| 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 4.50?·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 ?·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. |
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