水化介孔氧化硅表面酸碱平衡常数的测定

采用自动电位酸碱滴定技术研究了水化介孔氧化硅的表面脱质子反应.基于悬浮液的酸碱滴定数据,用Gran图法计算得到了介孔氧化硅表面氢离子键位点浓度.利用FITEQL4.0软件,采用双电层恒电容模型计算得到了相应的表面酸碱平衡常数.结果表明,与无定形氧化硅不同,介孔氧化硅表面存在对应于双齿表面硅羟基≡Si2OH和单齿表面硅羟基≡SiOH的两个脱质子常数,分别为pKa1=6.78±0.15,pKa2=10.25±0.22.根据测定得出的介孔氧化硅表面脱质子常数,构建了不同pH条件下,介孔氧化硅表面优势组分分布图,并讨论了表面电容预赋值对氧化硅表面组分分布的影响.

Determination of Acid-Base Equilibrium Constants on Aqueous Mesoporous Silica Surfaces

We used the potentiometric titration technique to study the deprotonation reactions at aqueous mesoporous silica surfaces. The concentration of surface proton binding sites was obtained by the Gran plot method using the acid-base titration data. The relevant equilibrium constants of the surfaces in terms of the constant capacitance model (CCM) were determined based on the experimental results using the FITEQL 4.0 program. The results indicate that the surface deprotonation behavior of the mesoporous silica suspensions is significantly different from that of amorphous silica. This behavior can be described by two surface reactions with surface bidentate and monodentate deprotonation constants of pK_a1=6.78±0.15 and pK_a2=10.25±0.22, respectively. Using these deprotonation constants, we established a surface speciation diagram for mesoporous silica in aqueous suspensions as a function of pH and discussed the effect of surface capacitance on surface speciation.