【作者】 刘鹏；

【导师】 胡艳宏；

【作者基本信息】 内蒙古科技大学 ， 材料与化工， 2022， 硕士

【摘要】 碳酸铈晶体的形貌、尺寸、分散性等物理化学性质决定了其在不同生产中的应用领域。因此本课题组以碳酸铈晶体为研究对象,前期实验中发现模板剂能够调控特殊形貌的碳酸铈晶体,但模板剂调控碳酸铈生长过程中的作用过程尚不明确。本论文以Ce（NO₃）₃为铈源,十二烷基苯磺酸钠（SDBS）,十二烷基磺酸钠（SDS）为模板剂,碳酸氢铵（NH₄HCO₃）为沉淀剂,采用液相沉淀法,制备具有六棱片状形貌的碳酸铈晶体。并利用电子扫描显微镜（SEM）、X射线衍射仪（XRD）、红外光谱分析（FTIR）等表征手段对制备的碳酸铈的形貌、物相、晶体结构等进行物理表征。同时采用分子动力学,密度泛函从头算理论,通过建立液相体系模型,吸附模型研究模板剂调控碳酸铈晶体生长机理。计算模拟与实验相辅相成,更加深入了解模板剂调控特殊形貌碳酸铈晶体的生长机理。主要研究结果如下:最佳碳酸铈晶体制备条件:SDBS浓度0.9g/L、陈化时间4h、Ce³⁺浓度0.05M、R值3.3:1;SDS浓度1.2g/L、陈化时间4h、Ce³⁺浓度0.05M、R值3.3:1。通过SEM、XRD、FTIR对添加SDBS,SDS为模板剂制备的碳酸铈晶体进行物理表征,表明SDBS,SDS对碳酸铈晶体具有明显的调控作用,并且各个晶面具有不同程度的调控作用,SDBS,SDS主要调控晶面（010）、（111）、（101）的生长速率,且SDBS调控制备碳酸铈晶体粒度小,结晶度更好。诱导形核阶段通过对SDBS,SDS分子结构的优化计算,找出了分子最优结构。构建液相反应模型,未加入沉淀剂,SDBS,SDS中的SO₃^2-与Ce³⁺结合,形成镧系磺酸盐络合物,为碳酸铈晶体生长提供形核位点。随着沉淀剂NH₄HCO₃的加入,CO₃^2-与Ce³⁺结合能力大于SO₃^2-与Ce³⁺结合能力,碳酸铈晶体开始在络合位点形核生长。生长阶段通过对晶面吸附能、COHP、ICOHP的分析,对比SDBS,SDS在碳酸铈晶体各晶面的吸附情况。寻找出最佳吸附晶面,SDBS,SDS在（010）晶面吸附能力强,即（010）晶面的生长受到的阻碍最大。在平衡状态下（010）晶面出现的概率最大,最终将出现围绕（010）晶面生长的六棱片状晶体结构。并通过采用从头算分子动力学模拟的方法在原子尺度下,模拟铈盐体系SDBS,SDS的添加对碳酸铈晶体生长的影响。并发现在未添加SDBS,SDS时,模拟结果为无规则的晶体形貌,在添加SDBS,SDS后,由于模板剂中磺酸基团的调控作用,使得模拟结果为六棱片状结构的晶体形貌。而SDS比SDBS少一个苯环,SDBS中苯环的极性作用,晶面吸附能、ICOHP、COHP值更稳定,SDS疏水链结构较短,空间位阻较小,不能有效阻止碳酸铈颗粒团聚,形成的产物有较明显团聚。SDS对于碳酸铈晶体调控能力较SDBS差。更多还原

【Abstract】 The physical and chemical properties of cerium carbonate crystal,such as morphology,size and dispersion,determine its application in different production fields.Therefore,the research group took cerium carbonate crystal as the research object.In the previous experiments,it was found that the template can regulate the cerium carbonate crystal with special morphology,but the role of the template in regulating the growth of cerium carbonate is not clear.In this paper,Ce（NO₃）₃was used as cerium source,sodium dodecylbenzene sulfonate（SDBS）,sodium dodecyl sulfonate（SDS）as template,ammonium bicarbonate（NH₄HCO₃）as precipitant,and cerium carbonate crystals with hexagonal lamellar morphology were prepared by liquid phase precipitation method.The morphology,phase and crystal structure of the prepared cerium carbonate were characterized by SEM,XRD and FTIR.At the same time,molecular dynamics and density functional ab initio theory were used to study the growth mechanism of cerium carbonate crystal regulated by template by establishing a liquid phase system model and an adsorption model.Numerical simulation and experiment complement each other to better understand the growth mechanism of cerium carbonate crystal with special morphology regulated by template.The main results are as follows:The optimum preparation conditions of cerium carbonate crystal:SDBS concentration0.9g/L,aging time 4h,Ce³⁺concentration 0.05M,R value 3.3:1;SDS concentration 1.2g/L,aging time 4h,Ce³⁺concentration 0.05M,R value 3.3:1.The physical characterization of cerium carbonate crystal prepared by adding SDBS and SDS as templates by SEM,XRD and FTIR shows that SDBS and SDS have obvious regulation effect on cerium carbonate crystal,and each crystal surface has different degrees of regulation effect.SDBS and SDS mainly regulate the growth rate of crystal surface（010）,（111）and（101）,and the particle size of cerium carbonate crystal prepared by SDBS regulation is small and the crystallinity is better.In the induced nucleation stage,the optimal molecular structure of SDBS and SDS was found by optimizing the molecular structure.A liquid-phase reaction model was established.SO₃^2-in SDBS and SDS combined with Ce³⁺to form lanthanide sulfonate complex,which provided nucleation sites for cerium carbonate crystal growth.With the addition of precipitant NH₄HCO₃,the binding ability of CO₃^2-to Ce³⁺was greater than that of SO₃^2-to Ce³⁺,and cerium carbonate crystals began to nucleate and grow at the complex sites.At the growth stage,the adsorption of SDBS and SDS on each crystal surface of cerium carbonate crystal was compared through the analysis of crystal surface adsorption energy,COHP and ICOHP.The best adsorption crystal surface was found.SDBS and SDS had strong adsorption capacity on（010）crystal surface,that is,the growth of（010）crystal surface was hindered the most.In the equilibrium state,the（010）crystal plane has the highest probability of occurrence,and finally there will be a hexagonal sheet crystal structure growing around the（010）crystal plane.At the atomic scale,ab initio molecular dynamics simulation was used to simulate the effect of the addition of SDBS and SDS in cerium salt system on the growth of cerium carbonate crystals.It was found that the simulation result was irregular crystal morphology when SDBS and SDS were not added.After SDBS and SDS were added,the simulation result was hexagonal sheet crystal morphology due to the regulation of sulfonic acid groups in the template.However,SDS has one benzene ring less than SDBS,the polarity of benzene ring in SDBS,the adsorption energy of crystal surface,ICOHP and COHP values are more stable,the hydrophobic chain structure of SDS is shorter and the steric hindrance is smaller,which can not effectively prevent the agglomeration of cerium carbonate particles,and the formed products have obvious agglomeration.SDS is inferior to SDBS in controlling cerium carbonate crystal.更多还原