facile and economic method for preparation of nano-colloidal silica with controlled size and stability

this study is focused on synthesis of nano-colloidal silica via alkaline water glass solution. sodium ions of water glass were removed by cation exchanging in a resin column to obtain the silicic acid which was titrated to the solution of sodium silicate. concentration of the colloidal silica and ph value of the solutions were controlled using different concentrations of alkaline sodium silicate and silicic acid solutions in constant temperature and titration rate. the synthesized colloidal silica was characterized by dynamic light scattering (dls), scanning electron microscopy (sem), x-ray powder diffraction (xrd), accelerated surface area and porosimetry analyzer (asap) and gravimetric method.  the results showed that the average particle size of colloids and their stability were also influenced by various important factors such as ph, temperature, concentrations of alkaline sodium silicate and silicic acid solutions. the results showed that the synthesized nano-colloidal silica suspensions in concentration up to 25 wt.%  of sio2  with average particle sizes in range of 23 to100 nm are stable more than one year. also, surface area and pore volume of the prepared spherical colloidal silica particles were160 m2/g and 0.27 cm2/g, respectively.