Pd/ZnO和Ag/ZnO复合纳米粒子的SPS和XPS研究

用焙烧前驱物碱式碳酸锌的方法制备了ZnO纳米粒子，采用光还原沉积贵金属的方法分别得到了质量分数为0.5％的Pd/ZnO和Ag/ZnO复合纳米粒子，并利用XRD、TEM、XPS和SPS等测试技术对样品进行表征.初步探讨了贵金属在ZnO纳米粒子表面形成原子簇的原因及沉积贵金属对ZnO纳米粒子表面光电压信号的影响.以光催化氧化气相正庚烷为模型反应，考察了沉积贵金属对ZnO纳米粒子光催化活性的影响，并探讨了光催化活性有所提高的内在原因.结果表明， ZnO纳米粒子沉积贵金属后，其表面光电压信号明显下降，而光催化活性却大大地提高，这说明可以通过表面光电压谱的测试来初步的评估纳米粒子的光催化活性，即粒子的表面光电压信号越弱，其光催化活性越高.     

ZnO纳米粒子的表面光电压谱和光催化性能

采用焙烧前驱物碱式碳酸锌的方法制备了不同粒径的ZnO纳米粒子，而用粒径 最小的作为光催化剂，通过光还原过程分别得了贵金属质量分数为0.5%和0.75%的 Pd/ZnO或Ag/ZnO复合纳米粒子。利用XRD，TEM，XPS，SPS和EFISPS等测试技术对样 品进行了表征，并通过光催化氧化气相正庚烷评估了样品的光催化活性，考察了微 晶尺寸和贵金属Pd或Ag的沉积对ZnO纳米粒子表面光电压信号以及光催化活性的影 响，探讨了样品表面光电压谱与其光催化活性的关系，说明了可以通过表面光电压 谱的测试来初步地评估纳米粒子的光催化活性。结果表明：随着ZnO纳米微晶尺寸 的减小，其SPS信号强度逐渐变弱，而光催化活性逐渐升高；沉积适量的贵金属Pd 或Ag后，ZnO纳米粒子的SPS信号强度明显下降，而其光催化活性却有所升高。此外 ，对ZnO纳米粒子光催化剂的失活机理进行了分析。     

ZnO纳米粒子的表面光电压谱和光催化性能

采用焙烧前驱物碱式碳酸锌的方法制备了不同粒径的ZnO纳米粒子，而用粒径 最小的作为光催化剂，通过光还原过程分别得了贵金属质量分数为0.5%和0.75%的 Pd/ZnO或Ag/ZnO复合纳米粒子。利用XRD，TEM，XPS，SPS和EFISPS等测试技术对样 品进行了表征，并通过光催化氧化气相正庚烷评估了样品的光催化活性，考察了微 晶尺寸和贵金属Pd或Ag的沉积对ZnO纳米粒子表面光电压信号以及光催化活性的影 响，探讨了样品表面光电压谱与其光催化活性的关系，说明了可以通过表面光电压 谱的测试来初步地评估纳米粒子的光催化活性。结果表明：随着ZnO纳米微晶尺寸 的减小，其SPS信号强度逐渐变弱，而光催化活性逐渐升高；沉积适量的贵金属Pd 或Ag后，ZnO纳米粒子的SPS信号强度明显下降，而其光催化活性却有所升高。此外 ，对ZnO纳米粒子光催化剂的失活机理进行了分析。     

ZnO和TiO2粒子的光催化活性及其失活与再生

 利用XRD，TEM，BET和UV－Vis等测试技术对商品的ZnO及TiO2和纳米ZnO及TiO2粒子进行了表征．无论是商品的还是纳米的，在光催化氧化降解气相n－C7H16和SO2及液相苯酚的反应中，TiO2均表现出比ZnO高的光催化活性，并从光腐蚀性和表面电荷两方面分析了其原因．在光催化氧化降解n－C7H16的反应中，ZnO粒子易失活，而TiO2粒子不易失活．但是，在光催化氧化降解SO2的反应中，ZnO和TiO2粒子均易失活．SPS和XPS测试结果表明，光催化剂表面的导电类型由反应前的n型变成了失活后的p型．这主要是由于反应产物发生吸附所致．失活后的光催化剂可以通过浸洗和干燥再生．     

贵金属负载的棒状ZnO复合光催化剂的制备及其提升的光催化性能

以水热制备的ZnO纳米棒为基底,通过乙二醇液相还原法负载不同贵金属颗粒(Pt、Pd、Ru)构筑贵金属负载的ZnO纳米棒复合光催化剂。实验结果表明在制备条件相同时,Pt/ZnO样品中Pt颗粒尺寸较小,分布均匀;Pd/ZnO样品中Pd颗粒尺寸较大且团聚严重;Ru/ZnO样品则几乎没有Ru颗粒负载。在紫外光照射下降解亚甲基蓝的反应中,Pt/ZnO表现出最高的光催化性能,Pd/ZnO样品次之,而Ru/ZnO则表现出与ZnO纳米棒相似的光催化活性;表明小尺寸和大小均匀的贵金属颗粒对ZnO纳米棒的催化性能有着显著的提升作用。对Pt/ZnO来说,当Pt载量为3.2%时Pt/ZnO催化剂的光催化活性最高。     

Ag改性纳米ZnO薄膜及光催化活性

采用溶胶-凝胶法和光还原沉积贵金属法结合制备出Ag改性的纳米ZnO薄膜。利用FESEM、XPS、ESR、UV-Vis分析了纳米Ag-ZnO薄膜的表面形貌、表面组成和光谱特征。FESEM分析表明银在纳米ZnO薄膜表面形成原子簇而没有形成均匀覆盖层。XPS分析表明负载在纳米ZnO薄膜表面的银以Ag⁰形式存在; 相对于纳米ZnO薄膜, 纳米Ag-ZnO薄膜中晶格氧的含量有所下降,而表面羟基氧和吸附氧的含量显著增加。纳米Ag-ZnO薄膜的ESR峰强比纳米ZnO薄膜大,表明纳米Ag-ZnO薄膜中束缚单电子的氧空位的浓度高于纳米ZnO薄膜。UV-Vis分析纳米Ag-ZnO薄膜的紫外可见吸收光谱可能是纳米银粒子与纳米ZnO薄膜共同作用的结果。以甲基橙为模拟污染物,考察了纳米Ag-ZnO薄膜的光催化活性以及银沉积量对催化剂活性的影响。光催化降解结果表明,银的沉积量为0.018 2 mg·cm^-2的纳米Ag-ZnO薄膜的光催化活性最高,在紫外光照射3 h后甲基橙降解率约为78%,而纳米ZnO薄膜约为62%。     

Ag／TiO2复合纳米催化剂的制备和表征及其光催化活性

 采用光还原沉积贵金属法，制备了Ag／TiO2复合纳米催化剂．通过调节溶液的pH值控制TiO2表面负载银的形貌，利用AAS，XRD，TEM和XPS等手段对样品进行了表征．以苯胺氧化为模型反应，考察了Ag／TiO2复合纳米催化剂样品的光催化活性以及银沉积量和沉积形貌对催化剂活性的影响．结果表明，通过调控光还原沉积条件，可在平均粒径为24nm左右的TiO2颗粒上获得3nm左右均匀分散的银粒子；在TiO2上沉积适量的具有较高分散度的金属Ag，能有效提高TiO2对苯胺氧化反应的光催化活性．     

纳米Ag/ZnO光催化剂及其催化降解壬基酚聚氧乙烯醚性能

采用氨浸法制备了不同Ag负载量的纳米Ag/ZnO光催化剂,并用X射线衍射、比表面积测定、X射线光电子能谱和漫反射紫外-可见光谱测定了Ag/ZnO的晶型结构、比表面积、表面组成和光谱特征.以壬基酚聚氧乙烯醚(NPE-10)为模型污染物,分别在紫外光和可见光照射下考察了纳米Ag/ZnO的光催化活性.结果表明,Ag能成功地负载到ZnO表面,且随着Ag负载量的增加,ZnO的粒径逐渐增大,比表面积逐渐减小.与纳米ZnO样品相比,Ag/ZnO中Ag 3d5/2结合能减小,而Zn 2p和O 1s结合能增大,ZnO表面的羟基氧和吸附氧含量增加.当Ag负载量大于0.5%时,Ag/ZnO样品的吸收光谱发生红移,在可见光区出现吸收.光催化降解结果表明,0.5%Ag/ZnO样品的光催化活性最高,在紫外光和可见光照射3 h后NPE-10降解率分别约为77%和56%,而ZnO样品的光催化活性仅约为61%和40%.     

复合Ag/ZnO分级结构微球的制备及其光催化性能研究

采用化学沉淀法制备ZnO微球,利用柠檬酸三钠（TCD）避光还原硝酸银在ZnO表面沉积银粒子制备Ag/ZnO复合材料.利用XRD、SEM、TEM、EDS、FTIR、UV-vis DRS、PL、BET等对Ag/ZnO的结构、组分、形貌及光谱性质进行了表征,通过紫外及可见光照降解甲基橙溶液评价样品的光催化性能.结果表明：ZnO纳米微球是由ZnO纳米片相互交错构筑而成的具有丰富孔道的分级结构,Ag纳米粒子均匀沉积在ZnO纳米片上.Ag的沉积显著增加了ZnO的可见光吸收,猝灭了ZnO荧光,提高了ZnO催化活性.     

微/纳米结构ZnO/TiO_2复合光催化剂的制备及其光催化性能研究

以微米尺寸的花状和棒状ZnO为载体,利用表面吸附层水解方法,制备了具有微/纳米结构的ZnO/TiO2复合光催化剂。采用SEM、XRD、EDS和UV对其形貌、结构、表面组成等进行了表征。结果表明,在棒状或花状微米尺寸ZnO表面能形成均一尺寸的TiO2纳米粒子。复合物中表面TiO2含量与Ti(OC4H9)4添加量呈正相关性。得到的复合物为纤锌矿型氧化锌和锐钛矿型氧化钛复合物。对不同组成ZnO/TiO2复合物的光催化活性进行了初步研究。     

Investigations on the surface modification of ZnO nanoparticle photocatalyst by depositing Pd

In this paper, ZnO nanoparticle photocatalysts were modified by depositing Pd on their surfaces with a photoreduction method. We mainly investigated the modification mechanisms as well as the effects on the photocatalytic activity of ZnO nanoparticles of deposited Pd by means of XPS and SPS (Surface Photovoltage Spectroscopy), and the effects of Pd content on SPS responses were also discussed from the point of the electronic energy level. The results showed that the content of crystal lattice oxygen on the surface of ZnO nanoparticle decreased after an appropriate amount of Pd was deposited, while that of adsorbed oxygen increased, indicating that Pd was mainly deposited on the crystal lattice oxygen. At the same time, the intensity of SPS responses of ZnO nanoparticles remarkably decreased. In addition, the activity of ZnO nanoparticles could be greatly improved by depositing an appropriate amount of Pd in the gas phase photocatalytic oxidation of n-C₇H₁₆. Thus, it could be concluded that the increase in surface content of adsorbed oxygen could facilitate the photocatalytic reaction, and there were close relationships between the SPS response and photocatalytic activity, i.e. the weaker the SPS response, the higher the photocatalytic activity, of Pd-deposited ZnO nanoparticles.     

Photocatalytic oxidation of organic dyes with nanostructured zinc dioxide modified with silver metals

Silver-doped nano-ZnO samples with different Ag loadings were prepared by a one-spot solvothermal method. The structure, physico-chemical and optical properties of the products are characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray analysis (EDS), diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL). The photocatalytic activity of the as-prepared samples was examined by using photocatalytic oxidation of methyl orange (MO) as a model reaction, and the effects of the noble metal content on the photocatalytic activity were investigated. The results indicated that the photocatalytic activity of ZnO nanoparticles can be greatly improved by depositing appropriate amount of noble metal on their surface as electron scavengers. In addition, a key mechanism was proposed in order to account for the enhanced activity. The enhancement for the photocatalytic activities can be attributed to the interaction between Ag particles and ZnO, which made Ag particles act as electron traps to effectively separate the excited electron-hole pairs.     

ZnO/Ag微米球的合成与光催化性能

用微波辅助多元醇法对预先制备的ZnO微米球进行修饰,合成了载银氧化锌微米球（ZnO/Ag）. 利用X射线衍射仪、场发射扫描电子显微镜、透射电子显微镜、X射线光电子能谱仪、紫外-可见双光束分光光度计和光致发光光谱仪等对样品的结构、形貌和光学性能进行了表征. 在紫外光照射下,通过亚甲基蓝的降解反应研究了样品的光催化活性. 结果表明,所制备的ZnO/Ag微米球是由面心立方的Ag纳米颗粒附着在纤锌矿结构的ZnO球表面形成;与ZnO相比,ZnO/Ag的紫外-可见光吸收光谱发生明显红移,在紫外和可见光范围均有较强的吸收;随着Ag含量的增加,ZnO/Ag荧光光谱强度先减弱后增强;与ZnO相比,ZnO/Ag的光催化活性明显提高,AgNO₃ 浓度为0.05 mol/L时制得的ZnO/Ag光催化活性最高.     

Ag/ZnO heterostructure nanocrystals: synthesis, characterization, and photocatalysis

A high yield of the dimer-type heterostructure of Ag/ZnO nanocrystals with different Ag contents is successfully prepared through a simple solvothermal method in the absence of surfactants. The samples are characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and IR spectroscopy. The results show that all samples are composed of metallic Ag and ZnO; Ag nanoparticles locate on the surface of ZnO nanorods; the binding energy of Ag 3d(5/2) for the Ag/ZnO sample with a Ag content of 5.0 atom % shifts remarkably to the lower binding energy compared with the corresponding value of pure metallic Ag because of the interaction between Ag and ZnO nanocrystals; the concentration of oxygen vacancy for the as-synthesized samples varies with the increasing Ag content, and the Ag/ZnO sample with a Ag content of 5.0 atom % has the largest density of oxygen vacancy. In addition, the relationship between their structure and photocatalytic property is investigated in detail. It is found that the photocatalytic property is closely related to its structure, such as heterostructure, oxygen defect, and crystallinity. The presence of metallic Ag nanoparticles and oxygen vacancy on the surface of ZnO nanorods promotes the separation of photogenerated electron-hole pairs and thus enhances the photocatalytic activity.     

Synthesis and photocatalytic performance of Ag/AgCl/ZnO tetrapod composites

Ag/AgCl is a visible-light plasmonic photocatalyst that has attracted considerable attention because of its high visible-light absorption and activity owing to the surface plasmon resonance of noble-metal nanoparticles. In this study, Ag/AgCl/ZnO tetrapod composite was prepared by introducing ZnO tetrapods into Ag/AgCl prepared by a polydopamine reduction route. Ag/AgCl was densely deposited on the three-dimensional support framework provided by the ZnO tetrapods. The framework possessed a certain degree of porosity, thereby improving the specific surface area of the Ag/AgCl/ZnO composite. The interaction of ZnO with Ag/AgCl further increased the separation and transfer of electron–hole pairs. The Ag/AgCl/ZnO composite showed excellent photocatalytic activity and good stability. Under xenon lamp irradiation for 20 min, degradation of rhodamine B reached 90%. After four recycling tests, degradation remained stable without any sign of reduction. Ag/AgCl/ZnO tetrapod composite is shown to be a kind of green photocatalyst offering high activity, good stability, and recyclability.

     

Microwave-assisted solution synthesis and photocatalytic activity of Ag nanoparticles supported on ZnO nanostructure flowers

Ag nanoparticles supported on the surface of three-dimensional (3D) flower-like ZnO nanostructure were synthesized by a microwave-assisted solution method. The obtained products were characterized by X-ray diffraction analysis, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectrophotometry, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The analytical results confirmed homogeneously distributed Ag nanoparticles supported on the surface of flower-like ZnO nanostructure. The photocatalytic effect of the heterostructure Ag/ZnO nanocomposites was investigated using photodegradation under ultraviolet (UV) light of methylene blue as model dye. The heterostructure Ag/ZnO nanocomposites exhibited much higher photocatalytic activity than pure ZnO flowers. The improved photocatalytic properties are attributed to formation of a Schottky barrier at the metal–semiconductor interface of the Ag/ZnO nanocomposites.