Qinrong He

One-pot synthesis of Au@TiO2 yolk-shell nanoparticles with enhanced photocatalytic activity under visible light

Natural biological systems often use hollow structures to decrease reflection and achieve high solar light utilization. Herein, bio-inspired Au@TiO2 yolk-shell nanoparticles (NPs) have been designed to combine the advantages of noble metal coupling and hollow structures, and subsequently synthesized via a facile one-pot hydrothermal approach. The Au@TiO2 yolk-shell NPs not only exhibit reduced reflectance by multiple reflections and scattering within the hollow NPs, but also show enhanced photocatalytic activity in Rhodamine B (RhB) degradation by simultaneously improving light harvesting, charge separation and reaction site accessibility. Specifically, compared to the commercial TiO2 (P25), Au/TiO2 hybrid and Au@TiO2 core-shell NPs, the Au@TiO2 yolk-shell NPs demonstrate lower reflectance over a broader range and superior photocatalytic activity with more than 98.1% of RhB decomposed within 4h under visible light. The bio-inspired nanostructure, as well as the facile and scalable fabrication approach, will open a new avenue to the rational design and preparation of efficient photocatalysts for pollutant removal.

Controllable growth of Au@TiO2 yolk–shell nanoparticles and their geometry parameter effects on photocatalytic activity

Yolk–shell nanoparticles (NPs) have attracted significant interest due to their decreased reflection and high solar light utilization. Herein, we precisely and independently controlled the geometrical parameters of the cavity diameter, shell thickness, and Au core diameter in the Au@TiO2 yolk–shell NPs using the hydrothermal method. Furthermore, the photocatalytic activities of these samples were systematically evaluated by the photocatalytic degradation of Rhodamine B (RhB). Smaller cavity size, thinner TiO2 shell, and medium AuNP diameter were found to facilitate more efficient photocatalysis. Overall, Au@TiO2 yolk–shell NPs with a cavity diameter of 121 nm, Au core diameter of 50 nm, and shell thickness of 26 nm demonstrated highest photocatalytic activity. These results are important for understanding the effects of the geometrical parameters of Au@TiO2 yolk–shell NPs on the photocatalytic performance and for designing novel yolk–shell nanostructures.

Bioinspired self-standing macroporous Au/ZnO sponges for enhanced photocatalysis

A self-standing macroporous noble metal-zinc oxide (ZnO) sponge of robust 3D network has been fabricated through in-situ growth method. The key to the construction of the bioinspired sponge lies in the choice of commercial polyurethane sponge (CPS) with interconnected and junction-free macroporous structure as the skeleton to support Au/ZnO nanorods (Au/ZnONRs). The resultant Au/ZnO/CPS not only exhibits hierarchical structures representing physical features of CPS, but also demonstrates durable superior photocatalytic activity and hydrogen generation capability. In addition, we have adopted various irradiations to investigate the effect of UV light and visible light on the photocatalytic performance of Au/ZnO/CPS individually. In detail, the photocatalytic properties of Au/ZnO/CPS and ZnO/CPS have been monitored and compared under irradiations of different wavelengths (200-1100, 350-780, 200-420 and 420-780 nm) for 90 min to reveal the effect of irradiation wavelength on the activity of photocatalysts. A possible mechanism between irradiation wavelength and photocatalytic degradation efficiency is proposed. The facile in-situ growth approach presented herein can be easily scaled up, affording a convenient method for the preparation of self-standing 3D macroporous materials, which holds great potential for the application in both environmental purification and solar-to-hydrogen energy conversion.

ZnO nanodisks decorated with Au nanorods for enhanced photocurrent generation and photocatalytic activity

A facile approach for the preparation of Au nanorod/ZnO nanodisks (AuNR/ZnONDKs) through in situ nucleation and growth of ZnO in AuNR colloidal solution was developed. This is the first report of AuNRs modified on the ZnO surface. Furthermore, the aspect ratios of AuNRs in nanohybrids of AuNR/ZnONDKs were also tuned to achieve tunable and broad LSPR bands for an optimized photocatalytic performance. All of the resultant AuNR/ZnONDK nanohybrids with exposed AuNRs exhibit much higher photocatalytic activity and photocurrent generation compared to commercial ZnO (C-ZnO). In particular, AuNR-707/ZnONDKs express a swift and steady photocurrent of 0.33 mA cm−2, which is 16.5 times higher than the photocurrent generated by C-ZnO. The facile approach presented here opens up a new avenue for the rational design and preparation of high-performance photocatalysts for the future applications in both environmental purification and photoelectric conversion.

Ag@Fe3O4 Core–Shell Surface-Enhanced Raman Scattering Probe for Trace Arsenate Detection

Developing an effective and reliable method for trace arsenic (As) detection is a prerequisite for improving the safety of drinking water. In this paper, we designed and prepared Ag@Fe3O4 core-shell nanoparticles (NPs), which were then used as Surface-Enhanced Raman Scattering (SERS) probe for trace arsenate (As(V)) detection. The Ag@Fe3O4 core-shell NPs were prepared by in situ growth of Fe3O4 NPs on the surface of AgNPs, which can effectively combine the strong adsorption ability of Fe3O4 nanoshells to As(V) with high SERS activity of Ag nanocores to decrease the detection limit. By use of Ag@Fe3O4 core-shell NPs for As(V) detection, the detection limit can be as low as 10 μg/L, and a good linear relationship between the SERS intensity of As(V) and their concentrations in the range from 10 to 500 μg/L was achieved. Furthermore, Ag@Fe3O4 core-shell NPs could be regenerated through desorption of As(V) from Fe3O4 nanoshells in NaOH solution, and then used for recyclic SERS detection. Therefore, it has been demonstrated for the first time that multifunctional Ag@Fe3O4 core-shell SERS probe could be applied to realize the highly sensitive and reversible detection of As(V).

Spiky nanohybrids of TiO2/Au nanorods for enhanced hydrogen evolution and photocurrent generation

The fabrication of photocatalysts to achieve efficient utilization of renewable solar energy has attracted broad interest. Herein, a plasmonic spiky TiO2/Au nanorod (NR) nanohybrid was prepared by in situ nucleation and growth of spiky TiO2 in AuNR colloidal solution. The spiky TiO2/AuNR nanohybrids demonstrated enhanced hydrogen evolution activity and photocurrent generation under both visible light and simulated solar light irradiation as compared to bare spiky TiO2 nanoparticles and commercial TiO2. Specifically, the spiky nanohybrids displayed a high H2 production rate of 1.81 mmol g−1 h−1 under simulated solar light irradiation, which is 1.7 times higher than that of TiO2/Au nanosphere nanohybrids, and remain stable for three cycles. The improved photocatalytic H2 evolution demonstrated by the nanohybrids can be ascribed to the coupling effect of the AuNRs and the unique spiky structure. Furthermore, the charge transfer process during H2 evolution was investigated by photocurrent and electrochemical impendence spectroscopy (EIS) measurements. A fast and stable photocurrent was observed for the spiky TiO2/AuNR nanohybrid photoelectrode under both visible light and simulated solar light irradiation, while the EIS plots indicate a rapid charge transfer within the nanohybrids. Such a nanohybrid with a bio-inspired structure will afford new insights for the fabrication of novel photocatalysts.