Preparation method of nanometer titanium dioxide

The invention discloses a preparation method of nanometer titanium dioxide. The preparation method comprises the following steps: mixing polyethylene glycol and deionized water in proportion, sequentially adding boric acid and urea, stirring, adding ammonium fluorotitanate, adjusting the pH to 3-6, and stirring to obtain a first solution; dissolving butyl titanate into the first solution in proportion at the pressure of 0.6MPa, and stirring to obtain a second solution; adding ferric chloride into a chitosan-acetic acid solution with the mass fraction of 2%, and performing ultrasonic dispersion for 10min to obtain a third solution; adding 5-13 parts of a titanate coupling agent and 3-7 parts of polystyrene into the second solution, performing ultrasonic dispersion, stirring, uniformly mixing with the third solution at the pressure of 0.6MPa, heating to 83-100 DEG C, continuing stirring for reaction, and centrifuging to obtain the nanometer titanium dioxide. The prepared titanium dioxide has good photocatalytic