【作者】 石建稳；

【导师】 郑经堂；

【作者基本信息】 中国石油大学 ， 环境化工， 2007， 博士

【摘要】 半导体TiO₂可有效降解水中难生物降解的有机污染物。本文采用溶胶-凝胶法,制备了纯TiO₂、过渡金属离子单掺杂TiO₂、稀土金属离子单掺杂TiO₂以及过渡金属离子与稀土金属离子共掺杂TiO₂,并以ACF为载体,制备了负载有TiO₂薄膜的复合光催化材料。以染料分子为模拟污染物考察了它们的光催化性能。以钛酸丁酯为前驱体,冰醋酸为水解抑制剂,乙醇为溶剂,制备TiO₂纳米粒子时,制备工艺参数对其光催化活性影响较大,其影响主次为煅烧温度、冰醋酸加入量、蒸馏水加入量、无水乙醇用量。煅烧温度对纳米TiO₂晶型、晶粒尺寸、光吸收特性等产生影响,从而影响TiO₂的光催化性能。过渡金属离子Cr、Fe的掺杂可抑制TiO₂晶粒的生长,引起TiO₂晶格的畸变和和晶胞体积的改变,拓宽TiO₂的光吸收范围,适量Cr、Fe的掺杂可提高TiO₂的光催化活性,最佳掺杂量均为0.05%。稀土金属离子的掺杂可抑制TiO₂晶粒的生长,阻碍TiO₂相变的发生,引起TiO₂晶格的畸变和膨胀,以及吸收带边的红移,适量的掺杂可提高TiO₂的光催化性能,Y、Ce、Sm、Eu的最佳掺杂量依次为0.1%、0.05%、0.1%、0.1%。煅烧温度可影响催化剂的晶粒尺寸、晶型、光吸收特性、晶格畸变和膨胀程度以及掺杂离子进入TiO₂晶格的能力,从而对掺杂纳米TiO₂的光催化性能产生影响。本实验的最佳煅烧温度为600℃。Sm掺杂纳米TiO₂在可见光下具有很好的光催化活性。在Fe、Ho共掺杂和V、La共掺杂体系中,过渡金属离子掺杂促进TiO₂晶型的转变,稀土金属离子掺杂则抑制晶型的转变,共掺杂时,两种作用相互中和,且抑制作用占优势。与单掺杂相比,共掺杂由于掺入的两种离子产生不同的作用,过渡金属离子掺杂拓宽TiO₂光吸收范围,稀土金属离子掺杂抑制光生电子-空穴对的复合,二者协同作用可进一步提高了TiO₂的光催化活性。Fe、Ho共掺杂提高了纳米TiO₂表面羟基基团的量,V、La共掺杂降低了表面羟基基团的量,导致Fe、Ho共掺杂TiO₂的光催化性能更高。共掺杂光催化性能不仅受各自掺杂量的影响,还受两种掺杂离子浓度配比的影响,Fe、Ho共掺杂体系,最佳掺杂离子浓度配比为0.05%的Fe和0.5%的Ho。V、La共掺杂体系,最佳掺杂离子浓度配比为0.05%的V和0.05%的La。煅烧温度对共掺杂TiO₂光催化性能影响较大,最佳煅烧温度为600℃。两种共掺杂TiO₂在可见光下具有光催化降解甲基橙的能力,且光催化活性较纯TiO₂有较大提高,这与掺杂使其粒径的减小、电子-空穴对复合的抑制、对可见光吸收的增强等因素有关。负载体系中,TiO₂以薄膜的形式包覆在ACF的表面,在ACF条带状沟槽处的薄膜煅烧时容易开裂,裂口处是负载体系结合性的薄弱环节。煅烧温度对ACF表面TiO₂的负载量和薄膜的最终结构形态起着十分重要的影响。负载样品的微孔分布集中,主要为2 nm以下的孔,并在0.82 nm和1.17 nm处呈强峰分布。在紫外光下,由于吸附和光催化的双重作用,可使有机污染物快速降解。负载体系由于自身孔结构的因素,可对目标分子的光催化降解性能产生影响,目标污染物的分子尺寸与负载体系孔径相匹配时,可被迅速地吸附进入材料的微孔内部,逐渐建立分子脱附与光催化降解反应的动态平衡。目标污染物的分子尺寸大于负载体系孔径时,则会产生孔屏蔽效应,负载体系不能对其产生有效捕捉,影响其光催化降解性能。更多还原

【Abstract】 Semiconductor TiO₂ can degrade organic pollutants in water efficiently, which is difficult to be degraded by biologic methods. In the current work, pure, transition metal ions single-doped, rare earth metal ions single-doped, transition metal ions and rare earth metal ions co-doped TiO₂ were prepared by sol-gel method. And activated carbon fibers （ACF） as the support for TiO₂ loading, TiO₂-loaded ACF （TiO₂/ACF） samples were prepared, also. The dye molecules were chosen as the model to evaluate the photacatalytic activity of all samples.The photocatalytic activity of samples was influenced greatly by processing parameter using tetra-n-butyl titanate as the precursor, acetic acid as the hydrolyzed inhibitor and ethanol as solvent. The influence factors from primary to secondary were calcined temperature, adding quantity of acetic acid, distilled water and ethanol. Calcined temperature could influence phase transformation, crystal size, the property of light absorption of TiO₂, and then influence the photocatalytic activity of TiO₂.Transition metal ions, Cr and Fe single-doping restrained the crystal size increase, led to distortion and change of crystal volume, and broaden light absorption range of TiO₂. The photocatalytic activity of TiO₂ was improved by doping with appropriate content Cr or Fe. The optimal doped molar fraction of two kinds of transition metal ions both were 0.05 percent. Rare earth metal ions doping restrained the crystal size increase, prevented phase transformation, led to distortion and expansion of crystal lattice and begot absorption profile red-shift of TiO₂. The photocatalytic activity of TiO₂ was improved by doping with appropriate content rare earth metal ions. The optimal doped molar fractions of Y, Ce, Sm and Eu were 0.1, 0.05, 0.1 and 0.1 percent in turns. Calcined temperature could influence crystal size, phase transformation, light absorption property, distortion and expansion degree of crystal lattice and the ability of doped ions entering into lattice TiO₂, and then influenced the photocatalytic activity of TiO₂. The optimal calcined temperature was 600℃in our experiment. Sm-doped TiO₂ was provided with good photocatalytic activity under visible light irradiation.In the systems of Fe, Ho co-doped and V, La co-doped TiO₂, transition metal ions doping promoted phase transformation, however rare earth metal ions doping restrained it. Two kinds of function counteracted and restrained function got the run upon promoted function when two kinds of ions were co-doped into TiO₂. Compare to single-doped TiO₂, photocatalytic activity of TiO₂ could be improved further by co-doping. This was ascribed to the fact that there was a cooperative action in the two doped elements. Transition metal ions doping broaden the absorption profile, rare earth metal ions doping retards the recombination of photo-generated electrons and holes. The photacatalytic activity of Fe and Ho co-doped TiO₂ was superior to V and La co-doped TiO₂. This was attributed to that hydroxyl group’s quantity on the surface of Fe and Ho co-doped TiO₂ was more than that of V and La co-doped TiO₂. The photacatalytic activity of co-doped TiO₂ was influenced not only doped concentration of two doped ions, but also their concentration ratio. The optimal concentration ratios were 0.05 percent Fe and 0.5 percent Ho in Fe and Ho co-doped system, and 0.05 percent V and 0.05 percent La in V and La co-doped system. The photocatalytic activity of co-doped TiO₂ could be influenced greatly by calcined temperature. The optimal calcined temperature was 600℃. Two kinds of co-doped TiO₂ could photodegradate methyl orange under visible light irradiation, furthermore, their photacatalytic activity were superior to pure TiO₂, which was related to decrease of crystal size, recombination retardance of photo-generated electrons and holes and enhancement of visible light absorption because of doping.In immobilization system, TiO₂ film covered on the surface of ACF. TiO₂ film located groove in ACF easy to craze and the crack was the combination weakness of support system. Calcined temperature played an important influence on supported quantity of TiO₂ and finial structure and morphology of film. The diameter of immobilized samples was mainly below 2 nm and had two peaks at 0.82 nm and 1.17 nm. Organic pollutants in water could be degraded fleetly because of the dual function of adsorption and photocatalysis. Pore structure of immobilized samples influenced the photocatalytic activity. When molecular size of pollutants matched with the pore size of immobilized samples, pollutants could be absorbed into pores of immobilized samples, and then a dynamic balance of desorption and photocatalytic degraded reaction would be established. When molecular size of pollutants was larger than the pore size of immobilized samples, pollutants couldn’t be catch effectively by immobilization system because of pore screening. So the photocatalytic activity of immobilization system was influenced.更多还原