铝掺杂酸性硅溶胶的制备及表征

Preparation and Characterization of Al-doped Acidic Silica Sol

以正硅酸盐甲酯(TMOS)、六水氯化铝(AlCl_3·6H_2O)为原料,稀盐酸为催化剂,采用酸催化溶胶–凝胶法制备了铝掺杂硅溶胶,利用透射电镜、Zeta电位、纳米粒度分布仪、黏度计、pH计等测试手段考察了酸浓度、反应时间、反应温度、铝元素掺杂量对硅溶胶粒子的形貌、粒径分布、分散性和稳定性等的影响规律。结果表明:在该反应体系中,H^+将TMOS中的–OR基团质子化,水分子中的–OH基团取代–OR基团,发生水解反应,水解产物在H^+催化下吸引SiOH、SiOR和铝水解产物发生缩聚反应形成铝掺杂硅溶胶粒子;随盐酸浓度增大、反应时间增大、反应温度提升,铝掺杂硅溶胶粒子呈现粒径变大且粒子形状不规则的趋势;当铝掺量过大时,体系中发生偏聚现象;当盐酸浓度为5 mmol/L,反应时间为0.5h,反应温度为25℃,铝元素掺杂量(摩尔比)为n(Al):n(Si)=0.04:1时,可以得到粒径为5～8nm、粒径分布均匀、分散性好、固相含量约为13%的铝掺杂酸性硅溶胶。

Al-doped silica sol was prepared by an acid-catalyzed sol-gel method with TMOS,AlCl3·6H2O and HCl as raw materials.The effects of acid concentrations,reaction time,reaction temperature and Al doping amount on the particle morphology,particle size distribution,dispersivity and stability of silica sol were characterized by transmission electron microscopy(TEM),particle size analysis,and viscosity measurement.The result shows that–OR groups of TMOS are protonated by H+and then replaced by–OH groups of H2O in the reaction system.TMOS hydrolysates react with SiOH,SiOR and Al(OH)4–via polycondensation,forming Al-doping acidic silica sol.Sol-particle increases and becomes irregular as the concentration of acid,reaction time and temperature increase.The segregation appears in the system at a great amount of Al doping.The Al-doped silica sol with a homogeneous distribution,a well-dispersivity and particle sizes of 5–8 nm,and solid-phase content of Al-doped silica sol of 13%can be obtained under the optimum condition,i.e.,the concentration of acid of 5 mmol/L,the reaction time of 0.5 h,the reaction temperature of 25℃,and the Al doping amount of n(Al):n(Si)=0.04:1(mole ratio).