Nanostructural Dimension and Oxygen Vacancy Synergistically Induced Photoactivity Across High Surface Area Monodispersed Aunps/Zno Nanorods Heterojunction
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Inhibiting the electron-hole recombination by adequate surface modification is a significant challenge for developing highly efficient photoanodes. This report envisions a structural synergism between a surface oxygen vacancy and metal/semiconductor contact area to significantly boost up the charge separation and injection efficiency of ZnO nanorods (NRs) in photoelectrochemical (PEC) performance. A three-dimensional photoanode is designed by vertically aligning the ZnO NRs and tuned their dimension by varying the annealing temperature and time followed by their decoration with AuNPs. Different stages of heat treatment created high oxygen vacancy, which is a key factor in tailoring the PEC activity. The ZnO NRs-A offered 75.5% average contact area for hosting the 16 nm diameter AuNPs, whereas, the ZnO NRs-B delivered 47.8%. The ZnO NRs-B with high oxygen defects exhibits a similar photoactivity shown by large dimensional ZnO NRs-A. After decorating with AuNPs, the AuNPs/ZnO NRs-A delivered ~3-fold increases in photocurrent than AuNPs/ZnO NRs-B, suggesting the photoactivity enhancement is mainly contributed from the effective charge transfer across the heterojunction between the electron mediating AuNPs and ZnO NRs, which reduces the electron-hole pair recombination. Besides, having higher oxygen vacancies, the AuNPs/ZnO NRs-B exhibited substantial photoactivity similar with AuNPs/ZnO NRs-A. The comparison of the incident photon-to-current and the applied bias photon-to-current efficiencies of the AuNPs/ZnO NRs with the reported photoanodes further authenticated the enhanced PEC performance of AuNPs/ZnO NRs. This work opens up a potential approach to metal-semiconductor heterojunction design by reduction of electron-hole recombination in PEC water splitting and solar energy conversion applications.Keywords:
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Mg germanide nanorods were successfully fabricated by interdiffusion of the Mg into Ge nanorods on Si substrates at 425 oC for 0.5 h. It was observed that the Mg2Ge nanorod structures were formed by an interdiffusion process between the deposited Mg atoms and the Ge nanorods. Moreover, Mg2Si nanorods were formed by additional interdiffusion between the Mg2Ge nanorods and the Si substrates at 425 oC for 4 h. The structural properties of the Mg2Ge and Mg2Si nanorods were characterized, and the growth evolution of the structural and morphological properties of the nanorods was discussed.
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CeO2 nanorods were synthesized by a hydrothermal method and used as the support for preparing a series of Ni/CeO2 nanorod catalysts. The surface area of the catalysts decreased when the Ni percent over the CeO2 nanorods was increased. SEM results showed that the CeO2 is formed by nanorods approximately 1 μm in length. TEM and HREM revealed that the width of the nanorods is about 8 nm and it grew along the [1 1 1¯] axis. The catalytic activity of the catalysts was improved as the Ni was loaded onto CeO2 nanorods. The exposed planes of the CeO2 nanorod structure along the zone axis [0 1 1] for Ni impregnation were (1¯ 1¯ 1), (1 1 1¯), (1 1¯ 1), (1¯ 1 1¯), (2 0 0) and (2¯ 0 0) and they were more reactive for methanol conversion than (2¯ 2¯ 0), (2¯ 0 2¯), (0 2 2¯), (0 2¯ 2), (2 0 2) and (2 2 0) planes from the [1 1 1¯] axis (growth direction of the nanorod). This finding is mainly ascribed to the synergistic effect of the CeO2 nanorods and the Ni.
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-Fe2O3@C core-shell nanorods with average diameter of 20 nm and length of 150 nm are synthesized by transforming FeOOH@PVA nanorods under the condition of high pressure and high temperature (HPHT). The FeOOH@PVA nanorods are prepared via a hydrothermal route. The best synthesis condition for transforming FeOOH@PVA core-shell nanorods into -Fe2O3@C nanorods is 400 ℃ under 1 GPa. Owing to high aspect ratios, the -Fe2O3@C nanorods present a high coercivity of 330 Oe (10 Oe=79.5775 A/m). The possible mechanism for the synthesis of -Fe2O3@C nanorods is also discussed. The HTHP method can provide a new way for preparing of one-dimensional core-shell nanostructures.
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We have simulated the heating process of gold nanorods, elucidating a mechanism by which nanorods alter their aspect ratio at higher temperatures. We also studied the relative stabilities of nanorods by constructing nanorods with varying ratios of {110} to {100} exposed surfaces along the body of the nanorod. The least stable nanorod was found to be the nanorod with the largest {110} surfaces, followed by the nanorod with the largest {100} surfaces, while the nanorod with approximately equal surface areas of {100} and {110} surface was found to be the most stable. It was also found that the addition of surface disorder increased the stability of nanorods with large {110} surfaces, while paradoxically decreasing the stability of nanorods with large {100} surfaces. The reasons for this are elucidated and compared to experimental laser-induced gold nanorod transformation studies.
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A chain of three silver nanorods with progressively decreasing sizes and separations is designed to focus the electric fields around the small nanorods. The optical properties of the chain of silver nanorods are investigated by the discrete dipole approximation method. The results show that, compared with the individual small nanorod and the chain of two nanorods, many enhanced electric fields are focused around the small nanorod of the chain of three nanorods due to the electric field couplings between adjacent nanorods. Therefore, the design of the chain of three nanorods provides a way to obtain stronger electric fields. In addition, how the structural parameters of the chain of three nanorods affect their optical properties is also studied.
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