稀土掺杂的纳米TiO2分散性及光学性能研究

采用溶胶凝胶法在同一条件下制备REa+:Ti4+=0.02和0.10的稀土掺杂的纳米TiO2材料,其中REn+为Nd3+,Ce4+,La3+,Er3+四种稀土元素.通过TG-DTG,XRD,TEM,UV-Vis等测试方法对所制备的纳米TiO2进行焙烧温度、晶胞尺寸、晶粒形貌、谱学特性等方面的研究.研究表明,稀土掺杂的纳米TiO2径粒尺寸均在20 nm左右,少量稀土掺杂不但有利于TiO2颗粒的分散,而且有利于TiO2向金红石相转变.同时,由于表面修饰作用和晶场效应的影响,掺杂使纳米材料在可见光范围内有不同程度的"红移"现象,Ce4+掺杂的纳米TiO2在可见光的"红移"程度最强.稀土掺杂的纳米TiO2在农用膜和节能材料上可广泛运用.     

La3+-SiO2掺杂纳米TiO2的合成及其光催化降解甲基橙的研究

以三嵌段非离子表面活性剂P123为模板,采用水热法合成了La3+-SiO2掺杂纳米TiO2,通过X射线衍射(XRD)、红外光谱(FT-IR)、紫外-可见漫反射吸收光谱(DRS)等手段,考察了La3+-SiO2掺杂纳米TiO2的结构与光学特性.实验结果表明,La3+和SiO2掺杂使TiO2的晶粒在生长过程中受到阻碍.Ti-O-Si键和Ti-O-La键的形成抑制了金红石相的形成和晶粒长大,提高了TiO2的热稳定性,有利于获得高纯度锐钛矿相纳米TiO2.La3+-SiO2掺杂将TiO2的光响应范围拓宽至可见光区,提高了纳米TiO2的光催化性能.与纯纳米TiO2相比,La3+-SiO2掺杂纳米TiO2光催化降解甲基橙的性能显著提高.     

疏水型纳米TiO_2膜的制备、表征及耐蚀性能研究

以乙酰乙酸乙酯(EAcAc)作稳定剂和阻聚剂制备超微TiO2溶胶,用提拉法在AISI316L不锈钢上构筑一层纳米TiO2膜,经水热后处理有效消除膜中的龟裂现象,经氟硅烷基化制备成疏水型纳米TiO2膜.用胶粒分布仪测定溶胶颗粒分布,接触角测试仪测定表面疏水性、XRD、SEM表征膜的形貌、结构,电化学线性极化法测定疏水型纳米TiO2膜在模拟体液(Ringer溶液)中的电化学行为.结果表明:TiO2膜呈多孔有序纳米膜,颗粒分布均匀,粒径约为15～18nm,厚度约375nm,TiO2为锐钛矿型,疏水型纳米膜可使不锈钢腐蚀电流降低3个数量级,其耐腐蚀性大幅度提高.     

ZrO2∶Tb3+纳米晶的离子交换法制备及其发光特性

以强碱性阴离子交换树脂为交换介质,采用离子交换法制备了稀土Tb3+离子掺杂的ZrO2:Tb3+纳米晶.通过XRD,TG-DSC,TEM,HRTEM等手段分析了样品制备过程的物相变化及晶粒形貌,用荧光光度计研究了样品的三维荧光光谱、激发光谱和发射光谱.结果表明:前驱沉淀物经800℃焙烧处理2 h,制备出近方型形貌,颗粒分散性好、尺寸约为40 nm的四方相ZrO2:Tb3+纳米晶.当焙烧温度升高到900℃以上时样品出现了少量单斜晶相,而经800℃焙烧处理的纯Zr02是以四方相和单斜相同时存在.说明稀土Tb3+离子的掺杂对ZrO2基质的四方晶相起到稳定作用.由ZrO2:Tb3+)的等角三维荧光光谱图显示Tb3+在ZrO2基质中的最佳激发波长为290 nm:在290 nm波长光的激发下观察到纳米ZrO2中Tb3+的发射峰位于491,545,582 nm分别对应于Tb3+的5D4→7F6、5D4→7F5、5D4→7F4、5D4→7F4能级跃迁,以491,545nm的发射峰最强,其中经800℃焙烧处理的样品其5D4→7F6跃迁发射与5D4→7F5跃迁发射强度几乎相同,说明该法制备的纳米ZrO2:Tb3+中5D4→7F6跃迁发射增强,使Tb3+发光的蓝色成分增加了.     

纳米TiO_2膜修饰电极异相电催化还原马来酸

通过电化学合成前驱体和溶胶 -凝胶法在Ti表面修饰一层纳米TiO2 膜 ,SEM ,XRD测试表明晶型为锐钛矿型 ,晶粒平均尺寸为 2 5nm .采用循环伏安法、循环方波伏安法和电解合成法研究了纳米TiO2 膜电极在硫酸介质中的氧化还原行为以及对马来酸 (maleicacid)还原的电催化活性 .结果表明 ,纳米TiO2 膜电极在阴极扫描时有两对可逆氧化还原峰 ,可逆半波电位Er1/ 2 分别为 -0 .5 3V和 -0 .92V (vs .SCE ,扫描速度 0 .0 5V·s-1) ,对应于TiO2 /Ti2 O3 和TiO2 /Ti(OH) 3 两个氧化还原电对的可逆电极过程 .其中TiO2 /Ti2 O3 电对对马来酸具有异相电催化还原活性 ,纳米TiO2 膜中的TiⅣ/TiⅢ 氧化还原电对作为媒质间接电还原马来酸为丁二酸 (butanediacid) ,反应机理为电化学偶联随后化学催化反应 (EC′)机理 .     

铁掺杂TiO_2微米带的制备及其光催化性能

采用模板法与溶胶-凝胶法结合,以脱脂棉为模板制备了掺杂Fe3+的TiO2微米带光催化材料.并利用红外光谱(FTIR)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)对掺杂不同比例Fe3+产物的表面形貌及晶型进行了表征.以甲基橙的脱色降解为模式反应,考察了样品的光催化性能.结果表明:以脱脂棉为模板在酸性条件下制备出了宽度5～8μm,厚度约100～500nm的TiO2带状体,此条件下生成的纳米TiO2晶体晶粒直径大小10～30nm,长度100～500nm,呈棒状.且得出当Fe3+掺杂量为0.04%时光催化效果最优,20min对甲基橙的催化效率为91%.     

TiO2/SiO2气凝胶微球的制备及其表征

以TiOSO4和硅溶胶为原料, 加入甲酰胺作为干燥控制化学添加剂, 采用W/O乳状液中的溶胶-凝胶法制备TiO2/SiO2凝胶微球, 通过正硅酸乙酯母液浸泡、溶剂交换、陈化和常压干燥技术制备TiO2/SiO2气凝胶微球, 采用光学显微镜、SEM、TEM和BET比表面及孔分布测定等手段对所得样品进行表征. 典型的气凝胶微球样品是由粒径15 nm左右, 粒度分布相当均匀的球状纳米粒子构成的轻质纳米多孔材料, 表观密度为177 kg•m-3, 比表面积372 m2•g-1, 平均孔径22.78 nm, 孔隙率高达92.0％, 微球的宏观粒径为50 m. 依据制备条件的变化, TiO2/SiO2气凝胶微球的宏观粒径可控在10～200 m之间, 表观密度为150～300 kg•m-3, 比表面积为300～400 m2•g-1, 平均孔径在18.71～22.78 nm之间变化.     

纳米Na_2SiF_6的电化学制备、表征与荧光性质

采用溶胶-凝胶法在Ti表面修饰一层纳米TiO2(nanoTiO2)膜,经X射线粉末衍射(XRD)和扫描电镜(SEM)表征,证明多孔TiO2膜的平均孔径为80 nm.以该多孔膜电极为模板,借助电化学沉积的方法制备了纳米Na2SiF6(nano Na2SiF6).经XRD和透射电镜(TEM)测试证实该Na2SiF6为均一的白锰钒型结构,平均粒径约为20 nm.初步研究了其荧光性质,发现在452.4 nm和285 nm处分别有强的荧光发射峰和激发峰.     

TiO2浓度对核-壳结构Ag/TiO2纳米复合粒子结构以及三阶非线性光学性质的影响

采用光还原方法制备了核-壳结构的Ag/TiO2纳米复合粒子, 通过TEM、UV-Vis光谱和XRD表征了不同TiO2浓度下Ag/TiO2纳米复合粒子的结构和光学性质. UV-Vis光谱证明了银颗粒的存在, 且复合粒子中的银粒径随着TiO2含量的增加而增加, 同时随着TiO2浓度的增加, 银的吸收峰出现明显的增强和展宽；从TEM照片 发现, Ag/TiO2纳米复合粒子是一种以Ag为核, 外面包覆一层TiO2的核-壳结构, TiO2浓度和Ag+浓度的增加, 使得复合粒子的银颗粒粒径增大. 用Z-扫描技术, 以锁模Ti:sapphire飞秒激光器发出的脉宽为130 fs激光做光源, 在790 nm波长的光作用下, 研究了0.5%(w)Ag+含量, 不同TiO2浓度的Ag/TiO2纳米复合粒子的非线性光学特性. 结果发现, 在790 nm激光作用下, 0.25%(w)TiO2样品膜有双光子吸收和自聚焦非线性折射现象; 而当TiO2浓度为0.70%(w)时, 样品膜的非线性吸收由反饱和吸收转变为饱和吸收.     

纳米晶粒TiO2多孔微球的合成与表征

 钛酸四丁酯经酸性水解得到TiO2溶胶，将溶胶与苯酚混合后加入到正庚烷分散介质中，再滴加甲醛水溶液，通过反相悬浮聚合和溶胶－凝胶过程制备了聚合物与TiO2的复合微球．对复合微球进行焙烧处理，使聚合物分解，从而得到由纳米TiO2晶粒组成的多孔微球．以示差扫描量热法、热重分析、X射线衍射、扫描电子显微镜和氮吸附等方法对TiO2多孔微球的物理性质进行了表征．结果表明，所得TiO2多孔微球主要由锐钛型TiO2纳米晶粒组成，晶粒尺寸为20～30nm；TiO2多孔微球的直径为200～500μm，比表面积为87．40m2／g，平均孔径为8．65nm，孔径的分布具有单分散特征．     

以TiO2多孔微球为载体的CuO/TiO2催化剂的制备、表征及CO氧化催化性能

利用高分子反相悬浮聚合技术结合溶胶-凝胶法制备了纳米TiO2晶粒组成的多孔微球. 以TiO2多孔微球为载体, 利用浸渍法制备了CuO/TiO2催化剂, 用示差扫描量热法、热重分析、X 射线衍射和X射线光电子能谱(XPS)对TiO2多孔微球和催化剂进行了表征, 并对其进行了CO催化氧化性能的评价. 结果表明, 于500 ℃焙烧的TiO2多孔微球基本为锐钛矿型结构, 其粒径为19.5 nm. XPS结果表明, 催化剂中载体和活性组分存在相互作用, Cu除了以Cu2+的形式存在外, 还以部分Cu+和Cu0的形式存在. CO催化氧化研究结果表明, 催化剂的催化活性与浸渍液的浓度和催化剂的焙烧温度有关. 用0.5 mol/L Cu(NO3)2·3H2O溶液浸渍得到的催化剂和于200 ℃焙烧得到的催化剂具有较好的催化活性.     

Influence of Pt nanocrystallinity on electrochromism of TiO2

The Pt nanocrystals as nanonetwork conductors improved electrochromic properties of TiO2 such as increased optical modulation and fast response time, compared to pure TiO2 as well as TiO2 incorporated by amorphous Pt nanophases. It is likely that an enhancement of cathodic electrochromism in TiO2-Pt is due to an improved injection or extraction of electron/proton caused by Pt nanocrystals.     

Ultrastable Au nanocatalyst supported on surface-modified TiO2 nanocrystals

The surfaces of TiO2 nanocrystals were modified with amorphous aluminum-oxide layers using a surface sol-gel process to control the interaction between supports and metal particles. Ultrastable Au nanocatalysts were prepared by the deposition of Au nanoparticles on the surface-modified TiO2 nanocrystals using a deposition-precipitation (DP) method. The TEM analysis showed that the Au nanoparticles on the surface-modified nanocrystal supports were highly stable with a sinter-resistant capability during high-temperature calcination. The HRTEM analysis revealed that the surface of the TiO2 nanocrystals was covered by an amorphous aluminum-oxide layer and the Au nanoparticles were primarily anchored to this amorphous layer. This amorphous aluminum-oxide layer played an extremely important role in the stabilization of the supported Au nanoparticles without affecting catalytic activities. The surface modification of nanocrystal supports highlights new opportunities in tailoring the stability and activity of supported nanocatalyst systems.     

A Raman Scattering Study of PbTiO3 and TiO2 Obtained by Sol-Gel

The mechanisms that give rise to the broadening and the shifts of the Raman peaks of titanium dioxide and lead titanate nanocrystals prepared by sol-gel are discussed. Phonon confinement and oxygen deficiency are competitive mechanisms in TiO2 obtained by different sol-gel preparations whereas pressure effects on the nanocrystals predominate in ferroelectric PbTiO3.     

Charge trapping and photoadsorption of O2 on dehydroxylated TiO2 nanocrystals--an electron paramagnetic resonance study.

The interaction of photogenerated charges with molecular oxygen was investigated on TiO2 nanocrystals by means of paramagnetic resonance (EPR) spectroscopy. Compared to photoactivation experiments in vacuum at P < 10(-6) mbar and T = 140 K, the presence of O2 enhances the concentration of persistently trapped electron and hole centres--by a factor of ten--due to the formation of adsorbed O2- species. The photoadsorption of oxygen was also tracked quantitatively by pressure measurements, and the number of trapped charges, hole centres and O2- was found to correspond to ten electron-hole pairs per TiO2 nanocrystal. Conversely, in experiments at P < 10(-6) mbar with one trapped electron-hole pair per particle, charge separation is not persistent and completely reversible with respect to temperature. Heating to 298 K causes the total annihilation of photogenerated and trapped charges.     

模板水热法纳米TiO2制备及光催化性能研究

以聚乙烯吡咯烷酮(PVP)为模板剂,钛酸四正丁酯(TBOT)为钛源,水热法制备纳米TiO2。采用XRD,SEM、TEM和UV-Vis DRS等测试手段对其形貌和结构进行表征。通过对甲基橙的光催化降解实验,探讨了焙烧温度、催化剂用量和溶液pH值对光催化性能的影响。结果表明,TiO2具有锐钛矿相,平均晶粒尺寸约为23.2 nm,TiO2颗粒呈片层状或由片层状堆积的疏松圆球形,经超声后即分散为八面体晶粒。550℃焙烧的样品,紫外光照3 h后,对甲基橙的降解率可达84.2%。相比普通水热法,采用模板剂法制得的TiO2吸收带发生红移,因而也具有较好的可见光催化活性。     

Single nanocrystals of anatase-type TiO2 prepared from layered titanate nanosheets: formation mechanism and characterization of surface properties

Anatase-type TiO2 single nanocrystals with boatlike, comblike, sheetlike, leaflike, quadrate, rhombic, and wirelike particle morphologies were prepared by hydrothermal treatment of a layered titanate nanosheet colloidal solution. The formation reactions and surface properties of the TiO2 nanocrystals were investigated using XRD, TEM, TG-DTA analyses, and measurements of BET specific surface area, photocatalytic activity, and ruthenium dye (N719) adsorption. The crystal morphology can be controlled by reaction temperature, pH value of reaction solution, and exfoliating agent. The titanate nanosheets were transformed to the TiO2 nanocrystals by two types of reactions. One is an in situ topotactic structural transformation reaction, and the other is a dissolution-deposition reaction on the surface. The anatase nanocrystals formed by the in situ topotactic structural transformation reaction retain the sheetlike particle morphology of the precursor, and they preferentially expose the (010) plane of anatase structure. The crystal surface of anatase nanocrystals prepared in this study showed higher photocatalytic activity and higher ruthenium dye adsorption capacity than did the Ishihara ST-01 sample, a standard anatase nanocrystal sample. The results indicated the (010) plane of the anatase structure has high photocatalytic activity and high ruthenium dye adsorption ability.     

Redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification with an inorganic barium hydroxide

The present paper describes the synthesis of the redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification reaction in an aqueous barium hydroxide solution. In our facile surface modification reactions, the surfaces of the TiO2 nanocrystals are coated by bimetallic TiOBa spices and saturated with BaOH terminal groups. The inherent characteristics such as morphology, size, crystallinity, and color of the nanocrystals remained almost unchanged after surface-treatment, but their dispersibility in organic media such as methanol and DMF were remarkably enhanced. It is ascribed that BaOH groups in the surface of the TiO2 nanocrystals prevented the formation of covalently bound agglomerates through Ti-O-Ti condensation reaction among the nanocrystals during the purification and water-elimination procedures.     

Fabrication of platy apatite nanocrystals loaded with TiO2 nanoparticles by two-step emulsion method and their photocatalytic activity

Nanometer-sized TiO(2) island structure on the platy hydroxyapatite nanocrystals (HAp) has been accomplished by two-step emulsion process. At the first step, platy HAp nanocrystals, of which size was in the range of 70-200 nm after heat-treatment at 1078 K for 1 h, were prepared using the W/O emulsion system. Before the second step, HAp nanocrystals were immersed in NaH(2)PO(4) solution for the formation of hydroxyl group on their surface. In the following, titanium tetraisopropoxide reacted with the hydroxyl group of HAp surface to form TiO(2) nanoparticles on the surface of HAp nanocrystals, which were dispersed in the micrometer-sized methanol droplets of polyethylene cetylether-cyclohexane mixture (methanol/oil emulsion). The resulting hydroxyapatite nanocrystals loaded with TiO(2) nanoparticles showed the high photocatalytic activity comparing to the commercial TiO(2) catalyst.     

UV induced local heating effects in TiO2 nanocrystals

When isolated TiO(2) nanocrystals are subjected to UV light at 77 K and pressures below 10(-6) mbar, trapping of photogenerated hole centers occurs on the surface of the nanocrystals and can be tracked by time-resolved electron paramagnetic resonance spectroscopy. Irrespective of the selected UV irradiance used, the maximum concentration of trapped charges was found to be constant for a given number of nanocrystals ( approximately 10(15)) and corresponds to one electron-hole pair per particle. On a time scale of seconds to minutes the dynamics for the trapping process depend on the number of photons with supra band gap energy. A local temperature rise of the TiO(2) nanocrystals was observed for irradiances above 1.55 mW cm(-2) (10(15) photons cm(-2) s(-1)). This is attributed to enhanced nonradiative recombination of photogenerated charge carriers via heat production and points to a substantial contribution of thermal chemistry in photocatalytic reaction cycles.