【作者】 海子彬；

【导师】 陈家富； Hynd REMITA；

【作者基本信息】 中国科学技术大学 ， 材料物理与化学， 2013， 博士

【摘要】 近来,光催化因其在裂解水产氢及污水处理方面潜在的商业和工业应用而受到广泛研究。在这类光催化半导体中,二氧化钛尤为引人关注,其不仅催化效率高,而且制备成本低、化学及生物稳定性好、无毒性。然而,它是一种宽禁带半导体,需要较高能量电磁辐射才可以激活。人们尝试采用各种手段如：金属表面修饰、离子掺杂等用以提升二氧化钛的光催化活性。此外,其它一些半导体,如铜氧化物和铜的硫化物由于其用于太阳光催化合适的禁带宽度也得到了相当多的关注与研究。本研究论文中,研究了两类不同的光催化剂：第一类为金-铜双金属纳米颗粒表面修饰的二氧化钛(TiO2);第二类是辐照合成铜基的光催化剂,包括具有特殊形貌的氧化亚铜、氧化铜和硫化铜。现分述如下：第一部分：用胶体沉积法制备Au-Cu双金属纳米颗粒修饰的P25(一种商品Ti02)。辐射法和THPC (四羟甲基氯化磷)化学法分别用于合成Au和(或)Cu的金属胶体溶液。通过辐射法,在稳定剂聚丙烯酸的存在下制备的胶体金属纳米颗粒尺寸小且分散均匀。当Au与Cu结合形成双金属时,纳米颗粒的平均尺寸明显下降。研究表明：相比单独使用聚丙烯酸而言,在聚丙烯酸及聚乙烯醇协同辅助下,能实现金属纳米颗粒在二氧化钛表面更好的负载,且Au-Cu双金属纳米颗粒修饰的P25表现出紫外光催化活性的提升；Au-Cu双金属纳米颗粒对P25的修饰比单金属Au的修饰在光催化降解染料污染物上效率更高。同时,利用时间分辨微波导(TRMC)技术研究紫外光激发后的TiO2中电荷载流子动力学及催化机理,TRMC信号表明二氧化钛负载的Au-Cu双金属纳米颗粒可以有效清除电子,因此促进了电子-空穴的分离,使紫外光催化活性大大提升。采用THPC化学法还原合成Au, Cu和Au-Cu双金属纳米颗粒,然后将其沉积在二氧化钛表面,通过煅烧和氢气还原用以除去稳定剂THPC。用HR-TEM, EDS, DRS和STEM等技术表征并确定Au-Cu双金属纳米颗粒具有合金结构。研究发现：金属纳米颗粒表面修饰的P25其紫外光光催化活性增加,且Au/Cu摩尔比为1：3的Au-Cu/TiO2光催化活性最高。TRMC研究表明沉积的金属纳米颗粒充当电子陷阱,阻碍了电荷载流子的复合；进一步研究发现双金属Au-Cu纳米颗粒对电子的捕捉效率比单一金属Au或Cu颗粒效率更高。此外,还采用尿素沉淀沉积法(使用γ-射线辐射原位还原沉积的金属离子)制备Au, Cu和Au-Cu双金属纳米颗粒修饰的P25。该方法能保证Au和Cu金属离子的高沉积产率,达～100%,同时,负载的Au-Cu双金属纳米颗粒为合金结构。P25的紫外光催化活性通过Au-Cu合金纳米颗粒的修饰而被提升。负载Au-Cu双金属纳米颗粒的中较高比例Cu能导致表面修饰的P25更高的光催化活性,这些结论与前述研究结论是一致的。第二部分：Y-射线辐射法可控合成铜基光催化剂。常温常压下,Y-射线辐射途径可控合成了不同形貌的铜的氧化物CuO和Cu2O。在这个研究体系中,利用γ-射线辐照含有氯化铜,氢氧化钠,十二烷基硫酸钠(SDS)和异丙醇的溶液,合成CuO纳米线和Cu2O微晶。首次发现：调节氢氧化钠的加入量可以改变产物成分；改变表面活性剂SDS及异丙醇的用量可以精确控制CuO和Cu20产物的形貌；考察了表面活性剂,异丙醇对产物形貌的影响与作用；探讨了产物形成的可能机制。在此基础上研究了它们可见光下的光催化性质,即：合成的相关铜氧化物在可见光照射下降解甲基橙水溶液。结果表明,具有特殊形貌的Cu2O表现出优异的可见光催化活性,相比而言截角八面体Cu20的光催化活性最高。这项工作有望拓展Cu2O在可见光催化领域的基础及应用研究。常温常压下,γ-射线辐射途径合成CuS纳米管。通过γ射线辐照含有硫代硫酸钠(Na2S2O3)的氯化铜(CuCl2)溶液,在无任何软模板条件下得到了均匀的CuS纳米管,CuS纳米管的半径～200nm,长度从几百nm到2μm左右,CuS纳米管的外径和壁厚分别为～220nm和～40nm。CuS纳米管的形貌可以通过控制反应物Na2S2O3与CuCl2的比例来实现。此外,利用合成的CuS纳米管在可见光下降解罗丹明B水溶液,研究了其光催化性质,研究发现,CuS纳米管对染料罗丹明B表现出优异的吸附能力及可见光催化活性。更多还原

【Abstract】 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.更多还原