Photo catalytic degradation

Figures 11.8-11.10 and Tables 11.8-11.10 explain the sono-photochemical degradation of phenol under sonicated and normal conditions and in the presence of photocatalyst (n-BuO Ti with and without Cu-Dy, Mn-Dy and Co-Dy composites respectively. These Figs. 11.8-11.10 show the percentage degradation of phenol during a period of 2 h through an interval of 30 min under sonicated, photocatalytic, sonophotocatalytic and crystal induced sono-photo-catalytic conditions.

The addition of Fe ions to the solution also increased the rate of photo-catalytic degradation. The TOC reduction was 80% in the presence of Fe ions and 10% in the absence of Fe ions. pH is the key parameter in determining the photocatalytic degradation of anilines as well as other compounds previously studied. The high photocatalytic degradation near the pHpzc has also been observed for other compounds studied with Ti and Zn. The major mechanism is the attack of photogenerated OH radicals on the aniline molecule under alkaline conditions. The addition of Fe ions to the solution can enhance the formation of OH radicals and lead to higher photocatalytic rates. 

Sherrard, K.B., P.J. Marriott, R.G. Amiet, R. Colton, M.J. McCormick, and G.C. Smith. 1995. Photo-catalytic degradation of secondary alcohol ethoxylate spectroscopic, chromatographic, and mass spectrometric studies. Environ. Sci. Technol. 29, 2235-2242. 

Pervaporation - photocatalysis In the described systems the membrane usually permeates water and rejects the reactants, enhancing their residence time in the photoreactor. However, it is known that some intermediate products of the photo-catalytic degradation of organic compounds can negatively affect the reaction rate, therefore, in some cases it is useful to eliminate these by-products in order to improve the thermodynamic and/or the kinetics of the reaction. 

Pichat P, Guillard C, Maillard C, Amalric L, D Oliveira JC. Ti02 photo-catalytic destruction of water aromatic pollutants intermediates properties-degradability correlation effects of inorganic ions and Ti02 surface area comparisons with H202 processes. In Ollis DF, Al-Ekabi H, eds. Photo-catalytic Purification and Treatment of Water and Air. Amsterdam Elsevier, 1993 207-223. 

Al-Ekabi, H. Serpone, N. Kinetic studies in heterogeneous photocatalysis. I. Photo-catalytic degradation of chlorinated phenols in aerated aqueous solutions over Ti02 supported on a glass matrix, J. Phys. Chem. 1988, 92, 5726. 

Yamashita H, Honda M, Harada M, et al. Preparation of titanium oxide photocatalysts anchored on porous silica glass by a metal ion-implantation method and their photo-catalytic reactivities for the degradation of 2-propanol diluted in water. J Phys Chem B 1998 102 10707-11. 

There is a general consensus (vide supra) on the environmental importance of catalytic reactions on the surface of many minerals. However, there is limited information in the literature about specific examples [9]. Systematic studies would allow the understanding of the dependence of the catalytic activity on mineral structure, mineral chemistry and surface reactivity. At the same time, this knowledge would be useful in designing remediation techniques based on minerals instead of synthetic catalysts. For example, sphalerite and ilmenite have been shown to be capable of degrading chlorinated carbon compounds via a photo catalytic mechanism [63]. 

Houas a, Lachheb H, Ksibi M, Elaloui E, Guillard C, Herrmann J-M (2001) Photo-catalytic Degradation Pathway of Methy-... 

Radical reactions can also be initiated by irradiation using UV light. Prominent examples include photocatalytic degradation of pollutants with catalysts incorporating Ti02. Frequently, these reactions proceed at ambient or even lower temperatures, which makes their investigation by EPR spectroscopy rather facile. Nonetheless, EPR spectroscopy has been used only rarely to monitor photo-catalytic reactions as they occur (33,87). An example is presented below. 

Although valence-band electron holes on most semiconductors are strong oxidants, their conduction-band electrons are not very powerful. In spite of persistant efforts, success in some reductive semiconductor-mediated photo-catalytic processes, such as fixation of carbon dioxide and nitrogen, has been limited. However, reductive degradation of some electron-deficient compounds such as polyhalogenated hydrocarbons and metal recovery have shown promising results [84]. In addition, a reductive process is easier to control and thus more suitable for organic synthesis. 

Ibrahim, H., and de Lasa, H., 2003, Photo-catalytic degradation of air bonre pollutants apparent quantum efficiencies in a novel photo-CREC-air reactor, Chem. Eng. Sci., 58(3-6) 943-949. 

Kalaiselvi, A., Roopan, S.M., Madhumitha, G., Ramalingam, C., Elango, G., 2015. Synthesis and characterization of palladium nanoparticles using Catharanthus roseus leaf extract and its application in the photo-catalytic degradation. Spectrochim. Acta A 135, 116-119. 

Table 7.13 Results of photo catalytic degradation of H2C2O4 and HCOOH and hydrogen generation from their solutions in presence of boron nitride based composites (Cg y =0.1 M Ch 0 =3.75x 10" M Cj yg = 50mgi = 200mg v-joi = 20mi T 40°C).

Djepang, S. A., Laminsi, S., Njoyim-Tamungang, E., Ngnintedem, C., Brisset, J. L. (2014). Plasma-chemical and photo-catalytic degradation of bromophenol blue. Chemical and Materials Engineering, 2(1), 14—23. 

Borello, R., C. Minero, E. Pramauro, E. Pehzzetti, N. Serpone, and H. Hidaka. Photo-catalytic Degradation of DDT Mediated in Aqueous Semiconductor Slurries by Simulated Sunhght, Environ. Toxicol Chem., 8(11) 997-1002 (1989). 

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