凝胶-溶胶法制备纳米二氧化钛的pH控制

利用凝胶-溶胶法制备纳米二氧化钛，采用透射电镜（TEM）和X射线衍射（XRD）对产物进行了表征，考察了体系pH变化和电解质（高氯酸钠）对它的影响，以及初始pH（pH0）对二氧化钛形貌及体系组成的影响。结果表明，产物为锐钛矿型二氧化钛，平均粒径5～15nm；体系pH变化是由于OH^-（或H^＋）在氢氧化钛或二氧化钛表面的吸附和脱附，添加0．1mol／L高氯酸钠能促进OH^-（或H^＋）的吸附和脱附过程。pH0显著影响二氧化钛形貌和体系组成，pH0=1．0时为球状晶体，pH0=9．4时为较规则的立方晶体，至pH0=11．5变为椭球形。pH0〉9．4时，二氧化钛物质的量分数显著下降，至pH0=12．0时无二氧化钛生成，因此应控制pH0〈9．4。

pH control on preparation of nano - TiO2 by gel - sol process

Nano-TiO2 was prepared by gel-sol method and were characterized by transmission electron microscopy(TEM) and X-ray diffraction patterns(XRD).The pH change and the effects of electrolyte(NaClO4) on it were studied.The effects of initial pH value(pH0) on the shapes of TiO2 and the system composition were also investigated.The results showed that the synthesized products were anatase TiO2 with the average diameter of 5-15 nm.The change in pH value was mainly governed by the adsorption and desorption process of H and OH-on the surface of Ti(OH)4 or TiO2.This process can be enhanced by adding 0.1 mol/L NaClO4.The shapes of TiO2 and the system composition were greatly influenced by different pH0.The spheroidal crystals of TiO2 at pH0=1.0 became cuboidal at pH0=9.4 and ellipsoidal at pH0=11.5.The fraction of a mount of substance of TiO2 decreased significantly at pH0>9.4 and no TiO2 was produced at pH0=12.0,so pH0 below 9.4 is the optimum parameter for TiO2 preparation in our experiments.