SERS Performance Of Graphene Oxide And Ag Nanoparticles Co-decorated TiO₂ Nanoarray

Surface-enhanced Raman scattering (SERS) is an ultrasensitive analytical technique, and it has been applied in environmental monitoring. chemical analysis and biomedical research due to its supersensitivity and rapid response. Since the surface morphologies and structures of the substrates determine the generation and intensity of Raman signals, the substrates play a vital role in SERS detection. Ag nanoparticles (Ag NPs) were widely used as a SERS substrate due to its high localized surface plasmon resonance. In addition, anatase TiO2 has been extensively used for photocatalytic degradation of organic compounds. Ag/TiO2 substrate could achieve self-cleaning function through photocatalytic degradation of organic molecules absorbed on the surface, thus it has been used as a recyclable SERS substrate. Graphene oxide (GO) is an ideal host material to adsorb a wide variety of organic molecules. Moreover, GO can chemically enhance the Raman signals of adsorbed molecules. GO decorated on the Ag/TiO2 nanotube array(GO/Ag/TiO2 NTA) designed as the SERS substrate could enhance the adsorption capability, and SERS detection of molecules with a weak adsorption affinity were achieved. In this paper, we prepared GO/Ag/TiO2 NTA for SERS detection of molecules with a weak adsorption affinity. We fabricated Ag/GO/TiO2 NTA by deposited GO and Ag NPs on the surface of TiO2 NTA, successively. Ag&GO/TiO2NTAwas formed by depositing Ag NPs and GO on the surface of TiO2 NTA by the one-step deposition. The influence of deposition order of Ag NPs and GO on the SERS performance of the substrates need to further explore. N-doped TiO2 NTA (N-TiO2 NTA) can extend the absorption edge to the visible light region. Ag/GO/N-TiO2 NTA could be designed as a SERS substrate used for SERS detection of molecules with a weak adsorption affinity. Meanwhile, it could achieve self-cleaning function through photocatalytic degradation of organic molecules absorbed on the surface of SERS substrate under the visible light. Main works are fisted as follows:(1) Preparation and SERS performance of GO/Ag/TiO2 NTA. GO decorated on the Ag/TiO2 NTA could enhance the adsorption capability, and SERS detection of molecules with a weak adsorption affinity were achieved. TiO2 NTA was synthesized by controlled anodic oxidation process. Ag/TiO2 NTA was formed by depositing Ag NPs on the surface of TiO2 NTA by the polyol process. GO/Ag/TiO2 NTA was prepared by decorating GO on the surface of Ag/TiO2 NTA through an impregnation process. The formed Ag/TiO2 NTA and GO/Ag/TiO2 NTA were used as the SERS substrates. Their adsorption capability and SERS activity were fully examined by MB using as the probe molecule. Experimental results showed that the adsorption ratio of MB was increased from 25.2% for Ag/TiO2 NTA up to 38.0% for GO/Ag/TiO2 NTA, presenting an obvious improvement of the adsorption capability. The analytical enhancement factor (AEF) was increased from 1.06×104 for Ag/TiO2 NTA up to 3.67×104 for GO/Ag/TiO2 NTA, presenting an obvious improvement of SERS detection performance. Ag/TiO2 NTA and GO/Ag/TiO2 NTA were further applied for SERS detection of BPA with a weak affinity. Raman characteristic peaks of BPA were observed on GO/Ag/TiO2 NTA. Comparatively, these characteristic peaks of BPA were not observed on Ag/TiO2 NTA. The above experimental results reveal that GO/Ag/TiO2 NTA could be used for sensitive SERS detection of BPA with weak affinity.(2) Preparation and SERS performance of Ag/GO/TiO2 NTA and Ag&GO/TiO2 NTA. The influence of deposition order of Ag NPs and GO on the SERS performance of the substrates need to explore. TiO2 NTA was synthesized by controlled anodic oxidation process. GO/TiO2 NTA was formed by decorating GO on the surface of TiO2 NTA through an impregnation process. Ag/GO/TiO2 NTA was formed by depositing AgNPs on the surface of GO/TiO2 NTA by the polyol process. Ag&GO/TiO2 NTA was prepared by immersing TiO2 NTA in Ag NPs and GO mixed solution. The formed Ag/GO/TiO2 NTA, Ag&GO/TiO2 NTA and GO/Ag/TiO2 NTA were used as the SERS substrates. MB was used as the probe molecule to evaluate their adsorption capability and SERS activity. Experimental results showed that the adsorption ratio of MB was 40.0% for GO/Ag/TiO2 NTA,38.0% for Ag/GO/TiO2 NTA and 36.5% for Ag&GO/TiO2 NTA. Their adsorption capability for MB were almost the same. They were used as SERS substrates to detect 1.0×10-5 M MB, the AEF was 4.42×104 for Ag/GO/TiO2 NTA,3.67×104 for GO/Ag/TiO2 NTA and 2.78×104 for Ag&GO/TiO2 NTA. It reveals that the deposition order of Ag NPs and GO has an effect on the SERS performance of the substrates. Ag/GO/TiO2 NTA has the best SERS performance, which formed by depositing GO and Ag NPs on the surface of TiO2 NTA, successively.Ag/GO/TiO2 NTA acting as a SERS substrate was applied in BPA detection. The SERS activity and self-cleaning SERS recyclability of Ag/GO/TiO2 NTA were evaluated. Experimental results showed that Ag/GO/TiO2 NTA substrate achieved a low detection limit at a scale of 5×10-7 M for BPA The used Ag/GO/TiO2 NTA substrate with 5×10-5 M BPA carried out photocatalysis self-cleaning process to form the recovered Ag/GO/TiO2 NTA substrate under UV light irradiation for 150 min. Self-cleaning SERS recyclability of Ag/GO/TiO2 NTA substrate was conducted for five recycles. The Raman characteristic peak intensity of BPA almost kept the similar level, RSD was 3.6%. The above results reveal that Ag/GO/TiO2 NTA was able to act as a SERS active substrate to detect BPA recycly under the UV light(3) Preparation and SERS performance of Ag/GO/N-TiO2 NTA. Ag/GO/N-TiO2 NTA could achieve self-cleaning function through photocatalytic degradation of organic molecules absorbed on the surface of SERS substrate under visible light. TiO2 NTA was synthesized by controlled anodic oxidation process. Then it was annealed in a pipe furnace with ammonia atmosphere to obtain N-TiO2 NTA. GO/N-TiO2 NTA was formed by decorating GO on the surface of N-TiO2NTA through an impregnation process. Ag/GO/N-TiO2 NTA was formed by depositing Ag NPs on the surface of GO/N-TiO2 NTA by the polyol process. Ag/GO/N-TiO2 NTA acting as a SERS substrate was applied in BPA detection. The SERS activity and self-cleaning SERS recyclability of Ag/GO/N-TiO2 NTA were evaluated. Experimental results showed that Ag/GO/N-TiO2 NTA substrate achieved a low detection limit at a scale of 5× 10-7 M for BPA. Ag/GO/N-TiO2 NTA was immersed in 5×10"5 M BPA solution for 150 min under visible light irradiation, the degradation ratio of BPA was 93.8% for Ag/GO/N-TiO2 NTA. The used Ag/GO/N-Ti02 NTAsubstrate with 5x 10-5 M BPA carried out photocatalysis self-cleaning process to form the recovered Ag/GO/N-TiO2 NTA substrate under the visible light irradiation for 150 min. Self-cleaning SERS recyclability of Ag/GO/N-TiO2 NTA substrate was conducted for five recycles. The Raman characteristic peak intensity of BPA almost kept the similar level, RSD was 4.2%. The above results reveal that Ag/GO/N-TiO2 NTA was able to act as a SERS active substrate to detect BPA recycly under the visible light.