【作者】 李雪；

【导师】 钱建华；

【作者基本信息】 东北大学 ， 材料物理与化学， 2019， 博士

【摘要】 锑掺杂二氧化锡(SbxSn1-xO2)导电粉包覆在TiO2基体表面可制备TiO2@SbxSn1-xO2浅色复合导电材料。TiO2@SbxSn1-xO2复合导电材料颜色较浅,可吸收紫外光,既具有优良的导电性能、又具有良好的耐候性及高温使用性能,可作为导电填料应用于制备各种颜色的导电高分子材料,如电磁屏蔽及抗静电材料、显示器的防辐射及抗静电涂层材料、气敏元件、红外吸收隔热材料和电极材料等。然而,由于导电壳层颗粒容易自身团聚,导致包覆层不均匀,使 TiO2@SbxSn1-xO2复合材料的导电性能较差;且TiO2@SbxSn1-xO2复合材料在高分子基体中的分散性较差,严重影响复合导电高分子材料中的导电性能,制约TiO2@SbxSn1-xO2的后续应用。针对上述问题,本文基于对基体和导电壳层的结构设计,采用沉淀法、溶胶-凝胶法和Pechini法制备了壳层颗粒大小均一、均匀包覆的TiO2@SbxSn1-xO2复合材料,并提出包覆机制。采用第一性原理计算(DFT)从原子角度分析Sb掺杂后复合材料导电性提升的原因。最后,以长链脂肪酸(油酸、硬脂酸)对复合材料的表面亲油性进行调变,改善其在高分子基体材料中的分散稳定性及其与有机聚合物之间的相容性。研究结果表明:采用SiO2对TiO2基体进行表面修饰,设计有利于导电层均匀包覆的基体表面。SiO2修饰后,基体表面电荷由正电荷变成负电荷,带有负电荷的基体表面更有利于吸引带有正电荷的Sn4+、Sb3+及其水解产物,使水解产物吸附于基体表面。另一方面,SiO2改性后颗粒表面羟基增多,为Sn4+、Sb3+及其水解产物的沉积提供更多的活性位点,使颗粒更加均匀地分布在基体表面,进而提升复合材料的导电性能。且SiO2与SbxSn1-xO2产生紫外吸收协同效应,使TiO2@SiO2-SbxSn1-xO2具有更好的紫外吸收性能,有效提高复合导电材料的耐候性。采用溶胶-凝胶法调控壳层SbxSn1-xO2结构的包覆均匀性,成功制备了TiO2@SbxSn1-xO2复合导电材料。乙酰丙酮分子中的烯醇基脱去质子,并与金属离子螯合配位形成环状结构,抑制Sn4+和Sb3+的快速水解,水解速率的减慢有利于形成颗粒粒径均一且均匀稳定的导电层结构。所制备的TiO2@SbxSn1-xO2复合导电材料具有良好的导电性能,最低体积电阻率可达4.50 Ω·cm。采用Pechini法调控SbxSn1-xO2壳层结构制备复合导电材料,有机羧酸与Sn4+、Sb3+离子反应生成络合物,能够有效减缓Sn4+、Sb3+离子的水解速率,避免因水解过快而产生沉淀,从而减少壳层颗粒团聚。此外,有机羧酸和乙二醇形成的聚酯具有空间位阻效应,能够降低Sn4+和Sb3+水解产物颗粒的表面能,促使水解产物生成颗粒大小均一、包覆层均匀的导电层结构,进而提高材料的导电性能。研究发现:有机羧酸中的羧基数量越多,壳层水解产物颗粒越大,颗粒间接触电阻增大,复合材料的导电性下降。可能归因于,羧基数量增多,其与金属离子的络合物稳定性增强,水解速度减慢,导致水解产物成核速率降低,生成的水解产物颗粒较大。乳酸(分子中含有一个羧基)为络合剂时,生成颗粒粒径较小,平均粒径为5.8 nm,复合材料的导电性得到进一步提高,电阻率为1.69 Ω·cm。在对SbxSn1-xO2壳层结构调控过程中,Sn4+和Sb3+离子与乙醇分子的乙氧基结合,再与络合剂反应生成络合物。络合物主要以氢键作用吸附在TiO2表面,并伴随着Sn4+、Sb3+离子的水解反应。络合物及其水解产物分子中的一部分羟基和乙氧基与TiO2基体表面羟基发生缩聚反应,另一部分发生自聚,使颗粒逐渐长大,包覆在TiO2表面。在焙烧过程中,Sb3+逐渐氧化成Sb5+掺杂到SnO2晶格中,形成具有n型半导体结构的SbxSn1-xO2壳层。DFT计算结果表明:与原TiO2体系相比,在TiO2@SnO2体系中,价带顶和导带底分别出现了 Sn5p、Sn5s电子态,它们与O2p电子态之间杂化,使价带和导带均向低能方向移动,且导带移动的距离更大,导致体系的禁带宽度减小。TiO2@Sb0.25Sn0.75O2体系中,Sb5s电子态能够占据原来最低未被填充电子的能带部分,并在导带底产生浅施主能级,使价带电子更容易激发到导带,材料的导电性增强。同时,费米能级进入导带,表现出n型半导体的特征。基于对复合导电材料表面亲油性的调变,采用油酸和硬脂酸对复合材料进行表面改性。利用有机酸中的羧基与复合材料表面羟基发生酯化反应,使有机长链分子接枝到复合材料颗粒表面,使材料表面呈现出较好的疏水性。酯化反应使复合材料表面羟基减少,导致粒子间氢键效应减弱,使粉体颗粒之间不易团聚。油酸和硬脂酸改性后,复合材料水的接触角测量值从原来的0°分别提高到119.05°和129.20°,表明改性后的复合导电材料亲水性发生根本性调变,得到具有良好亲油性的导电复合材料。更多还原

【Abstract】 TiO2@SbxSn1-xO2 light-colored conductive composite can be prepared by coating SbxSn1-xO2 conductive powder on TiO2 substrate surface.TiO2@SbxSn1-xO2 conductive composite possess a shallow color,ultraviolet absorption,good conductivity,good weather resistance and high temperature performance,which can be used as conductive filler to prepare conductive polymer materials with various colors,such as electromagnetic shielding and antistatic materials,radiation and antistatic coating materials of display,gas sensitive element,infrared absorbing and heat insulation materials and electrode materials.However,the agglomeration of the conductive shell particles often leads to uneven coating layer in the preparation process,which resulted in a poor electrical conductivity of TiO2@Sb,Sn1-xO2.In addition,the poor dispersility of TiO2@SbxSn1-xO2 in polymer matrix seriously also affects the conductivity of conductive polymer composite,which restricts the subsequent application of Tio2@SbxSn1-xO2 composite.Considering the problems mentioned above,TiO2@SbxSn1-xO2 composite with even coating and uniform size of shell particles were prepared by precipitation method,sol-gel method and Pechini method based on the structural design of matrix and conductive shell in this study,and the coating mechanism was proposed.The first principle calculation(DFT)was used to analyze the reason of the conductivity improvement of the composite doped by Sb from the atomic perspective.Finally,long-chain fatty acids(oleic acid and stearic acid)were used to modify the surface lipophilic properties of the composite to improve its dispersion stability and compatibility with organic polymers.The detailed experimental results are as follows:A modified TiO2 substrate with SiO2 was designed to facilitate the uniform coating of conductive layer on the substrate surface.After modification with SiO2,the surface charge of the substrate changed from positive to negative,which was more favorable to adsorb Sn4+,Sb3+and their hydrolyzed products.On the other hand,the surface hydroxyl of the particles could be increased after SiO2 modification,thus providing more active sites for the deposition of Sn4+,Sb3+ and their hydrolyzed products.Accordingly,the electrical conductivity of the composite was improved due to the more uniform distribution of the coating layer.Moreover,owing to the synergistic effect of the ultraviolet absorption of SiO2 and SbxSn1-xO2,TiO2@SiO2-SbxSn1-xO2 was found to represent a better ultraviolet absorption performance,which effectively improved the weather resistance of the conductive composite.TiO2@SbxSn1-xO conductive composite was successfully prepared by controlling the coating uniformity of SbxSn1-xO2 shell structure using sol-gel method.The deprotonation of enol group of the acetylacetone formed a coordinative ring structure by chelating with metal ions,which was effective to inhibit the rapid hydrolysis of Sn4+and Sb3+.The reduction of hydrolysis rate was also beneficial to the formation of a uniform and stable conductive layer structure.The as-prepared TiO2@SbxSn1-xO2 conductive composite exhibited a better electric conductivity,in which a minimum volume resistivity of 4.50Ω·cm was achieved.In the Pechini preparation process,the hydrolysis rate of Sn4+and Sb3+ions could be slowed down by the coordination of these ions with organic carboxylic acid,which can effectively avoid the rapid precipitation and agglomeration of shell particles.In addition,the steric hindrance effect of polyester formed by organic carboxylic acid and ethylene glycol could reduce the surface energy of Sn4+ and Sb3+ hydrolyzed product particles,which could promote the formation of an even conductive layer with a uniform particle size.Therefore,the conductivity of the composite could also be improved in accord.It was found that the particles of hydrolyzed products were increased with the increase of the number of carboxyl groups in organic carboxylic acids,and the electrical conductivity of composites decreased with the increase of the contact resistance between the larger particles.It may be attributed to the increased number of carboxyl groups,thereby leading to the enhanced stability of their complexes with metal ions.It is assumed that the strong stability of the complex could slow down the rate of hydrolysis and decrease of nucleation rate of hydrolyzed products,therefore resulting in the hydrolytic product with larger particles.When using lactic acid(contains one carboxyl group)as the coordinating agent,the electrical conductivity of the composite further improved the resistivity to 1.69 Ω·cm with a smaller particle size(average particle size of 5.8 nm).In the regulating process of Sbx3n1-xO2 shell,Sn4+ and Sb3+ ions bind with ethoxy group of ethanol molecule,and react with coordinating agent to form the corresponding complex.The complex adsorbed on the surface of TiO2 by hydrogen bonding,accompanied with the hydrolysis of Sn4+ and Sb3+ ions.Subsequently,the compounds formed by the condensation of hydroxyl and ethoxy groups with the hydroxyl group on the surface of the Ti02 substrate,and the self-polymerization of the rest functional groups make the particles grow up gradually and coating on the surface of TiO2.In the calcination process,Sb3+was gradually oxidized into Sb5+and doped into SnO2 lattice,forming SbxSn1-xO2 shell with n-type semiconductor.DFT calculation results showed that Sn5p and Sn5s electronic states appear at the top of valence band and bottom of conduction band in the TiO2@SnO2 system as compared with the original TiO2 system.The hybridization between Sn5p(or Sn5s)and O2p electronic states resulted in the movement of the valence band and conduction band to low energy direction,while the conduction band moved with a larger distance,thus leading to a decrease of the forbidden band width of the system.In TiO2@Sb0.25Sn0.75O2 system,the Sb5s electron states filled the original non-occupied state of the lowest energy band,and generated shallow donor level at the bottom of the conduction band.The valence electrons were easier excited to the conduction band due to the donor level,which increased the conductivity of the composite.Meanwhile,the Fermi energy level entered the conduction band and the composite exhibited the characteristics of n-type semiconductor.Based on the modification of the surface lipophilicility,oleic acid and stearic acid were used to modify the surface of the conductive composite.Long chain molecules were grafted onto the surface of composite particles by the esterification of carboxyl groups with organic acids and hydroxyl groups on the surface of composite,resulting in a better surface hydrophobicity.The esterification reaction reduced the number of the hydroxyl groups on the surface of the composite,which made it difficult for the particles to re-agglomeration owing to the weakened hydrogen bond effect between particles.After the modification with oleic acid and stearic acid,the measured water contact angle of the composite increased from 0° to 119.05° and 129.20° respectively.The results indicated that the hydrophilicity of the modified conductive composite was fundamentally changed,whereas the conductive composite with good lipophilic surface was obtained.更多还原