碳化合成纳米SiO2颗粒比表面积的控制机理

以Na2SiO3为前驱物，研究了碳化合成纳米SiO2颗粒比表面积的控制机理. 正交实验结果表明，影响其比表面积的次序为Na2SiO3浓度>PEG6000添加量>反应温度>CO2/N2混合气流量. 当反应温度80℃、Na2SiO3浓度40 g/L、PEG6000 4 g/L、CO2/N2混合气流量1.2 L/min时，所制SiO2颗粒的比表面积为318.9 m2/g. 随Na2SiO3 浓度增大，SiO2胶粒在pH>7的碳化液中Ostwald凝聚生长过程相对延长，颗粒的一次粒径增大，比表面积却随之减小. 由于温度对SiO2溶解度和胶粒Brownian运动的影响，降低反应温度可促进SiO2成核、减少Si(OH)4和≡SiOSi(OH)3的聚合，SiO2颗粒的比表积增大. 添加剂PEG6000的空间架构效应抑制纳米SiO2颗粒团聚，从而促进SiO2颗粒比表面积增大；但当其浓度大于7 g/L时，Na2SiO3分子进入缠绕着的PEG长链架构内部，所得SiO2颗粒比表面积有所降低.

Controlling Mechanism of Specific Surface Area of Silica Nanoparticles in Carbonation Process

Using sodium silicate as precursor, the controlling mechanism of specific surface area (SBET) of silica nanoparticles synthesized by carbonation process was investigated. The results of orthogonal experiments demonstrated that the order of factors affecting SBET was: sodium silicate concentration>added mass of PEG6000>reactive temperature>flow rate of CO2/N2 mixed gas. Under the optimal conditions of concentration of sodium silicate at 40 g/L, added mass of PEG6000 4 g/L, reactive temperature 80℃, and flow rate of CO2/N2 mixed gas 1.2 L/min, silica nanoparticles synthesized exhibited a high SBET of 318.9 m2/g. With the increase of concentration of sodium silicate, the size of primary particles increased, but SBET of silica particles decreased due to extension of Ostwald ripening process of SiO2 sol in the carbonation solution where pH>7. Due to the effect of temperature on the solubility and Brownian motion of SiO2 sol, the decrease of reaction temperature could accelerate the nucleation of silica and restrain the agglomeration of Si(OH)4 and ≡SiOSi(OH)3, therefore the SBET increased. The increase of SBET was facilitated by PEG6000 due to its steric hinderance effect. However, when PEG6000 in solution exceeded to 7 g/L, the precursor molecules entered into the PEG with tangled long chain, the SBET of synthesized silica nanoparticles would be decreased.