Ceria-Coated Gold Nanorods for Plasmon-Enhanced Near-Infrared

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Ceria Coated Gold Nanorods for Plasmon-Enhanced NearInfrared Photocatalytic and Photoelectrochemical Performances Jia-Hong Wang, Ming Chen, Zhi-Jun Luo, Liang Ma, Ya-Fang Zhang, Kai Chen, Li Zhou, and Qu-Quan Wang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b03753 • Publication Date (Web): 23 Jun 2016 Downloaded from http://pubs.acs.org on June 28, 2016

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The Journal of Physical Chemistry

Ceria Coated Gold Nanorods for Plasmon-enhanced Near-infrared Photocatalytic and Photoelectrochemical Performances Jia-Hong Wang,† Ming Chen,† Zhi-Jun Luo,† Liang Ma,† Ya-Fang Zhang,† Kai Chen,† Li Zhou,†,* and Qu-Quan Wang†,‡ †

Department of Physics, Key Laboratory of Artiﬁcial Micro- and Nano-structures of the Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, P. R. China ‡

The Institute for Advanced Studies, Wuhan University, Wuhan 430072, P. R. China

KEYWORDS. gold nanorods, ceria, near-infrared, hot-electron, photochemical

ACS Paragon Plus Environment

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ABSTRACT. The metal/semiconductor hetero-nanostructures perform widely applications in the light-driven physical and chemical processes, especially the nanomaterials based on the anisotropic metal nanocrystals with tunable plasmonic property have attracted intensive interest. Herein we report an efficient hydrothermal method for the synthesis of well-defined ceria (CeO2) coated gold nanorods (AuNRs) by employing the original hexadecyltrimethylammonium bromide (CTAB) as the ligands and soft-template. Importantly, the Au/CeO2 core/shell NRs have well maintained the tunable longitudinal plasmon resonance of AuNR in the near-infrared (NIR) region. We demonstrate that this hetero-nanostructure can accelerate the ceria dependent Fentonlike reaction through the plasmon-induced hot-electron injection under NIR light illumination. The generation of hot-electron is further revealed by detecting the NIR-light-driven photocurrent of a photoelectrochemical (PEC) cell base on the Au/CeO2 core/shell NRs modified electrode.


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1. Introduction Recently, light-driven physical and chemical processes are widely explored and applied in the applications of solar cells, photodetectors, photocatalysis, photoelectrochemical cells.1-4 How to improve the efficiency of light use is a significant problem. Plasmonic nanostructures have received extensive attention for their outstanding light collection and conversion abilities.5-7 Upon resonant excitation, the metal nanocrystals interact with light strongly, the collective oscillations of free charges lead to the surface plasmon resonance (SPR), thus, the extinction cross section of the nanostructure and the local electric field around the nanocrystal are largely enhanced, which is in favor of light-harvesting, photon-electron conversion, charge separation and transfer in the light-driven physical and chemical processes.7-9 Particularly, the metal/semiconductor hetero-nanostructures perform widely applications in various areas including photovoltaics, hydrogen generation, dye-degradation, and chemical transformations.10 In the metal/semiconductor hetero-nanostructures, the plasmonic nanocrystals could act as antennas through enhanced local field to enhance light absorption or amplify the photo signals of emission and scattering.9, 11-13 On the other hand, coherent excitations of free electrons would relax in tens of femtoseconds via electron-electron interaction to form hot electrons. The injection of hot electrons over the Schottky barrier to semiconductor makes the metal as an ideal sensitizer.14 The plasmon sensitized solar cells and photodetectors are recently demonstrated and attract broad attention.15 Moreover, hot electrons with high temperature could heat the lattice and the surrounding medium through electron-phonon and phonon-phonon interactions, and then accelerate the chemical reaction nearby. The intrinsic plasmonic photocatalysis would also happen through direct interactions like electron transfer between plasmonic nanostructures and molecules to catalyze molecular reactions near metallic surface.16-


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Usually, most study on the synthesis of metal/semiconductor hetero-nanostructures is focused on that can improve the visible light absorption.3, 11, 13, 17-19 However the infrared region also is nonnegligible for the fact that the solar energy lied in the infrared is over 40%.20 As a result, gold nanorod (AuNR) would be a good choice to fabricate the core/shell hybrid, which has tunable longitudinal SPR band from visible to near-infrared (NIR) region with a large cross section.21-24 Among the different strategies for the synthesis of metal/semiconductor heteronanostructures, using pre-grown metal nanocrystals as seeds to fabricate metal/semiconductor core/shell nanostructures is a common and widely studied method.19, 25-29 Comparing to other configuration like york/shell, half coating or the structures made by depositing metal nanocrystals on pre-grown semiconductor; the properties of the core/shell nanostructures can be well controlled by varying the core materials, core geometry, and shell material. In addition, the tight contact between core and shell will also benefit the charge transfer.10 In this work, we developed an efficient hydrothermal method for synthesis of complete semiconductor shell of ceria (CeO2) on AuNRs. The CTAB capped AuNRs was directly used for the growth without further modification. Here, the semiconductor shell material has been appointed as ceria, which has been widely used as ultraviolet (UV) absorber, and catalyst for carbon monoxide conversion.30-34 The reversibility between Ce3+ and Ce4+ also endows it with an anti-oxidant ability to protect cell from radiation damage or inflammation.35-38 Moreover, the Ce4+−Ce3+ redox cycle is benefit for the Fenton-like reaction.32-33, 39 The as-prepared Au/CeO2 core/shell NRs have well maintained the plasmon character in NIR region and the plasmonic band could be easily tuned in a wide region via adjusting the aspect ratio of AuNRs. Upon


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resonant excitation with NIR light illumination, we demonstrate the plasmon-enhanced NIR photocatalytic and photoelectrochemical (PEC) performances of Au/CeO2 core/shell NRs, and attempt to reveal and understand the NIR-light-driven physical and chemical processes underlying. Firstly, the Fenton-like reaction based on CeO2 and H2O2 is accelerated by hot electron injection from AuNRs to reduce Ce4+ toward Ce3+. The photocatalytic activities of Au/CeO2 NRs to degrade dye are greatly enhanced. Secondly, an obvious increase also investigated in the NIR induced photochemical current of Au/CeO2 NRs coated FTO electrode. Both these improved photochemical properties are ascribed to a synergistic effect between the AuNR core and the CeO2 shell; besides, the generation of hot-electron in the Au/CeO2 NRs is revealed at the same time.

2. Experimental Section 2.1 Materials. Chloroauric acid (HAuCl4·4H2O, 99.99%), hydrochloric acid (HCl, 36– 38%), hexamethylene tetramine (HMT, 99.99%), and Cerium(III) nitrate hexahydrate (Ce(NO3)3·6H2O, 99.99%) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai,

China).

Hexadecyltrimethylammonium

bromide

(CTAB,

97.0%),

sodium

borohydride (NaBH4, 96%), silver nitrate (AgNO3, 99.8%), and L-ascorbic acid (AA, 99.7%) were obtained from Sigma Aldrich (America). All of the chemicals were used as received without purification. Ultrapure water with a resistivity of approximately 18.25 MΩ·cm was used as the solvent in all the experiments. 2.2 Synthesis of AuNRs. A seed-mediated growth method was employed for the synthesis of the AuNRs in aqueous solution.40 For the preparation of the gold nano seeds with size 3−4


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nm, 4.5 mL of ultrapure water, 0.5 mL of 5 mM HAuCl4 and 5 mL of 0.2 M CTAB were mixed firstly. Then, 600 µL of freshly prepared ice-cold 10 mM of NaBH4 were immediately added into the vigorous stirring solution. After vigorous stirring for 2 min, the seed solution was left at room temperature for further use. In the AuNR synthesis, 18 mL of 5 mM HAuCl4, 225 µL of 0.1 M AgNO3 and 200 µL of 1.2 M HCl were successively added to 90 mL of 0.2 M CTAB, at last 11.1 mL of 10 mM ascorbic acid was added. After gently swirled, as the color had changed from dark orange to colorless, 150 µL of the CTAB-stabilized gold seed solution were rapidly injected into the above growth solution. The resulting solution was gently mixed for 10 s and left undisturbed overnight. Finally, the solution was centrifuged at 12,000 rpm for 15 min to stop the reaction. The supernatant was removed, and the precipitate was resuspended in ultrapure water. The centrifugation repeated for once again to ensure the free CTAB has been totally removed. The products are CTAB-coated AuNRs (CTAB-AuNRs) with aspect ratios up to 4.7. The concentration is estimated to be approximately 0.8 nM based on the extinction coefficient at the longitudinal SPR wavelength.41 2.3 Synthesis of Au/CeO2 NRs. For the synthesis of Au/CeO2 NRs, 5 mL of CTAB-AuNR solution was diluted with 14 mL water, 25 µL of 0.2 M CTAB, 0.5 mL of 0.1 M HMT aqueous solution and 0.5 mL of 0.01 M Ce(NO3)3 aqueous solution were added in order followed by gentle shaking to achieve a well-dispersed solution. The resulting mixture was transferred into a 40 mL Teflon-lined stainless autoclave and maintained at 85 °C for 5 h. The solution was centrifuged at 8,000 rpm for 8 min followed by removal of the supernatant, and the precipitate was re-dispersed in 5 mL of water. The products are Au/CeO2 NRs.


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For the control experiments to confirm the CTAB effect, the products are obtained in similar condition besides 0 µL or 100 µL of 0.2 M CTAB were added in the reaction solution, respectively. 2.4 Characterization. Transmission electron microscope (TEM) images were taken using a JEOL 2010 (HT) TEM at an accelerating voltage of 200 kV. High resolution TEM (HRTEM) images were taken on a JEOL 2100F TEM at an accelerating voltage of 200 kV. Energy dispersive X-ray spectroscopy (EDX) was performed on an EDAX equipped on JEOL 2100F TEM at an accelerating voltage of 200 kV. X-ray diffraction (XRD) patterns were obtained on a Bruker D8 advance X-ray diffractometer using Cu-Kα radiation (λ = 0.15418 nm). X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Fisher ESCALAB 250Xi instrument using monochromatic Al-Kα radiation (1486.68 eV). The hydrodynamic distribution of the samples was determined using a Zeta sizer (Nano ZS90, Malvern Instruments, UK) at 25 °C. Absorption spectra were acquired on a TU-1810 UV-VisNIR spectrophotometer (Purkinje General Instrument Co. Ltd. Beijing, China). 2.5 Photocatalytic Activity Measurement. The photocatalytic activity was evaluated in the dark and under the NIR irradiation. In the dark Fenton-like reaction, 10 mg catalyst powders was mixed with 100 µL H2O2 (30%) and the mixture was stirred for 5 min. Then, at the start of the reaction time, the mixture was dispersed in 20 mL of the 35 mg/L aqueous solution of acid orange 7 (AO 7) (pH 4.0). At the given time intervals, samples (2 mL) were taken from the mixture and UV-vis absorption spectra were recorded at different intervals to monitor the reaction progress. To prevent the influence of photocatalysts from the final results, the mixture was immediately centrifuged at 16,000 rpm for 5 min, and the supernatant was taken for each test.


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As for a typical NIR light irradiated experiment, a fiber-coupled continuous semiconductor diode laser (810 nm, KS-810F-8000, Kai Site Electronic Technology Co., Ltd. Shaanxi, China) with a power density of 3.5 W/cm2 and a beam diameter of approximately 2 cm was used for illumination. The laser beam was introduced vertically from the top surface into the solution. To avoid the heating of the solution by the photothermal effect, the cuvette was placed in a water bath kept at room temperature. 2.6 Photoelectrochemical Activity Measurement. In our experiments, a three-electrode configuration in a quartz cell is assembled to test the PEC activity of the samples on a VersaSTAT 3 electrochemical workstation (AMETEK, Inc., USA). A Pt plate and a commercially available Ag/AgCl electrode are used as the counter and reference electrodes. The work electrode was sample modified FTO electrode, which was prepared by the dip-coating method. Before modification, the FTO substrates were washed with acetone, Ethanol, and deionized water. The as prepared Au/CeO2 NRs (1.0 mL) was centrifuged and concentrate to 100 µL, then, the suspensions were dip-coated to form a homogeneous film. Subsequently, FTO glass was heated at 60 °C for 1 h to volatilize the solvent and steady the sample. For pure CeO2 nanoparticles (NPs) and CeO2 NPs-AuNRs mixture modified FTO electrode, the same method was followed. The effective surface area of the working electrode is 2 × 1 cm2. The supporting electrolyte was 0.1 M KOH, which was purged with high-purity nitrogen for at least 15 min prior to experiments. A fiber-coupled continuous semiconductor diode laser (810 nm, KS-810F-8000, Kai Site Electronic Technology Co., Ltd. Shaanxi, China) was employed as incident light source to study the PEC response of the samples, and its light intensity was 1.0 W with a spot size of 0.75 cm2. The laser beam was chopped on and off at an interval of 30 s.


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3. Results and Discussion 3.1 Synthesis and Characrizations of Au/CeO2 Core/Shell NRs. The AuNRs were firstly synthesized using a CTAB assisted seed-mediated method, in which the as-prepared AuNRs are capped by CTAB bi-molecular layer.42-43 The initial CTAB-AuNRs have the average diameter and length of 13±2 nm and 52±4 nm, respectively (see Figure S1). As shown in Figure 1a and Figure S2, uniform products of Au/CeO2 core/shell NRs exhibit prefect mono-dispersity and high yield with few byproducts. The hybrid NR is composed by an AuNR without any shape change and a well-coated ceria shell. The thickness of the shell is about 20 nm of the side and 10 nm on the end. Besides, the ceria shell is seemed like an aggregation of tiny crystals. The crystal fringes of the shell in Figure 1b are assigned to the {111} crystal plane of cubic phase CeO2. In the XRD pattern (Figure 1c), two sets of diffraction peaks are presents, which are assigned to the cubic Au phase (JCPDS No. 04-0784) and cubic CeO2 phase (JCPDS No. 04-0593). In addition, the diffraction peaks of the ceria shell are sharp and intense, suggesting the excellent crystalline of CeO2. After annealing at 300 °C for 3 h, the width and strength of the diffraction peaks changed little (Figure S3), which demonstrates that the CeO2 synthesized in this procedure is stable. According to the EDX results (Figure S4), the atom percentages of Au and Ce are 31.7% and 68.3%, respectively. The ratio between Au and Ce is quite close to the raw material ratio, indicating that the consumption of Ce(NO3)3 is thorough. It is well-known that there are two common different oxidation states of Ce3+ and Ce4+ for the element Ce, and there usually coexists a small amount of Ce3+ at the surface of CeO2.44 To examine the component of the CeO2 shell, the as-prepared Au/CeO2 NRs are determined by XPS spectrum. As shown in Figure 1d, the Ce 3d photoelectron peaks are labeled by Ce3+ or Ce4+,45 and the ratio of Ce3+/(Ce4+ + Ce3+)


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can be quasi-quantitatively determined as 18%, indicating the main valence of cerium in this core/shell structure is +4.

Figure 1. Characterizations of the as-prepared core/shell nanostructure. (a) Large scale TEM image, (b) HRTEM image, (c) XRD pattern, and (d) Ce 3d XPS spectrum of the as-prepared Au/CeO2 NRs.

3.2 Growth Mechanism of Au/CeO2 Core/Shell NRs. To investigate the growth process, the TEM images of the samples synthesized in different reaction times were obtained. As shown in Figure 2 and Figure S5b-d, some small particles were firstly generated on the side surface of AuNRs side in 1 h; then, after one another hour reaction, the particles grew large and the shell became more continuous; as the reaction was carried through 3 h, a well-packaged and complete shell was arisen on the AuNR core. In the HRTEM images, the shell obtained at the first hour is amorphous (Figure 2b). Considering the hydrolyzation of HMT during the hydrothermal reaction, the extension part stuck on the AuNR side may be Ce3+ hydroxide,46 which is verified


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by the XPS Ce 3d spectrum (Figure S6). In the second hour (Figure 2d), as the crystallization was arisen, some tiny crystals were emerged in the shell layer at 2 h. In addition, the contribution of Ce4+ is appeared in the XPS Ce 3d spectrum (Figure S6). It is believed that the Ce3+ has been oxidized in this stage, and a transformation from Ce3+ hydroxide to CeO2 was occurred in the shell. The appearance of CeO2 crystal seeds is quite critical that it provides a footstone for the further growth of complete ceria shell. After another one hour, the products obtained at 3 h have a complete shell of CeO2 coated on the AuNRs. The shell layer is much thicker and seems like an assemblage of lots of small ceria crystals with size over 5 nm. This result demonstrates that in this stage the shell was ripened quickly and further epitaxial growth of CeO2 nanoparticles was taken place. There is an interesting phenomenon help us to acquire deeper insight on the growth kinetics of Au/CeO2 core/shell NRs. In Figure 2a, the shell is separated about 2 nm from the surface of the gold core. Meanwhile, Ce3+ hydroxide prefers to be generated on the side of AuNRs rather than on the end of AuNRs. It is known that the CTAB molecules arrange densely on the side and sparsely on the end of AuNR surface, and the thickness of CTAB bi-molecular layer is about 2 nm.47 These facts imply that the CTAB plays a key role in the generation of amorphous hydroxide on AuNRs. Usually, attributing to the dissociation of Br−, the surface charge of CTAB-AuNRs is positive; on the other hand, due to the presence of abundant OH−, the hydroxide behaves electronegativity. Thus, the negative hydroxide tend to be attached to the positive CTAB-AuNRs, and the CTAB performs like soft template. Moreover, because of the more compact arrangement of CTAB on the AuNR side, the hydroxide prefer to coat on the side of AuNR. It is found that the separation between the Au core and ceria shell is decreased and finally disappeared at 3 h (Figure 2e, f). This change indicates a thorough transformation of


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hydroxide and subsequent growth of CeO2 shells. The final products have a tight contact between CeO2 shell and Au core, which would benefit the electron movement.

Figure 2. TEM images and corresponding HRTEM images of the samples obtained at (a) (b) 1 h, (c) (d) 2 h, and (e) (f) 3 h. The white arrows in TEM images indicate the about 2 nm separation between the cores and shells.

The dashed circles in HRTEM images indicate the crystal

domains.

In the growth strategy, appropriate CTAB was added in the reaction mixture to stabilize the sample. In order to confirm the critical role of CTAB, two control experiments without CTAB and with excessive CTAB were performed (Figure S7). Obviously, the CeO2 shell strongly tended to grow on the side of AuNR without the addition of CTAB, while the samples were


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aggregated along the longitudinal orientation due to the sparse CTAB on AuNR ends (Figure S7a). On the other hand, when excessive CTAB was added, massive free CeO2 NPs were generated as byproducts in the solution (Figure S7c). In brief, we suppose the growth process of ceria shell includes three steps: i) the nucleation of amorphous hydroxide assisted by CTAB; ii) the oxidation of hydroxide and the crystallization of CeO2; iii) the ripening of CeO2 crystals and the further epitaxial growth. Meanwhile, the CTAB acts as a ligand or soft-template for assisting the CeO2 shell growth, and also plays like a stabilizer for the final products.

3.3 Plasmonic Properties of Au/CeO2 NRs. Plasmon resonance is the most remarkable character of the AuNRs. Typical extinction spectra of the original CTAB-AuNRs and the asprepared Au/CeO2 NRs are presented in Figure 3. The longitudinal SPR band of CTAB-AuNRs is located at 752 nm, which red-shifts to 810 nm after the coating of CeO2. The great shift is as large as 54 nm indicates the good density of CeO2. The full width at half maximum(FWHM) of the longitudinal and the transverse SPR bands are both well maintained without obvious broaden, which suggests that the morphology of the AuNR core have not been damaged in the following shell growth and the sample is well-dispersed in aqueous solution. Furthermore, pure CeO2 NPs are also prepared in the similar condition in the absence of CTAB-AuNRs. The TEM image of CeO2 NPs (Figure S8) exhibits aggregation structure of small nanocrystals which is similar with the shell in Figure 1a. Meanwhile, the extinction spectrum reveals that the band in the UV region is belong to the inter-band absorption of CeO2. Based on the extinction spectrum of pure CeO2 NPs, the band gap of CeO2 is 3.1 eV (Figure S9). The Mott-Schottky curve of CeO2 suggests that


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the CeO2 is an n-type semiconductor and the flat band potential of CeO2 is about -0.68 V against the Ag/AgCl electrode in 0.1 M KOH (Figure S10). The extinction spectra of the samples obtained at different time (Figure S5a) also have provided some support on the shell formation mechanism. In the primary first hour, although some compounds are generated on the AuNRs side, the absorption spectrum is almost unchanged. As the reaction has carried 2 hours, the longitudinal SPR peak red-shifts a little and the absorption band in the UV region starts to rise. This phenomenon is consistent with the fact that some CeO2 nanocrystal seeds emerge in the shell. The significant absorption change is observed at 3 h that the UV absorption of CeO2 increases rapidly and the longitudinal SPR shifts obviously. This spectra evolution demonstrates the complete transformation of Ce3+ hydroxide to CeO2. In the further reaction, the unchanged absorption spectra suggested a saturated growth. The absorption spectra have introduced the perfect plasmonic property of the Au/CeO2 core/shell NRs. The large absorption across-section and tunable plasmon wavelength in the NIR region will offer some unique photoelectrical properties.

Figure 3. Normalized extinction spectra of the CTAB-AuNRs, as-prepared Au/CeO2 NRs, and pure CeO2 NPs.


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3.4 Photocatalytic Activity of Au/CeO2 NRs. To demonstrate the plasmonic effect on the photocatalytic reactivity of Au/CeO2 NRs in Fenton-like reaction, the degradation of AO7 in CeO2/H2O2 system was employed. Fenton-like reactions in the dark and under NIR light irradiation were performed with three types of catalysts (CeO2 NPs, Au/CeO2 core/shell NRs, and the mixture of AuNRs + CeO2 NPs). Particularly, a fiber-coupled continuous 810 nm semiconductor diode laser resonated with the longitudinal SPR of AuNRs is chosen as the NIR irradiation source. As shown in Figure 4a, compared with the blank sample without catalyst, the pure CeO2 NPs sample shows an effective degradation activity in the dark due to the Fenton-like reaction. However, the NIR light irradiation has no obvious improvement on the photocatalytic performance of the blank sample and the pure CeO2 NPs sample, because the dye and CeO2 have no absorption at this wavelength. In the dark condition, the degradation activity of Au/CeO2 NRs is similar to the pure CeO2 NPs samples. While under the NIR light irradiation, the photocatalytic degradation rate of Au/CeO2 NRs sample is about 1.9 folds higher than that of the CeO2 NPs at 5 h, which means the plasmonic AuNR core has obviously promoted the Fentonlike reactivity of the CeO2 shell under NIR irradiation. Whereas in a control experiment using the mixture of AuNRs and CeO2 NPs as catalysts, the degradation rate slightly increases under NIR irradiation (see Figure S11), because the contact probability for the AuNRs and CeO2 NPs in the solution is very little. In the Fenton-like degradation using H2O2 as a substrate, the previous work suggests that the catalytic activities of transition metal oxide materials are mostly derived from the valence state evolution of metal ions.33, 48 For the case of CeO2, this Fenton-like reaction performed on cerium ions is stated followed.32


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Ce3+ + H2O2 + H+ → Ce4+ + •OH + H2O •OH + H2O2 → •HO2 + H2O It is obvious that the key trigger of this reaction is the existence of Ce3+. In other words, the higher Ce3+ concentration in the catalysts leads to more free radicals of •OH and •HO2 and then the higher photocatalytic activity for dye degradation. Based on these processes in Fenton-like reaction, the proposed mechanisms of the NIR-light-driven photosensitization for plasmonenhanced photocatalytic activity are supposed in following (Figure 4b). Under the resonant excitation at 810 nm, the hot carriers (hot electrons and hot holes) are generated in gold. Then, the hot electrons would get over the interfacial barrier between the AuNR and the ceria and finally inject into ceria. The Ce4+ sites on the surface of ceria trap the electrons and transform into Ce3+. The high concentration of Ce3+ ions in CeO2 shells accelerate the Fenton-like reaction. As the hot electrons are injected into the ceria shell, the hot holes are left in the Au NR. Because these holes have a mild oxidation ability, they would participate in the oxidation process with Ce3+ and H2O2. Cooperating with the hydrogen ions in the solution, the hot holes promote the generation of •OH. At the same time, another four factors may perform positive influence on the dye degradation. Firstly, Considering the ceria shell is assembled by many small crystals, the gold nanorods would contact with the solution; as a result, the hot holes could be utilized for oxidation of dye molecules.49, 50 Secondly, the injected hot electrons in the conduction band (CB) of CeO2 would reduce H2O2 into •OH or reduce O2 into •O2−, which also accelerate the degradation of dye. Thirdly, the Fenton-like reaction taken on the ceria surface can be promoted by the local temperature rise, caused by the photothermal effect of AuNR. Fourthly, the rough surface of CeO2 shells provides a large specific surface area for the dye adsorption.


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Figure 4. Photocatalytic activity of Au/CeO2 NRs. (a) Photocatalytic degradation of dyes in dark and under NIR irradiation by adding different catalysts. (b) Proposed mechanism for the plasmon-enhanced photocatalytic activity of the Au/CeO2 NRs under NIR light illumination.

3.5 Photoelectrochemical Activity of Au/CeO2 NRs. We further study the PEC performance under NIR irradiation of Au/CeO2 hybrid NRs. The PEC cell is composed by a three-electrode system with 0.1 M KOH as the electrolyte. Upon NIR excitation of 810 nm laser, the photocurrent responses of the modified FTO electrode by Au/CeO2 NRs (red curve), AuNRCeO2 mixture (blue curve) and CeO2 NPs (black curve) are shown in Figure 5a. The as-obtained CeO2 NPs exhibit a small photocurrent density of 10 µA·cm−2 under NIR light irradiation (black curve). Causing the band-edge absorption of CeO2 is in the UV region, the NIR-light-induced current fluctuation is due to the slight temperature increasing induced by the thermal effect of NIR irradiation. In contrast, the photocurrent density of Au/CeO2 NRs (red curve) is about 120


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µA·cm−2. During the repeat of ON/OFF switching, no apparent photocurrent degradation is observed for Au/CeO2 NRs, which reveals the good reversibility of the process and well photostability of the samples. The controlled sample of mixing CeO2 NPs and AuNRs (blue curve) exhibits the photocurrent density of 22 µA·cm−2. The power-dependence of the photocurrent is measured and shown in Figure S12. The plasmon-induced electron transfer process is reported to exhibit the linear power-dependence relationship.51,

52

However, the

sublinear dependence of photocurrent versus excitation power is also reported in the plasmonsemiconductor hybrids due to the trap effect in semiconductor.53 The photocurrent behavior may be influenced by many factors including the plasmon damping process and the hot carrier generation54, 55 as well as other possible plasmon-induced charge transfer mechanism.52, 56 As shown in Figure 5c, upon 810 nm laser irradiation, the surface plasmons of AuNRs are excited and then relax into hot carriers through Landau damping (process 1).54, 55 Because the CeO2 is an n-type semiconductor, the energetic hot electrons get over the Schottky barrier and inject into the CB of CeO2 (process 2).57-59 Under external bias voltage, the electrons transfer to the FTO electrode and form current (process 3). The photocurrent responses of Au/CeO2 NRs and controlled samples (AuNRs + CeO2 NPs mixture) are both derived from the plasmonsensitized process via hot electron injection from AuNRs to CeO2. However, the photocurrent density Au/CeO2 NRs is 5.5 times larger than that of the controlled sample because there is tighter contact between AuNR core and the CeO2 shell in Au/CeO2 NRs, while the contact in the mixture film of AuNRs and CeO2 NPs is unexpected and random.


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Figure 5. (a) The photo-induced current of the samples with and without NIR laser excitation. The samples including: the pure CeO2 NPs (grey curve), mechanical mixture of CeO2 NPs and AuNRs (blue curve), and the Au/CeO2 core/shell NRs (red curve). (b) Bar chart displays the current intensity in Figure 5a. (c) Schematic illustrating the generation of photocurrent of Au/CeO2 NRs modified FTO electrode.


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4. Conclusion In conclusion, we have demonstrated a CTAB-templated approach towards direct coating of CeO2 on AuNRs. The critical effect of CTAB and the growth mechanisms have been investigated in detail. In the further photochemical measurements, plasmon-enhanced Fenton-like degradation of dye molecules by Au/CeO2 NRs is observed under plasmon resonant excitation with NIR light irradiation. In the photocatalytic reaction, plasmon-induced injection of hot electrons over interfacial barrier into CeO2 not only facilitates the transformation from Ce4+ to Ce3+ and then promote the Fenton-like chemical reaction, but also intrinsically accelerates the degradation of dye. Furthermore, we demonstrate that plasmon-mediated hot electrons driven by NIR irradiation could constitute photocurrent under external bias voltage in a PEC cell equipped with Au/CeO2 NRs electrode. Consequently, the synthesis strategy would provide valid experience in the fabrication of hetero-nanostructures and the growth of hybrids using CTAB-capped nanoparticles. Moreover, ceria coated AuNRs with plasmon-enhanced NIR photocatalytic and PEC performances would find promising applications in the field of energy and environment.

ASSOCIATED CONTENT Supporting Information. TEM image of AuNRs. Large scale TEM image and EDX spectrum of Au/CeO2 NRs. XRD patterns of as-prepared and annealed Au/CeO2 NRs. Absorption spectra and XPS spectrum of Au/CeO2 NRs with different reaction times. Samples prepared with different amount of CTAB. TEM image of pure CeO2 NPs. Photocatalytic activity of the mixture of AuNRs and CeO2 NPs. The photoinduced current−time curves of Au/CeO2 NRs under


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different light intensity. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] (L. Z.) Notes Any additional relevant notes should be placed here.

ACKNOWLEDGMENT The authors thank Dr. Zhong-Hua Hao for the technique help and Mr. Su-Jian You for the schematic design and drawing. The authors acknowledge financial support from the Natural Science Foundation of China (11374236 and 51372175), and the fundamental Research Funds for the Central Universities (2014202020203).

REFERENCES (1) Bach, U.; Lupo, D.; Comte, P.; Moser, J.; Weissörtel, F.; Salbeck, J.; Spreitzer, H.; Grätzel, M., Solid-State Dye-Sensitized Mesoporous TiO2 Solar Cells with High Photon-to-Tlectron Conversion Efficiencies. Nature 1998, 395, 583-585. (2) Shah, A.; Torres, P.; Tscharner, R.; Wyrsch, N.; Keppner, H., Photovoltaic Technology: the Case for Thin-Film Solar Cells. Science 1999, 285, 692-698.


21


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 29

(3) Li, Q.; Guo, B.; Yu, J.; Ran, J.; Zhang, B.; Yan, H.; Gong, J. R., Highly Efficient VisibleLight-Driven Photocatalytic Hydrogen Production of CdS-Cluster-Decorated Graphene Nanosheets. J. Am. Chem. Soc. 2011, 133, 10878-10884. (4) Grätzel, M., Photoelectrochemical Cells. Nature 2001, 414, 338-344. (5) Atwater, H. A.; Polman, A., Plasmonics for Improved Photovoltaic Devices. Nat. Mater. 2010, 9, 205-213. (6) Ferry, V. E.; Sweatlock, L. A.; Pacifici, D.; Atwater, H. A., Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells. Nano Lett. 2008, 8, 4391-4397. (7) Linic, S.; Christopher, P.; Ingram, D. B., Plasmonic-Metal Nanostructures for Efficient Conversion of Solar to Chemical Energy. Nat. Mater. 2011, 10, 911-921. (8) Schaadt, D.; Feng, B.; Yu, E., Enhanced semiconductor optical absorption via surface plasmon excitation in metal Nanoparticles. Appl. Phys. Lett. 2005, 86, 063106. (9) Tian, Y.; Tatsuma, T., Mechanisms and Applications of Plasmon-Induced Charge Separation at TiO2 Films Loaded with Gold Nanoparticles. J. Am. Chem. Soc. 2005, 127, 7632-7637. (10) Jiang, R.; Li, B.; Fang, C.; Wang, J., Metal/Semiconductor Hybrid Nanostructures for Plasmon-Enhanced Applications. Adv. Mater. 2014, 26, 5274-5309. (11) Wang, P.; Huang, B.; Qin, X.; Zhang, X.; Dai, Y.; Wei, J.; Whangbo, M. H., Ag@AgCl: a Highly Efficient and Stable Photocatalyst Active under Visible Light. Angew. Chem. Int. Ed. 2008, 47, 7931-7933. (12) Yu, K.; Tian, Y.; Tatsuma, T., Size Effects of Gold Nanaoparticles on Plasmon-Induced Photocurrents of Gold–TiO2 Nanocomposites. Phys. Chem. Chem. Phys. 2006, 8, 54175420. (13) Zhou, X.; Liu, G.; Yu, J.; Fan, W., Surface Plasmon Resonance-Mediated Photocatalysis by


22

Page 23 of 29

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


Noble Metal-Based Composites under Visible Light. J. Mater. Chem. 2012, 22, 2133721354. (14) Knight, M. W.; Sobhani, H.; Nordlander, P.; Halas, N. J., Photodetection with Active Optical Antennas. Science 2011, 332, 702-704. (15) Standridge, S. D.; Schatz, G. C.; Hupp, J. T., Distance Dependence of Plasmon-Enhanced Photocurrent in Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2009, 131, 8407-8409. (16) Hou, W.; Cronin, S. B., A Review of Surface Plasmon Resonance-Enhanced Photocatalysis. Adv. Funct. Mater. 2013, 23, 1612-1619. (17) Liu, Z.; Hou, W.; Pavaskar, P.; Aykol, M.; Cronin, S. B., Plasmon Resonant Enhancement of Photocatalytic Water Splitting under Visible Illumination. Nano Lett. 2011, 11, 1111-1116. (18) Seh, Z. W.; Liu, S.; Low, M.; Zhang, S. Y.; Liu, Z.; Mlayah, A.; Han, M. Y., Janus Au-TiO2 Photocatalysts with Strong Localization of Plasmonic Near-Fields for Efficient Visible-Light Hydrogen Generation. Adv. Mater. 2012, 24, 2310-2314. (19) Li, B.; Gu, T.; Ming, T.; Wang, J.; Wang, P.; Wang, J.; Yu, J. C., (Gold Core)@(Ceria Shell) Nanostructures for Plasmon-Enhanced Catalytic Reactions under Visible Light. ACS nano 2014, 8, 8152-8162. (20) Qin, W.; Zhang, D.; Zhao, D.; Wang, L.; Zheng, K., Near-Infrared Photocatalysis Based on YF3: Yb3+, Tm3+/TiO2 Core/Shell Nanoparticles. Chem. Commun. 2010, 46, 2304-2306. (21) Chen, H.; Shao, L.; Li, Q.; Wang, J., Gold Nanorods and their Plasmonic Properties. Chem. Soc. Rev. 2013, 42, 2679-2724. (22) Huang, X.; Neretina, S.; El-Sayed, M. A., Gold Nanorods: from Synthesis and Properties to Biological and Biomedical Applications. Adv. Mater. 2009, 21, 4880. (23) Pérez-Juste, J.; Pastoriza-Santos, I.; Liz-Marzán, L. M.; Mulvaney, P., Gold Nanorods:


23


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 29

Synthesis, Characterization and Applications. Coord. Chem. Rev. 2005, 249, 1870-1901. (24) Sau, T. K.; Murphy, C. J., Seeded High Yield Synthesis of Short Au Nanorods in Aqueous Solution. Langmuir 2004, 20, 6414-6420. (25) Fang, C.; Jia, H.; Chang, S.; Ruan, Q.; Wang, P.; Chen, T.; Wang, J., (Gold Core)/(Titania Shell) Nanostructures for Plasmon-Enhanced Photon Harvesting and Generation of Reactive oxygen Species. Energy Environ. Sci. 2014, 7, 3431-3438. (26) Hirakawa, T.; Kamat, P. V., Charge Separation and Catalytic Activity of Ag@TiO2 CoreShell Composite Clusters under UV-Irradiation. J. Am. Chem. Soc. 2005, 127, 3928-3934. (27) Li, M.; Yu, X. F.; Liang, S.; Peng, X. N.; Yang, Z. J.; Wang, Y. L.; Wang, Q. Q., Synthesis of Au-CdS Core-Shell Hetero-Nanorods with Efficient Exciton–Plasmon Interactions. Adv. Funct. Mater. 2011, 21, 1788-1794. (28) Zhang, L.; Blom, D. A.; Wang, H., Au–Cu2O Core–Shell Nanoparticles: a Hybrid MetalSemiconductor Heteronanostructure with Geometrically Tunable Optical Properties. Chem. Mater. 2011, 23, 4587-4598. (29) Zhang, N.; Liu, S.; Fu, X.; Xu, Y.-J., Synthesis of M@TiO2 (M= Au, Pd, Pt) Core–Shell Nanocomposites with Tunable Photoreactivity. J. Phys. Chem. C 2011, 115, 9136-9145. (30) Pan, C.; Zhang, D.; Shi, L.; Fang, J., Template-Free Synthesis, Controlled Conversion, and CO Oxidation Properties of CeO2 Nanorods, Nanotubes, Nanowires, and Nanocubes. Eur. J. Inorg. Chem. 2008, 2008, 2429-2436. (31) González-Rovira, L.; Sánchez-Amaya, J. M.; López-Haro, M.; Del Rio, E.; Hungría, A. B.; Midgley, P.; Calvino, J. J.; Bernal, S.; Botana, F. J., Single-Step Process to Prepare CeO2 Nanotubes with Improved Catalytic Activity. Nano Lett. 2009, 9, 1395-1400. (32) Heckert, E. G.; Seal, S.; Self, W. T., Fenton-Like Reaction Catalyzed by the Rare Earth Inner


24

Page 25 of 29

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


Transition Metal Cerium. Environ. Sci. Technol. 2008, 42, 5014-5019. (33) Xu, L.; Wang, J., Magnetic Nanoscaled Fe3O4/CeO2 Composite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of 4-Chlorophenol. Environ. Sci. Technol. 2012, 46, 10145-10153. (34) Wang, X.; Liu, D.; Li, J.; Zhen, J.; Zhang, H., Clean Synthesis of Cu2O@CeO2 core@shell Nanocubes with Highly Active Interface. NPG Asia Mater. 2015, 7, e158. (35) Kim, C. K.; Kim, T.; Choi, I. Y.; Soh, M.; Kim, D.; Kim, Y. J.; Jang, H.; Yang, H. S.; Kim, J. Y.; Park, H. K., Ceria Nanoparticles that can Protect Against Ischemic Stroke. Angew. Chem. 2012, 124, 11201-11205. (36) Lee, S. S.; Song, W.; Cho, M.; Puppala, H. L.; Nguyen, P.; Zhu, H.; Segatori, L.; Colvin, V. L., Antioxidant Properties of Cerium Oxide Nanocrystals as a Function of Nanocrystal Diameter and Surface Coating. ACS nano 2013, 7, 9693-9703. (37) Pagliari, F.; Mandoli, C.; Forte, G.; Magnani, E.; Pagliari, S.; Nardone, G.; Licoccia, S.; Minieri, M.; Di Nardo, P.; Traversa, E., Cerium Oxide Nanoparticles Protect Cardiac Progenitor Cells from Oxidative Stress. ACS nano 2012, 6, 3767-3775. (38) Wason, M. S.; Zhao, J., Cerium Oxide Nanoparticles: Potential Applications for Cancer and other Diseases. Am. J. Transl. Res. 2013, 5, 126. (39) Ge, L.; Zang, C.; Chen, F., The Enhanced Fenton-Like Catalytic Performance of PdO/CeO2 for the Degradation of Acid Orange 7 and Salicylic Acid. Chin. J. Catal. 2015, 36, 314-321. (40) Nikoobakht, B.; El-Sayed, M. A., Preparation and Growth Mechanism of Gold Nanorods (NRs) Using Seed-Mediated Growth Method. Chem. Mater. 2003, 15, 1957-1962. (41) Orendorff, C. J.; Murphy, C. J., Quantitation of Metal Content in the Silver-Assisted Growth of Gold Nanorods. J. Phys. Chem. B 2006, 110, 3990-3994.


25


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 29

(42) Gomez-Grana, S.; Hubert, F.; Testard, F.; Guerrero-Martínez, A.; Grillo, I.; Liz-Marzán, L. M.; Spalla, O., Surfactant (bi) Layers on Gold Nanorods. Langmuir 2011, 28, 1453-1459. (43) Nikoobakht, B.; El-Sayed, M. A., Evidence for Bilayer Assembly of Cationic Surfactants on the Surface of Gold Nanorods. Langmuir 2001, 17, 6368-6374. (44) Heckert, E. G.; Karakoti, A. S.; Seal, S.; Self, W. T., The Role of Cerium Redox State in the SOD Mimetic Activity of Nanoceria. Biomaterials 2008, 29, 2705-2709. (45) Larachi, F.; Pierre, J.; Adnot, A.; Bernis, A., Ce 3d XPS Study of Composite CexMn1−xO2−y Wet Oxidation Catalysts. Appl. Surf. Sci. 2002, 195, 236-250. (46) Sreeremya, T. S.; Krishnan, A.; Remani, K. C.; Patil, K. R.; Brougham, D. F.; Ghosh, S., Shape-Selective Oriented Cerium Oxide Nanocrystals Permit Assessment of the Effect of the Exposed Facets on Catalytic Activity and Oxygen Storage Capacity. ACS Appl. Mat. Interfaces 2015, 7, 8545-8555. (47) Pramod, P.; Thomas, K. G., Plasmon Coupling in Dimers of Au Nanorods. Adv. Mater 2008, 20, 4300-4305. (48) Gao, L.; Zhuang, J.; Nie, L.; Zhang, J.; Zhang, Y.; Gu, N.; Wang, T.; Feng, J.; Yang, D.; Perrett, S., Intrinsic Peroxidase-Like Activity of Ferromagnetic Nanoparticles. Nat. Nanotechnol. 2007, 2, 577-583. (49) Naya, S.-i.; Inoue, A.; Tada, H., Self-Assembled Heterosupramolecular Visible Light Photocatalyst Consisting of Gold Nanoparticle-Loaded Titanium (IV) Dioxide and Surfactant. J. Am. Chem. Soc. 2010, 132, 6292-6293. (50) Ng, C.; Cadusch, J. J.; Dligatch, S.; Roberts, A.; Davis, T. J.; Mulvaney, P.; Gómez, D. E., Hot Carrier Extraction with Plasmonic Broadband Absorbers. ACS Nano 2016, 10, 47044711.


26

Page 27 of 29

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


(51) Furube, A.; Du, L.; Hara, K.; Katoh, R.; Tachiya, M., Ultrafast Plasmon-Induced Electron Transfer from Gold Nanodots into TiO2 Nanoparticles. J. Am. Chem. Soc. 2007, 129, 1485214853. (52) Boerigter, C.; Campana, R.; Morabito, M.; Linic, S., Evidence and implications of direct charge excitation as the dominant mechanism in plasmon-mediated photocatalysis. Nat. comm. 2016, 7. (53) Pescaglini, A.; Martín, A.; Cammi, D.; Juska, G.; Ronning, C.; Pelucchi, E.; Iacopino, D., Hot-electron injection in Au nanorod–ZnO nanowire hybrid device for near-infrared photodetection. Nano Lett. 2014, 14 (11), 6202-6209. (54) Brongersma, M. L.; Halas, N. J.; Nordlander, P., Plasmon-Induced Hot Carrier Science and Technology. Nat. Nanotechnol. 2015, 10 (1), 25-34. (55) Manjavacas, A.; Liu, J. G.; Kulkarni, V.; Nordlander, P., Plasmon-Induced Hot Carriers in Metallic Nanoparticles. ACS Nano 2014, 8 (8), 7630-7638. (56) Boerigter, C.; Aslam, U.; Linic, S., Mechanism of Charge Transfer from Plasmonic Nanostructures

to

Chemically

Attached

Materials.

ACS

Nano

2016.

DOI:

10.1021/acsnano.6b01846. (57) Jiang, R.; Li, B.; Fang, C.; Wang, J., Metal/Semiconductor Hybrid Nanostructures for Plasmon‐Enhanced Applications. Adv. Mater. 2014, 26, 5274-5309. (58) Knight, M. W.; Sobhani, H.; Nordlander, P.; Halas, N. J., Photodetection with Active Optical Antennas. Science 2011, 332, 702-704.


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Page 28 of 29

(59) Mubeen, S.; Lee, J.; Singh, N.; Krämer, S.; Stucky, G. D.; Moskovits, M., An Autonomous Photosynthetic Device in which all Charge Carriers Derive from Surface Plasmons. Nat. Nanotechnol. 2013, 8, 247-251.


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Ceria-Coated Gold Nanorods for Plasmon-Enhanced Near-Infrared

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