CE was used to separate the components of a mixture for monitoring phenol and its byproducts with the P/ACE MDQ capillary electrophoresis system (Beckmann Coulter inc. Fullerton, Ca USA). CE uses a narrow capillary tube to separate large and small molecules in a high electric field. The separations were performed on a fused silica capillary 75 μm (i.d.) with a total length of 50 cm. The CE device was equipped with a photodiode array detector from (Beckmann Coulter inc.) with UV λ range started from 190 nm. The instrument was set up with the anode at the left side of the capillary and the cathode at the right. Data were collected, and processed with software called 32 Karat analyzer from Beckmann Coulter Inc. The buffer was prepared with 10 mmol sodium tetraborate and 10 mmol sodium dihydrogen phosphate in Milli-Q-purified water. The buffer prepared in the same way as the other chemical prepared in section
3.11 Capillary electrophoresis (CE) 113 3.6.4. The pH of the buffer was adjusted to 8.0 for 3 min at 3.5 kPa. The samples were injected to the electrophoresis with a constant voltage of 20 kV (reversed polarity) for 7 min between runs; the capillary was rinsed with NaOH 1 mol/L and Milli-Q-purified water (138kPa), 1 min at a constant capillary temperature of 25 °C. The preparation of NaOH was done the same way as explained in part 3.6.4. For the determination and quantification of phenol, HQ, BQ, Cat, Res, 2-P and AA, the detection was done at 254 nm. Timing of the sampling was controlled by the instrument software. The samples were centrifuged at (10 000 rpm, 5 min) first by using Eppendorf centrifuge (system model 5810R) and then filtered through 0.1 µm and analysed after dilution.
To determine the concentrations of the absorbed values, solutions of standards (from 0.5-12 ppm) were prepared from the 100 ppm, each of these standards used with the samples were injected using 20 psi pressure.
Table 14: Standard concentrations with the absorbance’s of phenol Standard Conc. (ppm) Absorbance
The values of CE standards are tabulated in Table 14 showed that the absorbance of samples increased linearly with an increase of the standard concentration. Table 14 shows the obtained absorbance of the prepared phenol standard concentrations. The results of the absorbance of the prepared standards were used to plot a calibration curve as shown in the Figure 10. The absorbance for all other standards of phenol byproducts which used in this section are prepared and compared in the same way as it prepared for phenol.
In Figure 10 the relation between phenol concentrations and its absorbance shows a straight line. The calibration curve shows a straight line passing through the origin, so
it obeyed the equation: y=mx, where y gives absorbance values, m gives the slope of the line and x shows the unknown concentration. y=0.0012x, then x=0.0012𝑦 , if the absorbance is measured on y-axis, the value on the x-axis could be calculated easily. In this way all the solutions of the standards, unknowns and the other byproducts can be extrapolated.
Figure 10: Calibration curve of absorbance vs. concentrations of phenol at t=0
3.11.1 Photolytic degradation
The influence of UV light was also examined without the catalyst on phenol photodegradation indicated very little catalytic activity, as the experiment was designed to determine the percentage of photolysis by UV illumination without the catalyst prior to the determination of the photocatalytic activity of SnO2. The results are explained in the coming Figures.
4.1 Motivation for studying phenol and its byproducts 115 4
Results and discussion
4.1
Motivation for studying phenol and its byproductsAs it was discussed in the previous chapters that Phenol is an organic compound found in surface and ground water, which has an endless effect on the creatures and the environment. Some high concentration of phenol was also found in some processing food [12]. Phenol and phenolic compounds are assigned as priority pollutants by the Environmental Protection Agency [379]. In fact, a small concentration of these toxins can prevent the development of many living organisms [380, 381]. Studies have been indicated that phenol might link to other chemicals such as parabens, benzoic acids and others. The results show that the problems created by phenolic compounds in the wastewater would become worse in the future. Phenol was taken as a pollutant since it linked with so many other groups. Consequently, there is a requirement to abolish phenol and its compounds from the environment. If phenol removed from the solvent the other groups would be easily degraded. In this study, phenol was chosen as a model pollutant to represent the group of its byproducts identified during different analytical analysis for photocatalytic degradation study. Complete photocatalytic degradation of phenol and other six byproducts such as (HQ, BQ, Cat, Res, AA and 2-P) were studied, to show the excellent ability of the Nps synthesized.
This chapter examines the efficiency of the photocatalytic systems synthesized for photodegrading phenol and its intermediates. The chemical structure of phenol and its byproducts are shown in Figure 1.
Also in this work synthesized undoped SnO2 and with differently doped ions photocatalyst were used. The photocatalytic activity of these Nps was examined by photodegradation of phenol in 3 different photocatalytic reactors explained in chapter III. The studied process composed of photocatalytic degradation in the presence of UV, sunlight, or visible light irradiation.