Preparation Of Activated Carbon Fibers Supported TiO₂ Photocatalyst And Evaluation Of Its Photocatalytic Reactivity

Anatase-type Titanium dioxide (TiO₂)has attracted much attention for its potential application in decomposition of various environmental pollutants in both gaseous and liquid phases. The photocatalytic degradation systems using fine TiO₂ powder under UV irradiation have been widely investigated . However, separation of the fine TiO₂ powder from the solution after degradation is time consuming and costly . Development of TiO₂ photocatalysts anchored on supporting materials with large surface areas, by which dilute polluted substances could be condensed, would be of great significance, not only to avoid the disadvantages of filtration and suspension of fine photocatalyst particles, but to lead to high photodecomposition efficiency . Recently, supported TiO₂ photocatalysts on various porous materials were prepared by a pasting treatment,a sol-gel method,or an ionized cluster beam (ICB) method.Activated carbon fibers (ACFs) are one kind of highly microporous carbon materials, having a larger pore volume and a more uniform micropore size distribution than granular activated carbons. Generally, activated carbon fibers are considered to have larger adsorption capacity and greater rates of adsorption and desorption process than granular activated carbons. However, so far there have been only a few reports to study preparation methods and applications of activated carbon fibers supported TiO₂ photocatalysts. Reported methods of depositing TiO₂ photocatalysts on ACFs include an ionized cluster beam , an impregnation method , and a coating treatment by loading commercial TiO₂ powder on ACFs with polymer binders. Precipitation of titania coating on microporous carbon surface by a molecular adsorption-deposition method was once studied by Matsumoto et al.to modify carbon surface to improve its adsorptive properties for gases. In this paper, this method will be introduced as a new way to prepare ACFs supported TiO₂ photocatalyst with the expectation of combining the effects of high adsorption capacity of ACFs and photocatalytic reactivity of anatase-type TiO₂.In the present study, the preparation of activated carbon fibers supported TiO₂ photocatalyst and its characterization are addressed in detail. The effective photocatalytic reactivity of the photocatalyst produced has been demonstrated by its photocatalytic degradation of volatile organic compounds in air.Activated carbon fibers (ACFs) supported TiO₂ photocatalyst was successfully prepared by an sol-gel , soakage-adsorption and supercritical fluid dry method followed by calcination in vaccum.The amount of deposited TiO₂ could be adjusted by controlling the centrifugal time. Titanium dioxide was found to be loaded on almost all carbon fibers. And a combination( TiO₂/ACFsd) had aerogel properties be obtained.The photocatalyst developed was characterized by SEM, XRD, BET surface area. SEM observation showed the particles of TiO₂ are uniform with an average size of about 40nm ,and TiO₂ was deposited on almost each carbon fiber ,and the space between adjacent fibers was remained unfilled after coating , to allow UV light to penetrate into the felt-form photocatalyst to a certain depth, to form a three-dimensional environment for photocatalytic degradation. BET surface area of TiO₂ aerogol was above 500m²/g,however , BET surface area of TiO₂ xerogel was only 0.1828 m²/g.And after the supercritical fluid CO₂ dry and calcination process, TiO₂/ACFsd could have large BET surface area, BET surface area of TiO₂/ACF-388 could be up to 1604.2 m²/g,was higher than ACF's. As confirmed by XRD examinations, after TiCVACFsd was calcined at temperature 450℃in vaccum stove,Tight contact of thin TiO₂ coating to carbon fibers surfaces was supposed to transformation from anatase to rutile-form, and to keep high crystallinity and rate of anatase. All those exhibited the very good photocatalytic actvity of TiO₂/ACFsd, and make it very suitable for configurating an efficient photoreactor for purification of polluted water and air.The comparative experiments indicated the photocatalyst prepared had a combined effect of photocatalytic reactivity of TiO₂ with adsorptive property of activated carbon fibers. After the supercritical fluid CO₂ dry and calcination process, ,the photocatalytic activity of TiO₂/ACFsd was higher than TiO₂/ACFnd that was prepared on normal dry condition. Moreover, it can be used repeatedly without any deline as confirmed by photodegradation of formaldehyde indoor air. In addition, For the photocatalytic degradation of other organic pollutants , toluene, dimethylbenzene and VOCs , the photocatalytic activity of TiO₂/ACFsd was also effective.Therefore, the combination of photocatalytic activity of TiO₂ and ACF was effective for degration organic pollutants in air.