Modification Of Titania With Gold-Copper Bimetallic Nanoparticles And Preparation Of Copper-Based Photocatalysts And Applied Basic Research

Photocatalysis is recently extensively studied because it implies a variety of potential commercial and industrial applications ranging from the hydrogen generation from water splitting to the treatment of waste water. Among all the semiconductors, TiO2has attracted the most attention. However, it is a wide band-gap semiconductor and thus requires high energy electromagnetic radiation. Various methods are developed to enhance the photoactivity of TiO2. Other semiconductors like copper oxides and copper sulfides also attracted respectable attentions due to their appropriate band-gap for solar photocatalysis.Two different kinds of photocatalysts were studied in this thesis work. The first part reports on the modified TiO2with Au-Cu bimetallic nanoparticles (NPs) surface modification. The second part represents the radiolytic synthesis of copper-based photocatalysts including Cu2O, CuO and CuS with special morphologies.Part I:Colloid deposition method was used to prepare modified P25(a commercial TiO2) with Au-Cu bimetallic NPs. Au or/and Cu metallic colloidal solutions were synthesized by radiolytic and chemical methods respectively. By radiolysis, preparation of colloids in the presence of stabilizing agent polyacrylic acid (PAA) led to small size and homogeneous distribution of the metallic NPs. The mean nanoparticle size decreased obviously when Au is associated with copper. Surface deposition with the help of polyvinyl alcohol contributed to a better surface loading of metal NPs on TiO2than PAA only. The modified P25with Au-Cu bimetallic NPs exhibited an enhancement of photoactivity under UV illumination. The Au-Cu bimetallic nanoparticie modified TiO2were more efficient in dye pollutants photodegradation than monometallic Au one. Time resolved microwave conductivity (TRMC) measurements were conducted to study the charge-carrier dynamics in TiO2after UV excitation. TRMC signals showed the modification of TiO2with Au-Cu bimetallic NPs were efficient in scavenging electrons, prompting electron-hole separation and finally contributing to an enhancement of photoactivity under UV illumination.By chemical method, Au, Cu and bimetallic Au-Cu NPs synthesized by the reduction of Tetrakis Hydroxymethyl Phosphonium Chloride (THPC) were prepared on the surface of TiO2. Calcination and hydrogen reduction were conducted to remove the stabilizer THPC. The alloyed structure of Au-Cu bimetallic NPs was confirmed by HR-TEM, EDS, DRS and STEM techniques. The modification with metal NPs induced an increase in the photocatalytic activity under UV light. The highest photocatalytic activity was obtained with Au-Cu/TiO2(Au/Cu1:3). TRMC measurements showed that the modification of TiO2with Au, Cu and Au-Cu nanoparticles played a role in charge-carrier separations increasing the activity under UV-light. Indeed, the metal nanoparticles act as a sink for electron, hindering the charge carrier recombination. The TRMC measurements showed also that the bimetallic Au-Cu nanoparticles were more efficient in electron scavenging than the monometallic Au and Cu ones.Besides, Au, Cu and Au-Cu bimetallic NPs modified P25were also achieved by deposition precipitation method with urea (DPU), followed by gamma irradiation to in-situ reduce the deposited metal ions. This method ensures a high yield of deposition of Au and Cu metal ions up to100%. The supported Au-Cu bimetallic NPs have alloyed structure. Photocatalytic activity of TiO2under UV illumination was enhanced by the modification with Au-Cu alloyed NPs. A higher Cu proportion in supported Au-Cu bimetallic NPs resulted in a higher photoactivity of modified TiO2.Part II:the controllable synthesis of copper oxide including CuO and Cu2O was carried out and their photocatalytic performance under visible light was investigated. Copper oxide (CuO) nanowires and cuprous oxide (Cu2O) crystals have been synthesized through y-irradiation of aqueous solutions containing CuCl2, NaOH, sodium dodecyl sulfate (SDS) and isopropyl alcohol under ambient conditions. The product composition can be changed by modulating the amount of base, NaOH. The morphology of the products can be accurately controlled by changing the concentrations of SDS and isopropyl alcohol. The effects of the surfactant and isopropyl alcohol on the product morphology were discussed. A possible formation mechanism was also proposed. The photocatalytic property of the synthesized copper oxides was evaluated for the degradation of a model pollutant (methyl orange, MO) under visible illumination. Cu2O crystals with specific morphology have excellent photocatalytic activity for dye degradation under visible illumination. Especially, truncated octahedral Cu2O exhibits the highest photoactivity.In addition, uniform CuS nanotubes (NTs) with a diameter of200nm were synthesized without template by gamma irradiation of aqueous solutions of CuCl2and Na2S2O3. The length of the CuS NTs are from hundreds nanometers up to～2 micrometers. The external diameter and wall thickness are respectively～220nm and-40nm. The morphology of CuS NTs depends on the ratio of N2aS2O3to CuCl2. The photocatalytic activity of the as-prepared CuS NTs was investigated for decomposition of rhodamine B in aqueous solution. The synthesized CuS NTs exhibit a photocatalytic activity under visible light.