Photocatalysts immobilization

Dhananjeyan, M.R., Mielczarski, E., Thampi, R.K., Buffat, P., Bensimon, M., Kulik, J., Mielczarski, J. and Kiwi, J. (2001) Photodynamics and surface characterization of Ti02 and Fe203 photocatalysts immobilized on modified polyethylene films. J. Phys. Chem. B 105, 12046-12055. 

Pozzo, R. L., Giombi, J. L., Baltanas, M. A., and Cassano, A. E., 2000, Performance in a fluidized bed reactor of photocatalysts immobilized onto inert supports. Catalysis Today, 62 175-187. 

Different methods of preparation of photocatalytic membranes have been developed. In the case of polymer membranes they include (i) methods in which a photocatalyst is supported on a membrane surface and (ii) methods in which a photocatalyst is being entrapped within a membrane structure. In the case of ceramic membranes the photocatalyst can be supported on a membrane, entrapped in it, or the membrane can be made from the photocatalytic material only. The stability and photoactivity of the photocatalytic membranes depend not only on the membrane material (polymer or ceramic) but also on parameters applied during photocatalyst immobilization. 

Possibility of fouling mitigation due to enhanced hydrophilicity of the TiOj-modified membrane Possibility of fouling mitigation due to decomposition of organic contaminants forming the gel layer or filtration cake Contaminants could be decomposed either in feed or in permeate Higher decomposition rate in case of the gas-phase reactions compared to conventional photoreactors with photocatalyst immobilized on a non-porous support... 

State of the photocatalyst reactors with suspended photocatalyst particles (slurry) and reactors with photocatalyst immobilized on the inert surfaces... 

Systems that contain the photocatalyst as a suspended powder or colloid are not convenient in continuous flow or circulation arrangements in which the photoactive system is held in place and can readily be removed for regeneration. CdS can be produced or immobilized in a Nafion membrane together with finely dispersed platinum... 

ZnO photocatalyst can also be coupled with other materials in order to improve its chemical and physical properties [183] and photocatalytic activity [184]. Nanosized ZnO was immobilized on aluminum foil for the degradation of phenol [185]. Lanthanum and ZnO were combined to degrade 2,4,6-trichlorophenol [186]. Compared with Ti02 nanomaterial, ZnO nanomaterial generally absorbs a significant amount of the solar spectrum in the visible range therefore, ZnO nanomaterials were combined with Ti02 nanomaterials used as a photocatalyst [187]. 

Other composite photocatalysts were prepared by mounting immobilized anatase particles on mesoporous silica and silica beads [189-191], The behavior of anatase-mounted activated carbons was also studied in detail [192-194], It was even suggested that carbon-coated anatase exhibits better performance in photocatalysis than anatase itself, demonstrating high adsorptivity, inhibition of interaction with organic binders, etc. [195,196],... 

The abihty to modify the surface of the CdS nanoparticle within the cavity of the w/o microemulsions has been extended for their immobihzation. CdS nanoparticles (e.g., prepared in AOT/isooctane w/o microemulsions) were immobilized onto thiol-modified aluminosihcate particles [218] and thiol-modified alumina [219] by a simple addition of thiol-modified aluminosih-cates and alumina, respectively, in the micellar solution. The resulting CdS nanoparticles-aluminosihcate composites were used as photocatalysts for H2 generation from 2-propanol aqueous solution. 

The idea of using fluidized bed as both uniform light distribution and an immobilizing support for photocatalysts has been originally proposed and theoretically evaluated by Yue and Khan [3]. Experimental application of this idea has been demonstrated by Dibble and Raupp [4] who designed a bench scale flat plate fluidized bed photoreactor for photocatalytic oxidation of trichloroethylene (TCE). Recently, Lim et al. [5,6] have developed a modified two-dimensional fluidized bed photocatalytic reactor system and determined the effects of various operating variables on decomposition of NO. Fluidized bed photocatalytic reactor systems have several advantages over conventional immobilized or slurry-type photocatalytic reactors [7,8]. The unique reac-... 

Heterogeneous catalysis is a surface phenomenon, therefore the overall kinetic parameters are dependent on the real exposed catalyst surface area. In the supported systems only a part of the photocatalyst is accessible to light and to substrate. Besides, the immobilized catalyst suffers from the surface deactivation since the support could enhance the recombination of photogenerated electron-hole pairs and a limitation of oxygen diffusion in the deeper layers is observed. 

The recovery of the photocatalyst from the reaction environment represents one of the main problems of the photocatalytic process that limits its industrial application. Although this process step can be obviated by the use of immobilized catalyst, the suspended system has more attractive features [76]. Therefore, the separation of the photocatalyst from the treated solution and its recycle is one of the challenges in further development of this technology. 

Photocatalytic methods involve illumination of a large band gap semiconductor particle such as Ti02 either dispersed as a slurry in the contaminated aqueous solutions or as immobilized films. While a substantial body of literature exists on photocatalysis [29-40], barriers to successful commercialization still prevail. The major problems with this technique include deactivation of the photocatalyst surface, and recovery of the photocatalyst in slurry systems. 

The study of the possible cooperation of the photo-Fenton reagent with a semiconductor photocatalyst showed that the Fenton catalyst immobilized in Ti02 reveals enhanced photocatalytic activity and is more effective in pollutant degradation this was revealed in the case of such electron donors as citric acid [20], maleic acid [41], chlorinated solvents [42], resorcinol [43], quinoline [44], herbicides [45, 46], and pesticides [47], The optimization of the combined photocatalytic systems... 

Lee, S., Nishida, K., Otaki, M. and Ohgaki, S. (1997) Photocatalytic inactivation of phage Q-beta by immobilized titanium-dioxide mediated photocatalyst. Water Sci. Technol. 35, 101-106. 

To increase catalyst recovery, efforts have been directed toward immobilization of the photocatalyst on a wide variety of materials. However, there is an inherent decrease of catalytic activity due to a reduced surface area. As such, Fe could be used to minimize or compensate for the catalyst deactivation due to the support preparation. New methods must be developed to ensure Fe ions stay adsorbed onto the photocatalyst surface to avoid further reactivation posttreatments. 

Tennakone, K., and K.G.U. Wijayantha. 1998. Heavy-metal extraction from aqueous medium with an immobilized Ti02 photocatalyst and a solid sacrificial agent. Journal of Photochemistry and Photobiology A Chemistry 113(1) 89-92. 

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