Study Of The Synthesis Of Nano-TiO₂ Photocatalyst And Its Decomposition Activity In Phenol-contaminated Water

Water pollution is a serious environmental problem. There are massive organic hydroxybenzene compounds which are difficult to be decomposed, but nano-TiO₂ photocatalysts are able to decompose almost any hydroxybenzene compounds. The administering technology of waste-water treatment based on TiO₂ photocatalysts is very promising and has already received much attention. However, the preparation of nano-TiO₂ is still the core problem in the field.Nano-TiO₂ has the characteristics of safety, stabilization, economy, innocuity, and environmental-friendly, and can also be re-used. It could decompose any organic contaminants that were harmful, noxious and difficult to be decomposed, without producing secondary pollution. Therefore, there are practical meanings to decompose organic hydroxybenzene-contaminated water using nano-TiO₂ photocatalysts.In this project, two methods (sol-gel method and hydrolyze method of TiCl₄) were used to prepare nano-TiO₂ for the aim of "preparation of nanophotocatalysts". The catalysts were examined by the means of BET, TG-DTA, XRD, Raman and UV-V spectrum. The activity of catalysts was reviewed when phenol was used as the decomposed molecules. The main conclusions from this study are as followings:1. Preparation of TiO₂ photocatalysts by S-G and TiCl₄ hydrolyze methodCrystal had prodigious effect on the activity of TiO₂ photocatalysts. TiO₂ of bodiless crystal hardly had any photocatalytic activity, whereas anatase crystal had the best activity, with the activity of rutile in the between. The effects of particle size on catalyst activity were obvious, i.e. the smaller the particle size, the higher activity of catalyst was. Catalyst concentrations also affected phenol decomposation, and the best concentration of catalysts was 2g/L in our reaction system. In addition, the beginning concentration of phenol affected the decomposation obviously, i.e. the lower the beginning concentration of phenol, the better decomposition was, and vice versa. Addition of oxidants increased the activity of TiO₂ photocatalysts enormously, even though the concentration of H₂O₂ was just 1 mL/L.2. Preparation of extra fine TiO₂ photocatalysts by improved S-G methodThe TiO₂ photocatalysts prepared by improved S-G method had better activity when stearic acid was used as dispersant. The presence of stearic acid could aggrandize the BET of TiO₂ photocatalysts availably and also restrain the increment of particle size in the process of calcination. When the mol-ratio of stearic acid to titanum tetraisopropoxide was 1.5:1, the TiO₂ powder was pure anatase crystal with a particle size of 11 nm, and its BET was 117.13 m /g after calcination at 450℃. This BET was bigger than that of a German product - P25. There was a clear blue-shift at 141 cm^-1 in the Raman spectrum, a 3.3 cm^-1 displacement. A decomposition rate of up to 97.0% was obtained by calcination at 450℃, catalyst concentration of 2 g/L, beginning concentration of phenol at 10 mg/L, and 2-hour illumination.3. Preparation of TiO₂ photocatalyst by TiCl₄ hydrolyze modified with (NH₄)₂SO₄(NH₄)₂SO₄ was added to TiCl₄ water solution, and the deposition of TiO₂ powder was sped-up by high temperature water bath. Photocatalysts with bigger BET, smaller average particle size and better heat stability were prepared. Under the conditions of water bath temperature at 90℃, the mol-ratio of Ti to (NH₄)₂SO₄ at 1:2 and calcine temperature at 400℃, the BET was still 138.2 m²/g and average particle size was only 9 nm. The heat stability of TiO₂ anatase crystal was improved greatly after being modified with (NH₄)₂SO₄. The results of XRD and Raman showed that when the calcination temperature was up to 700℃, the crystal just began transitting to rutile. The effect of water bath temperature on crystal of TiO₂ photocatalysts was small, but that on particle size of the photocatalysts was big, i.e. the higher the water bath temperature, the smaller the particle size of TiO₂ photocatalysts was. The activity of TiO₂ photocatalysts was greatly increased after modification with (NH₄)₂SO₄. The decomposation rate of phenol reached 99.7% when the mole ratio of (NH₄)₂SO₄ to Ti was 2:1, at water bath temperature of 90℃and calcine tmperature at 700℃, with 1 -hour illumination.