Design, Controlled Synthesis And Catalytic Properties Study Of Ag/g-C₃N₄ And Au/g-C₃N₄ Nanocomposites

As an analogue of graphite, graphitic carbon nitride (g-C3N4) has attracted extraordinary interest for fundamental studies as well as for potential applications. Owing to its intense visible light response, high chemical stability and thermal stability, non toxicity, rich source and simple preparation process, g-C3N4 based materials have shown promising applications in catalysis. In this dissertation, Ag/g-C3N4 and Au/g-C3N4 nanocomposites with differing Ag and Au content have been designed and synthesized, respectively. The photocatalytic performance of Ag/g-C3N4 and the catalytic hydrogenation properties of Au/g-C3N4 are investigated. The main contributions of this dissertation are described as follows:(1) Design and control synthesis of Ag/g-C3N4 and Au/g-C3N4 nanocomposite materials.Ag/g-C3N4 and Au/g-C3N4 nanocomposites with differing Ag and Au content have been respectively designed and prepared via a simple in-situ growth method using the metal salt (Ag, Au) as metal nanoparticle source and g-C3N4 nanosheet as support material. Ag/g-C3N4 and Au/g-C3N4 nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The results show that g-C3N4 sheets are decorated with highly dispersed Ag and Au nanoparticles having an average size of 5.6 nm and 2.8 nm, respectively.(2) The photocatalytic performance and photodegradation mechanism study of the Ag/g-C3N4 nanocomposites as photocatalyst under visible light irradiation.The photocatalytic activities of the Ag/g-C3N4 nanocomposites were evaluated by the degradation of methylorange (MO), methylene blue (MB), and neutral dark yellow GL (NDY-GL) under visible light irradiation. The photocatalytic activity measurements demonstrate that the photocatalytic degradation rates of MO, MB, and NDY-GL over Ag/g-C3N4-4 can reach up to 98.2,99.3 and 99.6% in the presence of borohydride ions (BH4-) only for 8,45, and 16 min visible light irradiation, respectively. The significant enhancement in photoactivity of the catalyst is mainly attributed to the high dispersity and smaller size of Ag nanoparticles, the strong surface plasmon resonance (SPR) effect of metallic Ag nanoparticles, the efficient separation of photogenerated charge carriers, the additional superoxide radicals (O2·-) generated from the reduction of dissolved oxygen in the presence of BH4- and the synergistic effect of Ag nanoparticles and g-C3N4.(3) Catalytic hydrogenation properties and mechanism study of Au/g-C3N4 nanocomposites.The catalytic hydrogenation properties of Au/g-C3N4 nanocomposites with differing Au content were evaluated by reductive catalysis of o-nitrophenol (o-NP), m-nitrophenol (m-NP), p-nitrophenol (p-NP),2,4-dinitrophenol (2,4-DNP),2,4,6-trinitrophenol (2,4,6-TNP) using NaBH4 as reducing agent. The experimental results show that the Au/g-C3N4 (with 6 wt% Au) nanocomposite gave the highest catalytic activity which can be attributed to the high dispersity and smaller size of Au nanoparticles, the synergistic effect of the combination of Au nanoparticles and g-C3N4.