Study On Optimization Procedure Of Nano-TiO₂'s Preparation And It's Absorption-photocatalytic Oxidation Of Indoor Volatile Organic Gas Formaldehyde When Loaded On Activated Carbon Fibres

Indoor air quality has been taken more and more into account in recent years. Indoor decoration, air conditioning and central heating system and a wide application of chemical articles in everyday use have resulted in serious indoor air contamination, especially volatile organic compounds (VOCs) plays an important part in it. Formaldehyde is a commonly detected VOCs pollutant in the door. However, there hasn't been a satisfactory method for controlling small sources of indoor air organic pollutants at present. In fact the conditional negative ion air cleaner is unable to decompose the pollutants but only refresh the air; activated carbon air cleaner is confined to its saturation absorption while photocatalytic oxidation can solve these problems and clean the air completely as well as conveniently. So how to improve photocatalytic oxidation efficiency of low-contamination volatile organic compounds is mainly studied.TiO₂ was used as photocatalyst and loaded on activated carbon fibre in an indoor air contamination box simulator to study photocatalytic oxidation of gas formaldehyde. Amending TiO₂ material and reaction condition increased the photocatalytic oxidation efficiency.TiO₂ nano-material was prepared by sol-gel method and modified with Fe³⁺ to enhance its photocatalytic activity. In order to get a highly activated photocatalyst, the affection of some preparation conditions on titanium dioxide's activity have been studied such as the kinds of solvents, the pH of solution, the sorts and different contents of doping metal irons, the value of R, and the sintering temperature and the hours of sintering. It showed that when absolute alcohol was chose as solvent and the pH of the solution was kept around 8.00, R=50 and the doping Fe³⁺ was at 3.5wt%, TiO₂ behaved a much higher activity after being sintered at 650℃ for 2 hours. The crystal type of the sample was found to possess a mixture of 70% anatase and 30% rutile by XRD. It was obtained by scanning electron microscope (SEM) that its average pore size was 30nm.ACF was firstly used as supporter in our research. TiO₂ samples prepared under the optimal condition were respectively supported on glass, granule activated carbon(GAC) and activated carbon fibres (ACF) separately to carry out the reaction of photocatalytic oxidation of formaldehyde. It indicated that ACF was superior to the other supports and exhibited a higher efficiency under the same conditions. So ACF was elected as the support in the following experimentation.Using a 20W pen lamp emitting light at a wavelength of 254 nm as the light source, the photocatalytic reaction was carried out at room temperature and atmospheric pressure. The roles of reaction conditions such as gas velocity, light source, reaction time, usage of TiO2 and concentration of formaldehyde were studied. It was found that the light, the concentration of formaldehyde and the dosage of TiO2 have distinct influence over the efficiency of photocatalytic oxidation. A processing rate more than 90% could be obtained when 3.5g TiC>2 was loaded on 23.5g ACF and the concentration of formaldehyde was within 18mg/m3. The test of used ACF in photocatalytic reaction showed it still had a good absorption capacity. It also indicated that photocatalytic oxidation can be an effective regenerative technique for ACF.TiC?2 is of high photocatativity and stable nature, and it is abundant to be obtained at low cost. When loaded on ACF, a highly effective adsorbent, it can be attached to air conditioning equipment or used alone to clean the air in residence, supermarket, hotel and museum and etc.