0 and F0.75 are calculated to be 36.7% and 34.2%, respectively. The slightly reduced surface hydroxyl content of F doped (NH4)0.33WO3 may be attributed to the substitution of some hydroxyl group by fluorine ions during solvothermal process. The peak at 684.2 eV can be regarded as F 1s peak in lattice (Fig.4d). The F/W molar ratio of the samples was determined by the atomic percentages of F and W. As shown in Table1, the F/W molar ratio of the samples increases as the increasing usage of HF, indicating the increasing dopant loading of F ions in ammonium tungsten bronze crystals. The binding energy of 401.0-402.0 eV can be attributed to N1s of NH4+ in the ammonium tungsten bronze (Fig.4e). Table 1 Molar ratio of F/W determined by XPS, band gap (Eg), and degradation rate constant (K) of the samples. 12


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Sample F0 F0.25 F0.5 F0.75

F/W 0 0.54 0.63 0.73

Eg(eV) 2.86 2.80 2.76 2.66

K(min-1) 0.0012 0.0034 0.0038 0.0102

Optical and photoelectrochemical properties

Fig.5 (a) UV−VIS absorption spectrum of ammonium tungsten bronze, (b) band-gap of ammonium tungsten bronze, (c) NIR absorption spectra of ammonium tungsten bronze. Fig. 5a shows the UV-VIS absorption spectra of the samples prepared with different F dopant loading. It is obvious that the absorption spectra of the samples shift to longer wavelength direction with increasing F dopant loading. The 13



corresponding color of the particles changes from blue to grey. Optical band gap of Fdoped ammonium tungsten bronze could be obtained by the following equation: 66

α∝

(ℎ𝑣 ― 𝐸𝑔)2 ℎ𝑣

(1)

Where Eg, α, ℎ𝑣 are band gap, optical absorption coefficient, and photonic energy, respectively. A plot of (αℎ𝑣)2 vs ℎ𝑣 gives the band gap (Fig.5b). The calculated band gap of the samples was summarized in Table 1. As the increase of F dopant loading, the band gap decreases from 2.86eV to 2.66 eV. Therefore, the doping of F ions in ammonium tungsten bronze can widen the absorption range of the samples. As can be seen from Fig.5c, an obvious plasmon band can be observed in the NIR region. Compared to that of pure ammonium tungsten bronze, the plasmon band of F doped (NH4)0.33WO3 shifts to shorter wavelength. The plasmon shift can be quantitatively explained by Durde-Lorentz theory. The surface plasmon frequency (ωp) can be calculated by the following equation: 67

𝜔𝑝 =

𝑁𝑒2 𝑚 ∗ 𝜀𝑜𝑝𝑡𝜀0

(2)

Where m* refers to the effective mass of the electron, N is the free carrier concentration, ε0 is regarded as the vacuum permittivity, εopt is the dielectric constant of the semiconductor. As can be seen from Eq. (2), there is a positive correlation between the plasmon frequency (ωp) and the square root of the free carrier concentration.

𝐹

―

𝑂2 ―

― 𝐹· 𝑂 +𝑒

(3)

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It is well known that the replacement of O2- ions by F- ions would generate an electron due to the difference in the electrovalence of fluorine (F-) and oxygen (O2-). Therefore, the free carrier concentration of F doped (NH4)0.33WO3 is higher than that of pure (NH4)0.33WO3. As a result, the doping of fluorine ions results in the blue shift of the plasmon bands. Furthermore, as shown in Fig.5c, F doped ammonium tungsten bronze show stronger NIR absorbance than that of the undoped ammonium tungsten bronze. Significantly, with increasing amount of F, F doped ammonium tungsten bronze show a continuously enhanced absorbance in the NIR range, suggesting an enhanced solar light utilization ability of the samples. The enhanced NIR absorbance can also be explained by modified Durde-Lorentz theory. 68 𝑒2𝑁

α = 𝑚 ∗ 𝜀 𝑛𝑐𝜏𝜔2

(4)

0

Where α is free carrier absorption coefficient, N is free carrier concentration, c and ω are the speed and frequency of the light, n refers to the refractive index of the semiconductor, e is the electron charge, and τ is regarded as the mean time between two electron scattering events. Eq.(4) indicates that absorption coefficient (α) enhances as the increase of the free carrier concentration. Moreover, Eq.(3) indicates that the free carrier concentration of ammonium tungsten bronze increases as the increasing dopant loading of F ions. Therefore, NIR absorbance of (NH4)0.33WO3 enhances as the increase of F dopant loading.

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Fig.6 (a) Photoluminescence spectrum for pure (NH4)0.33WO3 (F0) and F doped (NH4)0.33WO3 (F0.75). (b) Electrochemical impedance spectroscopy (EIS) of pure (NH4)0.33WO3 (F0) and F doped (NH4)0.33WO3 (F0.75). The extent of charge separation of the pure (NH4)0.33WO3 and F doped (NH4)0.33WO3 was characterized by photoluminescence (PL) spectroscopy. The PL spectrum of F doped ammonium tungsten bronze is similar to that of pure (NH4)0.33WO3 (Fig.6a), but the overall emission intensity decreases remarkably, suggesting the significantly suppressed recombination of photogenerated charge carriers. Therefore, the charge carrier separation efficiency is enhanced after F doping. The charge carrier separation of F doped ammonium tungsten bronze was further investigated by the EIS experiments. As show in Fig.6b, the diameters of the arc radii of F doped (NH4)0.33WO3 is clearly much smaller than that of pure (NH4)0.33WO3, further confirming a higher charge transfer efficiency on the surface of the F doped (NH4)0.33WO3.

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Photocatalytic activity

Fig.7 (a) Photodecomposition of RhB by F doped ammonium tungsten bronze when exposed to NIR light. (b) Photocatalytic degradation of RhB in the presence of F doped ammonium tungsten bronze nanorods under different light source. (c) Linear fitting of

ln(C0 / C )  f (t )

for the samples under NIR irradiation. (d) The cycling

experiments in the photodegradation of RhB by F doped (NH4)0.33WO3 (F0.75) under NIR irradiation. To illustrate the photocatalytic performances of the F doped ammonium tungsten bronze, the degradation of RhB exposed to different light source (UV, VIS, and NIR) had been performed. Hardly any RhB was decomposed when there were no catalysts (Fig.7a). Under the NIR irradiation (Fig. 7a), only 20% of RhB is removed by pure (NH4)0.33WO3. However, the decomposition efficiency of RhB by F doped 17



(NH4)0.33WO3 ranges from 47% to 83%. Moreover, the degradation efficiency of RhB by F doped (NH4)0.33WO3 enhances as the increase dopant loading of F ions. To further confirm the solar driven photocatalytic performance of F doped (NH4)0.33WO3, the remove efficiency of RhB exposed to UV and visible light were investigated (Fig.7b). 36% of RhB was degraded by F doped (NH4)0.33WO3 when exposed to UV light. The remove efficiency of RhB under visible light for 120min was determined to be approximately 93%. Moreover, as shown in Fig.S1, 32% of methylene blue (MB) and 80% of MB was removed by the F doped (NH4)0.33WO3 nanorods when exposed to NIR and visible light, respectively. Therefore, the solar light responsive photocatalytic performances of F doped (NH4)0.33WO3 were confirmed. Furthermore, as shown in Fig.S2, F doped (NH4)0.33WO3 exhibited enhanced UV and visible photocatalytic activities than those of pure (NH4)0.33WO3, which can be ascribed to the reduced band gap of F doped (NH4)0.33WO3. The kinetic analyses of NIR photocatalytic processes were performed. The photocatalytic kinetics had been proposed to fit ln (C0/C) = Kt, where K is the degradation rate constant. 69 The plots of ln (C0/C) as a function of irradiation time with different catalysts is shown in Fig. 7c. A linear trend is observed for all the samples, which suggests that the photocatalytic degradation of RhB under these reaction conditions followed pseudo-first-order kinetics. The value of K is provided in Table 1. Remarkably, the NIR photodegradation rate of the optimal F doped (NH4)0.33WO3 for RhB was 0.0102 min−1, about 7.2 times higher than that of pure

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(NH4)0.33WO3. Moreover, the reaction rate constant of ammonium tungsten bronze increases as the increasing dopant loading of F ions. Cycling use of photocatalysts with stable activity is a key to the long-term practical applications. No obvious performance decrease after five consecutive cycles can be observed from Fig. 7d, suggesting the stability of as prepared F doped (NH4)0.33WO3. Mechanism of enhanced NIR plasmonic photocatalysis

Fig.8 Photocatalytic degradation of RhB by F doped (NH4)0.33WO3 (F0.75) with different scavengers. The main active species in the NIR photocatalytic process were investigated by trapping experiments. The scavengers were EDTA-2Na for holes, tert-butyl alcohol (t-BuOH) for ·OH, silver nitrate (AgNO3) for photo-induced electron and N2 for · 𝑂2 ― . As shown in Fig.8, when EDTA-2Na and t-BuOH were added, the degradation rate for RhB over F doped (NH4)0.33WO3 decreased significantly, indicating the major role of holes and ·OH in the photocatalytic process. When N2 was pumped into the 19



solution, the degradation rate also decreased, suggesting that ·𝑂2 ― also participate in the photocatalytic process. However, a negligible inhibition of degradation rate was observed when AgNO3 as a scavenger for electron was added, indicating that electron do not play predominant roles in the photocatalytic process. The generation of reactive species over F doped (NH4)0.33WO3 under NIR light irradiation was further investigated by an electron spin resonance (ESR) spectroscopy technique. No ESR signal could be observed without the irradiation (Fig. 9). An obvious four-line ESR signal appeared when exposed to NIR light, suggesting the presence of DMPO-·𝑂2 ― . Moreover, the ESR signal of ·OH radical also appeared. Therefore, as confirmed by trapping experiments and ESR results, h + ,· OH, and ·𝑂2 ― are the major oxidation active species in NIR photocatalytic process.

Fig.9 DMPO spin-trapping ESR spectra of F doped (NH4)0.33WO3 in (a) methanol dispersion for superoxide ion and (b) aqueous dispersion for hydroxyl radical irradiated by NIR light.

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Fig.10 Schematic illustration of the NIR photocatalytic mechanism of F doped (NH4)0.33WO3. Based on the above analysis, a LSPR enhanced NIR photocatalytic mechanism was presented (Fig.10). The doping of fluorine leads to the increase of free electrons in ammonium tungsten bronze. Due to the reduction of W6+ ions by free electrons, the concentration of W5+ ion in the F-(NH4)0.33WO3 increases. The high concentration of W5+ creates a defect energy level under the conduction band of (NH4)0.33WO3. By illuminating the catalyst with NIR light, the electron is excited from the valence band (VB) to the defect energy level (process 1 in Fig.10). The excited electrons react with the absorbed molecular oxygen at defect sites, producing ·𝑂2 ― . The holes left in the valence band accelerate the generation of ·OH. Moreover, the excess free electrons can be localized nearby the Fermi level of ammonium tungsten bronze. 61 Due to the large numbers of surface electrons, LSPR of F doped (NH4)0.33WO3 can be excited by NIR. 50 As a result, the localized electrons can be exited to the conduction band (CB) of ammonium tungsten bronze, generating plasmonic hot electrons (process 2 in Fig.10). Then, the hot electrons transfer to 21



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oxygen adsorbed on the surface of F doped (NH4)0.33WO3, generating ·𝑂2 ― . Furthermore, the LSPR induced strong electric field promotes the separation of electrons and holes. Finally, the produced h + ,·OH, and ·𝑂2 ― can degrade RhB. The detailed chemical reaction mechanism are as follows: + Process 1: F ― (𝑁𝐻4)0.33𝑊𝑂3 + NIR→𝑒 ― (𝑊5 + ) + ℎ𝑉𝐵

Process 2: F ― (𝑁𝐻4)0.33𝑊𝑂3 + NIR 𝑒 ― + O2→·𝑂2 ―

(5)

LSPR ―

𝑒 (ℎ𝑜𝑡 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛) (6)

(7)

h + + H2O→·OH (8) h + , ·OH,·𝑂2 ― +𝑅ℎ𝐵→Degradation

(9)

Conclusions In summary, F doped (NH4)0.33WO3 nanorods were synthesized as an effective NIR responsive photocatalyst. Due to the increased amounts of free electrons after F doping, the NIR absorbance of F doped (NH4)0.33WO3 was enhanced due to LSPR. The F doped (NH4)0.33WO3 nanorods exhibited superior full solar driven photocatalytic removal efficiency of RhB. Moreover, the NIR photodegradation rate of the optimal F doped (NH4)0.33WO3 for RhB was about 7.5 times higher than that of (NH4)0.33WO3. A combination of improved NIR absorbance and enhanced generation and separation of electron–hole pairs by LSPR contributed much to this improved NIR photocatalytic performance of F doped (NH4)0.33WO3 nanorods. The main reactive species included h + ,·OH, and·𝑂2 ― , which further degraded the RhB degradation. Therefore, our prepared F doped (NH4)0.33WO3 nanorods have great

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potential to be used as full solar energy driven photocatalysts for environmental remediation.

Supporting information Photodegradation of MB by F doped (NH4)0.33WO3, photodegradation of RhB on UV and visible light irradiated catalysts.

Acknowledgements The work was financially supported by National Natural Science Foundation of China (NO.51702105), Science and Technology Project of Guangdong Province (NO.2016A040403042), China Postdoctoral Science Foundation (No.2017M620372, No.2018T110864), and Science and Technology Program of Guangzhou (NO.201707010336).

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Graphical abstract

Synopsis In this work, F doped (NH4)0.33WO3 nanorods was first synthesized as a novel nearinfrared (NIR) photocatalyst with enhanced photocatalytic activity, which has great potential in making full use of solar energy for environmental remediation

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Plasmonic-Enhanced Near-Infrared Photocatalytic Activity of F Doped

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