The surface charge density of cationic silica sol can be controlled by introducing different types of cations and adjusting their concentrations. For example, by introducing cations such as Al3+ and Fe3+, they can be bonded with silicate on the surface of silica sol particles to form positively charged silica sol. At the same time, by adjusting the concentration of cations, the charge density on the surface of silica sol particles can be controlled, thereby affecting its adsorption performance and catalytic activity.