الفهرس 
Photolysis of ChlorophenolsOnly 14 pages are availabe for public view
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Abstract
The following pages can cite beneficial conclusions through which we can draw very important points concerning the Photocatalytic degradation of chlorocompounds in water:-
• Characterization experimental methods will show their role in illustrations of the results. The X-ray diffraction (XRD) analysis employed to characterize the crystallinity of the catalysts showed a number of trends.
1. First, the diffractograms recorded from 2θ to 7θ exhibited location of peaks as ordered mesoporous materiales. The mesoporous materials TiO2/Si-MCM-41, Ti-MCM-41(20) and TiO2/Fe-MCM-41 exhibited well-defined (100) reflections in their XRD patterns.
2. The second part of the XRD analysis was performed in the range of 20 θ to 50 θ in order to assess the crystallinity of TiO2 loaded onto MCM-41 support.
For Ti-MCM-41, Si/Ti = 20 sample no peaks corresponding to crystalline titania can be identified. This indicates that titania clusters should be very small (less than ~ 3 nm) and incorporated in MCM-41 framework.
In contrast, TiO2/Si-MCM-41 and TiO2/Fe-MCM-41 samples exhibit low crystallinity of titania. There are strict hindrances associated with the formation of titania clusters inside mesoporous molecular sieves due to the low pore size of these materials. However, low intensity and broad peak characteristic of XRD spectrum of supported TiO2 on Fe-MCM-41 indicate that highly dispersed fine particles of anatase TiO2 were formed on this support.
In contrast, TiO2/SBA-15 sample gives two peak at very low 2θ = 1.7o and 1.9o equivalent to a d-value of 56.6 Ǻ, 48.9 Ǻ, two XRD lines indexed as d-spacing (110), (200) reflections corresponding to a two-dimensional hexagonal structure with long-range order can be clearly seen. from the wide-angle XRD results, high intensity peaks corresponding to crystalline titanium oxide (anatase phase) can be identified. Indicating the formation of bigger titania particles.
• BET specific surface areas of the samples were determined using the adsorption isotherms of nitrogen measured at 77 K. The adsorption and desorption isotherms of nitrogen on each sample show the typical type IV isotherm according to the IUPAC nomenclature for MCM-41, which characteristic for spherical pores.
For Ti-MCM-41(10) and Ti-MCM-41(20) samples. The difference in pore volume and surface area in the two catalysts is attributed to the dispersed of TiO2 inside the supports and causes partial blockage of the pores.
The pore volume reduction in TiO2/MCM-41 sample would indicate that most of the semiconductor particles loading take place within the ordered channels of the support.
One can observe that the presence of transition metal ions in the gel during synthesis lowers the surface area (SA) of the resulting MCM-41 material such shows in TiO2/Fe-MCM-41 and Fe-Ti-MCM-41catalysts.
The mesoporous material, TiO2/SBA-15, presented a BET surface area value lower than that presented by the TiO2/MCM-41 material. SBA-15 unlike MCM-41 contains micropores within the walls of mesopores forming 3-D connected pore network with connections between mesopores. However, pore diameter value for TiO2/SBA-15 catalyst is wider than TiO2/MCM-41. This is a logical conclusion of the loss of surface area and higher pore diameter due to the different surfactant template was utilized for the synthesis of both siliceous materials.
• FT-IR spectra in the range from 400 to 4000 cm-1 for the prepared samples.
Ti-MCM-41(20) has higher OH groups on the surface. This may increase the photoactivity of this catalyst.
For iron samples, FT-IR spectra results of iron samples show no presence of Fe2O3 due to the lack of a Fe-O stretch vibration band. This result confirms that the iron incorporated in framework of MCM-41. Bisubstituted Fe-Ti-MCM-41 FTIR spectra prove the Szegedi’s theory. As the titanium incorporation increase as the tension into a silicate structure increase. However, the characteristic bands of mesoporous materials softly appear.
FT-IR spectra for the TiO2/MCM-41 and TiO2/SBA-15 samples show characteristic bands of mesoporous materials. FTIR spectra of impregnated samples point to incorporation of some titanium into framework of TiO2/MCM-41 and TiO2/SBA-15.
• Morphology of the catalysts was determined using SEM micrographs. TEM image on iron samples show some sort of mesoporous structure.
• The decay of TCP during its photolysis (photodegradation in absence of a catalysis) applying UV irradiation at a wave length of 254 nm investigated, up to 285 min using the first order rate equation, the reaction rate constant for TCP degradation, k, amounts to 0.031 min-1. On TCP photolysis, we observed two major components appearing in HPLC chromatogram. The components are dihydroxytrichlorobenzene (DHTCB) and 3,5-dichlorocatecol (3.5-DCC). Other two minor components; dichlorobenzoquinone (DCBQ), and dichlorotrihydroxy benzene (DCTHB) observed. The PH of solution decrease as the formed chloride increase, point to the increase in acidity.
• Irrespective of the more favorable physical properties of Ti-MCM-41(10) catalyst compared to Ti-MCM-41(20) catalyst, it is found that the activity for 2,4,6-TCP photodegradation on Ti-MCM-41(20) catalyst is higher than on Ti-MCM-41(10) catalyst. The faster Cl- photo removal from chlorophenols may act as inhibitor via adsorption on the catalyst surface. This causes the accumulation of organic acids as final photodegradation product on catalyst’s surface, and so causes mineralization delay. Higher OH* on the surface of Ti-MCM-41(20) catalyst may explain its high photocatalytic activity (FTIR spectrum).
• In spite of the rapid degradation of 4-CP in the initial irradiation time on Ti-MCM-41 (20) catalyst, it is found that the photodegradation rate of 2,4,6-TCP is higher, this is due to: (a) the higher adsorption of TCP on the Ti-MCM-41 (20) surface which facilitates the degradation, (b) the lower chloride formation and hence no poisoning of catalyst, (c) lower organic acid formation and rapid mineralization of them.
• The lower concentrations of TCP, the faster the mineralization were achieved. Applying Arrhenius equation for the photodegradation at temperatures 20, 30 and 40oC. It was found that the activation energy reported of photocatalytic reaction of TCP is 17.41 kcal.mol-1. It is close to that of a hydroxyl radical reaction, suggesting hydroxyl radical reaction as the controlling factor in the photocatalytic degradation of 2,4,6-TCP.
• The introduction of titanium in the iron-modified MCM-41 by impregnation technique leads to additional formation of finely dispersed anatase nanoparticles. The highest catalytic activity is observed for the sample obtained by impregnation procedure TiO2/Fe-MCM-41. Bisubstituted materials Fe-Ti-MCM-41 obtained by direct sol–gel synthesis possess lower catalytic activity. Simultaneous participation of iron-, titanium- and mixed iron–titanium active sites is assumed. Higher titanium incorporation could be concluded in the case of bisubstituted directly synthesized material, leads to decrease in surface area and increase in pore diameter.
• Effect of visible irradiation on Photocatalytic Activity of 2,4,6-TCP using TiO2/Fe-MCM-41 catalyst is investigated. However, only 22 ppm of TCP disappeared after 110 min of visible irradiation. UV light provides the photons required for the electron transfer from valence band to conduction band of the photocatalyst. The energy of a photon is related to its wavelength and the overall energy input to a photocatalytic process is dependent upon the light wavelength.
• The higher catalytic activity is observed for the sample obtained by impregnation procedure TiO2/MCM-41 catalyst. However, TiO2/SBA-15 catalyst exhibits some higher activity during the initial 10 min of irradiation, beyond which the increase of irradiation time using the latter catalyst becomes a much less active for the photodegradaion rate of 2,4,6-TCP. It can conclude that the rapid degradation on TiO2/MCM-41 catalyst is due to: (a) the higher surface area, (b) the lower chloride formation and hence no poisoning of catalyst, (c) the rapid mineralization of organic acid formed during photocatalysis.
• The efficiency of the current catalysts for the photodegradation of 4-chlorophenol as a starting material in deionized water using UV light is investigated. As a general the disappearance of 4-CP is very high at initial time of irradiation due to the rapid formation of hydroquinone and chloride ions in solution. The substitution of P-chloride by hydroxyl radical occurs immediately in reaction medium via formation of dihydroxychlorocyclohexadienyl radical.