Catalytic Performance Of Au-based Nanocatalysts And In Situ SERS Monitoring Catalytic Reaction

Au metal nanoparticles (NPs) exhibiting the exceptional physical and chemical properties has been created and demonstrated the high potential for catalysis and sensors. However, the small size Au NPs often leaded to aggregation and catalyst deactivation. To solve those problems, we loaded the Au nanoparticles in the other function materials. With the developing of catalytic reaction research, we needed to use the refined analytical instrument to monitor the reaction process. In this paper, we use the SERS (Surface-Enhanced Raman Spectroscopy) technique in situ to monite the catalytic reaction and the research’s works were carried out by the following several parts:1) Magnetically Recyclable Catalytic Activity of the Spiky Fe3O4@Au NanoparticlesThe 4nm Au NPs were adsorbed on the Fe3O4@PEI and then spiky Au-shell coating was achieved on the surface of the Fe3O4@PEI-Au to prepare the 100nm spiky Fe3O4@Au using the reduction method. We evaluate the catalytic rate using the reduction of 4-nitrophenol reaction in the presence of NaBH4. The rate constant for 4-nitrophenol reduction is 0.0116 min-1 using core-satellite Fe3O4@Au NPs, whereas the rate constant for 4-nitrophenol reduction catalyzed by spiky Fe3O4@Au NPs is 0.058 min-1,5 times higher than core-satellite Fe3O4@Au NPs. Because of high magnetization, the spiky NPs exhibit good separation ability and reusability, which can be repeatedly applied for the nearly complete reduction of 4-nitrophenol for at least four successive cycles. The spiky Fe3O4@Au nanocomposites not only had high efficiency of catalytic activity, but also multiple recycle catalytic reaction.2) Enhanced Photocatalytic Activity of the Hollow TiO2-Au-TiO2 Sandwich Structured NanocompositeThe mesoporous hollow TiO2-Au-TiO2 (MHTAT) sandwich structured nanocomposite was synthesized using resorcinol-formaldehyde resin polymer nanospheres as templates, followed by TiO2 coating, Au NP deposition, and external TiO2 coating, and then hydrothermal treatment and calcination for post-treatment of template removal. The The TiO2-Au-TiO2 (MHTAT) nanocomposites have enhanced visible light harvesting efficiency through their unique hierarchical nanostructure and high surface-to-volume ratio, which are beneficial to enhancing visible photocatalytic performance. The Au NPs were sandwiched between two shells of TiO2 in the MHTAT nanocomposites, which formed close Schottky contact for electron transfer through the interface between TiO2 and Au in the photocatalytic reaction. The photocatalytic activity of MHTAT sandwiched nanocomposites was fully demonstrated in degradation reactions of organic compounds under visible light irradiation (0.023 min-1), suggesting their intriguing potential as effective visible-light induced photocatalysts.3) Fe3O4@Au@Ag Nanoplates 3D Fe3O4@Au@Ag Magnetoplasmonic Chains for in situ SERS Monitoring of Catalytic ReactionThe Fe3O4@Au NPs as building blocks were used to fabricate 1D MPNCs through magnetic field induced assembly. With the help of silver growth solution, the Fe3O4@Au@Ag nanoplates assembled 3D magnetoplasmonic chains (Fe3O4@Au@Ag NAMPCs) were prepared by in situ reduction method. The Fe3O4@Au@Ag NAMPCs possessed large numbers of hot spots within the structure and used as the SERS substrate to enhance detection sensitivity. After that, the Fe3O4@Au@Ag NAMPCs, integrating a heterogeneous catalysis and in situ SERS detection, is assessed to monitoring the catalytic reduction of 4-NTP to DMAB. This reaction can be dramatically influenced by varying the duration of laser exposure and laser power. The apparent rate constants of the reactions catalyzed by 0.2mW and 0.5mW are smaller than 1mW excitation power obtained, giving k1=2.09 × 10-3 s-1,k0.5=2.02 ×10-4 s-1 and k0.2=4.62 × 10-5 s-1, respectively.4) SiO2@Au NPs as the SERS substrate for monitoring the 4-NTP to 4-ATP through SERS technique.SiO2@Au NPs were synthesized through the seed-growth method. The distance of Au nanoparticles out of SiO2 NPs could be adjusted by the concentration of HAuCl4. And then, the different morphology nanoparticle used as the SERS substrate. Reasoning by theory and experiment results, the coupling effect between 5-10 nm particles (Au) spacing of SiO2@Au nanoparticles had high SERS signal enhancement effect. Then, we used this SERS substrate employed for the in situ SERS monitoring of a catalytic reaction of p-nitrothiophenol (p-NTP) to p-aminothiophenol (p-ATP) and getted the reaction rate was 0.040 s-1. Then, we used the UV-Vis absorption spectrum monitoring the reaction rate (0.048 s-1) which is similar with the reaction rate using SERS technique. The SERS technique could monite the reaction intermediates.5) High-density SERS active Fe3O4@Au nanostar assemblies in capillary for colorants detectionWe prepared the Fe3O4@Au nanostars with the size between 20nm to 50nm and demonstrated the fabrication of ultrasensitive SERS substrates based on the high-density gold nanostars assemblies in capillary which can obtain the simple in situ detection. The Fe3O4@Au nanostars with different tips could be synthesized quickly and easy. Taking advantage of the electromagnetic field coupling between tips of adjacent individual nanostars, the self-assembled substrate of gold nanostars exhibited a better SERS performance than that of gold nanoparticles. Then the Fe3O4@Au nanostars with magnetic core can be mixed with the colorant and then the nanostar absorbed the colorant by the physical adsorption. The Fe3O4@Au nanostars building blocks were used to fabricate the film through magnetic field induced assembly. The limit of detection (LOD) is 0.5mg/kg,3 to 4 orders smaller than that of the conventional GB protocols.