In the present paper, we report on the design and fabrication of a recyclable microfluidic SERS chip with an integrated Au@Ag/TiO2 NTs (gold core silver shell nanoparticles (NPs) with decorated TiO2 nanotube arrays (NTs)) composite SERS substrate. The stripped TiO2 NTs with regularly arranged pore structures were prepared on a Ti foil by easy tape lithography followed by anodic oxidation. The Au@Ag NPs were fabricated on the mouth surface and the inner walls of the TiO2 NTs within a microchannel without clogging via a facile self-assembly chemical plating composite method. Under optimized conditions, the microfluidic SERS chip provided excellent sensitivity to R6G molecules with a detection limit of 10−10 M and a SERS enhancement factor (EF) of 1.15 × 108. Versus single Au NPs, Au@Ag NPs and the Au@Ag/TiO2 plate, the optimized Au@Ag/TiO2 NTs showed improved SERS peak intensities for the C–C–C bending (613 cm−1) of 20, 2.3 and 1.6 times enhancement, respectively. The enhancement effect was attributed to both electromagnetic and chemical enhancement. The photocatalytic performance of the Au@Ag/TiO2 NTs was exploited to recycle the microfluidic SERS chip through UV light photocatalytic purification. The experimental result shows that the microfluidic SERS chip featured high reproducibility and could be used as an efficient SERS detector for many biochemical molecules.
A green bioreduction method was used to prepare highly efficient supported TiO 2 photocatalysts with bimetallic (Au-Ag) nanoparticles at room temperature using Cinnamomum camphora leaf extract as both the protective agent and reducing agent. The resulted Au-Ag/TiO 2 exhibits high photocatalytic activity toward the degradation of organic dyes. It was demonstrated that after some of the biomolecules were removed through ionic-liquid extraction and/or calcinations, the Au-Ag/TiO 2 photocatalyst exhibits significantly enhanced catalytic performance toward the degradation of methyl orange compared to the pristine untreated catalyst. As a result, 300 mL of 20 mg/mL methyl orange can be fully degraded in 30 min. These can be explained by the sufficient biomolecules could protect the nanoparticles stay in small size, but excess biomolecules played an unfavorable role in hindering the electron transportation during the catalytic reaction. The low-cost preparation, the high activity, together with the good stability and recyclability make this developed Au-Ag/TiO 2 a promising photocatalyst toward the degradation of wastewater.
The fast recombination of photogenerated electrons and holes in the pure TiO 2 leads to a low photocatalytic efficiency in hydrogen generation or solar energy conversion. Noble metal nanoparticles have been used to combine with TiO 2 for effective photocatalysis. Herein, Au@Ag@TiO 2 nanorods (NRs) with core–shell structure have been prepared by hydrolysis the precursor of titanium in acid environment. UV light–driven H 2 generation rate of Au@Ag@TiO 2 samples demonstrated 14 times enhancement compared to P25 TiO 2 at the same experimental conditions. The improved photocatalytic performance was due to the charge transfer from the conduction band of excited TiO 2 to Au@Ag NRs leading to effective separation of electron–hole pairs. This mechanism has been proved by transient absorption spectroscopy and photo-electrochemical (PEC) measurements. The time resolved photocurrents of P25 TiO 2 NPs is ~ 13 times higher that of Au@Ag@TiO 2 , indicating that a fraction of the photogenerated electrons of TiO 2 driven by UV light transfer to Au@Ag nanocores instead of transporting entirely to the ITO substrates. The ultrafast transient absorption and pump-probe measurements demonstrated a faster decay in Au@Ag@TiO 2 NRs compared to pure TiO 2 system, indicating that the photogenerated electron–hole recombination in TiO 2 is substantially suppressed by Au@Ag@TiO 2 NRs attributed to the effective trapping of the photogenerated electrons by the Au@Ag cores. Graphic Abstract Au@Ag@TiO 2 nanocomposites with core-shell structure have been prepared and its UV light–driven H 2 generation rate has been demonstrated 14 times enhancement compared to P25 TiO 2 at the same experimental conditions. The improved photocatalytic performance was due to the charge transfer, which has been proved by photocurrent measurement and the ultrafast transient absorption and pump-probe measurements.
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