【作者】 刘晔；

【导师】 戴长虹；

【作者基本信息】 青岛理工大学 ， 市政工程， 2009， 硕士

【摘要】 近年来,水体污染已成为人类社会面临和亟需解决的重大课题。在众多水处理技术中,光催化氧化法以其环保、高效、节能而越来越受到人们的重视。纳米尺度的TiO₂被认为是一种极具前途的光催化剂,但由于其带隙较宽、光生载流子的复合率高等缺点而限制了它的实际应用。因此,制备和研究新型的高活性光催化剂是很有必要的。钒酸盐是一类极具潜力的光催化剂,已报导的如BiVO₄、InVO₄、Ag₃VO₄等都具有很窄的带隙宽度,从而能够更充分地利用太阳能光催化降解污染物。本文首先以硝酸铋（Bi（NO₃）₃·5H₂O）和偏钒酸铵（NH₄VO₃）为原料,通过氨水沉淀获得BiVO₄先驱体;然后采用低温熔盐法,在先驱体与熔盐（复合熔盐46wt%NaNO₃+54wt%LiNO₃或LiNO₃熔盐）比例为1:8的条件下,分别于不同温度下煅烧8h合成出了形貌各异、大小不同、结晶度良好的BiVO₄粉体;以硝酸钇（Y（NO₃）₃·6H₂O）和偏钒酸铵（NHO4VO₃）为原料,通过氨水沉淀获得YVO₄先驱体:再采用低温熔盐法,在先驱体与熔盐比例为1:8的条件下,分别于不同温度下煅烧8h合成出了具有良好结晶度的球状YVO₄纳米粉体。然后,通过X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）和紫外-可见分光光谱（UV-Vis）等测试仪器对样品进行表征;最后,以YVO₄纳米粉体为光催化剂,以罗丹明B为对象模拟染料废水进行光催化降解实验,采用正交实验和单因素实验的方法,考察了水溶液的pH值、光催化剂的粒径、光催化剂的浓度对水溶液中罗丹明B降解率的影响,并初步探讨了YVO₄的光催化机理,研究结果如下:（1）煅烧温度对BiVO₄形貌尺寸、相结构和光吸收均具有明显的影响。XRD图谱显示:200℃下合成的BiVO₄为四方相,270℃及以上温度合成的BiVO₄皆为单斜相;SEM照片表明:四方相BiVO₄粒径大于单斜相的BiVO₄粒径;UV-Vis光谱分析表明:单斜相的BiVO₄比四方相BiVO₄和TiO₂具有更广的可见光谱响应。（2）熔盐的加入和煅烧温度对YVO₄结晶度、粒径和光吸收均具有显著的影响。XRD图谱显示:熔盐的加入明显改善了产物YVO₄的结晶度;TEM照片表明YVO₄的粒径则随煅烧温度的提高而增大;UV-Vis光谱分析表明:粒径10nm的YVO₄粉体吸光强度最强。（3）采用正交实验法,研究了YVO₄光催化剂的粒径、光催化剂的浓度和水溶液的pH值对YVO₄光催化降解罗丹明B的影响,得到了实验因素对罗丹明B降解率影响的主次顺序为:水溶液的pH值＞光催化剂的浓度＞光催化剂的粒径。（4）在正交实验的基础上,采用单因素实验的方法,进一步研究水溶液的pH值和光催化剂的浓度对YVO₄光催化降解罗丹明B的影响,结果表明,最佳条件为:pH值为4、光催化剂浓度为1g/L、10nm的YVO₄纳米粉体。通过一元线性回归,研究了不同条件下光催化降解速率的关系。（5）分析推测YVO₄光催化过程是光敏化和光催化联合作用的结果,其中光敏化起着主导作用;当两者达到平衡后,光催化效果达到最佳值。更多还原

【Abstract】 In recent years,water pollution has become an urgent and serious problem for human society.Among the water treatment technologies,the photocatalytic oxidation has drawn widely attention for its environment-friendly,high efficient and energy saving.TiO₂ is considered as a promising photocatalyst.However,its large band gap and fast recombination rate of photogenerated charge hinder its application.Therefore, it is necessary to develop new photocatalyst with high activity.The vanadate is a kind of photocatalyst with great potential,it has been reported that BiVO₄,InVO₄,Ag₃VO₄ have a very narrow band gap,enabling the lull utilization of solar to degrade pollutants.In this thesis,Bi（NO₃）₃·5H₂O and NH₄VO₃ were used as raw materials to obtain BiVO₄ precursor by adding ammonia solution.And then,well-crystallized BiVO₄ powders with different morphologies and particle sizes were synthesized via a low temperature molten salt method at different temperatures for 8h in a weight ratio of 1:8 of the precursor to the molten salt;Starting from Y（NO₃）₃·6H₂O and NH₄VO₃,YVO₄ precursor was formed by adding ammonia solution as a co-precipitant.Then, well-crystallized YVO₄ nanoparticles were synthesized via a low temperature molten salt method at different temperatures for 8h in a weight ratio of 1:8 of the precursor to the molten salt.The samples were characterized with X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,UV-visible absorption spectra（UV-Vis） respectively.Finally,the photocatalytic degradation was carried out by using YVO₄ nanoparticles as photocatalyst and Rhodamine B as dye wastewater.The effects of the particle size,the pH value and the dosage of the YVO₄ photocatalyst on photodegradation were studied.In addition,the YVO₄ photocatalytic mechanism was also proposed,Results were as following:（1） The calcining temperature had a significant impact on morphology,particle size,crystalline phases and optical absorption of BiVO₄ particles.XRD patterns showed that:At 200℃,a pure tetragonal-phase BiVO₄ could be obtained,with the increasing of the calcining temperature from 270℃to 410℃,the tetragonal phase BiVO₄ gradually transformed to the monoclinic phase.SEM images revealed that: tetragonal-phase BiVO₄ particles were bigger than monoclinic-phase BiVO₄;The UV-Vis absorption spectra presented that:compared with tetragonal-phase BiVO₄ and TiO₂,monoclinic-phase BiVO₄ had a broader visible-light spectral response.（2） The molten salt and calcining temperature had great effects on the crystallinity, particle size and optical absorption of YVO₄ nanoparticles.XRD patterns showed that: the addition of the molten salt obviously improved the crystallization of YVO4;TEM images indicated that YVO₄ particles remarkably growed up with the increase of the calcining temperature;Their UV-Vis absorption spectra revealed that YVO₄ nanoparticles with 10nm possess the strongest UV absorption.（3） By adopting the orthogonal experimental method,the effects of the particle size, the pH value and the dosage of the YVO₄ photocatalyst on rhodamine B’s photodegradation were studied.The order of the factors which influence the degradation was as follows:the pH value＞the dosage of photocatalyst＞the particle size.（4） For more detail,on the basis of the orthogonal experiment,the experiment of single-factor was carried out to fine the best conditions for the photodegradation of rhodamine B were:pH value for 4,the dosage of photocatalyst for 1g/L,YVO₄ nanoparticle size for 10nm.By using the unitary linear regression method,we could find out the relation of the degradation rates under different conditions.（5） It was predicted that the process of YVO₄ photodegradation was under the photocatalysis and photosensitization’s association action.Moreover,the photosensitization played a major role.When the two factors reached a balance,the maximum rate was presented.更多还原