| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 103 === Recently, graphene has emerged as a key material or support for the various applications owing to its excellent physical, chemical and electronic properties. As the derivatives of graphene, graphene oxide (GO) and reduced graphene oxide (rGO) are widely used as starting materials for the fabrication of composites due to their low-cost property, large scale production and easy functionalization owing to the many reactive oxygenated functional groups.
This dissertation includes four parts: 1. Green synthesis and synergistic catalytic effect of Ag/reduced graphene oxide nanocomposite; 2. Microwave-assisted green synthesis of Ag/reduced graphene oxide nanocomposite as a surface-enhanced Raman scattering substrate with high uniformity; 3. Fabrication of Ag/TiO2/reduced graphene oxide nanocomposite as a reusable surface-enhanced Raman scattering substrate with high sensitivity and uniformity; 4. One-step solvothermal synthesis of TiO2/reduced graphene oxide composite as a visible light photocatalyst.
In the first part, a nanocomposite of silver nanoparticles and reduced graphene oxide (Ag/rGO) has been developed as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with sodium borohydride, owing to the larger specific surface area and synergistic effect of rGO. A facile and rapid microwave-assisted green route has been used for the formation of Ag nanoparticles and the reduction of graphene oxide simultaneously with L-arginine as the reducing agent. The resulting Ag/rGO nanocomposite contained about 51 wt% of Ag, and the Ag nanoparticles deposited on the surface of rGO had a mean diameter of 8.6 ± 3.5 nm. Also, the Ag/rGO nanocomposite exhibited excellent catalytic activity and stability toward the reduction of 4-NP to 4-AP with sodium borohydride. The reduction reaction obeyed the pseudo-first-order kinetics. The rate constants increased not only with the increase of temperature and catalyst amount but also with the increase of initial 4-NP concentration, revealing that the support rGO could enhance the catalytic activity via a synergistic effect. A mechanism for the catalytic reduction of 4-NP with NaBH4 by Ag/rGO nanocomposite via both the liquid-phase and solid-phase routes has been suggested.
In the second part, Ag/rGO composites are applied as surface-enhanced Raman scattering (SERS) substrates owing to the large surface area and two-dimensional nanosheet structure of rGO. A facile and rapid microwave-assisted green route has been used for the uniform deposition of Ag nanoparticles and the reduction of graphene oxide simultaneously with L-arginine as the reducing agent. By increasing the cycle number of microwave irradiation from 1 and 4 to 8, the mean diameters of Ag nanoparticles deposited on the surface of rGO increased from 10.3 ± 4.6 and 21.4 ± 10.5 to 41.1 ± 12.6 nm. The SERS performance of Ag/rGO nanocomposite was examined using the common Raman reporter molecule 4-aminothiophenol (4-ATP). It was found that the Raman intensity of 4-ATP could be significantly enhanced by increasing the size and content of silver nanoparticles deposited on rGO. Although the Raman intensities of D-band and G-band of rGO were also enhanced simultaneously by the deposited Ag nanoparticles which limited the further improvement of SERS detection sensitivity, the detectable concentration of 4-ATP with Ag/rGO nanocomposite as the SERS substrate still could be lowered to be 10−10 M and the enhancement factor could be increased to 1.27 × 1010. Furthermore, it was also achievable to lower the relative standard deviation (RSD) values of the Raman intensities to below 5%. This revealed that the Ag/rGO nanocomposite obtained in this work could be used as a SERS substrate with high sensitivity and homogeneity.
In the third part, to solve the problem we met in the second part, Ag/TiO2/rGO nanocomposite was developed as a more powerful SERS substrate with high sensitivity and uniformity by using TiO2 intermediate layer to diminish the interference from the Raman intensities of D-band and G-band of rGO. The detectable limit of 4-ATP could be further lowered from 10-10 M to 10-14 M. In the meanwhile, the RSD values remained below 10%. This revealed that the strategy using TiO2 intermediate layer to restrain the enhancement effect of Ag nanoparticles on the SERS intensity of rGO is indeed effective. Moreover, by UV irradiation in water, the photocatalytic property of TiO2 could eliminate the Raman signal of 4-ATP efficiently and made this substrate reusable. After reuse for 5 times, the excellent SERS performance of Ag/TiO2/rGO nanocomposite was retained. Accordingly, the Ag/TiO2/rGO nanocomposite developed in this work could be excellent candidates as a reusable SERS substrate with outstanding sensitivity and uniformity.
In the fourth part, a composite of titanium dioxide nanoparticles and reduced graphene oxide (TiO2/rGO) have been prepared via a one-step solvothermal process of titanium(IV) butoxide and GO in the mixed solution of ethylene glycol and water. TiO2 nanoparticles could be deposited uniformly on the surface of rGO. The result revealed that TiO2/rGO composites possessed enhanced photocatalytic activities than pure TiO2 nanoparticles. The incorporation of rGO not only could extend the absorption to the visible light region and narrow the band gap of TiO2 nanoparticles, but also could facilitate the electron transfer from TiO2 nanoparticles to rGO and lead to the separation of the photogenerated electron-hole pairs. Hence, the resulting TiO2/rGO composites exhibited enhanced photocatalytic performance and were expected to be useful in the treatment of organic pollutants.
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